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Geochemical characterization of rocks and glasses from dykes in selected sites in Kaua’i, Hawai’i : implications… Utami, Sri Budhi Mar 31, 2013

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GEOCHEMICAL CHARACTERIZATION OF ROCKS AND GLASSES FROM DYKES IN SELECTED SITES IN KAUA’I, HAWAI’I: IMPLICATIONS ON THE LOA AND KEA TREND   by  SRI BUDHI UTAMI     A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  BACHELOR OF SCIENCE (HONOURS)  in   THE FACULTY OF SCIENCE  (GEOLOGICAL SCIENCES)     This thesis conforms to the required standard  ……………………………………… Supervisor  THE UNIVERSITY OF BRITISH COLUMBIA  (Vancouver)  MARCH 2013    © Sri Budhi Utami, 2013     ii ABSTRACT Petrological and geochemical characterization (major element, trace element and Pb isotopes) is done on 11 rock and 13 glass samples from dykes in selected sites in the island of Kaua’i (4.0-5.1 Ma). Petrography of hand sample and thin section indicate dykes are composed of tholeiitic basalt and picritic basalt. Major element analyses show all dykes are tholeiitic with consistent enrichment in major elements consistent with the mineralogy, with significant overlap in glass and rock composition in each location. Tholeiitic sample signature suggests dyke magma may be from the shield-building stage of Kaua’i. C1 Chondrite-normalized REE plots indicate dykes are consistent with geochemical signature typical of tholeiitic ocean island basalts. Binary trace element plots represent complex melting processes within the Hawaiian mantle plume resulting from partial melting of a depleted peridotite lithology source. Primitive mantle-normalized extended trace element diagram show typical composition of mantle-plume derived ocean island basalt with primitive mantle source, with enrichment in LIL and HFS elements. Pb isotopes composition show relatively low 206 Pb/ 204 Pb for a given 208 Pb/ 204 Pb and indicate dyke samples plotted on the Loa trend field with significant overlap with Kea trend lavas, and straddles the Loa-Kea trend boundary line. Comparison with Kaua’i rejuvenated lavas indicate dykes have higher concentrations of radiogenic 206 Pb/ 204 Pb and 208 Pb/ 204 Pb, and there is significant overlap between dykes and shield stage Kaua’i lavas indicating that overall, Kaua’i shield stage lava sampled transitional to Loa trend magmatism.  iii  TABLE OF CONTENTS ABSTRACT ............................................................................................................................... i TABLE OF CONTENTS ......................................................................................................... iii TABLE OF FIGURES .............................................................................................................. v LIST OF TABLES ................................................................................................................... vi ACKNOWLEDGEMENTS .................................................................................................... vii 1. INTRODUCTION AND SCOPE OF STUDY ..................................................................... 1 1.1 Mantle Plumes.............................................................................................................................. 1 1.2 Geochemistry and the Hawaiian Islands ...................................................................................... 2 1.3 Scope of Study ............................................................................................................................. 4 2. GEOLOGICAL SETTING ................................................................................................... 5 2.1. Geology of the Hawaiian Islands ................................................................................................ 5 2.2. The Loa and Kea Geochemical trends ........................................................................................ 9 2.3. Geology of Kaua’i ..................................................................................................................... 11 3. METHODOLOGY ............................................................................................................. 13 3.1 Sample Collection ...................................................................................................................... 13 3.2 Whole Rock Petrography ........................................................................................................... 13 3.3 Thin Section Preparation ............................................................................................................ 13 3.4 Sample Preparation .................................................................................................................... 13 3.4.1 Sample Cleaning ................................................................................................................. 14 3.4.2 Sample Cutting ................................................................................................................... 14 3.4.3 Sample Crushing ................................................................................................................. 14 3.4.4 Sample Pulverization .......................................................................................................... 14 3.5 Major Element Analyses ............................................................................................................ 14 3.6 Trace Element Analyses ............................................................................................................. 15 3.6.1 Sample Weighing................................................................................................................ 15 3.6.2 Digestion ............................................................................................................................. 15 3.6.3 Dilution ............................................................................................................................... 16 3.6.4 Trace Element Analyses by High Resolution Inductively Coupled Plasma Mass Spectrometer (HR ICP-MS) ........................................................................................................ 16 3.7 Sr, Nd, Hf and Pb Isotopic Compositions .................................................................................. 17 3.7.1 Sample Selection ................................................................................................................ 17 3.7.2 Sample Weighing and Loading........................................................................................... 17 3.7.3 Leaching ............................................................................................................................. 17 3.7.4 Digestion ............................................................................................................................. 18 3.7.5 Column Chemistry .............................................................................................................. 18 3.7.6 Pb Isotopic Analyses by MC-ICP-MS ................................................................................ 18  iv 4. RESULTS ........................................................................................................................... 32 4.1 Petrography ................................................................................................................................ 32 4.2 Major Element............................................................................................................................ 34 4.2.1 Silica Content Plots............................................................................................................. 34 4.2.2 MgO Content Plots ............................................................................................................. 39 4.3 Trace Elements ........................................................................................................................... 42 4.3.1 Rare Earth Elements (REE) Plot ......................................................................................... 42 4.3.2 Extended Trace Element Diagrams .................................................................................... 44 4.3.3 Nb/Y vs Zr/Y Plot ............................................................................................................... 46 4.3.4 MgO content vs. Trace Element ......................................................................................... 48 4.3.5 Binary Trace Elements ....................................................................................................... 49 4.4 Pb Isotopic Composition ............................................................................................................ 51 5. DISCUSSION ..................................................................................................................... 55 5.1. Spatial Variability in Major and Trace Element Compositions of Dykes ................................. 55 5.2. Trace Element Variations of Dykes: Implications on Mineral Chemistry ................................ 61 5.3. Dyke Pb Isotopic Composition and the Loa Geochemical trend .............................................. 63 6. CONCLUSION ................................................................................................................... 66 7. REFERENCES ................................................................................................................... 68 APPENDIX ............................................................................................................................. 76 1. Rock Samples ............................................................................................................................... 76 2. Glass Samples .............................................................................................................................. 78 3. Thin Section ................................................................................................................................. 81     v  TABLE OF FIGURES Figure 1.1: Bathymetric map of Hawaiian Islands and Emperor Seamounts ........................... 2 Figure 1.2: A map of the Hawaiian Islands showing Loa and Kea trends................................ 4 Figure 2.1: Satellite image of Hawaiian Islands with radiometric ages.. ................................. 7 Figure 2.2: Stages of ocean island growth. ............................................................................... 8 Figure 2.3: Updated bathymetric map of the Hawaiian Islands with Loa and Kea trend  ...... 10 Figure 2.4: map of Kaua’i with locations of sites of dykes sampled. ..................................... 12 Figure 4.1: XPL photomicrographs of textures in NIU-1A and North Shore #6. .................. 33 Figure 4.2: Silica content vs. Al2O3, CaO, Na2O, MgO, K2O for Kaua’i dykes .................... 38 Figure 4.3: MgO content vs. CaO/Al2O3 ratio for all dyke samples....................................... 39 Figure 4.4: MgO content vs. Al2O3, CaO, Na2O, MgO, K2O for all dykes samples .............. 41 Figure 4.5: C1 chondrite normalized REE plot diagram for all dyke samples ....................... 43 Figure 4.6: C1 chondrite normalized La vs. Yb for all dyke samples .................................... 44 Figure 4.7: Primitive mantle normalized spider diagram of all dyke samples. ...................... 45 Figure 4.8: Nb/Y vs. Zr/Y plot of all dyke samples ............................................................... 47 Figure 4.9: MgO content vs. Sc, Cr, and Ni concentrations for all dyke samples .................. 48 Figure 4.10: Binary trace element plots for all dyke samples. ............................................... 50 Figure 4.11: 208 Pb/ 204 Pb vs. 206 Pb/ 204 Pb ratios and 207 Pb/ 206 Pb vs. 206 Pb/ 204 Pb ratios plots. .... 52 Figure 4.12: 208 Pb*/ 204 Pb* vs. distance from Kilauea ............................................................ 53 Figure 5.1: Annotated Total-Alkali Silica (TAS) diagram of dyke samples. ......................... 56 Figure 5.2: Annotated MgO content vs. CaO/Al2O3 ratio plot ............................................... 59 Figure 5.3: Annotated REE diagram and extended trace element diagram ............................ 60 Figure 5.4: Annotated Binary trace element diagram of Zr vs. Cr and Ni. ............................ 62 Figure 5.5: Annotated Radiogenic 208 Pb*/ 206 Pb* correlated with distance from Kilauea ...... 65 Figure 5.6: Annotated 206 Pb/ 204 Pb and 208 Pb/ 204 Pb graph ....................................................... 64   vi LIST OF TABLES Table 3.1: Summary of petrographical information for all Kaua’i dykes .............................. 20 Table 3.2: Summary of major element composition for all Kaua’i dykes. ............................. 24 Table 3.3: Summary of trace element composition for all Kaua’i dykes (Rare Earth Elements). ............................................................................................................................... 26 Table 3.3: Summary of trace element composition for all Kaua’i dykes (HFSE). ................. 28 Table 3.4: Summary of Pb isotopic composition for all Kaua’i dykes. .................................. 31 Table 4.1: K2O/P2O5 ratios for Kauaì dykes. .......................................................................... 36   vii  ACKNOWLEDGEMENTS Firstly, I would like to thank my thesis supervisor Dr. Dominique Weis for the opportunity to work on this project and providing her expertise on the subject matter for the past year; her advice, support, and enthusiasm have been invaluable. I am sincerely grateful for her patience and encouragement, for the time and effort she has put into editing and critiquing this thesis, helping me examine my data and answering my questions. I would also like to thank Dr. Michael Garcia for the time and effort spent collecting dyke samples on Kaua’i.  I would like to thank the staff at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) for the analyses and expertise involved in performing this thesis. Special thanks go to Vivian Lai for trace element analyses by HR-ICP-MS, digesting and performing Pb column chemistry for Pb isotope analyses. Special thanks also go to Kathy Gordon for her assistance in performing the Pb isotope analyses in MC-ICP-MS. I would also like to thank Dr. Bruno Kieffer and Richard Friedman for their advice and general lab assistance.  I would like to thank Diane Hanano, Lauren Harrison, Dr. Emily Mullen, Corey Wall Marina Martindale and Anais Fourny for their assistance in sample preparation and pulverization, for sharing their knowledge and expertise, and their encouragements and patience. Thanks also go to the Matt Manor, Sarah Jackson-Brown and the rest of the crew at room 305 for their enthusiasm and encouragement for the past year. Thanks also go to Luke Hilchie for general petrography advice.  Finally I would like to thank my whole family (Bapak, Ibu, Riri, Mas Wahyu) and friends for their unconditional love, patience, and support.      1 1. INTRODUCTION AND SCOPE OF STUDY 1.1 Mantle Plumes  Mantle plumes are focused upwellings of hot solid material within the mantle, formed due to the cooling of Earth’s core, and caused by a physical and thermal imbalance in the mantle (Ribe and Christensen, 1999). In a typical plume, buoyant solid piece of mantle ascends from as deep as the core-mantle boundary beneath the crust (Sleep, 1990). During a plume's ascent, low degrees of partial melting occur at shallow depths due to decompression melting; these melts migrate and rupture through to Earth's surface, producing oceanic islands and continental flood basalts (Weis et al., 2011). Partial melting of a plume creates unique surface expressions on Earth's surface; plume heads typically produce flood basalts whereas plume tails generate intra-plate volcanism (Richards, 1989). Arguably one of the best studied of mantle plume derived volcanism and geological phenomena are the Hawaiian Islands, which is the focus of this study.  The Hawaiian Island chain and the Emperor seamounts are products of mantle plume activity. Evidences include the island chain’s intra-plate volcanism, linear island and seamount chain configuration and the correlation of increasing ages away from the centre of the plume (currently Kilauea) as seen in Figure 1.1; these are caused when the rigid Pacific plate move over the Hawaiian mantle plume, underplating the Pacific plate and creating the linear chain of islands and seamounts (McDougall and Duncan, 1980). The sharp 60° Hawaiian Emperor Bend (HEB) in the Hawaiian Islands and Emperor seamounts may correspond to a change in the direction of movement of the Pacific plate (Koppers et al., 2005; Humphreys and Niu, 2009). The entire volcanic chain span 6000 km from the Hawaiian Islands in the southeast Pacific Ocean to the Emperor seamounts; as a consequence, the chain records evidence of the Pacific plate tectonics and mantle plume activity (MacDougall and Duncan, 1980). Geochemical and isotopic research has been done on the Hawaiian Islands, yet questions remain regarding the geochemical composition of the Hawaiian plume    2  Figure 1.1: Bathymetric (ETOPO1) map of Hawaiian Islands, Hawaiian Ridge, Midway Islands, and Emperor Seamounts (Adapted from the USA National Geophysical Data Center).  1.2 Geochemistry and the Hawaiian Islands  Geochemistry is effective in differentiating geochemical fingerprint of source regions within Earth’s and tracing the evolution of the mantle’s composition. Analysing observed geochemical variations in the lithology allow inferences to be made on the chemical processes occurring within in the source region.  These geochemical processes are controlled by properties and behaviour of elements between liquid and mineral phases, such as ionic radii and charge. Each geological setting will have a unique chemical composition, allowing constraints to be made on the source composition and its geological history.   Geochemical analyses of lavas from volcanoes along the Hawaiian Islands are used Emperor Seamounts Hawaiian Ridge Hawaiian Islands Hawaiian Emperor Chain bend   3 to trace and constrain sources of magma within the Hawaiian mantle plume. For example compared to mid-ocean ridge basalts (MORB), ocean island basalts (OIB) have relatively high 3 He/ 4 He ratio indicating a lower mantle origin, whereas low 3 He/ 4 He ratio found in MORB composition indicates a shallow depleted mantle source (Hilton and Porcelli, 2007; Mukhopadhyay et al., 2003). A study by Hanano et al. (2010) shows geochemical variation within the mantle plume through horizontal and vertical zoning of heterogeneities; these heterogeneities evolve both spatially and through time. Abouchami et al. (2005) indicate features in the Hawaiian Islands that are common to all mantle plume derived ocean islands, which are two distinct sub-parallel geochemical trends sampled by adjacent volcanoes in the island chain along parallel geographical trends as seen on Figure 1.2. This bimodal heterogeneity is observed in other mantle plume-derived ocean islands such as the Society Islands that also display two similar geochemical trends with one enriched region and one depleted region (Payne et al., 2012). Results of such geochemical studies have been used to understand the distribution of the Large Low Velocity Province (LLVP), a region from which plume magmas are sourced. However due to the lack of high-resolution geophysical data, accurate mapping of the LLVP has not yet been achieved (Weis et al., 2011).  Geochemical analyses of basalts sampled from different locations around the Hawaiian Islands show temporal and geographical variations, reflecting heterogeneities in chemical composition of source regions feeding the Hawaiian mantle plume. In Kaua’i, He isotopic ratios in Kaua’i lava samples are found to be particularly high (Mukhopadhyay et al., 2003). Sr, Nd, Hf and Pb isotopes records heterogeneities present in the source mantle plume, with distinct end-members sampled by individual volcanoes (Weis et al., 2011).    4  Figure 1.2: A map of the Hawaiian Islands showing two sub-parallel Loa and Kea trends (Adapted from Abouchami et al., 2005). Kaua’i is circled.  1.3 Scope of Study  The purpose of this study is to characterize using detailed petrography and geochemical analyses 11 basalts and 13 glass samples chosen from four localities from the north and west of Kaua’i: Waimea Canyon, the North Shore area divided into Kalalau Trail and Wet Cave, and Niu Valley. These four localities are chosen due to the prevalence of basaltic dykes intruded into Waimea Canyon basalts, the main shield and post-shield volcanic rocks on the island (Stearns, 1985; Reiners and Nelson, 1998). Petrographical description of hand sample and thin sections are done on 2 basalt samples from Niu Valley Kalalau Trail, selected because their size and freshness allows for thin sections and detailed petrographic analyses. Detailed geochemical characterization involve geochemical analyses of major and trace elements on all samples; 8 samples are further selected based on loss-on-ignition (LOI) values derived from major element analyses for Pb-Sr-Nd-Hf isotopic analyses to   5 characterize geochemical trends and variations found, and relating them to the growth of Kaua’i. Implications of this study also extend to the distribution of the Loa or Kea geochemical trend, where Pb isotopic analyses aim to identify whether dykes sampled have Loa or Kea geochemical signature.  This study presents new petrographic and geochemical data on basaltic dykes of Kaua’i, which complements current research into the evolution of heterogeneities within the Hawaiian mantle plume during the build-up of Kaua’i, as well as temporal and geographical sampling of Loa and Kea geochemical trends along the Hawaiian Islands and Emperor Seamounts. This study addresses the hypothesis that dykes on northern and western Kaua’i may represent late stage rejuvenated volcanism intruding in tholeiitic shield and post-shield stage volcanic rocks during Kaua’i’s geological history. Additionally, this study also will address whether the Loa geochemical trend is sampled by dykes on Kaua’i, potentially extending the trend to be sampled by volcanoes to at least 5 Ma from the current volcanism observed on the Island.  2. GEOLOGICAL SETTING 2.1. Geology of the Hawaiian Islands The Hawaiian Islands chain is a product of intra-plate volcanism associated with the Hawaiian mantle plume, the second oldest active mantle plume active for 80 Ma with the highest volume of magmatic flux on Earth (Duncan and Keller, 2004). The linear chain of subaerial Hawaiian Islands and Emperor Seamounts provide evidence for Hawaiian mantle plume activity, as oceanic island volcanoes erupt lava from the molten core region of the plume tail when they are on the axis of the plume (Farnetani et al., 2002). Defining characteristics of the Hawaiian Islands are the intraplate volcanism, the linear chain of volcanic islands consistent with movement of the Pacific plate, the progressively increasing ages of ocean islands and seamounts on the volcanic chain, and the topographic Hawaiian swell (Wolfe et al., 2009; Farnetani and Hoffman, 2011).   6 Hawaiian volcanic chain is produced through decompression melting in the plume’s core, rising upwards from the Hawaiian plume and erupting through the lithosphere onto the ocean floor, producing fissure eruptions or rifting events producing steep-sided cones of pillow basalts (Stearns, 1985; DePaolo and Weis, 2007). The resultant structure consists of 3 layers with subaerial lavas underlain by an apron of volcaniclastics covering a pillow lava seamount centre (Walker, 1990; DePaolo and Weis, 2007). Subaerial Hawaiian lavas vary in morphology, ranging from aa flow, pahoehoe flow, pillow basalts and hyaloclastites (Macdonald and Katsura, 1964; Stearns 1985; Francis and Oppenheimer, 2004). Magma production varies during the growth of each ocean island; the maximum growth and hence most voluminous output of lava occurs when the ocean island is directly above the axis of the plume and waning when the ocean island moves away from the mantle plume axis due to the Pacific plate movement (DePaolo and Weis, 2007). As a consequence, each Hawaiian Island increase systematically in age with increasing distance away from the current plume axis underneath Kilauea to the northernmost islands Ni`ihau and Kaua’i as shown on Figure 2.1 (Stearns, 1985; Clague and Dalrymple, 1987, Duncan and Keller, 2004; Garcia et al., 2006; Weis et al., 2011). The volcanic Hawaiian Island chain is composed of basalts with significant compositional varieties (Macdonald and Katsura, 1964). Hawaiian basalts vary from the common tholeiitic basalt to the rarer Hawai’ite and mugearite (Stearns, 1985). Each type of basalt is classified according to its total alkali and silica composition as either tholeiitic basalts or alkaline basalts (Macdonald and Katsura, 1964, Le Bas et al. 1985). According to Le Bas et al. (1985), tholeiitic basalts are rich in Mg and Fe, whereas alkaline basalts are rich in Na, Ca and K. These differences in composition are reflected in the mineral assemblage of Hawaiian basalts; typical mineralogy of tholeiitic basalts is rich in olivine, clinopyroxene and orthopyroxenes whereas alkaline basalt is rich in melilite, nepheline and clinopyroxene (Stearns, 1985; Clague and Dalrymple, 1987; Garcia et al., 2006; Garcia et al., 2010). Clague and Dalrymple (1987) propose that Hawaiian volcanoes erupt lavas of different compositions depending on the growth stage the volcanoes are in, as seen in Figure 2.2. Initiation of the Hawaiian stage begins with a submarine alkali pre-shield stage, followed by voluminous outpourings of tholeiitic shield stage lava accounting for more than 95% of the volcano’s volume, and followed by an eruption of a small volume of post-shield alkali   7 basalt. After a quiescent stage varying from 2.5 Ma to less than 0.4 Ma, a small volume of silica-poor rejuvenated lava erupts as the last stage of volcanism; eventually the volcano subsides and form seamounts, as summarized in Figure 2.2 (Clague and Dalrymple, 1987). Figure 2.1: Google Earth satellite image of Hawaiian Islands with corresponding ages from the southernmost Big Island of Hawai’i to Ni’ihau and Kaua’i. (Adapted from Google Earth). Radiometric ages are derived from K-Ar and Ar-Ar system dating from McDougall (1964); Naughton et al. (1979); Guillou et al. (1999); Sano et al. (2006); Greene et al. (2010); Garcia et al. (2010)   8  Figure 2.2: Stages of a typical ocean island building with present eeamples (adapted from Stock, 2006). Arrow shows progression through time.  Quiescent stage of 0.4-2.5 million years Lo’ihi Kilauea No present volcano Hualalai Koloa Volcanics Series, Kaua’i   9 2.2. The Loa and Kea Geochemical trends A distinctive feature of Hawaiian Islands chain, as first noted by Dana (1895) and Jackson (1972), is the parallel chain of volcanoes, as seen in Figure 2.3. Each volcano along these parallel geographical trends sample distinct geochemical composition of basalts. Radiogenic isotopes provide evidence for the parallel bilateral trend, called Kea and Loa trend volcanism (Jackson et al., 1972; Tatsumoto, 1978). Weis et al. (2011) shows that the Loa trend lava exhibits wider variety in isotopic compositions than the Kea trend, indicating the mixing of several components. Volcanoes sample lava from these trends when they pass over the axis of the mantle plume, thus preserving their distinct geochemistry in Hawaiian volcanoes in a linear chain extending throughout the whole length of the Hawaiian Island chain (Abouchami et al., 2005). Mukhopadhyay et al. (2003), Garcia et al. (2010) and Greene et al. (2010) have analyzed lavas from the eastern side of Kaua’i and determine these as Loa trend lava. Similar bilateral trends like the Loa and Kea trends are found in other volcanic ocean island chains such as the Marquesas and Society Islands (Chauvel et al., 2012; Payne et al., 2012). These island chains display similar bilateral geographic and geochemical trends, and can be used to trace a large enriched regions in the lower mantle from addition and mixing of components; these regions are called the Large Low Velocity Province (LLVP) or the Ultra- Low Velocity Zone (ULVZ) (McNamara et al., 2010; Jackson et al., 2012; Payne et al., 2012). Radiogenic isotopes and trace elements can be used to trace elemental and isotopic geochemical signature of ocean islands to geochemically map regions like the LLVP within the lower mantle, and deduce processes responsible for producing these regions (Weis et al., 2011; Payne et al., 2012). Arguably one of the most important isotopic systems used in mantle dynamic studies up to date is the Pb isotopic system. Pb isotopes have been used to differentiate Loa and Kea trends in Hawaiian basalts, recording trends showing mixing of different relatively old mantle reservoirs (Hoffman, 2003). Weis et al. (2011) proposes that Loa trend volcanoes are more radiogenic than the Kea trend volcanoes with only two volcanoes overlapping the trends; of the Kea volcanoes that overlaps with Loa trend lava (Kohala and Waianae), these represents the least radiogenic Pb ratios within the Kea volcanoes and are thought to belong   10 to the Loa composition despite the volcanoes being on the Kea trend (Weis et al., 2011). The radiogenic Pb isotopic ratio 208 Pb*/ 206 Pb* is derived from subtracting Pb isotopes produced from the radioactive decay of U and Th from the initial Pb composition of the Earth, thus reflecting the ratio of U/Th of the soure region through Earth’s history (Hoffman, 2003; Weis et al., 2011). Loa trend lava is found to have overall higher isotopic ratios of 208 Pb*/ 206 Pb* compared with Kea trend lava with a clear break between the two trends (Blichert-Toft et al., 2003; Abouchami et al., 2005; Weis et al., 2011).   Figure 2.3: Bathymetric map of the Hawaiian Island chain showing the relative positions of the Loa and Kea trend volcanoes (adapted from Weis et al., 2011). Kaua’i is circled. Inset shows magmatic volume flux compared to distance of each volcano from Kilauea.    11 2.3. Geology of Kaua’i Kaua’i is the second oldest Hawaiian island at 4.0-5.1 Ma, and has the highest volume of exposed rejuvenated volcanoes recording volcanic activity spanning around 2.5 million years, as seen in Figure 2.4 (Garcia et al., 2010). The island of Kaua’i is comprised of a dissected basalt dome and two former calderas (Stearns, 1985). Due to its age and extensive erosion rates, mostly horizontal and resistant caldera and the western portion of the caldera rim are exposed; dykes are exposed along steep, weathered cliffs (Stearns, 1985). The tholeiitic shield lavas have K-Ar radiometric ages ranging from 4.0 to 5.1 Ma and younger inter-bedded capping alkalic lavas are aged 3.87 to 3.95 Ma as seen on Figure 2.4 (McDougall, 1964; Clague and Dalrymple 1987). The rejuvenated volcanics are 0.68-2.44 Ma (Garcia et al., 2010). Petrological and geochemical analyses indicate that subaerial Kaua’i lavas are composed of rejuvenated Koloa Volcanics Series overlying tholeiitic shield- stage Waimea Canyon Series; recent sediments cover parts of the island (Feigenson, 1984; Garcia et al., 2010). The Waimea Canyon Series on the western side of the island consists of tholeiitic basalt, with post-shield minor Hawai’ite and mugearite lavas. Within the series, the Napali Formation consists of gently dipping tholeiitic shield-stage basaltic flows; the Olokele Formation is composed of thick basaltic flows infilling the main caldera; the Haupu Formation are made up of massive basalt flows, and the Makaweli Formation is similar in lithology and composition as the Olokele Formation (Macdonald et al. 1960; McDougall, 1964; Stearns, 1985). The Koloa Volcanic Series is exposed on the eastern side of the island and consists of the Palikea Formation, which are under-saturated alkaline lava flows that covered by recent sediment fans, talus, and mudflows and separated by a steep unconformity (Stearns, 1985). The Koloa Volcanic Series rocks are comprised of olivine-phyric alkali basalt with nepheline, melilite and phlogopite (Garcia et al., 2010). Geochemical studies on samples from the tholeiitic shield-stage lavas are collected from the Napali Member and Olokele Member (Maaloe et al., 1992; Mukhopadhyay et al., 2003). Due to poor accessibility and extensive alteration of outcrops, the western side of the island is sparsely sampled, although these are inferred to belong to the Napali formation (Macdonald et al., 1960; Stearns, 1985).   12  Figure 2.4: General map of Kaua’i annotated with locations of sites of dykes sampled (adapted from Mukhopadhyay et al. 2003). Niu Valley Waimea Canyon Wet Cave Kalalau Trail   13 3. METHODOLOGY 3.1 Sample Collection 11 rock and 13 glass samples were collected by Dr. Michael Garcia of the University of Hawai’i at Manoa from several exposed fresh dyke outcrops in Waimea Canyon and Niu Valley in the southwest of the island, and Kalalau Trail and Wet Cave in the North Shore area of Kaua’i. Field descriptions of each dyke was noted, thickness of dyke, strike and dip, degree of weathering, as well as presence of glass, as summarized in Table 3.1. 3.2 Whole Rock Petrography 2 rock samples were selected from Kalalau Trail (‘North Shore #6’) and Niu Valley (‘NIU-1A’) sites based on their volume and degree of freshness of each sample. Whole rock petrography was done, with the other 22 samples summarized in Table 3.1. Photographs were reported in the Appendix. 3.3 Thin Section Preparation Billets of NIU-1A and North Shore #6 were prepared using the diamond embedded rock saw. Billets were then abraded with sandpaper to eliminate alteration and saw traces. Two polished 26 mm x 46 mm thin sections are produced by Vancouver Petrographics. Thin section petrography was done to assess modal mineralogy of each sample, phenocryst minerals, and visible alteration. Photographs were taken in plane polar and cross-polar light, and reported in the Appendix. 3.4 Sample Preparation  Samples were prepared for major element, trace element and isotopic analyses at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia.    14 3.4.1 Sample Cleaning  Samples larger than 5 cm x 5 cm were rinsed with tap water and cleaned with scrubbing brush to remove surface soil and alteration. Samples smaller than 5 cm x 5 cm were cleaned by rinsing in ethanol and de-ionized water, air-dried and immersed in deionized water again, and then cleaned in an ultrasonic bath for multiple cycles until the supernatant water was clear. Each cycle lasted 30 minutes before repeating. 3.4.2 Sample Cutting  Samples larger than 5 cm x 5 cm were cut using diamond embedded rock saw at PCIGR to reduce sample size, remove surface alteration and expose fresh surface. Afterwards, samples were abraded using sandpaper and water to remove saw traces and surface alteration, and air- dried in preparation for the crushing stage. 3.4.3 Sample Crushing  Samples larger than 1 cm x 1 cm dimensions were crushed at Rocklabs, PCIGR using a hydraulic piston crusher to reduce sample size to chips around 0.5 cm or less for the pulverization stage in either the Fritsch planetary mill or the agate mortar and pestle. 3.4.4 Sample Pulverization  Samples with masses heavier than 100g with were pulverized using the Fritsch planetary mill in agate bowls filled with 10 agate balls set at 380 rpm for 5 minutes for 3 cycles lasting 20 minutes each to reduce to powder form; samples with mass lighter than 100g were pulverized using an agate pestle and mortar. 3.5 Major Element Analyses  Results were reported in Table 4.1. 24 samples, one basalt sample 4722A4 (Greene, PhD thesis, 2008) and 3 randomly selected blind duplicate samples were analysed for major element compositions by X-Ray Fluorescence (XRF) at Activation Laboratory, Vancouver. Samples NIU- 1A, North Shore #6 and WC 4 values reported were calculated mean averages of 2 duplicate analyses. XRF analyses at Activation Laboratory were reported according to the methodology outlined in Norrish and Hutton (1969). Loss-on-ignition (LOI) values were determined from   15 weight loss after heating at 1050°C for 2 hours. Fusion disks were made per sample by combining lithium metaborate, lithium tetraborate and lithium bromide. Each sample was fused in Pt crucibles, poured into Pt molds and analysed on the Panalytical Axios Advanced wavelength dispersive XRF. Intensities were measured and concentrations of each major element oxides calculated relative to the G-16 standard. Matrix corrections were calculated using oxide alpha-influence coefficients, both of which were provided by Dr. K. Norrish of Commonwealth Scientific and Industrial Research Organisation, Australia. Limit detection was set at about 0.01 wt. % for most elements. 3.6 Trace Element Analyses  Samples were analyzed at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia following the methods outlined in Pretorius et al. (2006), Hanano et al. (2009), and Carpentier et al. (2013). The procedure involved loading, digestion, dilution, and analyses for trace elements using the Thermo Finnigan ELEMENT2 High Resolution ICP-MS (HR-ICPMS). Trace element compositions were reported in Table 3.2. 3.6.1 Sample Weighing  15ml empty Savillex beakers used for each sample was weighed precisely on the Mettler Toledo analytical weigh balance. Approximately 0.1g of each sample`s powder was added to the beakers and accurately weighed. All 24 samples, one procedural blank and three USGS reference materials, BHVO-2 (Hawaiian Volcanic Observatory) Kil-93 (Kilauea) and BCR-2 (Columbia River Basalt) were analysed and compared according to values from studies by Weis et al (2005, 2006). One duplicate of BHVO-2 and one duplicate sample NIU-1A were analysed for trace element concentrations to check for accuracy and reproducibility in results. Replicate analyses were conducted to monitor instrument drift during the analyses. 3.6.2 Digestion  Pretorius et al. (2006) outlined digestion procedures followed. 1 ml concentrated HNO3 and 10 ml concentrated HF were added to the Savillex beaker, capped and heated on a hotplate at 120-130°C for around 5 days, and then opened to dry completely. Concentrated HCl solution was added to the resulting powder, the beaker was capped and heated on the hotplate to dissolve   16 again at around 120°C for approximately 2 days. Around 1ml digested solution was taken and weighed, then added to a pre-weighed 7 ml Savillex beaker. The digested HCl solution was opened and heated for 2 days until completely dried. Approximately 1 ml concentrated HNO3 solution was added to the solution, which was capped and heated on the hotplate for around 24 hours at 120°C, and opened to dry completely. Each sample or reference comprised one aliquot ready to be diluted for the ICP-MS analyses stage. 3.6.3 Dilution  All sample and reference aliquots were each diluted into 1% HNO3, 0.05% HF and 10ppb Indium solution. The Indium solution comprised concentrated HNO3, concentrated HF and dissolved Indium. To each 7 mL Savillex beaker containing one dried down aliquot, approximately 2 mL of the Indium solution was added using a pre-cleaned 125 mL bottle dispenser and heated on the hot plate at around 80-90°C for 10 minutes and sonicated for a further 10 minutes. The resulting solution was transferred into a HDPE bottle and the Savillex solution was rinsed with more Indium solution until a targeted 5000X dilution weight was reached. 3.6.4 Trace Element Analyses by High Resolution Inductively Coupled Plasma Mass Spectrometer (HR ICP-MS)  All diluted samples were analysed on the Thermo Finnigan Element2 HR-ICP-MS at PCIGR at the University of British Columbia according to procedures outlined by Pretorius et al. (2006). Trace element concentrations were measured using high, medium and low resolution for REE, HFSE, and Pb, Th and U respectively to prevent isobaric interference and ensure high sensitivity in measurements. Analyses of reference materials BCR-2, BHVO-2, and Kil-93 were performed to calibrate and monitor for variations in trace element concentrations. 3 Procedural blanks were run throughout the analyses for internal standards purposes, mass correction and monitor sensitivity drift from matrix effect; each blank contained 1% HNO3 + 1ppm In solution. BHVO-2 solution was used in bracketing procedures to derive correction factors for each sequence of 5-7 samples. Memory effects were corrected by analysing blank solutions and minimized by rinsing the instrument with 4% Aqua Regia + 0.5% HF. To ensure reference materials were reproducible within error, Kil-93 and BHVO-2 values were compared with   17 previous analyses of BHVO-2 in 2008 at PCIGR (Vivian Lai, unpublished data) and with trace element data from analyses of Kil-93 sample outlined in Norman et al. (1993).  Trace element concentrations of reference materials were within error of both analyses. 3.7 Sr, Nd, Hf and Pb Isotopic Compositions  Solutions for Sr, Nd, Hf, and Pb isotopic analyses were prepared at PCIGR at the University of British Columbia using the procedure outlined by Weis et al. (2006, 2007) and Nobre Silva et al. (2009). Samples were selected based on major and trace element variations. Pb isotopic analyses were done using the Nu Plasma (#21) multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Pb isotopic results were reported in Table 3.4. 3.7.1 Sample Selection  Selection of samples was initially based on Loss-on-ignition (LOI) values from major element analyses performed by Activation Laboratory to determine the degree of alteration. Further selection were based on results from several X-Y plots of trace elements plotted on the Data Desk software such as Zr/Y vs. Nb/Y and Zr vs. Ce and MgO vs. major element plots. Samples were selected based on enrichment in different trace elements occurring in several binary trace element plots. Other criteria for selecting samples included choosing representative samples from each location, samples from end-members of geochemical trends, and samples that represent the average of samples. 3.7.2 Sample Weighing and Loading  11 dyke and glass samples, 1 BHVO-2 and 1 Kil-93 samples and one procedural blank were loaded and prepared for leaching. 0.3-0.4 g of each powdered sample was weighed on the Mettler Toledo analytical weighing scale on one pre-cleaned and pre-weighed 15 mL Savillex beaker prior to leaching. 3.7.3 Leaching  Samples were leached according to procedures outlined by Weis et al. (2005), Nobre Silva et al. (2009, 2010). After weighing, 10 mL of 6N sub-boiled HCl were added to the rocks powders and ultra-sonicated for 20 minutes, and the supernatant solution was decanted and   18 discarded. This process was repeated until the sample colour was pale-yellow to clear; the colour and degree of clarity indicated the extent of each sample's alteration and weathering removed from rock powder. This step was repeated two further times with milli-Q H2O instead of HCl. The leached rock powder was dried on a hot plate at approximately 120°C and weighed after cooling. 3.7.4 Digestion  Samples were digested according to procedures outlined in Weis et al. (2005). Each leached sample powders were placed on a screw-top Savillex beakers with 10 mL of 48% HF and 1.0 mL of 14N HNO3 and ultra-sonicated. Samples were then dried down on a hotplate at approximately 130°C, and reconstituted in 6.0 mL sub-boiled HCl, dissolving at 130°C in preparation for column chemistry. 3.7.5 Column Chemistry  Column chemistry procedure was outlined in Weis et al. (2005). The sample was loaded on a 200 μL column of Biorad AG1-X8 100-200 mesh resin and Frits filters. The column was conditioned with a solution comprising of 1 mL each of 18 Megohm water, 0.5 N HBr, 6N HCl for repetitive two cycles. Samples were conditioned with 18 Mega ohm water followed with 0.5 HBr, and the conditioning solution were discarded as waste. Samples were then taken up in 0.5 HBr, heated and ultra-sonicated for equal amounts of time until completely dissolved. This solution was then centrifuged at 14500 rpm for 6 minutes, and the supernatant loaded onto the column. Sr, Hf and REE were washed from the column with 0.5 N HBr, collected in 15mL Savillex beakers and retained for Sr and Nd isotope analyses. Pb was eluted in 6 N HCl and collected into 7 mL Savillex beakers, then dried for the analyses stage. 3.7.6 Pb Isotopic Analyses by MC-ICP-MS  Pb isotopic analyses were carried out over two days following procedures outlined in Weis et al. (2005, 2006). All aliquots of sample solutions were analysed using the Element 2 HR- ICP-MS to determine the exact amount of Pb available for isotopic analyses. Sample solutions were analysed with the same [Pb]/[Tl] ratio as the standard Pb solution NBS 981. Standard solutions of Pb and Tl were prepared to maintain average values for [Pb]/[Tl] = 2.8772 ± 0.5760   19 for day 1 and [Pb]/[Tl] = 3.1104 ± 0.0092 for day 2 to ensure consistent [Pb]/[Tl] ratio of around 3. Each sample was dissolved with 1 mL 0.05 M HNO3 and spiked with 1 μL of Specpure® Tl standard solution to correct for instrumental mass fractionation. Mass fractionation of samples were corrected using 205 Tl/ 203 Tl = 2.4318 for day 1, and  205 Tl/ 203 Tl = 2.4315 for day 2. Aliquots of each solution were diluted with around 2 mL 0.05 M HNO3 to ensure a value of around 4V 208 Pb signal was met by all samples analyzed. Mass interference correction for 204 Pb was done using correction values 202 Hg = 0.29863 204 Hg = 0.06865. Bracketing procedures involved analyses of NBS 981 solutions.  For day 1, 16 analyses were conducted prior to sample analyses, after every 2 samples and analysed once in the end. For day 2, 7 standard solutions were analysed prior to sample analyses, once after every 2 samples, and twice at the end. After each analyses, the uptake tube was dipped in H2O followed by 3% HNO3 for rinsing.  Pb isotopic analyses were done in static mode using a desolvating nebulizer (Nu DSN 100). MC-ICP-MS was already normalized with NBS-981 standard solution. Average triple spike values over the two days for NBS-981 solution were 206 Pb/ 204 Pb = 18.3265 ± 0.0009, 207 Pb/ 204 Pb = 15.4628 ± 0.008 and 208 Pb/ 204 Pb = 38.0080 ± 0.0023. All 3 lead isotopic ratios were compared with accepted triple spike values from Galer and Abouchami (1998) ( 206 Pb/ 204 Pb = 16.9405, 207 Pb/ 204 Pb = 15.4963, and 208 Pb/ 204 Pb = 36.7219).   20 Table 3.1: Summary of petrographical information for all Kaua’i dykes Sample location Sample name Sample Type Hand sample Texture Wet Cave Kaua’i 2b/No. Shore Volcanic glass chips glass Kalalau Trail Kalalau Trail #5 Volcanic glass chips glass Wet Cave North Shore #3/Wet Cave Volcanic glass chips glass Wet Cave North Shore #4/Wet Cave Volcanic glass chips glass Kalalau Trail North Shore #6 Volcanic glass chips glass Kalalau Trail Trail 7 Volcanic glass chips glass Niu Valley Niu 1b Volcanic glass chips glass Niu Valley Niu 2 Volcanic glass chips glass Niu Valley Niu 3 Volcanic glass chips glass Waimea Canyon Waimea Canyon 2 Volcanic glass chips glass Waimea Canyon Waimea Canyon 3 Volcanic glass chips glass Waimea Canyon Waimea Canyon 4 Volcanic glass chips glass Waimea Canyon Waimea Canyon 5 Volcanic glass chips glass Kalalau Trail North Shore #6 rock sample >5cm weakly porphyritic Niu Valley NIU1A rock sample >5cm porphyritic Wet Cave Kaua'i, N.S. 3 – 4/3/93 1cm<rock samples <5cm aphanitic, partially vitric Waimea Canyon 4 Wet 1cm<rock samples <5cm aphanitic, partially vitric with glassy rind Waimea Canyon WC-4 1cm<rock samples <5cm aphanitic to weakly porphyritic, highly vesicular with pahoehoe texture Waimea Canyon WC 5 1cm<rock samples <5cm aphanitic Kalalau Trail #5 trail 1cm<rock samples <5cm aphanitic to weakly porphyritic. Mildly vesicular. Heavily altered and palagonitized. Niu Valley NIU-1B 1cm<rock samples <5cm porphyritic Niu Valley NIU-3 1cm<rock samples <5cm porphyritic Wet Cave 3A 1cm<rock samples <5cm aphanitic, highly vesicular with evidence of columnar jointing. Waimea Canyon Waimea Canyon #2 1cm<rock samples <5cm aphanitic, vesicular  .   21 Table 3.1: Summary of petrographical information for all Kaua’i dykes.  Sample location Sample Sample Type Thin section texture Wet Cave Kaua’i 2b/No. Shore Volcanic glass chips Kalalau Trail Kalalau Trail #5 Volcanic glass chips Wet Cave North Shore #3/Wet Cave Volcanic glass chips Wet Cave North Shore #4/Wet Cave Volcanic glass chips Kalalau Trail North Shore #6 Volcanic glass chips Kalalau Trail Trail 7 Volcanic glass chips Niu Valley Niu 1b Volcanic glass chips Niu Valley Niu 2 Volcanic glass chips Niu Valley Niu 3 Volcanic glass chips Waimea Canyon Waimea Canyon 2 Volcanic glass chips Waimea Canyon Waimea Canyon 3 Volcanic glass chips Waimea Canyon Waimea Canyon 4 Volcanic glass chips Waimea Canyon Waimea Canyon 5 Volcanic glass chips Kalalau Trail North Shore #6 rock sample >5cm Porphyritic with microphenocrysts of glomeroporphyritic plagioclase; Niu Valley NIU1A rock sample >5cm Aphanitic to weakly porphyritic Wet Cave Kaua'i, N.S. 3 – 4/3/93 1cm<rock samples <5cm Waimea Canyon 4 Wet 1cm<rock samples <5cm Waimea Canyon WC-4 1cm<rock samples <5cm Waimea Canyon WC 5 1cm<rock samples <5cm Kalalau Trail #5 trail 1cm<rock samples <5cm Niu Valley  NIU-1B 1cm<rock samples <5cm Niu Valley NIU-3 1cm<rock samples <5cm Wet Cave 3A 1cm<rock samples <5cm Waimea Canyon Waimea Canyon #2 1cm<rock samples <5cm     22  Table 3.1: Summary of petrographical information for all Kaua’i dykes.  Sample location Sample Phenocryst (Modal %) Groundmass (Modal %) Other (Modal %) Name of rock Wet Cave Kaua’i 2b/No. Shore  Kalalau Trail Kalalau Trail #5  Wet Cave North Shore #3/Wet Cave   Wet Cave North Shore #4/Wet Cave   Kalalau Trail North Shore #6   Kalalau Trail Trail 7  Niu Valley Niu 1b  Niu Valley Niu 2  Niu Valley Niu 3   Waimea Canyon Waimea Canyon 2   Waimea Canyon Waimea Canyon 3   Waimea Canyon Waimea Canyon 4   Waimea Canyon Waimea Canyon 5   Kalalau Trail North Shore #6 olivine (10) plagioclase (50), olivine (5), glass (35) minor palagonite, iddingsite (~1), opaques (<1) basalt Niu Valley NIU1A olivine (29) glass, plagioclase and olivine (50) Glass (15), palagonite (5), iddingsite (~1), opaques (<1) picritic basalt   23  Table 3.1: Summary of petrographical information for all Kaua’i dykes.  Sample Location Sample Phenocryst (Modal %) Groundmass (Modal %) Other (Modal %) Name of rock Wet Cave Kaua'i, N.S. 3 – 4/3/93    basalt Waimea Canyon 4 Wet  basalt Waimea Canyon WC-4 olivine (5) aphanitic minerals (40) Glass (15), iddingsite (1), vesicles (40) basalt Waimea Canyon WC 5  minor palagonite (<1) basalt Kalalau Trail #5 trail olivine (?) aphanitic minerals (?) Glass (?) basalt Niu Valley NIU-1B olivine (?) aphanitic minerals (?)  basalt Niu Valley NIU-3 olivine (?) aphanitic minerals (?)  basalt Wet Cave 3A  vesicles (45) basalt Waimea Canyon Waimea Canyon #2  minor palagonite (<1) basalt     24 Table 3.2: Summary of major element composition for all Kaua’i dykes.  Sample Location Type SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O #5 trail Kalalau Trail Rock 44.59 9.69 1.89 0.175 19.56 6.17 1.29 0.21 North Shore #6  Rock 48.87 13.82 2.32 0.169 9.08 10.5 2.29 0.24 Kalalau trail #5  Glass 45.51 9.71 1.51 0.165 19.46 6.56 1.4 0.27 North Shore #6  Glass 48.45 13.84 2.31 0.157 8.95 9.87 2.15 0.33 Trail 7  Glass 49.06 14.03 3.46 0.163 8.29 9.93 1.87 0.36 Kaua'i, N.S. 3 – 4/3/93 Wet Cave Rock 49.95 13.8 3.45 0.175 7.93 9.98 2.11 0.34 3A  Rock 48.71 12.14 1.35 0.163 12.58 8.16 1.82 0.24 4 Wet  Rock 51.19 13.34 2.23 0.168 8.34 9.92 2.11 0.32 Kaua’i 2b  Glass 48.89 13.4 2.65 0.167 9.73 9.68 1.79 0.26 North Shore #3  Glass 51.51 13.49 0.65 0.17 8.02 10.1 2.12 0.38 North shore #4  Glass 51.73 13.41 0.9 0.168 8.38 10.1 2.11 0.39 NIU1A Niu Valley Rock 45.66 7.71 0.83 0.168 24.77 5.96 1.1 0.14 NIU-1B  Rock 45.31 7.21 1.07 0.164 26.3 5.55 1.04 0.13 NIU-3  Rock 48.27 11.5 5.09 0.155 12.63 8.27 1.64 0.21 Niu 1b  Glass 45.86 7.95 1.69 0.164 23.98 6.15 1.13 0.16 Niu 2  Glass 46.98 13.06 4.93 0.163 10.42 8.74 1.55 0.31 Niu 3  Glass 49.09 11.4 3.76 0.158 12.29 8.49 1.62 0.26 Waimea Canyon #2 Waimea Canyon Rock 48.81 11.91 5.11 0.167 10.72 9.03 1.75 0.25 WC-4  Rock 47.64 13.8 6.48 0.177 7.49 9.51 1.85 0.18 WC 5  Rock 49.85 13.72 4.76 0.162 6.46 10.3 1.96 0.35 WC2  Glass 49.94 11.95 1.28 0.166 11.16 9.32 1.83 0.35 WC3  Glass 47.78 10.79 4.66 0.168 14.21 8.38 1.47 0.27 WC4  Glass 49.68 13.13 2.3 0.168 8.63 9.98 1.86 0.32 Waimea Canyon 5  Glass 50.44 13.77 4 0.174 6.52 10.6 1.95 0.38     25 Table 3.2: Summary of major element composition for all Kaua’i dykes.  Sample Location Type TiO2 P2O5 Cr2O3 V2O5 FeO LOI Total #5 trail Kalalau Trail Rock 1.93 0.2 0.15 0.032 11.5 1.44 100.1 North Shore #6  Rock 2.75 0.28 0.09 0.055 9.6 -0.36 100.8 Kalalau trail #5  Glass 1.9 0.21 0.14 0.036 11.6 0.36 100.1 North Shore #6  Glass 2.75 0.28 0.07 0.056 9.7 0.33 100.3 Trail 7  Glass 2.76 0.27 0.07 0.052 8.2 1.08 100.5 Kaua'i, N.S. 3 – 4/3/93 Wet Cave Rock 2.35 0.25 0.06 0.052 7.8 1 100.1 3A  Rock 2.04 0.18 0.09 0.04 10.3 1.2 100.1 4 Wet  Rock 2.25 0.21 0.07 0.051 9.2 -0.06 100.4 Kaua’i 2b  Glass 2.24 0.2 0.07 0.05 9.4 0.93 100.5 North Shore #3  Glass 2.28 0.22 0.06 0.05 10.6 -0.55 100.3 North shore #4  Glass 2.24 0.22 0.07 0.05 10.4 -0.8 100.5 NIU1A Niu Valley Rock 1.25 0.11 0.2 0.031 11.3 0.2 100.6 NIU-1B  Rock 1.17 0.1 0.21 0.028 11 0 100.6 NIU-3  Rock 2.04 0.14 0.13 0.045 7.3 1.88 100.1 Niu 1b  Glass 1.31 0.12 0.19 0.033 10.5 -0.05 100.2 Niu 2  Glass 2.7 0.26 0.11 0.053 8.3 1.84 100.3 Niu 3  Glass 2.08 0.19 0.12 0.047 8.5 1.45 100.4 Waimea Canyon #2 Waimea Canyon Rock 2.29 0.22 0.11 0.047 7.2 1.99 100.4 WC-4  Rock 2.56 0.2 0.08 0.054 6.5 3.03 100.3 WC 5  Rock 2.6 0.24 0.05 0.053 7.1 2.11 100.5 WC2  Glass 2.3 0.22 0.1 0.048 10.6 0.44 100.9 WC3  Glass 2.14 0.2 0.12 0.046 8.3 1.24 100.7 WC4  Glass 2.47 0.22 0.08 0.053 9.8 0.97 100.7 Waimea Canyon 5  Glass 2.63 0.26 0.04 0.054 7.9 1.23 100.8     26 Table 3.3: Summary of trace element composition for all Kaua’i dykes (Rare Earth Elements).  Sample Location Type La Ce Pr Nd Pm Sm Eu Gd Tb #5 trail Kalalau Trail Rock 52.83 37.34 47.23 45.29  35.96 33.09 31.45 24.10 North Shore #6 ave   Rock 56.25 55.23 50.81 48.32  39.22 34.83 32.34 27.16 Kalalau trail #5  Glass 52.61 34.80 48.69 46.08  36.51 32.38 30.53 25.23 North Shore #6  Glass 57.17 51.62 52.17 50.30  39.65 38.31 34.14 28.05 Trail 7  Glass 58.66 50.40 55.25 54.15  44.35 40.96 36.63 33.83 Kaua'i, N.S. 3 – 4/3/93 Wet Cave Rock 37.22 37.90 35.57 35.82  31.01 27.45 26.28 23.41 3A  Rock 40.33 33.04 38.58 36.99  31.32 28.11 25.78 23.36 4 Wet  Rock 38.67 39.26 38.06 36.78  32.14 29.72 27.16 22.99 Kaua’i 2bave  Glass 41.65 35.85 40.24 39.96  34.46 31.94 29.77 24.58 North Shore #3  Glass 40.02 39.97 37.50 37.28  32.38 29.89 29.29 23.67 North shore #4  Glass 37.99 38.76 37.70 36.01  31.37 29.24 28.54 21.63 NIU1A Niu Valley Rock 20.36 21.40 19.56 19.64  16.81 15.68 13.45 12.37 NIU-1B  Rock 18.54 18.02 17.48 17.67  15.52 13.81 13.46 11.18 NIU-3  Rock 39.76 32.43 38.18 36.27  31.44 29.17 24.79 22.95 Niu 1b  Glass 20.37 21.23 19.56 20.23  17.84 15.01 15.04 12.55 Niu 2  Glass 54.74 53.25 49.03 47.67  38.08 34.13 29.52 24.83 Niu 3  Glass 40.13 35.90 38.58 38.43  32.50 26.39 25.04 23.32 Waimea Canyon #2 Waimea Canyon Rock 41.05 40.07 38.35 37.73  32.73 30.27 26.55 22.77 WC-4  Rock 50.82 46.69 48.49 46.56  39.17 34.89 32.85 27.29 WC 5  Rock 45.72 42.25 44.04 41.19  35.31 30.76 30.29 24.93 WC2  Glass 41.58 40.12 37.81 38.04  32.64 29.15 27.13 23.64 WC3  Glass 37.80 36.32 35.40 34.56  28.97 25.16 23.49 19.91 WC4 ave   Glass 48.95 45.15 45.54 44.58 37.09 33.82 30.21 25.83 Waimea Canyon 5  Glass 48.95 47.60 45.04 45.18  37.38 32.41 30.37 25.47     27 Table 3.3: Summary of trace element composition for all Kaua’i dykes (Rare Earth Elements).  Sample Location Type Dy Ho Er Tm Yb Lu #5 trail Kalalau Trail Rock 20.91 16.49 15.69 13.38 11.58 10.21 North Shore #6 ave   Rock 22.85 17.94 16.59 13.99 12.41 11.00 Kalalau trail #5  Glass 20.72 17.57 16.30 13.31 11.08 9.72 North Shore #6  Glass 25.23 18.06 16.73 15.02 12.94 10.94 Trail 7  Glass 27.62 22.27 19.24 18.24 14.61 12.92 Kaua'i, N.S. 3 – 4/3/93 Wet Cave Rock 19.74 16.69 15.23 13.59 11.91 11.01 3A  Rock 18.61 15.82 14.02 13.03 11.67 10.38 4 Wet  Rock 20.43 16.38 16.06 14.27 12.41 11.41 Kaua’i 2b ave  Glass 22.00 18.15 16.44 15.21 13.69 11.79 North Shore #3  Glass 21.72 18.02 15.88 14.38 11.62 11.33 North shore #4  Glass 21.96 16.69 14.99 13.93 11.98 11.68 NIU1A Niu Valley Rock 11.56 9.29 8.28 8.37 7.16 6.21 NIU-1B  Rock 10.10 8.59 7.48 7.01 6.71 5.56 NIU-3  Rock 19.79 14.83 14.20 13.73 11.51 9.31 Niu 1b  Glass 10.96 9.15 8.34 8.51 7.22 6.45 Niu 2  Glass 20.52 16.24 13.97 13.24 11.62 9.45 Niu 3  Glass 19.05 16.20 13.53 12.66 11.49 9.58 Waimea Canyon #2 Waimea Canyon Rock 20.15 15.69 14.35 14.35 11.72 10.75 WC-4  Rock 25.02 19.89 18.22 17.55 14.67 13.43 WC 5  Rock 22.74 17.58 17.21 15.50 14.23 12.10 WC2  Glass 19.60 14.97 13.17 13.45 11.34 10.58 WC3  Glass 16.21 13.49 12.83 10.38 11.05 8.84 WC4 ave  Glass 21.97 18.53 16.86 15.26 14.54 13.48 Waimea Canyon 5  Glass 21.80 19.21 17.37 15.65 13.26 12.26     28 Table 3.3: Summary of trace element composition for all Kaua’i dykes (HFSE).  Sample Location Type Li Nb Mo Cd Sn Sb Cs Hf #5 trail Kalalau Trail Rock 4.16 11.64 0.42 0.16 0.85 0.02 0.04 2.92 North Shore #6 ave  Rock 4.48 16.95 0.69 0.20 1.17 0.02 0.03 4.11 Kalalau trail #5  Glass 4.31 11.40 0.42 0.15 0.91 0.021 0.04 2.87 North Shore #6  Glass 5.65 16.21 0.60 0.24 0.81 n/d 0.05 3.96 Trail 7  Glass 5.80 17.06 0.57 0.23 0.72 n/d 0.09 4.06 Kaua'i, N.S. 3 – 4/3/93 Wet Cave Rock 9.05 12.19 0.58 0.25 0.92 0.01 0.09 3.47 3A  Rock 4.66 10.00 0.39 0.16 0.96 0.02 0.05 2.98 4 Wet  Rock 5.61 11.47 0.57 0.19 0.80 0.02 0.06 3.35 Kaua’i 2bave  Glass 5.31 11.19 0.48 0.19 1.03 0.02 0.06 3.33 North Shore #3  Glass 5.82 11.79 0.54 0.21 1.01 0.020 0.06 3.42 North shore #4  Glass 5.59 11.35 0.56 0.20 0.63 n/d 0.06 3.23 NIU1A Niu Valley Rock 3.03 6.37 0.34 0.10 0.56 0.01 0.04 1.82 NIU-1B  Rock 3.05 5.96 0.29 0.10 0.54 0.01 0.04 1.68 NIU-3  Rock 3.40 11.20 0.47 0.16 1.02 0.03 0.04 3.09 Niu 1b  Glass 3.39 6.81 0.38 0.11 0.63 n/d 0.04 1.99 Niu 2  Glass 3.74 18.12 0.58 0.22 1.12 n/d 0.06 4.12 Niu 3  Glass 3.88 11.37 0.47 0.17 0.93 n/d 0.05 3.11 Waimea Canyon #2 Waimea Canyon Rock 4.55 12.02 0.55 0.16 1.12 0.06 0.07 3.50 WC-4  Rock 4.66 14.63 0.51 0.26 1.03 0.03 0.05 4.05 WC 5  Rock 4.06 13.54 0.60 0.20 1.13 0.04 0.11 3.61 WC2  Glass 4.79 12.12 0.57 0.16 1.15 0.003 0.07 3.61 WC3  Glass 3.99 11.76 0.48 0.18 0.91 n/d 0.08 3.26 WC4 ave  Glass 4.03 14.47 0.60 0.22 1.14 0.01 0.07 3.98 Waimea Canyon 5  Glass 4.57 14.58 0.63 0.19 1.16 n/d 0.09 3.91     29 Table 3.3: Summary of trace element composition for all Kaua’i dykes (HFSE).  Sample Location Type Ta W Bi V Cr Co Ni Cu #5 trail Kalalau Trail Rock 0.70 0.18 0.01 204.90 1089.71 93.19 1078.39 95.99 North Shore #6 ave   Rock 1.04 0.67 0.01 307.78 528.49 50.67 244.96 113.49 Kalalau trail #5  Glass 0.70 0.13 0.01 198.09 1079.87 86.19 1032.89 95.43 North Shore #6  Glass 0.99 0.16 0.01 299.00 568.70 50.98 293.59 115.97 Trail 7  Glass 1.03 0.16 0.01 284.41 551.38 48.48 298.34 125.92 Kaua'i, N.S. 3 – 4/3/93 Wet Cave Rock 0.75 2.10 0.01 289.50 442.41 47.16 188.59 120.70 3A  Rock 0.63 1.94 0.00 226.08 661.80 60.15 546.87 105.17 4 Wet  Rock 0.70 1.59 0.01 277.90 502.48 48.57 175.22 125.23 Kaua’i 2bave  Glass 0.69 0.12 0.01 280.29 597.28 51.95 296.21 129.23 North Shore #3  Glass 0.72 0.14 0.01 287.62 505.22 46.72 148.53 127.97 North shore #4  Glass 0.68 0.14 0.01 278.41 503.36 47.19 164.29 125.30 NIU1A Niu Valley Rock 0.41 0.79 0.00 165.80 1229.72 100.93 1436.27 95.67 NIU-1B  Rock 0.37 0.07 0.00 152.45 1134.35 102.84 1540.67 79.58 NIU-3  Rock 0.70 0.98 0.00 258.87 682.32 63.27 606.14 83.90 Niu 1b  Glass 0.42 0.08 0.00 176.79 1563.74 97.11 1382.98 97.71 Niu 2  Glass 1.06 0.19 0.01 294.90 894.30 57.15 507.07 106.19 Niu 3  Glass 0.68 0.12 0.01 252.10 685.58 60.97 571.49 100.73 Waimea Canyon #2 Waimea Canyon Rock 0.71 0.39 0.00 261.08 844.10 59.65 407.85 107.03 WC-4  Rock 0.90 0.63 0.01 294.13 600.22 54.05 198.11 124.47 WC 5  Rock 0.82 1.60 0.01 271.26 320.26 39.63 111.88 139.48 WC2  Glass 0.71 0.14 0.00 265.94 837.02 58.22 378.56 111.86 WC3  Glass 0.70 0.12 0.01 247.98 880.60 69.33 679.80 118.99 WC4 ave  Glass 0.85 0.15 0.01 297.56 577.68 51.05 203.63 108.82 Waimea Canyon 5  Glass 0.86 0.17 0.01 300.94 335.82 42.96 102.85 139.58     30 Table 3.3: Summary of trace element composition for all Kaua’i dykes (HFSE).  Sample Location Type Zn Ga Rb Sr Zr Ba #5 trail Kalalau Trail Rock 112.53 16.35 3.82 230.37 110.78 59.16 North Shore #6 ave  Rock 108.05 22.98 3.44 361.55 154.92 70.71 Kalalau trail #5  Glass 107.63 15.97 4.30 214.35 106.82 63.31 North Shore #6  Glass 116.42 22.43 4.92 331.67 151.84 90.35 Trail 7  Glass 108.35 22.87 6.67 325.94 156.34 117.02 Kaua'i, N.S. 3 – 4/3/93 Wet Cave Rock 105.21 21.57 5.65 282.63 127.77 109.08 3A  Rock 93.69 18.19 3.44 230.15 108.81 64.02 4 Wet  Rock 99.60 21.16 5.36 286.70 125.46 70.17 Kaua’i 2b  Glass 101.44 20.17 4.03 268.55 124.00 71.86 Kaua’i 2b-dup  Glass 101.90 20.92 4.24 278.33 126.83 74.95 Kaua’i 2b-rep  Glass 103.32 20.49 4.03 267.74 123.37 71.95 Kaua’i 2bave  Glass 102.22 20.53 4.10 271.54 124.73 72.92 North Shore #3  Glass 103.57 21.39 5.27 285.11 127.51 70.83 North shore #4  Glass 98.77 20.87 5.15 277.78 124.70 66.77 NIU1A Niu Valley Rock 93.06 11.92 2.45 147.34 65.78 38.29 NIU-1B  Rock 92.48 10.72 2.15 134.31 60.20 33.19 NIU-3  Rock 97.22 18.02 3.43 239.47 113.70 61.78 Niu 1b  Glass 97.84 12.39 2.76 154.04 70.29 40.31 Niu 2  Glass 109.76 21.94 6.01 297.18 157.13 97.42 Niu 3  Glass 94.15 17.79 4.34 237.68 113.42 71.37 Waimea Canyon #2 Waimea Canyon Rock 109.03 19.51 5.31 295.80 129.28 84.99 WC-4  Rock 115.13 21.83 2.54 302.15 152.21 80.38 WC 5  Rock 97.35 20.23 6.61 298.24 139.58 99.01 WC2  Glass 116.29 19.97 5.98 297.44 132.41 89.32 WC3  Glass 110.92 17.75 4.77 265.36 120.47 136.80 WC4 ave  Glass 111.15 21.40 5.41 302.77 145.92 85.51 Waimea Canyon 5  Glass 103.64 21.76 6.77 322.25 147.02 96.32     31 Table 3.4: Summary of Pb isotopic composition for all Kaua’i dykes.  Sample Name Description Distance from Kilauea (km) 206 Pb/ 204 Pb 2SD 207 Pb/ 204 Pb 2SD 208 Pb/ 204 Pb 2SD NIU1A rock 525 18.2816 0.0006 15.4591 0.0006 37.9849 0.0016 Kaua'i, N.S. 3 – 4/3/93 rock 525 18.2944 0.0008 15.4601 0.0008 37.9827 0.0021 WC-4 rock 525 18.3528 0.0009 15.4662 0.0007 38.0231 0.0018 #5 trail rock 525 18.4375 0.0010 15.4679 0.0008 38.0839 0.0022 NIU-1B rock 525 18.2831 0.0008 15.4602 0.0007 37.9875 0.0020 Kaua’i 2b/No. Shore glass 525 18.1477 0.0013 15.4527 0.0012 37.8679 0.0032 North Shore #6 glass 525 18.4405 0.0010 15.4673 0.0007 38.1029 0.0018 Trail 7 glass 525 18.4432 0.0008 15.4679 0.0008 38.1045 0.0022 Waimea Canyon 3 glass 525 18.3200 0.0010 15.4622 0.0009 37.9970 0.0024 Waimea Canyon 5 glass 525 18.3362 0.0009 15.4637 0.0007 37.9957 0.0017 Niu 2 glass 525 18.3741 0.0009 15.4636 0.0009 38.0714 0.0024     32 4. RESULTS 4.1 Petrography North Shore # 6 is from Kalalau Trail and is comprised of massive aphanitic to weakly porphyritic basalt with 0.5-1 mm anhedral phenocrysts of olivine in holocrystalline groundmass composed of microlites of plagioclase and olivine. NIU-1A is from the Niu Valley dykes and is comprised of porphyritic picritic basalt with subhedral to euhedral equant 0.1-10 mm olivine phenocrysts set in holocrystalline groundmass. Common alteration products in both samples are iddingsite and palagonite from alteration of olivine and glass respectively. Iddingsite alterations typically occur in olivine rims of and affect a minor (1- 5%) population of olivine grains. Thin section petrography of both North Shore #6 and NIU-1A allow analyses of groundmass composition and mineral composition. North Shore #6 has abundant 0.1-0.5 mm plagioclase laths (50 vol. % modal abundance) in its groundmass along with 0.1-0.3 mm olivine microphenocrysts (10 vol. %). Typical textures of olivine include embayed texture and microphenocrysts of glomeroporphyritic plagioclase, as seen in Figure 4.1. Each glomerule comprises of olivine core surrounded by radiating plagioclase laths. The groundmass is holocrystalline with 0.1 mm anhedral to subhedral olivine, glass and simple-twinned plagioclase. NIU-1A shows strong porphyritic texture with 29 vol. % subhedral olivine phenocrysts set in a holocrystalline groundmass with microphenocrysts of plagioclase and olivine. Olivine grains range from 0.1-0.2 mm microphenocrysts to 10 mm megacrysts. Fluid and mineral inclusions are present in olivine grains. Based on hand a sample and thin section analysis, NIU-1A is classified as massive picritic basalt, and North Shore #6 is classified as massive tholeiitic basalt.   33  Figure 4.1: XPL photomicrographs of textures in NIU-1A and North Shore #6. From top left: A) Elongated megacryst of olivine, in NIU-1A. B) Embayed and resorbed olivine grains, in North Shore #6. C) Skeletal olivine rimmed by subhedral olivine, in NIU-1A. D) Plagioclase microlites surrounding a glomeroporphyroclast of plagioclase and olivine grains in North Shore #6. . E) Olivine phenocryst in NIU-1A. F) Embayed olivine grains with a mineral inclusion, in North Shore #6. 2mm 4 mm A B C D E F 0.1 mm mm 1 mm 4 mm 8 mm 0.5 mm 0.1 mm   34 4.2 Major Element 4.2.1 Silica Content Plots Total alkali-silica (TAS) plot of all rock and glass samples is reported in Figure 4.2. Dykes from all four sites have tholeiitic composition, consistent with previous major element analyses of Kaua’i shield-stage basalt by Mukhopadhyay et al. (2003) and the tholeiitic post- shield lavas reported in Garcia et al (2010). Hence all dykes have similar major element compositions as the surrounding shield-stage Waimea Canyon Series and the tholeiitic post- shield lava. All samples also show compositions ranging from tholeiitic basalt to picritic basalt according to the classification system by Le Bas et al. (1987). There are no differences between glass and rock samples composition, suggesting minimal fractional crystallization occurred. Niu Valley and Kalalau Trail dykes have the largest range of silica content out of all samples, with both sites varying from 45-50 wt. % silica content. Wet Cave samples have the overall highest silica content at 49-52 wt. %. Waimea Canyon samples has moderate to high silica content ranging from 48-51 wt. %.  The total alkali (Na2O+K2O) content for all samples ranges from 1.2-2.6 wt. % alkali content. Samples with the largest ranges of total alkali content are comprised of all Kalalau Trail (1.5-2.5 wt. %) and Niu Valley (1.2-1.9 wt. %). Waimea Canyon and Wet Cave dykes have relatively high total silica content out of all samples, with total silica content ranging from 1.8-2.4 wt. %. There appears to be a compositional gap in both silica and total alkali content at 47-48 wt. % silica content and around 1.8 wt. % total alkali content. K2O/P2O5 values are reported in Table 4.1. According to Frey et al. (1991), samples with K2O/P2O5 < 1 are shown to have undergone minor post-eruptive alteration, and the extent of post-eruptive alteration in Hawaiian basalts will likely increase with increasing age and environmental exposure. Most of the samples analysed in this study have K2O/P2O5 > 1, suggesting that they are not derived from post-eruptive alteration. Samples which had K2O/P2O5 < 1 were from Kalalau Trail (‘North Shore #6’) and Waimea Canyon (‘WC-4’); these samples likely have minor post-eruption alteration.   35   Figure 4.2: Total-Alkali Silica (TAS) diagram of dyke samples. The tholeiite/alkali division line is derived from Mcdonald and Katsura (1964).   36  Table 4.1: K2O/P2O5 ratios for Kaua’i dykes. Samples with K2O/P2O5 < 1 indicated post- eruptive alteration occurred (Frey et al., 1991) Sample Location Type K2O/P2O5 K-3-6 (#5 trail) Kalalau Trail Rock 1.05  K-2-1/North Shore #6  Rock 0.86  Kalalau trail #5  Glass 1.29 North Shore #6  Glass 1.18 Trail 7  Glass 1.33 K-3-1 (Kaua'i, N.S. 3 – 4/3/93) Wet Cave Rock 1.36 K-3-9 (3A)  Rock 1.33 K-3-2 (4 Wet)  Rock 1.52 Kaua’i 2b  Glass 1.3 North Shore #3  Glass 1.73 North shore #4  Glass 1.77 K-2-2/NIU1A Niu Valley Rock 1.27 K-3-7 (NIU-1B)  Rock 1.3 K-3-8 (NIU-3)  Rock 1.5 Niu 1b  Glass 1.33 Niu 2  Glass 1.19 Niu 3  Glass 1.37 K-3-10 (Waimea Canyon #2) Waimea Canyon Rock 0.9 WC-4  Rock 1.14 K-3-5 (WC 5)  Rock 1.46 WC2  Glass 1.59 WC3  Glass 1.35 WC4  Glass 1.45 Waimea Canyon 5  Glass 1.46    37 Silica content vs. major element oxides plots are reported in Figure 4.2. Silica content display strong positive correlations with CaO, Na2O and K2O, and in silica content plotted with MgO and Cr2O3 display strong negative correlations. Al2O3 content for all dykes vary between 7.21 wt % and 14.03 wt%. Niu Valley has the lowest Al2O3 content with values at 7.21 wt %; Kalalau Trail has the highest Al2O3 content with 14.03 wt % with the largest range of all the samples. Wet Cave and Waimea Canyon have intermediate values between Niu Valley and Kalalau Trail. CaO content varies between 5.55 wt% and 10.50 wt%, with similar trends being observed as in Al2O3. Na2O content varies between 1.04 wt% and 2.09 wt%. K2O content varied between 0.13 wt% and 0.39 wt%. Niu Valley samples have the lowest K2O content with 0.13 wt%, whilst Wet Cave have the highest K2O content at 0.39 wt%. Kalalau Trail and Waimea Canyon have intermediate values between Niu Valley and Wet Cave. MgO content varies between 6.46-26.30 wt% with Niu Valley recording the highest MgO content at 26.30 wt% and Waimea Canyon recording the lowest MgO content at 6.46 wt%. Kalalau Trail and Wet Cave plot intermediate values between Niu Valley and Waimea Canyon.  MgO vs. CaO/Al2O3 plot is reported in Figure 4.3. Plotting MgO content vs. CaO/Al2O3 ratios determines if changes in melt compositions are related to either clinopyroxene, olivine or plagioclase crystallization, as reported by Greene et al. (2010). Calculated CaO/Al2O3 ratios of dyke samples vary with values of 0.64-0.78, which are consistent with ratios derived for the tholeiitic basalts on Kaua’i by Greene et al. (2010). Most samples plotted ratios of 0.67-0.78 within a narrow range of MgO content (7.5-14 wt. %). However, several Niu Valley and Kalalau Trail samples plot as outliers: Kalalau Trail samples have lower CaO/Al2O3 (0.64-0.68) with high MgO content (20 wt. %), while Niu Valley samples have higher CaO/Al2O3 ratios (around 0.77) and the highest MgO content (24-26 wt. %).   38  Figure 4.3: Silica content vs. Al2O3, CaO, Na2O, MgO, K2O for Kaua’i dykes, separated by location (Niu Valley, Kalalau Trail, Wet Cave, and Waimea Canyon) and types of sample (rock or glass)   39  Figure 4.4: MgO content vs. CaO/Al2O3 ratio for all rock and glass samples at each dyke location.  4.2.2 MgO Content Plots  MgO plots are reported in Figure 4.4. All dyke samples plots between 6-26 wt. % MgO content, showing large variability between all dyke sample compositions. Niu Valley and Kalalau Trail samples have the widest range of MgO content, as Kalalau Trail samples had MgO content of 8-20 wt. %, and Niu Valley samples have 10-26 wt. %. Waimea Canyon have Wet Cave have relatively low MgO content with low range, recording MgO content with 6-14 wt. % and 8-13 wt. % respectively. A compositional gap is observed between MgO contents of 14-19 wt. %. These trends reflect compositions comparable to or elevated than MgO content of Koloa volcanics from previous studies by Mukhopadhyay et al. (2003) and Garcia et al. (2010). When MgO is plotted against Al2O3, CaO, Na2O and K2O, the resultant plots display negative correlations with increasing MgO content; in contrast, a positive correlation is observed when MgO is plotted against Cr2O3. Al2O3, CaO, Na2O and K2O all have similar systematic differences in relative major element oxide contents compared to MgO content; Niu Valley has the lowest CaO, Na2O and K2O contents with the largest range out of all the samples, Kalalau Trail has the highest CaO and Na2O contents with a wide range of values,   40 and Waimea Canyon and Wet Cave having similar contents as Kalalau Trail with smaller ranges. Wet Cave has the highest K2O content out of all samples with the narrowest range. Al2O3, CaO and Na2O have stronger negative correlation overall than K2O with MgO, as Waimea Canyon samples have a wider range of both MgO and K2O content. These correlations can be explained by the behaviour of MgO in mineral phases and the melt, where MgO is compatible in mafic minerals that crystallize first, thus decreasing in content in relation to other major element oxides in the melt. Conversely, Cr2O3 and MgO content increases as each major element oxide became incorporated into mafic minerals such as spinel and olivine.    41 Figure 4.5: MgO content vs. Al2O3, CaO, Na2O, MgO, K2O for Kaua’i dykes, separated by location (Niu Valley, Kalalau Trail, Wet Cave, and Waimea Canyon) and types of sample (rock or glass)   42 4.3 Trace Elements 4.3.1 Rare Earth Elements (REE) Plot The C1 chondrite normalized REE patterns for Kaua’i dyke samples are plotted using C1 chondrite values from McDonough and Sun (1995) as shown in Figure 4.5. REE plot show overall enrichment of LREE with La abundances ranging from 17.8-58.7 (4.4–13.9 ppm), with Lu abundances ranging from 5.56-13.48 (0.1–0.3 ppm). Samples from Waimea Canyon, Wet Cave, Kalalau Trail and 3 Niu Valley have La abundances between 8.8-13.9 ppm to Lu abundances of 0.3-0.4 ppm. 3 Niu Valley (NIU-1A rock, NIU-1B rock, Niu 1b glass) samples have the overall lowest REE abundances with La values of 4.3-4.8 ppm and Lu values of 0.1-0.2 ppm. Unexpected Ce depletion anomalies are observed in 3 samples from Kalalau Trail (#5 Trail glass, North Shore 6 rock, Trail 7 glass) 1 sample from Wet Cave (3A) and 1 sample from Niu Valley (Niu 3 rock), which have loss- on-ignition (LOI) values above 1 wt% except for North Shore 6, which has an LOI value 0.36 wt%. As the slope of REE patterns vary, C1 normalized (La/Yb)n ratios are calculated and plotted for a given Zr concentration on Figure 4.6. Kalalau Trail have (La/Yb)n ratios between 4.01-4.75, Wet Cave samples have between 3.04-3.44, Waimea Canyon have ratios between 3.21-3.69, and Niu Valley samples have ratios between 2.76-4.71, recording the largest range of ratios. There are distinct breaks between (La/Yb)n ratios for almost all locations.   43  Figure 4.6: C1 chondrite normalized REE plot diagram for all rock and glass samples from Kaua’i. C1 normalizing values were derived from McDonough and Sun, 1995.   44  Figure 4. 7: C1 chondrite normalized La vs. La/Yb for all Kaua’i samples, showing the relative slope values for dyke samples.  4.3.2 Extended Trace Element Diagrams  A primitive mantle normalized extended trace element is plotted for all Kaua’i samples using primitive mantle normalizing values from Sun and McDonough (1989) as shown on Figure 4.7. The same 3 samples from Niu Valley that have lower LREE abundances also showed low abundances of elements compared to Kalalau Trail, Waimea Canyon, Wet Cave and the other Niu Valley samples. All samples recorded abundances in Th (4.2-12.5), Pb (2.6-10.4), Zr (5.7-15.0) and Hf (6.0-14.5), with 1-3 samples from all sites displaying lower than expected abundances for Sr. Pb depletion and high Nb and Ta abundances in all samples was typical behaviour for ocean islands basalt (OIB) Niu Valley samples plotted overall lower mantle-normalized concentrations than all other samples.   45  Figure 4.8: Primitive mantle normalized spider diagram of all samples from Kaua’i. Normalizing values for primitive mantle came from Sun and McDonough (1989).   46 4.3.3 Nb/Y vs Zr/Y Plot Nb/Y vs. Zr/Y plot is shown for all Kaua’i samples in this study, along with Koolau samples from Frey et al. (1994) and Garcia et al. (2010), with lower and upper bounds of Iceland array defined by Fitton et al. (1997) as shown in Figure 4.8.  All Kaua’i samples have Zr/Y values between 3.9-6.2, and Nb/Y values of 0.33- 0.71, progressively increasing for all sites with increasing Zr/Y. All samples plot Nb/Y values slightly above the lower bound. Kalalau Trail samples plot the highest Nb/Y and Zr/Y ranges (0.42-0.56 and 3.9-5.0) out of all the dyke sites, with Wet Cave samples having the lowest Nb/Y and Zr/Y values (0.40-0.46 and 4.4-4.8). Niu Valley samples have the largest range out of all samples with Zr/Y values of 4.4-6.2 and Nb/Y values of 0.43-0.71. Dyke samples are comparable to abundances of Kaua’i shield stage lava samples from Garcia et al (2010). Hence Kaua’i dyke samples have similar to slightly elevated abundances of Nb to the Kaua’i shield and post-shield lavas rather than the rejuvenated volcanic Koloa Volcanics Series, which plot overall higher Nb/Y values, indicating the rejuvenated volcanism have higher concentrations of Nb compared to shield stage Kaua’i lavas. The Koolau Series lavas plot below the lower bound of the Iceland Array, with Zr/Y ratio values of 5.8-7.3 and Nb/Y ratio values of 0.36-0.52 indicating that the Koolau series are the most depleted in Nb of all of the samples. The post-shield lavas from Kaua’i have transitional values between the rejuvenated volcanism and the shield stage, indicating a progressive enrichment in Nb. In comparison with west Ka’ena ridge basalts from Greene et al. (2010), Kaua’i dykes have comparable values to the tholeiitic basalts (dark green squares) and Kaua’i shield lava from Mukhopadhyay et al. (2003).   47  Figure 4.9: Nb/Y vs. Zr/Y plot of Kaua’i dyke samples in comparison with data from previous studies of Koloa Volcanic Series (Garcia et al., 2010), Kaua’i Shield (Mukhopadhyay et al., 2003) Kaua’i Post-shield (Garcia et al., 2010) and Koolau (Frey et al., 1994). Inset: Fitton plot from Greene et al. (2010) Iceland array lower bound (LB) and upper bound (UB) were derived from Fitton et al. (1997).   48 4.3.4 MgO content vs. Trace Element MgO content is plotted against trace elements Ni, Sc and Cr for Kaua’i dyke samples, as shown on Figure 4.9. Ni concentrations of all dyke samples range from 103-1540 ppm, Cr concentrations from 320-1560 ppm, and Sc concentrations from 16.1-32.0 ppm. Ni and Cr are positively correlated with MgO content. A positive correlation is observed in all samples with no difference between rock and glass. Sc show negative correlations with increasing MgO content, with Waimea Canyon samples having the highest Sc concentrations (25.76- 33.69), followed by Wet Cave samples (26.43-32.34 ppm), Kalalau Trail (29.54-21.32 ppm) and Niu Valley (16.08-28.94 ppm).  Figure 4.10: MgO content vs. Sc, Cr, and Ni concentrations for Kaua’i dykes.    49 4.3.5 Binary Trace Elements Zr concentration is plotted against Hf, Nb, La and Th, as shown in Figure 4.10. Niu Valley samples recording the lowest Zr concentrations at 60.2 ppm and Kalalau Valley records the highest Zr concentrations at 156.3 ppm. Waimea Canyon and Wet Cave samples record moderate Zr concentrations in between the Niu Valley and Kalalau Trail concentrations. When Zr concentrations are plotted with Nb, Hf, Th and La concentrations, strong positive correlations are observed. Hf and Nb have stronger positive correlation with Zr than La and Th, with the same sequence of samples plotting increasing concentrations: Niu Valley has both the lowest and the highest values with the widest range of concentrations, and Kalalau Trail has the highest concentration. Wet Cave and Waimea Canyon have intermediate values between Niu Valley and Kalalau Trail, with Wet Cave having the smallest range of concentrations. Nb is plotted against Zr, Rb, Sr, Ce, and La to examine their behaviour when compared with increasing Nb in Figure 4.9. Nb show positive correlation between Ta, Sr, and Ce but not Rb. Nb initially positively correlated with Rb in Niu Valley samples, but show large spread with no correlations at Nb concentrations of 11.6 ppm onwards. Niu Valley has the lowest Nb concentration at 6.0 ppm and Kalalau Trail has the highest Nb at 18.1 ppm. When compared with La concentrations, Kalalau Trail record elevated La concentrations at 52.6-58.7 ppm. Niu Valley has the largest range of La and Nb concentrations at 18.5-58.7 ppm and 6.0-18.1 7 ppm respectively. Wet Cave and Waimea Canyon plot La and Nb values intermediate between Niu Valley and Kalalau Trail.   50  Figure 4.10: Binary trace element plots for all dyke samples.  Top four panels, clockwise from top left: Zr concentrations plotted against Hf, Nb, La and Th. Bottom four panels: Nb concentrations plotted against Rb, Sr, Ce, and La.   51 4.4 Pb Isotopic Composition Pb-Sr-Hf-Nd isotope composition analyses are prepared, and Pb isotope composition results are reported in this study. 208 Pb/ 204 Pb isotopic ratios are plotted against 206 Pb/ 204 Pb ratios, and 207 Pb/ 206 Pb ratios are plotted against 206 Pb/ 204 Pb; samples are divided into type of sample and by site. Radiogenic 208 Pb*/ 206 Pb* and 206 Pb/ 204 Pb ratios are plotted with distance from Kilauea. 208 Pb/ 204 Pb isotopic ratios are plotted against 206 Pb/ 204 Pb ratios to compare relative isotopic ratios of dyke samples with samples from West Kaena Ridge, South Kaua’i Swell, and shield-stage tholeiitic lava.  208 Pb/ 204 Pb ratios are 37.9-38.1 and 206 Pb/ 204 Pb ratios are 18.1-18.4, shown in Figure 4.11. Glass samples have the widest range of isotopic ratios; defining both the lowest and highest values for both 208 Pb/ 204 Pb and 206 Pb/ 204 Pb ratios. 208 Pb/ 204 Pb ratio values for glasses are 37.9-38.1, while 206 Pb/ 204 Pb ratio values are 18.1-18.4. Rock samples have moderate to high isotopic ratio values for both 208 Pb/ 204 Pb and 206 Pb/ 204 Pb, with values ranging between 18.3-18.4 for 206 Pb/ 204 Pb, and around 37.99-38.02 for 208 Pb/ 204 Pb. 207 Pb/ 204 Pb ratio values range between 15.45-15.47, with glass samples defining both the lowest and highest ratio values. Most rock samples have over a narrow range except for 2 samples from Wet Cave and Kalalau Trail, which have elevated values of 15.466 and 15.468 respectively. Wet Cave samples have the overall lowest 208 Pb/ 204 Pb isotopic ratios ranging from 37.9-38.1 and 206 Pb/ 204 Pb ratios ranging from 18.148-18.438. Kalalau Trail samples have the overall highest 208 Pb/ 204 Pb isotopic ratios, ranging 38.08-38.10 and 206 Pb/ 204 Pb ratios ranging from 18.437-18.443 as well as the narrowest range. Niu Valley and Waimea Canyon samples have values between Kalalau Trail and Wet Cave. Radiogenic 208 Pb*/ 206 Pb* and 206 Pb/ 204 Pb ratios are plotted against distance from Kilauea, considered to be the current axis of the Hawaiian mantle plume as shown in Figure 4.12. Samples plot ratios similar to and slightly higher than Kaua’i shield lavas from Mukhopadhyay et al. (2003), with a narrower range than samples from Mukhopadhyay et al (2003) and Swinnard et al (2008). 206 Pb/ 204 Pb ratios are plotted against distance from Kilauea as seen in Figure 4.6, and isotope ratios range from 18.148-18.438, with similar range of isotopic ratio as Kaua’i shield stage samples from Mukhopadhyay et al (2003).   52 206 Pb/ 204 Pb are plotted against 208 Pb/ 204 Pb for all Kaua’i dykes and compared with data from other shield stage Kaua’i lavas (Mukhopadhyay et al., 2003), South Kaua’i Swell (Swinnard et al., 2008), and West Kaena Ridge (Greene et al., 2010), shown in Figure 4.13. Kaua’i dykes plot a positive correlation between the two isotope ratios, plotting moderate to highest Pb ratios of all samples. Kaua’i dykes plot between shield lava samples from Mukhopadhyay et al. (2003), and West Kaena ridge from Greene et al. (2010) and South Kaua’i Swell from Swinnard et al. (2008). In the context of the Loa and Kea geochemical trend, samples plot straddle the Loa-Kea division line defined by Abouchami et al. (2005), indicating that Kaua’i dykes showed either transitional composition between Loa and Kea trend lavas, or define the boundary between Loa and Kea trends. Dyke sample ratio values are comparable with samples from West Kaena Ridge that had low 206 Pb/ 204 Pb and 208 Pb/ 204 Pb ratio values.  Figure 4.11: 208 Pb/ 204 Pb vs. 206 Pb/ 204 Pb ratios and 207 Pb/ 206 Pb vs. 206 Pb/ 204 Pb ratios plots arranges by type of sample and by site. Note the error bars are smaller than symbols, and correspond to 2 standard deviations.   53 Figure 4.12: 208 Pb*/ 204 Pb* vs. distance from Kilauea comparing Kaua’i dykes with previously published data. Note the error bars are smaller than the symbols, and correspond to 2 standard deviations.   54 Figure 4.12 continued: 206 Pb/ 204 Pb vs. distance from Kilauea comparing Kaua’i dykes with previously published data. Note the error bars are smaller than the symbols, and correspond to 2 standard deviations.     55  Figure 4.13: 208 Pb/ 204 Pb vs. 206 Pb/ 204 Pb ratio plots comparing dyke sample compositions with shield stage lava (Mukhopadhyay et al., 2003), South Kaua’i Swell (Swinnard et al., 2008), and West Kaena Ridge (Greene et al., 2010). Note the error bars are smaller than the symbols, and correspond to 2 standard deviations.  5. DISCUSSION 5.1. Spatial Variability in Major and Trace Element Compositions of Dykes   The dykes analyzed are characterized according to their sampling location to examine distinct variations in major elements and trace elements. The comparison of individual site (Kalalau Trail, Wet Cave, Niu Valley and Waimea Canyon) reveals distinct trends in the geochemical signature of dykes at each location. There are no differences observed between glass and rock samples, suggesting that even before the lava extruded to the surface to form   56 basalt or quenched to form glass, compositional variations are pre-determined in the mantle plume. All dykes are tholeiitic, as seen in Figure 5.1, with low total alkali content (1.2-2.6 wt%); this suggest lava trapped in these dykes are likely erupted as part of the shield building stage of the island of Kaua’i (Garcia et al., 2010). Most Waimea Canyon and Wet Cave samples show silica contents >51 wt%, suggesting these dykes have high silica basalts, while Niu Valley and Kalalau Trail plot lower silica contents, similar to silica content of transitional and rejuvenated lavas analyzed by Greene et al. (2010). Some dykes plott close to the alkali-tholeiitic divide, suggesting a slight trend towards transitional compositions.  Figure 5.1: Total-Alkali Silica (TAS) diagram of dyke samples, with tholeiitic and alkali composition fields labelled. The tholeiite/alkali division line was derived from Mcdonald and Katsura (1964).  As seen in Figure 5.2, Waimea Canyon and Wet Cave have relatively low MgO and Cr2O3 content compared to Kalalau Trail and Niu Valley dykes, which have the highest MgO and Cr2O3 contents out of all sites. The strong inverse correlation observed in silica content and MgO and Cr2O3 contents can be accounted by crystallization of Cr-spinel and Mg-rich Tholeiitic Alkalic   57 olivine, as confirmed by petrographical observation: olivine is the dominant phenocryst in Niu Valley sample ‘NIU-1A’. The relative enrichment and depletion trends observed in total alkali content are also reflected in other major element oxides. Niu Valley and Kalalau Trail record low CaO, Na2O and K2O content, whereas Wet Cave and Waimea Canyon both record higher concentrations. These observations are consistent with petrographical observations that abundant plagioclase microphenocrysts and phenocrysts are present in the Kalalau Trail sample ‘North Shore #6’. As silica content increase during mafic mineral formation, major element oxides such as MgO and Cr2O3 become incorporated into mafic mineral structure, and CaO, Na2O and K2O become incorporated in phases such as plagioclase. The difference in the relative major element composition and subsequent crystallization of different minerals suggest that the magma feeding dykes in Kalalau Trails are more evolved melts than the magma feeding dykes in Niu Valley.  Figure 5.2: silica content vs. MgO content of Kaua’i dykes indicating trends observed when minerals crystallize from the melt. Olivine crystallization   58   Figure 5.2 continued: silica content vs. Cr2O3 content of Kaua’i dykes indicating trends observed when minerals crystallize from the melt.  Evidence of specific phase crystallization such as olivine is corroborated with trends observed in MgO content vs. CaO/Al2O3 ratio, as seen in Figure 5.3. High CaO/Al2O3 ratio values indicate plagioclase crystallization, whereas ratio values correlated with low MgO content indicate olivine accumulation. Both Waimea Canyon and Wet Cave samples have high CaO/Al2O3 ratios with low MgO content, whereas Niu Valley have a range of extremely high to low MgO content with low CaO/Al2O3 ratios (<1), indicating progressive olivine accumulation. Kalalau Trail has both low CaO/Al2O3 ratios and low MgO content, which suggests more evolved melt where olivine crystallized. The high CaO/Al2O3 ratios coupled with low silica content indicate partial melting of depleted peridotite source than a fertile one, consistent with findings by Mukhopadhyay et al. (2003). Cr-spinel crystallization   59  Figure 5.3: MgO content vs. CaO/Al2O3 ratio of Kaua’i dykes indicating direction of trends observed when minerals olivine (ol), plagioclase (plg) and clinopyroxene (cpx) crystallize from the melt.  Both REE and extended trace element diagrams reported in Figure 5.4 reveal patterns typical of ocean island basalts. REE patterns are typical of ocean island tholeiites, with slight enrichment in LREE compared to HREE, and a gentle slope <10 and low (La/Yb ratios) gradient. Kalalau Trail samples have the steepest slope with the widest range of gradients indicating that Kalalau Trail is likely transitional lavas. Most samples from Waimea Canyon, Wet Cave, and Niu Valley plot REE trends with gentle gradients of around 4-5.The overall shape of the trace element patterns in primitive mantle normalized diagrams are typical of ocean island basalts with a broad hump characterized by enrichment of increasingly incompatible LIL and HFS elements, reflecting formation by a single stage process from partial melting of peridotite source concentrating incompatible elements (Winter, 2001). Overall depletion of Pb in all dyke samples is observed, which is typical of ocean island basalts geochemical signature. Niu Valley samples have mostly relatively lower trace element abundances, but with a large range such that these samples have both the highest and Plg Ol Cpx   60 lowest trace element abundances. Kalalau Trail, Waimea Canyon and Wet Cave samples have more homogeneous values to each other with limited variation in abundances. Kaua’i samples, all of them tholeiitic, have overall lower abundances of elements compared to Koloa Volcanics and alkali post-shield basalts, but have similar to lower ranges of abundances with shield and tholeiitic post-shield. Figure 5.4: REE diagrams showing characteristic patterns of ocean island basalts, observed in the gentle slope and slight enrichment in LREE relative to HREE.   61   Figure 5.4 continued: REE and extended trace element diagrams showing characteristic patterns of ocean island basalts, with the characteristic ‘hump’ typical of ocean island basalts due to enrichment in LIL and HFS elements. Arrows indicate relative enrichment direction.  5.2. Trace Element Variations of Dykes: Implications on Mineral Chemistry As seen in Figure 5.5, trace element variation in Kaua’i dykes show trends which are controlled by the relative compatibilities of the The overall strong inverse correlation observed between Zr, a HFSE and incompatible element, and Ni indicate that Ni is incorporated into olivine’s mineral structure for all dykes. Niu Valley has the highest Ni concentrations and the lowest Zr concentrations, indicating that there is abundant olivine accumulation. Conversely Waimea Canyon has the highest Zr concentration and lowest Ni, suggesting that dykes have low olivine accumulation, and is likely composed of higher proportions of residual melt than mineral phases. Wet Cave and Kalalau Trail are comparable to Waimea Canyons. Cr is not as strongly correlated with Zr, suggesting there is evidence   62 that Cr incorporated into Cr-spinel and that Cr-spinel is not abundant in dykes. According to Mukhopadhyay et al. (2003), clinopyroxene crystallization could have occurred, however evidence against clinopyroxene crystallizing come from the inverse correlation observed between Sc and MgO content. Inversely, when Zr or Nb is compared with similarly incompatible elements such as Hf and Ta, the strong positive correlation indicate that both Zr and Nb were concentrated into the residual melt after mineral crystallization. Both Waimea Canyon and Wet Cave dykes are strongly correlated with relatively high concentrations of all incompatible elements (Zr, Nb, Hf, Ta) indicating that a higher proportion of residual melt after phase crystallization, whereas Niu Valley and Kalalau Trail dykes have lower concentrations of incompatible elements, with a higher proportions of mineral phases than residual melt prior to eruption. Figure 5.5: Binary trace element diagram of Zr vs. Cr and Ni showing negative correlation due to incorporation of Ni and Cr into olivine and Cr-spinel respectively. MgO content vs. Sc shows negative correlation due to low clinopyroxene formation.  Olivine crystallization Cr-spinel crystallization   63  5.3. Dyke Pb Isotopic Composition and the Loa Geochemical trend  An important goal of this study is to address whether dykes on western Kaua’i sampled Loa type magma, and that the Loa trend can be extended past Oahu up to 5 Ma, as seen in Figure 5.6 and Figure 5.7.  In comparison with previous Kaua’i studies in Figure 5.6, the dykes have more radiogenic 206 Pb/ 204Pb than the shield lavas from the Ha’upu Tunnel (Garcia et al., 2010), West Kaena Ridge (Greene et al., 2010) but overlap with shield lavas of Mukhopadhyay et al. (2003) that also have lower 208 Pb/ 204 Pb values, which reflect differences in the accuracy of analyses using thermal ionization mass spectrometer; for this study MC-ICP-MS is  used for analyses. Comparison between Kaua’i dykes and eastern shield stage Kaua’i lavas reveals systematic differences in Pb isotope composition. Kaua’i dykes have systematically higher 206 Pb/ 204 Pb and 208 Pb/ 204Pb ratios than Ha’upu ridge samples analysed by Garcia et al. (2010), but lower radiogenic 208 Pb*/ 206 Pb* ratios, indicating that there is a systematic increase in radiogenic 208 Pb*/ 206 Pb* from west to east, but a systematic increase from east to west in 206 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios. These observations are consistent with findings of systematic east-west differences from Garcia et al. (2010). Another implication is that Loa trend magmatism has been present in the plume at around 4.3 Ma, rather than appearing at around 3 Ma as proposed by Abouchami et al. (2005).  By examining trends in Pb composition, small-scale heterogeneities in the Hawaiian mantle plume can be inferred. Firstly, by comparing 206 Pb/ 204 Pb with 208 Pb/ 204 Pb ratios as seen in Figure 5.7, dyke samples straddles the Loa/Kea division line proposed by Abouchami et al. (2005) forming Pb-Pb trend with compositions in the range of Loa trend magmatism. The linear trend also suggests the array of Pb isotopic compositions correspond a mixing line from two distinct small heterogeneities in the mantle plume.  Additionally when comparing radiogenic 208 Pb*/ 206 Pb* ratios, most samples plot 208 Pb*/ 206 Pb* = 0.94-95, thus straddling along the transition between Kea-Loa magmatism. As radiogenic 208 Pb*/ 206 Pb* ratio enable tracking of time-integrated evolution of 232 Th/ 238 U over Earth’s history according to Abouchami et al. (2005), subtle increase in radiogenic 208 Pb*/ 206 Pb* ratio observed over geographical distance from the axis of the plume at Kilauea   64 indicate that Loa trend magmatism not only vary over time, but is observed to be at its lowest at the time these dykes are formed, such that the Pb compositions overlap the boundary with with Kea trend magmatism. However to determine whether Loa enriched characteristics are present in Kaua’i dykes, it will take integration of other radiogenic isotope data (Sr-Nd-Hf) to fully characterize these dykes and infer characteristics of the source region In terms of inferring large-scale heterogeneities in the mantle plume, Kaua’i dyke samples plot values similar to Mauna Loa samples (Weis et al., 2011). Kaua’i dykes plot comparable Pb-Pb comparable to those formed by other Loa trend volcanoes.    Figure 5.6: 206 Pb/ 204 Pb and 208 Pb/ 204Pb graph showing the position of Kaua’i dykes relative samples from previous studies by Mukhopadhyay et al. (2003), Garcia et al. (2010) and Greene et al. (2010)   65   Figure 5.7: Radiogenic 208 Pb*/ 206 Pb* correlated with distance from Kilauea, the present location of mantle plume axis showing all analyses of Hawaiian ocean island basalts up to date. Kaua’i dyke samples are circled. Studies included are Pietruszka and Garcia (1999), Mukhopadhyay et al. (2003), Eisele et al. (2003), Coombs et al. (2004), Abouchami et al. (2005), Yamasaki et al. (2005), Xu et al. (2005), Gaffney et al. (2004, 2005), Kimura et al. (2006), Marske et al. (2007), Tanaka et al. (2007), Hanano et al. (2010), Huang et al. (2009), Fekiacova et al. (2005, 2007), Ren et al. (2006, 2009), Dixon et al. (2008), Garcia et al. (2010), Weis et al. (2011).   66  6. CONCLUSION  The aim of this study is to characterize major and trace element geochemistry of rock and glass samples collected from dykes on western Kaua’i in selected sites (Kalalau Trail, Waimea Canyon, Niu Valley and Wet Cave) to determine whether differences exist between each dyke location and to infer magmatic processes producing the geochemical variations observed. As well, this study is aimed to determine if the dykes belong to either Loa or Kea geochemical trend. Implications of Pb isotopic composition results determined whether the Loa geochemical trend has been sampled by volcanism on Kaua’i at 4-5.1 Ma, meaning that the time-dependent primitive Loa trend is older than previously thought. Major findings from the study are as followed: 1. Dykes on western Kaua’i are composed of tholeiitic basalt and picritic basalt with variable degrees of glass content. Olivine is the dominant phenocryst and microphenocryst in the picritic basalt from Niu Valley and the tholeiitic basalt from Kalalau Trail, and plagioclase is present as microphenocrysts in the tholeiitic basalt from Kalalau Trail. From crosscutting relationships, dykes on western Kaua’i likely intruded into the Waimea Canyon shield basalts in 4.35-4.43 Ma, further supporting the evidence of rapid growth in Kaua’i’s shield-stage volcanism. 2. Major element variations on Kaua’i’s dykes indicate systematic variation in dykes from each site, with Kalalau Trail and Niu Valley both recording relatively high MgO and Cr2O3 content, with lower CaO, K2O and Na2O content whilst Waimea Canyon and Wet Cave dykes show the opposite characteristics. These observations indicate evidence of major element partitioning into specific mineral phase crystallization such as MgO in olivine, Cr2O3 in Cr-spinel, and CaO, K2O and Na2O in plagioclase. 3. Trace element trends observed in Kaua’i’s dykes suggest typical geochemical signature of ocean island basalts, with typical enrichments in HFS and LIL elements, reflecting partial melting of a depleted peridotite source lithology. 4. Pb isotope systematics of dyke samples plot in the field of Loa trend magmatism and straddle along the line or slightly above the Loa-Kea division line. Radiogenic   67 208 Pb*/ 206 Pb* indicate similar trends observed in 206 Pb/ 204 Pb with 208 Pb/ 204 Pb slopes. Comparison of radiogenic 208 Pb*/ 206 Pb* with distance from Kilauea indicate a progressive increase in 208 Pb*/ 206 Pb* and that Kaua’i dykes plot the lowest ratios out of all the Loa trend lavas, such that it overlap partly with Kea trend magmatism. Comparison with a previous study by Garcia et al. (2010) indicates higher radiogenic 206 Pb/ 204Pb than Ha’upu Tunnel samples. Findings from this study will complement ongoing research in mantle dynamics and the Hawaiian mantle plume composition and structure. Further work stemming from this study will include Sr-Nd-Hf isotopic analyses to characterize dykes’ source region, determining Ar-Ar geochronology of dykes from fluid inclusions in olivine grains and correlating Kaua’i dyke data with samples from the Hawaiian Ridge to find the initiation point of Loa trend magmatism.   68 7. 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Glass Samples  Sample Name  Sample photo Kaua’i 2b/No. Shore  Kalalau Trail #5  North Shore #3/Wet Cave  North Shore #4/Wet Cave  North Shore #6    79 Sample Name  Sample photo Trail 7  Niu 1b  Niu 2  Niu 3  Waimea Canyon 2    80 Sample Name  Sample photo Waimea Canyon 3  Waimea Canyon 4  Waimea Canyon 5       81 3. Thin Section  Sample Information Sample Photo Name: NIU-1A Location: Niu Valley, Kaua’i Dimensions: 46 mm x 26 mm Sample Information: Plane polarized light. Notes: Collected by Dr. Michael Garcia on April 1994     82 Sample Information Sample Photo Name: NIU-1A Location: Niu Valley, Kaua’i Dimensions: 46 mm x 26 mm Sample Information: Cross polarized light. Notes: Collected by Dr. Michael Garcia on April 1994     83 Sample Information Sample Photo Name: North Shore #6 Location: Kalalau Trail, Kaua’i Dimensions: 46 mm x 26 mm Sample Information: Plane polarized light. Notes: Collected by Dr. Michael Garcia on April 1994     84 Sample Information Sample Photo Name: North Shore #6 Location: Kalalau Trail, Kaua’i Dimensions: 46 mm x 26 mm Sample Information: Plane polarized light. Notes: Collected by Dr. Michael Garcia on April 1994   

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