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Tectonometamorphic evolution of the Hindu Kush, North West Pakistan Fasial, Shah 2015

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  Tectonometamorphic Evolution of the Hindu Kush, North West Pakistan   by   Shah Faisal    A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF   Doctor of Philosophy    in   THE COLLEGE OF GRADUATE STUDIES (Environmental Sciences)    THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan)   May 2015   © Shah Faisal, 2015  ii Abstract New U-(Th)/Pb geochronology, geochemical analyses of plutonic bodies and thermochronologic constraints from the Hindu Kush range, NW Pakistan, provide insight on the crustal growth and tectonic evolution of the southern Eurasian margin and Himalaya-Karakoram-Tibet orogen. Monazite and zircon data record a protracted deformational, metamorphic, and magmatic history that spans the Cambrian to the Neogene. The Cambrian-Ordovician Kafiristan pluton yields geochemical signatures consistent with extensional plutonism and rifting of the Hindu Kush and Karakoram terranes, which now comprise the field area, away from Gondwana. The Hindu Kush accreted to the southern Eurasian margin during the Late Triassic followed closely by the Karakoram terrane in the Early Jurassic. An Andean-style subduction margin was established at the southern Eurasian boundary in the Cretaceous, which lead to the intrusion of the Tirich Mir and Buni-Zom plutons. The attendant volcanic arc magmatism ended with the docking of the Kohistan island arc and the emplacement of the Kohistan-Ladakh batholith during the Late Cretaceous. Eocene 40Ar/39Ar muscovite ages in close proximity to the Tirich Mir fault indicate reactivation of the structure during the onset of continent-continent collision. This collision evolved into widespread crustal thickening, high-temperature metamorphism, and associated anatexis in the late Oligocene and early Miocene culminating locally with the emplacement of the Garam Chasma pluton. Thermochronologic data from near the pluton indicate immediate cooling after crystallization, followed by uplift and exhumation during the Neogene. Moreover, a young (1.4 ± 0.5 Ma) apatite fission track date from the Tirich Mir pluton is consistent with active exhumation and uplift of the 7700+ m Tirich Mir peak. This study and the data presented herein provide important new constraints on the nature and timing of  iii tectonic events along the developing south Eurasian margin before and after the continued India-Asia collision.                                 iv Preface The research and writing associated with this thesis is my own work. Three geologic field seasons were carried out in the Hindu Kush, NW Pakistan, during which more than 170 specimens were collected for subsequent investigation. The interpretations of the geochronologic, geochemical, and thermochronologic data produced are my own with input from various contributors (see below). Dr. Kyle Larson provided directional aid, guidance for specimen selection, interpretation advice, and editing and proof reading for the entire thesis. Specific contributions are noted below.  Chapters 4, 5, and 6 are written as self-contained manuscripts. Because of this, there is minor overlap/repetition within the introduction of each chapter. Chapter 4 provides U-Th monazite geochronologic constraints on the different metamorphic events in the Hindu Kush and explores their relationship to the evolution of the Himalayan-Tibetan system. (This chapter has been published in Terra Nova: Faisal et al., 2014). Monazite dating was conducted at the University of California, Santa Barbara (UCSB) under the supervision of Dr. J. M. Cottle, while Jaida Lamming located monazite grains using electron microprobe maps.  Chapter 5 investigates the petrogeneis and tectonic significance of pre- and syn-Himalayan magmatic events along the southern margin of Asia. (The findings of this Chapter are under review in Gondwana Research). Geochronological analyses of zircon and monazite were carried out under the direction of Dr. J. M. Cottle at UCSB. Dr. Cottle also contributed to the interpretation of the geochronologic data. Dr. Jess King from the University of Hong Kong provided support for geochemical interpretations. Chapter 6 presents new thermochronogic data that help constraint the thermal evolution and exhumation history of rocks in the map-area. 40Ar/39Ar thermochronology  v was conducted at the University of Manitoba in Winnipeg, Manitoba under the direction of Dr. Alfredo Camacho. Dr. Camacho helped in calculation of the final dates based on the isotopic data collected and contributed to their interpretation. Apatite fission tracking thermochronology was carried out at Dalhousie University Halifax, Nova Scotia under the supervision of Dr. Isabelle Coutand. Dr. Coutand was responsible for counting fission tracks and determining the ages for the specimens.  vi Table of Contents Abstract .............................................................................................................................. ii Preface ............................................................................................................................... iv Table of Contents ............................................................................................................. vi List of Tables .................................................................................................................... ix List of Figures .................................................................................................................... x Acknowledgements ......................................................................................................... xii  Chapter 1 Introduction .................................................................................................... 1 1.1. Study Area ............................................................................................................ 1 1.2 Problem Statement ................................................................................................. 5 1.3 Methodology .......................................................................................................... 6  Chapter 2 Regional Geology and Tectonic Evolution of the NW Himalaya ............... 9 2.1 Tectonic Evolution of the Himalaya Orogen ......................................................... 9 2.1.1. Pre-Cenozoic convergence ............................................................................. 9 2.1.2. The India-Eurasia Collision ......................................................................... 13 2.2 Evolution of the Hindu Kush Region .................................................................. 15 2.2.1. Late Triassic-Middle Jurassic Orogeny ....................................................... 15 2.2.2. Middle Cretaceous Kohistan-Ladakh Accretion with Eurasia ..................... 15 2.2.3 Early Cenozoic Himalayan Orogeny ............................................................ 18 2.2.4 Late Cenozoic Orogeny ................................................................................ 18  Chapter 3 Geology of the Hindu Kush, Chitral area, NW Pakistan .......................... 21 3.1 Background .......................................................................................................... 21 3.2 Previous Work ..................................................................................................... 21 3.3. Lithotectonic Units ............................................................................................. 25 3.3.1. Wakhan Block .............................................................................................. 25 3.3.2 Broghil Block ................................................................................................ 36 3.3.3 Yarkhun Block .............................................................................................. 36   vii Chapter 4 Building the Hindu Kush: Monazite Records of Terrane Accretion, Plutonism, and the Evolution of the Himalaya-Karakoram-Tibet Orogen............... 45 4.1. Background ......................................................................................................... 45 4.2. Geology of the Garam Chasma Region .............................................................. 47 4.3. Monazite Petrochronology ................................................................................. 49 4.4. Petrochronology Results ..................................................................................... 49 4.4.1. Interpretations .............................................................................................. 52 4.5. Discussion ........................................................................................................... 54 4.6. Summary ............................................................................................................. 58  Chapter 5 Rifting, subduction and collision records from pluton petrogenesis and geochronology in the Hindu Kush, NW Pakistan ........................................................ 59 5.1. Background ......................................................................................................... 59 5.1.1. Geology and Existing Chronology ............................................................... 60 5.2. Pluton Description .............................................................................................. 63 5.3. Whole Rock Geochemistry ................................................................................. 65 5.3.1 Kafiristan Pluton ........................................................................................... 65 5.3.2. Tirich Mir Pluton ......................................................................................... 67 5.3.3. Buni-Zom Pluton ......................................................................................... 74 5.3.4. Garam Chasma Pluton ................................................................................. 75 5.4. Interpretation and Petrogenesis ....................................................................... 75 5.4.1 Kafiristan Pluton ........................................................................................... 76 5.4.2. Tirich Mir Pluton ......................................................................................... 80 5.4.3. Buni-Zom Pluton ......................................................................................... 82 5.4.4. Garam Chasma Pluton ................................................................................. 83 5.5. Geochronology ............................................................................................................. 86 5.5.1 Kafiristan Pluton ........................................................................................... 86 5.5.2. Tirich Mir Pluton ......................................................................................... 91 5.5.3. Buni-Zom Pluton ......................................................................................... 92 5.5.4. Garam Chasma Pluton ................................................................................. 93 5.6. Discussion and Tectonic Significance ................................................................ 95  viii 5.7. Summary ............................................................................................................. 98  Chapter 6 Cooling and Exhumation History of the Hindu Kush ............................. 100 6.1. Background ....................................................................................................... 100 6.2. Chronologic Methodology ................................................................................ 102 6.2.1 40Ar/39Ar Chronology .................................................................................. 102 6.2.2. Apatite Fission Track Dating ..................................................................... 104 6.3. Results .............................................................................................................. 105 6.3.1 40Ar/39Ar Chronology .................................................................................. 105 6.3.2. Apatite Fission  .......................................................................................... 111 6.4. Discussion and Interpretations .......................................................................... 111 6.4.1 40Ar/39Ar Data ............................................................................................. 111 6.4.2. Apatite Fission  .......................................................................................... 114 6.5. Cooling and Exhumation Rates ........................................................................ 116 6.5. Summary ........................................................................................................... 119  Chapter 7 Discussion and Conclusions ....................................................................... 120 7.1. Rifting of Gondwana (Cambrian) ..................................................................... 120 7.2. Cimmerian Orogeny (Triassic-Jurassic) ........................................................... 121 7.2.1 Tirich Mir Fault Zone ................................................................................. 121 7.3. Andean-Type Setting (Jurassic-Cretaceous) .................................................... 122 7.4. Docking of Kohistan Island Arc (Late Cretaceous) ......................................... 122 7.5. Collision and Crustal Thickening (Eocene-Miocene) ...................................... 122 7.6. Cooling History/Thermochronology ................................................................ 123 7.7. Significance of the Pre-Himalayan History ...................................................... 124 7.8. Future Work ...................................................................................................... 125  References ...................................................................................................................... 127 Appendices ..................................................................................................................... 143 Appendix A: Geochronological methods  ....................................................................... 143 Appendix B: XRF and ICP-MS techniques .................................................................... 158  ix  List of Tables Table 5.1 Major elements (%), trace elements and rare-earth elements (ppm) data ........ 68 Table 5.2 LA-ICP-MS U-Pb geochronology data for spot analysis of zircon of plutons . 87 Table 5.3 LA-ICP-MS U-Th/Pb geochronology data for spot analysis of monazite ........ 94 Table 6.1 Muscovite and biotite specimens selected for 40Ar/39Ar analysis ................... 108 Table 6.2 Apatite fission track results of specimens collected from the study area ....... 112 Table 6.3 Estimated 40Ar/39Ar and apatite fission track closure temperatures and ages 117    x  List of Figures  Figure 1.1. A shaded elevation map of the Himalayas ....................................................... 2 Figure 1.2. Physiography of the Chitral District showing the Hindu Kush Range. ............ 3 Figure 2.1. Tectonic framework of the northern Pakistan mountain ranges. .................... 10 Figure 2.2. Pangea near the end of the Paleozoic ............................................................. 11 Figure 2.3. Simplified sketch of Cimmerian continent ..................................................... 12 Figure 2.4. Paleogeographic maps through Middle-Jurassic to Late-Oligocene .............. 14 Figure 2.5. Tectonic map of Northern Pakistan and surrounding regions. ....................... 16 Figure 2.6. Structural map of NW Pakistan.. .................................................................... 17 Figure 2.7. Tectonic model showing the present-day reactivation of the Chitral ............. 20 Figure 3.1. Geological map of the Hindu Kush range. ..................................................... 22 Figure 3.2. Tectonic subdivision of the Chitral region into three tectonic blocks ............ 24 Figure 3.3. Outcrop photo and photomicrograph of garnet-staurolite schist. ................... 26 Figure 3.4. Plane and crossed polarized, photomicrograph of sillimanite-garnet schist .. 26 Figure 3.5. Psammite beds and its photomicrograph ........................................................ 27 Figure 3.6. Intensely folded leucosomes parallel to schistosity in a migmatitic rock ...... 27 Figure 3.7. An outcrop photo of isoclinaly folded rock body. .......................................... 27 Figure 3.8. Plane and crossed polarized light photomicrograph of amphibolite .............. 29 Figure 3.9. Plane and crossed polarized light photomicrograph of the amphibolite, ....... 29 Figure 3.10. Calcsilicate unit exposed to the north of the Basti village. .......................... 30 Figure 3.11. Outcrop photo of leucogranite vein and view of Garam Chasma pluton. .... 32 Figure 3.12. Photomicrographs of Garam Chasma leucogranite ...................................... 33 Figure 3.13. An outcrop photograph and thin section photomicrographs of Tirich Mir pluton... .................................................................................................................. 34 Figure 3.14. An outcrop exposure of Tirich pluton along the Garam Chasma road ......... 35 Figure 3.15. Outcrop exposures of phyllite and photomicrographs .................................. 37 Figure 3.16. An outcrop and thin section photos of the Kafiristan pluton. ....................... 38 Figure 3.17. An outcrop and thin section photos of the Buni-Zom pluton ....................... 38 Figure 3.18. Photography of Reshun Fault and conformable contact between phyllite, marble and slate. Photomicrography of marble .................................................... 40  xi Figure 3.19. An outcrop exposure of Chitral Slate in the Chitral valley .......................... 41 Figure 3.20. An outcrop photography and close-up view of greenschist ......................... 42 Figure 3.21. Lithological units of the Reshun Formation around the Reshun Village ..... 44 Figure 4.1. Tectonic setting map of the Hindu Kush terrane and surrounding regions .... 46 Figure 4.2. Geological map of the Hindu Kush in the Garam Chasma ............................ 48 Figure 4.3. Elemental thin section maps of Fe and K and photomicrographs .................. 50 Figure 4.4. U-Th/Pb concordia plots of monazite analyses from specimen S15 and S4. Th concentrations and Gd/Yb ratios versus 208Pb/232Th age plots ............................. 51 Figure 4.5. Schematic tectonic evolution model of the Hindu Kush ................................ 55 Figure 5.1. Geology map of the Chitral region  ................................................................ 61 Figure 5.2. Cross-polarized photomicrographs of plutons ................................................ 64 Figure 5.3. The classification of the plutons in the SiO2 vs. Na2O + K2O diagram ......... 66 Figure 5.4. Chemical variation Harker diagrams of plutons ............................................. 70 Figure 5.5. MORB-normalized trace element plots of plutons ......................................... 72 Figure 5.6. Chondrite normalized REE diagrams of plutons. ........................................... 73 Figure 5.7. Ternary plot of Al2O3-(CaO+Na2O)-K2O of plutons ..................................... 77 Figure 5.8. FeOtot/(FeOtot + MgO) versus weight per cent SiO2 diagram ......................... 79 Figure 5.9. Rb/Sr versus Sr and Ba diagram  .................................................................... 85 Figure 5.10. Tera–Wasserburg concordia diagrams of plutons. ....................................... 90 Figure 5.11. Schematic cross-sectional evolutionary model ............................................ 96 Figure 6.1. Geological map of the study area, showing specimens locations ................ 101 Figure 6.2. 40Ar/39Ar age spectra for muscovite and biotite specimens dated ................ 106 Figure 6.3. Cooling and exhumation rate profiles for various specimen pairs ............... 115          xii Acknowledgements I would like to express my deepest appreciation to my supervisor Kyle Larson for his supervision and helpful guidance in all aspects of the work, which helped me to complete this study. His supervision, patience, wisdom and enthusiasm throughout this PhD project is highly appreciated. I would like to thank other members of my committee: Dr. John Greenough, Dr. Yuan Chen and Dr. Alfredo Camacho for constructive feedback and support through the writing process. I also appreciate the constructive review of my thesis by Dr. Dan Gibson (Simon Fraser University) and Dr. Matthijs Smit (University of British Columbia, Vancouver). I am very grateful to all my Tectonic and Geodynamic Group fellows at the University of British Columbia, Okanagan (Sudip, Tyler, Heather, Jaida, and Kumar) for their invaluable input in this work and the time spent playing ping-pong.  Thanks are also directed to Steven Creighton, Marion McConnell and Robert Millar of the Saskatchewan Research Council for helping with geochemical analyses and microprobe data, Dr. John Cottle (University of California, Santa Barbara) for carrying out the geochronological analyses, Dr. Alfredo Camacho (University of Manitoba) for conducting Ar-Ar analysis and Dr. Isabelle Coutand (Dalhousie University) for helping with fission track thermochronology.  It would be unfair not to recognize the hospitability and extraordinary welcome I received from wonderful people of Chitral area. Special thanks goes to Taj Mohammad (driver), Arif Jan, Prince Major Mohiyuddin, Ali Khan, Mohamamd Noor, Aftab Ali, and Dr. Nusrat Ali. Thanks also go to Asad Ali Shah, Fawad Ayub, Dr. Asghar Ali, Ilyas Ahmad and Asif Khan Durrani (driver National Centre of Excellence in Geology, University of Peshawar, Pakistan), who were prepared to come out and accompany me in the field.  This project would not have been possible without financial support from a Natural Research Council of Canada Discovery Grant to Kyle Larson and NSF grant EAR-1119380 awarded to J. Cottle. I also acknowledge financial support from Geological Society of America Student Research Grants, University of British Columbia Graduate Fellowships, and logistical support from the National Centre of Excellence in Geology, University of Peshawar, Pakistan.  xiii Finally, I would like to thank my beloved family for the support they provided me throughout my educational career and especially during this process. I must acknowledge my wife and boys for putting up with an always-busy husband and father during this process. Khushi has provided unfailing support and has borne the many burdens that have fallen in her lap as I spent my time and energy pursuing my goals. I wish there was space on my degree to write the names of my very supportive wife, Khush Bakht and boys, Abdullah, Momin and Umar.  	  Chapter 1 Introduction  This research project seeks to elucidate the structural, metamorphic and exhumation history of the eastern Hindu Kush range in the Chitral region of the NW Pakistani, far western flank, of the Himalayan orgoenic system (Fig. 1.1). Due to its remoteness and complex geopolitical situation, the geology of the eastern Hindu Kush has not been investigated in detail. The area has, however, attracted the focus of a few geoscience investigations due, primarily, to its potential for preserving both pre- and syn-Himalayan orogenic records. The published literature that is available indicates that its tectonic evolution is both complex and quite different from the	   rest	   of	   the	  Himalaya.	  Because of its unique setting within the Eurasian plate north of the Indian-Eurasian suture, it provides an opportunity to examine both pre-Himalayan features associated with subduction of the Tethys ocean and docking of outboard terranes, which are not well preserved in other parts of the orogen, and geological records of the Cenozoic continental collision.  1.1 STUDY AREA The study area for this PhD project is the eastern Hindu Kush range surrounding the town of Chitral in northern Pakistan (Fig. 1.1). The Chitral District is bounded to the west and north by Afghanistan (and the Wakhan corridor), to the east by the Gilgit District, and to the south by the Dir and Swat districts (Fig. 1.2). The Chitral River, which bisects the region, originates as the Yarkhun River at the northeastern corner of the district from Karamabr glacial lake at an altitude of 4500 m (Fig. 1.2). The river passes out of the district and into Afghanistan (as the Kunar River) within the SW corner of the district at Arandu at an altitude of 1070 m (Fig. 1.2). 1100°0'0"E90°0'0"E80°0'0"E70°0'0"E60°0'0"E40°0'0"N30°0'0"N20°0'0"N10°0'0"N0 500Kilometers1000Tar im BasinPamirTuranBlockAfghanBlockI N D I A N  P L AT EE U R A S I A N  P L AT ETibetan PlateauHinduKush    Ka r a k o r a m- H i m a l a y a n  m o u n t a i n  c h a inNamcha BarwaNanga ParbatFigure 1.1 A shaded elevation map of the Himalayas, showing the distribution of different tectonic blocks and plates involved in the Himalayan orogeny. The NE-SW trend-ing Hindu Kush Range is located to the NW of the Indian plate, north of Afghan Block, and south of the Pamir. The black transparent area shows the location of the Figure 1.2. Source data compiled from:       http://www.arcgis.com/home/webmap/viewer.html?useExisting=1.2H igh Hindu KushLesser Hindu KushCHITRALFigure 1.2 Physiography of the Chitral Disrict showing the Hindu Kush running in a NE-SW direction (redrawn after Kamp et al., 2004). See Figure. 1.1 for the location of the Map. The green transparent area outlines the present study area. The cream colour depicts the extent of the Chitral district.3	  The Hindu Kush is a NE-SW oriented mountain belt that stretches for more than 600 km in northern Pakistan and adjacent Afghanistan. The Hindu Kush range is commonly divided into two belts: (1) the eastern Hindu Kush located in NW Pakistan, and (2) the western Hindu Kush (Nuristan Range), in NE Afghanistan (Figs. 1.1 and 1.2). (For simplicity, the eastern Hindu Kush is referred as ‘the Hindu Kush’ throughout the rest of this thesis). To the east, the range swings eastward and merges with the east-southeast trending Karakoram Ranges and the western continuation of the Himalaya-Tibetan system (Buchroithner and Gamerith, 1986). The Pamir range of central Asia, developed at the junction of the Himalaya, Karakoram, and Hindu Kush Ranges, lies to the north of the Hindu Kush (Fig. 1.1), while the Kohistan (Hindu Raj) Ranges of the Swat and Dir districts bound the Hindu Kush range to the south (Fig. 1.2).  The Hindu Kush in northwestern Pakistan can be divided into two parts: the High Hindu Kush and the Lesser Hindu Kush, where the High Hindu Kush is dominated by Tirich Mir, a peak that reaches an elevation of 7706 m (Kamp et al., 2004, Fig. 1.2). The geology and physiography of the High Hindu Kush are dominated by the NE-SW trending Tirich Mir and Kafiristan plutonic bodies (Hildebrand et al., 2000), whereas the Lesser Hindu Kush is cored by the similarly oriented Buni Zom-Zargar-Umalist pluton (Calkins et al., 1981; Pudsey et al., 1985). The region between the plutonic belts consists of metasedimentary rocks of various ages dominated by the Chitral slate which underlies the middle of the Chitral Valley between Reshun and Gahirat (Calkins et al., 1981; Pudsey et al., 1985; Figs. 1.2 & 1.3).   4	  1.2 PROBLEM STATEMENT When compared to the better studied Karakoram and Himalayan ranges our knowledge of the tectonic evolution of the Hindu Kush range is insufficient to understand how it fits into the larger orogenic framework. The goal of this project is to address the following specific problems: 1) Hildebrand et al (1998; 2000; 2001) inferred multiple metamorphic events in the Chitral region; however, their history has not been integrated with the regional deformational events. The existing U-Pb geochronologic data used to constrain the timing of metamorphism in the Hindu Kush range are based on whole grain analyses that are generally discordant and yield a wide range of ages. Controls on spatial and temporal variation in metamorphism in the Hindu Kush range are, therefore, essentially non-existent and as such require further investigation to elucidate the tectonometamorphic evolution of this region.  2) The existing Rb-Sr and U-(Th)-Pb geochronological data used to constrain magmatic evolution of the Hindu Kush range are, as with the metamorphic constraints, based on whole grain or whole rock analyses, are generally discordant, often yield a wide range of ages for each body (e.g. Desio, 1964; Debon et al., 1987; Hildebrand et al, 1998; 2000; 2001, Heuberger et al., 2007). This limits their potential use in understanding the tectonics of the region through time. 3) The Kafiristan, Buni-Zom, Tirich Mir and Garam Chama plutons within the Chitral region have been variably attributed to subduction or collision-related thickening processes, however, their petrogeneses have not been investigated. A better understanding of plutonic petrogenesis in the region will improve our knowledge of the 5	  evolution of the Hindu Kush range, the southern margin of Asia, and the subduction dynamics of Tethyan oceanic crust. Moreover, the ages of the plutons along with their tectonic setting will help elucidate the timing of deformation structures in the region and whether they developed in association with Mesozoic or Cenozoic processes.  4) Little effort has hitherto been made to document the uplift/exhumation history of the Hindu Kush range through thermochronometry. Application of 40Ar/39Ar and fission track dating will help to elucidate the exhumation and cooling histories of the Hindu Kush range through time. The post-Miocene deformation in the Hindu Kush range is characterized by oblique convergence and development of left-lateral strike-slip faults. The kinematic significance of these faults, beyond the lateral translation across them, is not well understood. It is not known what role the faults may have played in the exhumation and uplift of the plutonic and metamorphic rocks in the area, which today exceed 7700 m in height locally.   1.3 METHODOLOGY Geological mapping paired with analytical work was carried out to address the problems mentioned above. Selected specimens collected during fieldwork were analyzed to constrain the geochronologic (U-(Th)-Pb), thermochronologic (40Ar/39Ar and fission track), and petrogenetic histories recorded in the region. In situ monazite Th-Pb geochronology data were acquired using Laser Ablation paired with a Multicollector Inductively Coupled Plasma-Mass Spectrometer (LA-MC-ICP-MS) at the University of Santa Barbara, California to help constrain the timing of metamorphism in metapelites from the study area. Because monazite can record multiple 6	  metamorphic episodes as different growth zones, in situ microanalysis of individual growth domains can be used to place timing constraints on these events and avoid problems of mixing of different age zones. Moreover, the specific method of dating employed also allowed simultaneous collection of rare earth element data from the different growth zones within monazite grains. Combining trace element data with age constraints provides information about metamorphic processes active when the monazite was growing.  Specimens from the Kafiristan, Tirich Mir, Buni-Zom and Garam Chasma plutonic bodies were subjected to X-ray fluorescence (XRF) analysis to determine major element (weight %) and some trace element concentrations (ppm). The XRF major element data analysis allowed for the description of the Kafiristan, Tirich Mir, Bun-Zom and Garam Chasma plutons and provided a first order classification of the parental magma source. The concentration of major elements was also used to understand potential fractional crystallization of minerals and alumina saturation characteristics. Lithium metaborate fusion with analysis by inductively coupled plasma mass spectrometer (ICPMS) was used to determine trace and rare earth elements. The ICPMS multi-elemental technique can produce high quality data on a wide range of low trace and rare earth element concentrations. The data obtained from the rock specimens of the Hind Kush ranges using ICPMS were instructive in assessing the mobility or immobility of specific elements and discriminating between potential source regions for the plutonic bodies. The XRF and ICPMS data for the plutonic bodies from the Hindu Kush ranges were evaluated using IoGas software. Finally, the exhumation history of the Hindu Kush range was investigated utilizing laser – step heating 40Ar/39Ar dating techniques at the University of Manitoba, Canada, while 7	  apatite fission track thermochronology was carried out at the Department of Earth Sciences at Dalhousie University. 	  8 Chapter 2  Regional Geology and Tectonic Evolution of the NW Himalaya  2.1 TECTONIC EVOLUTION OF THE HIMALAYAN OROGEN The Himalaya extend for ~2500 km between the Namcha Barwa syntaxis in the east and the Nanga Parbat syntaxis in the west (Valdiya, 2002; Figs. 1.1 & 2.1). The spectacular exposure and vertical relief in the Himalaya make it an ideal natural laboratory to study the various geological processes related to orogenesis. The advances in knowledge made in the Himalaya orogen can be applied in other ancient orogens to help interpret kinematics, anatexis, and metamorphic processes.  The evolution of the rocks involved in the Himalaya can be broadly divided into two phases 1) Pre-Cenozoic convergence and 2) Cenozoic evolution of the continent-continent collision.   2.1.1 Pre-Cenozoic convergence During the Paleozoic all of the continents amalgamated to build a single landmass, Pangea, comprising Gondwana to the south and Laurasia to the north (Rogers et al., 1995; Kazmi and Abbasi, 2008; Fig. 2.2). Pangea began to fragment during late-Paleozoic and this resulted in the opening of Palaeo-Tethys (Rogers et al., 1995).  From Paleozoic to Cenozoic time, various small landmass fragments were excised from Gondwana (Fig. 2.3) and traveled across the Paleo-Tethys where they were successively sutured to the southern margin of the Eurasian plate (Boulin, 1981; Tapponnier et al., 1981, Hildebrand, 1998) (Fig. 2.1). Sengor (1979) termed the collage of continental fragments rifted from the northern side of Gondwana, the Cimmerian continent (Fig. 2.3), while others have described them as the Mega-Lhasa block (Gaetani, 1997). The collision between 970 80 90N40383634323028KF = Karakoram FaultNP = Nanga Parbat SyntaxisISZ = Indus Suture ZoneMMT = Main Mantle ThrustHerat FaultTADJIK BASINAFGHANISTANChaman FaultKabulKhost SutureKunlunSutureRushan-PshartSutureN. PamirS. PamirKarakoramHindu Kush     Shyok SutureKohistanMMTPAKISTANNPK2LadakhIndus SutureKashmirZanskarKarakax FaultSiachenNubraKFKFBangong SutureTARIM PLATESONGPAN-GANZEQIANGTAN TERRANEJinsha SutureLHASA BLOCKKailasGANGDESEISZYarlung Tsangpo SutureNEPALKatmanduDarjeelingBHUTANLhasaINDIAMain Boundary ThrustKUNLUNKunlun SutureAltyn Tagh FaultHI MA L AYAKumaon Garhwal0 100 200 300 400 500kmFigure 2.1 Tectonic framework of the northern Pakistan mountain ranges and adjacent central Asia (Redrawn after Searle and Tirrul, 1991).1011Figure 2.3 Simplified sketch of Cimmerian continent (Heuberger, 2004).12 Eurasia and these fragments, between the Late Triassic to Middle Jurassic, led to the closure of the Paleotethys and opening of the Neotethys. During the Early Cretaceous (~130 Ma), a series of intra-oceanic arcs including the Kohstan-Ladakh, Nuristan and Kandhar island arcs were accreted to the western portion of the Eurasian margin while an Andean-style margin developed farther east resulting in the Trans-Himalayan batholiths (e.g. Tahirkhelli et al., 1979; Searle, 1991; Treloar and Izatt, 1993; Windley, 1983; Wandrey et al., 2004).   2.1.2 The India-Eurasia Collision The Indian plate was located in the southern hemisphere with Africa, Antarctica, and Australia (Patriat and Achache, 1984; Wandrey et al., 2004, Fig. 2.4) from the Permian to the Middle Jurassic. In the Middle Jurassic (~ 167 Ma ago) the Australian, Indian and Antarctic continents began to move away from Africa as Gondwana broke apart (Wandrey et al., 2004). Following that, in the Early Cretaceous, the Indian plate separated from Australia and Antartica, and began moving rapidly northward (Fig. 2.4). The Indian plate traveled northward a distance of ~5000 km (Patriat and Achache, 1984), at the expanse of northward subduction of Tethys Ocean beneath Eurasia leading to the collision of India and Eurasia (upon the closure of Tethys), which initiated around 50-55 myr ago (e.g. Jan and Khan, 1981; Tahirkhelli, 1982; Beck et al., 1995; Green et al., 2008; Najman et al., 2010). At this time, as a result of the initiation of continent-continent collision, the northward movement of the Indian plate slowed down from 15-25 cm/yr to 4.5 cm/yr (Powell, 1979; Patriat and Achache, 1984). In the time since initial collision it is estimated that ~2600 ± 900 km of convergence has been accommodated within the Himalayan-Tibetan system (Patriat and Achache, 1984).   13Late-Cretaceous (~94 Ma)Middle-Eocene (~50 Ma) Late-Oligocene (~27 Ma)Latest-Cretaceous (~69 Ma)Middle-Jurassic (~166 Ma) Early-Cretaceous (~130 Ma)Figure 2.4 Paleogeographic maps through Middle-Jurassic to Late-Oligocene Epoch (After Scotese et al., 1988; Scotese, 1997, as cited in Wandrey et al., 2004).14 2.2 EVOLUTION OF THE HINDU KUSH REGION Based on previous work, the evolution of the Hindu Kush region can be summarized as below. 2.2.1 Late Triassic-Middle Jurassic Orogeny The collision between terranes of Mega-Lhasa affinity and Eurasia initiated with contact of the Iran Spur in Late Triassic (Zanchi et al., 2000). This collision, which has been refered to as the Cimmerian orogengy (Stocklin, 1974; Sengor, 1979) gradually propagated eastwards with final suturing with Eurasia, and closure of the Paleo-Tethys by the Middle Jurassic (Hildebrand et al., 2000; 2001; Zanchi et al., 2000). This Jurassic collision between Mega-Lhasa and Eurasia is believed to be the earliest recorded orogenic event recorded in the Chitral region (Gaetani; 1997; Zanchi et al., 20000; Hildebrand et al., 2000). Subsequently, the Hindu Kush region (now part of the Eurasian Plate) was transformed into an Andean-type convergent margin, which is thought to be recorded by intrusion of the Tirich Mir, Buni-Zom and Kafiristan plutons in a subduction related environment along the southern margin of Eurasia (Hildebrand et al., 2000; 2001; Heuberger, 2004). Moreover, Hildebrand (1998) proposed that the common occurrence of andalusite and minor sillimanite in metasediments in the Hindu Kush indicated a high geothermal gradient that he linked with an active continental margin.   2.2.2. Middle Cretaceous Kohistan-Ladakh Accretion with Eurasia In the mid-Cretaceous, the Tirich Mir suture zone (Figs. 2.5 and 2.6), which is thought to have been first active during the Middle Jurassic (Hildebrand, 1998; Zanchi et al., 2000; Hildebrand et al., 2000; 2001), was reactivated into the south-verging Tirich Mir fault 151235798640 200 kmA68o 70o 78oN72o 74o 76o36o38oTURKESTANTARIMMFTHerat F.WASSSRPZSE-PKTIEN-SHAN N-PC-PACMSW-P   Altyn Tagh FaultKUN LUNQIANG TANGKillik FaultHunzaKARAKORAMTMFWakhanKafiristanNuristan CHITRALEHKKOHISTANMMTIslamabadWAZHELMANDFARAHROD    Wasser-PanjaoChaman FaultBAND EBAYAN LAKAKHHIMALAYAMBTBFigure 2.5 Tectonic map of Northern Pakistan and surrounding regions. MFT, Main Frontal Thrust; MBT, Main Boundary Thrust; MMT, Main Mantle Thrust; SS, Shyok Suture; TMF, Tirich Mir Fault Zone; EHK, East Hindu Kush; ACM, Alitchur mountains; RPZ, Rushan-Pshart Zone; WAS, Wanch-Ak Baital Suture; N-P, North Pamir; C-P, Central Pamir; SE-P, SE-Pamir; SW-P, SW-Pamir; WAZ, Waziristan; K, Kabul. 1, Quaternary; 2, Tertiary foredeeps; 3, Palaeozoic belts; 4, Terranes of Gondwanan affinity; 5, Kabul Block; 6, Wasser-Panjao Suture; 7, Waziristan ophi-olitic complex; 8, Kohistan- Ladakh arc terranes; 9, Himalaya. Heavy lines repre-sent main sutures (Redrawn after Gaetani et al., 1996; Zanchi et al., 2000). Insert rectangle (B) shows the location of Fig. 2.6.16LEGENDMesozoic TertiaryintrusivesE-HINDU KUSHAtark UnitWakhan SlatesArkari Fm.Reshun Fm.Krinji Fm.MarblesTIRICH BOUNDARYZONE SHYOK SUTUREKARAKORAMAmphibolites,serpentinitesKogozi GreenschistsChitral SlateShah Jinali Phyllites,Lun Shales, Lutkho Fm.Owir Series, ShogramFm., Lasht Unit (D-P)Tash Kupruk Unitdolostones, volcanicsSed. and Metased.of KarakoramSS MelangeKOHISTAN ARCKohistan Arc Undi ff .AFGHANISTANEHKPPAKISTANArkari GolTirich MirT i r i ch  G olT i r ic h  M i r F ZTMPLutkho V.ChitralBarum GolReshunBuni  R e sh un  F au ltMastujY ar k un  RMirgash   R ic h Go lMorichShah Jinali PS hy ok  S ut u reFigure 2.6 Lithotectonic map of NW Pakistan. EHKP, East Hindu Kush plutonic belt; TMP, Tirich Mir Pluton (Redrawn after Gaetani et al., 1996; Zanchi et al., 2000).N10 kmIRAN A F GH A NI S T ANKabulIslamabadKarachiCHINAINDIANOCEANB17 which facilitated exhumation of the Tirich Mir pluton body to the surface and crosscut the Tirich Mir mélange zone (Hildebrand et al., 2000; 2001). Subsequently, in the Late Cretaceous, the Kohistan Island Arc was accreted to the southern Eurasian margin along the Shyok suture (Fig. 2.5); Petterson et al., 1991; Fraser et al., 2001; Treloar et al., 1989; Searle et al., 1999). Subduction moved to the southern margin of the newly accreted material and a new Andean-type margin developed resulting in the intrusion of the Karakoram axial pluton in the Karakoram, however, no similar record is present in the Hindu Kush.   2.2.3. Early Cenozoic Himalayan Orogeny The suture between the Indian plate and Eurasia is marked by the Main Mantle Thrust (MMT) in Pakistan (Tahirkheli, 1979; 1982), which is equivalent to the Indus Suture in other areas (Gansser, 1964; Fig. 2.5). While the Karakoram terrane records evidence of this initial collision at ~50 Ma such a record in the Chitral region has not been observed (Hildebrand, 1998).   2.2.4. Late Cenozoic Orogeny Radiometric dating by Hildebrand (1998) outlined two major tectonic events in the Late Cenozoic in the Chitral region, which can be categorized as follow: At ~24 Ma, deformation, crustal melting, migmatisation and the intrusion of leucogranite, including the Garam Chashma pluton and associated dykes, took place synchronously with the intrusion of the Baltoro pluton in the Karakoram to the east (Hildebrand et al., 1998). This thermal event resulted in silliminite-K-feldspar grade metamorphism and is associated with exhumation by thrust faulting that exposed gneisses and deep-crustal metapelitic rocks 18 in the region. This record of pluton intrusion and metamorphism in the Miocene is generally synchronous along the entire length of Himalaya (Hildebrand et al., 1998).  The dominant present-day regional strike in the Chitral region is NE-SW, with the main foliation dipping to the NW (Hildebrand, 1998). This includes the Tirich Mir Fault, as well as the Reshun Fault, which record E– to SE– directed thrusting, potentially as recent as 24 Ma. The present-day orientation of these structures, however, is not consistent with the N-S compression expected from N– to NW– directed Cretaceous subduction and accretion, and initial collision during the Himalayan orogen. It has been interpreted the structures were initially E-W striking and N-dipping and that they were rotated anticlockwise because of its position at the far NW end of the Himalayan orogeny. The continued northward movement of India into Asia would have reoriented the original structures such that they entered into a new position favorable for sinistral strike-slip movement (Fig. 2.7). This recent strike-slip deformation is represented by sub-horizontal stretching lineations and variably oriented fold axes along the Tirich Mir fault zone (Hildebrand 1998; Hildebrand et al., 2000). While this strike-slip deformation is thought to post-date the 24 Ma intrusion of the Garam Chasma pluton (Hildebrand 1998; Hildebrand et al., 2000), it is not clear if it was a localized event of short duration or whether it has persisted through the post-24 Ma geological history of the Chitral region.   19??Dorah PassplutonKohistan arcKafiristanplutonTirich MirplutonGharamChasmapluton     Reshun FaultNorthern suture zoneDorah Pass plutonKohistan arcKafiristanplutonTirich Mir faultTirich Mir plutonGharamChasmapluton     Reshun FaultNorthern suture zoneNTMZTMZ10 kmca. 24 MaN10 kmPresent dayFigure 2.7 Tectonic model showing the present-day reactivation of the Chitral region including the Tirich Mir Fault, Reshun Fault and Northern suture into a strike-slip setting from the original thrust-tectonic setting (Redrawn after Hildebrand, 1998). TMZ = Tirich Mir Zone. 20	  Chapter 3    Geology of the Hindu Kush, Chitral area, NW Pakistan  3.1 BACKGROUND The rocks of the Hindu Kush range from Paleozoic to Cenozoic in age. They consist mainly of metasediments and intruded by Paleozoic to Cenozoic igneous rocks (e.g. Calkins et al., 1981; Pudsey et l., 1985, Fig. 3.1). The metasediments themselves have typically experienced low to medium grade metamorphism, and are now slate, phyllite and schist, though examples of higher grade (sillimanite) rocks occur locally. This chapter discusses the geology of the Hindu Kush range based on previous work, field observations, and petrographic examination of rock specimens collected during fieldwork.  3.2 PREVIOUS WORK Early records of Hindu Kush geology can be found in the descriptions of British military surveying missions, however, the pioneering work of Hayden (1915) on the general geology and fossil description deserves recognition. Later research was mostly focused on establishing and correlating the stratigraphy of the Chitral region (e.g. Desio, 1959; 1966; 1975) and the main tectonic framework of the Hindu Kush range in the Chitral region was interpreted based on the derived stratigraphic relationships. Pluton age information, as summarized by Zanchi et al. (2000), include Rb-Sr whole rock radiometric age data that indicate an age of ~480 Ma for the Kafirsitan pluton (Debon et al. 1987a), and 115 ± 4 Ma for the Tirich Mir pluton (Desio, et al., 1964), while the Shushar pluton yielded a K/Ar age of 171 ± 3 Ma (Gaetani et al., 1996). Studies have also been carried out to describe the geology, metamorphism, potential economic resources, and structural styles of the Hindu Kush region (Calkins et al., 1981; Pudsey et al., 1985). Buchroitner and Gamerith (1986), carried out 21B om bo r at e  Va l l eyL u t k h o  G o lArkariGolR um bo o r Va l l e y B ag ho st  Go lBasti Gol7 0827 01 57 56 07 58 48 07 24 46 18 56 76 38 57 84 0828 76 38 66 64 58 25 55 88 07 0357 05 15 72 68 85 53 5 4 56 04 65 67 8307 58 56 56 08 58 25 55 25 1767 6787 66 16 15 86 26 66 05 6447 2474 58 27 06 6R es h un  Fa u lt  T i ri c h Mi r  Fa ul tCHITRALShoghorG ar a mC ha s maBarenis71˚30′ 71˚45′ 72˚00′3 6˚ 15 ′71˚15′71˚13′3 6˚ 00 ′3 5˚ 45 ′36˚15′Buni-Zom/Kesu-Kohuzi PlutonTirich Mir PlutonGaram Chasma PlutonKafiristan PlutonCarbonatesCalcsilicateTirich MirAmphiboliteGreenschistReshunConglomeratePsammite UnitsMetasedimentry rocks(Undifferentiated)Chitral SlateDorah An PlutonINDEX0 4kmCleavage/schistosityFaultSettlementStream/RiverSnow8 12LEGENDNGCPF = Garam Chasma               Pluton FaultKabulIslamabadCHINAINDIAAFGHANISTANPAKISTANFigure 3.1 Geological map of the Hindu Kush range, District Chitral, Kyber Pukhtoon Khawa, Pakistan.22	  mapping in the Tirich Mir region and described different possible origins for economic mineral deposits of the area. The map area has been interpreted to comprise different tectonically juxtaposed fault-bound blocks of Gondwana affinity (Gaetani, 1997; Zanchi et al., 2000). The Hindu Kush region was originally divided by Pudsey et al. (1985) into two tectonic zones 1) the Northwestern or (Paleozoic) Lutkho-Torikho Unit, and 2) Central or (Paleozoic-Mesozoic) Kunar-Yarkhun Unit separated by the NE-SW trending Reshun Fault (Calkins et al., 1981; Zanchi et al., 1997). Later work by Gaetani and co-workers (Gaetani, 1997; Gaetani et al., 1996; Zanchi et al., 1997; 2000; Gaetani et al., 2004) outlined the Tirich Mir Fault Zone within the Northwestern Unit of Pudsey et al. (1985). Metabasalts and ultramafic rocks believed to be of mantle origin were observed within the Tirich Mir fault structure, which led to its interpretation as a suture between the Hindu Kush and Karakoram block (Zanchi et al., 2000). Based on the research of Gaetani, (1997), Gaetani et al. (1996), Zanchi et al. (2000), Hildebrand et al. (1998; 2000; 2001), and Heuberger et al. (2007), the Chitral region can now be broadly be subdivided into three fault bounded tectonic blocks that from northwest to southeast include 1) the Wakhan Block, 2) the Broghil Block and 3) the Yarkhun Block (Fig. 3.2). The Tirich Mir fault separates the Wakhan and Broghil blocks, while the Reshun fault marks the boundary between the Broghil and Yarkhun blocks. Farther to the south, the Yarkhun Block is in tectonic contact with the Kohistan island arc block along the Kohistan-Karakoram Suture, marked by the Main Karakoram Thrust (MKT) (Fig. 3.2). Some of the most recent work in the region was conducted by the Geological Survey of Pakistan who published a geological map (1:375000 scale) of the Chitral district (Aslam et al., 2007).  23LegendNTirich Mir FaultReshun FaultMain Karakoram FaultWAKHANBLOCKYARKHUNBLOCKKOHISTAN ISLANDARC TERRANEBAROGHILBLOCKFigure 3.2 Tectonic subdivision of the Chitral region into three tectonic blocks 1) Wakhan Block, 2) Baroghil Block, 3) Yarkhun Block. Tirich Mir fault separates the blocks 1 and 2, and the Reshun fault separates Blocks 2 and 3. The Chitral region is sepa-rated to the south from the Kohistan island arc terrane by the Main Karakoram fault. See Figure 1.2 for location (after Aslam et al., 2000). 24	  3.3 LITHOTECTONIC UNITS 3.3.1 WAKHAN BLOCK Metasediments (biotite-garnet, staurolite-garnet, and sillimanite-garnet schist) No precise age data are available for the protoliths of these metapelitic rocks; however, they have been interpreted to represent the southwestern continuation of the Wakhan Formation which is Permian-Triassic in age (Hayden, 1915; Desio, 1963; Kafarskyi and Abdullah, 1976; Aslam et al., 2007). The Wakhan Formation comprises a continuous sequence of dark, homogeneous slate, phyllite and quartzite with some minor limestone and calcareous schist extending from across the Afghanistan boarder into the Lutkho gol towards the Shah Jinali/Baroghil pass (Aslam et al., 2007; Figs. 3.2 and 2.6). The intensity of metamorphism in this unit increases gradually along the Lutkho Gol to the northwest towards the Garam Chasma pluton from biotite to garnet-staurolite and finally to sillimanite-bearing schist (Figs. 3.3 and 3.4). It is important to mention that “Gol” is a local name for a stream. Farther to the NW along the Lutkho gol, metapsammitic layers are intercalated with these schistose rocks. These metapsammites commonly contain quartz, plagioclase, alkali feldspar and minor biotite (Fig. 3.5). Close to the Garam Chasma intrusion, the schist is characterized by sillimanite, garnet, muscovite and biotite (Fig. 3.3). Rocks close to the Garam Chasma pluton are also pervasively deformed and migmatitic (Fig. 3.6). Similar schists are exposed in the Arkari gol to the east (Fig. 3.1), where deformation is manifested as isoclinal folding (Fig. 3.7).    25(b)(a)SilBtGrtQzSilBtFigure 3.4 (a) Plane and (b) crossed polarized, photomicrograph of sillimanite-garnet schist in close vicinity of Garam Chasma pluton, showing biotite (Bt) being replaced by silli-manite (Sil). Other minerals are Garnet (Grt), quartz (Qz) and muscovite (Ms). BtGrtQtzBtQzSil(a) (b)StGrtMsBtQzBtMsFigure 3.3 (a) An outcrop photo of garnet-starolute schist with blebs of garnet on surface and (b) photomicrograph of the specimen shows garnet (Grt), staurolite (St), biotite (Bt), muscovite (Ms) and quartz (Qz) in plane polarized light. Mineral abbrevia-tions after Whitney and Evans (2010).26Figure 3.7 An outcrop photo of isoclinaly folded rock body in the Arkari gol.Figure 3.6 Intensely folded leuco-somes parallel to schistosity in a migmatitic rock exposed in the upper Lutkho gol near the contact zone of Garam Chasma plutonic body.(a)BtQzEpPlPl(b)Figure 3.5 (a) Psammite beds exposed along the Lutkho gol and (b) photomicrograph of the psammite shows metamorphic minerals such as biotite (Bt), epidote (Ep), coarse-grained, strain-free quartz (Qz) and plagioclase (Pl). Cross polarized light.27	  Tirich Mir Amphibolite unit  Amphibolite rocks occur along the northwestern boundary of the Tirich Mir pluton along the Arkari gol (Hildebrand, 1998; Zanchi et al., 2000; Fig. 3.1). In agreement with the observations of Hildebrand (1998), this amphibolite is also mapped to the NW along the Lutkho Gol (Fig. 3.1). The amphibole unit observed in the Arkari Gol mainly consists of hornblende, biotite, quartz, plagioclase and ± clinopyroxene while in the Lutkho Gol it contains hornblende, quartz, chlorite and garnet (skeletal form) (Figs. 3.8 and 3.9). The difference in mineralogy may indicate a slightly different protolith or perhaps different metamorphic conditions between the two gols. A similar rock unit known as the Tash Kupruk Unit of Late Devonian-Early Carboniferous age (Kafarskyi and Abdullah, 1976; Gaetani et al., 1996; Hildebrand, 1998; Aslam et al., 2007), is exposed adjacent to Tirich Mir fault along the Morich Valley and Shah Jinali Pass to the NW of the study area (Fig. 2.6).  Calcsilicate  White to green, fine- to medium-grained calc-silicate lenses occur commonly with the schistose rocks of the Wakhan zone. A major calcsilicate unit runs along strike of rocks from Lutkho Gol, near the Garam Chasma pluton to the Basti gol, in the north (Fig. 3.1). The rock unit has generally granular texture and consists mainly of quartz, dolomite, feldspar and garnet. It shows strong deformation and alteration along the Basti gol with development of graphite, chlorite and talc minerals (Fig. 3.10).     28(a) (b)HblGrtQzPlHblFigure 3.9 (a) Plane polarized and (b) crossed polarized light photomicrograph of the amphibolite specimen in the Lutkho gol, showing garnet as compared to the specimen in the Arkari Gol that lack garnet. Quartz (Qz), hornblende (Hbl), and plagioclase (Pl).QzBtPlQzHbl(a) (b)Figure 3.8 (a) Plane polarized and (b) crossed polarized photomicrographs of amphibolite specimen from Arkari Gol showing hornblende (Hbl), biotite (Bt), quartz (Qz) and plagioclase (Pl). The oriented Hbl, as well as some Bt define a pervasive foliation.HblBtBt29(a)(b)(c)Figure 3.10 Calcsilicate unit exposed to the north of the Basti village. (a) A granular calacsili-cate outcrop photo shows spotted garnet and some grapite on the surface in the Basti gol. (b) Green colored calcsilicate with chlorite and talc. (C) Vertical cliff of highly weathered calcsilicate beds north of Basti Village. 30	  Plutons of the Wakhan block The above-described metasediments are intruded by the Tirich Mir and Garam Chasma plutons (Fig. 3.1). These bodies have been interpreted to be Cretacous (Tirich Mir) and Early Miocene (Garam Chasma) in age based on limited U-Pb dating  (Hildebrand et al., 1998; 2000). These grantic bodies are briefly described here with more detail provided in  Chapter 5.  The garnet-staurolite schist in the Lutkho gol is intruded by the Garam Chasm leucogrante (Fig. 3.11), which has an overall exposure of ~185 km2.  The main Garam Chasma body consists of undeformed, medium-grained leucogranite that comprises uartz, alkali feldspar, plagioclase, muscovite, biotite, as well as local silliminate, garnet, zircon and tourmaline (Fig. 3.12).  Mineralogically, the Tirich Mir pluton mainly consists of quartz, plagioclase, K-feldspar, biotite, muscovite, with accessory minerals zircon, apatite, tourmaline and opaque (Fig. 3.13). The SE contact of the Tirich Mir pluton is marked by the Tirich Mir Thrust fault while the NW is considered intrusive (Hildebrand, 1998). The Tirich Mir pluton in the Arkari gol has a variably developed foliation defined by the alignment of muscoivte, biotite and plastically deformed quartz and alkali feldspar (Fig. 3.13). Moreover, alkali feldspar megacrysts occur along the Tirich Mir fault zone and range in size from 2-5 cm defining a horizontally aligned foliation (Fig. 3.13). In contrast, the Tirich Mir pluton in the Lutkho gol is generally equigranular (Fig. 3.14). This may be indicate multiple episodes of magma generation Or that the Tirich Mir fault only affected the eastern margin of the pluton.    31Garam Chasma leucograniteGarnet-staurolite schist(a)(b)Leucogranitic vein(a)Figure 3.11 (a) Outcrop photo of leucogrante vein intruded along as well as across the foliation planes of schistose rock. Also note a network of veins in the left side of photograph (b) view of Garam Chasma pluton from Sepokht village (photos taken facing north). 32BtQtzMsPlAfs(a)(b)GrtPlMsQzSilBtFigure 3.12 Photomicrographs of Garam Chasma leucogranite (a) shows biotite (Bt), sillimi-nate (Sil), and Garnet (Grt); view in plane polarized light and (b) alkali feldspar (Afs), muscovite (Ms), biotite, quartz (Qz) and plagioclase (Pl) that shows char-acteristic albite twining (crossed polarzied light). 33Tirich Mirgranite(c)(a)MsMcMcQzBtPlAfsAfs(d) (e)(b)Figure 3.13 (a) An outcrop photograph of Tirich Mir pluton in the Arkari gol (b) foliation/magmatic fabric defined by aligned alkali feldspar, (c) large phenocrysts of alkali feldspar, (d) and (e) are thin section photomicrographs with large grains of microcline (Mc) characterized by tartan twining, Alkali feldspar (Afs), muscovite (Ms), biotite (Bt), quartz (Qz) and plagioclase (Pl). Note the augen textures in (b) and some mylonization in (d) and (e) are indica-tive of deformaiton of parts of the Tirich Mir leucogranite.Ms34(a) (b)Tirich MirgraniteMetasedimentsMetasedimentsTirich Mir graniteQz MsPlPlPlMsPlQzTurAfsPlQzBtMsMsQzAfsAfs(c) (d)(e) (f)Figure 3.14 (a) An outcrop exposure of Tirich Mir pluton along the road to the Garam Chasma village in the Lutkho gol; whereas (b) shows a leucogranitic dyke and similar dyke swarms may be observed all around Tirich Mir pluton. (c) – (f) photomicro-graphs of the specimens from the Tirich Mir granite body in the Lutkho gol. The inequant grains (c and e) do not show the effect of any directed stress, but quartz (Qz) are highly strained or have a morter texture, which may be caused by shearing/deformation. Note alteration in alkali feldspar (Asf). The intensity of deformation is reflected by pronounced alignment (foliation) of muscovite (Ms) and biotite (Bt) in (d) and (f). Tur = Tourmaline; other abbreviations are the same as in  Fig. 3.13.QzPlMsPlBtQzQz35	  3.3.2 BAROGHIL BLOCK  The Baroghil Block is a linear belt of metasedimentary rocks bounded by the Tirich Mir fault to the north and by the Reshun fault to the south (Fig. 3.1). The rock units of this block are considered Jurassic in age on the basis of beleminite fossils (Pascoe, 1924 cited by Leake et al., 1989).   Phyllite Units  Rocks exposed in the vicinity of Shoghor, Momi and Rugi are phyllitic in nature (Fig. 3.1), are green to grey in color, very fine-grained, with a well-developed foliation (Fig. 3.15). The phyllite is commonly graphitic and consists dominantly of quartz, muscovite, chlorite, and carbonate (Fig. 3.15). This phyllite is considered a continuation of the Shah Jinali phyllites in the Lutkho and Arkari gols and has been called the Lun Shales/ or Lutkho Formation in the literature (Pudsey et al., 1985; Leake et al., 1989). The Broghil Block rocks are intruded by the Kafiristan pluton in the  southwest (Fig. 3.1). The Kafiristan pluton is foliated and consists of alkali feldspar, quartz, plagioclase, bioitite and muscovite (Fig. 3.16).   3.3.3 YARKHUN BLOCK  The Yarkhun Block occurs in the footwall of the Reshun fault and extends south to the Main Karakoram fault (Fig. 2.6). This block includes marble, slate, greenschist and quartzite, which are intruded by a linear plutonic complex including the Buni-Zom pluton (discussed in Chapter 5; Figs. 3.3 and 2.6). The Buni-Zom body is generally intermediate in composition, consisting of hornblende, biotite, plagioclase and accessory titanite and zircon (Fig. 3.17).   36QzMsChlPlMsQzFigure 3.15 Outcrop exposures of phylitte with photomicrographs on the right. The rocks are characterized by muscovite (Ms) and chlorite (Chl) defining the cleavage/foliation planes. 37HblBtTtnHblPlQz(a) (b)PlFigure 3.17 (a) The Buni-Zom pluton is fine-grained and fresh; (b) thin section shows abun-dant mafic mineral such as Hbl, Bt and minor Titanite (Ttn).BtPlQzBtMs(a) (b)Figure 3.16 (a) Outcrop of the Kafiristan pluton, which is equigranular and shows a well-developed foliation. (b) The foliation is defined by the alignment of micas in thin section photomicrograph. Plagioclase (Pl), biotite (Bt) and quartz (Qz).38	  Marble/Limestone The Kringi carbonate unit is a narrow belt of marble that crops out along the entire length of the Reshun fault footwall (Fig. 3.1). It has been interpreted as Cretaceous in age based on fossil material (Pudsey et al., 1985). The marble is usually massive, banded grey to white, and forms nearly vertical ridges. Near Shoghar, the unit has a faulted western contact with the phyllites of Baroghil block (Fig. 3.18a). The eastern contact varies along its length, but is interpreted to have a conformable contact with the Chitral slates near Shoghor village (Fig. 3.18b).   Chitral Slate  The majority of the Yarkun block in the Chitral district is underlain by the Chitral Slate unit which includes dark grey slates, fine-to-medium grained sandstone, and dark grey phyllite (Fig. 3.19). The age of Chitral slate is controversial, but Calkins et al. (1981) interpreted it to be Cretaceous. More recently, the Chitral Slate has been considered to be Jurassic-Cretaceous in age (Aslam et al., 2007).   Greenschist The rocks exposed around the village of Koghuzi are part of a continuous belt of greenschist extending from Barenis in the NE to Kuru the SW (Figs. 3.1; 3.2). In literature, this greenschist has been described as the Koghuzi Schist of unknown age. The rocks are pale-green to grey in color and consist of quartz, alkali feldspar, plagioclase, carbonate and chlorite (Fig. 3.20c and d).    39           Reshun FaultPhylliteMarbleMarbleChitral Slate(a) (b)Lutkho River(c)Figure 3.18 (a) Phyllite of the Baroghil block is overriding the marble unit of the Yarkhun block along the Reshun fault in Shoghor village (photo taken looking north-ward). (b) Conformable contact between Chitral Slate and marble units just to the south of Shoghor village along the Lutkho Gol (looking south). (c) Cross polar-ized light photomicrography of the calcite marble showing twin bands.40(a)(b) (c)Figure 3.19 (a) An outcrop exposure of Chitral Slate in the Chitral valley; photo taken while looking SW. (b) Close-up view of (a).  (c) General view in cross polarized light of the Chitral slate, showing slaty cleavage defined by an alignment muscovite (pinkish) and grey quartz, which alos indicate a low grade of metamorphism. 41PlCbChlChlQzChlCbQz(a) (b)(c) (d)QzFigure 3.20 (a) An outcrop photograph and (b) close-up view of greenschist exposed in and around the Koghuzi village along the Mustug valley. (c) Photomicrograph show large grains of carbonate (Cb), brown chlorite (Chl), and checkerboard quartz grains and (d) a large grain of plagioclase (albite) surrounded by a fine-grained matrix of chlorite and quartz (Qz). 42	  Reshun Formation The Cretaceous Reshun formation crops out in the footwall of Reshun Fault to the north of Barenis (Fig. 3.1), and has an unconformable lower contact with the Chitral Slate and Koghuzi Schist (Pudsey eta l., 1985; Gaetani et al., 2004). The formation has a variable lithology consisting of conglomerate, phyllite, marble, shale, and sandstone/quartzite (Fig. 3.21) typically with a characteristic reddish color. These rocks are the least metamorphosed in the mapped area.  43RFShalePhyllite ConglomerateShaleConglomerate(a)(b)Figure 3.21 (a) Lithological units of the Reshun Formation around the Reshun Village (photo taken looking northward). (b) A close-up view of Reshun Formation along the Reshun gol (photo taken while looking WNW). RF = Reshun Fault.44 Chapter 4  Building The Hindu Kush: Monazite Records of Terrane Accretion, Plutonism, and the Evolution of the Himalaya-Karakoram-Tibet Orogen  4.1. BACKGROUND Northern Pakistan, where the Himalaya, Karakoram, and Hindu Kush mountain ranges meet, is a critical location for understanding plate convergence processes along the southern margin of Eurasia. The Hindu Kush is the western continuation of the Himalaya-Karakoram-Tibet (HKT) orogenic system, forming a 600 km long, NE-SW oriented, mountain belt running from northern Pakistan into adjacent Afghanistan (Fig. 4.1). The rocks within the range record a protracted tectonic history that includes multiple deformational and metamorphic events associated with Mesozoic subduction and accretion and Cenozoic continental collision (e.g. Hildebrand et al., 1998; 2001; Heuberger et al., 2007). Previous work has shown that the Hindu Kush consists of a collage of tectonically juxtaposed fault bounded terranes of Gondwanian affinity (Zanchi et al., 2000; Hildebrand et al., 2001). As part of the southern margin of Eurasia the Hindu Kush terrane was subjected to a series of deformational and magmatic events that record the evolution of the HKT system including: 1) the suturing of the Karakoram terrane to the Hindu Kush terrane sometime between the Jurassic and Early Cretaceous (Hildebrand et al., 2001); 2) the development of a Mesozoic continental magmatic arc above a north dipping subduction zone (Searle et al., 1989); 3) docking of the Kohistan Island Arc during the Late Cretaceous (Petterson et al., 1991); 4) collision between India and Eurasia (Beck et al., 1985; Yin and Harrison, 2000; and references therein); and; 5) subsequent widespread crustal thickening, Early Miocene anatexis and the formation of large leucogranite plutons such as the Garam Chasma pluton in the Hindu Kush (Hildebrand et al., 1998).  451235798640 200 km72o 74o36o38o68o 70o 78o76oNTURKESTANTARIMMFTH e r a t F a u l tWASSSRPZSE-PTIEN-SHAN N-PC-PACMS W- P   Altyn Tagh Fault KUN LUNQIANG TANGKillik FaultKARAKORAMT MFWa k h anKOHISTANM MTIslamabadWAZFARAH ROD    Wa ss er - Pa nj aoC ha ma n Fa ul tB A N D E B AYA N LAKAKHHIMALAYAMBTChitralH in du  K us hKFigure 4.1 Tectonic setting map of the Hindu Kush terrane and surrounding regions. MFT, Main Frontal Thrust; MBT, Main Boundary Thrust; MMT, Main Mantle Thrust; SS, Shyok Suture; TMF, Tirich Mir Fault Zone; ACM, Alitchur mountains; RPZ, Rushan-Pshart Zone; WAS, Wanch-Ak Baital Suture; N-P, North Pamir; C-P, Central Pamir; SE-P, SE-Pamir; SW-P, SW-Pamir; WAZ, Waziristan; K, Kabul. 1, Quaternary; 2, Tertiary foredeeps; 3, Palaeozoic belts; 4, Terranes of Gondwanan affinity; 5, Kabul Block; 6, Wasser-Panjao Suture; 7, Waziristan ophiolitic complex; 8, Kohistan- Ladakh arc terranes; 9, Himalaya. Heavy lines represent main sutures (Modified from Gaetani et al., 1996; Zanchi et al., 2000). The small box shows the location of Fig. 4.2.46 The pre-Himalayan (Mesozoic) record of orogenesis, which is of fundamental importance to understand how the Cenozoic tectonic history of the Himalayan orogen may relate to antecedent structures and thermal history, is obscured, destroyed, or not recorded in most parts of the orogen especially, within Indian plate rocks. Investigating the rock record in the Hindu Kush provides a unique opportunity to examine rocks that record this protracted history and provide geological constraints critical to understanding the tectonic evolution of the broader HKT system.  4.2. GEOLOGY OF THE GARAM CHASMA REGION The geology of the area surrounding the hamlet of Garam Chasma in the Chitral region of the NW Pakistan Hindu Kush is dominated by the Kafiristan, Tirich Mir, and Garam Chasma plutons (Fig. 4.2, Pudsey et al., 1985; Hildebrand et al., 2001). The rocks between the NE-SW trending plutonic belts in the region comprise a variety of metasedimentary rocks including variably metamorphosed metapelites with localized calcsilicate rock lenses (Hildebrand et al., 2001; Zanchi et al., 2000) that have been interpreted to have a Devonian depositional age (Gaetani et al., 1996).  Previous investigation has indicated that the metasedimentary rocks in the vicinity of Garam Chasma were deformed, metamorphosed and intruded by subduction-related plutonic rocks in the Mesozoic before further metamorphism, deformation and intrusion during the Cenozoic (Hildebrand et al., 2001). While existing U-Pb dates from the Buni-Zom/Phargram, Tirich Mir, and Garam Chasma plutons provide constraints on the timing of intrusive activity in the region (Hildebrand et al., 1998; 2001; Heuberger et al., 2007), the timing of deformation and metamorphism in the area is poorly constrained. Moreover, the few 47Plutons (O-P) Calcsilicaterocks(?)Carbonates (K)Amphibolite (C-P)Metasediments (D)Strike-slip fault Road Settlement Stream/RiverGaramChasmaRESHUN  F AULTTIRICH  MIR  FAULTShoghor36˚ 00′0 2 4 6kmTirich MirKafiristanε  Slates (T )RεO = Ordovician   D = Devonian   C = Carboniferous   P = Permian   T  = Triassic   K = Cretaceous   P = Paleogene RTectonic Foliation? = Unknown71˚45′Figure 4.2 Geological map of the Hindu Kush in the Garam Chasma region, NW Pakistan. The locations of Pb/U-Th specimens examined in this study are shown. Inset map shows location of this map within Central Asia. Stratigraphic unit ages are after Pudsey et al. (1985) and Zanchi and Gaetani (2011).S4S15AfghanistanKabulIslamabadChinaPakistan IndiaGaramChasma70636050 707880 6063 44808472707544756066707560 65658567657557 64 4083595963157563286982894270606471˚30′48 constraints that do exist yield a complex array of generally discordant Mesozoic ages derived from monazite and uraninite whole grain U-Pb Isotope Dilution Thermal Ionization Mass Spectrometry analyses (Hildebrand et al., 2001).  4.3. MONAZITE PETROCHRONOLOGY To gain better constraints on the timing of metamorphic, deformational, and thermal events in the Hindu Kush, in situ monazite Pb/U-Th petrochronologic analyses were carried out on two garnet + staurolite metapelitic specimens (Fig. 4.3) collected near Garam Chasma along the Lutkho valley (Fig. 4.2). These are the same approximate locations as previous specimens used for whole grain geochronology (PH009b and Ph113 of Hildebrand et al., 2001). In situ monazite Pb/U-Th petrochronologic analyses were conducted at the Laser Ablation Split Stream (LASS) facility at the University of California, Santa Barbara following similar procedures to those described in Cottle et al. (2011; 2013) and Kylander-Clark et al., (2013). See Appendix A for a full description of the methodology. The LASS system allows the simultaneous collection of rare earth element (REE) data and Pb/U-Th isotopic measurements from the same ablated volume. These chemical data can be used to separate distinct monazite age populations and potentially relate chronometric data to bulk rock petrologic processes such as garnet growth, or anatexis (e.g. Pyle et al., 2001; Yang and Pattison, 2006; Larson et al., 2013).   4.4. PETROCHRONOLOGY RESULTS Monazite in specimens S4 and S15 are compositionally zoned with respect to Th (Fig. 4.4). With the exception of grain S4_10, no significant Y zonation was observed (See 495 mm 5 mm K Ka Eds 20kV5 mm5 mmS4StStStGrtGrtBtBtMsMsBtPlPlNENE123411109 87 654123S15Fe Ka Eds 20kVFe Ka Eds 20kV K Ka Eds 20kVFigure 4.3 Elemental thin section maps of Fe and K (created using a Cameca SX-100 electron probe microanalyzer with a 30-μm step size). Similar maps of Ce and Y (not shown) were used to locate the position of monazite grains for analyses. The actual mona-zite grains dated are shown by white circles numbered as in the data appendix A table. Inset plane light photomicrographs of S15 and S4 help depict the mineralogy of the specimens. They are located within the elemental maps by yellow rectangles. Mineral abbreviations after Whitney and Evans  (2010). 501002003004000.000 0.008 0.0160.000.020.040.06208Pb /232Th206 Pb/238 U0.0040.0080.0120.01640Th (ppm)208 Pb / 232Th Age (Ma)208 Pb / 232Th Age (Ma)Th (ppm)40801200200 300 400 5000 100Gd/Yb408012008000 12000 16000 4000Gd/Yb200100300200 400 600 80000.020010030000.0 500 1000 1500 2000(b)(c)S15 S15S4 S423.9 ±0.6322.5 ±0.522.3 ±0.5105.6 ±3.322.8 ±0.55412S4_9189.2 ±3.6234561184.6 ± 3.4201.5 ± 3.6186.0 ± 4.8189.5 ± 3.2142.7 ± 2.4S15_3(a)++++++++2080100452.5 ± 7.9 Ma211.0 ± 7.9 – 201.5 ± 3.6 Ma189.7 ± 4.8 – 184.6 ± 3.4 Ma175.0 ± 11.2 –101.8 ± 2.3 Ma87.0 ± 1.7 – 82.9 ± 1.8 Ma81.0 ± 1.7 – 72.4 ± 1.8 Ma29.3 ± 1.1 – 22.3 ± 0.5 Ma 49.8 ± 1.6 – 36.3 ± 1.6 MaFigure 4.4 (a) Pb/U-Th concordia plots of monazite analyses from specimen S15 and S4 (details of S4 are inset). Plots were constructed using Isoplot/Ex (full data are listed in the data appendix A). Also shown are representative Th elemental maps of mona-zite grains with corresponding 208Pb/232Th  ages (in Ma). The size of the error crosses have been increased by 100% to improve readability and clarity at the scale of the plot. Plots (b) and (c) are Th concentrations Gd/Yb ratios versus 208Pb/232Th age for specimens S15 and S4, respectively. The oldest age from S15 is not plotted to maintain a useful vertical scale. The oldest age from S4 is not plotted as REE data were not collected. The colors used to depict the analyses in a, b, and c corre-spond to age populations discussed in the text. 51 appendix A). Spot Pb/U-Th and REE analyses were obtained from different compositional domains while avoiding fractures and inclusions. Follow-up imaging using a scanning electron microscope was conducted to investigate the position of laser pits relative to their target. This allowed the removal of data from laser pits that missed their intended target and interacted with the rock matrix or a crack in the crystal. The results of the spot analyses are presented as 206Pb/238U versus 208Pb/232Th concordia diagrams (Fig. 4.4). Ages mentioned in the text below are 208Pb/232Th ages unless otherwise noted. All Pb/U-Th ages are reported with 2σ uncertainties; associated data are provided in the data appendix A. Full description of the petrochronologic results and REE plots for both specimens are also available in the data appendix A.   4.4.1. Interpretations The oldest single spot age is Ordovician, 452.5 ± 7.9 Ma, measured in specimen S15 (grain S15_2) is interpreted as a detrital age that may be related to metamorphism coeval to crustal extension along the Gondwana margin and opening of the Paleotethys (Le Fort et al., 1994; Rolland, et al., 2001a; Fernández et al., 2012; von Raumer et al., 2013).  The oldest non-detrital monazite population is Late Triassic to Early Jurassic in age (211 ± 7.9 – 201.5 ± 3.6 Ma) and is associated with low Th concentrations and low Gd/Yb ratios relative to the other data from this specimen (Fig. 4b). This is consistent with monazite growth during prograde metamorphism coeval with the growth of a HREE sink, likely garnet (e.g. Pyle et al., 2001; Kohn et al., 2005; Yang and Pattison, 2006). The Early Jurassic age domains, 189.7 ± 4.8 – 184.6 ± 3.4 Ma, have a wide range of Th concentrations that do not vary systematically with age (Fig. 4.4b). The Gb/Yb ratios for 52 those same ages also do not vary with age and are similar to the absolute values of the older population (Fig. 4.4a). These two older populations may reflect growth during the same protracted metamorphic event, or two events in close succession that began with garnet-grade conditions in the Late Triassic, as recorded by the old ages exclusively from monazite included in garnet grains, and progressed to staurolite grade growth in the Early Jurassic. The younger, 175 ± 11.2 –101.8 ± 2.3 Ma ages are associated with a diverse range of Th concentrations and Gd/Yb ratios. This variation may reflect monazite growth related to more local factors such as heating or fluid circulation, rather than a single, related, large-scale event.  The Late Cretaceous monazite ages (87.9 ± 1.8-72.4 ± 1.8 Ma) from specimen S4 are typically associated with higher Th concentrations and lower Gd/Yb ratios than the other monazite analyses in this specimen. The Gd/Yb ratios are consistent with growth during either the early prograde phase of a metamorphic event or late stage garnet breakdown (Pyle et al., 2001; Yang and Pattison, 2006). The Eocene ages, 49.8 ± 1.6 to 36.3 ± 1.6 Ma, are associated with lower Th concentrations than those of the Late Cretaceous ages (Fig. 4.4c). Their Gd/Yb ratios are broadly similar to the Late Cretaceous ages, though they appear to increase with decreasing age. An increasing Gd/Yb ratio with younger ages may reflect simultaneous growth of monazite with garnet during prograde metamorphism, however, this trend is based on only three data points. The Oligocene – Miocene age population in specimen S4 generally has the lowest Th concentrations, while its Gd/Yb ratios have a wide range (Fig. 4.4c). This range in Gd/Yb ratios may reflect incongruent melting and/or crystallization controlling the local dissolution 53 or growth of garnet, setting up a local-scale open-type system of the REE and actinide elements (Larson and Cottle, 2015). This interpretation is consistent with the generation and crystallization of the Garam Chasma pluton in the area during the same time period (Hildebrand et al., 1998).   4.5. DISCUSSION In the following we discuss the petrochronologic history recorded in the Hindu Kush and correlate that to the regional orogenic record (Fig. 4.5). The data presented herein can be separated into multiple different monazite growth events related to tectonic activity between c. 211 and 22 Ma in the Hindu Kush.  The Late Triassic prograde metamorphism is interpreted to record the collision of the Hindu Kush-SW Pamir terrane to central Pamir, then the southern Eurasian margin, along the Rushan-Pshart suture (Fig. 4.5). This marks the first phase of the Cimmerian orogeny; the lateral equivalent of the accretion of Qiantang block to Eurasia (Zanchi et al., 2000; Zanchi and Gaetani, 2011; Angiolini et al., 2013). This accretion continued into the start of the Jurassic when the Karakoram terrane accreted to the southern Eurasian margin (Fig. 4.5), which was defined by the Hindu Kush terrane in the far west (Zanchi and Gaetani, 2011, Angiolini et al., 2013). The timing of that accretionary event, which has been interpreted to be marked by the development of the Tirich Mir-Wakhan Boundary zone between the Hindu Kush and Karakoram terranes across NW Pakistan and adjacent regions (Zanchi et al., 2000, 2011; Angiolini et al., 2013), is constrained by the Early Jurassic monazite ages of 189.7 ± 4.8 – 184.6 ± 3.4 Ma from monazite inclusions within both garnet and staurolite grains in specimen S15. An unconformity above deformed lowermost Jurassic/uppermost Triassic 54Andean-style volcanic arc along the Karakoram and intrusion of Karakoram batholith+ ++ ++ + ++ + + ++ +++++CP TWS KIAKK IndiaPT NTc. 175 - 101 MaRPS+ ++ +++++ +++++ ++ ++ + ++ + + ++ ++++++ ++ +++++ +++++ ++ ++++SP-HKCollision of India with Eurasia and intrusion of leucograniteRPS TWSMKTISZMBTMFTHIMALAYAN RANGEKIAKKIndiac. 29 - 22 Ma+ ++ ++ ++ ++++ + ++ +++++ +++++ ++ +++++ ++ ++ +++++ ++ +++++ ++ ++++++++ +++ ++ ++++ + ++ ++ ++ ++ +++++ ++ ++ + ++ + + ++ +++++SP-HKCPRifting of blocks from Gondwana  NGKKSP-HKCPRPB TWB PTNAccretion of the Hindu Kush terrane during the first phase of Cimmerian orogenyPTc. 211 - 201 Ma+ +++++ ++ ++++CPSP-HKTWBKK NGCollision of Karakoram to Hindu Kush during second phase of Cimmerian orogeny+ ++ ++++ + ++ ++ ++ +++++ ++ ++++ PTRPSc. 189 - 184 MaKK NGSP-HKCPDocking of KIA and intrusion of Kohistan batholith in an Andean-type marginKIAKK IndiaRPS TWSMKTNT+ ++ ++ ++ ++++ + ++ +++++ ++ +++++ ++ ++ + ++ + + ++ +++++ + ++ +++++ ++ ++ ++ ++ +++++++ ++ +SP-HKCPc. 88 - 72 MaOrdovicianFigure 4.5 Schematic tectonic evolution model of the Hindu Kush and southern Eurasia. See text for discussion. RPB = Rushan-Pshart Basin, TWB = Tirich-Wakahn Basin, PT = Paleotethys, RPS = Rushan-Pshart Suture, NG = Northern Gondwana, NT = Neo-tethys, TWS = Tirich-Wakhan Suture, SP-HK = South Pamir – Hindu Kush, KK = Karakoram, CP = Central Pamir, KIA = Kohistan Island Arc, MKT (Northern Suture) = Main Karakoram Thrust, ISZ = Indus Suture Zone, MBT = Main Bound-ary Thrust, MFT = Main Frontal Thrust.55 flysch deposits in SE Pamir, also interpreted to be associated with the Cimmerian orogeny (Angiolini et al., 2013), is consistent with these new constraints. Moreover, these new geochronologic data further support the existence of a metamorphic event described in the Baltoro region of the Karakoram at the Triassic – Jurassic boundary (Searle et al., 1989) and overlap with a 195 to 188 Ma age of a foliated, boudinaged, leucogranite dyke from the Garam Chasma area thought to reflect an early orogenic event in the Hindu Kush (Hildebrand et a., 2001).  Subduction of the Paleotethys beneath the Eurasian margin following the accretion of the Hindu Kush and Karakoram terranes transformed it into an Andean-style arc, as evidenced by the intrusion of subduction–related plutonic rocks (Fig 4.5; Searle et al., 1989; Hildebrand et al., 2001; Searle et al., 2010). This subduction of Tethyan oceanic lithosphere beneath Eurasia led to the intrusion of the Karakoram batholith and its equivalents, which extend for ~700 km along strike in Afghanistan, Pakistan, and Ladakh (Searle et al., 1989; Searle et al., 2010). Monazite growth reported in this study is coeval with the development and intrusion of these plutons in the Garam Chasma region during the Middle Jurassic to the mid-Cretaceous (175 ± 11.2 –101.8 ± 2.3 Ma), which may reflect growth or recrystallization during related thermal activity. The monazite ages overlap with the ages of plutonic rocks exposed in the Hindu Kush: Shushar – 171.1 ± 3.4 Ma (Gaetani et al., 1996), Tirich Mir – 121 ± 1 Ma and Buni-Zom/Phargram – 103.79 ± 0.27 Ma (Heuberger et al., 2007), the Karakoram: Hushe complex – 163 ± 7 Ma and 142 ± 6 Ma (Searle et al., 1989), K2 – 115–120 Ma (Searle et al., 1990), Darkot Pass – 111 ± 6 Ma (Debon et al., 1987), and Hunza – 105.7 ± 0.5 Ma (Fraser et al., 2001). The magmatic events ceased during the Late Cretaceous 56 upon collision of the Kohistan Island Arc with the Eurasia margin (Rolland et al., 2002; Mahéo et al., 2004).  The collision of the Kohistan island arc is interpreted to have initiated around ~90 – 85 Ma (Petterson et al., 1991; Fraser et al., 2001). This accretion event and subsequent re-establishment of north-dipping subduction farther south is interpreted to have triggered monazite growth in the Hindu Kush across a time interval spanning between 87.9 ± 1.8 Ma and 72.4 ± 1.8 Ma (Fig. 4.5) and was followed by the Late Cretaceous intrusion of the Kohistan batholith (Petterson and Windley, 1991). The development of the Reshun Fault (Fig. 4.2) and the Cretaceous Reshun conglomerate in its footwall to the southeast may also be related to the Late Cretaceous collision of the Kohistan island arc to the Karakoram-Hindu Kush (Pudsey et al., 1985). The ages from this study are broadly incompatible with an Eocene collision of Kohistan Island Arc with India as proposed by Bouilhol, et al. (2013). A single spot date of 49.8 ± 1.6 Ma in specimen S4 is consistent with the initiation of continental collision between India and Eurasia at the western extremity of the Himalayas (Beck et al., 1995). While the spot date appears to be robust, and the spot does not overlap multiple age domains, further study is required to confirm this age population. Subsequent to the initiation of India-Eurasia collision, protracted regional-scale kyanite- and sillimanite-grade metamorphism and associated anatexis occurred in the Karakoram and Hindu Kush regions between c. 28 Ma and c. 22 Ma (Searle et al., 1992; Hildebrand et al. 1998; Rolland, et al., 2001b; Searle, et al., 2010). This resulted in the extensive development of plutonic bodies such as the Mango Gusar, Baltoro, Garam Chasma, Trango Tower, and Bale Cathedral plutons between the Oligocene and Miocene. The youngest age population from this study in the Hindu Kush, 29.3 ± 1.07 Ma to 22.3 ± 0.5 Ma, is consistent with 57 metamorphism and anatexis and intrusion of leucogranite within the Himalaya, Karakoram and Tibet during Early Miocene.   4.6. SUMMARY New petrochronologic data from two specimens from the Hindu Kush of NW Pakistan record a protracted history of metamorphism, deformation, and intrusion that can be related to the broader history variably recorded within the Karakoram, Himalaya and Tibet. These new data help provide insight into the tectonic history of the Himalayan system, and in particular the pre-continental collision history which informs the conditions of the Eurasian margin before collision with India. Understanding the antecedent structure of the Eurasian margin is an important constraint in developing orogenic models for the subsequent growth of the Tibetan plateau and the Himalaya.	  58	  Chapter 5  Rifting, Subduction and Collisional Records from Pluton Petrogenesis and Geochronology in the Hindu Kush, NW Pakistan  5.1. BACKGROUND The NE-SW trending Hindu Kush range stretches for more than 600 km from northwestern Pakistan into adjacent Afghanistan (Figs. 2.5 and 2.6). The geology of the range records a complex history of magmatism, deformation, and metamorphism spanning the early Paleozoic to the present day (Debon et al., 1987; Hildebrand, 1998; Zanchi and Gaetani, 2011; Chapter 4). Because the Hindu Kush records evidence of the evolution of Eurasia prior to continental collision (Zanchi et al., 2000; Hildebrand et al., 2001; Zanchi and Gaetani, 2011; Chapter 4), which is not well preserved in other parts of the orogen, the geologic history of the Hindu Kush is important for our understanding of the tectonic, magmatic and metamorphic evolution of the southern Eurasian margin. The Hindu Kush terrane, which comprises most of the study area (Chapter 4), was detached from Gondwana in the Paleozoic (Zanchi and Gaetani, 2011, Angiolini et al., 2013) and accreted to the southern margin of Eurasia in the Late Triassic (Chapter 4). Its accretion was followed closely by the collision and accretion of the Karakoram terrane in the Early Jurassic (Zanchi et al., 2000; Chapter 4). Continued northward subduction of the Paleotethys from the Middle Jurassic to the Early Cretaceous along the southern margin of Eurasia resulted in the intrusion of plutonic bodies in the Tirich Mir-Wakhan and Karakoram belts in an Andean-style margin (Searle et al., 1989, Hildebrand et al., 2001; Searle et al., 2010). The Kohistan island arc is interpreted to have developed within the Paleotethys sometime in the Mesozoic above a northward-dipping subduction zone (Tahirkheli et al., 1979) and was accreted to Eurasia in the Late Cretaceous (Petterson et al., 1991; Fraser et al., 2001; Chapter 59	  4). Continued subduction thereafter resulted in the development of a second Andean-style margin marked by the intrusion of the Kohistan Batholith (Petterson and Windley, 1991). Ultimately, the Kohistan island arc was sandwiched between India and Eurasia during the Cenozoic initiation of their collision (Beck et al., 1995).  While timing constraints on accretion events and metamorphism now exist for the Hindu Kush (Zanchi et al., 2000; Hildebrand et al., 2001; Heuberger et al., 2007; Chapter 4) relatively little is known about the various plutonic bodies that intrude the region. There have been no systematic geochemical studies of the plutons of the Pakistani Hindu Kush, and therefore, the geochemical characteristics, potential sources, and the tectonic evolution of the Kafiristan, Tirich Mir, Buni-Zom (exposed along Golen Gol) and Garam Chasma plutonic bodies (Fig. 5.1) remain poorly constrained. Their occurrence has been variably attributed to subduction and/or collision-related crustal thickening processes (e.g. Desio, 1964; Debon et al., 1987; Hildebrand 1998, Hildebrand et al., 2000; Hildebrand et al., 2001; Zafar et al., 2000; Zanchi et al., 2000; Heubergar et al., 2007). This paper examines the petrogenesis and tectonic significance of the Kafiristan, Tirich Mir, Buni-Zom and Garam Chasma plutons based on new major, trace and rare earth element (REE) data and integrated Pb/U-Th (zircon/monazite) geochronology. This work contributes to the record of major tectonic events in the Hindu Kush and helps improve our understanding of the evolution of the southern margin of Eurasia, subduction dynamics of the Tethys, and the evolution of the Himalaya-Karakoram-Tibetan orogenic system.   5.1.1 Geology and Existing Chronology The present work is focused on the Hindu Kush in the Chitral region, NW Pakistan 60B om bo r at e  Va l l eyL u t k h o  G o lArkariGolR um bo o r Va l l e y B ag ho st  Go lS 10 BS 1 0C65 S 9 BS9AS80S81S 6 0S 47S 9 6S95S 29S 2 8 S 26S 24 S 6 27 0827 07 81 57 56 07 58 48 07 24 46 18 56 76 38 57 84 0828 76 38 66 64 58 25 55 88 07 0357 05 15 72 68 85 53 5 4 56 26 04 65 67 8307 58 56 56 08 58 25 55 25 1767 6787 66 16 15 86 26 66 05 6447 2474 58 27 06 6R es h un  Fa ul t  T i ri c h Mi r  Fa ul tCHITRALShoghorG ar a mC ha s maBarenis71˚30′ 71˚45′ 72˚00′3 6˚ 15 ′71˚15′71˚13′3 6˚ 00 ′3 5˚ 45 ′36˚15′ReshunConglomerateMetasedimentry rocks(Undifferentiated)Chitral Slate0 4kmCleavage/schistosityFaultSettlementStream/RiverSnow8 12LEGENDNPsammite UnitsBuni-Zom/Kesu-Kohuzi PlutonTirich Mir PlutonGaram Chasma PlutonKafiristan PlutonCarbonatesCalcsilicateTirich MirAmphiboliteGreenschistDorah An PlutonINDEXKabulIslamabadCHINAINDIAAFGHANISTANPAKISTANFigure 5.1. Geology map of the Chitral region showing Kafiristan, Tirich Mir, Bun-Zom and Garam Chasma with specimen locations used for geochemical and geochronogical analyses noted.61	  (Figs. 5.1). The geology of the area is characterized by multiply deformed, variably metamorphosed, Paleozoic to Mesozoic sedimentary rocks intruded by the elongate Kafiristan, Tirich Mir, Buni-Zom, Kesu-Kohuzi and Garam Chasma plutons (Calkins et al., 1981; Hildebrand et al., 2000; Fig. 5.1). The plutonic bodies typically form physiographic peaks in the region, which reach elevations of 7700 + m locally. Published constraints on the age of plutonic rocks in the Hindu Kush vary considerably. Existing whole rock Rb-Sr data from the Kafiristan and Tirich Mir plutons outline ages of 483 ± 21 Ma (Debon et al., 1987) and 115 ± 4 Ma (Desio, 1964), respectively. U-Pb Isotope Dilution Thermal Ionization Mass Spectrometry (ID-TIMS) analysis on monazite and uraninite grains from a pegmatite dyke in the Tirich Mir fault zone, thought to be related to the main Tirich Mir plutonic body, yielded a discordant, interpreted intrusion age of 114 ± 2 Ma (Hildebrand et al., 2000). More recently, zircon grains analyzed from a different specimen of the Tirich Mir body yielded two concordant analyses interpreted to comprise an age of 121 ± 1 Ma (Heuberger et al. 2007). Both U-Pb age estimates for the Tirich Mir pluton are consistent with a 110.6 ± 3.2 Ma post-magmatic 39Ar-40Ar (muscovite) date (Heuberger et al., 2007). A specimen of the Buni-Zom plutonic body collected to the northeast of study area yielded a U-Pb (zircon; ID-TIMS) age of 103.79 ± 0.27 Ma defined by two concordant data points (Heuberger et al., 2007). Finally, U-Pb ID-TIMS analyses on monazite and xenotime grains from a specimen collected from the Garam Chasma pluton yielded a discordant age of 24 ± 0.5 Ma (Hildebrand et al. 1998). This is consistent with 20 – 18-Ma K-Ar (biotite) dates from the same body if they are interpreted to represent cooling and not crystallization (Zafar et al., 2000).   62	  5.2. PLUTON DESCRIPTIONS  Plutonic rocks are a major constituent of the eastern Hindu Kush comprising ~35% of the bedrock in the region (Fig. 5.1). The grayish white (fresh) Kafiristan pluton exposed along the Bomborate and Rumboor valleys (Fig. 5.1) is a foliated body characterized by a porphyritic texture with K-feldspar megacrysts ranging in size from 3–4 cm. The matrix minerals consist of Qz + Kfs + Pl + Bt ± Hbl and accessory Zrn + Tur + Ap + Ep (Fig. 5.2A and B). The alkali feldspar and plagioclase locally display perthitiic and myrmetic textures, respectively. Minor sericitization is observed in one specimen of the Kafiristan pluton (S60; Fig. 5.1). Initial petrographic observation indicates the pluton includes at least two phases; a Bt + Hbl bearing phase along the Bomborate valley and a Hbl free phase exposed along the Rumboor valley (Fig. 5.1).  The grayish white and pinkish (fresh) Tirich Mir pluton is variably foliated and porphyritic with K-feldspar megacrysts ranging in size from 4–5 cm. The Tirich Mir intrusive has abundant Qz + Kfs + Pl + Bt + Ms, ± Grt, and accessory Zrn + Ap (Fig. 5.2C and D). Hbl has been reported from Tirich Mir pluton (Searle et al., 2001), but it was not observed in this study. Perthite, myrmekite, and zoned Pl are common locally. Petrographically, the Tirich Mir pluton can be divided into at least three phases (1) Ms + Bt  (2), Ms + Bt + Grt, and (3) Ms + Tur.  Previous studies have mapped the Buni-Zom and Kesu Kohuzi plutons as separate bodies (e.g. Aslam et al. 2007). Fieldwork in the Golen Gol area during this study, however, shows that the Buni-Zom pluton extends much farther southwest than previously thought, almost to the Kesu Kohuzi body. In this study the Buni-Zom and Kesu Kohuzi are considered as part of the same plutonic body (Fig. 5.1). For simplicity, they are collectively referred to 63AfsAfsBtQzPlPlAfsQzQzPlPlBtBtBtBtPlPlPlHblQzTtnHblTtnQzAfsPlBtQzPlGrtFiBtGrtTtnBtPlPlQz BtMsMsPlQzAfsAfsBtPlPlAfsAfsQzQzMsA BC DE FG HFigure 5.2 Cross-polarized photomicrographs of the Kafiristan (A, B), Tirich Mir (C, D), Buni-Zom (E, F) and Garam Chasma (G, H). Mineral abbrevia-tions after Whitney and Evans (2010).64	  as ‘Buni-Zom’ here forward. The dark gray to white (fresh) Buni-Zom plutonic body, which crops out along the Golen Gol, consists of Afs + Pl + Hbl + Bt with accessory Ttn, Zrn, Ap and opaques (Fig. 5.2E and F). Plagioclase crystals are generally zoned and perthitic textures are observed in alkali feldspar locally. Petrographically, the Buni-Zom pluton can be divided into two phases: (1) biotite + feldspar + titanite, and (2) biotite + hornblende. The leucocratic fresh Garam Chasma pluton consists of Afs + Pl + Ms + Bt and subordinate Grt + Sil bearing leucogranite (Fig. 5.2G and H) with accessory Tur + Zrn + Xtm + Urn + Mzn + Ap. Rare sericitization of alkali feldspar is observed. The leucocratic Garam Chasma pluton occurs as a single phase.   5.3. WHOLE ROCK GEOCHEMISTRY Specimens from the Kafiristan, Tirich Mir, Buni-Zom, and Garam Chasma plutons were analysed for whole rock major and select trace element compositions through X-Ray fluorescence (XRF) on pressed pellet using a Bruker S8 TIGER instrument at the Saskatchewan Research Council (SRC) Geoanalytical Laboratories, Saskatoon, Canada. Additional trace and REE concentrations in select specimens were determined by lithium metaborate fusion – inductively coupled plasma mass spectrometry also at the SRC (see appendix B for the specimen preparation and methodology).  5.3.1. Kafiristan Pluton Two specimens from the Kafiristan pluton (S60 and S81) were analyzed for major, trace and REE. Chemically, the specimens plot across the alkali granite and granitic fields of the Cox et al. (1979) classification diagram (Fig. 5.3). The two specimens have variable SiO2 651816141210864235 40 45 50 55 60 65 70 75AlkalineSubalkalineUltrabasic Basic Intermediate AcidSyeniteSyen-dioriteGabbroGabbroIjoliteSyen-dioriteQuartz-DioriteDioriteGraniteNephline SyeniteSyeniteAlkali GraniteKafiristan PlutonTirich Mir PlutonBuni-Zom PlutonGaram Chasma PlutonSiO2 (wt%) Na 2O + K2O (wt%)Figure 5.3 The classification of the Kafiristan, Tirich Mir, Buni-Zom and Garam Chasma plutons in the SiO2 vs. Na2O + K2O diagram (after Cox et al., 1979).66	  (67.9–75.9 wt.%), Al2O3 (13.1–14.4 wt.%), MgO (0.16–0.9 wt %), P2O5 (0.09–0.25 wt%), CaO (0.6 –1.92 wt%) and Fe2O3 (1.29–4.76 wt%), and high K2O (4.48–5.70 wt.%) relative to Na2O (2.53–3.26 wt.%). Harker plots of major elements within the two analyzed specimens from the Kafiristan pluton show a significant difference in K2O, Na2O, CaO, MgO, Al2O3, TiO2, Fe2O3, and P2O5 contents between specimens when plotted against SiO2 (Fig. 5.4). Similarly, differences between specimens also exist in trace element concentration (e.g. Rb, Sr, Ba, Zr and Th) vs. SiO2 plots (Fig. 5.4).  MORB–normalized spider plots of the Kafiristan pluton specimens show relative enrichment in Large Ion Lithophile Elements (LILE: e.g. Rb) compared to High Field Strength Elements (HFSE: e.g. Nb), with pronounced negative anomalies in Sr and enrichments in Th (Fig. 5.5a). While on chondrite-normalized REE plots, S60 shows a moderate negative Eu anomaly and depleted HREE (Fig. 5.6a), whereas S81 has a ‘V’ shaped REE pattern and a pronounced negative Eu anomaly (Fig. 5.6a).   5.3.2 Tirich Mir Pluton The five specimens of the Tirich Mir plutonic body (S24, S26, S28, S29 and S62) generally have restricted range in SiO2 (70.0–73.9 %) and Al2O3 contents (14.4–16.2 wt%), and wide ranges in K2O (2.17–6.22 wt%), Na2O (2.18–4.83 wt%), P2O5 (0.17–0.28 wt%), MgO (0.09–0.82 wt%) and Fe2O3 (0.59–2.32 wt%) (see Table 5.1). With the exception of S62, which has an affinity more toward alkali granite, the Tirich Mir specimens plot in the granite field of the Cox et al. (1979) K2O + Na2O vs SiO2 classification diagram (Fig. 5.3). Major element Harker plots show generally negative slopes in K2O, MgO, Fe2O3 and TiO2 when plotted against SiO2; Na2O has a positive slope (Fig. 5.4). Furthermore, trace element 67S-60 S-81 S-24 S-26 S-28 S-29 S-62 S-47 S-95 S-96 S-9A S-9B S-10 S-10BNa2O 2.53 3.26 2.84 4.83 3.62 2.72 2.18 3.46 3.96 2.49 3.33 2.61 3.26 3.79MgO 0.90 0.16 0.63 0.09 0.37 0.82 0.40 0.94 0.91 3.82 0.24 0.11 0.17 0.19Al2O3 14.4 13.1 14.6 16.2 14.4 14.8 18.4 14.4 15.0 14.4 14.3 14.6 15.5 17.3SiO2 67.9 75.9 72.2 73.9 73.2 71.0 70.0 71.8 70.1 57.1 74.1 75.0 73.7 72.2P2O5 0.25 0.09 0.28 0.19 0.17 0.30 0.22 0.20 0.26 0.43 0.08 0.10 0.17 0.12K2O 5.70 4.48 4.57 2.17 4.57 5.04 6.22 3.55 3.14 2.08 4.11 5.39 4.59 4.98CaO 1.92 0.69 1.37 0.60 1.50 1.61 0.55 2.10 2.98 7.12 1.32 0.69 1.09 0.99TiO2 0.67 0.15 0.39 0.02 0.23 0.46 0.43 0.33 0.38 1.12 0.21 0.08 0.11 0.112MnO 0.08 0.02 0.05 0.10 0.03 0.04 0.02 0.04 0.05 0.16 0.01 0.02 0.01 0.013Fe2O3 4.76 1.29 2.32 0.590 1.51 2.77 0.94 2.36 2.27 8.65 1.41 0.63 0.71 1.10Total 99.1 99.1 99.3 98.7 99.6 99.5 99.4 99.2 99.1 97.4 99.1 99.2 99.3 101S 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01Sc 7.90 3.10 5.10 1.50 1.50 7.80 5.70 2.50 4.00 22.0 1.50 4.60 1.50 4.00V 44.0 0.80 19.6 0.50 5.40 26.3 16.2 26.4 32.1 191.8 0.80 0.50 0.50 5.00Cr 18.2 12.4 10.9 43.8 19.4 24.7 23.3 16.9 31.1 22.2 17.9 6.6 17.2 171Co 2.30 1.50 1.50 1.50 2.30 1.50 5.80 1.50 1.50 25.8 1.50 1.50 1.50 1.50Ni 7.2 9.2 7.6 10.7 8.3 14.0 13.1 10.0 12.4 22.0 9.7 8.5 11.0 9.0Cu 22.8 2.5 2.5 2.5 3.4 2.5 4.0 2.5 2.5 17.7 2.5 2.5 16.8 6.0Zn 55.9 12.1 68.0 17.3 38.5 72.4 2.30 47.6 56.6 89.2 46.2 17.0 45.1 57.0Ga 18.5 21.0 21.7 24.5 19.9 21.3 18.6 18.9 21.2 17.8 19.7 22.4 28.3 30.0As 2.30 1.5 1.5 1.5 1.5 1.5 2.9 1.5 1.5 0.9 1.5 1.5 0.5 18.0Se 5.0 22.3 5.0 44.4 13.8 5.00 26.5 5.0 5.0 5.0 18.7 22.7 28.0 19.0Br 4.0 14.9 10.5 23.4 13.3 8.1 17.6 11.1 5.0 5.0 14.6 15.0 17.5 5.0Rb 127 285 295 221 229 288 279 68.4 103 73.5 209 274 329 281Sr 131 60.8 104 15.7 84.0 144 62.0 826 809 619 395 128 161 107Zr 268 81.3 126 7.8 104 175 87 197 226 165 147 66.7 36.1 37.0Mo 2.0 1.0 2.0 5.0 1.7 3.0 2.1 1.0 2.0 2.3 11.0 6.0 6.0 2.2Sn 2.20 6.5 1.5 23.2 7.5 1.5 10.6 1.5 1.5 1.8 1.5 6.6 9.5 11.3Sb 1.00 9.7 3.8 5.8 1.0 8.0 6.9 1.0 1.0 1.0 1.0 2.9 4.0 0.50Cs 2.2 7.2 11.9 2.5 7.7 5.7 3.8 2.5 5.1 0.7 5.3 11.6 2.5 3.6Ba 619 138 226 2.5 212 298 358 1147 717 631 773 103 158 182Hf 7.5 15.4 13.2 17.8 3.1 12.3 2.6 12.0 11.6 3.6 13.9 14.1 13.8 1.3W 5.0 32.8 17.4 43.5 20.4 5.0 35.6 18.9 10.6 5.0 32.0 33.1 26.9 0.5Pb 28.0 27.0 50.0 32.9 53.1 49.7 44.6 22.2 24.9 7.60 58.9 74.6 89.8 54.7Bi 2.5 18.5 13.6 50.4 23.7 2.5 31.6 16.8 6.7 2.5 22.5 27.9 35.4 1.6Ce 128 36.0 39.0 41.0 32.0 46.0 54.0 42.0 26.0Dy 5.16 9.67 2.57 2.55 1.64 1.92 3.69 0.89 1.71Er 2.88 6.06 1.08 1.53 0.82 0.89 2.05 0.34 0.48Eu 1.32 0.31 0.58 0.59 0.44 1.10 1.51 0.64 0.68Gd 6.87 6.20 3.30 2.87 2.18 2.64 4.50 1.53 2.41Ho 1.23 2.54 0.52 0.63 0.36 0.45 0.92 0.18 0.28La 63.0 19.0 21.0 2.50 19.0 19.0 17.0 21.0 24.0 26.0 27.0 13.0 10.0 13.0Lu 0.40 1.20 0.17 0.20 0.10 0.16 0.30 0.05 0.05Nb 14.0 22.2 16.0 22.0 10.0 17.6 9.00 8.10 18.0 8.00 7.0 11.0 9.7 10.0Nd 46.3 18.1 18.3 15.6 11.9 21.1 25.2 15.5 10.1Table 5.1. Major elements (%), trace elements and rare-earth elements (ppm) of the plutonic bodies in the&&&&&&&&&&&&&&&&&&&&&&   Hindu Kush, from the Chitral area, NW Pakistan.Kafiristan Tirich Mir Buni-Zom Garam ChasmaSamples68Pr 14.00 5.19 5.38 4.55 3.54 6.10 6.46 5.03 2.98Sm 8.40 5.09 3.80 3.36 2.48 3.52 5.24 2.26 2.70Ta 1.37 5.80 2.96 4.72 2.36 2.76 1.96 2.16 1.56 0.72 0.98 1.50 9.10 1.92Tb 0.98 1.37 0.48 0.45 0.33 0.36 0.66 0.20 0.38Th 20.3 20.8 11.4 5.0 12.4 9.7 9.49 5.0 13.8 5.05 10.0 11.6 5.0 8.77Tl 0.02 0.24 0.34 0.01 0.01 0.09 0.02 0.29 0.01Tm 0.44 1.22 0.21 0.27 0.13 0.18 0.33 0.05 0.06U 2.59 7.88 4.20 17.7 3.12 3.90 3.66 3.90 2.15 2.00 2.49 12.3 10.0 7.58Y 29.8 60.0 11.7 22.8 17.2 28.5 9.38 16.5 9.62 21.7 3.83 25.2 28.6 7.71Yb 2.68 7.94 1.14 1.67 0.82 0.96 1.94 0.33 0.31ASI 1.06 1.15 1.24 1.45 1.07 1.18 1.66 1.10 0.99 0.76 1.16 1.29 1.27 1.30ΣFeO/ΣFeO+MgO 0.841 0.890 0.786 0.868 0.803 0.772 0.701 0.715 0.714 0.694 0.855 0.851 0.807 0.853La/Yb 23.5 2.39 18.4 11.4 20.7 25.0 13.4 81.8 41.9Y/Nb 2.13 2.70 0.731 1.036 1.72 1.62 1.042 2.037 0.53 2.71 0.55 2.29 2.95 0.771Yb/Ta 1.96 1.37 0.385 0.708 0.418 0.615 2.69 0.337 0.161Nb+Y 43.8 82.2 27.7 44.8 27.2 46.1 18.4 24.6 27.6 29.7 10.8 36.2 38.3 17.7Rb/Sr 0.969 4.69 2.84 14.10 2.73 2.00 4.5 0.083 0.127 0.119 0.529 2.14 2.04 2.6169543260 65 70 75Na 2O %SiO2 %23456K2O %65 70 7560SiO2 %Al 2O3 %18171615141360 65 70 7565 70 7560SiO2 %CaO %86420SiO2 %SiO2 %Fe2O3 %0.060 65 70 752.55.07.5SiO2 %MgO %70 7565600123650.00SiO2 %MnO %60 70 750.050.100.1560SiO2 %P2O5 %0.10.20.30.465 70 7560TiO2 %SiO2 %65 70 750.00.51.0Rb ppmSiO2 %10020030060 65 70 7570SiO2 %60Sr ppm65 70 750200400600800SiO2 %60Ba ppm65 70 7550025075010000SiO2 %Th ppm65 70 75105152060SiO2 %Zr ppm65 70 7510050150200060250Figure 5.4 Chemical variation Harker diagrams of the Kafiristan, Tirich Mir, Buni-Zom and Garam Chasma plutons.Kafiristan Tirich Mir Buni-Zom Garam ChasmaFigure 5.4 continued71100.0S60S81KAFIRISTAN PLUTONRb Ba Sr Th Ta Nb Ce Hf Zr Sm Y Yb1000.010.01.0(a) (b)100.0TIRICH MIR PLUTONRb Ba Sr Th Ta Nb Ce Hf Zr Sm Y Yb1000.010.01.00.1S24S28S62(d)S96S95S47100.0BUNI-ZOM PLUTONRb Ba Sr Th Ta Nb Ce Hf Zr Sm Y Yb1000.010.01.0(c)100.0GARAM CHASMA PLUTONRb Ba Sr Th Ta Nb Ce Hf Zr Sm Y Yb1000.010.01.00.1S9BS9AS10BS10Figure 5.5 MORB-normalized trace elements plots of the Kafiristan, Tirich Mir, Buni-Zom and Garam Chasma specimens (after Sun and McDonough, et al., 1989).72KAFIRISTAN PLUTON10010L a C e P r N d S m E u G d T b D y H o E r Y b L uTIRICH MIR PLUTONBUNI-ZOM PLUTON GARAM CHASMA PLUTONS60S81 10010L a C e P r N d S m E u G d T b D y H o E r Y b L uS24S28S62L a P rC e N d S m E u G d T b D y H o E r Y b L u10010S95S96L a P rC e N d S m E u G d T b D y H o E r Y b L u10010S9AS10B(a) (b)(c) (d)Figure 5.6. Chondrite normalized REE diagrams of the Kafiristan (a), Tirich Mir (b), Buni-Zom (c) and Garam Chasma (d) specimens. Normalizing values are from McDonough and Sun (1995). 73	  Harker plots of Ba, Sr and Zr show negative relationships with SiO2 while Th has a variable relationship (Fig. 5.4).  On MORB-normalized trace element diagrams, S24, S28, and S62 have similar LILE and HFSE values, with relative enrichment in Rb, Th, and variably negative Sr and Nb anomalies (Fig. 5.5b). Chondrite-normalized spider plots of the Tirich Mir specimens show relative enrichment in light REE ((La/Yb)N = 8–14)), depletion in heavy REE and moderate negative Eu anomalies (Fig. 5.6b).  5.3.3 Buni-Zom Pluton The three specimens analyzed (S47, S95 and S96) from the Buni-Zom pluton show a wide compositional range in SiO2 (57.1–71.8 wt%), MgO (0.91–3.82 wt%), P2O5 (0.2–0.43 wt%), CaO (2.1–7.12 wt%), and F2O3 (2.27–8.65 wt%). Na2O within a specimen is typically higher than K2O. The Buni-Zom specimens variably plot within the diorite and granite fields of Cox et al. (1979) (Fig. 5.3). Major-element Harker diagrams show negative relationships for CaO, MnO, P2O5, TiO2, MgO, Fe2O3 with increasing SiO2 (Fig. 5.4). In contrast, Sr shows a positive relationship with SiO2; a similar, though weaker, relationship may exist with Ba and Rb (Fig. 5.4).  MORB-normalized trace element plots for the Buni-Zom specimens show some variation in LILE and HFSE (Fig. 5.5c; Table 5.1). The specimens show generally similar distributions of LILE with a pronounced negative Sr anomaly, however, specimen S95 shows more enrichment in Th and less depletion in Nb compared to S47 and S96. The chondrite-normalized REE pattern of the two specimens analysed have uniform negative slopes with 74	  minor positive Ho anomalies (Fig. 5.6c), however, specimen S96 (La/Yb)N = 9) is more enriched in heavy REE than S95 ((La/Yb)N = 17)).   5.3.4 Garam Chasma Pluton The four specimens analyzed from the Garam Chasma pluton have a narrow range of compositional variation in SiO2 (72.2–75.0 wt%), MgO (0.11–0.24 wt%), P2O5 (0.08–0.17 wt%), CaO (0.69–1.32 wt%), F2O3 (0.63–1.41 wt%); K2O (4.11–5.39 wt%) and Na2O (2.61–3.79 wt%). Compositionally, the Garam Chasma specimens plot in the alkali granite and granite fields of the Cox et al. (1979) discrimination diagram (Fig. 5.3). The only trends apparent on major element Harker plots are negative relationships between Na2O and Al2O3 against SiO2 (Fig. 5.4).  The MORB-normalized spidergram of specimens S9A, S9B, S10 and S10B from the Garam Chasma pluton show similar concentrations in LILE with strong negative Sr anomalies. Moreover, Th shows moderate enrichment in the specimens while Nb shows minor relative depletion (Fig. 5.5d). The two specimens, S9A and S10B, of the Garam Chasma pluton analyzed for REE concentrations show enrichment in light REE ((La/Yb)N = 29–56)), with similar decreasing slopes towards heavy REE on chondrite-normalized plots (Fig. 5.6d).   5.4. INTERPRETATIONS AND PETROGENESIS Frost et al. (2001) devised a granitic intrusive classification schemed based on three basic parameters that can be derived from major element chemistry. These parameters are defined as Fe* (iron number), the modified alkali-lime index (MALI), and aluminum 75	  saturation index (ASI). The iron number Fe* [FeOtotal/(FeOtotal + MgO)] separates specimens of ferroan affinity from those of or magnesian affinity. The MALI plots Na2O + K2O-CaO against SiO2 with separate fields for alkali, alkali-calcic, calcic-alkalic and calcic affinities. ASI is defined by molecular ratio of Al/(Ca-1.67P+Na+K), which differentiates plutonic rocks into peralkaline, metaluminous and peraluminous suites. Peraluminous plutons have ASI > 1.0, metaluminous have ASI < 1.0 and (Na+K) <Al, and peralkaline have ASI <1.0 and (Na+K) > Al. The Frost et al. (2001) classification scheme is adopted below for the basic classification and interpretation of the specimens examined in this study.  5.4.1 Kafiristan Pluton As noted above, minor sericitization was observed in the specimens of Kafiristan pluton. In order to assess the potential effects of this alteration, ternary plot of Al2O3–(CaO + Na2O)–K2O (mol) was constructed (Fig. 5.7). Nesbitt and Young (1984; 1989) outline a weathering trend from an average granite composition to an illite composition, and an advanced weathering trend from illite to a kaolinite composition end member (Fig. 5.7). Kafiristan specimens plot together near the position of ‘average granite’ (from Nesbitt and Young (1984; 1989) with no evidence of an alteration trend (Fig. 5.7). The chemical data from these specimens are therefore interpreted to be robust.   Though only constrained by two specimens, apparent decreasing K2O, CaO, MgO, Al2O3, TiO2, Fe2O3, and P2O5 with increasing SiO2 in the Kafiristan pluton (Fig. 5.4) are consistent with fractionating of hornblende, plagioclase, and potentially biotite (e.g. White and Chappell, 1983). In addition, decreasing Sr, Ba, and Zr and increasing Rb contents from S60 to S81 are also consistent with a fractionating plutonic body (Crawford and Searle, 1992; 76Alteration TypeK-MetasomatismSericitisationSilicification-HematisationChoritisationAverage GraniteAdvanced Weathering TrendGaram Chasma PlutonCaO+Na2O10 9020 8030 706040706050403060 40K2OAl2O3Figure 5.7 Ternary plot of Al2O3-(CaO+Na2O)-K2O, showing common alteration trend of an average granitic composition. Data from the Hindu Kush plutons (Kafiristan, Tirich Mir, Buni-Zom and Garam Chasma) bodies generally cluster together (weathering trend and weathering data after Nesbitt and Young (1984; 1989). See text for discussion.Kafiristan PlutonTirich Mir PlutonPlag KfsparMuscoviteIlliteKaoliniteBuni-Zom Pluton77	  Chappell and White, 1992; King et al., 1997; Dostal and Chatterjee, 2000; Liu et al., 2012). Moreover, the overall negative anomalies of Eu, Sr, and Nb in spidergrams of the two specimens (Fig. 5.6) may indicate significant fractional crystallization of plagioclase and titanite/ilmenite minerals (Wu et al., 2003). Enrichment of the Kafiristan specimens in heavy REE relative to chondrite may be attributed to the dissolution of either garnet/monazite and or allanite thereby liberating these elements (Crawford and Searle, 1992; Zhang et al., 2014). S60 plots within the ferroan field of the Fe* diagram and has alkali – calcic and peraluminous affinities (Fig. 5.8a, b; Table 1). S81 has a similar ferroan and peraluminous signature, but has a calc-alkalic composition (Fig. 5.8a, b; Table 1). As noted by Frost et al. (2001), rock specimen with such signatures are typically associated with a ‘A-type’ plutons and represent magma derivation from a reduced basaltic source (Frost and Frost, 1997). The variable MALI composition of the Kafiristan pluton specimens (Fig. 5.8b) may indicate magma differentiation (Frost et al., 2001), consistent with Harker diagram observations. Finally, the weakly to moderately peraluminous signatures of the Kafiristan specimens may also reflect differentiation, an aluminum-rich source, or assimilation of pelitic or semi-pelitic material. Such an interpretation is consistent with the enrichment of Rb and Th relative to Nb and Ta noted in the trace element spidergrams (Fig. 5.5; Pearce et al., 1984; Yang, et al., 2010). The Kafiristan pluton specimens have generally high Na2O + K2O, Fe/Mg ratios show pronounced negative Sr anomalies (Figs. 5.4, 5.5). These signatures, along with high Rb (Fig. 5.5) and high total REE (Table 1) with significant negative Eu anomalies (Fig. 5.6) are consistent with geochemical signatures of plutonic bodies that have evolved from the partial melting of lower crust from a basaltic source (White and Chappell, 1983; Whalen et al., 78FeOtot /(FeOtot +MgO)0.40.50.60.70.80.91.050 60 70 80Garam ChasmaBuni-ZomTirich MirKafiristanFe Numberferroanmagnesian12.0010.008.006.004.002.000.00-2.00-4.0055.00 60.00 70.00 80.00% SiO2Na 2O + K2O - CaOA-type granitesCordilleran granitesPeraluminous leucogranitealkalicalkalic - calciccalc - alkaliccalcicMALI% SiO2(a)(b)Figure 5.8 a) FeOtot/(FeOtot + MgO) versus weight per cent SiO2 diagram showing the boundary between ferroan (Kafiristan and Garams Chasma) and magnesian (Tirich Mir and Buni-Zom) plutons (after Frost et al., 2001). b) NaO + K2O – CaO versus weight per cent SiO2 plot showing the compositional range of Kafiristan, Tirich Mir, Buni-Zom and Garam Chasma plutons (after Frost et al., 2001).79	  1987; Eby 1990; Whalen et al., 1997; Wu et al., 2002; Li et al., 2007; King et al., 1997; Yang et al., 2011). Furthermore, high LILE/HFSE, Y/Nb (2.13–2.70) and Yb/Ta (1.37–1.96) ratios, and with strong fractionation of Ba, Sr and Eu are also consistent with derivation from a basaltic source (Figs. 5.4 and 5.7; Table 1; Eby 1990; Li et al., 2013). The two specimens of the Kafiristan pluton are therefore, interpreted to have resulted from the variable fractionation of magma from basaltic source in an anorogenic, perhaps rift-type, environment.  5.4.2 Tirich Mir Pluton Minor sericitization was observed in specimens S24 and S62 from the Tirich Mir pluton, and minor chloritization was also noted in specimen S24. In both specimens the alteration typically follows fractures in alkali feldspar. In specimens S28 and S29, fractures in plagioclase crystals variably contain secondary calcite and/or chlorite minerals. The affect of chloritization and sericitization appear to be minor, as these specimens do not show any significant alteration trend and generally plot within range of an average fresh granitic body (Fig. 5.7). All specimens are, therefore, considered for interpretation below.  The general trends of decreasing K2O, Fe2O3, MgO, and TiO2 with increasing SiO2 in the Tirich Mir pluton is consistent with crystal fractionation of K-bearing, Fe-Mg rich minerals (biotite or perhaps hornblende as reported by Searle et al., 2001), and plagioclase (White and Chappell; Li et al., 2007). Moreover, the negative Ba and Sr anomalies also indicate removal of a K-bearing phase by fractionation crystallization (Rex et al., 1988; Guillot and Le Fort, 1995; Liu et al., 2012). The negative Eu anomalies in the Tirich Mir specimens are consistent with plagioclase-controlled magmatic fractionation or occurrence in 80	  the residuum. The higher light REE relative to heavy REE in the Tirich Mir specimens may indicate accessory mineral, such as monazite/allanite, fractionation and retention of garnet in the residue (Rex et al., 1988).  The Tirich Mir specimens are dominantly magnesian; one specimen, with the highest silica content, plots in the ferroan field (Figure 5.8a). That ferroan specimen also has calc-alkalic affinity and is strongly peraluminous (Fig. 5.8b; Table 1). The magnesian specimens of the Tirich Mir pluton are calc-alkalic to alkali-calcic and are also peraluminous. This general magnesian association, along with calc-alkalic to alkali-calcic MALI characteristics (Fig. 5.8a, b) of the Tirich Mir pluton, is consistent with oxidizing differentiation trends of island arc magmas (Frost et al., 2001). In addition, the increasing magnesian trend and calc-alkalic to alkali-calcic compositional signatures of the Tirich Mir pluton suggest affinity with central arc plutons to more inboard plutons in a continental arc orogenic system (Moore, 1959; Bateman and Dodge, 1970, as cited in Frost et al., 2001). The peraluminous nature and moderately high silica content (SiO2 <73%) of the specimens, in addition to the single ferroan specimen at high SiO2%, are consistent with the assimilation of some crustal material by during magma ascent, and/or higher fluid activities (Frost et al., 2001).  Most of the Tirich Mir specimens generally have high K2O (Na2O/K2O <1), low heavy REE, are associated with a moderately negative Eu anomaly, and low Sr/Y and Nb/Ta ratios, all consistent with derivation from partial melting of mafic/ultramafic lower crustal and upper mantle (mantle wedge) material in a continental arc setting (White and Chappell, 1983; Li et al., 2007; Zhang et al., 2014). Moreover, the high LILE/HFSE ratios with notable negative Nb anomalies of the Tirich Mir specimens are characteristic of subduction-related melting (Li et al., 2007; Zhang et al., 2014). This interpretation is also supported by a 81	  pronounced negative Sr anomaly and more moderately negative Ba and Eu anomalies, indicative of fractionation of arc magmas (Li et al., 2007; Yang et al., 2010; Ji et al., 2009; Zhang et al., 2014). The Tirich Mir pluton is, therefore, interpreted to have evolved from a fractionated, subduction-related igneous magma source with variable contribution from sedimentary/crustal rocks through assimilation.   5.4.3 Buni-Zom Pluton Major element composition, hand specimen, and petrographic examination outline two distinct phases in the Buni-Zom pluton: 1) a low silica phase and 2) a high silica phase. The low silica phase specimen (S96) is dominated by Pl, Afs, Bt, Hbl, and Ttn, while the high silica phase specimen (S95) has a similar mineralogy but lacks hornblende. The relatively low ASI values 0.7-1.1 (Table 1), wide ranging compositions, and presence of Hbl and Ttn (accessory) are characteristic of a intrusive rocks generated from an igneous protolith (White and Chappell, 1983; Chappell and White, 2001). Major-element Harker diagrams show negative relationships between CaO, MnO, P2O5, TiO2, MgO, and Fe2O3 with SiO2 while K2O shows the opposite, consistent with a fractionation of minerals such as hornblende, biotite, and plagioclase. Moreover, the amphibole free specimen (S95) has higher alkali, LILE and HFSE also consistent with a fractionating magmatic source (Whalen et al., 1987; Crawford and Windley, 1990; Chappell, 1999; Chu et al., 2009; Deng et al., 2011). Chondrite-normalized REE patterns have fairly uniform negative slopes with the less evolved diorite, specimen S96, showing more enrichment in heavy REE ((La/Yb)N = 9) than the more evolved S95 ((La/Yb)N = 17)), consistent with fractional crystallization of magma. 82	  The absence of a Eu anomaly and the high Sr (663–826 ppm) content of the Buni-Zom specimens are compatible with plagioclase incorporated into the melt or a plagioclase-free source. The depletion in Nb and Ti and very low Nb/Ta ratios (0.1–0.7) indicates that the protolith to the Buni-Zom pluton has amphibole, titanite and/or rutile in the residuum (Mahoney et al., 1998, Zhang et al., 2014). Using the Frost et al. (2001) classification scheme, the Buni-Zom pluton specimens are magnesian, calcic to calc-alkalic and metaluminous to weakly peraluminous (Fig. 5.8a, b; Table 1). Their low Fe-number and narrow range about the calcic to calc-akalic boundary for MALI (Fig. 5.8b) demonstrates an affinity with calcic plutons that are observed to lie on the ocean-ward portions of the Arc-related granite belts (Frost et al., 2001). Furthermore, the marked negative Nb anomaly and high Sr are typical signatures of a plutonic body generated in a continental arc system (Martin, 1999; Rolland et al., 2002). It is interpreted, therefore, that the Buni-Zom pluton developed in an Andean-Type tectonic setting as a result of the subduction of (Tethys) oceanic lithosphere.   5.4.4 Garam Chasma Pluton Harker plots of the Garam Chasma pluton are typically scattered, however, Na2O has a negative relationship with SiO2, consistent with the fractionation of plagioclase. Using the Frost et al. (2001) classification scheme, the Garam Chasma specimens range from ferroan (dominantly) to magnesian, from calc-alkalic (dominantly) to alkali-calcic, and are all strongly peraluminous (Fig. 5.8b). As the Garam Chasma is a periluminous leucogranite body, the variable Fe* and MALI signatures of the Garam Chasma pluton likely reflect variation in the source material (Frost et al., 2001). These geochemical signatures are 83	  consistent with a plutonic body derived from a sedimentary magma source (White and Chappel, 1983, Pearce et al., 1984; Frost et al., 2001). Such an interpretation is consistent with higher K2O (5.4–4.1 wt%) over Na2O (3.3–2.6 wt%), and high Rb, as well as the presence of aluminous phases such as garnet and sillimanite in the Garam Chasma specimens (e.g. Chappell and White, 2001; Villaros, 2010).  The very high LILE/HFSE (high Rb/Nb+Y ratios) and LREE/HREE ratios in the specimens (La/Yb = 41.94–81.82), and a relatively pronounced negative Nb anomaly are consistent with a magma from a crustal source (Chappell, 1999; Chu et al., 2009; Deng et al., 2011). Relative depletion of heavy REE and the absence of a negative Eu anomaly indicates that REE-bearing phases such as garnet/monazite/allanite remained in the source while and plagioclase was either absent in the source or contributed to the melt. Trace element abundances of Rb, Ba and Sr define an array of strongly increasing Rb/Sr with decreasing Ba (Fig. 5.9) indicative of vapor-absent incongruent melting of muscovite (Harris and Inger, 1992; Inger and Harris, 1993). Similar vapor-absent melting of a muscovite-bearing protolith has been found to be associated with decompressional melting along the Himalayan orogen (Langtang, Fig. 5.9; Harris and Massey 1994; Prince et al., 2001; Searle et al., 1999; King et al, 2011; King and Harris, 2013). The geochemical and geochronological (discussed below) similarities of the Garam Chasma specimens to the Baltoro (Karakoram; Searle et al., 1989), Bhagirathi lecucogranite (Garhwal, India; Stern et al., 1989), and Manaslu (Nepal; Guillot and Le Fort, 1995) plutons of the Himalaya, and North Himalayan decompression-related plutons: Gomdre, Kouwu and Majia (King et al., 2011) and Leo Pargil dome (NW India; Lederer et al., 2013), indicate that the Garam Chasma leucogranite may have evolved through a similar processes of crustal anatexis during collisional orogenesis.  8410.01.00.110.0 30.0Garam ChasmaPlutonLangtang Pluton100.0 1000.0Rb/SrBa ppmF=0.12 F=0.28F=0.4Mu (VP)Mu(VA) Bi(VA)KspPlagBiFigure 5.9 Rb/Sr versus Ba diagram (after Inger and Harris, 1993) for Garam Chasma and Langtang (from Inger and Harris, 1993) leucogranites. Mu (VA)-vapour-absent muscovite melting; Bi (VA)-vapour-absent biotite melting; Mu (VP)-vapour-present muscovite melting. F=melt fraction.85	  5.5. GEOCHRONOLOGY Considerable variation is observed in published data, with a wide range of variably concordant dates for specimens from the Tirich Mir, Buni-Zom and Garam Chasma plutonic bodies. Published ages are typically interpreted based on only a few concordant analyses or extrapolated from arrays of data variably affected by Pb loss (Hildebrand et al., 1998; Hildebrand et al., 2000; Heuberger et al., 2007); moreover, there is no previous record of U-Pb geochronology from the Kafiristan pluton. New U-(Th)/Pb geochronology data were acquired using laser ablation paired with a multicollector inductively coupled plasma-mass spectrometer (LA-MC-ICP-MS) at the University of Santa Barbara, California (for detailed methodology see Cottle et al., 2011; 2013; and Appendix A). This approach to dating specimens collected from the Hindu Kush allows specific domains of zircon and/or monazite, imaged through cathodoluminescence (CL) and/or electron backscatter imaging to be targeted, avoiding potential problems associated with mixing of distinct age domains.  Isoplot v2.4 (Ludwig 2000) was used to calculate Tera–Wasserburg concordia diagrams (Fig. 5.10) for the Kafiristan, Tirich Mir and Buni-Zom plutons, and modified Wetherill concordia plot for the Garam Chasma pluton using the 238U, 235U and 232Th decay constants of Steiger and Jäger (1977).   5.5.1. Kafiristan Pluton The LA-MC-ICP-MS results for two specimens, S80 and S60, from the Kafiristan pluton are reported along with isotopic ratios and calculated ages in Table 5.2. Zircon grains from the two specimens of the Kafiristan pluton are euhedral and typically show oscillatory zonation under CL consistent with the zircon grains being magmatic (Corfu et al., 2003; Fig. 86Measured Isotopic Ratios Measured Isotopic AgesU Th Pb Th/U 207Pb/206Pb 2s % 207Pb/235U 2s % 206Pb/238U 2s % Rho 206Pb/238U 2s abs207Pb corrected 206Pb/238U date2s absS80_01 450 246 55 0.55 0.05719 0.33 0.62650 0.67 0.079 0.63 0.87 492.1 3.0 492.0 3.2S80_02 904 260 59 0.29 0.05712 0.30 0.63670 0.77 0.081 0.74 0.91 502.1 3.6 502.2 3.8S80_03 3191 360 106 0.11 0.05807 0.65 0.64100 1.87 0.080 1.62 0.97 497.3 7.6 496.8 8.3S80_04 190 34 9 0.18 0.05580 2.15 0.51100 6.65 0.068 3.84 0.96 422.0 16.0 422.0 16.6S80_05 2215 409 95 0.19 0.05749 0.19 0.64250 0.76 0.081 0.68 0.97 504.2 3.3 504.1 3.5S80_06 1427 442 101 0.31 0.05785 0.22 0.64070 0.81 0.080 0.77 0.96 498.6 3.7 498.2 3.9S80_07 2025 381 88 0.19 0.05785 0.19 0.65390 0.81 0.082 0.78 0.97 509.1 3.8 508.9 4.1S80_08 612 145 35 0.24 0.05740 0.33 0.64910 0.74 0.082 0.74 0.88 508.9 3.6 509.0 3.9S80_09 3199 435 101 0.14 0.05821 0.16 0.65120 0.69 0.081 0.74 0.97 504.5 3.6 504.0 3.8S80_10 3123 512 119 0.17 0.05849 0.17 0.65750 0.75 0.082 0.70 0.97 505.9 3.4 505.2 3.6S80_11 894 250 57 0.28 0.05772 0.29 0.64350 0.81 0.081 0.66 0.92 501.1 3.2 500.8 3.4S80_12 1028 341 81 0.34 0.05772 0.24 0.66740 0.67 0.084 0.59 0.94 520.5 3.0 520.5 3.2S80_13 2578 620 146 0.24 0.05815 0.19 0.66520 0.68 0.083 0.63 0.97 514.7 3.1 514.4 3.3S80_14 1430 302 68 0.21 0.05790 0.22 0.64450 0.65 0.081 0.69 0.93 501.6 3.3 501.2 3.6S80_15 278 147 33 0.53 0.05793 0.55 0.64290 0.86 0.080 0.76 0.80 498.7 3.6 498.2 3.9S80_16 1866 407 93 0.22 0.05778 0.24 0.65710 0.73 0.083 0.63 0.94 511.4 3.1 511.3 3.3S80_17 368 186 42 0.50 0.05731 0.52 0.63650 0.94 0.081 0.77 0.81 499.6 3.7 499.6 3.9S80_18 1955 477 106 0.24 0.05767 0.21 0.63290 0.70 0.079 0.58 0.74 492.7 2.7 492.3 2.9S80_19 460 267 64 0.58 0.05753 0.35 0.66700 0.88 0.084 0.83 0.91 521.7 4.1 521.9 4.5S80_20 1055 376 85 0.36 0.05749 0.30 0.65200 0.94 0.082 0.86 0.94 510.3 4.2 510.3 4.5S80_21 1147 285 67 0.25 0.05746 0.31 0.66830 0.79 0.084 0.82 0.92 521.8 4.1 522.1 4.4S80_22 3880 463 105 0.12 0.05862 0.16 0.64280 0.75 0.080 0.71 0.98 494.8 3.4 493.8 3.6S80_23 4493 572 124 0.13 0.05839 0.13 0.63730 0.64 0.079 0.64 0.98 492.3 3.1 491.5 3.2S80_24 4110 982 215 0.24 0.05836 0.14 0.66050 0.74 0.082 0.74 0.98 509.4 3.6 508.9 3.9S80_25 1589 372 85 0.24 0.05794 0.24 0.65730 0.90 0.082 0.90 0.97 510.3 4.4 510.1 4.7S80_26 451 254 57 0.56 0.05762 0.47 0.65900 0.86 0.083 0.80 0.85 513.8 3.9 513.8 4.2S80_27 1295 333 73 0.26 0.05761 0.26 0.63670 0.75 0.080 0.69 0.83 497.4 3.3 497.2 3.5S80_28 1779 543 119 0.31 0.05772 0.21 0.64240 0.83 0.081 0.76 0.96 500.7 3.6 500.4 3.9S80_29 1236 255 56 0.21 0.05768 0.26 0.63130 1.00 0.079 0.88 0.97 492.9 4.2 492.6 4.5S80_30 2875 715 164 0.25 0.05829 0.16 0.66440 0.71 0.083 0.71 0.97 512.9 3.5 512.5 3.7S80_31 108 57 16 0.53 0.08033 1.15 0.84300 1.42 0.076 0.80 0.51 472.6 3.7 459.1 3.8S80_32 2454 545 124 0.22 0.05780 0.19 0.65340 0.69 0.082 0.62 0.96 509.6 3.0 509.4 3.2S80_33 400 200 45 0.50 0.05734 0.33 0.63860 0.86 0.081 0.74 0.90 501.8 3.6 501.7 3.8S80_34 1605 427 99 0.27 0.05765 0.23 0.67660 0.81 0.085 0.76 0.92 526.1 3.9 526.2 4.1S80_35 4620 826 0 0.18 -7.08000 -5.51 -0.00053 -28 0.000 22.25 -0.72 0.0 0.0 0.0 0.0S80_36 2530 374 81 0.15 0.05771 0.23 0.66600 0.47 0.084 0.44 0.88 518.3 2.2 518.3 2.4S80_37 1289 351 84 0.28 0.05746 0.24 0.67080 0.54 0.085 0.42 0.90 524.2 2.1 524.4 2.3S80_38 3756 593 138 0.16 0.05824 0.17 0.65880 0.41 0.082 0.33 0.94 508.8 1.6 508.3 1.7S80_39 2414 557 126 0.23 0.05807 0.21 0.64740 0.36 0.081 0.28 0.70 502.1 1.4 501.6 1.5S80_40 1691 368 82 0.22 0.05766 0.21 0.63920 0.38 0.080 0.29 0.89 498.8 1.4 498.5 1.5S60_001 555 201 47 0.36 0.05762 1.31 0.62790 1.42 0.079 0.56 0.80 487.7 3.6 487.2 2.8S60_002 861 252 61 0.30 0.05719 1.22 0.63980 1.56 0.081 0.98 0.78 504.1 3.1 504.2 5.1S60_003 1553 421 100 0.28 0.05607 1.12 0.63010 1.27 0.081 0.59 0.91 503.6 4.2 504.4 3.1S60_004 963 311 74 0.33 0.05614 1.16 0.62060 1.29 0.081 0.56 0.84 500.2 3.9 500.9 2.9S60_005 280 127 30 0.46 0.05566 0.83 0.61290 1.24 0.080 0.92 0.65 498.9 2.8 499.8 4.7S60_006 191 80 19 0.42 0.05687 0.90 0.63320 1.05 0.081 0.54 0.64 501.7 3.7 502.0 2.8S60_007 462 127 32 0.28 0.05673 1.49 0.64150 1.81 0.082 1.02 0.63 509.4 3.6 509.8 5.4S60_008 969 282 66 0.29 0.05696 1.19 0.62490 1.31 0.080 0.56 0.90 498.2 3.8 498.3 2.9S60_009 316 128 31 0.41 0.05780 0.78 0.64700 0.95 0.081 0.54 0.67 505.0 3.7 504.7 2.8S60_010 547 198 48 0.36 0.05828 1.33 0.63270 1.67 0.080 1.01 0.74 494.1 3.0 493.4 5.1Sample Name                  Tirich Mir and Buni-Zom plutons.Concentration (ppm)Table. 5.2. LA-ICP-MS U-Pb geochronology data for spot analysis of zircon of the Kafiristan,87S60_011 386 121 30 0.31 0.05834 0.75 0.64700 1.29 0.081 1.05 0.68 504.1 3.4 503.4 5.4S60_012 274 124 31 0.46 0.05827 0.88 0.64800 1.30 0.081 0.97 0.61 504.6 2.9 504.1 5.0S60_013 245 93 23 0.38 0.05840 0.89 0.64730 1.35 0.081 1.02 0.56 502.2 3.2 501.5 5.3S60_014 549 108 28 0.20 0.05810 1.27 0.66250 1.41 0.083 0.62 0.84 514.0 4.4 513.7 3.3S60_015 421 108 28 0.26 0.05859 0.80 0.65520 1.01 0.082 0.61 0.69 508.8 4.2 508.2 3.2S60_016 432 152 38 0.35 0.05774 1.44 0.63900 1.55 0.081 0.58 0.75 500.7 3.9 500.4 3.0S60_017 2468 412 102 0.17 0.05783 0.97 0.63310 1.44 0.079 1.06 0.94 492.4 3.4 491.9 5.4S60_018 1018 109 30 0.11 0.05766 1.10 0.67320 1.25 0.085 0.60 0.86 523.3 4.4 523.4 3.2S60_019 438 182 45 0.42 0.05714 1.29 0.63470 1.43 0.080 0.62 0.81 498.2 4.2 498.2 3.2S60_020 362 106 26 0.28 0.05710 1.36 0.63520 1.52 0.081 0.67 0.83 499.4 4.5 499.5 3.5S60_021 290 189 46 0.65 0.05683 1.49 0.62350 1.59 0.080 0.56 0.71 493.7 3.7 493.9 2.9S60_022 404 199 54 0.49 0.05725 1.38 0.68650 1.49 0.087 0.57 0.77 538.1 4.4 538.8 3.2S60_023 640 196 47 0.31 0.05671 1.26 0.62410 1.40 0.080 0.62 0.84 493.2 4.1 493.5 3.2S60_024 2611 590 141 0.23 0.05740 1.01 0.62790 1.22 0.079 0.68 0.95 491.8 4.5 491.7 3.5S60_025 585 221 52 0.38 0.05672 1.38 0.61890 1.49 0.079 0.55 0.79 488.6 3.6 488.8 2.8S60_026 976 384 92 0.39 0.05694 1.24 0.62770 1.64 0.080 1.07 0.86 493.5 3.5 493.6 5.4S60_027 1690 457 106 0.27 0.05692 1.05 0.61580 1.50 0.078 1.07 0.88 486.7 3.4 486.7 5.4S60_028 151 80 19 0.53 0.05661 1.18 0.61960 1.39 0.079 0.73 0.64 491.8 4.8 492.1 3.7S60_029 203 111 26 0.55 0.05791 1.04 0.63930 1.19 0.080 0.59 0.39 495.8 3.9 495.3 3.0S60_030 267 155 36 0.59 0.05712 0.89 0.62740 1.09 0.080 0.63 0.64 494.8 4.2 494.8 3.2S24_001 3240 74 5 0.02 0.04918 0.35 0.13211 0.49 0.019 0.35 0.76 124.0 0.4 123.9 0.4S24_002 2408 67 4 0.03 0.04862 0.60 0.13106 0.67 0.019 0.57 0.59 124.3 0.7 124.2 0.7S24_003 1642 1257 70 0.77 0.04883 0.43 0.13054 0.60 0.019 0.42 0.68 123.5 0.5 123.5 0.5S24_004 4340 2391 131 0.56 0.04909 0.26 0.13267 0.57 0.020 0.49 0.87 125.0 0.6 124.9 0.6S24_005 2037 597 33 0.29 0.04873 0.53 0.13160 0.76 0.020 0.51 0.72 124.6 0.6 124.6 0.6S24_006 772 112 7 0.15 0.05108 0.72 0.13920 0.86 0.020 0.49 0.51 126.3 0.6 125.9 0.6S24_007 1875 237 57 0.13 0.05920 0.22 0.69760 0.46 0.085 0.40 0.86 528.6 2.0 527.8 2.2S24_008 766 670 36 0.88 0.04860 0.64 0.12960 0.77 0.019 0.41 0.57 123.4 0.5 123.4 0.5S24_009 535 154 9 0.29 0.05152 1.79 0.13770 2.03 0.019 0.52 0.54 123.8 0.7 123.3 0.7S24_010 2050 26 2 0.01 0.04858 0.43 0.13114 0.61 0.020 0.45 0.68 125.1 0.6 125.1 0.6S24_011 756 60 5 0.08 0.05220 2.30 0.14360 1.81 0.020 1.01 0.01 126.5 1.3 125.9 1.3S24_012 549 225 162 0.41 0.09998 0.18 3.36300 0.51 0.245 0.45 0.93 1410.2 5.6 1393.0 6.7S24_013 678 384 21 0.57 0.04886 0.80 0.13210 0.91 0.020 0.49 0.54 125.4 0.6 125.4 0.6S24_014 2204 134 8 0.06 0.04903 0.41 0.13311 0.68 0.020 0.56 0.80 126.4 0.7 126.3 0.7S24_015 931 232 13 0.25 0.04906 0.71 0.13350 0.97 0.020 0.48 0.61 126.6 0.6 126.6 0.6S92_001 359 202 10 0.57 0.04967 1.05 0.11420 1.14 0.017 0.57 0.46 107.1 0.6 106.9 0.6S92_002 633 348 16 0.55 0.04864 0.76 0.11154 0.74 0.017 0.49 0.19 106.5 0.5 106.4 0.5S92_003 489 247 12 0.50 0.04923 0.81 0.11190 0.88 0.017 0.41 0.31 106.2 0.4 106.0 0.4S92_004 285 172 13 0.57 0.04844 1.47 0.12360 1.46 0.019 0.64 0.29 119.0 0.8 119.0 0.8S92_005 392 211 11 0.53 0.04831 1.14 0.11060 1.08 0.017 0.54 0.23 106.4 0.6 106.3 0.6S92_006 452 210 10 0.47 0.04798 0.98 0.10950 1.10 0.017 0.48 0.50 106.1 0.5 106.1 0.5S92_007 531 337 16 0.64 0.04839 0.91 0.11020 0.91 0.017 0.48 0.37 105.7 0.5 105.7 0.5S92_008 175 57 3 0.33 0.04813 1.64 0.11020 1.63 0.017 0.56 0.24 106.7 0.6 106.7 0.6S92_009 744 695 32 0.93 0.04846 0.87 0.11020 1.00 0.016 0.46 0.51 105.2 0.5 105.1 0.5S92_010 411 260 14 0.63 0.05546 1.79 0.12910 1.86 0.017 0.37 0.31 108.2 0.4 107.2 0.4S92_011 1028 2060 92 1.95 0.04948 0.77 0.10957 0.88 0.016 0.58 0.53 103.6 0.6 103.5 0.6S92_012 529 730 35 1.37 0.04799 0.85 0.11150 0.99 0.017 0.65 0.53 107.9 0.7 107.9 0.7S92_013 244 140 7 0.57 0.04831 1.32 0.10880 1.47 0.016 0.57 0.36 104.6 0.6 104.6 0.6S92_014 228 75 4 0.33 0.04913 1.24 0.11410 1.31 0.017 0.56 0.41 108.1 0.6 108.0 0.6S92_015 661 537 28 0.81 0.04846 0.70 0.11522 0.78 0.017 0.49 0.45 110.2 0.5 110.1 0.5S92_016 487 343 17 0.71 0.04975 0.90 0.11360 0.97 0.017 0.47 0.43 105.8 0.5 105.6 0.5S92_017 363 256 13 0.68 0.04857 1.01 0.11360 1.23 0.017 0.59 0.60 109.2 0.6 109.1 0.6S92_018 646 335 16 0.52 0.04890 0.92 0.11050 1.09 0.016 0.53 0.54 104.7 0.6 104.6 0.6S92_019 450 219 11 0.48 0.04892 1.08 0.11350 1.23 0.017 0.57 0.49 107.6 0.6 107.5 0.6S92_020 602 273 13 0.46 0.04902 0.71 0.11271 0.84 0.017 0.54 0.60 106.6 0.6 106.4 0.6S92_021 1041 855 41 0.82 0.04799 0.65 0.10959 0.83 0.017 0.55 0.69 106.3 0.6 106.3 0.6S92_022 1523 2280 104 1.50 0.04847 0.58 0.11113 0.66 0.017 0.38 0.47 106.0 0.4 105.9 0.4S92_023 148 127 8 0.84 0.04865 1.66 0.12240 1.88 0.018 0.83 0.48 115.8 1.0 115.8 1.088S92_024 1113 577 27 0.52 0.04795 0.67 0.10893 0.76 0.016 0.50 0.61 105.2 0.5 105.2 0.5S92_025 553 341 16 0.62 0.04838 0.91 0.11020 1.00 0.017 0.49 0.45 105.6 0.5 105.5 0.5S92_026 1016 680 32 0.67 0.04797 0.67 0.10938 0.81 0.017 0.45 0.57 105.8 0.5 105.8 0.5S92_027 953 650 31 0.69 0.04795 0.67 0.11041 0.79 0.017 0.51 0.54 106.3 0.5 106.3 0.5S92_028 844 582 27 0.68 0.04879 0.84 0.11140 0.99 0.017 0.57 0.60 105.7 0.6 105.6 0.6S92_029 1083 633 30 0.59 0.04863 0.68 0.11290 0.76 0.017 0.53 0.56 107.2 0.6 107.1 0.6S92_030 790 506 25 0.64 0.04916 0.73 0.11428 0.77 0.017 0.50 0.45 107.5 0.5 107.4 0.5S92_031 511 366 17 0.72 0.04815 0.96 0.11090 1.17 0.017 0.60 0.60 106.1 0.6 106.1 0.6S92_032 515 282 13 0.55 0.04860 0.84 0.11130 0.90 0.017 0.50 0.50 106.1 0.5 106.0 0.5S92_033 211 143 49 0.69 0.06716 0.60 1.12000 1.16 0.120 0.80 0.60 732.0 5.5 729.0 6.0S92_034 384 220 11 0.57 0.04849 1.22 0.11330 1.15 0.017 0.77 0.33 107.7 0.8 107.7 0.8S92_035 382 677 31 1.81 0.04843 1.12 0.11460 1.31 0.017 0.64 0.42 109.7 0.7 109.7 0.7S92_036 398 296 14 0.74 0.04861 1.11 0.11140 1.17 0.017 0.66 0.47 106.0 0.7 105.9 0.7S92_037 202 184 9 0.91 0.05027 1.47 0.11990 1.42 0.017 0.76 0.32 109.9 0.8 109.6 0.8S92_038 633 437 22 0.70 0.05316 0.88 0.12230 0.98 0.017 0.45 0.35 106.3 0.5 105.6 0.5S92_039 105 22 1 0.21 0.04880 2.46 0.11360 2.46 0.017 0.58 0.32 108.4 0.6 108.3 0.7S92_040 609 20 1 0.02 0.04781 0.88 0.10500 1.05 0.016 0.63 0.60 101.8 0.7 101.8 0.6S95_01 439 432 21 0.98 0.05673 1.67 0.13030 2.00 0.017 0.57 0.50 106.6 0.6 105.5 0.6S95_02 363 259 12 0.71 0.04804 1.14 0.10850 1.38 0.016 0.67 0.51 105.2 0.7 105.2 0.7S95_03 380 255 12 0.67 0.04868 1.09 0.11130 1.26 0.017 0.60 0.52 106.1 0.6 106.0 0.6S95_04 427 311 15 0.73 0.04830 0.97 0.11200 1.16 0.017 0.59 0.60 107.5 0.7 107.5 0.6S95_05 371 239 11 0.63 0.04907 1.00 0.11320 1.06 0.017 0.60 0.43 106.9 0.7 106.7 0.6S95_06 353 317 14 0.89 0.04794 1.25 0.10830 1.39 0.016 0.59 0.45 104.6 0.6 104.6 0.6S95_07 559 252 12 0.46 0.04807 0.94 0.11170 1.16 0.017 0.71 0.64 108.0 0.7 108.0 0.8S95_08 294 156 7 0.53 0.04956 1.57 0.11160 1.61 0.016 0.57 0.34 104.7 0.6 104.6 0.6S95_09 563 539 26 0.96 0.04949 0.99 0.11400 1.05 0.017 0.57 0.55 106.8 0.6 106.6 0.6S95_10 416 328 15 0.79 0.04842 0.95 0.10930 1.10 0.016 0.67 0.56 104.6 0.7 104.6 0.7S95_11 424 324 15 0.77 0.04831 0.93 0.10900 1.10 0.016 0.61 0.52 105.0 0.7 105.0 0.6S95_12 353 278 13 0.79 0.04855 1.09 0.11190 1.25 0.017 0.54 0.44 106.2 0.6 106.1 0.6S95_13 589 414 19 0.71 0.04858 1.03 0.11280 1.15 0.017 0.66 0.67 107.1 0.7 107.0 0.7S95_14 400 304 14 0.78 0.04821 1.14 0.10910 1.28 0.016 0.61 0.41 105.3 0.6 105.3 0.6S95_15 302 232 11 0.78 0.04977 1.39 0.11360 1.50 0.017 0.66 0.45 105.9 0.7 105.7 0.7S95_16 513 494 23 0.97 0.04850 1.07 0.11020 1.09 0.017 0.59 0.52 105.5 0.6 105.5 0.6S95_17 348 215 10 0.62 0.04914 1.04 0.11280 1.15 0.017 0.60 0.35 107.2 0.7 107.0 0.6S95_18 598 638 31 1.08 0.04990 0.92 0.11320 1.15 0.017 0.55 0.58 105.6 0.6 105.3 0.6S95_19 335 205 10 0.62 0.04864 1.15 0.11080 1.17 0.017 0.66 0.44 106.1 0.7 106.1 0.7S95_20 445 412 20 0.94 0.04840 0.87 0.11130 1.08 0.017 0.65 0.62 107.4 0.7 107.4 0.7S95_21 426 430 20 1.03 0.04891 0.94 0.11070 1.26 0.016 0.73 0.74 105.0 0.8 104.9 0.8S95_22 236 149 7 0.64 0.04980 1.77 0.11410 2.89 0.017 1.73 0.97 107.1 1.8 106.9 1.9S95_23 248 156 7 0.63 0.04851 1.40 0.10990 1.46 0.016 0.73 0.90 105.2 0.8 105.2 0.8S95_24 403 336 16 0.84 0.04802 1.02 0.10930 1.28 0.016 0.73 0.62 105.4 0.8 105.4 0.8S95_25 450 352 17 0.79 0.04985 1.12 0.11550 1.30 0.017 0.66 0.60 107.2 0.7 107.0 0.7S95_26 476 293 14 0.62 0.04858 0.95 0.10980 1.00 0.017 0.67 0.64 105.6 0.7 105.6 0.7S95_27 453 281 13 0.62 0.04821 1.08 0.10850 1.29 0.016 0.79 0.49 104.6 0.8 104.6 0.8S95_28 548 475 22 0.86 0.04775 0.88 0.10820 1.11 0.016 0.73 0.64 105.2 0.7 105.2 0.8S95_29 505 399 19 0.79 0.04869 0.92 0.11100 1.08 0.017 0.66 0.62 106.7 0.7 106.6 0.7S95_30 290 244 13 0.84 0.05959 1.63 0.14110 1.91 0.017 0.70 0.56 109.1 0.8 107.6 0.8S95_31 475 549 25 1.16 0.04843 0.99 0.10890 1.19 0.016 0.73 0.61 104.8 0.8 104.8 0.8S95_32 645 681 31 1.06 0.04811 0.89 0.10850 1.11 0.016 0.67 0.78 104.5 0.7 104.5 0.7S95_33 342 210 10 0.61 0.04894 1.16 0.11010 1.18 0.017 0.73 0.47 105.5 0.7 105.4 0.8S95_34 422 356 16 0.85 0.04837 1.01 0.10920 1.19 0.017 0.67 0.66 105.6 0.7 105.6 0.7S95_35 322 208 10 0.66 0.04919 1.20 0.11250 1.51 0.017 0.72 0.51 105.9 0.8 105.8 0.8S95_36 423 278 13 0.66 0.04840 1.07 0.11000 1.18 0.017 0.66 0.56 106.1 0.7 106.0 0.7S95_37 765 315 15 0.42 0.04836 0.79 0.11220 1.16 0.017 0.94 0.81 108.4 1.0 108.3 1.0S95_38 390 252 12 0.65 0.04734 1.14 0.10860 1.29 0.017 0.72 0.57 106.7 0.7 106.7 0.8S95_39 407 304 14 0.75 0.04808 0.87 0.10860 1.10 0.016 0.73 0.68 105.2 0.8 105.2 0.8S95_40 427 359 17 0.85 0.04820 1.06 0.10860 1.29 0.016 0.79 0.61 105.3 0.8 105.3 0.889207 Pb/206Pb0.047 0.049 0.051 0.053 49.4 49.8 50.2 50.6 51.0 51.4 51.8 52.2 123 124 125 126 127 128 129 Specimen S24 Tirich Mir Pluton 238U/206Pb100 μmdata-point error ellipses are 2207 Pb/206PbSpecimen S92 Buni-Zom Pluton 0.045 0.047 0.049 0.051 0.053 0.055 0.057 58 60 62 64 102 108 100 104 106 110 112 238U/206Pb100 μmdata-point error ellipses are 2Specimen S80 Kafiristan Pluton 207 Pb/206Pb0.055 0.056 0.057 0.058 0.059 0.060 11.4 11.6 11.8 12.0 12.2 12.4 12.6 12.8 510 520 530 540 500490 238U/206Pb100 μm data-point error ellipses are 2Specimen S60 Kafiristan Pluton 207 Pb/206Pb0.055 0.056 0.057 0.058 0.059 0.060 11.0 11.4 11.8 12.2 12.6 13.0 490 530 550 510 238U/206Pb100 μmdata-point error ellipses are 20.044 0.048 0.052 0.056 0.060 58 59 60 61 62 110 207 Pb/206PbSpecimen S95 Buni-Zom Pluton data-point error ellipses are 2238U/206Pb108 106 104 100 μm22 26 28 0.0032 0.0036 0.0040 0.0044 0.0048 0.00105 0.00115 0.00125 0.00135 0.00145 Specimen C65 Garam Chasma Pluton 208Pb/232Th206 Pb/238U500 μmdata-point error crosses are 224 Figure 5.10 Tera–Wasserburg concordia diagrams showing analytical data for zircons from Kafiristan, Tirich Mir and Buni-Zom plutons. Concordia diagram for Garam Chasma pluton specimen with 208Pb/232Th ratios along the x-axis. Note, the Garam Chasma data are shown as crosses because errors are not correlated. See text for details. Cathodoluminescence images of representative zircons from Kafiristan, Tirich Mir and Buni-Zom are shown with the relevant concordia plots along with a backscattered monazite image from the Garam Chasma pluton.90	  5.10) The rims of the grains were the primary targets during analysis to avoid any potential inherited domains. Forty spot analyses were obtained while targeting the outer rims of thirty-seven zircon grains from S80. Two anomalously young zircon ages (S80_04 and S80_31) and a single spot missing the target (S80_35) were excluded from interpretation (Table 5.2). Tera–Wasserburg concordia (uncorrected for common Pb) exhibit a broad dispersion between 525–495Ma (Fig. 5.10). While most of the data are concordant, some show a slight discordance consistent with a minor common Pb component (Fig. 5.10). The youngest concordant age from S80 is 492 ± 3.2 Ma, which is taken as the minimum crystallization age of this specimen. Thirty analyses were obtained from an equal number of zircon grains separated from S60. The dates from this specimen are generally concordant and spread between ~525 Ma and 487 Ma (Fig. 5.10), with a minimum crystallization age of 486.7 ± 5.4 Ma. Some of the analyses are slightly discordant suggestive of minor common Pb or minor Pb loss (Fig. 5.10).  The two analyzed specimens of the Kafiristan pluton outline a protracted magmatic history spanning between ca. 525–488 Ma. Dates from both specimens (representing geochemically distinct phases in the Kafiristan pluton as observed above) overlap and are, therefore, interpreted to indicate that the two phases are the result of a single protracted magmatic event. The new dates obtained are within uncertainty of a previous whole rock Rb/Sr crystallization age of 483 ± 21 Ma (Debon et al., 1987).   5.5.2. Tirich Mir Pluton U-Pb dating on zircon was carried out on specimen S24 of the Tirich Mir pluton. CL images of euhedral zircon from the Tirich Mir specimen display undisturbed oscillatory 91	  patterns indicating that the zircon grains are magmatic (Fig. 5.10). Fifteen spot analyses were obtained from eight zircon grains (Table 5.2). Two of the analyses (S24_007 and S24_012) were excluded as they yield anomalously older ages (early Paleozoic and Mesoproterozoic, respectively) than most of the specimen (Early Cretaceous). The two old analyses may reflect detrital/inherited zircon components. The remaining analyses from specimen S24 spread between ca. 127 and 123 Ma (Fig. 5.10). Most of the data acquired are concordant but three spots suggest the presence of some common Pb (Fig. 5.10).  The spread in dates from the Tirich pluton specimen is interpreted to indicate continuous crystallization from ca. 127–123 Ma with a final crystallization age of 123.7 ± 0.7 Ma. This minimum age is similar to, but somewhat older than, the previously published date of Heuberger et al. (2007), 121 ± 1 Ma, and significantly older than the 114 ± 2 Ma date of Hildebrand et al., (2001), indicating that crystallization/magmatism within the pluton may have a protracted history.   5.5.3. Buni-Zom Pluton The U-Pb analytical results on two specimens, S92 (intermediate phase) and S95 (high SiO2 phase) of the Buni-Zom body are given in Table 5.2. Zircon from both specimens are typically elongate and euhedral with oscillatory zoning, consistent with a magmatic origin (Fig. 5.10). A total of forty analyses were obtained from the rims of thirty-four zircon crystal from S92. Three of the analyses (S92_004, S92_023 and S92_033) yielded anomalous ages and were excluded from further interpretation. Two of the excluded zircon ages, 119 ± 0.8 Ma (S92_004) and 115.8 ± 1 Ma (S92_023), may be associated with earlier magmatism in an Andean-type setting along the southern margin of Eurasia (discussed below), while 727 92	  ± 6 Ma (S92_033) is considered an inherited age. The remaining concordant dates spread between ~110 and 102 Ma (Fig. 5.10), with a minimum age of 101.8 ± 0.6 Ma. Similarly, forty spot ages were obtained from targeting the rims of thirty-six zircon grains from specimen S95 (Table 5.2). The data acquired from these analyses yield dates that spread between ~109 and 105 Ma (Fig. 5.10), yielding a minimum date of 104.7 ± 0.7 Ma.  The ages from the two specimens of the Buni-Zom representing geochemically distinct phases overlap entirely and are interpreted to have evolved in a nearly continuous magmatic event spanning for ca. 8 Myr. The previously reported 103.8 ± 0.27 Ma crystallization age from the Buni-Zom (Heuberger et al., 2007) is in general agreement with the range of new data presented herein.   5.5.4 Garam Chasma Pluton Monazite U-Th-Pb dating of the Garam Chasma leucogranite was performed on specimen C65 (Table 5.3). Because 207Pb/235U dates are relatively imprecise in young monazite, 208Pb/232Th dates are reported (Fig. 5.10). Most of the monazite dates are concordant, however, some reverse discordance is apparent in the 208Pb/232Th vs. 206Pb/238U plot indicating ‘unsupported 206Pb from the decay of 230Th (Schärer, 1984). Specimen C65 of the Garam Chasma pluton yields two apparent age populations: the older age population yields a weighted mean age (208Pb/232Th) of 27.1 ± 0.3 (MSWD 0.6) and younger age population with a weighted mean 208Pb/232Th date of 23.6 ± 0.1 Ma (MSWD 0.8). These two populations may indicate an episodic emplacement history. The dominant phase outlined in this study is consistent with the age of ca. 24 Ma interpreted by Hildebrand et al (1998) from discordant monazite and uraninite dates.  93Pb U Th Th/U 207Pb/206Pb 2s % 207Pb/235U 2s % 206Pb/238U 2s % Rho 208Pb/232Th 2s % 208Pb/232Th 2s absC-65_001 67 11820 51900 4.39 0.0523 1.86 0.0256 2.347 0.00355 1.717 0.68 0.001147 2.131 23.2 0.5C-65_002 72 11140 54000 4.85 0.0507 1.84 0.0260 2.075 0.00372 1.424 0.50 0.001158 1.854 23.4 0.4C-65_003 85 9800 63500 6.48 0.0530 2.08 0.0265 2.298 0.00362 1.272 0.43 0.001170 1.668 23.6 0.4C-65_004 69 11920 53100 4.45 0.0487 1.68 0.0254 2.202 0.00376 1.277 0.57 0.001149 1.605 23.2 0.4C-65_005 67 10430 49200 4.72 0.0500 2.20 0.0258 2.833 0.00369 1.381 0.51 0.001173 1.664 23.7 0.4C-65_006 65 17090 50500 2.95 0.0490 1.39 0.0245 1.963 0.00361 1.496 0.68 0.001127 1.808 22.8 0.4C-65_007 75 8560 56300 6.58 0.0517 2.32 0.0274 2.812 0.00383 1.514 0.55 0.001174 1.918 23.7 0.5C-65_008 73 6840 53800 7.87 0.0528 2.46 0.0290 2.763 0.00396 1.414 0.53 0.001163 1.848 23.5 0.4C-65_009 98 6280 64200 10.22 0.0561 2.14 0.0344 2.353 0.00447 1.455 0.47 0.001331 1.878 26.9 0.5C-65_010 67 16390 50900 3.11 0.0495 1.80 0.0241 1.989 0.00359 1.423 0.55 0.001160 1.938 23.4 0.5C-65_011 66 13050 50600 3.88 0.0507 1.70 0.0270 2.594 0.00384 1.640 0.71 0.001143 2.137 23.1 0.5C-65_012 60 6260 38700 6.18 0.0535 2.24 0.0322 2.767 0.00434 1.497 0.54 0.001351 1.928 27.3 0.5C-65_013 62 16270 46500 2.86 0.0499 1.74 0.0247 2.106 0.00355 1.154 0.51 0.001164 1.503 23.5 0.4C-65_014 74 7410 55300 7.46 0.0528 2.08 0.0290 2.931 0.00395 1.316 0.60 0.001157 1.769 23.4 0.4C-65_015 87 9290 65000 7.00 0.0532 2.07 0.0269 2.643 0.00364 1.319 0.63 0.001161 1.764 23.5 0.4C-65_016 76 11570 56100 4.85 0.0498 1.73 0.0256 2.113 0.00376 1.488 0.67 0.001181 1.993 23.9 0.5C-65_017 78 8720 58700 6.73 0.0508 1.97 0.0272 2.461 0.00388 1.496 0.52 0.001163 1.762 23.5 0.4C-65_018 70 13740 52800 3.84 0.0507 1.40 0.0252 2.107 0.00364 1.677 0.66 0.001175 1.917 23.7 0.5C-65_019 68 15350 51600 3.36 0.0500 1.44 0.0245 2.166 0.00358 1.958 0.71 0.001153 2.121 23.3 0.5C-65_020 64 9580 47700 4.98 0.0499 2.20 0.0258 2.250 0.00379 1.372 0.50 0.001170 1.838 23.6 0.4C-65_021 77 17120 57500 3.36 0.0501 1.70 0.0244 2.414 0.00356 1.545 0.70 0.001155 1.772 23.3 0.4C-65_022 67 8700 49500 5.69 0.0514 2.33 0.0271 3.026 0.00375 1.815 0.59 0.001161 2.195 23.5 0.5C-65_023 64 15630 48300 3.09 0.0483 1.47 0.0244 2.299 0.00368 1.551 0.71 0.001169 2.096 23.6 0.5C-65_024 69 8740 50600 5.79 0.0516 2.33 0.0266 2.972 0.00371 1.781 0.64 0.001179 2.336 23.8 0.6C-65_025 64 7540 46080 6.11 0.0511 2.54 0.0266 2.783 0.00381 1.705 0.53 0.001210 2.283 24.4 0.6C-65_026 71 10850 52300 4.82 0.0503 2.19 0.0265 3.014 0.00383 1.595 0.65 0.001188 2.236 24.0 0.5C-65_027 72 8310 52700 6.34 0.0523 1.91 0.0286 2.410 0.00394 1.421 0.47 0.001180 1.741 23.8 0.4C-65_028 64 14030 47500 3.39 0.0492 1.56 0.0247 2.230 0.00362 1.739 0.69 0.001167 2.271 23.6 0.5C-65_029 77 8730 57600 6.60 0.0502 2.19 0.0257 2.721 0.00374 1.497 0.59 0.001183 2.244 23.9 0.5C-65_030 60 14030 44270 3.16 0.0498 1.79 0.0272 2.425 0.00397 1.536 0.65 0.001167 1.928 23.6 0.5C-65_032 64 10060 47800 4.75 0.0497 2.21 0.0257 2.806 0.00374 1.525 0.59 0.001175 1.917 23.7 0.5C-65_033 71 11870 53100 4.47 0.0492 1.69 0.0256 2.269 0.00373 1.581 0.66 0.001170 1.924 23.6 0.5C-65_034 76 12010 57200 4.76 0.0475 1.81 0.0247 2.634 0.00380 1.606 0.79 0.001151 2.125 23.2 0.5C-65_035 67 13660 50200 3.67 0.0509 1.67 0.0253 2.213 0.00359 1.391 0.64 0.001165 1.845 23.5 0.4C-65_036 66 15700 48900 3.11 0.0499 1.42 0.0250 2.201 0.00363 1.542 0.79 0.001178 1.828 23.8 0.4C-65_037 67 7930 49600 6.25 0.0492 2.24 0.0258 2.825 0.00384 1.799 0.54 0.001181 2.078 23.9 0.5C-65_038 65 14510 49700 3.43 0.0487 1.50 0.0240 2.039 0.00353 1.388 0.63 0.001144 1.961 23.1 0.5C-65_039 75 13340 54700 4.10 0.0510 1.88 0.0253 2.137 0.00364 1.539 0.50 0.001181 1.824 23.9 0.4C-65_041 63 12870 47900 3.72 0.0501 1.68 0.0247 2.142 0.00360 1.527 0.67 0.001163 2.020 23.5 0.5C-65_042 52 12100 39760 3.29 0.0512 1.86 0.0248 2.178 0.00354 1.612 0.67 0.001142 1.964 23.1 0.5C-65_043 68 19260 50890 2.64 0.0506 2.37 0.0287 3.382 0.00407 1.523 0.60 0.001161 2.195 23.5 0.5C-65_044 66 13340 49900 3.74 0.0501 1.66 0.0245 2.450 0.00357 1.735 0.72 0.001142 1.964 23.1 0.5C-65_045 91 5430 59300 10.92 0.0540 2.22 0.0339 2.950 0.00450 1.710 0.65 0.001340 1.942 27.1 0.5C-65_046 59 12300 44400 3.61 0.0494 1.60 0.0244 2.457 0.00361 1.498 0.74 0.001161 1.937 23.5 0.5C-65_047 77 11180 56200 5.03 0.0498 1.67 0.0270 2.374 0.00392 1.481 0.68 0.001193 1.809 24.1 0.4C-65_048 55 13140 41520 3.16 0.0504 1.94 0.0253 2.488 0.00362 1.547 0.64 0.001157 1.942 23.4 0.5Sample Name    Concentrations (ppm) Measured Isotopic Ratios  measured Isotopic AgeTable 5.3. LA-ICP-MS U-Th/Pb geochronology data for spot analysis of monazite of the Garam Chasm pluton.94	  5.6 DISCUSSION AND TECTONIC SIGNIFICANCE Recent metamorphic monazite ages from the Hindu Kush range (Chapter 4), along with sedimentary records from the nearby Pamir (Angiolini et al., 2013) outline a protracted tectonic history for the southern Eurasian margin in the region involving terrane accretion, plutonism, and related mountain building processes from the Mesozoic to the Cenozoic. The present study builds on this earlier work and outlines four distinct magmatic events in the Hindu Kush area spanning the Cambrian–Early Ordovician to the late Oligocene with affinities to a) intraplate extension/rifting, b) subduction-derived melts into a continental arc and c) synorogenic crustal anatexis. These magmatic episodes outline the regional magmatic and metamorphic history of the Hindu Kush and aid in a broader understanding of Himalaya geology and the tectonic evolution of the southern margin of Eurasia.  Geochemically, the Kafiristan pluton is ferroan, calc-alkalic to alkali-calcic, and weakly peraluminous to peraluminous consistent with generation in anorogenic extensional tectonic environment (Fig. 5.11a). The crystallization ages from the two specimens examined are indistinguishable, which indicates that the two phases of the pluton were part of the same magmatic event between 487 and 538 Ma. Such an event may reflect post-collisional rifting of the Gondwana supercontinent during the Paleozoic (e.g. Dèzes, 1999; Fernández et al., 2012) with the Kafiristan pluton intruded as the Cimmerian terranes, including the Hindu Kush and Karakoram, rifted and drifted away from peri-Gondwana toward the Eurasia (Sengör, 1979; Rogers et al., 1995; Gaetani, 1997; Heuberger, 2004; Zanchi and Gaetani, 2011). Similar Cambro-Orovician plutons interpreted to be related to the same rifting event have been identified in the nearby Zanskar (Dèzes, 1999), Karakoram (Le Fort et al., 1986; 95+ +++++ ++ ++ + ++ + + ++ ++++++ +++++ ++ ++ + ++ + + ++ ++++++ ++ +++++ ++ +++++ ++ ++ + ++ + + ++ ++++++ ++ ++ + ++ + + ++ ++++++ +++++ ++ +++++ ++++ + ++ ++ + ++ + + ++ ++++++ +++++ ++ +++++ ++ ++ ++ ++ ++ + ++ + + ++ ++++++ ++ +++++ ++++ + ++ ++ + ++ + + ++ ++++++ +++++ ++ +++++ ++ ++ +?+ ++ ++ +++++ +++++ +++++ ++ ++ ++ +++++++ ++ +++ ++ ++ +++++ ++ ++++++++ ++ +++ ++ ++ +++++ ++ ++++++ ++ +++++ ++++++ ++ +++ ++++ ++ +++++++++++KKSP-HK NGRPBCPTMBZPTPTTWBSP-HKKIAPTPTbasaltic magmaIndiaCPCPCPCPSP-HKSP-HKSP-HKKKKKKKKKNTSP-HKCP KKNGNGIndiaNSNTRPSRPS TMBZTMBZTMBZRPSRPSMKTMKTISZKIAKIAc. 538-487 Maa) Hindu Kush and Karakoram terranes detachment from the northern periphery of  Gondawana and intrusion of Kafiristan pluton.b) Subsequent to extension, the Hindu Kush terrane accreted to Eurasia during the first phase of Cimmerian orogeny.c. 211-201 Mac. 189-184 Mac) The Cimmerian orogeny continued with the accretion of the Karakoram terrane followed by northward subduction transforming the margin into acontinental arc.c. 127-105 Mad) Intrusion of the Tirich Mir and Buni-Zom plutons in a continental arc setting.c. 86-72 Mae) Demise of the Paleotethys with the docking of the KIA and intrusion of the subsequent intrusion of the Kohistan batholith.c. 27-23 Maf) Crustal thickening associated with the continued India-Eurasia collision results in crustal anatexis and the formation of the Garam Chasma pluton.foliated leucograniteU-Pb 188-195 MaTirich MirplutonBuni-ZomplutonKafiristanplutonTMFTMFGaram ChasmaplutonTWBpartilal melting formingKafiristan plutonFigure 5.11. Schematic cross-sectional evolutionary model of the southern Eurasian margin. See text for discussion (modified after Hildebrand et al., 2001; Burg 2011; Zanchi and Gaetani 2011; Angiolini et al., 2013, Faisal et al., 2014). Abreviaitons:  CP = Central Pamir, SP-HK = South Pamir – Hindu Kush, KK = Karakoram, NG = Northern Gondwana, KIA = Kohistan Island Arc, RPB = Rushan-Pshart Basin, RPS = Rushan-Pshart Suture, TWB = Tirich-Wakhan Basin, TMBZ = Tirich Mir Boundary Zone, PT = Paleotethys, NT = Neotethys, MKT (Northern Suture) = Main Karakoram Thrust, ISZ = Indus Suture Zone.96	  Noble and Searle, 1995; Rolland et al., 2002; Zanchi and Gaetani, 2011) and Wakhan (Debon et al., 1987) regions. Following the accretion of the Hindu Kush and Karakoram blocks in the Early Jurassic (Chapter 4), the southern margin of Eurasia was transformed into an Andean-style convergent zone (Fig. 5.11b and c). The continued subduction of Paleotethys oceanic lithosphere beneath the Hindu Kush-Karakoram led to the intrusion of the Tirich Mir and Bun-Zom plutons in the Cretaceous (Fig. 5.11d). U-Pb zircon geochronology from the Tirich Mir pluton outlines a magmatic event spanning 127 to 123 Ma, coeval with subduction-related magmatic activity and the intrusion of the Karakoram batholith farther east (Searle et al., 1989; Hildebrand et al., 2001; Heuberger et al., 2007 and references therein).  While like the Tirich Mir specimens, the Buni-Zom rocks show geochemical signatures of a plutonic body generated above a subduction zone (Fig. 5.11d), the absence of trends in Al2O3, Na2O, P2O5, CaO and MgO in Buni-Zom specimens when plotted against SiO2 (Fig. 5.4), indicate that its source is less evolved. Moreover, high molecular Mg content as well as a close association with the calcic to calc-akalic boundary on the MALI (Figs. 5.8a and b) compared to the calc-alkalic to alkali-calcic nature of Tirich Mir specimens indicates that the Buni-Zom plutonic body was located farther toward the oceanic portions of the Andean –Arc related belt. This is consistent with is consistent with their relative proximity to the paleo-Eurasian margin (to the SE of the field area) in the Cretaceous.  The protracted Andean-style magmatism in the Hindu Kush recorded during the Early Cretaceous intrusion of the Tirich Mir and Buni-Zom plutons ceased as the Kohistan Island arc docked along the southern margin of Eurasia during the Late Cretaceous (Petterson et al., 1991; Fraser et al., 2001; Chapter 4; Fig. 5.11e). The continued subduction of the Neotethys 97	  along the accreted Kohistan arc to Eurasia culminated with the collision of India and Eurasia in the Eocene (Patriat and Achache, 1984; Beck et al., 1995). The crustal shortening and thickening of the Indian and Eurasian margins during collision led to widespread anatexis and the intrusion of the Garam Chasma pluton in the Hindu Kush region during the Oligocene/Miocene (Fig. 5.11f). The general similarity in the geochemistry and age of the Garam Chasma pluton with other Cenozoic leucogranites from the Himalaya, e.g. Baltoro (Parrish and Tirrul, 1989), Langtang (Inger and Harris, 1993), Manaslu (Guillot and Le Fort, 1995) and North Himalaya lecucogranite (Gomdre, Kouwu and Majia, King et al., 2011) is consistent with regional scale anatexis across the Himalaya, Karakoram, Tibet and Hindu Kush. The monazite dates from the Garam Chasm pluton are also consistent with published metamorphic monazite dates from the same area (Chapter 4) indicating that anatexis and metamorphism occurred synchronously in the Hindu Kush terrane during the Late Oligocene/Early Miocene.   5.7. SUMMARY The geochemical and geochronological data from the plutonic bodies of the Hindu Kush outline a protracted tectonomagmatic history of the southern margin of Eurasia that spans from the early Paleozoic into the Cenozoic. These data provide constraints on crustal growth and paragenesis along the southern margin of Eurasia prior to Cenozoic initiation of continental collision with India.  1. The Kafiristan pluton is a Cambro-Ordovician body interpreted to be associated with the break-up of Gondwana.  98	  2. Subduction of the Paleotethys beneath the southern Eurasian margin after the accretion of the Hindu Kush and Karakoram terranes developed an Andean-style margin resulting in the Cretaceous emplacement of the Tirich Mir and Buni-Zom plutons.  3. The origin of the Cenozoic Garam Chasma pluton is attributed to crustal anatexis associated with the India-Eurasia collision. The crystallization age of the Garam Chasma leucogranite is coeval with sillimanite-grade metamorphism and intrusion of leucogranite bodies within the nearby Karakoram, Himalaya and Tibet regions. 	  99	  Chapter 6  Cooling and Exhumation History of the Hindu Kush  6.1. BACKGROUND New 40Ar/39Ar and fission track thermochronological data constrain the evolution and cooling history of the Hindu Kush, in the region surrounding Chitral, NW Pakistan (Fig. 6.1). The Hindu Kush consists of tectonically juxtaposed blocks of Gondwana affinity (Hildebrand, 19989; Hildebrand et al., 2001; Chapters 4 & 5). These blocks were assembled and deformed during multiple events spanning the Mesozoic to the present (Chapters 4 & 5). Although the timing of deformation and associated metamorphic events in the Hindu Kush have been established (e.g. Hildebrand et al., 2000; Zanchi et al., 2000; Chapter 4), there are few data available that enable understanding the cooling history of the Hindu Kush region.  The role of post-Eocene deformation characterized by present day oblique convergence (causing the exhumation of mid-crustal rocks) and development of extreme topography (e.g. Tirich Mir peak lying at an elevation of 7700+ m) is not clear. Moreover, the role of the Tirich Mir fault (thrust motion is interpreted to be significantly older than current strike-slip movement) in the development of present-day topography is not known. Therefore, 40Ar/39Ar and fission track analyses are critical for establishing the roles that strike-slip faulting and/or thrust faulting may have played in the exhumation, cooling, and uplift of rocks in the Hindu Kush. No systemic efforts have hitherto been made to examine and document the exhumation and cooling history of the Hindu Kush range. An existing 40Ar/39Ar muscovite age of 110.6 ± 3.2 Ma from one specimen of the Tirich Mir pluton has been interpreted to represent post-magmatic recrystallization (Heuberger et al., 2007). Biotite from specimens of the Garam Chasma pluton yielded K-Ar ages of 20–18 Ma (Zafar et al., 2000), which are 100B om bo r at e  Va l l eyL u t k h o  G o lArkariGolR um bo o r Va l l e y Ba gh os t Go lBasti GolS 72C65C 9 5S8S81S 9 6C 2 0C 7S 24S 6 2S 1 2S 1 5C69C 1 0 8 C 11 0C 9 1Cxx Sxx7 0827 01 57 56 07 58 48 07 24 46 18 56 76 38 57 84 0828 76 38 66 64 58 25 55 88 07 0357 05 15 72 68 85 53 5 4 56 04 65 67 8307 58 56 56 08 58 25 55 25 1767 6787 66 16 15 86 26 66 05 6447 2474 58 27 06 6R es h un  Fa ul t  T i ri c h Mi r  Fa ul tCHITRALShoghorG ar a mC ha s maBarenis71˚30′ 71˚45′ 72˚00′3 6˚ 15 ′71˚15′71˚13′3 6˚ 00 ′3 5˚ 45 ′36˚15′ReshunConglomeratePsammite UnitsMetasedimentry rocks(Undifferentiated)Chitral Slate0 4kmCleavage/schistosityFaultSettlementStream/RiverSnow8 12LEGENDNBuni-Zom/Kesu-Kohuzi PlutonTirich Mir PlutonGaram Chasma PlutonKafiristan PlutonCarbonatesCalcsilicateTirich MirAmphiboliteGreenschistDorah An PlutonINDEXSpecimen NumbersKabulIslamabadCHINAINDIAAFGHANISTANPAKISTANFigure 6.1 Geological map of the study area showing the specimens location.101	  interpreted to represent cooling after its ca. 23.6 Ma crystallization (Hildebrand et al., 1998; Chapter 5).  This work presents new 40Ar/39Ar and apatite fission track data from the Chitral portion of the Hindu Kush region (Fig. 6.1) to help elucidate the low-temperature history of the region and distinguish between the role that early orthogonal compressional events and more recent strike-slip motion may have played in the exhumation and uplift of rocks in the area. Understanding the potential roles of these different kinematic situations will help elucidate the complex recent kinematic history of the Hindu Kush and have the potential to provide insight on the processes active in orogenic syntaxis in general.  6.2. CHRONOLOGIC METHODOLOGY 6.2.1 40Ar/39Ar Chronology 40Ar/39Ar analyses (laser step-heating) were performed at the 40Ar/39Ar Laboratory facility at the University of Manitoba, Canada. Fifteen specimens, including plutonic and metapelitic rocks, were selected for 40Ar/39Ar analysis based on the availability of muscovite and biotite grains while also considering the spatial distribution of specimens across the area (Fig. 6.1). Twenty-three mica separates, eleven muscovite and twelve biotite, were collected from those fifteen specimens. The muscovite and biotite separates were wrapped in aluminum foil and loaded into an aluminum circular configuration disk (18 mm in diameter and 2mm deep) together with GA-1550 biotite (98.5 ± 0.8 Ma; Spell and McDougall, 2003). Planar regressions were fit to the standard data, and the 40Ar/39Ar neutron fluence parameter, J, interpolated for the unknowns. Uncertainties in J are estimated at 0.2–0.4% (1s), based on Monte Carlo error analysis of the planar regressions (Best et al., 1995).  102	  Specimens and standards were irradiated for 7.5 hours in the Cadmium-Lined In-Core Irradiation Tube (CLICIT) TRIGA reactor facility at the Oregon State University, to transform 37Cl and 39K to 38Ar and 39Ar, receptively. Irradiated samples were loaded in a Cu sample tray in a high vacuum extraction line and were either fused or step-heated using a 100 W CO2 laser. Sample viewing during laser fusion was monitored by a video camera system and positioning was via a motorized sample stage. Reactive gases were removed by three NP-10 SAES getters (two at room temperature and one at 450 °C) prior to being admitted to an ARGUS VI mass spectrometer by expansion. Five argon isotopes were measured simultaneously over a period of 7 min. Measured isotope abundances were corrected for extraction-line blanks. A value of 295.5 was used for the atmospheric 40Ar/36Ar ratio (Steiger and Jäger, 1977) for the purposes of routine measurement of mass spectrometer discrimination using air aliquots, and correction for atmospheric argon in the 40Ar/39Ar age calculation. Despite potential complications, the 40Ar/39Ar technique has been successfully employed across Pakistan and the Himalaya to elucidate the thermal history of the orogen (e.g. Zeitler, 1985; Treloar et al., 2000; Kali et al., 2010; Kellett et al., 2013). It is possible for extraneous Ar (i.e. Ar not produced through the decay of parent isotopes within a crystal) to be incorporated into dated material through diffusion across grain boundaries possibly assisted by fluids carrying degassed Ar from adjacent minerals. The uptake of such Ar has the potential to alter the makeup of the existing reservoir of argon in a mineral during complex thermal histories of a rock body (Ruffet et al., 1995; Treloar et al., 2000; Kelley, 2002). The anomalously old ages that would result from this process are attributed to excess radiogenic Ar in the system. The Ar reservoir can also be affected through deformation-103	  related recrystallization, which obliterates previous Ar fingerprints. In such a scenario the 40Ar/39Ar method would date the timing of deformation (McDougall and Harrision, 1999; Rolland et al., 2008; Bröcker et al., 2013).   6.2.2 Apatite Fission Track Dating In the apatite Fission Track (FT) dating technique, constraint on the timing of cooling through temperatures as low as 70-110 °C is provided by retained FTs within a grain caused by the spontaneous nuclear fission of 238U. If exposed to elevated temperature, the FTs anneal and the age is reset to zero (van de Beek et al., 2006; Patel et al., 2007). Depending upon the cooling rate and chemical composition of apatite, the annealing temperature can range from 90 ˚C at a low rate of cooling to 140 °C at a high rate of cooling (Gleadow and Duddy, 1981; Zeitler, 1985; Green, 1988; Yamada, et al., 1995; Patel et al., 2007, Lisker et al., 2009). Apatite FT samples were processed and analysed at the Department of Earth Sciences at Dalhousie University. Apatite aliquots were mounted in araldite epoxy on glass slides, ground and polished to expose internal grain surfaces, then etched for 20s in 5.5M HNO3 at 21 °C to reveal spontaneous fission tracks. All mounts were prepared using the external-detector method (Hurford and Green, 1983). Samples and CN5 glass standards were irradiated with thermal neutrons at the Forschungneutronenquelle Heinz Maier-Leibnitz at Technische Universität München. After irradiation, the low-U muscovite detectors that covered apatite grain mounts and glass dosimeters were etched in 40% HF for 45 min at 21°C to reveal induced fission tracks. Samples were analysed using a Kinetek computer-controlled stage driven by the FTStage software (Dumitru, 1993) attached to a Zeiss Axioplan microscope. Dry counting was done at a magnification of x1000 and between 9 to 20 grains 104	  per sample were analysed. FT ages were calculated using a weighted mean Zeta (ζ) calibration factor (Hurford and Green, 1983) based on IUGS ages standards (Durango, Fish Canyon and Mount Dromedary apatites) [Hurford, 1990; Miller et al., 1985). Based on 23 analyses, the ζ for the operator (I. Coutand) is 369.8 ± 4.8. AFT ages were calculated using the BINOMFIT software of Brandon (2002).  6.3. RESULTS  6.3.140Ar/39Ar Chronology Most of the 40Ar/39Ar age spectra resulting from the incremental step-heating experiments of muscovite and biotite samples yield plateaus representing > 68% of 39Ar released with MSWD values ranging between 0.02–1.1, and errors ranging between 1.1–6.5 Ma (Fig. 6.2 and Table 6.1). The presence of such a plateau is interpreted to reflect that a specimens’ Ar systematics have not been significantly disturbed since it was acquired (e.g. Snee, 2002). In presence of a distributed age-spectra/lack of defined plateau, an integral age, which represents the sum of all the steps, essentially equivalent to a total fusion age, was ascertained. All of the 40Ar/39Ar ages discussed in the following are reported ± 2σ error. Muscovite and biotite were analyzed from specimen S81 of the Kafiristan pluton collected along the Rumboor valley (Fig. 6.1). The 40Ar/39Ar of the muscovite exhibit a poorly defined age spectrum and yield an integrated age of 407.3 ± 17.9 Ma (Table 6.1; Fig. 6.2). In contrast, biotite analyses define a plateau that comprises 95.4% of the 39Ar released yielding an age of 50.1 ± 2.7 Ma (Table 6.1; Fig. 6.2). The first 4.6% 39Ar released records large variability and error (Fig. 6.2).  1050 200 400 600 800 0 20 40 60 80 100 Age (Ma) 0 20 40 60 80 0 20 40 60 80 100 S81- MuscoviteS81- BiotiteCumulative 39Ar %Integrated Age = 407.3 ±17.9 MaAr released 74.2 % Age (Ma) Cumulative 39Ar %Plateau Age = 50.1 ±2.9 MaAr released 95.4 % 0 20 40 60 80 100 120 140 0 20 40 60 80 100 C20 - Muscovite0 20 40 60 0 20 40 60 80 100 S62- MuscoviteAge (Ma) Cumulative 39Ar %Plateau Age = 111.5 ± 1.9 MaAr released 98.35 % Age (Ma) Cumulative 39Ar %Plateau Age = 48.2 ± 1.7 MaAr released 95.4 % 0 10 20 30 40 50 0 20 40 60 80 100 S8- Muscovite0 10 20 30 40 0 20 40 60 80 100 S8- BiotiteCumulative 39Ar %Age (Ma) Plateau Age = 19.6 ± 1.8 MaAr released 99.3 % Plateau Age = 18.5 ± 2.9 MaAr released 97.2 % Cumulative 39Ar %Age (Ma) 0 10 20 30 40 0 20 40 60 80 100 C69- Muscovite (m)0 10 20 30 40 0 20 40 60 80 100 C69- Muscovite (m2)Plateau Age = 21.5 ± 2.6 MaAr released 98.4 % Cumulative 39Ar %Age (Ma) Integrated Age = 18.3 ± 3.9 MaAr released 89.0 % Cumulative 39Ar %Age (Ma) 0 20 40 60 0 20 40 60 80 100 0 10 20 30 40 50 0 20 40 60 80 100 C110 - Muscovite C110- BiotiteCumulative 39Ar %Age (Ma) Plateau Age = 32.2 ± 4.1 MaAr released 90.4 % Cumulative 39Ar %Age (Ma) Plateau Age = 21.9 ± 6.1 MaAr released 96.1 % 0 10 20 30 40 50 60 70 0 20 40 60 80 100 C108- Muscovite0 10 20 30 0 20 40 60 80 100 C108- BiotiteCumulative 39Ar %Age (Ma) Plateau Age = 28.4 ± 4.0 MaAr released 94.7 % Plateau Age = 24.9 ± 1.1 MaAr released 99.4 % Cumulative 39Ar %Age (Ma) 0 10 20 30 40 50 0 20 40 60 80 100 C7 - BiotiteAge (Ma) Cumulative 39Ar %Plateau Age = 23.5 ± 2.3 MaAr released 92.3 % 0 10 20 30 40 0 20 40 60 80 100 S12 - MuscoviteCumulative 39Ar %Age (Ma) Plateau Age = 17.6 ± 2.2 MaAr released 95.0 % 0 10 20 30 40 50 0 20 40 60 80 100 C69 - BiotiteAge (Ma) Cumulative 39Ar %Plateau Age = 19.4 ± 1.9 MaAr released 97.9 % 1060 10 20 30 40 50 60 70 0 20 40 60 80 100 S15 - MuscoviteAge (Ma) Cumulative 39Ar %Plateau Age = 23.1 ± 6.3 MaAr released 98.8 % 0 10 20 30 40 50 0 20 40 60 80 100 S72 - MuscoviteCumulative 39Ar %Age (Ma) Plateau Age = 21.7 ± 3.7 MaAr released 96.1 % 0 10 20 30 40 0 20 40 60 80 100 C91 - Muscovite (m)0 10 20 30 40 50 0 20 40 60 80 100 C91 - Muscovite (m2)0 10 20 30 40 50 60 70 0 20 40 60 80 100 C91 - BiotiteAge (Ma) Cumulative 39Ar % Cumulative 39Ar %Age (Ma) Cumulative 39Ar %Age (Ma) Plateau Age = 20.6 ± 3.4 MaAr released 96.1 % Plateau Age = 17.5 ± 3.2 MaAr released 95.9 % Integrated Age = 26.6 ± 5.3 MaAr released 84.2 % 0 20 40 60 80 0 20 40 60 80 100 S96 - MuscoviteCumulative 39Ar %Age (Ma) Plateau Age = 61.6 ± 1.1 MaAr released 68.6 % Figure 6.2 continuedFigure 6.2 40Ar/39Ar age spectra for muscovite and biotite specimens dated, both plateau and integrated ages are shown. Steps used to calculate plateau ages are filled with light grey while unfilled steps are not including in plateau ages.107 Sample No. Grain Plateau Age (Ma) ±2σ MSWD Integrated Age (Ma) ±2σMuscovite 407.3 ± 17.9Biotite 50.1 ± 2.7 1.02C20 Muscovite 11.5 ± 1.9 0.52S62 Muscovite 48.2 ± 1.7 0.63Muscovite 28.4 ± 4 0.08Biotite 24.9 ± 1.3 1.13Muscovite 32.8 ± 4.0 0.44Biotite 21.9 ± 6.5 0.02S96 Biotite 61.6 ± 1.1 0.68C7 Biotite 23.5 ± 2.2 0.66Muscovite 19.6 ± 1.8 0.06Biotite 18.5 ± 2.9 0.19Muscovite (m) 21.5 ± 2.6 0.20Muscovite (m2) 18.3 ± 3.9Biotite 19.4 ± 1.9 0.10S12 Muscovite 17.6 ± 2.2 0.04S15 Muscovite 23.1 ± 6.3 0.11Muscovite (m) 20.6 ± 3.4 0.04Muscovite (m2) 17.5 ± 3.2 0.64Biotite 26.6 ± 5.3S72 Muscovite 21.7 ± 3.7 0.02Table 6.1. Muscovite and biotite specimens selected for 40Ar/39Ar analysis and their                  respective plateau and integrated ages. C91S81C108C110S8C69108	  Specimens C20 and S62, both from the Tirich Mir pluton, yielded two different muscovite 40Ar/39Ar dates (Table 6.1). Specimen C20 was collected from the same approximate location as the Heuberger et al. (2007) specimen (ZP 22) along the Dir gol (Fig. 6.1), which yielded a 40Ar/39Ar age of 112 ± 3.2 Ma for them. Muscovite heating steps from specimen C20 defines a plateau, which incorporates 98.4% of the 39Ar and yields an age of 111.5 ± 1.9 Ma (MSWD 0.52). The first 1.6% of the 39Ar released records larger variability and errors (Fig. 6.2). In contrast, muscovite from specimen S62, which was collected along the Arkari Gol in the immediate hanging wall of the Tirich Mir fault (Fig. 6.1), yielded a plateau age of 48.2 ± 1.7 Ma that comprises 99.2% of the 39Ar (MSWD 0.6; Table 6.1; Fig. 6.2). Two specimens, C108 and C110, collected from the footwall of the Tirich Mir fault (Fig. 6.1), yield younger 40Ar/39Ar dates than muscovite in the hanging wall (specimen S62). Muscovite and biotite from specimen C108 yield well-defined age spectra, with indistinguishable apparent 40Ar/39Ar ages of 28.4 ± 4.0 Ma (MSWD 0.08; comprising 94. 7% 39Ar) and 24.9 ± 1.3 Ma (MSWD 1.13; incorporating 99.4% of 39Ar), respectively (Table 6.1; Fig. 6.2). Muscovite from specimen C110 generated a plateau spectra with an age of 32.8 ± 4.1 Ma (MSWD 0.4) that assimilates 90.4% of the 39Ar, while biotite from the same specimen defines a plateau with a slightly younger age of 21.9 ± 6.5 Ma (MSWD 0.02), incorporating 96.1% of 39Ar (Table 6.1; Fig. 6.2).  Biotite specimen C7 (garnet-mica schist) from the Arkari Gol to the north of the Tirich Mir pluton (Fig. 6.1), displays a plateau which incorporates 92.3% of the 39Ar and yields an age of 23.5 ± 2.2 Ma (MSWD 0.66) (Table 6.1; Fig. 6.2). Specimen S96 was collected from the Buni-Zom pluton across the Reshun Fault to the southeast of the Tirich 109	  Mir body (Fig. 6.1). A biotite separate from S96 defines a plateau age at 61.6 ± 1.1 Ma (MSWD 0.68), comprising 68.6% of 39Ar (Table 6.1; Fig. 6.2). Two specimens, S8 and C69, sampled from the Garam Chasma pluton give indistinguishable ages. Muscovite and biotite from specimen S8 produced age spectra with defined plateaus and ages of 19.6 ± 1.8 (MSWD 0.06; incorporating 99.3% 39Ar) and 18.5 ± 2.9 Ma (MSWD 0.19; assimilating 97.2% of 39Ar), respectively (Table 6.1; Fig. 6.2). One of the two muscovite separates from C69, ‘m’, defines a plateau age of 21.5 ± 2.6 Ma (MSWD 0.20; comprising 98.4% 39Ar), while the ‘m2’ 40Ar/39Ar age spectra (Fig. 6.2) is highly discordant, but the bulk of the steps yield apparent ages between 99.7–12.5 Ma, with an interpreted integrated age of 18.3 ± 3.9 Ma (Table 6.1; Fig. 6.2). Biotite from specimen C69 displays a flat plateau (Fig. 6.2) corresponding to an age of 19.4 ± 1.9 Ma (MSWD 0.10) with 97.7% of 39Ar.  Metapelitic specimens collected along the Lutkho Gol near the Garam Chasma pluton (S12, S15 and C91; Fig. 6.1) yield muscovite ages that are largely indistinguishable within uncertainty. The 40Ar/39Ar muscovite dates from metapelites also overlap with muscovite and biotite dates from the Garam Chasma pluton specimens (S8 and C69). Muscovite from specimen S12 forms a flat plateau age of 17.6 ± 2.2 Ma (MSWD 0.11), comprising 95.0% 39Ar (Table 6.1; Fig. 6.2). Similarly, muscovite analysed from S15 also yields a well-behaved age spectra with a plateau age of 23.1 ± 6.3 Ma (MSWD 0.11), incorporating 98.8% of 39Ar (Table 6.1; Fig. 6.2). Two muscovite separates, ‘m’ and ‘m2’, from C91 yielded plateau ages of 20.6 ± 3.4 Ma (MSWD 0.04; assimilating 96.1% of 39Ar) and 17.5 ± 3.2 Ma (MSWD 0.64; incorporating 95.9% of 39Ar) respectively, (Table 6.1; Fig. 6.2). In contrast, biotite 40Ar/39Ar age spectra from C91 (Fig. 6.2) is highly discordant and yields an integrated age of 110	  26.6 ± 5.3 Ma (Table 6.1; Fig. 6.2). Finally, muscovite from specimen S72, a calc-silicate collected along the Besti Gol (Fig. 6.1) north of the main pluton, yielded an age spectra with an inferred plateau age of 21.7 ± 3.7 Ma (MSWD 0.02), comprising 96.1% 39Ar (Table 6.1; Fig. 6.2).   6.3.2 Fission Track A suite of nine specimens were selected and processed for apatite FT dating from the study area. Only three of those specimens, however, yielded enough datable material to analyse; only those specimens are reported below (see Table 6.2 and Fig. 6.1). Specimen S24, obtained from the Tirich Mir pluton (Fig. 6.1), yielded 9 apatite grains in which tracks were measured yielding a representative age of 1.4 ± 0.5 Ma (± 1σ) (Table 6.2). Specimen C65, collected from the Garam Chasma pluton (Fig. 6.1), had 20 apatite grains that were analysed resulting in an age of 3.5 ± 0.2 Ma (± 1σ). Finally, a metapelitic specimen, C95, collected along the Lutkho Gol near Garam Chasma (Fig. 6.1) yielded thirteen apatite grains and an age of 9.7 ± 2.1 Ma (± 1σ) (Table 6.2).  6.4. DISCUSSION AND INTERPRETATION 6.4.1 40Ar/39Ar Data The muscovite and biotite 40Ar/39Ar dates of ~400 and 50 Ma, respectively (specimen S81) are younger than the ~500 Ma crystallization age of the Kafiristan pluton (Chapter 5). It is possible that the muscovite (407.3 ± 17.9 Ma) date represents a cooling age, however, there is no additional information about the events at that time with which to aid an interpretation. Moreover, the poorly behaved age spectrum (Fig. 6.2) indicates disturbance of 111 Table 6.2. Apatite fission track results of specimens collected from the study area. Sample Number of grains Spontaneous Track Density rs x 106 cm-2 (Ns) Induced Track Density ri x 106 cm-2 (Ni)  Dosimeter Track Density rd x 106 cm-2 (Nd)  P(c2) Central Age ± 1s U           (%) (Ma) (ppm) S24 9 0.0482 (32) 9.1871 (6105) 1.4510 (5291) 10.6 1.41 ± 0.25 88.47 C65 20 0.1425 (247) 11.0782 (19200) 1.4527 (5291) 27.1 3.46 ± 0.24 100.54 C95 13 0.0369 (19) 1.0942 (564) 1.4544 (5291) 98.3 9.07 ± 2.12 10.06                                                                                                                                                Operator: I. Coutand, Zeta = 370.0 ± 5.0  Abbreviations: rs, spontaneous track density; Ns, number of spontaneous tracks counted in the sample; ri, induced track density in the external detector (muscovite); Ni, number of induced tracks counted in external detector; rd, induced track density in external detector adjacent to CN5 dosimetry glass; Nd number of induced tracks in external detector adjacent to dosimeter; and P(C2), chi-square probability. 112	  the Ar system. The biotite date of 50.1 ± 2.7 Ma from the Kafiristan may reflect a transient thermal perturbance associated with the initiation of continental collision, which occurred at this time (Beck et al., 1995; Green et al., 2008).  Muscovite specimens from different locations within the Tirich Mir pluton yield two distinct ages. The 111.5 ± 1.9 Ma muscovite date from specimen C20 (Fig. 6.1), which is undeformed, is significantly younger than the minimum U-Pb zircon crystallization age of 123.5 ± 0.5 Ma of the pluton (Chapter 5) and therefore interpreted to reflect cooling through muscovite closure to Ar diffusion. The much younger age of specimen S62 (48.2 ± 1.7 Ma), which is foliated, in the proximal hanging wall of the Tirich Mir fault (Fig. 6.1) may be explained in two ways. 1) The age may correspond to a significantly deeper level of erosion and more recent exhumation/cooling than C20 (S62 was collected at an altitude of ~ 2047 m while C20 was collected at 3708 m), or 2) S62 records recrystallization during reactivation of the Tirich Mir fault. The second interpretation is thought to be more likely as the Tirich Mir body is foliated in proximity to the Tirich Mir fault (Chapter 3) consistent with recrystallization during movement across it. Reactivation of the fault at this time would be coeval with the initial continental collision between India and Eurasia (e.g. Beck et al., 1995; Green et al., 2008). Thrusting along the Tirich Mir fault ca. 48 Ma is also consistent with the occurrence of younger 40Ar/39Ar ages from the nearby footwall specimens C108 and C110 (32.8 ± 4.1 Ma to 24.9 ± 1.3 Ma) that would have been buried at that time and subsequently exhumed. The Buni-Zom pluton is separated from the Tirich Mir pluton to the southeast by the Tirich Mir and Reshun faults (Fig. 6.1). The Buni-Zom pluton crystallized in the mid–Cretaceous and is essentially undeformed with no evidence of late fluid alteration (Chapter 113	  5). The biotite 40Ar/39Ar age of 61.6 ± 1.1 Ma for the pluton is, therefore, interpreted to reflect cooling through biotite closure to Ar migration.  The Garam Chasma pluton is the youngest plutonic body in the study area (Hildebrand et al., 1998; Chapter 5). Muscovite and biotite ages from specimen S8 are younger than the main monazite crystallization age of the Garam Chasma pluton (23.6 ± 0.1 Ma; Chapter 5). Muscovite 40Ar/39Ar ages from specimen C69 are similar but biotite ages are somewhat younger than the crystallization age of the Garam Chasma pluton. Dates from S8 and C69 are therefore, interpreted to indicate rapid cooling of the Garam Chasma pluton immediately after intrusion (Fig. 6.3). Cooling of the Garam Chasma pluton may have been facilitated by thrust-assisted intrusion of the pluton (Hildebrand et al., 2001 and reference therein; Fig. 6.1) paired with erosion. Comparable 40Ar/39Ar dates from metapelites (C91, S12 and S15) in the surroundings of the Garam Chasma pluton are interpreted to reflect that same cooling/exhumation event across a broader area. This affected area may be extended even farther to the locations from where specimens C7 and S72 were collected (Fig. 6.1), and implies that the Ar systematics of the metapelites were reset during Cenozoic metamorphism and associated anatexis and emplacement of the Garam Chasma pluton.   6.4.2 Fission Track  Apatite FT ages from the study area are significantly younger than the 40Ar/39Ar ages measured. The youngest apatite age from this study, 1.4 ± 0.5 Ma (specimen S24), is from the western end of the Tirich Mir pluton (Fig. 6.1). The Pleistocene age recorded in the apatite indicates that the Tirich Mir pluton is actively exhuming/uplifting. This is consistent with the extreme topography in the area (Tirich Mir peak is 7700+ m). The very young 114S8 - C65(Biotite - Apatite)Age Temperature MsBtAp Ap = ApatiteBt = BiotiteMs = Muscovite50 150 250 350 450 550 650 2 6 10 14 18 22 2 6 10 14 18 22 7 9 11 13 15 17 19 Age Depth Exhumation Rate1.9±0.9 mm/yearS12-C95(Muscovite - Apatite)ApBtGARAM CHASMA PLUTONGARAM CHASMA PLUTON50 150 250 350 450 7 9 11 13 15 17 19 Age TemperatureS12-C95(Muscovite - Apatite)Cooling Rate45.7±18 oC/MaCooling Rate21.4±9.6 oC/MaMETAPELITE(close to the Garam Chasm pluton)METAPELITE(close to the Garam Chasm pluton)2 6 10 14 18 22 2 6 10 14 18 22 Age DepthExhumation Rate0.7±0.3 mm/yearS8 - C65(Biotite - Apatite)BtApMsa bcBtApdFigure 6.3 Cooling and exhumation rate profiles for various specimen pairs from the Hindu Kush. See text for discussion. Plots were constructed using Isoplot/Ex and error envolopes fit were carried out by adobe illustrator best fit. 115	  apatite age from the Tirich Mir pluton also indicates that the strike-slip component along the Tirich Mir fault may be a very young/recent phenomenon and/or that deformation is partitioned between present-day discrete strike-slip motion and diffuse crustal thickening leading to uplift within the Tirich Mir body. The 3.5 ± 0.2 Ma date from specimen C65 (Fig. 6.1) is interpreted to indicate relatively recent cooling and exhumation of the Garam Chasma pluton following its crystallization and initial rapid cooling in the Miocene. The oldest fission track age, 9.7 ± 2.1 Ma (specimen C95; Fig. 6.1), indicates that this specimen cooled through its FT retention temperature ~4-7 Ma earlier than the nearby Garam Chasma pluton (Fig. 6.1). This may reflect differential uplift/exhumation across the thrust fault that bounds the southeast side of the pluton (Fig. 6.1).  6.5. COOLING AND EXHUMATION RATES Cooling histories of an area may be derived from the time at which different thermochronologic systems reached their closure temperatures (e.g. Zeitler, 1985). To enable this type of work, the closure temperatures of dated muscovite and biotite grains were estimated following Dodson (1973), which is based on grain size, cooling rate, geometry, and experimentally derived diffusion parameters. These results are presented in Table 6.3. Where possible, muscovite or biotite 40Ar/39Ar ages were used with nearby apatite FT ages to calculate cooling rates (Fig. 6.3). A 90 ± 20 °C annealing temperature for apatite (e.g. Zeitler, 1985; Green, 1988; Yamada, et al., 1995; Lisker et al., 2009; Table 6.3) is assumed when making the calculations. Pluton crystallization ages from the region are not used for these types of calculations due to the difficulty in accurately assessing the temperature of 116Sample Mineral Grain Size (µm) Closure Temperature °C Age (Ma) Rate (°C/Ma)S8 Biotite 900 ± 200 411 ± 131 18.5 ± 2.10C65 Apatite 90 ± 20 3.5 ± 0.2S12 Muscovite 550 ± 100 451 ± 24 17.6 ± 2.2C95 Apatite 90 ± 20 9.7 ± 2.145.7 ± 1821.4 ± 4.9Table 6.3. Estimated 40Ar/39Ar and apatite fission track closure temperatrues and ages                  to claculate cooling rates.117	  crystallization for the mineral used for geochronologic control. Moreover, as constraints on the depths of intrusion are not available, nor is there information on the thermal conductivity of the country rock or the local geothermal gradient near the plutons, these data are also excluded from uplift rate calculations made below. The previously acquired thermochronology dataset of Zeitler (1985) are the only data from NW Pakistan available for comparison with the present study. Because the Hindu Kush region is located within the broader western Syntaxial zone, cored by the Nanga Parbat Massif (Fig. 1.1), and because appropriate thermochrometer data exist (Zeitler, 1985), the cooling and exhumation rates derived from the massif are used as a comparators. A cooling rate of 21.4 ± 9.6 °C/Ma is estimated from the Garam Chasma pluton between the closure temperatures of biotite in S8 (411 ± 131 °C at 18.5 ± 2.1 Ma) and that of apatite in C65 (90 ± 20 °C at 3.5 ± 0.2 Ma). This is significantly lower than the cooling rate (50.4 ± 13 °C/Ma) calculated from the Zeitler (1985) specimens 79I-1 from the Nanga Parbat Massif between apatite (90 ± 20 °C at 0.7 ± 0.2 Ma and biotite (4.9 ± 0.06 Ma at 300 ± 50 °C).  Cooling in the metasedimentary rocks around the Garam Chasma pluton is constrained by specimens S12 (muscovite) and C95 (apatite). The two specimens outline an estimated cooling rate of 45.7 ± 18 °C/Ma, between 451 ± 24 ˚C at 17.6 ± 2.2 (muscovite) and 90 ± 20 ˚C at 9.7 ± 1.4 Ma (apatite; Fig. 6.3b). This rate is within error of the biotite-apatite rates estimated for both the Garam Chasma pluton and Nanga Parbat Massif.  Assuming a geothermal gradient of 30 °C/km for a collisional orogen (e.g. Zeitler, 1985), data from the Garam Chasma pluton may be used to estimate an exhumation rate of 0.7 ± 0.3 mm/year from a depth of 13 ± 4 km (biotite cooling) to 3.0 ± 0.7 km (apatite 118	  cooling) over a time period of ~15 Ma (Fig. 6.3c). This exhumation rate is lower than the Nanga Parbat Massif (1.7 ± 0.4 mm/year, between apatite and biotite), calculated using the data of Zeitler (1985). Similarly, the estimated exhumation rate for metapelite specimens, S12 and C95, is 1.9 ± 0.9 mm/year (18 ± 3 km, muscovite cooling; 3 ± 0.7 km, apatite cooling; Fig. 6.3d), which is within error of that from both the Garam Chasma pluton and Nanga Parbat Massif.   6.6. SUMMARY 40Ar/39Ar and FT thermochronology help constrain the recent tectonic evolution of the Hindu Kush, Chitral region, NW Pakistan: 1. An Eocene 40Ar/39Ar muscovite date from the Tirich Mir pluton is interpreted to record reactivation of thrusting along the Tirich Mir fault during initial continental collision.  2. Very young apatite FT ages from the Tirich Mir pluton reveal active exhumation and uplift of the body consistent with extreme topography in the area. This may represent deformation partitioning between strike-slip faulting and diffuse crustal thickening in the region.  3. Cooling and uplift rates from the Garam Chasma pluton are largely lower than previously published data, while those from the metapelite are consistent with previously published data from the region. 	  119	  Chapter 7  Discussion and Conclusions The Himalaya are one of the foremost natural laboratories in which to study continental collisions. Because of this there has been an enormous research effort made to constraint the history and characteristics of the Cenozoic India-Asia collision. The pre-Himalayan history, however, which preserves records of terrane accretion, subduction, metamorphism and plutonic intrusion, as well their potential antecedent impact on the geology of the southern margin of Eurasia, has remained relatively under-documented and poorly understood. The major focus of this research project has been to constrain the pre- to syn–Himalayan history of the southern Eurasian margin in the Hindu Kush near Chitral, NW Pakistan. The results from this study provide important constraints on the pre-continental collision tectonomagmatic and metamorphic events, and the subduction of Tethys oceanic crust. In addition, new thermochronologic data provide insight into the recent cooling and exhumation history of the study area. The main findings of this study are outlined chronologically below.  7.1. Rifting of Gondwana (Cambrian) The Kafiristan pluton formed in an anorogenic tectonic environment. U-Pb zircon data indicate protracted crystallization between ca. 538 and 487 Ma synchronous with rifting within the Gondwanan supercontinent (e.g. Dèzes, 1999; Fernández et al., 2012; Gaetani, 1997; Heuberger, 2004; Zanchi and Gaetani, 2011). Generation of similar aged Cambro-Ordovician lecucogranite in Zanskar (Dèzes, 1999) and granodiorite in the Karakoram area (Zanchi and Gaetani, 2011) has also been attributed to rifting within Gondwana following the Pan-African Orogenic event. During this extensional event several different continental 120	  blocks were excised from the northern margin of Gondwana. Some of these blocks, including the Hindu Kush and Karakoram, were eventually accreted to the southern margin of Eurasia during the Mesozoic Cimmerian Orogenic event.  7.2. Cimmerian Orogeny (Triassic-Jurassic) Evidence of the Cimmerian orogeny comes from ca. 211–184 Ma Th-Pb monazite ages from garnet + staurolite schist sampled in the study area. This is consistent with a Triassic-Jurassic metamorphic event recognized in the Baltoro region of the nearby Karakoram (Searle et al., 1989). The present study interprets these data to indicate Late Triassic (211 – 201 Ma) accretion of Hindu Kush-SW Pamir block to the southern margin of Eurasia along the Rushan-Pshart suture followed closely by the accretion of Karakoram block during Early Jurassic (189 – 184 Ma) to the Hindu Kush along the Tirich Mir-Wakhan Boundary zone. A similar lateral equivalent to the Karakaroam, the Qiantang block, was also accreted to the Eurasian margin during the same Cimmerian event (Angiolini et al., 2013 and references therein).   7.2.1 Tirich Mir Fault Zone As indicated above, the Tirich Mir fault has been interpreted as a suture marked by metabasalts and ultramafic rocks of mantle origin that delineate the boundary between the Hindu Kush and Karakoram blocks (Gaetani et al., 1996; Zanchi et al, 2000). A minimum age of ca. 184 Ma is interpreted for the structure based on the suspected timing of accretion of the Karakoram block. This is significantly older than previous estimates, which suggested a Cretaceous age (Hildebrand et al., 2001; Heuberger et al., 2007).  121	  7.3. Andean-Type Setting (Jurassic-Cretaceous) There is persuasive evidence that the southern margin of Eurasia, at least in the Hindu Kush, remained an active margin and locus of subduction similar to the present day Andes throughout the Jurassic-Cretaceous. During this time, the Shushar, Tirich Mir and Buni-Zom plutons were intruded into the Chitral region. This also coincides with the intrusion of Hushe Complex, Darkot Pass and Hunza plutonic bodies in the Karakoram terrane (Searle et al., 1989; Debon et al., 1987; Fraser et al., 2001). This Andean-style convergent margin temporarily ceased with the collision of the Kohistan island arc with the southern Eurasian margin, but was subsequently re-established (Petterson and Windley, 1991).  7.4. Docking of Kohistan Island Arc (Late Cretaceous) It is postulated that the Kohistan Island arc developed during the Mesozoic in an intra-oceanic setting over a north dipping subduction zone (Yoshida et al., 1996; Van der Voo et al., 1999). This was followed by Late Cretaceous collision of the island arc along the southern margin of Eurasia (Petterson et al., 1991; Fraser et al., 2001 and references therein), consistent with monazite ages from this study (ca. 88–72 Ma). After the accretion event, north-dipping subduction stepped outboard to the southern margin the Kohistan Island arc, then the southern margin of Eurasia, leading to the intrusion of the Kohistan batholith (Petterson and Windley, 1991).   7.5. Collision and Crustal thickening (Eocene-Miocene) Closure of Tethyan ocean basin ~50 Ma ago coincides with the initial collision of India with Eurasia (e.g. Beck et al., 1995; Green et al., 2008). This collision event was 122	  followed by the onset of kyanite to sillimanite-grade metamorphism, synchronous partial melting, and the intrusion of the Garam Chasma pluton. This is as recorded in metamorphic monazite from metapeltic rocks and crystallization ages from leucogranitic intrusions of ca. 24–23 Ma from the Garam Chasma region. The timing of metamorphism and lecucogranite intrusion reported from the Garam Chasma area is similar to anatexis and intrusion events across the Himalaya, Karakoram and Tibet regions in the Miocene  (Searle et al., 1992; Inger and Harris, 1993; Hildebrand et al. 1998; Rolland, et al., 2001; Searle, et al., 2010; King et al., 2011).  7.6. Cooling History/Thermochronology  The new thermochronologic data (40Ar/39Ar and fission track) presented in this study help unravel a complex history of cooling and deformation in the Hindu Kush. 40Ar/39Ar muscovite dates from the Tirich Mir pluton indicate cooling at ca. 110 Ma shortly after crystallization (ca. 124 Ma). In contrast, an Eocene muscovite date from the Tirich Mir pluton in immediate hanging wall of the Tirich Mir fault is interpreted to indicate recrystallization related to re-activation of the structure during initial continent-continent collision. A ca. 1.4 Pleistocene apatite age also from the Tirich Mir pluton is considered to reflect active exhumation and uplift of the body, consistent with the extreme present-day topography. This young exhumation and uplift of the Tirich Mir pluton may reflect deformation partitioning between strike-slip movement on the Tirich Mir fault and diffuse crustal thickening driving uplift of the Tirich Mir pluton.  The 40Ar/39Ar dates from the Garam Chasma pluton and surrounding metapelites record ages contemporaneous with Miocene crustal thickening, shortening, and leucogranite 123	  intrusion associated with the India-Asia collision. Nearly synchronous crystallization and 40Ar/39Ar ages reflect nearly immediate cooling of the Garam Chasma pluton and surrounding metapelites perhaps facilitated by movement along a thrust fault (with paired erosion). This record of exhumation continued into the Pliocene as recorded in a ca. 3 Ma apatite FT age from the Garam Chasma pluton.  7.7. Significance of the Pre-Himalayan History As noted previously, existing models of the evolution of the Himalaya are generally focused on its Cenozoic history (e.g. Searle et al., 1987; Harris and Messey, 1994; Beck et al., 1995; Guillot and Le Fort; 1995; Searle, et al., 1999; Yin and Harrison, 2000; DeCelles et al., 2002; Bignold and Treloar, 2003; Yin, 2006; Larson et al., 2011; Bouilhol et al., 2013; Larson et al., 2013; Lederer et al., 2013), with little attention paid to the potential role of the southern Eurasian margin in that evolution. The present study demonstrates that the Hindu Kush experienced a complex tectonic history spanning from the Cambrian to the present-day. This protracted history outlines a tectonically active margin throughout the Mesozoic, akin to the mobile belts of Hyndman et al. (2005). Such belts are characterized by a hot and weak lithosphere, making them susceptible to deformation from applied stresses. This potential heat-weakening of the lithosphere is linked to vigorous convection of hot asthenosphere above a subducting slab enabled by reduced viscosity as consequence of interaction with fluids/water sourced from the slab (Hyndman et al, 2005; Currie and Hyndman, 2006). This fluid-enhanced convection both facilitates the removal of the subcontinental lithospheric mantle and thermally supports the relatively high-elevation common in such regions. 124	  A mobile belt antecedent for the Eurasian lithosphere would have pre-conditioned the margin for the subsequent Himalaya-Karakoram-Tibet orogeny. For example, it has been previously suggested that orogenic heat within the Himalaya was generated in the lower crust by radioactive decay after the onset of the India-Eurasia collision resulting in the generation of maximum temperature generation at ~ 22 Ma (Searle et al., 1992; Rolland et al., 2001). The near synchronous growth of garnet in Tibet, at 54.3 ± 0.6 Ma (Smit et al., 2014), with the initiation of continent-continent collision (Beck et al., 1995; Green et al., 2008), and the presence of early Eocene prograde monazite from the exhumed Himalayan metamorphic core (Larson and Cottle, 2015 and references therein) may indicate, however, that an already hot southern Eurasian margin contributed to the orogenic heat budget increasing the speed at which metamorphic conditions were obtained. In addition, thermo-mechanical models that evoke melt-weakening to enable lateral flow to explain the evolution of the Himalaya (e.g. Beaumont et al., 2001; Grujic et al., 2002), predict that this takes place ~27 myr after the initiation of collision (i.e. it starts between 25 and 22 Ma; Beaumont et al., 2004, 2006). Studies of exhumed mid-crustal rocks exposed in the Mabja Dome in southern Tibet, however, have concluded that midcrustal flow was active at ca. 35 Ma (Lee and Whitehouse, 2007). This discrepancy in the timing of observed and modeled mid-crustal flow may also reflect additional thermal input towards the orogenic heat budget from hot Eurasian lithosphere.   7.8. Future Work This project has provided new and important constraints on the tectonic evolution of the Hindu Kush that can be related to the broader history of the Himalaya-Karakoram-Tibet 125	  system. It has produced insight into the tectonic evolution of the orogen, including both the pre-continental and continued post-initial collision tectonic history. Further related work that would expand complimentary upon these data include:  1. Additional geochronologic work combined with phase equilibria modeling to contribute to a better understand the pressure-temperature-time paths experienced by these rocks.  2. A more detail analysis of microstructures preserved within different generations of porphyroblasts (e.g. foliation intersection/inflection axes technique; Johnson, 1999; Yeh 2003) to gain a better understanding of the related deformation and metamorphic histories.  3. Sr-Nd isotopic data for the plutons of the Hindu Kush region to help better understand crustal assimilation and potential sources of magma mixing, especially for the more complicated Tirich Mir pluton. 4.  More detailed investigation into the low temperature cooling history of the Hindu Kush region by obtaining a more dense and spatially expansive data through U-Th/He and zircon fission track techniques. Such analyses will help to better constrain the cooling and uplift history of the area perhaps allowing for better insight into possible strain portioning across various structures in the region.   126!REFERENCES  Angiolini, L., Zanchi, A., Zanchetta, S., Nicora, A. and Vezzoli, G., 2013. 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Selected monazite grains were then investigated at high resolution (step size of ~1 micron) to identify possible internal zoning by whole-grain element mapping of Ce, U, Th, and Y.  Zircon and monazite separates (Chapter 5) were obtained by standard crushing and grinding methods followed by heavy mineral separation using a Rogers GoldTM table, heavy liquids, and FranzTM magnetic techniques. This made it possible to select, clear, crack- and inclusion free monazite and zircon for geochronological analyses.   All U-Th/Pb monazite (Chapters 4 and 5) and zircon (Chapter 5) geochronological and trace element abundance work was performed at the University of California, Santa Barbara (UCSB), using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), which collects U, Th, and Pb isotopic ratios and trace element concurrently.  Instrumentation Instrumentation, summarized in Table A (see below), consists of a Nu Plasma high resolution MC-ICP-MA (Nu Instruments, Wrexham, UK), a Nu AttomM SC-ICPMS and a 193nm ArF LA system equipped with a two volume “HelEx” ablation cell that expedites  143 Table A Instrument parameters (after Cottle et al., 2013) Nu Instruments ‘HR Nu Plasma’ MC-ICPMS Carrier gas & flow rate 09 l min-1 (He) + 0.98/1.08 (HR/HR-ES) l min-1_Ar makeup from onboard mass flow controllers. Ar added half way between cell and torch via ‘T’-piece Auxillary gas flow rate  0.8 l min-1 (Ar) Cool gas flow rate 13 l min-1_(Ar) RF power  1300 W Reflected power  <1 W Sample cone  Ni (1 mm orifice) Skimmer cone  Ni (0.7 mm orifice) Collector types  12 Faradays and 4 electron multipliers Integration times  200 ms Isotopes measured  206,207,208Pb on SEMs; 232Th, 238U, 235U on Faraday cups Reference Material  Managotry: age = 554 Ma, b FC-1: age = 55.7 Ma, c 44096: age = 424 Ma,d 91500: age = 1065 Ma.e, Plešsovice: age = 337 Ma.f  Photon machines 193 mn ArF excimer laser Cell  Two volume Helex cell (Eggins et al., 1998) Sample transport tubing  0.5 m length, Teflon Washout timea  <1 s Wavelength  193 nm ArF Fluence  1–4 J cm-2	  Pulse width  <4 ns @ 1064 nm Cell volume  3 cm3 Drill depth/pulse  0.13 mm@35 mm diameter spot (50% power)  aTime taken for signal to reduce to 1% of peak intensity. bPaquette et al. (1994). cHorstwood et al. (2003). dAleinikoff et al. (2006). eWiedenbeck et al. (1995). fSlama et al. (2008).      144rapid transfer and washout of ablated material (Photon Machines, San Diego, USA). For Pb/U-Th measurements, the collector arrangement on the Nu Plasma at UCSB allows for simultaneous determination of 232Th and 238U on high-mass side Faraday cups equipped with 1011 ohm resistors and 208Pb, 207Pb, 206Pb and 204X (where X represents the isotopes of Pb and Hg) on four low-mass side ETP discrete dynode electron multipliers. Analysis of U, Th, and Pb isotopes were conducted for 30s each, using spot diameters ranging from 7 to 20 µm in diameter, a frequency of 3 Hz, and 0.75 J/cm2 fluence (equating to crater depths of ~7-8 µm). While, trace element abundances (in monazite grains; Chapter 4) were measured on an AttoM SC-ICPMS using E-Scan mode. In this mode, the magnet is set to a fixed position and the post-electrostatic analyzer deflector voltages are modified to change the mass seen by the detector (Kylander-Clark et al., 2013). The deflector voltages are usually altered every 10 µs, which permit for setting (typically set to 30µs). The total acquisition time for 1 sweep of the masses of interest is generally kept to ca. 2.5–4 ms to minimize short-term measurement uncertainty associated with plasma flicker. Elemental abundances and their uncertainties are determined by interleaving using matrix-matched references materials among specimens. Reduction of both elemental and geochronology were performed with IgorPro and Iolite software at UCSB. Monazite unknowns were normalized against primary reference material “Managotry” monazite (554 Ma Pb/U isotope dilution–thermal ionization mass spectrometry (ID-TIMS) age; Paquette et al., 1994) to monitor and correct for mass bias, as well as Pb/U and Pb/Th down-hole fractionation. To monitor accuracy, two secondary reference monazite “FC-1” (55.7 Ma Pb/U ID-TIMS age; Horstwood et al., 2003) and “44096” (424 Pb/U Ma ID-TIMS age; Aleinikoff et al., 2006) were analyzed concurrently (once 3-5 unknowns). Mass bias- 145and fractionation were normalized and corrected on the basis of measured isotopic ratios of the primary reference material. While for zircon geochronology, two reference materials were used, the 91500 (1065 Ma age; Wiedenbeck et al., 1995) and Plešsovice zircon (337 Ma age; Slama et al., 2008).   Analytical Protocols One of the main advantages of the LA-MC-ICP-MS technique is that no real preparation of specimen is required (Cottle et al., 2009). The main requirement is to make sure that crystal surfaces and thin section surfaces are clean to minimize surface contamination, such as common-lead. Monazite and zircon grain separate (Chapter 5), along with reference materials were washed thoroughly in alcohol, 2% nitric acid and highly purity water. These crystals were then mounted on doubled-sided sticky tap on the surface of a pre-cleaned 1-inch diameter eposy resin disc. The top surface of polished thin section used for in situ work (Chapter 4), were also cleaned in a similar way. Prior to analysis the outer surfaces of samples and reference materials were further cleaned by rastering the laser beam using a large spot size (~100 µm) at low fluence (~0.6 J cm-2), to remove any contamination arising from fall-out from previous analysis (Cottle et al., 2009).    GEOCHRONOLOGY RESULTS Specimen S15 Twenty spot analyses on four monazites located in three different garnet grains and one staurolite grain (Fig 4.4) were measured in specimen S15. Two of those spot analyses were excluded because of matrix overlap noted during post-laser SEM imaging (Table 1). The 146monazite grains yield ages that range from 453 ± 8 Ma to 102 ± 2 Ma with two main age populations at 211 ± 8–202 ± 4 Ma and 190 ± 5 –185 ± 3 Ma (Fig. 4.4). The Late Ordovician (453 ± 8 Ma) age from monazite embedded in garnet has a Th concentration of 1747 ppm and a Gd/Yb ratio of 168.9. The older age population, 211 ± 8 – 202 ± 4 Ma, is recorded exclusively in monazite grains included in garnet and has Th concentrations ranging between 13 – 541 ppm and Gd/Yb ratios between 63.9 and 277 (Fig. 4.4b). The Early Jurassic, 190 ± 5 – 185 ± 3 Ma, ages are from monazite found in both staurolite and garnet grains and are associated with Th concentrations between 430 and 2010 ppm and Gb/Yb ratios between 76.9 and 235 (Fig. 4.4b). The Jurassic to the middle Cretaceous, 175 ± 11 –102 ± 2 Ma, monazite ages in the specimen are associated with variable Th concentrations ranging between 14 and 960 ppm and Gd/Yb ratios between 9.6 and 824 (Fig. 4.4b).   Specimen S4 A total of 49 spot analyses were measured on 11 monazite grains in specimen S4. Most grains, which are typically elongate and anhedral in form (Figure A), are located in the matrix with the exception of two grain that is included within staurolite (Fig. 4.3). Two of the 49 laser spots proved to be off target and are thus excluded from further consideration (Figure A). The ages from this specimen fall between 106 ± 3 Ma and 22.3 ± 0.5 Ma and define two main populations in the early Late Cretaceous (87.9 ± 1.8 – 72.4 ± 1.8 Ma) and the Early Miocene (29.3 ± 1.07 Ma to 22.3 ± 0.5 Ma) respectively.  The 105.5 ± 3.3 Ma age is associated with a Th concentration of 496 ppm (REE data were not collected for this spot analysis, Figure B). The Late Cretaceous population is associated with Th concentrations ranging between 136 and 378 ppm and Gd/Yb ratios that 147range between 366 and 9430 (Fig. 4.4c). The Eocene ages from the specimen, 49.8 ± 1.6, 40.3 ± 1.6 and 36.3 ± 1.6 Ma, are associated with Th concentrations of 170, 181 and 52 ppm and Gd/Yb ratios of 436 1557, and 2748 respectively. The 29.3 ± 1.07 Ma to 22.3 ± 0.5 Ma Miocene age population is characterized by low Th concentrations, ranging from 30 to 167 ppm, and generally high, though broad-ranging Gd/Yb ratios between 2179 and 16963 (Fig. 4.4c).                  14810 μm Y La 20. kVY24.2 ± 0.549.8 ± 1.623.4 ± 0.523.5 ± 0.51234S4_124.2 ±0.523.4 ±0.5S4_424.4 ±0.624.4 ±0.624.3 ±0.5 24.2 ±0.4123 4520 μm U Ma 20. kV 20 μm Y La 20. kV175.0 ± 11.6S15_1208.1 ± 4.8205.3 ± 5.6207.0 ± 5.21324110.6 ± 3.83245189.7 ± 4.8211.4 ± 7.9156.3 ± 4.9S15_2452.5 ± 9.4 1189.2 ±3.6234561184.6 ± 3.4201.5 ± 3.6 186.0 ± 4.8189.5 ± 3.2142.7 ± 2.4S15_3101.8 ±2.3185.3 ±3.6186.1 ±3.2S15_421310 μm U Ma 20. kVYUYYUUThThUU YThThThThUY14950 μm U Ma 20. kV 50 μm Y La 20. kV72.4 ±1.813487.7±279.5 ±1.722.6 ±.5S4_2250 μm Y La 20. kV23.3 ±0.422.7 ±0.422.8 ±0.531 2S4_350 μm U Ma 20. kV25.1 ± 0.5132425.8 ± 0.627.9 ± 0.6S4_586.8 ± 1.7S4_623.4 ±0.52487.9 ±1.882.9 ±1.840.3±1.61324.3 ±0.623.3 ±0.523.3 ±0.523.7 ±0.51234S4_720 μm U Ma 20. kV20 μm U Ma 20. kV20 μm U Ma 20. kV24.0 ±0.522.6 ±0.423.1 ±0.522.4 ±0.4123420 μm Y La 20. kVS4_827.7 ±0.75ArialFigure A continuedYYYYYYUUUUUUThThThThThTh15023.9 ±0.6322.5 ±0.522.3 ±0.5105.6 ±3.322.8 ±0.55412S4_920 μm U Ma 20. kV 20 μm Y La 20. kV81.2 ± 1.72323.4 ± 0.523.3 ± 0.529.1 ±1.123.6 ± 0.575.9 ± 1.585 ± 1.923.9 ± 0.5S4_101786541S4_1136.6 ± 1.6UYYYU UThThThFigure A continuedFigure A Elemental maps of U, Th, and Y for all monazite grains dated in specimens S15 and S4. Ellipses on each monazite grain shows the spot analyses locations and corresponding 208Pb/232Th ages (in Ma). The name of the monazite grain and the spot number are the same as that listed in Table 1.151452.5 ± 7.9 Ma211.0 ± 7.9 – 201.5 ± 3.6 Ma189.7 ± 4.8 – 184.6 ± 3.4 Ma175.0 ± 11.2 –101.8 ± 2.3 Ma87.0 ± 1.7 – 82.9 ± 1.8 Ma81.0 ± 1.7 – 72.4 ± 1.8 Ma29.3 ± 1.1 – 22.3 ± 0.5 Ma 49.8 ± 1.6 – 36.3 ± 1.6 Ma208Pb / 232Th Age (Ma)208Pb / 232Th Age (Ma)Figure B Chondrite-normalized concentration of rare earth element of both specimens corre-sponing to different metamorphic events/ chemical domains as discussed in the text. The colour of the spider plot correspond to ages. 152Sample Monazite Pb U Th 206Pb/204Pb 207Pb/206Pb 2s % 206Pb/238U 2s % 208Pb/232Th 2s % 208Pb/232Th 2s absS15_1 1150 903 13 4000 0.0528 2.27 0.03109 1.74 0.01029 2.54 207 5S15_2 1680 1050 14 6500 0.05167 1.88 0.03112 2.06 0.00869 6.40 175 11S15_3 950 854 13 3000 0.0515 2.91 0.03070 1.76 0.01021 2.75 205 6S15_4 982 942 15 200 0.0537 2.23 0.03115 1.51 0.01035 2.33 208 5S15_5 5310 53900 1750 1500 0.05476 1.08 0.06960 1.72 0.02264 2.07 453 9S15_6 1970 20900 325 2300 0.053 2.45 0.02636 2.73 0.01051 3.73 211 8S15_7 2870 31600 430 3300 0.0534 2.81 0.02581 2.79 0.00943 2.53 190 5S15_8 5550 35200 283 1010 0.0652 1.69 0.02019 2.77 0.00549 3.40 111 4S15_9 6830 33900 386 650 0.0894 1.79 0.02525 2.50 0.00776 3.14 156 5S15_10 856 21700 299 1000 0.0605 3.64 0.03232 2.69 0.00924 2.57 186 5S15_11 9430 56600 569 1900 0.05211 1.00 0.02246 1.34 0.00709 1.70 143 2S15_12 6230 73000 960 1200 0.05245 1.07 0.03070 1.34 0.00942 1.68 190 3S15_13 3550 144000 1830 8000 0.05778 1.23 0.03035 1.48 0.00917 1.83 185 3S15_14 6090 38600 541 4000 0.0522 1.11 0.03021 1.22 0.01002 1.80 202 4S15_15 6700 89000 1150 1100 0.05379 0.99 0.03073 1.46 0.00941 1.89 189 4S15_16 8190 63400 425 1200 0.0549 2.00 0.01686 2.08 0.00505 2.28 102 2S15_17 5020 161000 2010 2200 0.05593 1.13 0.03058 1.57 0.00925 1.71 186 3S15_18 4350 150000 1890 400 0.05563 1.19 0.03017 1.49 0.00921 1.93 185 4S15_19* 3790 113000 1490 2900 0.05578 1.29 0.03087 1.59 0.00959 1.76 193 3S15_20* 1220 36100 539 520 0.0558 2.51 0.03052 2.52 0.01075 3.28 217 7S4_1 6530 50100 81 3700 0.0812 3.45 0.00372 1.97 0.00116 2.10 23.5 0.5S4_2 8760 52700 85 400 0.0785 2.80 0.00364 1.73 0.00116 2.11 23.4 0.5S4_3 5420 49200 170 6000 0.0608 3.95 0.00947 2.75 0.00247 3.30 49.8 1.6S4_4 5350 53000 87 1200 0.1512 3.24 0.00416 1.76 0.00120 1.97 24.2 0.5S4_5 4740 62500 97 2200 0.0956 3.14 0.00376 1.70 0.00112 2.00 22.6 0.5S4_6 6210 77200 379 22000 0.0648 2.62 0.01235 2.35 0.00359 2.53 72.4 1.8S4_7 4520 22600 136 9000 0.0527 2.09 0.01278 1.96 0.00435 2.30 87.7 2.0S4_8 5310 53800 294 13000 0.0556 1.98 0.01335 1.72 0.00394 2.15 79.5 1.7S4_9* 4050 39700 64 1100 0.0817 2.57 0.00358 1.59 0.00113 1.99 22.7 0.5S4_10 3020 30300 49 2600 0.0794 3.15 0.00368 1.90 0.00113 2.16 22.8 0.5S4_11 3710 39800 63 2900 0.0852 2.93 0.00369 1.52 0.00112 1.72 22.7 0.4S4_12 3480 40200 66 500 0.0847 2.95 0.00371 1.56 0.00115 1.86 23.3 0.4S4_13 2820 24000 40 3300 0.0938 7.46 0.00375 2.35 0.00121 2.37 24.4 0.6S4_14 2310 20900 36 2900 0.1045 5.93 0.00381 2.18 0.00121 2.45 24.4 0.6S4_15 2200 18900 32 4200 0.0785 3.31 0.00370 1.65 0.00120 1.88 24.3 0.5Table 1. U-Th/Pb Geochronologic and Rare Earth Element data12341234153S4_16 2390 18000 30 5000 0.0882 3.51 0.00370 1.57 0.00120 1.72 24.2 0.4S4_17 2210 19900 32 6100 0.086 3.84 0.00371 2.00 0.00116 2.20 23.4 0.5S4_18* 2690 21600 35 4500 0.0767 3.52 0.00361 2.13 0.00115 2.04 23.3 0.5S4_19 3340 38700 74 3100 0.1062 3.01 0.00465 2.00 0.00138 2.18 27.9 0.6S4_20 2650 24500 43 1200 0.1118 3.58 0.00400 1.95 0.00128 2.18 25.8 0.6S4_21 2240 23200 40 200 0.1229 3.82 0.00411 2.07 0.00124 2.07 25.1 0.5S4_22 2930 55800 340 5000 0.0617 1.78 0.01382 1.52 0.00430 1.90 86.8 1.7S4_23 3320 35000 213 20000 0.0601 1.83 0.01343 1.64 0.00436 2.00 87.9 1.8S4_24 2730 40600 232 7000 0.0613 2.28 0.01348 1.85 0.00411 2.20 82.9 1.8S4_25 3520 66500 181 4400 0.0747 3.48 0.00792 3.03 0.00200 4.06 40.3 1.6S4_26 6170 34200 56 2300 0.0699 2.43 0.00362 1.58 0.00116 2.03 23.4 0.5S4_27 4800 31000 50 15000 0.0716 3.07 0.00375 1.98 0.00120 2.55 24.3 0.6S4_28 2780 24800 41 2100 0.0805 3.35 0.00377 1.91 0.00115 1.95 23.3 0.5S4_29 3660 36700 61 5000 0.0879 2.62 0.00383 1.80 0.00118 2.26 23.7 0.5S4_30 3130 25800 42 5000 0.0861 3.14 0.00377 1.70 0.00116 2.12 23.3 0.5S4_31 2530 27800 44 1400 0.0791 3.67 0.00373 1.66 0.00112 1.91 22.6 0.4S4_32 2750 20800 35 3200 0.1327 2.41 0.00388 2.14 0.00119 2.23 24.0 0.5S4_33 3220 28200 46 4600 0.0927 2.91 0.00384 1.75 0.00114 2.05 23.1 0.5S4_34 3420 38400 60 800 0.0963 2.80 0.00374 1.87 0.00111 1.75 22.4 0.4S4_35 3250 35900 69 4500 0.0821 2.92 0.00443 1.94 0.00137 2.63 27.7 0.7S4_36 5720 38600 62 3000 0.0748 2.94 0.00370 1.79 0.00113 2.08 22.8 0.5S4_37 4190 32300 50 900 0.0824 3.52 0.00367 1.80 0.00112 2.18 22.5 0.5S4_38 4270 21100 34 1200 0.0834 3.84 0.00368 2.04 0.00118 2.33 23.9 0.6S4_39 5260 37900 59 800 0.0849 3.18 0.00364 2.01 0.00111 2.02 22.3 0.5S4_40 6260 70100 496 27000 0.0592 2.03 0.01750 2.74 0.00524 3.16 106 3S4_41 6160 48600 251 5000 0.06055 1.55 0.01155 1.65 0.00376 2.03 75.9 1.5S4_42 5660 87600 170 4000 0.0987 4.26 0.00552 3.44 0.00144 3.70 29.1 1.1S4_43 4890 45400 74 1500 0.0874 2.75 0.00376 1.81 0.00117 2.01 23.6 0.5S4_44 6020 48400 78 600 0.0825 2.55 0.00369 1.85 0.00116 2.12 23.3 0.5S4_45 5450 45700 73 100 0.0826 2.91 0.00366 1.75 0.00116 2.03 23.4 0.5S4_46 5130 62800 352 14000 0.05949 1.51 0.01295 1.78 0.00402 2.09 81.2 1.7S4_47 5120 64100 374 7000 0.05736 1.73 0.01318 1.90 0.00421 2.25 85.0 1.9S4_48 4590 102000 167 3200 0.1105 2.17 0.00385 1.61 0.00118 1.99 23.9 0.5S4_49 11 1300 20600 52 5200 0.2093 3.54 0.00467 3.43 0.00180 4.47 36.3 1.6* Ablation spot excluded due to matrix interaction / off target10456789154Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Gd/Yb105000 11600 41300 7610 700 6120 660 3180 376 462 48.7 94.4 3.37 65108000 12400 43600 7500 780 7000 710 3300 393 435 44.5 86.8 3.16 81106000 11300 38700 6910 760 6140 690 3920 478 459 44.1 80.5 2.59 76106000 11800 38500 7980 770 5780 620 3340 398 477 47.1 90.5 2.94 64235000 32000 119000 26200 1620 20100 2070 10400 1370 1180 83.2 119 3.33 169109000 13800 53700 8300 660 7700 710 3000 351 319 20.3 27.8 0.51 277107000 13500 46000 7740 550 6500 780 2670 306 290 19.8 26.8 0.58 243117000 14200 54100 8100 631 8900 1010 3500 420 166 9.12 10.8 0.23 824103000 12900 42900 7160 580 7500 720 2820 326 227 15.9 21.0 0.47 357116000 14200 44800 7470 505 7300 560 2970 347 287 19.9 28.0 0.68 261103000 13600 46300 8800 595 8900 720 3840 467 191 10.0 17.3 0.36 514103000 13900 50600 9100 582 9200 1050 4180 514 532 33.4 45.7 1.04 20189200 11600 48500 8700 530 14300 1040 5200 655 667 45.8 60.7 1.64 236108000 13800 47500 8400 624 7800 930 4170 513 711 45.2 76.2 1.61 10298900 14600 49900 9900 870 11300 1160 5820 741 960 68.1 147 2.41 77109000 13700 50400 8420 121 9000 1040 6310 808 2740 320 941 31.8 1082300 12600 46700 7900 430 11700 1420 5100 641 1110 78.0 135 2.21 8788000 12600 48700 8400 420 10000 830 6100 779 797 65.5 97.0 0.93 10384500 11800 52100 10500 410 11200 1040 4500 558 552 40.2 63.0 1.56 178104000 14100 48100 8400 120 7900 930 5270 665 610 60.3 110 3.99 7284700 12600 45500 8400 609 6170 483 1440 80.3 53.7 2.07 1.17 0.03 527082600 12300 46000 7700 658 5910 518 1650 95.7 72.5 3.28 2.14 0.09 276087400 13000 43400 7480 651 6110 614 2190 175 185 9.60 14.0 0.39 43669100 10300 37900 6060 469 4990 377 1180 72.7 48.2 1.84 2.29 0.08 218085300 12700 44200 7460 543 5420 422 1140 61.2 47.9 1.70 0.92 0.05 589080000 11900 44400 7250 607 6510 640 2360 192 193 12.8 17.8 0.43 36674400 11100 40200 7320 521 5610 538 2190 182 194 11.0 15.3 0.26 36785500 12700 46700 7650 531 6380 561 2600 213 243 15.2 19.8 0.31 32296700 14400 51300 7990 561 5890 478 1150 61.6 34.7 1.17 0.86 0.10 6850112000 16700 61500 9840 631 7230 565 1590 89.2 59.4 2.21 1.90 0.04 3810103000 15300 57900 9530 620 7030 542 1500 78.9 49.5 1.72 1.38 0.08 509096200 14300 52800 9020 584 6050 485 1210 60.4 35.0 1.39 1.05 0.07 5760108000 16100 57400 9700 653 6950 464 1360 61.3 40.8 1.72 0.74 0.08 939075000 11200 41100 6680 435 5220 358 940 48.6 28.6 0.86 0.69 0.04 757095000 14100 50800 8990 596 6680 498 1340 74.5 53.2 1.95 1.26 0.06 5300Table 1. Continued 15593800 14000 46200 7780 503 5610 476 1110 70.8 40.8 2.08 1.51 0.07 372086000 12800 44100 7850 485 5320 421 1160 72.2 44.1 2.13 1.40 0.08 380099700 14800 50400 9280 638 6990 530 1490 81.5 55.2 2.20 0.97 0.08 721087400 13000 46500 7430 520 6120 473 1610 92.6 61.2 2.88 2.18 0.12 281088000 13100 46000 7670 496 5710 445 1210 72.2 49.8 1.67 0.49 0.08 1170075400 11200 42300 6750 489 4910 406 1120 60.4 44.3 1.64 1.22 0.07 4020101000 15000 52500 9560 554 6890 634 2120 169 170 10.3 12.4 0.22 556102000 15200 56300 9280 449 6130 526 1470 98.0 82.0 4.97 6.30 0.16 97399300 14800 52000 8700 630 7010 660 2470 217 176 8.40 9.40 0.17 74684100 12500 47600 8000 457 5390 432 1210 77.9 66.0 2.99 3.46 0.15 156071300 10600 37900 6770 433 5600 369 780 47.3 26.0 0.71 0.44 0.06 1270064100 9540 37900 6310 440 5240 402 1070 56.4 31.9 1.13 0.63 0.09 832074400 11100 39800 6550 429 4690 428 952 51.4 30.8 0.97 0.68 0.07 690066800 9950 36600 5980 368 4580 286 552 25.5 11.0 0.36 0.27 0.05 1700072400 10800 36600 6370 493 4560 368 1110 71.6 49.7 1.98 1.96 0.03 233070700 10500 37700 6980 465 4840 374 970 57.8 35.8 1.41 0.97 0.05 499055500 8270 31500 5470 396 4220 324 970 52.4 37.6 1.44 1.66 0.02 254066000 9820 38300 6660 521 4800 418 1210 73.7 55.1 1.80 2.06 0.05 233065900 9810 36200 6740 539 5170 403 1100 72.6 56.6 2.24 1.83 0.08 283060100 8950 32100 6100 365 4190 297 616 34.4 19.5 0.74 0.73 0.04 574061100 9090 32300 5640 409 4280 285 707 37.1 23.4 0.64 0.54 0.01 793060800 9060 32600 5710 412 4240 280 669 36.4 24.8 0.81 0.47 0.07 902059400 8850 33300 5410 414 4080 323 744 33.7 21.6 0.56 0.70 0.04 583058600 8730 32000 5430 390 3570 261 500 23.0 11.5 0.32 0.28 0.01 12800112000 16600 58800 9250 667 6140 340 680 57.5 49.1 3.67 5.00 0.14 123098000 14600 54900 9180 752 7200 777 2820 324 295 17.8 20.8 0.39 34682000 12200 47500 7800 531 5820 371 920 77.0 60.4 2.41 2.15 0.07 2710113000 16700 54800 9730 632 6510 484 1000 69.1 23.4 0.56 0.77 0.02 8450109000 16200 59500 9580 635 7410 529 1120 88.2 27.4 0.63 0.41 0.03 18100101000 15100 57900 9600 662 7170 506 1050 100 25 0.60 0.76 0.05 943088900 13200 49800 8210 501 6760 473 1450 222 77 3.93 3.62 0.08 187097900 14600 52500 9370 551 6600 544 1630 329 110 5.05 5.08 0.08 130064500 9610 35200 6280 481 4040 302 768 136 23 0.82 1.47 0.08 2750156Reference: Aleinikoff, J.N., Schenck, W.S., Plank, M.O., Srogi, L., Fanning, C.M., Kamo, S.L. and Bosbyshell, H., 2006. Deciphering igneous and metamorphic events in high grade rocks of the Wilmington Complex, Delaware: Morphology, CL and BSE zoning, and SHRIMP U-Pb geochronology of zircon and monazite: Geological Society of America Bulletin, v. 118, 39-64.  Cottle, J.M., Burrows, A.J., Kylander-Clark, A., Freedman, P.A. and Cohen, R.S., 2013. Enhanced sensitivity in laser ablation multi-collector inductively coupled plasma mass spectrometry. Journal of Analytical Atomic Spectrometry 28, 1700–1706.  Cottle, J.M., Horstwood, M.S.A. and Parrish, R.R., 2009. A new approach to single laser ablation analysis and its application to in situ Pb/U geochronology. Journal of Analytical Atomic Spectrometry 24, 1355-1363.  Horstwood, M.S.A., Foster, G.L., Parrish, R.R., Noble, S.R. and Nowell, G.M., 2003. Common-Pb corrected in situ U-Pb accessory mineral geochronology by LA-MC-ICP-MS. Journal of Analytical Atomic Spectrometry 18, 837–846.  Kylander-Clark, A.R.C., Hacker, B.R. and Cottle, J.M., 2013. Laser-ablation split-stream ICP petrochronology. Chemical Geology 345, 99-112.  Paquette, J.L., Nedelec, A., Moine, B. and Rakotondrazafy, M., 1994. U – Pb, single zircon Pb-evaporation, and Sm-Nd isotopic study of a granulite domain in SE Madagascar. The Journal of Geology 102, 523–538  Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W. L., Meier, M., Oberli, F., Von Quadt, A., Roddick, J. C.  and Spiegel, W., 1995. Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses. Geostandards Newsletter, 19, 1–23.  Slama J., Kosler J., Condon D.J., Crowley J.L., Gerdes A., Hanchar J.M., Horstwood M.S.A., Morris G.A., Nasdala L., Norberg N., Schaltegger U.,Schoene B., Tubrett M.N., Whitehouse M.J., 2008. Plesovice zircon – a new natural reference material for U-Pb and Hf isotopic microanalysis. Chemical Geology 249, 1–35. 	  157Appendix B: XRF and ICP-MS Techniques 1. XRF Analysis XRF is a non-destructive analytical technique first used by Glocker and Schreiber in 1928 to perform quantitative analysis of materials (as cited in Guthrle, 2012; PleBow, 2013) and is now a very common method used for the analysis of major and trace elements in geological samples. In this technique a primary X-ray beam excites secondary X-rays (XRF) with energy characteristic of elements present in the specimen. Counting the XRF/photon emitted from a sample can identify and quantify a specific element. XRF analyses are useful as they can be applied directly to solid rock powder samples with a minimal sample preparation. Glass bead (also called glass disk) XRF analyses were carried out using Brucker S8 TIGER instrument at the SRC Geoanalytical Laboratories Saskatoon, Saskatchewan, Canada.  Sample Preparation Glass bead– 1.25 grams of crushed and ground sample is mixed with 10 grams of lithium borate flux mixture, heated at approximately 1100 °C, and then poured into heated 40mm moulds. The melting, swirling, pouring, and cooling operations are all carried out automatically to preset timers. The production of a homogenous glass eliminates particle size and mineralogical effects but dilutes the sample, making it unsuitable for trace analysis.  Fused Beads are analyzed under vacuum conditions.  Analytical conditions The XRF is equipped with a 4kW X-ray tube and the following crystals: 158Ø LiF(200) Crystal Ø LiF(220) Crystal Ø LiF(420) Crystal Ø PET Crystal Ø XS-55 Crystal Ø XS-Ge-C Crystal  Quality Control Instrument drift checks are done daily, using a certified XRF Drift Monitor. Analytical performance checks are done weekly, using several certified reference materials. 	  XRF QAQC Protocol Standards Ø Bruker’s GRA, SQ1, SQ2, SQ3, drift control standards - used to correct instrument drift. Ø Bruker’s STG2 , DC73301(granite), and DC73324(soil) - used to monitor instrument performance. Ø User Application standards and reference materials.  1. Canmet GSP2 2. Canmet SY3 3. Canmet Oka2 4. Canmet CUP2 5. Canmet BL-1 6. Canmet BL-5 1597. Canmet BL-3  Method Validation and Quality Checks Ø The QE Check Application is analyzed daily, using Bruker’s STG2 standard, before samples are anlayzed. Ø DC73301and DC73324 are analyzed once per shift week using the GEO-QUANT application, provided by Bruker. Ø All Application Validation Standards are analyzed once per shift week. Ø Appropriate Application Validation Standards are analyzed and reported with each sample batch along with a duplicate sample every 20 samples. Ø The QE Check results, GEO-QUANT results, and weekly Application Validation results are manually compiled and monitored on an ongoing basis.  2. ICP-MS Lithium metaborate fusion by inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine trace and REE at the SRC Geoanalytical Laboratories Saskatoon, Saskatchewan, Canada. The ICP-MS multielemental technique can produce high quality data on a wide range of low trace and REE elements concentration. An aliquot of specimen is mixed with lithium metaborate in graphite crucibles. The mixture is fused in induction furnaces at ~ 1050°C, which is then dissolved in dilute HNO3. The solution/sample is generally pumped into the analytical nebulizer of ICP-MS, generating an aerosol. The aerosol is carried to the secondary excitation source of the instrument, a plasma torch, for digestion and ionization. The excited ionized material is then introduced into a mass spectrometer to 160analyze for elemental concentration. In this analytical technique chemical analysis are performed to ppm detection levels.  Sample Preparation: Depending on the sample type (non-mineralized, mineralized, etc.) each preparation step was performed in the designated sample preparation area. Rock samples were dried in their original plastic bags, and then jaw crushed. A subsample was split out using a riffler. The subsample was pulverized using a grinding mill. An agate mill is used, unless the sample is radioactive and then they are ground by puck and ring mill. The grinding mills were, at minimum, cleaned between samples, silica sand cleaning was employed in between groups. The pulp was transferred to a barcode labeled plastic snap top vial.   Sample Fusion: An aliquot of sample was combined with flux and fused in the Ox automated fusion instrument. After the fusion, the molten material was poured into solution. The solution was then vigorously stirred until the bead was dissolved. The solution was then topped up and analyzed by ICP-MS.  Sample Analysis: The instrument, a Nexion ICP-MS, was calibrated using certified commercial solutions.    161Quality Control: A control sample is prepared and analyzed with each batch of samples. One in every 40 samples was analyzed in replicate. All quality control results must be within specified limits (3 standard deviations) otherwise an investigation will proceed and appropriate corrective action taken. Quality control measures and data verification procedures applied also include the preparation and analysis of 3 standards and 1 blank. The blank is flux only.  Reference: Glocker, R. and Schreiber, H., 1928. Quantitative Roentgen Spectrum Analysis by Means of Cold Excitation of the Spectrum. Annals of Physics 85, 1089-1102.  Guthrle, M., 2012. Overview of X-ray Fluorescence. http://archaeometry.missouri.edu/xrf_overview.html.  PleBow, A., 2013. X-ray-induced alteration of specimens as crucial obstacle in XRF spectrometry of fluorine in rocks and soils. X-Ray Spectrometry 42, 19-32. 162

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