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Flood basalts from Mt. Capitole in the central Kerguelen Archipelago: insights into the growth of the.. Weis, Dominique 2011

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Flood basalts from Mt. Capitole in the central Kerguelen Archipelago: Insights into the growth of the archipelago and source components contributing to plume-related volcanism Guangping Xu and Frederick A. Frey Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (gpxu@mit.edu) Dominique Weis and James S. Scoates Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, Canada V6T 1Z4 André Giret Laboratoire de Géologie-Petrologie, Université Jean Monnet, CNRS-UMR 6524, 23 Rue du Docteur Paul Michelon, F-42023 Saint-Étienne, France [1] The Kerguelen Archipelago, constructed on the submarine Northern Kerguelen Plateau, is attributed to Cenozoic volcanism arising from the Kerguelen hot spot. Geochemical studies of 325 to 1000 m thick lava sections of the 30 to 25 Ma flood basalt forming the bulk of the archipelago show a temporal change from older tholeiitic basalt to younger slightly alkalic basalt. This compositional transition is expressed in a 630 m lava section at Mt. Capitole where the lava sequence is lowermost tholeiitic basalt overlain by slightly alkalic basalt overlain by plagioclase-rich cumulates that are mixtures of plagioclase-phyric basalt and more evolved magmas. During growth of the archipelago, magma supply from the hot spot was variable and at times sufficiently low to enable extensive crystal fractionation; e.g., at Mt. Capitole and nearby Mt. Tourmente only 10 of 120 lava flows have >6 wt% MgO. On the basis of this study and previous isotopic data for the 34 Ma submarine lavas erupted on the Northern Kerguelen Plateau, other flood basalt sections in the Kerguelen Archipelago, and younger lavas erupted in the archipelago and at Heard Island, there is significant Sr, Nd, Hf, and Pb isotopic heterogeneity that can be explained by two stages of mixing. The first mixing event, best shown by the submarine lavas, is between components that are related to Indian Ocean mid-ocean ridge basalt (MORB) and the Kerguelen hot spot. From 34 Ma to <1 Ma, on average the proportion of the MORB-related component decreased. Subsequently, a second mixing process involved addition of a component with relatively high 87Sr/86Sr (>0.7060) and low 143Nd/144Nd (<0.5125) and 176Hf/177Hf (<0.2827) and nonradiogenic Pb isotope ratios (<17.9 for 206Pb/204Pb). We infer that this component was lower continental crust. Components: 21,781 words, 17 figures, 10 tables. Keywords: Kerguelen mantle plume; Kerguelen Archipelago; Mt. Capitole; lower continental crust; Sr; Nd; Hf; Pb isotopic ratios. Index Terms: 1037 Geochemistry: Magma genesis and partial melting (3619); 1038 Geochemistry: Mantle processes (3621); 1065 Geochemistry: Major and trace element geochemistry. Received 13 February 2007; Accepted 15 March 2007; Published 12 June 2007. G3GeochemistryGeophysicsGeosystems Published by AGU and the Geochemical Society AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Article Volume 8, Number 6 12 June 2007 Q06007, doi:10.1029/2007GC001608 ISSN: 1525-2027 Copyright 2007 by the American Geophysical Union 1 of 34 Xu, G., F. A. Frey, D. Weis, J. S. Scoates, and A. Giret (2007), Flood basalts from Mt. Capitole in the central Kerguelen Archipelago: Insights into the growth of the archipelago and source components contributing to plume-related volcanism, Geochem. Geophys. Geosyst., 8, Q06007, doi:10.1029/2007GC001608. 1. Introduction [2] The Kerguelen hot spot has produced 15 to 24 106 km3 of basaltic magma over 120 My [Coffin and Eldholm, 1994; Coffin et al., 2002]. This long volcanic record includes a large igneous province (Kerguelen Plateau-Broken Ridge), a hot spot track (the >5000 km long 82–38 Ma Ninetyeast Ridge), and the recently active islands (Kerguelen Archipel- ago, McDonald and Heard Islands) [e.g., Wallace et al., 2002]. Determination of spatial and temporal variations in geochemical characteristics of the basalt forming the Kerguelen Plateau, Ninetyeast Ridge and Kerguelen Archipelago are essential for understand- ing the history of the Kerguelen hot spot. The early, dominantly Cretaceous, volcanic activity of the Ker- guelen hot spot is recorded in basalt recovered from the Kerguelen Plateau and Broken-Ridge by the Ocean Drilling Program (Legs 119, 120 and 183). Studies of these drill cores show a complex record of varying magma production rates [Coffin et al., 2002] and changes in the relative proportions of magma source components, including mantle plume, mid- ocean ridge basalt (MORB) and continental-related components [e.g., Mahoney et al., 1995; Frey et al., 2002b; Ingle et al., 2002; Kieffer et al., 2002; Neal et al., 2002; Weis and Frey, 2002; Frey et al., 2003]. [3 ] The Cenozoic Kerguelen Archipelago (6500 km2) formed on the Northern Kerguelen Pla- teau (Figure 1). The archipelago has a history of volcanism from 30 to 0.1 Ma that is interpreted as magmatism resulting from the stem of the Kerguelen mantle plume [e.g., Weis et al., 1993; Nicolaysen et al., 2000]. Unlike the submarine Kerguelen Plateau and Ninetyeast Ridge, the Kerguelen Archipelago is currently a subaerial expression of the Kerguelen hot spot that can be studied in detail. The archipelago is largely, 85% of the surface, formed of flood basalt ranging from 28–29 Ma tholeiitic basalt in the northwest (Mts des Ruches, Fontaine, Bureau and Rabouillère) to 24–26 Ma alkalic basalt in the east (Mt. Crozier and sections at Ravin Jaune and du Charbon) (Figure 1). A transition from tholeiitic to alkalic volcanism occurs in flood basalt sections from the Plateau Central. For example, at Mt. Tourmente (Figure 1), a 597 m section of lava flows ranges from 26 Ma transitional basalt (i.e., near the tholeiitic- alkalic boundary line on a total alkalis versus SiO2 plot) in the lower 80% of the section to overlying 25.3 Ma alkalic basalt in the upper 20% of the section. In contrast, at Mt. Marion Dufresne, also in the Plateau Central (Figure 1), the lowermost lavas in a 700 m section are alkalic basalt and the lavas become less alkaline upward in the section [Annell et al., 2007]. If tholeiitic basalt reflects higher magma flux than alkalic basalt, as commonly inferred, the temporal variations in magma flux were different at Mts Tourmente and Marion Dufresne. [4] With the objective of understanding fluctua- tions in magma flux arising from the Kerguelen hot spot, we studied a 630 m lava section from Mt. Capitole at an intermediate location on the Plateau Central (Figure 1). We find an upward, i.e., de- creasing age, change from slightly tholeiitic to slightly alkalic basalt in the Mt. Capitole section, but the uppermost plagioclase-phyric lavas reflect a plagioclase accumulation process similar to that forming plagioclase-phyric to -ultraphyric basalt at Mt. Marion Dufresne [Annell et al., 2007]. The accumulation of plagioclase phenocrysts in sub- groups of lavas at Mts Capitole and Marion Dufresne provide further evidence for periods of reduced basaltic magma flux from the hot spot. [5] An important result is that isotopic data for Sr, Nd, Hf and Pb for Mt. Capitole lavas combined with previously published isotopic data for other archipelago lavas can be explained by mixing between three components. First mixing between a component, such as mid-ocean ridge basalt or its source, with relatively low 87Sr/86Sr, high 143Nd/144Nd and 176Hf/177Hf and intermediate 206Pb/204Pb, with a plume-related component with intermediate 87Sr/86Sr, 143Nd/144Nd and 176Hf/177Hf and high 206Pb/204Pb, 18.5, followed by addition of a component with high 87Sr/86Sr, low 143Nd/144Nd and 176Hf/177Hf and quite low 206Pb/204Pb (<18). This last component is isotopi- cally similar to some lower continental crust. 2. Geology [6] Mt. Capitole in the central part of the Kergue- len Archipelago, near the eastern edge of the Cook Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 2 of 34 ice cap (Figure 1), has a NE–SWorientation and is asymmetric with average slopes of 32 for the western flank and 18 for the eastern flank. It is cut by basaltic dikes with east–west orientation. In this region of the glaciated plateau, it is not possible to identify individual volcanic centers. [7] Fifty-five samples from distinct basalt flows were collected on a westward traverse from the summit (sample 93–459) with an altitude of 860 m to the Vallée des Merveilles, an altitude of 230 m (sample 93–514); intercalated within the basalt flows are sedimentary breccias and conglomerates which indicate temporal breaks in eruption (Figure 2). For example, there is a 4 m thick breccia with angular pebbles of basalt located at 700 m (be- tween samples 93–473 and 93–474), a 0.2 m thick red bed consisting of basaltic pebbles in a red matrix located at 670 m (between samples 93– 477 and 93–478), and a 1.5 m thick breccia at 565 m (between samples 93–485 and 93–486). No age information is available but we assume that the Mt. Capitole section formed at 25 Ma, i.e., similar to the age of lavas from Mts Tourmente [Nicolaysen et al., 2000] and Marion Dufresne [Annell et al., 2004]. 3. Analytical Techniques [8] Ten samples, mostly plagioclase-phyric, were chosen for analyses of phenocrysts, xenocrysts and amphibole inclusions within plagioclase (Table 1). Olivine, plagioclase, clinopyroxene and amphibole Figure 1. Map of the Kerguelen Archipelago [after Yang et al., 1998] showing the major geologic units, the location of studied stratigraphic sections of flood basalt, and Mt. Ross, which is the youngest volcanic edifice in the archipelago. Mt. Capitole (red dot) is in the Plateau Central. Ages for these sections are from Weis et al. [1993, 1998], Nicolaysen et al. [2000], Doucet et al. [2002], and Annell et al. [2004]. Inset is a map showing the Southeast Indian Ocean Ridge (SEIR), the Kerguelen Plateau, forming a Cretaceous large igneous province, and the Cenozoic Kerguelen Archipelago and Heard Islands located on the Northern and Central Kerguelen Plateau, respectively. Filled stars show Kerguelen Plateau drill sites discussed in the text (Site 738, Mahoney et al. [1995]; Site 747, Frey et al. [2002b]; Site 1137, Ingle et al. [2002]; Site 1140, Weis and Frey [2002]). Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 3 of 34 were analyzed with the 4-spectrometer JEOL 733 microprobe at Massachusetts Institute of Technol- ogy, using 15 kV accelerating voltage, 10 nA beam current and a beam size of 1 mm (10 mm for plagioclase). The counting time was 40 seconds for all elements except for Ca and Al (30 seconds) and Na (5 seconds) in plagioclase; Na was counted for 15 seconds for pyroxene and amphibole. Anal- yses of plagioclase, pyroxene, olivine and amphi- bole are in Tables 2a–2d. [9] For whole rock analyses, samples were abraded with sand-paper to remove surficial alteration fea- tures and contaminants introduced by sawing. Then they were coarse-crushed in a hydraulic piston crusher and reduced to powder in an agate shatter- box. Major element and some trace element (such as Cr, Ni and V) concentrations were determined by X-ray fluorescence spectrometry at the Univer- sity of Massachusetts, Amherst (Tables 3 and 4). Major element compositions are reported as the mean of duplicate analyses and loss on ignition (LOI) is the weight loss after heating 10 min at 1020C using Pt-Au crucibles. Estimates of accu- racy and precision were discussed by Rhodes [1996]. Most trace element abundances (Table 4) were determined at MIT by inductively coupled plasma mass spectrometry using a Fisons VG Plasmaquad 2 + S with both internal and external drift monitors. The relative standard deviation for all trace elements determined in BHVO-2 (15 analyses, Table 4) is less than 3% [Huang and Frey, 2003]. Scandium was determined by instrumental neutron activation analysis in 21 Figure 2. Location of studied samples (black horizons with sample numbers) in the Mt. Capitole section. The base is at 691705100E and 491903200S, and the summit is at 691900000E and 491905100S. The vertical exaggeration is a factor of 5. The open regions indicate no outcrop or extremely weathered rocks. Samples with elevation greater than 690 m form the Upper Transitional Group, which is defined on the basis of petrography (Table 1) and lava compositions. Sample 93–491, lower in the section, has the characteristics of this group. The Low-Silica Group lavas from 660 m to 560 m have relatively low SiO2/Fe2O3* (Fe2O3* is total iron). All other lavas belong to the Lower Transitional Group. Also shown are layers of sedimentary breccias and conglomerates, such as a 4 m thick breccia with angular pebbles of basalt at 700 m, a 0.2 m thick red matrix containing basaltic pebbles at 670 m, and a 1.5 m thick breccia at 565 m. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 4 of 34 Table 1. Petrographic Characteristics of Mt. Capitole Samples Group Sample Height, ma Phenocryst/Xenocryst,b volume% Upper Transitional Group (UTG)d 93–459c 860 40% plagioclase 93–460 840 35% plagioclase 93–461 840 25% plagioclase 93–462 825 20% plagioclase and <1% augite 93–463 815 3% plagioclase 93–464 810 <1% plagioclase 93–465 800 25% plagioclase 93–467 780 none 93–468 760 2% plagioclase 93–469 750 5% plagioclase 93–470 740 15% plagioclase 93–471 735 10% plagioclase 93–472 730 2% olivine, 1% augite and 5% plagioclase 93–473 715 40% plagioclase 93–474 690 15% plagioclase Lower Transitional Groupd 93–475 690 2% plagioclase 93–476 685 2% plagioclase 93–477 680 10% plagioclase Low-Silica Groupd 93–478 660 3% plagioclase 93–479 640 None 93–480 630 None 93–481 610 <1% plagioclase 93–482 600 <1% plagioclase 93–483 590 <1% plagioclase 93–484 580 12% plagioclase and 3% augite 93–485 570 93–486 560 18% plagioclase and 2% augite Lower Transitional Groupd 93–487 560 <1% plagioclase 93–488 550 10% plagioclase 93–489 540 15% plagioclase 93–490 540 <1% plagioclase and augite UTGd 93–491 540 25% plagioclase and 15% augite Lower Transitional Groupd 93–492 540 15% plagioclase 93–493 530 <1% plagioclase and augite 93–494 520 <1% plagioclase and augite 93–495 510 <1% plagioclase 93–496 505 <1% plagioclase 93–497 490 <1% plagioclase 93–498 480 <1% plagioclase 93–499 470 <1% plagioclase and augite 93–500 465 <1% plagioclase and augite 93–501 455 <1% plagioclase 93–502 440 none 93–503 435 <1% plagioclase 93–504 430 <1% plagioclase 93–505 420 <1% plagioclase 93–506 410 <1% plagioclase 93–507 400 <1% plagioclase 93–508 390 none 93–509 380 none 93–510 350 <1% plagioclase and augite 93–511 310 <1% plagioclase 93–512 270 none 93–513 250 none 93–514 230 <1% plagioclase Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 5 of 34 samples, following the procedures of Ila and Frey [2000] (Table 4). [10] Eighteen relatively fresh samples with mini- mum alteration were chosen for Sr, Nd, Hf and Pb isotopic analyses at the Pacific Centre for Isotopic and Geochemical Research at the University of British Columbia (UBC). Prior to isotopic analysis of Sr, Nd and Pb the samples were leached repeat- edly in an ultrasonic bath with 6N HCl following the procedure described by Weis et al. [2005]. Analysis of leached and unleached aliquots for sample 93–465 shows that leaching resulted in residues with slightly higher 143Nd/144Nd and distinctly lower 87Sr/86Sr and Pb isotopic ratios (Table 5). At UBC Sr and Nd isotopic ratios were determined using a thermal ionization mass spectrometer (Triton) and Pb isotopic ratios were determined using a multiple-collector ICP-MS (Nu021) [Weis et al., 2005, 2006]. Normalization procedures and data for standards are in the foot- notes for Table 5. [11] About 200 mg of unleached rock powder was dissolved for Hf isotopic analyses, following the procedure of Blichert-Toft et al. [1997]. The Hf isotopic compositions were measured by MC-ICP- MS (Nu021) at UBC. The 176Hf/177Hf ratios are normalized to the Hf JMC 475 in-house standard value of 0.282160 [Blichert-Toft et al., 1997]. Exter- nal reproducibility based on three duplicates is within in-run uncertainties, i.e., <6  106 (Table 5). [12] For Sr and Pb isotopic analyses, plagioclase grains with relatively few inclusions were picked from two samples, 93–459 and 93–471, using a binocular microscope. Leaching procedures fol- lowed those of Housh and Bowring [1991]: grains were leached using 7N HNO3 for 30 min on a hotplate (125C); the residue was rinsed with Milli-Q H2O, leached by 6N HCl on a hotplate for 30 min and rinsed with Milli-Q H2O; this residue was leached with 5% HF + 0.5N HBr (8:1) for 10 min on a hotplate stirring every 2 min followed by rinsing twice with Milli-Q H2O. This last step was repeated until the sample was white with no visible black inclusions. The final residue was dissolved by concentrated HF and 7N HNO3. An aliquot was taken for ICP-MS analyses to determine the parent/daughter abundance ratios (Table 6). The remaining aliquots were passed through 120 mL Pb and 50 mL Sr columns and analyzed by a thermal ionization multicollector mass spectrom- eter (Micromass Isoprobe-T) at MIT using dynamic mode for Sr and static mode for Pb (Table 5). 4. Results 4.1. Petrography [13] The textures of Mt. Capitole lavas range from aphyric to moderately phyric (Table 1), typically with a fine-grained groundmass of plagioclase, clinopyroxene, olivine, opaque minerals and devit- rified, altered brown glass. Sample 93–472 is an exception; it has an intergranular texture with a coarse-grained groundmass of plagioclase and clinopyroxene and is altered (loss on ignition = 4.4 wt%, Table 3). Most samples (38) contain less than 5 vol% phenocrysts (>0.7 mm), and 8 samples are aphyric. Most of these aphyric to slightly phyric lavas are found in the lower part of the section. In contrast, 16 samples contain abundant phenocrysts or xenocrysts (10 vol% and up to 40 vol%), dominantly plagioclase with sparse clinopyroxene; olivine phenocrysts occur only in sample 93–472; nine of these 16 samples are from the uppermost 170 m (Table 1). Most of these plagioclase grains are 0.7–3 mm in width, but a few laths are up to 7 mm in length; some grains are resorbed (Figure 3a). [14] The phenocryst assemblages in each of the three studied sections in the Plateau Central (Figure 1) are quite different. Lavas from Mt. Tourmente are largely aphyric; i.e., 62 of 64 samples have less than 5 vol% phenocrysts [Frey et al., 2002a]. Lavas from the lowermost 300 m of the Mt. Marion Dufresne section are also domi- nantly aphyric but with decreasing age plagioclase- phyric, up to 60 vol%, lavas are abundant [Annell et al., 2007]. This upward succession from aphyric to plagioclase-phyric occurs at Mt. Capitole and Mt. Marion Dufresne. However, the latter section is unique in that olivine-phyric, up to 20 vol%, lavas Notes to Table 1: a Meters above sea level. b Phenocrysts/xenocrysts are crystals with size  0.7 mm. Volume proportions estimated from observation of thin sections using a polarizing microscope. c Sample numbers in bold indicate samples with mineral analyses determined by electron microprobe. d On the basis of petrography and whole rock composition, the Mt. Capitole lavas are divided into three groups that correlate with their stratigraphic positions. See the text for details. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 6 of 34 Table 2a. Plagioclase Compositions of Mt. Capitole Lavasa Type SiO2 Al2O3 FeO MgO CaO Na2O K2O Total An Ab Or Upper Transitional Group 93–459 plag1 core 50.66 31.12 0.59 0.18 14.30 3.32 0.13 100.3 69.9 29.4 0.8 93–459 plag1 rim 49.36 32.03 0.66 0.15 15.03 2.57 0.11 99.9 75.9 23.5 0.7 93–459 plag2 core 49.65 31.65 0.57 0.14 14.88 2.78 0.10 99.8 74.3 25.1 0.6 93–459 plag2 rim 52.05 30.13 0.76 0.09 12.84 3.85 0.22 99.9 64.0 34.7 1.3 93–459 plag3 core 49.22 32.36 0.57 0.15 15.36 2.68 0.09 100.4 75.6 23.9 0.5 93–459 plag3 rim 48.90 32.50 0.69 0.08 15.55 2.35 0.09 100.2 78.1 21.4 0.6 93–459 plag4 core 48.04 33.02 0.56 0.13 15.18 2.34 0.09 99.3 77.8 21.7 0.5 93–459 plag4 rim 48.66 31.58 0.63 0.14 14.87 2.87 0.09 98.9 73.7 25.8 0.5 93–459 plag5 core 51.16 30.56 0.59 0.13 13.69 3.64 0.17 100.0 66.8 32.1 1.0 93–459 plag5 mid-core 49.35 32.03 0.59 0.15 14.98 2.63 0.11 99.8 75.4 24.0 0.7 93–459 plag5 rim 49.21 32.23 0.59 0.11 15.16 2.56 0.11 100.0 76.1 23.3 0.6 93–459 plag5 rim 49.28 31.93 0.57 0.13 15.07 2.66 0.13 99.8 75.2 24.0 0.8 93–459 plag6 core 49.31 31.87 0.54 0.15 14.84 2.82 0.12 99.7 73.9 25.4 0.7 93–459 plag6 rim 49.02 31.67 0.58 0.14 15.09 2.83 0.12 99.5 74.1 25.2 0.7 93–459 plag7 core 48.89 31.90 0.56 0.16 15.13 2.90 0.11 99.7 73.8 25.6 0.7 93–459 plag7 core 48.81 32.45 0.59 0.17 15.52 2.57 0.09 100.2 76.5 23.0 0.5 93–459 plag7 core 48.22 32.62 0.53 0.16 15.97 2.37 0.08 99.9 78.5 21.1 0.5 93–459 plag7 rim 48.86 32.35 0.59 0.13 15.26 2.48 0.13 99.8 76.7 22.6 0.8 93–459 plag7 rim 48.66 32.22 0.60 0.10 15.37 2.66 0.11 99.7 75.6 23.7 0.7 93–459 plag8 core 48.60 32.55 0.52 0.15 15.65 2.61 0.11 100.2 76.4 23.0 0.6 93–459 plag8 rim 54.91 27.88 0.96 0.09 10.34 5.52 0.43 100.1 49.6 47.9 2.5 93–459 plag8 rim 48.28 32.94 0.62 0.13 15.61 2.46 0.08 100.1 77.5 22.1 0.5 93–459 plag9 core 48.87 32.61 0.56 0.16 15.78 2.67 0.09 100.7 76.1 23.3 0.5 93–459 plag9 rim 49.31 32.02 0.82 0.15 15.03 3.08 0.12 100.5 72.5 26.8 0.7 93–459 plag10 core 49.10 31.79 0.52 0.15 15.62 2.58 0.08 99.8 76.6 22.9 0.5 93–459 plag11 core 48.81 32.51 0.57 0.13 15.46 2.64 0.09 100.2 76.0 23.5 0.5 93–459 plag11 rim 49.01 32.06 0.68 0.11 15.16 2.85 0.11 100.0 74.2 25.2 0.6 93–459 plag12 groundmass 55.52 27.84 0.84 0.05 10.22 5.53 0.48 100.5 49.1 48.1 2.8 93–459 plag13 groundmass 52.69 29.70 1.09 0.16 12.40 4.14 0.25 100.4 61.4 37.1 1.5 93–460 plag1 core 48.00 33.22 0.58 0.13 16.37 2.03 0.08 100.4 81.3 18.2 0.5 93–460 plag1 core 49.08 32.88 0.63 0.17 15.86 2.42 0.09 101.1 77.9 21.5 0.6 93–460 plag1 mid-core 47.93 33.58 0.54 0.14 16.64 1.67 0.07 100.6 84.2 15.3 0.4 93–460 plag1 rim 52.52 30.08 0.61 0.15 13.10 3.75 0.20 100.4 65.1 33.7 1.2 93–460 plag1 rim 48.52 33.00 0.52 0.13 15.92 2.37 0.07 100.5 78.4 21.1 0.4 93–460 plag1 rim 48.00 33.62 0.53 0.14 16.50 2.07 0.08 100.9 81.1 18.4 0.5 93–460 plag1 rim 52.10 30.51 0.67 0.14 13.34 3.64 0.18 100.6 66.3 32.7 1.0 93–460 plag1 rim 47.50 33.66 0.51 0.14 16.61 2.15 0.06 100.6 80.7 18.9 0.4 93–460 plag2 core 50.77 31.55 0.53 0.16 14.42 3.26 0.11 100.8 70.5 28.8 0.7 93–460 plag2 core 48.67 32.99 0.58 0.14 16.24 2.08 0.08 100.8 80.8 18.7 0.5 93–460 plag2 core 49.38 32.50 0.60 0.14 15.45 2.57 0.09 100.8 76.4 23.0 0.6 93–460 plag2 core 48.92 32.68 0.61 0.15 15.66 2.45 0.09 100.6 77.5 21.9 0.5 93–460 plag2 rim 53.07 30.02 0.66 0.13 12.74 3.92 0.22 100.8 63.4 35.3 1.3 93–460 plag2 rim 49.13 32.71 0.59 0.11 15.69 2.56 0.09 100.9 76.8 22.7 0.5 93–460 plag3 core 50.58 31.41 0.61 0.13 14.35 3.46 0.13 100.7 69.1 30.1 0.7 93–460 plag3 core 49.37 32.68 0.60 0.14 15.36 2.99 0.10 101.2 73.5 25.9 0.6 93–460 plag3 rim 52.39 30.36 0.62 0.16 13.38 3.82 0.17 100.9 65.3 33.8 1.0 93–460 plag4 core 50.05 32.20 0.58 0.17 15.00 3.02 0.11 101.1 72.8 26.5 0.7 93–460 plag4 core 49.28 32.80 0.61 0.15 15.55 2.52 0.10 101.0 76.9 22.5 0.6 93–460 plag4 rim 49.56 32.69 0.64 0.12 15.69 2.49 0.09 101.3 77.3 22.2 0.5 93–460 plag4 rim 52.72 29.98 0.74 0.13 12.75 3.91 0.23 100.5 63.4 35.2 1.4 93–460 plag5 core 50.60 31.85 0.65 0.14 14.46 3.23 0.14 101.1 70.6 28.6 0.8 93–460 plag5 core 50.24 31.85 0.55 0.15 14.64 2.89 0.12 100.4 73.1 26.2 0.7 93–460 plag5 rim 48.92 32.90 0.67 0.15 15.94 2.42 0.10 101.1 78.0 21.4 0.6 93–460 plag5 rim 49.60 32.32 0.55 0.13 15.23 2.67 0.12 100.6 75.3 23.9 0.7 93–460 plag6 core 50.24 31.44 0.55 0.23 14.83 3.00 0.14 100.4 72.6 26.6 0.8 93–460 plag6 rim 48.19 33.54 0.63 0.14 16.50 2.01 0.08 101.1 81.5 18.0 0.5 93–460 plag6 rim 49.31 32.53 0.60 0.18 15.28 2.72 0.10 100.7 75.2 24.2 0.6 93–460 plag7 core 48.99 32.59 0.61 0.17 15.75 2.27 0.11 100.5 78.8 20.6 0.6 93–460 plag7 rim 49.14 32.75 0.53 0.17 15.90 2.30 0.11 100.9 78.8 20.6 0.7 93–460 plag8 core 47.44 33.96 0.48 0.14 17.44 1.72 0.06 101.3 84.5 15.1 0.4 93–460 plag8 rim 49.07 33.04 0.52 0.14 15.99 2.17 0.10 101.0 79.8 19.6 0.6 Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 7 of 34 Type SiO2 Al2O3 FeO MgO CaO Na2O K2O Total An Ab Or 93–460 plag8 rim 52.73 29.78 0.68 0.15 12.63 3.78 0.26 100.0 63.9 34.6 1.6 93–460 plag9 groundmass 52.65 30.08 0.77 0.16 12.85 3.97 0.21 100.7 63.3 35.4 1.2 93–462 plag1 core 49.14 32.01 0.59 0.15 15.28 2.67 0.08 99.9 75.6 23.9 0.5 93–462 plag1 rim 48.27 32.54 0.64 0.13 16.02 2.55 0.05 100.2 77.4 22.3 0.3 93–462 plag2 core 49.10 32.14 0.60 0.13 15.42 2.73 0.08 100.2 75.4 24.1 0.5 93–462 plag2 rim 49.07 33.10 0.60 0.13 15.79 2.35 0.08 101.1 78.4 21.1 0.5 93–462 plag2 rim 54.70 28.25 0.64 0.10 11.05 4.99 0.34 100.1 53.9 44.1 2.0 93–462 plag3 core 49.12 32.37 0.53 0.14 15.53 2.44 0.10 100.2 77.4 22.0 0.6 93–462 plag3 rim 53.73 29.06 0.76 0.09 11.82 5.18 0.30 100.9 54.8 43.5 1.7 93–462 plag4 core 48.26 32.90 0.62 0.13 16.05 2.08 0.08 100.1 80.6 18.9 0.5 93–462 plag4 rim 55.69 27.01 1.56 0.33 9.64 5.54 0.47 100.2 47.7 49.5 2.8 93–462 plag5 core 48.67 32.45 0.58 0.14 15.53 2.60 0.10 100.1 76.3 23.1 0.6 93–462 plag5 rim 49.83 31.75 0.63 0.17 15.25 2.89 0.12 100.6 74.0 25.4 0.7 93–462 plag6 core 50.59 31.78 0.63 0.15 14.65 3.12 0.11 101.0 71.7 27.6 0.6 93–462 plag6 rim 58.41 26.02 0.79 0.03 7.96 7.13 0.66 101.0 36.8 59.6 3.6 93–462 plag7 core 53.10 29.65 0.96 0.16 12.46 4.29 0.23 100.9 60.8 37.9 1.3 93–462 plag7 rim 62.35 22.62 1.34 0.29 4.09 7.76 1.74 100.2 20.2 69.5 10.3 93–465 plag1 core 47.65 33.00 0.55 0.17 16.41 2.17 0.07 100.0 80.4 19.2 0.4 93–465 plag1 rim 48.77 32.14 0.71 0.12 15.40 2.82 0.13 100.1 74.6 24.7 0.7 93–465 plag1 rim 48.71 32.11 0.75 0.11 15.49 2.75 0.14 100.1 75.1 24.1 0.8 93–465 plag2 core 48.45 32.56 0.58 0.15 15.99 2.16 0.07 100.0 80.0 19.6 0.4 93–465 plag2 rim 48.78 32.28 0.62 0.13 15.50 2.41 0.09 99.8 77.6 21.9 0.5 93–465 plag2 rim 48.62 32.60 0.65 0.14 15.95 2.20 0.06 100.2 79.7 19.9 0.4 93–465 plag3 core 48.32 33.00 0.59 0.14 16.19 2.16 0.06 100.5 80.3 19.4 0.4 93–465 plag3 rim 48.35 32.61 0.65 0.13 16.12 2.31 0.06 100.2 79.1 20.5 0.3 93–465 plag4 core 48.99 31.64 0.58 0.17 15.09 2.73 0.09 99.3 74.9 24.6 0.5 93–465 plag4 rim 47.98 32.92 0.62 0.12 15.94 2.34 0.06 100.0 78.7 20.9 0.4 93–465 plag4 rim 48.58 32.48 0.62 0.12 15.68 2.43 0.09 100.0 77.7 21.8 0.5 93–465 plag5 core 48.46 32.49 0.62 0.16 15.63 2.88 0.08 100.3 74.7 24.9 0.4 93–465 plag5 rim 48.32 32.38 0.59 0.17 15.79 2.34 0.05 99.6 78.6 21.1 0.3 93–465 plag5 rim 48.71 32.29 0.66 0.12 15.57 2.78 0.09 100.2 75.2 24.3 0.5 93–465 plag6 core 47.66 32.72 0.51 0.13 16.16 2.27 0.05 99.5 79.5 20.2 0.3 93–465 plag6 rim 53.13 29.25 0.73 0.11 12.19 4.40 0.23 100.0 59.7 39.0 1.4 93–465 plag6 rim 47.57 32.64 0.70 0.12 16.01 2.37 0.06 99.5 78.6 21.1 0.4 93–465 plag7 core 48.13 32.48 0.59 0.16 15.85 2.58 0.07 99.9 77.0 22.6 0.4 93–465 plag7 core 48.33 33.22 0.72 0.08 16.18 2.16 0.08 100.8 80.2 19.3 0.5 93–465 plag7 rim around olivine inclusion 54.43 28.64 1.00 0.12 11.37 5.12 0.29 101.0 54.2 44.1 1.7 93–465 plag7 core 48.50 32.93 0.74 0.06 15.90 2.13 0.08 100.3 80.1 19.4 0.5 93–465 plag7 core 65.53 20.90 0.46 0.02 2.10 8.25 3.62 100.9 9.8 70.0 20.2 93–465 plag7 core 58.76 25.91 0.49 0.04 7.93 6.96 0.64 100.7 37.3 59.2 3.6 93–465 plag7 core 49.41 32.15 0.70 0.11 15.12 2.65 0.12 100.3 75.3 23.9 0.7 93–465 plag7 core 49.50 32.73 0.54 0.16 15.66 2.38 0.13 101.1 77.8 21.4 0.7 93–465 plag7 core 48.91 33.33 0.64 0.15 16.22 2.03 0.11 101.4 81.0 18.3 0.6 93–465 plag7 rim 47.86 32.90 0.58 0.16 16.29 2.23 0.06 100.1 79.9 19.8 0.3 93–465 plag7 rim 49.11 31.78 0.60 0.16 15.18 2.69 0.08 99.6 75.4 24.1 0.5 93–465 plag7 rim around amphibole inclusion 53.91 29.04 0.96 0.28 12.01 4.34 0.29 100.8 59.5 38.8 1.7 93–465 plag7 rim around amphibole inclusion 56.49 27.42 0.55 0.15 9.95 5.60 0.45 100.6 48.2 49.1 2.6 93–465 plag7 rim around amphibole inclusion 57.53 26.68 0.39 0.17 9.16 5.93 0.69 100.6 44.2 51.8 4.0 93–465 plag7 rim around amphibole inclusion 57.06 27.45 0.46 0.07 9.66 6.03 0.56 101.3 45.5 51.4 3.2 93–465 plag7 rim around amphibole inclusion 52.80 30.07 0.64 0.22 13.23 4.11 0.29 101.4 62.9 35.4 1.7 93–465 plag7 rim around amphibole inclusion 56.15 27.69 0.45 0.16 10.22 5.58 0.50 100.8 48.9 48.3 2.9 93–465 plag7 rim around olivine inclusion 56.23 27.82 0.83 0.14 10.25 5.17 0.37 100.8 51.1 46.7 2.2 93–465 plag7 rim around pyroxene inclusion 66.95 20.16 0.47 0.03 1.08 7.58 4.76 101.1 5.3 67.0 27.7 93–465 plag7 rim around pyroxene inclusion 59.19 26.03 0.60 0.09 7.48 6.80 0.73 100.9 36.2 59.6 4.2 93–465 plag7 rim around pyroxene inclusion 54.70 28.18 1.14 0.24 10.47 5.00 0.38 100.1 52.4 45.3 2.2 93–465 plag7 rim around pyroxene inclusion 56.89 27.70 0.69 0.11 9.56 5.44 0.49 100.9 47.8 49.3 2.9 93–465 plag7 rim around pyroxene inclusion 58.11 27.00 0.61 0.10 8.92 5.97 0.55 101.3 43.8 53.0 3.2 93–465 plag8 core 48.62 33.14 0.62 0.20 15.80 2.51 0.14 101.0 77.0 22.2 0.8 93–465 plag8 rim 53.10 29.38 0.98 0.13 12.37 4.65 0.29 100.9 58.5 39.8 1.7 93–465 plag9 core 49.85 31.39 0.57 0.17 14.61 3.24 0.08 99.9 71.1 28.5 0.4 93–465 plag9 rim 48.54 32.35 0.56 0.16 15.56 2.58 0.08 99.8 76.6 23.0 0.5 93–465 plag9 rim 47.90 32.43 0.57 0.15 15.75 2.58 0.06 99.5 76.9 22.8 0.4 Table 2a. (continued) Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 8 of 34 Type SiO2 Al2O3 FeO MgO CaO Na2O K2O Total An Ab Or 93–465 plag9 rim 48.00 32.75 0.62 0.12 15.97 2.37 0.07 99.9 78.5 21.1 0.4 93–465 plag10 core 47.91 33.04 0.54 0.16 16.05 2.27 0.05 100.0 79.4 20.3 0.3 93–465 plag10 rim 47.60 32.62 0.52 0.13 16.00 2.55 0.07 99.5 77.3 22.3 0.4 93–465 plag11 core 47.88 32.87 0.52 0.15 16.02 2.32 0.05 99.8 79.0 20.7 0.3 93–465 plag11 rim 48.02 32.66 0.74 0.11 16.04 2.25 0.07 99.9 79.4 20.2 0.4 93–465 plag12 core 48.72 32.71 0.54 0.15 15.96 2.73 0.08 100.9 76.0 23.5 0.4 93–465 plag12 rim 48.38 32.68 0.52 0.13 16.06 2.23 0.08 100.1 79.6 20.0 0.5 93–465 plag12 rim 53.51 29.40 0.69 0.12 12.07 4.52 0.25 100.6 58.7 39.8 1.4 93–465 plag12 rim 47.79 33.03 0.54 0.01 16.22 1.97 0.03 99.6 81.8 18.0 0.2 93–465 plag12 rim 54.97 28.86 0.65 0.00 11.30 4.96 0.31 101.1 54.7 43.5 1.8 93–465 plag13 core 48.77 33.06 0.52 0.00 16.29 2.39 0.05 101.1 78.8 20.9 0.3 93–465 plag13 rim 48.90 33.33 0.53 0.03 16.11 2.19 0.05 101.1 80.0 19.7 0.3 93–465 plag14 groundmass 59.49 24.67 0.79 0.13 7.02 6.92 1.06 100.1 33.7 60.2 6.1 93–471 plag1 core 50.62 31.65 0.58 0.18 14.96 2.80 0.10 100.9 74.2 25.2 0.6 93–471 plag1 core 50.02 32.10 0.62 0.18 15.06 2.83 0.10 100.9 74.2 25.2 0.6 93–471 plag1 core 49.89 32.09 0.57 0.17 15.24 2.56 0.09 100.6 76.2 23.2 0.5 93–471 plag1 core 50.49 31.66 0.56 0.18 14.68 2.96 0.10 100.6 72.9 26.6 0.6 93–471 plag1 core 48.34 33.14 0.48 0.16 16.42 1.84 0.08 100.4 82.8 16.8 0.5 93–471 plag1 core 49.72 32.20 0.60 0.22 15.30 2.76 0.08 100.9 75.0 24.5 0.4 93–471 plag1 core 48.83 32.71 0.54 0.19 15.92 2.49 0.08 100.8 77.6 22.0 0.4 93–471 plag1 rim 48.86 32.77 0.53 0.12 15.76 2.37 0.07 100.5 78.3 21.3 0.4 93–471 plag1 rim 49.27 32.52 0.50 0.17 15.79 2.54 0.07 100.9 77.1 22.5 0.4 93–471 plag1 rim 48.45 33.26 0.55 0.17 16.26 2.26 0.06 101.0 79.6 20.1 0.4 93–471 plag1 rim 48.43 33.14 0.56 0.15 16.15 2.10 0.07 100.6 80.6 19.0 0.4 93–471 plag1 rim 48.41 33.22 0.57 0.16 16.47 2.06 0.07 101.0 81.2 18.4 0.4 93–471 plag1 rim 48.67 32.86 0.60 0.15 16.02 2.34 0.07 100.7 78.8 20.8 0.4 93–471 plag1 rim 48.82 32.93 0.59 0.17 15.82 2.33 0.07 100.7 78.6 21.0 0.4 93–471 plag1 rim 49.20 32.91 0.58 0.18 15.82 2.51 0.08 101.3 77.3 22.2 0.5 93–471 plag2 core 48.14 33.36 0.53 0.17 16.50 1.94 0.06 100.7 82.2 17.5 0.4 93–471 plag3 core 49.30 32.32 0.56 0.17 15.58 2.58 0.08 100.6 76.6 22.9 0.5 93–471 plag3 rim 47.98 33.28 0.59 0.12 16.37 1.78 0.05 100.2 83.3 16.4 0.3 93–471 plag4 core 48.34 33.44 0.58 0.14 16.27 1.92 0.05 100.7 82.1 17.6 0.3 93–471 plag5 core 48.63 32.78 0.54 0.16 16.02 2.15 0.06 100.4 80.2 19.4 0.4 93–471 plag5 rim 48.72 32.96 0.61 0.14 15.86 2.15 0.07 100.5 80.0 19.6 0.4 93–471 plag6 rim 54.43 29.09 0.54 0.11 11.58 4.66 0.22 100.6 57.1 41.6 1.3 93–471 plag7 core 49.41 32.38 0.61 0.21 15.61 2.49 0.09 100.8 77.2 22.3 0.5 93–471 plag7 core 49.10 32.57 0.53 0.20 15.46 2.63 0.07 100.6 76.1 23.5 0.4 93–471 plag7 core 48.51 33.20 0.54 0.21 16.22 2.27 0.06 101.0 79.5 20.1 0.3 93–471 plag7 rim 48.53 33.09 0.52 0.23 15.91 2.23 0.08 100.6 79.4 20.1 0.5 93–471 plag7 rim 50.94 31.42 0.55 0.23 14.40 3.22 0.11 100.9 70.7 28.6 0.6 93–471 plag7 rim 49.17 32.80 0.58 0.21 15.54 2.44 0.09 100.8 77.4 22.0 0.5 93–471 plag8 core 49.12 32.72 0.58 0.24 15.49 2.61 0.08 100.8 76.3 23.2 0.5 93–471 plag9 core 49.49 32.78 0.49 0.20 15.58 2.54 0.07 101.2 76.9 22.7 0.4 93–471 plag10 groundmass 53.07 29.20 0.90 0.07 12.15 4.14 0.27 99.8 60.9 37.5 1.6 93–472 plag1 core 50.25 31.38 0.45 0.17 14.32 3.23 0.09 99.9 70.6 28.8 0.5 93–472 plag1 rim 50.78 31.25 0.50 0.14 14.26 3.34 0.10 100.4 69.8 29.6 0.6 93–472 plag2 groundmass 51.10 30.67 0.47 0.20 13.82 3.53 0.12 99.9 67.9 31.4 0.7 93–473 plag1 core 50.37 31.83 0.51 0.16 14.86 2.94 0.12 100.8 73.1 26.2 0.7 93–473 plag1 rim 50.85 31.42 0.54 0.16 14.19 3.59 0.13 100.9 68.1 31.2 0.8 93–473 plag2 core 50.18 31.70 0.52 0.17 14.63 2.97 0.11 100.3 72.6 26.7 0.7 93–473 plag2 rim 48.84 32.62 0.53 0.17 15.75 2.73 0.09 100.7 75.7 23.7 0.5 93–473 plag3 core 51.01 30.97 0.52 0.19 14.07 3.66 0.13 100.5 67.5 31.8 0.7 93–473 plag4 core 48.44 32.91 0.46 0.13 16.05 2.39 0.07 100.5 78.5 21.1 0.4 93–473 plag4 rim 49.80 31.82 0.55 0.14 14.88 3.17 0.10 100.5 71.7 27.7 0.6 93–474 plag1 core 51.13 31.08 0.62 0.20 13.87 3.46 0.16 100.5 68.3 30.8 0.9 93–474 plag1 rim 51.83 30.55 0.74 0.16 13.65 3.98 0.22 101.1 64.7 34.1 1.2 93–474 plag2 core 53.92 28.91 0.62 0.19 11.98 4.60 0.26 100.5 58.1 40.4 1.5 93–491 plag1 core 50.19 31.17 0.67 0.19 14.29 2.94 0.11 99.6 72.4 27.0 0.6 93–491 plag1 rim 54.69 28.20 0.73 0.11 10.92 4.98 0.32 100.0 53.8 44.4 1.9 93–491 plag1 rim 52.85 29.51 0.58 0.17 12.62 4.20 0.18 100.1 61.8 37.2 1.0 93–491 plag2 core 51.68 30.42 0.62 0.20 13.44 3.72 0.15 100.2 66.1 33.0 0.9 93–491 plag2 rim 53.23 29.34 0.58 0.14 12.14 4.19 0.22 99.8 60.7 38.0 1.3 Table 2a. (continued) Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 9 of 34 dominate the uppermost 400 m [Annell et al., 2007]. In contrast, only one olivine-phyric (2 vol%) lava occurs in the Mt. Capitole section (Table 1). 4.2. Mineral Compositions 4.2.1. Plagioclase [15] Plagioclase is the most abundant phenocryst/ xenocryst in Mt. Capitole basalt, especially in the uppermost 170 m of the section which we refer to as the Upper Transitional Group (Table 1). Within this group plagioclase cores range from An85 to An56 (Table 2a and Figure 4); a similarly wide range of plagioclase core compositions, An85 to An63, occurs in the plagioclase-phyric lavas ex- posed further south on the Plateau Central at Mt. Marion Dufresne (Figure 4). Annell et al. [2007] concluded that the wide range of plagioclase core compositions in individual samples, including cores >An80, reflect mixing of magmas with distinct population of plagioclase phenocrysts. Consistent with this conclusion, the plagioclase phenocrysts/ xenocrysts in the Upper Transitional Group are texturally distinct from those in the other groups; they are commonly resorbed (Figure 3a) and con- tain inclusions of olivine, pyroxene, amphibole, Fe-Ti oxides and rare apatite (Figures 3b, 3c, 3d, 3e, and 3f). Rims of large plagioclase grains span a wide compositional range, from sodic-rich compo- sitions (An47) to An83 (Tables 2a–2d). Even more sodic plagioclase (An30–An61) occurs as inclu- sions (Figures 3c, 3d, 3e, and 4) and as partial rims surrounding inclusions of olivine, clinopyrox- ene, amphibole and Fe-Ti oxide (Figures 3c, 3d, and 3e). The large compositional variation of the plagioclase rims surrounding inclusion minerals (Figures 3d and 3e), ranging from labradorite to anorthoclase within less than 50 mm, reflects non- equilibrium crystallization. The large plagioclase Type SiO2 Al2O3 FeO MgO CaO Na2O K2O Total An Ab Or 93–491 plag3 core 50.54 31.07 0.66 0.17 14.19 3.16 0.15 99.9 70.7 28.5 0.9 93–491 plag3 rim 54.12 28.81 0.66 0.12 11.47 4.84 0.28 100.3 55.8 42.6 1.6 93–491 plag4 core 50.54 31.33 0.64 0.16 14.36 3.16 0.10 100.3 71.1 28.3 0.6 93–491 plag4 rim 52.52 30.07 0.66 0.16 12.90 4.21 0.16 100.7 62.3 36.8 0.9 93–491 plag4 rim 53.18 29.46 0.62 0.16 12.27 4.27 0.21 100.2 60.6 38.2 1.2 93–491 plag5 core 54.15 28.83 0.58 0.14 11.56 4.76 0.25 100.3 56.5 42.1 1.4 93–491 plag5 rim 53.86 28.69 0.86 0.31 11.53 4.59 0.24 100.1 57.3 41.3 1.4 93–491 plag6 rim 52.66 29.60 0.63 0.16 12.53 4.26 0.21 100.0 61.1 37.7 1.2 93–491 plag6 core 53.07 29.42 0.58 0.17 12.34 4.14 0.20 99.9 61.5 37.3 1.2 93–491 plag7 core 51.13 30.92 0.64 0.16 13.88 3.33 0.13 100.2 69.2 30.0 0.8 93–491 plag7 rim 51.19 30.53 0.70 0.18 13.75 3.60 0.14 100.1 67.3 31.9 0.8 93–491 plag8 core 50.44 31.14 0.67 0.16 14.38 3.04 0.10 99.9 71.9 27.5 0.6 93–491 plag8 rim 53.34 29.62 0.55 0.16 12.27 4.46 0.21 100.6 59.6 39.2 1.2 93–491 plag9 core 53.34 29.41 0.61 0.14 12.32 4.51 0.19 100.5 59.5 39.4 1.1 93–491 plag10 core 53.07 29.77 0.63 0.16 12.49 4.46 0.20 100.8 60.0 38.8 1.1 93–491 plag11 plag inclusion in plag11 52.94 29.94 0.71 0.14 12.75 3.98 0.20 100.7 63.2 35.7 1.2 93–491 plag12 core 48.86 32.50 0.59 0.13 15.57 2.51 0.08 100.3 77.0 22.5 0.5 93–491 plag12 rim 52.10 30.43 0.56 0.19 13.26 3.88 0.15 100.6 64.8 34.4 0.8 93–491 plag12 rim around pyroxene inclusion 53.38 29.48 0.68 0.19 12.29 4.20 0.32 100.6 60.6 37.5 1.9 Low-Silica Group 93–486 plag1 core 53.50 29.20 0.54 0.13 11.92 4.56 0.22 100.1 58.4 40.4 1.3 93–486 plag1 core 53.30 29.39 0.50 0.12 12.34 4.20 0.20 100.1 61.2 37.7 1.2 93–486 plag1 core 53.56 29.38 0.63 0.11 12.05 4.61 0.20 100.5 58.4 40.5 1.1 93–486 plag1 core 52.98 29.49 0.50 0.13 12.33 4.21 0.22 99.9 61.0 37.7 1.3 93–486 plag1 rim 55.42 27.82 0.76 0.10 10.55 4.99 0.37 100.0 52.7 45.1 2.2 93–486 plag2 core 53.70 28.77 0.55 0.17 11.78 4.81 0.22 100.0 56.8 42.0 1.2 93–486 plag2 core 50.04 31.71 0.57 0.14 14.79 2.95 0.11 100.3 73.0 26.3 0.7 93–486 plag2 rim 51.93 30.32 0.61 0.12 13.09 3.68 0.16 99.9 65.7 33.4 1.0 93–486 plag2 rim 56.01 27.86 0.68 0.09 10.42 5.41 0.35 100.8 50.5 47.4 2.0 93–486 plag2 rim 52.80 29.89 0.70 0.12 12.62 4.19 0.21 100.5 61.7 37.1 1.2 93–486 plag2 rim 51.98 30.48 0.62 0.14 13.22 4.12 0.17 100.7 63.3 35.7 1.0 93–486 plag2 rim 54.59 28.25 0.67 0.10 11.10 5.34 0.31 100.4 52.5 45.7 1.7 93–486 plag3 core 51.19 30.85 0.56 0.13 13.74 3.48 0.14 100.1 68.0 31.2 0.8 aCompositions are in wt% and were determined by electron microprobe at MIT. Table 2a. (continued) Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 10 of 34 Table 2b. Pyroxene Compositions of Mt. Capitole Lavasa SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O Total Mg# 93–459 cpx inclusion in plag5 50.08 1.19 2.00 0.02 10.75 0.23 14.34 20.61 0.34 99.6 70.4 93–459 cpx in groundmass 49.07 1.95 4.14 0.04 10.93 0.20 13.73 19.85 0.33 100.2 69.1 93–459 cpx in groundmass 48.07 2.36 5.05 0.06 10.65 0.20 13.49 20.06 0.37 100.3 69.3 93–459 cpx in groundmass 48.48 2.19 3.79 0.00 12.60 0.30 12.80 19.23 0.49 99.9 64.4 93–459 cpx in groundmass 48.88 2.01 4.79 0.31 8.47 0.16 14.18 20.96 0.37 100.1 74.9 93–459 cpx in groundmass 50.98 1.20 2.17 0.00 10.84 0.26 14.10 19.94 0.43 99.9 69.9 93–460 cpx1 core 49.92 1.69 3.84 0.09 9.24 0.20 14.15 21.21 0.30 100.6 73.2 93–460 cpx1 rim 51.12 1.36 1.72 0.00 12.19 0.27 13.11 20.02 0.28 100.1 65.7 93–460 cpx1 rim 52.16 1.14 1.85 0.00 10.20 0.27 14.56 20.67 0.32 101.2 71.8 93–460 cpx2 core 51.97 1.00 2.56 0.06 9.08 0.21 15.80 19.82 0.28 100.8 75.6 93–460 cpx2 core 50.43 1.31 3.99 0.20 8.05 0.19 14.76 21.22 0.36 100.5 76.6 93–460 cpx2 rim 51.57 1.11 2.06 0.02 9.69 0.24 14.40 20.68 0.33 100.1 72.6 93–460 cpx3 core 52.29 0.82 2.17 0.08 8.17 0.23 16.05 20.24 0.27 100.3 77.8 93–462 cpx in groundmass 52.00 1.02 1.76 0.00 11.35 0.16 14.32 19.72 0.20 100.5 69.2 93–465 pigeonite inclusion1 in plag7 51.25 0.32 0.10 0.02 33.31 0.72 12.99 3.08 0.12 101.9 41.0 93–465 pigeonite inclusion2 in plag7 50.59 0.48 0.50 0.02 32.67 0.63 12.41 3.16 0.12 100.6 40.4 93–465 pigeonite inclusion3 in plag7 49.85 0.47 0.16 0.12 33.16 0.62 14.13 2.89 0.00 101.4 43.2 93–465 cpx inclusion1 core in plag7 51.43 1.13 2.32 0.04 8.84 0.21 14.62 20.82 0.38 99.8 74.7 93–465 cpx inclusion1 rim in plag7 50.47 1.46 3.22 0.25 9.33 0.17 14.51 20.37 0.36 100.1 73.5 93–465 cpx inclusion2 core in plag7 51.42 1.17 1.70 0.00 10.47 0.17 14.24 20.35 0.40 99.9 70.8 93–465 cpx inclusion2 rim1 in plag7 52.43 1.22 1.62 0.00 12.07 0.26 14.12 20.18 0.31 102.2 67.6 93–465 cpx inclusion2 rim2 in plag7 51.16 1.47 2.14 0.00 11.54 0.24 13.66 20.51 0.44 101.2 67.9 93–465 cpx inclusion3 in plag7 52.40 1.28 0.97 0.00 15.83 0.40 12.77 18.33 0.39 102.4 59.0 93–465 cpx inclusion4 in plag7 51.33 1.10 1.18 0.00 14.25 0.40 13.05 18.66 0.30 100.3 62.0 93–465 cpx inclusion5 in plag7 51.19 1.43 1.82 0.00 14.39 0.38 11.72 18.56 0.31 99.8 59.2 93–465 cpx inclusion6 in plag7 51.04 1.45 2.22 0.00 10.68 0.20 13.62 20.73 0.38 100.3 69.5 93–465 cpx inclusion in plag12 51.05 1.51 2.64 0.00 13.21 0.12 14.15 18.61 0.46 101.8 65.6 93–465 cpx in groundmass 48.07 1.27 4.86 0.26 12.45 0.29 12.97 17.60 0.52 98.3 65.0 93–465 cpx in groundmass 49.17 1.67 4.47 0.38 10.54 0.26 13.86 19.99 0.42 100.8 70.1 93–465 cpx in groundmass 52.16 0.82 1.94 0.21 8.54 0.24 16.84 18.63 0.39 99.8 77.9 93–465 cpx in groundmass 51.55 1.06 2.14 0.08 9.90 0.26 15.18 19.64 0.37 100.2 73.2 93–465 cpx in groundmass 49.69 1.49 4.16 0.30 9.00 0.23 14.84 20.34 0.35 100.4 74.6 93–471 cpx inclusion1 in plag1 50.66 1.39 3.19 0.07 9.23 0.17 15.24 20.50 0.32 100.8 74.6 93–471 cpx inclusion2 in plag1 50.63 1.53 2.78 0.04 10.66 0.23 14.33 20.56 0.37 101.2 70.5 93–471 cpx inclusion3 in plag1 52.38 0.73 1.17 0.01 14.78 0.33 14.97 16.40 0.31 101.1 64.4 93–471 cpx inclusion1 in plag5 52.26 0.94 2.10 0.06 9.58 0.20 16.18 19.05 0.32 100.7 75.1 93–471 cpx inclusion2 in plag5 51.07 1.31 2.75 0.05 14.18 0.33 17.01 13.91 0.17 100.8 68.1 93–471 cpx in groundmass 50.73 1.21 2.49 0.09 10.93 0.24 14.43 20.18 0.34 100.6 70.2 93–472 cpx1 core 50.07 1.79 3.70 0.17 9.31 0.19 14.28 20.00 0.28 99.8 73.2 93–472 cpx1 rim 49.32 2.08 3.58 0.03 11.02 0.21 13.43 19.77 0.35 99.8 68.5 93–472 cpx2 core 50.48 1.10 1.42 0.04 15.09 0.29 12.44 18.36 0.22 99.5 59.5 93–472 cpx3 core 52.13 1.03 1.94 0.20 8.50 0.19 15.76 20.15 0.26 100.2 76.8 93–472 cpx3 rim 50.64 1.00 1.29 0.06 16.19 0.38 12.24 17.67 0.23 99.7 57.4 93–473 cpx inclusion core in plag2 49.00 2.15 3.81 0.11 11.56 0.23 13.36 19.88 0.29 100.4 67.3 93–473 cpx inclusion rim in plag2 50.15 1.86 2.27 0.00 14.32 0.36 13.35 18.04 0.26 100.6 62.4 93–486 cpx1 core 51.54 1.21 2.49 0.19 9.79 0.23 15.31 19.92 0.31 101.0 73.6 93–486 cpx1 rim 51.35 1.18 2.50 0.15 9.47 0.23 15.43 19.86 0.29 100.5 74.4 93–486 cpx2 core 51.04 1.13 2.91 0.23 8.66 0.22 15.52 20.05 0.21 100.0 76.2 93–486 cpx2 rim 51.15 1.09 1.55 0.01 14.80 0.37 13.10 17.81 0.27 100.2 61.2 93–486 cpx2 rim 51.61 1.20 2.29 0.08 9.20 0.20 15.60 19.79 0.27 100.2 75.1 93–486 cpx3 core 52.28 0.90 2.35 0.12 8.28 0.17 15.92 20.36 0.26 100.6 77.4 93–486 cpx3 core 51.66 1.10 2.03 0.08 9.35 0.25 15.39 19.40 0.32 99.6 74.6 93–486 cpx3 rim 51.40 1.03 1.47 0.01 12.64 0.35 14.42 18.38 0.31 100.0 67.0 93–486 cpx3 rim 51.39 1.07 1.73 0.02 13.14 0.30 14.47 17.96 0.26 100.3 66.3 93–486 cpx3 rim 52.03 0.98 2.35 0.14 8.90 0.23 15.72 20.09 0.26 100.7 75.9 93–491 cpx1 core 51.68 0.93 2.76 0.34 7.57 0.17 16.23 20.21 0.26 100.2 79.3 93–491 cpx1 rim 51.38 0.95 2.56 0.28 7.94 0.21 16.19 20.47 0.33 100.3 78.4 93–491 cpx2 core 51.41 0.81 2.63 0.40 7.55 0.18 16.03 20.39 0.25 99.6 79.1 93–491 cpx2 rim 51.63 0.80 2.46 0.52 6.98 0.15 16.28 20.43 0.27 99.5 80.6 93–491 cpx2 rim 51.56 1.20 1.44 0.08 11.65 0.23 14.98 18.58 0.24 100.0 69.6 93–491 cpx3 core 51.48 0.86 2.27 0.24 7.75 0.17 16.07 20.27 0.25 99.4 78.7 93–491 cpx3 rim 51.82 0.93 2.51 0.26 7.77 0.21 15.95 20.31 0.23 100.0 78.5 Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 11 of 34 grains are sieve-textured plagioclase [e.g., Nelson and Montana, 1992]. 4.2.2. Pyroxene [16] Clinopyroxene is a more common phenocryst in Mt. Capitole lavas than olivine, but it rarely exceeds 3 vol%; sample 93–491 with 15 vol% clinopyroxene is an exception (Table 1). The Mg# of clinopyroxene phenocrysts ranges from 57 to 81 (Table 2b). Plagioclase phenocrysts in the Upper Transitional Group contain abundant inclusions of clinopyroxene with a similar range in Mg#, but rare pigeonite inclusions with low Mg# (40 to 43) also occur (Figure 3d). [17] High Al2O3 clinopyroxene (5 – 8.6 wt%) occurs in a section of mildly alkaline lavas from Mt. Crozier in the eastern archipelago (Figure 1). Damasceno et al. [2002] concluded that high- pressure (up to 12 kbar) fractionation of high- Al2O3 clinopyroxene was an important process for these alkalic basalts. Such aluminous clinopyr- oxene phenocrysts are not present in Mt. Capitole lavas; they range from 1.29–4.71 wt% Al2O3, and crystallization pressures inferred from clinopyrox- ene/melt thermobarometers are 1 to 2.7 kbar at 1130C [Putirka et al., 2003]. 4.2.3. Olivine [18] Olivine phenocrysts, 2 vol%, occur only in sample 93–472 (Table 1) which has the highest MgO content (8.0 wt%) among Mt. Capitole lavas. These olivines are normally zoned, ranging from cores with Fo76–82 to rims with Fo74–77 (Table 2c). SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O Total Mg# 93–491 cpx4 core 51.75 0.96 2.53 0.23 8.08 0.17 15.92 20.58 0.22 100.5 77.8 93–491 cpx4 rim 52.08 0.81 2.20 0.30 7.23 0.20 16.40 20.44 0.26 99.9 80.2 93–491 cpx4 rim 51.43 0.82 1.14 0.05 15.95 0.46 14.08 16.39 0.18 100.5 61.1 93–491 cpx4 rim 52.22 0.88 1.83 0.30 9.29 0.21 16.22 18.90 0.27 100.1 75.7 93–491 cpx5 core 52.11 0.86 1.92 0.22 8.40 0.23 16.30 19.96 0.24 100.2 77.6 93–491 cpx5 rim 51.78 0.91 2.38 0.23 8.35 0.22 16.02 19.79 0.28 100.0 77.4 93–491 cpx6 core 49.34 1.46 4.71 0.51 9.42 0.25 16.29 16.74 0.35 99.1 75.5 93–491 cpx6 rim 52.37 0.83 1.61 0.40 8.74 0.27 17.05 18.38 0.22 99.9 77.7 93–491 cpx7 core 50.54 1.17 3.58 0.39 8.78 0.21 15.50 19.78 0.30 100.3 75.9 93–491 cpx7 rim 52.21 0.97 1.39 0.15 11.26 0.23 16.51 17.19 0.21 100.1 72.3 93–491 cpx8 core 50.30 1.31 3.93 0.27 9.32 0.14 15.97 18.31 0.32 99.9 75.3 93–491 cpx8 rim 51.43 1.28 2.18 0.12 11.52 0.23 15.27 18.21 0.23 100.5 70.3 93–491 cpx9 core 51.42 1.10 2.82 0.25 8.13 0.16 16.06 20.49 0.30 100.7 77.9 93–491 cpx inclusion1 in plag11 49.00 1.57 3.19 0.00 17.13 0.29 13.26 14.72 0.15 99.3 58.0 93–491 cpx inclusion2 in plag11 49.94 1.62 2.11 0.03 17.66 0.37 11.20 18.39 0.26 101.6 53.1 a Compositions are in wt% and were determined by electron microprobe at MIT. Table 2b. (continued) Table 2c. Olivine Compositions of Mt. Capitole Lavasa SiO2 Cr2O3 FeO MnO MgO CaO NiO Total Mg# 93–465 olivine inclusion1 core in plag7 35.07 0.01 37.12 0.55 26.16 0.38 0.06 99.4 55.7 93–465 olivine inclusion1 rim in plag7 34.67 0.06 42.64 0.61 20.29 0.27 0.07 99.0 45.9 93–465 olivine inclusion2 in plag7 35.72 0.02 32.04 0.40 30.98 0.34 0.08 99.6 63.3 93–465 olivine in groundmass near plag7 34.65 0.07 43.39 0.64 23.39 0.36 102.6 49.0 93–472 olivine1 core 39.38 0.01 17.06 0.24 41.94 0.30 0.18 99.1 81.4 93–472 olivine1 rim 38.27 0.03 20.86 0.27 39.45 0.30 0.12 99.3 77.1 93–472 olivine1 rim 38.84 0.03 22.43 0.25 37.60 0.35 0.15 99.7 74.9 93–472 olivine2 core 38.41 0.02 19.18 0.26 40.44 0.31 0.17 98.8 79.0 93–472 olivine2 rim 38.65 0.04 21.57 0.32 38.42 0.36 0.22 99.6 76.0 93–472 olivine3 core 38.89 0.05 19.36 0.31 40.85 0.28 0.24 100.0 79.0 93–472 olivine4 core 38.24 0.03 22.27 0.32 38.42 0.40 0.12 99.8 75.5 93–472 olivine5 core 38.26 0.03 21.21 0.31 39.26 0.38 0.10 99.6 76.7 93–472 olivine6 core 39.43 0.01 16.99 0.18 42.61 0.27 0.11 99.7 81.7 93–472 olivine6 rim 38.23 0.02 22.72 0.27 37.48 0.35 0.13 99.3 74.6 93–472 olivine7 core 38.35 0.01 20.47 0.29 39.52 0.36 0.11 99.2 77.5 93–472 olivine7 rim 38.06 0.01 23.06 0.31 37.62 0.38 0.09 99.6 74.4 a Compositions are in wt% and were determined by electron microprobe at MIT. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 12 of 34 Highly evolved olivine (Fo46–63) also occurs as inclusions in the abundant plagioclase phenocrysts/ xenocrysts that characterize the Upper Transitional Group (Tables 1 and 2c and Figure 3d). 4.2.4. Amphibole [19] Amphibole phenocrysts/microphenocrysts oc- cur in alkaline Kerguelen Archipelago lavas [Giret et al., 1980; Damasceno et al., 2002; Gagnevin et al., 2003]. Amphibole crystals in the Mt. Capitole section are present in the groundmass and as inclusions in plagioclase xenocrysts (Figures 3e and 3f). They are calcic-amphibole ranging from (titano-) magnesiohornblende to tschermakite according to the classification of Leake et al. [1997] (Table 2d). Amphibole inclusions in plagio- clase phenocrysts/xenocrysts are commonly enclosed by Na-rich plagioclase rims that vary in composition along the elongated amphibole inclu- sion (Figure 3e). 4.3. Whole-Rock Compositions 4.3.1. Major Elements [20] Like other sections of flood basalt from the northern and central part of the Kerguelen archi- pelago, lavas from the Mt. Capitole section are dominantly tholeiitic to transitional basalt on the basis of a silica-total alkalis diagram (Figure 5). They are evolved basalts with 46 to 53 wt% SiO2 and 3.3 to 8 wt% MgO (Table 3). Although there are no simple geochemical variations with relative eruption age, i.e., stratigraphic height in Figure 6, the lava compositions can be divided into three groups that correlate with stratigraphic position. The first group is the uppermost 15 tholeiitic/ transitional lavas from above 690 m. These lavas are dominantly plagioclase-phyric (Table 1) and are characterized by relatively high Al2O3 coupled with relatively low TiO2 and Fe2O3 (as total iron) (Figure 6). They are designated as the Upper Transitional Group. Sample 93–491, lower in the section at 540 m, is compositionally and petro- graphically similar to this group (Table 1 and Figure 6). For this group, abundances of SiO2, Al2O3, Na2O and K2O are negatively correlated with MgO, whereas CaO shows a slight positive correlation (Figure 7). The negative Al2O3 – MgO trend of this group contrasts with the positive trend of other Mt. Capitole and Mt. Tourmente lavas (Figure 7). Neither TiO2 nor P2O5 is inversely correlated with MgO in this group (Figure 7). [21] The second group of Mt. Capitole lavas are samples 93–478 to 93–486 from 660 m to 560 m. They have relatively low SiO2 contents and SiO2/ Fe2O3* ratios, high TiO2 and Fe2O3* contents and are alkalic or very close to the tholeiitic-alkalic Table 2d. Compositions of Amphibole Inclusions in Plagioclase Phenocrysts/Xenocrysts in Mt. Capitole Lavasa SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O Total Mg# 93–459 amph inclusion in plag4 43.82 4.91 3.12 0.04 21.90 0.42 11.93 12.67 0.50 99.3 49.3 93–459 amph inclusion in plag4 43.27 4.66 2.77 0.04 22.34 0.47 11.61 12.22 0.53 97.9 48.1 93–459 amph inclusion in plag7 42.61 5.41 2.35 0.05 23.49 0.36 12.05 13.19 0.38 99.9 47.8 93–459 amph inclusion in plag7 43.83 5.09 3.11 0.01 23.78 0.31 11.49 11.89 0.55 100.1 46.3 93–459 amph inclusion in plag7 43.98 5.37 3.22 0.08 22.99 0.33 11.17 12.14 0.59 99.9 46.4 93–459 amph inclusion in plag8 44.55 4.25 5.47 0.04 22.65 0.29 12.08 11.56 1.13 102.0 48.7 93–459 amph inclusion in plag8 43.82 4.79 2.90 0.10 21.08 0.38 12.83 12.72 0.84 99.5 52.0 93–460 amph inclusion in plag3 44.26 5.05 2.70 0.02 17.15 0.25 13.21 16.07 0.80 99.5 57.9 93–462 amph inclusion in plag2 43.91 4.79 3.95 0.05 18.38 0.46 12.19 13.15 0.64 97.5 54.2 93–465 amph inclusion1 rim1 in plag7 48.42 2.15 2.02 0.03 20.86 0.43 14.06 10.93 0.28 99.2 54.6 93–465 amph inclusion1 core in plag7 45.14 5.07 3.08 0.00 20.55 0.29 15.91 8.86 0.26 99.2 58.0 93–465 amph inclusion1 rim2 in plag7 44.62 4.64 4.66 0.05 23.89 0.48 10.86 10.02 0.62 99.8 44.8 93–465 amph inclusion1 rim3 in plag7 45.35 4.80 3.92 0.08 22.47 0.39 12.84 9.85 0.66 100.4 50.4 93–465 amph inclusion1 rim4 in plag7 43.70 4.69 2.89 0.04 22.56 0.36 12.81 10.70 0.39 98.1 50.3 93–465 amph inclusion1 rim5 in plag7 44.30 4.14 2.47 0.05 22.56 0.40 13.91 9.96 0.58 98.4 52.4 93–465 amph inclusion9 in plag7 45.64 5.10 2.97 0.07 18.54 0.34 15.35 11.52 0.51 100.0 59.6 93–465 amph inclusion11 in plag8 42.65 4.52 3.24 0.01 21.29 0.37 12.71 12.81 0.36 98.0 51.6 93–465 amph inclusion12 in plag9 45.87 4.16 4.28 0.07 19.17 0.48 12.82 11.21 0.46 98.5 54.4 93–471 amph inclusion in plag7 45.00 4.35 3.37 0.06 21.41 0.43 13.36 12.05 0.57 100.6 52.6 93–491 amph inclusion in plag7 41.16 5.32 4.20 0.09 24.62 0.64 9.82 10.79 0.40 97.0 41.5 93–491 amph inclusion3 in plag11 43.32 5.26 2.64 0.05 23.81 0.60 10.71 11.17 0.31 97.9 44.5 a Compositions are in wt% and were determined by electron microscope at MIT. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 13 of 34 Table 3. Major Element Compositions in Basalt From Mt. Capitolea Sample Height, m SiO2 TiO2 Al2O3 Fe2O3* b MnO MgO CaO Na2O K2O P2O5 Total LOI c Upper Transitional Group Lavas 93–459 860 48.71 2.04 18.05 10.97 0.17 4.78 11.57 2.74 0.67 0.26 99.96 1.36 93–460 840 48.69 2.39 16.80 12.44 0.19 4.67 10.52 2.91 0.88 0.34 99.83 2.99 93–461 840 48.77 2.60 15.35 13.35 0.20 4.93 10.56 3.01 0.78 0.34 99.89 0.57 93–462 825 48.49 2.33 16.22 12.41 0.19 5.46 11.00 2.65 0.64 0.29 99.68 5.20 93–463 815 48.13 2.33 15.71 12.92 0.19 6.47 10.76 2.43 0.66 0.28 99.88 1.62 93–464 810 48.18 2.76 14.55 13.89 0.20 5.81 10.44 2.88 0.70 0.32 99.73 2.20 93–465 800 48.50 2.27 16.20 12.17 0.18 6.00 11.10 2.55 0.69 0.26 99.92 2.29 93–467 780 48.50 2.61 14.29 13.39 0.21 6.54 10.91 2.66 0.48 0.32 99.91 1.94 93–468 760 48.45 2.53 14.94 13.19 0.18 6.42 11.00 2.04 0.51 0.30 99.56 4.42 93–469 750 48.89 2.49 14.54 13.05 0.19 6.27 10.90 2.46 0.56 0.30 99.65 1.91 93–470 740 47.95 2.35 15.92 12.25 0.18 6.30 10.75 2.93 0.54 0.27 99.44 2.47 93–471 735 48.52 2.38 15.91 12.50 0.19 6.24 11.13 2.46 0.59 0.28 100.20 2.94 93–472 730 47.24 2.27 15.10 12.90 0.19 8.00 11.15 2.27 0.46 0.29 99.87 4.39 93–473 715 47.89 2.50 15.89 13.30 0.20 5.93 10.37 2.88 0.55 0.31 99.82 4.23 93–474 690 48.57 2.73 15.00 13.08 0.19 5.48 10.80 2.79 0.57 0.37 99.58 1.18 93–491 540 48.58 2.52 14.49 12.96 0.19 7.12 11.01 2.12 0.20 0.29 99.48 3.07 Lower Transitional Group Lavas 93–475 690 49.51 3.26 13.31 14.65 0.20 4.55 10.19 2.86 0.77 0.45 99.75 1.95 93–476 685 49.12 3.23 13.20 14.80 0.20 5.06 9.74 2.90 1.00 0.45 99.70 2.20 93–477 680 48.50 3.17 14.25 14.31 0.18 5.22 10.08 2.85 0.76 0.41 99.73 1.49 Low-Silica Group Lavas 93–478 660 47.88 3.87 12.95 16.39 0.26 4.62 9.76 2.73 0.47 0.50 99.43 1.66 93–479 640 49.33 3.74 13.18 15.84 0.20 4.19 9.42 2.85 0.97 0.50 100.22 2.04 93–480 630 48.55 3.89 12.59 16.42 0.24 4.58 9.38 2.76 0.80 0.48 99.69 0.77 93–481 610 47.12 4.20 13.27 16.47 0.24 4.82 9.83 2.95 0.71 0.52 100.13 1.40 93–482 600 46.17 4.47 13.30 17.31 0.26 4.59 9.13 2.72 0.98 0.55 99.48 1.17 93–483 590 47.69 4.02 13.34 15.72 0.27 4.65 10.32 2.60 0.75 0.47 99.83 2.18 93–484 580 47.46 3.78 13.52 15.98 0.24 4.93 10.47 2.40 0.41 0.43 99.62 1.91 93–485 570 47.76 3.75 13.38 15.85 0.22 5.18 10.21 2.39 0.60 0.44 99.78 1.14 93–486 560 47.33 3.83 14.18 16.01 0.22 4.61 10.11 2.92 0.42 0.45 100.08 1.68 Lower Transitional Group Lavas 93–487 560 48.75 3.56 12.93 15.70 0.22 4.95 9.75 2.36 0.47 0.45 99.14 0.92 93–488 550 49.25 3.48 13.16 15.12 0.23 5.05 10.08 2.34 0.44 0.42 99.57 0.89 93–489 540 48.58 3.29 13.60 14.74 0.22 5.39 10.40 2.53 0.35 0.40 99.50 1.53 93–490 540 51.66 3.82 12.87 14.51 0.18 3.77 8.60 2.80 1.02 0.48 99.71 0.94 93–492 540 47.84 3.33 13.70 15.00 0.25 5.82 10.31 2.53 0.40 0.41 99.59 1.54 93–493 530 47.57 3.35 13.84 15.31 0.19 5.84 10.41 2.29 0.23 0.37 99.40 2.98 93–494 520 49.66 3.34 12.97 15.01 0.22 5.01 9.53 2.78 0.74 0.40 99.66 0.33 93–495 510 49.88 3.32 13.20 14.44 0.19 4.94 9.42 2.80 0.83 0.40 99.42 0.40 93–496 505 50.29 3.50 13.39 14.41 0.24 4.56 8.66 2.95 1.02 0.44 99.46 0.75 93–497 490 49.10 3.55 13.32 15.30 0.25 5.10 9.25 2.80 0.57 0.44 99.68 0.93 93–498 480 49.86 3.63 13.30 15.36 0.20 4.69 9.28 2.74 0.50 0.44 100.00 1.61 93–499 470 49.48 3.23 13.23 14.31 0.23 5.43 10.08 2.74 0.45 0.39 99.57 1.21 93–500 465 49.73 3.57 13.24 14.74 0.26 5.34 9.55 2.86 0.63 0.43 100.35 1.04 93–501 455 49.39 3.14 13.93 14.35 0.22 5.17 10.26 2.98 0.49 0.37 100.30 1.20 93–502 440 48.52 3.00 14.26 13.60 0.22 5.96 10.72 2.66 0.51 0.33 99.78 1.31 93–503 435 48.53 3.31 13.62 14.82 0.21 5.58 10.49 2.38 0.33 0.39 99.66 1.29 93–504 430 48.25 3.90 13.33 15.86 0.30 5.05 9.19 2.17 0.90 0.47 99.42 6.31 93–505 420 51.43 3.93 13.31 14.15 0.18 3.95 8.54 2.69 0.98 0.50 99.66 2.26 93–506 410 49.76 3.46 13.80 14.67 0.27 4.73 8.69 2.97 0.89 0.49 99.73 1.84 93–507 400 50.18 3.44 13.71 14.95 0.21 4.37 8.63 3.00 1.08 0.49 100.06 1.27 93–508 390 50.22 3.72 12.91 15.17 0.20 4.37 8.34 2.97 1.19 0.48 99.57 1.16 93–509 380 50.54 3.51 13.15 14.38 0.21 4.39 8.67 3.23 0.99 0.47 99.54 0.61 93–510 350 52.88 3.50 13.41 13.48 0.18 3.29 7.14 3.30 1.62 0.69 99.49 0.57 Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 14 of 34 boundary (Figures 5, 6, and 7). They are designat- ed as the Low-Silica Group. This group does not vary widely in MgO (4.1 to 5.2 wt%); in general its compositional range overlaps with the uppermost group of slightly alkalic lavas in the Mt. Tourmente section (Figure 7). [22] All other samples from Mt. Capitole, 30 lavas from 680–690 m and 230–560 m (Figure 6) form the third group designated as Lower Transitional Group. The major element compositions of this group largely overlap the transitional lavas that occur in the lower 80% of the Mt. Tourmente section (Figure 7). [23] In summary, as at Mt. Tourmente, at Mt. Capitole there is a transition from tholeiitic to alkalic basalt with decreasing age; however, pla- gioclase-rich lavas are abundant in the upper part of the Mt. Capitole section. Plagioclase-phyric lavas are absent at Mt. Tourmente [Frey et al., 2002a], but they also occur at Mt. Marion Dufresne [Annell et al., 2007]. 4.3.2. Trace Elements [24] Abundances of Th, Nb, Pb, Zr and Yb are highly correlated in Mt. Capitole lavas; in contrast abundances of K, Rb, Sr and Ba are poorly correlated with Th abundance (Figure 8). The ranges in Rb and K contents (factors of 33 and 8, respectively) are much greater than those for rela- tively immobile incompatible elements, such as Nb, Zr and Th (factors of 2 to 4). The ranges for Ba and Sr (factors of 3.8 and 3.1, respectively) are comparable to those for immobile incompatible elements. We infer that Mt. Capitole samples experienced post-magmatic alteration and that Rb and K were mobile during the alteration, but that Ba and Sr were less mobile. Despite their relatively low Th content the plagioclase-rich Upper Transi- tional Group lavas have K, Rb, Sr and Ba contents similar to lavas in the other groups (Figure 8). Note that there is a relative Sr depletion, i.e., relatively low Sr/Ce and Sr/Nd ratios, in the Lower Transi- tional Group and Low-Silica Group lavas but not in the plagioclase-rich Upper Transitional Group (Figure 9). [25] All Mt. Capitole samples are enriched in incompatible elements relative to primitive mantle (Figure 9). The highest incompatible element con- tents are in the low MgO (3.3 to 3.8 wt%) lavas of the Lower Transitional Group; the lowest contents are in the plagioclase-rich Upper Transitional Group; incompatible element contents in the Low-Silica Group overlap with those of alkalic lavas at Mt. Tourmente (Figure 9). At a given MgO content, incompatible element contents increase in the order: Upper Transitional Group < Lower Transitional Group < Low-Silica Group. [26] All Mt. Capitole lavas contain relatively low and variable abundances of transition elements (Ni = 34–128 ppm; Cr = 2–272 ppm, Table 4) that are positively correlated with MgO. Abundance of Sc ranges from 28 to 32 ppm for lavas with MgO greater than 5.5 wt%, but ranges to lower Sc (24 ppm) with decreasing MgO content (Table 4). Like TiO2, the Upper Transitional Group samples have the lowest V contents while Low-Silica Group lavas have relatively high Vabundances (Table 4). 4.4. Sr, Nd, Hf, and Pb Isotopes [27] Although there are no long-term systematic temporal variations of Sr, Nd, Hf and Pb isotopic ratios with stratigraphic height, i.e., inferred erup- tion age, in the Mt. Capitole section, samples of the Upper Transitional and Low-Silica Groups define trends of increasing 87Sr/86Sr and decreasing 143Nd/144Nd, 176Hf/177Hf with decreasing height; in contrast the lower Transitional Group lavas show no systematic variations of isotope ratios with height (Figure 10). [28] Most of the Mt. Capitole lavas define an inverse correlation of 87Sr/86Sr and 143Nd144Nd, Table 3. (continued) Sample Height, m SiO2 TiO2 Al2O3 Fe2O3* b MnO MgO CaO Na2O K2O P2O5 Total LOI c 93–511 310 51.39 3.68 13.60 14.37 0.23 3.78 8.37 2.81 1.01 0.60 99.84 1.93 93–512 270 50.93 2.90 13.50 13.71 0.20 5.12 9.53 2.83 0.65 0.37 99.74 0.43 93–513 250 50.68 2.83 13.88 13.62 0.21 5.35 9.76 2.48 0.48 0.36 99.65 0.88 93–514 230 50.14 3.30 13.42 14.45 0.19 4.74 9.04 3.13 0.71 0.41 99.53 1.24 a Major oxide abundances (wt.%) were determined by X-ray fluorescence (XRF) at the University of Massachusetts following the procedures of Rhodes [1996]. b Fe2O3* indicates all iron reported as Fe2O3. c Loss on ignition (LOI) indicates weight loss after heating to 1020C for 30 min. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 15 of 34 Table 4. (Representative Sample). Trace Element Abundances in Basalt From Mt. Capitolea [The full Table 4 is available in the HTML version of this article at http://www.g-cubed.org.] Rb Ba Th U Nb Ta La Ce Pb Pr Nd Sr Zr Upper Transitional Group Lavas 93–459 7.97 168 1.83 0.321 16.0 1.00 14.3 35.1 1.43 4.31 18.2 410 124 93–460 14.4 231 2.31 0.360 20.4 1.24 18.9 41.0 1.73 5.44 22.8 379 163 93–461 15.2 186 2.00 0.444 20.0 1.26 18.1 41.3 1.83 5.75 24.0 367 171 93–462 8.04 152 1.74 0.322 15.9 1.01 14.7 34.5 1.38 4.45 19.6 362 137 93–463 8.47 150 1.59 0.298 16.1 1.00 14.4 32.2 1.35 4.39 18.6 331 132 93–464 7.57 188 2.14 0.381 19.2 1.23 18.1 41.5 1.70 5.33 23.3 361 159 93–465 9.85 170 1.53 0.315 14.1 0.91 13.1 31.5 1.26 3.93 17.2 349 118 93–467 3.05 182 1.92 0.389 18.2 1.13 16.2 40.7 1.71 5.22 22.4 329 155 93–468 6.02 235 1.75 0.229 16.6 1.02 14.7 36.8 1.54 4.64 20.3 298 139 93–469 5.13 159 1.76 0.353 16.9 1.03 14.9 36.5 1.53 4.63 20.1 317 143 93–470 6.65 176 1.69 0.275 16.7 1.04 14.4 36.2 1.52 4.61 19.8 349 137 93–471 8.60 164 1.55 0.284 16.8 1.03 14.9 34.2 1.36 4.66 20.1 331 143 93–472 6.17 114 1.34 0.171 14.2 0.89 12.8 30.9 1.11 4.01 17.6 389 127 93–473 7.23 147 1.83 0.222 16.1 1.01 15.2 33.5 1.46 4.56 19.7 291 145 93–474 3.56 198 2.58 0.500 22.0 1.33 20.5 42.8 2.10 6.01 26.0 349 195 93–491 1.17 96 1.89 0.340 17.0 1.08 14.7 35.1 1.49 4.75 21.0 301 160 Lower Transitional Group Lavas 93–475 6.33 232 3.02 0.648 26.6 1.60 24.0 51.8 2.23 7.08 30.1 323 233 93–476 17.1 224 2.93 0.620 25.9 1.56 22.8 51.3 2.25 6.81 29.5 300 225 93–477 7.05 201 2.52 0.441 22.6 1.38 21.2 47.2 2.02 6.24 26.7 343 203 Low–Silica Group Lavas 93–478 8.86 210 2.97 0.555 29.1 1.72 24.4 54.5 2.28 7.64 33.0 323 262 93–479 21.8 214 2.92 0.654 29.1 1.71 23.7 53.9 2.27 7.55 32.0 298 249 93–480 7.79 218 2.97 0.637 28.5 1.73 24.5 56.2 2.29 7.55 32.2 306 258 93–481 5.35 202 2.83 0.526 29.4 1.74 23.2 52.9 2.21 7.38 31.8 297 251 93–482 14.1 219 3.27 0.661 34.0 2.08 26.5 60.9 2.42 8.55 37.2 347 298 93–483 21.1 177 2.56 0.564 27.5 1.69 23.3 53.8 2.56 7.34 32.3 330 244 93–484 3.15 166 2.51 0.516 24.9 1.53 21.4 48.4 1.86 6.61 29.2 329 226 93–485 9.70 164 2.67 0.607 25.0 1.53 22.2 49.3 2.12 6.86 29.8 327 236 93–486 1.97 200 3.00 0.531 29.0 1.83 23.6 56.7 2.36 7.60 33.3 355 259 Lower Transitional Group Lavas 93–487 8.84 185 2.71 0.588 25.6 1.59 21.8 51.8 2.16 6.89 30.0 306 233 93–488 9.59 158 2.54 0.558 25.5 1.60 21.6 49.8 2.11 6.79 29.7 302 231 93–489 4.58 159 2.70 0.518 24.9 1.58 21.9 52.5 2.03 6.69 29.4 344 232 93–490 18.3 227 3.25 0.737 28.1 1.78 25.7 57.9 2.57 7.67 33.6 333 268 93–492 3.95 158 2.54 0.503 25.1 1.49 20.2 48.7 1.98 6.37 27.8 318 227 93–493 2.00 192 2.27 0.424 23.8 1.52 19.1 46.5 1.97 6.32 26.9 304 216 93–494 9.52 184 2.51 0.591 25.5 1.59 21.9 51.0 2.07 6.95 30.7 316 233 93–495 12.7 172 2.61 0.603 24.2 1.48 21.1 46.1 1.94 6.47 28.5 340 227 93–496 21.0 206 3.05 0.690 26.9 1.66 24.2 48.5 2.38 7.22 30.9 313 252 93–497 5.09 210 3.10 0.635 26.0 1.62 24.6 51.9 2.33 7.36 31.7 324 247 93–498 14.1 182 3.02 0.607 29.0 1.85 25.6 58.1 2.49 7.86 33.3 323 265 93–499 8.80 182 2.64 0.578 25.3 1.54 21.3 50.8 2.05 6.68 29.3 337 228 93–500 13.1 211 3.01 0.650 27.0 1.69 24.5 54.3 2.33 7.28 31.2 317 249 93–501 4.00 156 2.18 0.441 19.8 1.24 17.6 40.1 1.75 5.43 23.7 317 184 93–502 3.13 149 1.96 0.389 19.1 1.20 16.0 37.1 1.59 5.09 22.2 306 171 93–503 1.61 157 2.54 0.579 24.1 1.44 20.3 47.1 1.97 6.40 27.2 309 219 93–504 12.6 187 2.84 0.653 25.2 1.67 20.4 52.7 2.23 7.17 29.6 290 226 93–505 18.9 215 3.22 0.732 28.2 1.76 24.5 56.2 2.56 7.45 32.6 336 271 93–506 9.89 245 3.54 0.737 31.6 1.87 26.9 60.8 2.49 8.38 35.7 344 291 93–507 19.6 232 3.35 0.789 31.3 1.95 26.3 61.0 2.75 8.26 35.0 322 289 93–508 26.6 241 3.40 0.790 32.2 2.02 28.2 65.2 2.73 8.72 38.0 313 292 aTrace element abundances are in ppm. Ni, Cr, and V were determined by XRF at the University of Massachusetts following the procedures of Rhodes [1996]. Sc was determined by INAA at MIT following the procedures of Ila and Frey [2000]. All others were determined by ICP-MS at MIT. The abundances for BHVO-2 are the average values of 15 analyses, with relative standard deviation of 3% [Huang and Frey, 2003]. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 16 of 34 T a b le 5 . S r, N d , H f, an d P b Is o to p e C o m p o si ti o n s fo r M t. C ap it o le W h o le R o ck L av as an d P la g io cl as e P h en o cr y st sa 8 7 S r/ 8 6 S r 2 s (8 7 S r/ 8 6 S r) i 1 4 3 N d /1 4 4 N d 2 s (1 4 3 N d /1 4 4 N d ) i 1 7 6 H f/ 1 7 7 H f2 s (1 7 6 H f/ 1 7 7 H f) i 2 0 6 P b /2 0 4 P b 2 s (2 0 6 P b /2 0 4 P b ) i 2 0 7 P b /2 0 4 P b 2 s (2 0 7 P b /2 0 4 P b ) i 2 0 8 P b /2 0 4 P b 2 s (2 0 8 P b /2 0 4 P b ) i U p p er T ra n si ti o n a l G ro u p 9 3 – 4 5 9 0 .7 0 4 8 3 5 1 0 0 .7 0 4 8 1 0 .5 1 2 6 8 5 8 0 .5 1 2 6 6 0 .2 8 2 8 6 3 4 0 .2 8 2 8 6 1 8 .4 4 1 8 1 3 1 8 .3 8 4 1 5 .5 5 1 2 1 5 1 5 .5 4 8 3 8 .9 6 9 9 3 6 3 8 .8 6 1 9 3 – 4 5 9 0 .7 0 4 8 2 0 .5 1 2 6 5 1 8 .3 8 7 1 5 .5 4 9 3 8 .9 2 6 9 3 – 4 5 9 p la g 0 .7 0 4 7 4 0 1 0 0 .7 0 4 7 4 1 8 .4 6 5 2 3 1 8 .4 5 1 5 .5 8 4 1 9 1 5 .5 8 3 8 .8 9 4 5 2 3 8 .8 8 9 3 – 4 6 3 0 .7 0 4 8 3 2 9 0 .7 0 4 8 1 0 .5 1 2 6 9 7 6 0 .5 1 2 6 7 0 .2 8 2 8 7 6 4 0 .2 8 2 8 7 1 8 .3 9 7 3 1 1 1 8 .3 4 1 1 5 .5 3 9 8 9 1 5 .5 3 7 3 8 .8 8 2 1 2 2 3 8 .7 8 3 9 3 – 4 6 5 0 .7 0 4 8 2 8 9 0 .7 0 4 8 0 0 .5 1 2 6 9 3 7 0 .5 1 2 6 7 0 .2 8 2 8 8 6 4 0 .2 8 2 8 8 1 8 .4 1 9 3 8 1 8 .3 5 6 1 5 .5 4 2 6 7 1 5 .5 4 0 3 8 .8 9 3 7 2 0 3 8 .7 9 2 9 3 – 4 6 5 0 .7 0 4 8 0 8 7 0 .7 0 4 7 8 0 .5 1 2 6 9 7 3 0 .5 1 2 6 7 0 .2 8 2 8 8 2 5 0 .2 8 2 8 8 1 8 .4 1 9 1 1 1 1 8 .3 5 5 1 5 .5 4 2 4 9 1 5 .5 3 9 3 8 .8 9 1 5 2 1 3 8 .7 8 9 9 3 – 4 6 5 U L 0 .7 0 4 8 7 5 7 0 .5 1 2 6 8 0 5 1 8 .4 2 3 6 8 1 8 .3 6 0 1 5 .5 4 5 9 8 1 5 .5 4 3 3 8 .9 1 2 4 2 1 3 8 .8 1 0 9 3 – 4 7 1 0 .7 0 4 8 0 2 7 0 .7 0 4 7 7 0 .5 1 2 7 0 5 6 0 .5 1 2 6 8 0 .2 8 2 8 8 4 4 0 .2 8 2 8 8 1 8 .4 0 3 7 8 1 8 .3 5 1 1 5 .5 4 2 1 7 1 5 .5 4 0 3 8 .8 6 5 8 2 0 3 8 .7 7 0 9 3 – 4 7 1 0 .7 0 4 7 8 0 .5 1 2 6 7 1 8 .3 3 7 1 5 .5 3 9 3 8 .8 1 4 9 3 – 4 7 1 p la g 0 .7 0 4 7 6 1 8 0 .7 0 4 7 6 1 8 .4 6 2 3 5 1 8 .4 5 1 5 .6 4 0 2 9 1 5 .6 4 0 3 8 .9 1 0 7 0 3 8 .9 0 9 3 – 4 7 2 0 .7 0 4 7 7 2 6 0 .7 0 4 7 6 0 .5 1 2 7 0 4 5 0 .5 1 2 6 8 0 .2 8 2 8 8 5 4 0 .2 8 2 8 8 1 8 .4 7 1 8 2 6 1 8 .3 9 1 1 5 .5 5 3 6 2 4 1 5 .5 5 0 3 8 .9 4 1 4 5 7 3 8 .8 4 0 L o w -S il ic a G ro u p 9 3 – 4 7 9 0 .7 0 4 7 8 3 7 0 .7 0 4 7 1 0 .5 1 2 7 1 7 5 0 .5 1 2 6 9 0 .2 8 2 9 0 5 4 0 .2 8 2 9 0 1 8 .4 7 2 1 8 1 8 .3 9 9 1 5 .5 5 0 5 7 1 5 .5 4 7 3 8 .9 1 5 5 1 9 3 8 .8 0 7 9 3 – 4 8 2 0 .7 0 4 7 1 6 8 0 .7 0 4 6 7 0 .5 1 2 7 2 8 5 0 .5 1 2 7 0 0 .2 8 2 8 9 7 4 0 .2 8 2 8 9 1 8 .4 5 6 2 1 3 1 8 .3 8 6 1 5 .5 4 8 8 1 2 1 5 .5 4 6 3 8 .8 7 6 2 2 8 3 8 .7 6 2 9 3 – 4 8 3 0 .7 0 4 7 7 6 9 0 .7 0 4 7 1 0 .5 1 2 7 1 4 5 0 .5 1 2 6 9 1 8 .4 3 8 6 1 0 1 8 .3 8 2 1 5 .5 5 2 0 9 1 5 .5 4 9 3 8 .8 9 9 1 2 6 3 8 .8 1 4 L o w er T ra n si ti o n a l G ro u p 9 3 – 4 7 6 0 .7 0 4 9 1 3 6 0 .7 0 4 8 5 0 .5 1 2 6 8 6 7 0 .5 1 2 6 6 0 .2 8 2 8 8 4 5 0 .2 8 2 8 8 1 8 .3 9 5 4 8 1 8 .3 2 5 1 5 .5 4 4 9 8 1 5 .5 4 2 3 8 .8 7 4 8 2 2 3 8 .7 6 5 9 3 – 4 9 0 0 .7 0 5 0 4 6 6 0 .7 0 4 9 9 0 .5 1 2 6 9 4 6 0 .5 1 2 6 7 0 .2 8 2 8 7 1 4 0 .2 8 2 8 7 1 8 .3 7 6 9 1 0 1 8 .3 0 4 1 5 .5 5 1 4 9 1 5 .5 4 8 3 8 .8 1 0 2 2 6 3 8 .7 0 4 9 3 – 4 9 0 0 .7 0 5 0 3 9 7 0 .7 0 4 9 8 0 .5 1 2 6 9 0 6 0 .5 1 2 6 7 0 .2 8 2 8 6 9 3 0 .2 8 2 8 6 1 8 .3 9 0 6 1 4 1 8 .3 1 8 1 5 .5 5 2 0 1 3 1 5 .5 4 9 3 8 .8 2 9 9 3 2 3 8 .7 2 4 9 3 – 4 9 5 0 .7 0 4 7 7 0 6 0 .7 0 4 7 3 0 .5 1 2 7 2 2 6 0 .5 1 2 7 0 0 .2 8 2 8 9 7 5 0 .2 8 2 8 9 1 8 .4 6 1 8 1 3 1 8 .3 8 2 1 5 .5 5 5 3 1 2 1 5 .5 5 2 3 8 .8 6 8 2 3 4 3 8 .7 5 4 9 3 – 5 0 5 0 .7 0 5 0 6 0 9 0 .7 0 5 0 0 0 .5 1 2 6 8 9 5 0 .5 1 2 6 6 0 .2 8 2 8 6 9 4 0 .2 8 2 8 6 1 8 .3 9 3 8 7 1 8 .3 2 1 1 5 .5 4 9 4 7 1 5 .5 4 6 3 8 .8 4 2 5 1 8 3 8 .7 3 6 9 3 – 5 0 7 0 .7 0 4 8 4 1 8 0 .7 0 4 7 8 0 .5 1 2 7 0 6 5 0 .5 1 2 6 8 0 .2 8 2 8 9 1 5 0 .2 8 2 8 9 1 8 .4 2 0 0 5 1 8 .3 4 7 1 5 .5 4 0 7 6 1 5 .5 3 7 3 8 .8 4 8 8 1 5 3 8 .7 4 6 9 3 – 5 1 0 0 .7 0 4 9 3 5 6 0 .7 0 4 8 2 0 .5 1 2 7 0 4 5 0 .5 1 2 6 8 0 .2 8 2 8 9 4 5 0 .2 8 2 8 9 1 8 .4 2 4 3 9 1 8 .3 3 1 1 5 .5 4 0 5 7 1 5 .5 3 6 3 8 .8 5 3 4 1 9 3 8 .7 2 1 9 3 – 5 1 2 0 .7 0 4 7 9 0 7 0 .7 0 4 7 6 0 .5 1 2 7 1 7 6 0 .5 1 2 6 9 0 .2 8 2 8 8 7 5 0 .2 8 2 8 8 1 8 .4 3 8 2 1 5 1 8 .3 6 7 1 5 .5 4 2 1 1 3 1 5 .5 4 5 3 8 .8 8 0 0 3 5 3 8 .7 7 0 9 3 – 5 1 2 0 .7 0 4 8 0 3 7 0 .7 0 4 7 7 0 .5 1 2 7 0 6 5 0 .5 1 2 6 8 0 .2 8 2 8 8 1 6 0 .2 8 2 8 8 1 8 .4 4 5 1 1 4 1 8 .3 7 4 1 5 .5 4 8 7 1 3 1 5 .5 3 9 3 8 .9 0 0 4 3 3 3 8 .7 9 0 a N o te s: (1 ) W it h in ea ch g ro u p , sa m p le s ar e in st ra ti g ra p h ic o rd er . (2 ) P ri o r to is o to p ic an al y se s, al l sa m p le s w er e ac id -l ea ch ed fo ll o w in g th e p ro ce d u re s o f W ei s et a l. [2 0 0 5 ]. T h e ef fe ct s o f ac id le ac h in g ar e sh o w n b y d at a fo r le ac h ed an d u n le ac h ed (U L ) al iq u o ts o f sa m p le 9 3 – 4 6 5 . (3 ) M ea su re d S r is o to p ic ra ti o s w er e n o rm al iz ed to 8 6 S r/ 8 8 S r = 0 .1 1 9 4 , an d N d ra ti o s w er e n o rm al iz ed to 1 4 6 N d /1 4 4 N d = 0 .7 2 1 9 . M ea n m ea su re d 8 7 S r/ 8 6 S r fo r S R M 9 8 7 at U B C d u ri n g th e co u rs e o f st u d y w as 0 .7 1 0 2 6 0 ± 1 3 (2 s , n = 4 2 ), an d 1 4 3 N d /1 4 4 N d fo r L a Jo ll a st an d ar d w as 0 .5 11 8 5 8 ± 7 (2 s , n = 1 8 ). T h e 8 7 S r/ 8 6 S r d at a fo r p la g io cl as e p h en o cr y st s w er e n o rm al iz ed to S R M 9 8 7 S r st an d ar d o f 0 .7 1 0 2 6 0 to av o id in te r- la b b ia s. 1 7 6 H f/ 1 7 7 H f ra ti o s re p o rt ed w er e n o rm al iz ed to JM C 4 7 5 H f st an d ar d o f 0 .2 8 2 1 6 0 . P b is o to p ic ra ti o s w er e m ea su re d u si n g T l sp ik in g (w it h a 2 0 5 T l/ 2 0 3 T l = 2 .3 8 8 5 ) fo r fr ac ti o n at io n co rr ec ti o n [W ei s et a l. , 2 0 0 5 ]. M ea n m ea su re d 2 0 6 P b /2 0 4 P b , 2 0 7 P b /2 0 4 P b , an d 2 0 8 P b /2 0 4 P b fo r S R M 9 8 1 P b st an d ar d at U B C w er e 1 6 .9 4 1 8 ± 2 2 (2 s , n = 9 4 ), 1 5 .4 9 7 9 ± 2 6 (2 s, n = 9 4 ), an d 3 6 .7 1 8 4 ± 6 3 (2 s , n = 9 4 ), re sp ec ti v el y. T h e P b is o to p ic ra ti o s o f p la g io cl as e w er e an al y ze d b y T IM S at M IT u si n g a fr ac ti o n at io n co rr ec ti o n o f 0 .1 2 ± 0 .0 3 % /a m u , b as ed o n th e v al u es o f T o d t et a l. [1 9 9 6 ]. (4 ) T w o si g m a (2 s ) er ro rs ap p ly to la st d ec im al p la ce . T h e ex te rn al re p ro d u ci b il it ie s fo r 8 7 S r/ 8 6 S r an d 1 4 3 N d /1 4 4 N d b as ed o n th re e d u p li ca te s (9 3 – 4 6 5 , 9 3 – 4 9 0 , an d 9 3 – 5 1 2 ) ar e b et te r th an 2 0  1 0 6 an d 1 1  1 0 6 , re sp ec ti v el y, w h ic h is w it h in o r sl ig h tl y la rg er th an th e m ac h in e in -r u n u n ce rt ai n ti es . T h e ex te rn al re p ro d u ci b il it ie s at U B C fo r 2 0 6 P b /2 0 4 P b , 2 0 7 P b /2 0 4 P b , an d 2 0 8 P b /2 0 4 P b ar e b et te r th an 7 4 4 p p m , 4 2 8 p p m , an d 5 2 5 p p m , re sp ec ti v el y. (5 ) S u b sc ri p t ‘‘ i’ ’ (i n it ia l) m ea su re d ra ti o s co rr ec te d to 2 5 .7 M a, th e ag e o f la v as fr o m n ea rb y M t. T o u rm en te . P ar en t/ d au g h te r ab u n d an ce ra ti o s u se d fo r ag e co rr ec ti o n s ar e d at a fo r u n le ac h ed sa m p le s (T ab le 4 ) ex ce p t fo r sa m p le 4 7 2 , w h ic h h as a v er y h ig h N b /U ra ti o in d ic at in g U lo ss ; th er ef o re N b /U = 4 0 w as u se d to ca lc u la te U co n te n t, w h ic h w as u se d to ca lc u la te th e in it ia l P b is o to p e ra ti o s. F o r sa m p le s 9 3 – 4 7 1 an d 9 3 – 4 5 9 , p ar en t/ d au g h te r ra ti o s ar e al so av ai la b le fo r le ac h ed sa m p le s; th e ca lc u la te d in it ia l ra ti o s fo r th e tw o se ts o f p ar en t/ d au g h te r ra ti o s ar e w it h in an al y ti ca l u n ce rt ai n ti es . Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 17 of 34 but two samples of the Lower Transitional Group are offset to higher 87Sr/86Sr (Figure 11a). The lowest 87Sr/86Sr ratios are in the lavas of the Low- Silica Group and one of these samples (93–482) has the lowest 87Sr/86Sr and highest 143Nd/144Nd; the Low-Silica Group lavas overlap with the field for Mt. Tourmente but the other two groups include samples that range to higher 87Sr/86Sr and lower 143Nd/144Nd (Figure 11a). [29] Mt. Capitole lavas define a positive trend in 143Nd/144Nd versus 176Hf/177Hf overlapping with the field of Mt. Tourmente lavas but extend to lower 143Nd/144Nd and 176Hf/177Hf (Figure 11b); this trend is parallel to the slope of mantle-OIB array [Vervoort et al., 1999]. [30] In plots of 208Pb/204Pb and 207Pb/204Pb versus 206Pb/204Pb, there is overlap among the three compositional groups of Mt. Capitole lavas (Figure 12a). Also the two samples of the Lower Transitional Group that are offset to high 87Sr/86Sr (Figure 11a) have anomalously high 207Pb/204Pb (Figure 12b); one of these samples (93–490) was analyzed in duplicate (Table 5). As with Sr, Nd and Hf isotopic ratios, Pb isotopic ratios in the Low- Silica Group lavas overlap with the field for Mt. Tourmente lavas, but lavas from the Upper and Lower Transitional Group range to higher 87Sr/86Sr, lower 143Nd/144Nd and 176Hf/177Hf and higher 208Pb/204Pb at a given 206Pb/204Pb (Figures 11 and 12). [31] The Upper Transitional Group lavas from Mt. Capitole show a correlation between (206Pb/204Pb)i and (Sr/Nd)PM (PM stands for primitive mantle value of Sun and McDonough [1989]) (Figure 13). Since high (Sr/Nd)PM is characteristic of plagio- clase (Table 6), the plagioclase-rich component is inferred to have relatively high 206Pb/204Pb. Pla- gioclase grains from two Upper Transitional Group samples, 93–459 and 93–471, which have the extremes in Sr/Nd ratios among the five samples analyzed for radiogenic isotopes, were analyzed for Sr and Pb isotopes (Table 5). Plagioclase xeno- crysts from these two samples have the same Sr and Pb isotope ratios within analytical uncertainties (Figure 12a and Table 5), indicating that these plagioclase xenocrysts were derived from the same source. The plagioclases and whole-rock have similar 87Sr/86Sr, but as expected from the correla- tions between Sr/Nd versus 206Pb/204Pb (Figure 13), the plagioclase xenocrysts have more radiogenic Pb isotope ratios than their whole rocks (Figure 12a and Table 5). 5. Discussion 5.1. Origin of Compositional Variations in Mt. Capitole Lavas 5.1.1. Role of Crystal Fractionation and Accumulation [32] Mt. Capitole lavas define two different Al2O3 versus MgO trends, a positive trend, similar to Mt. Tourmente lavas, for the Low-Silica and Lower Transitional Group lavas and a negative trend for the Upper Transitional Group (Figure 14). A neg- ative Al2O3 versus MgO trend defined by Mt. Crozier lavas, in the northeast part of the archipel- ago (Figure 1), was inferred to reflect fractionation of a clinopyroxene-dominated assemblage at high pressure by Damasceno et al. [2002] and Scoates et al. [2006]. They inferred that lithospheric thick- ness increased as the archipelago evolved from a near-ridge setting at 40 Ma to its present intra- plate location (see inset of Figure 1); therefore younger flood basalts, such as at Mt. Crozier, were likely to stagnate at higher pressure where the fractionating mineral assemblage has a high pro- portion of clinopyroxene. We favor a different interpretation, i.e., plagioclase accumulation, for Table 6. Selected Trace Element Ratios for Whole Rocks and Plagioclase Phenocrysts (Sr/Nd)PM 87Rb/86Sr 87Sr/86Sr 147Sm/144Nd 143Nd/144Nd 238U/204Pb 235U/204Pb 232Th/204Pb 93–459 plagioclase 28.5 0.00157 0.704750 0.138 3.19 0.0232 9.6 93–459 whole rock leacheda 2.74 0.054 0.196 12.6 0.091 34 93–459 whole rock unleachedb 1.45 0.056 0.704835 0.140 0.512685 14.4 0.104 86 93–471 plagioclase 22.1 0.00193 0.704771 0.127 1.81 0.0132 7.5 93–471 whole rock leached 2.44 0.067 0.207 15.2 0.111 41 93–471 whole rock unleached 1.05 0.075 0.704802 0.141 0.512705 13.3 0.097 76 a Whole rock was leached repeatedly in 6 N HCl following the same procedures used in Sr, Nd, and Pb isotope analyses before dissolving for ICP-MS analyses. b Results from Table 4. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 18 of 34 Figure 3. Backscattered electron images of polished thin sections of Upper Transitional Group samples. (a) Plagioclase xenocryst from sample 93–471 showing irregular morphology that is interpreted as resorption. (b) Sieve-textured plagioclase xenocryst from 93–465 showing abundant inclusions of clinopyroxene, olivine, amphibole, and Fe-Ti oxide. (c) Expanded scale of Figure 3b showing Na-rich plagioclase domains. (d) Expanded scale of Figure 3b showing olivine, clinopyroxene, pigeonite, amphibole, Fe-Ti oxide, and apatite inclusions. The inset with increased contrast shows the Na-rich plagioclase rims around the olivine, clinopyroxene, amphibole, and Fe-Ti oxide inclusions. These Na-rich plagioclase rims have variable compositions ranging from An5 to An54. (e) Expanded scale of Figure 3c showing the amphibole inclusion. The inset with increased contrast shows the Na- rich plagioclase rim partly surrounding the amphibole inclusion. Note that the plagioclase An composition decreases systematically along the elongated direction of the amphibole, which indicates nonequilibrium crystallization. (f) Another example of an amphibole inclusion in a plagioclase xenocryst from sample 93–459. PLAG, plagioclase; CPX, clinopyroxene; PIG, pigeonite; OL, olivine; AMPH, amphibole; TMT, titanomagnetite. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 19 of 34 the negative Al2O3 versus MgO trend defined by the Upper Transitional Group at Mt. Capitole. The abundant plagioclase (Table 1) is obvious evidence for plagioclase accumulation. In addition, these lavas have the geochemical characteristics of plagioclase, that is, relatively high Al2O3 content, relatively low abundance of incompatible elements, (Sr/Nd)PM and Eu/Eu* >1, relatively high Ba/Th, and positive correlations of Sr/Nd and Eu/ Eu* with Al2O3/TiO2 (Figures 9, 14, and 15). In contrast, the Low-Silica Group and Lower Transi- tional Group lavas have (Sr/Nd)PM and Eu/Eu* <1 with (Sr/Nd)PM decreasing as MgO decreases (Figure 15). Such trends are consistent with co- fractionation of plagioclase and a mafic phase, such as clinopyroxene, which decreased Al2O3 and MgO, respectively. 5.1.2. Role of Magma Mixing [33] Several characteristics of plagioclase in the Upper Transitional Group of Mt. Capitole indicate magma mixing: (1) many plagioclase grains are resorbed (Figure 3a); (2) the plagioclase grains have abundant olivine, pyroxene and amphibole inclusions with low Mg# and Na-rich plagioclase rims partly surrounding these inclusions (Figures 3d and 3e and Table 2), indicating that a plagioclase- rich magma was invaded by a more evolved magma which reacted with the plagioclase crystals via interconnecting channels formed by dissolu- tion; and (3) plagioclase is not in isotopic equilib- rium with their whole rocks, i.e., plagioclase xenocrysts have more radiogenic Pb isotope ratios (Figure 12a and Table 5). 5.1.3. Role of Variable Extents of Melting [34] In the lower 500 m of the Mt. Capitole section slightly alkaline lavas (Low-Silica Group) overlie tholeiitic lavas (Lower Transitional Group) (Figures 2 and 5). The nearby Mt. Tourmente section (Figure 1) records a similar compositional change. Moreover the Low-Silica Group at Mt. Capitole is similar in major and trace element compositions and isotopic ratios (Sr, Nd and Pb) to the upper alkalic lavas in the Mt. Tourmente section (Figures 7, 9, 11, and 14). Frey et al. [2002a] inferred that this temporal, tholeiitic to alkalic transition, reflects a decrease in extent of melting with decreasing eruption age. 5.2. Inferences From Flood Basalt Compositions at Three Locations in the Plateau Central [35] From northwest to southeast in the Kerguelen Archipelago, the exposed flood basalt changes from older, 29 to 26 Ma, tholeiitic and transitional basalt (Mts de Ruches, Fontaine, Bureau and Rabouillère; Figure 1) to younger, 25 to 24 Ma, slightly alkalic basalt (Mt. Crozier, Ravin Jaune and Charbon; Figure 1) [Frey et al., 2000; Damasceno et al., 2002]. Frey et al. [2000] pro- posed that this change in composition reflects a decrease in melting extent of the Kerguelen mantle Figure 4. Variation of plagioclase phenocryst and xenocryst compositions (An, in mol%) as a function of stratigraphic height (meters above sea level) in the Mt. Capitole and Mt. Marion Dufresne sections of the Plateau Central (this paper and Annell et al. [2007]). Plagioclase-phyric basalt dominantly occurs within the Upper Transitional Group (UTG) at Mt. Capitole (Table 1) and from near the base of the Mt. Marion Dufresne section. In both sections, plagioclase cores range widely in composition with >An80 cores occurring in the upper part of the Mt. Capitole section and the lower part of the Mt. Marion Dufresne section. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 20 of 34 plume as lithosphere thickness increased during the transition from a ridge-centered to intraplate setting in the Northern Kerguelen Plateau (see Figure 1 inset). Also the increasing proportion of highly evolved magmas with decreasing eruption age indicates a decrease in supply of basaltic magma to the crust [Weis et al., 1998; Frey et al., 2000]. The flood basalt sections in the Plateau Central are consistent with these interpretations. At Mt. Cap- itole alkalic basalt overlies tholeiitic basalt; the youngest lavas are plagioclase-phyric lavas that formed by mixing of plagioclase-rich magma with a highly evolved magma. At Mt. Tourmente [Frey et al., 2002a] alkalic basalt overlies tholeiitic to transitional basalt, most lavas are aphyric with low MgO contents (4.05 to 6.38 wt% in 64 lavas). At Mt. Marion Dufresne [Annell et al., 2007] the lower 300 m of alkalic lavas with <5.2 wt% MgO grades upward to plagioclase-phyric lavas overlain by 400 m of olivine-phyric, less alkalic lavas with 7 to 11 wt% MgO; within this upper interval there are three quartz-bearing basaltic andesites that reflect mixing of an evolved, quartz-bearing magma with basaltic magma. These characteristics of flood basalt in the Plateau Central show that these sections recorded a complex tem- poral transition from tholeiitic to alkaline volca- nism and that the accompanying decrease in flux of basaltic magma provided time intervals for cooling and fractionation of basaltic magma. 5.3. Origin of Isotopic Variability in Kerguelen Archipelago Lavas [36] Basalt from the Cenozoic Northern Kerguelen Plateau, the Kerguelen Archipelago, and Heard Figure 5. Na2O + K2O versus SiO2 classification plot showing that the Mt. Capitole lavas straddle the alkalic- tholeiitic dividing line of Macdonald and Katsura [1964]. The filled squares indicate 15 samples from the uppermost 170 m of the section and 93–491 from the lower section, designated as the ‘‘Upper Transitional Group.’’ The 9 filled circles indicate ‘‘Low-Silica Group’’ lavas; they have low SiO2/Fe2O3* ratios and are from the elevation range of 560 m to 660 m. The other 29 samples define the ‘‘Lower Transitional Group’’; labeled sample 93–510 near the bottom of the section (Figure 2) is the most evolved lava with the lowest MgO and highest SiO2. Major element data were adjusted to a Fe2+/Fetotal ratio of 0.85. In general, Mt. Capitole lavas are less alkalic than flood basalts erupted in the Southeast Province [Frey et al., 2000] and at Mt. Crozier in the Courbet Peninsula [Damasceno et al., 2002]. They generally overlap with lavas from Mt. Tourmente [Frey et al., 2002a] and lavas erupted in the north-central (Mt. Bureau and Mt. Rabouillère) and northwest (Mt. des Ruches and Mt. Fontaine) parts of the archipelago [Yang et al., 1998; Doucet et al., 2002]. Figure 6. Abundance of TiO2, Fe2O3*, and Al2O3 (wt.%) and SiO2/Fe2O3* ratio versus stratigraphic height (meters) in the Mt. Capitole section. Fe2O3* is total iron as Fe2O3. Compared to the Lower Transitional Group, the Upper Transitional Group lavas (elevation greater than 690 m, except for 93–491 at 540 m) have relatively low TiO2 and Fe2O3* and high Al2O3 and SiO2/Fe2O3*, whereas Low-Silica Group lavas (elevation between 560 m and 660 m) have low SiO2/Fe2O3* and high TiO2 and Fe2O3*. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 21 of 34 Island define an inverse trend between 87Sr/86Sr and 143Nd/144Nd that ranges from the field of Southeast Indian Ridge (SEIR) MORB to 87Sr/86Sr of 0.7060 (Figure 11a). This trend is commonly inferred to reflect mixing of a plume-related com- ponent with relatively high 87Sr/86Sr and low 143Nd/144Nd with a component similar to SEIR MORB [e.g., Gautier et al., 1990]. This conclusion is especially robust for the 34 Ma submarine Ocean Drilling Program (ODP) Site 1140 basalt recovered from the Northern Kerguelen Plateau, which erupted within 50 km of the SEIR [Weis and Frey, 2002]. Among lavas forming the Kerguelen Archipelago, the MORB-like component is mini- mal in the youngest alkalic lavas (e.g., Mt. Ross and Southeast Province Upper Miocene Series) and some of the oldest tholeiitic lavas (Group P of Mts Bureau and Rabouillère, where P indicates plume- derived [Yang et al., 1998]) and most abundant in some of the older tholeiitic to transitional basalt (e.g., Group D lavas from Mt. Bureau, where D Figure 7. TiO2, P2O5, CaO, Al2O3, K2O, Na2O, SiO2, and Fe2O3* abundance versus MgO content (all in wt%) for Mt. Capitole samples. The encircled fields shown for comparison are transitional lavas (open field) and alkalic lavas (gray field) from nearby Mt. Tourmente [Frey et al., 2002a]. Note that there is a negative Al2O3 – MgO trend for the Upper Transitional Group lavas that contrasts with other Mt. Capitole lavas and the Mt. Tourmente fields. In general, the Low-Silica Group lavas and Lower Transitional Group lavas from Mt. Capitole overlap the alkalic and transitional lavas from Mt. Tourmente, respectively. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 22 of 34 indicates relatively depleted [Yang et al., 1998]) (Figure 11a). [37] In contrast to the well-defined linear trend in Figure 11a, plots of 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf and 208Pb/204Pb versus 206Pb/204Pb show more complexity (Figure 16). As in Figure 11a, in Figure 16 Site 1140 basalts from the Northern Kerguelen Plateau extend from the SEIR N-MORB field toward the Kerguelen plume field (87Sr/86Sr 0.7052, 143Nd/144Nd 0.5126, 176Hf/177Hf 0.2829 and 206Pb/204Pb 18.53); two-component mixing between Kerguelen plume and MORB-like components is inferred [Weis and Frey, 2002]. However, lavas collected from some sections of the flood basalt forming the Kerguelen Archipelago define trends that are at high angles to the Site 1140 trend (Figure 16). Some trends, such as the Charbon/Jaune lavas from the Southeast Province, range from the plume field to higher 87Sr/86Sr and lower 206Pb/204Pb; the Southeast Province UMS field has a similar slope but at higher 87Sr/86Sr, lower 143Nd/144Nd and 206Pb/204Pb and higher 208Pb/204Pb at a given 206Pb/204Pb; other groups, such as lavas from Mt. Capitole and Mts des Ruches and Fontaine, define trends subparallel to the trends of the Southeast Province lavas, but they originate from the plume- Figure 8. Abundance of Rb, K2O, Sr, Ba, Nb, Pb, Zr, and Yb versus Th content (all in ppm, except K2O in weight percent) for Mt. Capitole samples. The 2s standard deviation indicated in each panel is ±3%. The highest Th and other incompatible element abundances are in two samples (93–510 and 93–511) with the lowest MgO contents (Table 3). Sample 93–483 has higher Pb abundance at a given Th content possibly due to Pb contamination. Abundances of K, Rb, Sr, and Ba do not vary systematically with Th content, but Rb and K abundances are much more variable than Sr and Ba abundances. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 23 of 34 SEIR MORB mixing trend. Other than Northern Kerguelen Province Site 1140 lavas, the largest proportion of a MORB-related component is in Group D lavas from Mt. Bureau (Figure 16). [38] We conclude that some lavas, such as Group P of Mt. Bureau and Mt. Rabouillère, Charbon/Jaune and Upper Miocene Series from the Southeast Province, and Heard Island (Big Ben Series) define isotopic fields consistent with mixing of a plume component with a component having higher 87Sr/86Sr, and lower 143Nd/144Nd, 176Hf/177Hf and 206Pb/204Pb and high 208Pb/204Pb at a given 206Pb/204Pb (Figure 16). However, other groups, such as Group D of Mt. Bureau and Mt. Rabouil- lère, Mt. des Ruches, Mt. Fontaine, Mt. Tourmente and Mt. Capitole lavas, were created by two distinct mixing processes; the first process involv- ing variable proportions of MORB-like and plume- related components followed by variable addition of a component with high 87Sr/86Sr, and low 143Nd/144Nd, 176Hf/177Hf and 206Pb/204Pb (Figure 16). Evidence that such a component is present in the mantle below the archipelago is a metasomatized, clinopyroxene-bearing dunite xe- nolith found in a Upper Miocene Series basanite breccia; it has acid-leached whole-rock 206Pb/204Pb of 17.72 and 87Sr/86Sr of 0.7072 and an acid- leached clinopyroxene separate has 87Sr/86Sr of 0.7056 [Mattielli et al., 1999] (see arrow in Figure 16a). The metasomatic component may be derived from the plume, perhaps originating as deeply recycled continental lithosphere [Barling et al., 1994; Doucet et al., 2005] or deeply recycled oceanic crust containing sediment. Alternatively as concluded by Mattielli et al. [1999] and consis- tent with the two stage mixing model presented here, this component may have been introduced relatively recently during ascent of plume-derived magma, perhaps by interaction with continental components in the underlying Cretaceous Kergue- len Plateau (e.g., ODP Site 747 in Figure 16e). Figure 9. Incompatible trace element abundance in Mt. Capitole lavas normalized to the primitive mantle estimates of Sun and McDonough [1989]. The field for alkalic lavas from Mt. Tourmente overlaps with the Low-Silica Group lavas from Mt. Capitole. Important features are the negative slopes from Nb to Yb with a pronounced relative depletion in Sr for the Low-Silica Group and Lower Transitional Group lavas. The Upper Transitional Group lavas are not depleted in Sr. Mt. Capitole lavas range to high Ba/Rb ratios as a result of Rb depletion. Figure 10. Initial (a) 87Sr/86Sr, (b) 143Nd/144Nd, and (c) 176Hf/177Hf versus stratigraphic height (meters) in the Mt. Capitole section calculated at 25.7 Ma. Although there is no long-term correlation, if grouped together, the Upper Transitional and Low Silica Groups define trends of increasing 87Sr/86Sr and decreasing 143Nd/144Nd and 176Hf/177Hf with decreasing eruption age. The 2 sigma errors shown are for analyses of SRM 987 (Sr), La Jolla (Nd), and JMC475 (Hf) standard (see Table 5). Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 24 of 34 Figure 11. (a) Initial (87Sr/86Sr)i versus ( 143Nd/144Nd)i showing that lavas from the Kerguelen Archipelago and Heard Island define a trend ranging from the field for Southeast Indian mid-ocean ridge basalt (SEIR N-MORB) to relatively high 87Sr/86Sr and low 143Nd/144Nd. ‘‘K. Plume’’ is the average Kerguelen plume composition from Table 3 ofWeis and Frey [2002]. Red squares show data for Mt. Capitole lavas. The fields designate data for submarine basalt from ODP Site 1140 on the Northern Kerguelen Plateau [Weis and Frey, 2002], several stratigraphic sections from the 29-25 Ma flood basalt forming the Kerguelen Archipelago (i.e., the 28–30 Ma northern sections of Group P (plume) and Group D (relatively depleted) lavas from Mts Bureau and Rabouillère [Yang et al., 1998]), lavas from Mts Fontaine and des Ruches in the north [Doucet et al., 2002], 25–26 Ma lavas from Mt. Capitole and Mt. Tourmente [Frey et al., 2002a] in the Plateau Central, 25 Ma lavas from Charbon/Jaune in the Southeast Province [Frey et al., 2000], two groups of younger (<10 Ma) and more alkalic lavas with MgO > 3 wt% (i.e., lavas from Mt. Ross [Weis et al., 1998] and basanites of the Upper Miocene Series (UMS) in the Southeast Province [Weis et al., 1993]), and Pleistocene/Holocene lavas (Big Ben Series) from Heard Island [Barling et al., 1994], a recently volcanically active island 440 km southeast of the archipelago (Figure 1 inset). A second group of Heard Island lavas, Laurens Peninsula Series, overlaps with the field for Mt. des Ruches and Fontaine. The 2s uncertainties are less than the size of the symbol. All the data are age-corrected to their eruption ages. Data sources are this study, the above references, and Mahoney et al. [2002] for SEIR N-MORB. (b) Expanded scale of Figure 11a showing data for the two sections sampling the Plateau Central, i.e., a field for Mt. Tourmente and data points for the 3 Mt. Capitole groups. (c) Initial (143Nd/144Nd)i versus ( 176Hf/177Hf)i for Kerguelen Archipelago lavas. The fields designate data for submarine basalt from ODP Site 1140 on the Northern Kerguelen Plateau [Weis and Frey, 2002], the 30-25 Ma flood basalt forming the Kerguelen Archipelago (lavas from Mts Bureau, Fontaine, Rabouillère, des Ruches, and Tourmente), and two groups of younger (<10 Ma) and more alkalic lavas with MgO > 3 wt% from the archipelago (Mt. Ross [Weis et al., 1998] and basanites of the UMS from the Southeast Province [Weis et al., 1993]). ODP Site 747 lavas, age-corrected to 26 Ma, from the Central Kerguelen Plateau are shown as an example of inferred lower continental crust contamination in the Cretaceous basalt forming the Kerguelen Plateau [Frey et al., 2002b]. Mantle OIB array is taken from Vervoort et al. [1999]. (d) Expanded scale of Figure 11c showing data for the two lava sections from the Plateau Central. Data sources are the same as for Figure 11a plus Mattielli et al. [2002], Chauvel and Blichert-Toft [2001], Hanan et al. [2004], and Graham et al. [2006]. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 25 of 34 [39] What is the origin of the component with low 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb and high 87Sr/86Sr ratios? Both ancient sediment and sub- continental lithosphere (lower continental crust and mantle) may have these characteristics [e.g., Huang et al., 1995; Rehkämper and Hofmann, 1997; Downes et al., 2001; Liu et al., 2004; Janney et al., 2005; Lustrino, 2005]. A difficulty with attrib- uting low 206Pb/204Pb to recycled sediment is that sediment is likely to be accompanied by a much larger mass of altered igneous crust; this basaltic crust may mask the effects of sediment. For exam- ple, altered MORB can have very high 238U/204Pb, and this ratio is further increased by subduction zone processes [Kelley et al., 2005], which coun- teracts the effect of the low 238U/204Pb in sediment. Consequently, models favoring recycled sediments may assume extreme, perhaps unrealistic, values for sediment. As an example, a model for explain- ing the DUPAL anomaly of Indian Ocean MORB [Rehkämper and Hofmann , 1997] used a 238U/204Pb ratio of 2, whereas GLOSS (Global subducted sediment) has 238U/204Pb of 5.1 [Plank and Langmuir, 1998], and a Pb content of 55 ppm, whereas GLOSS has 20 ppm Pb [also see Zhang et al., 2005]. In contrast, lower continental crust has a relatively low 238U/204Pb ratio (3 [Rudnick and Gao, 2004]), which will lead to a relatively low 206Pb/204Pb ratio with increasing age. [40] There is evidence for subcontinental litho- spheric mantle beneath the Kerguelen Archipelago; i.e., some harzburgite xenoliths in basanite dikes in the Courbet Peninsula (Figure 1) have the low 187Os/188Os characteristic of subcontinental litho- spheric mantle [Hassler and Shimizu, 1998]. How- ever, basalts from the Kerguelen Archipelago [Yang et al., 1998; Weis et al., 2000] and Heard Island [Barling et al., 2003] are not characterized by such low Os isotopic ratios. Therefore it is unlikely that subcontinental lithospheric mantle was the major source component that led to the Figure 12. Initial (206Pb/204Pb)i versus ( 208Pb/204P)i and ( 207Pb/204Pb)i for Mt. Capitole lavas. (a) The data define a linear trend in 208Pb/204Pb versus 206Pb/204Pb, overlapping with one end of the measured field defined by Mt. Tourmente lavas. Plagioclase xenocrysts from Upper Transitional Group lavas have higher initial 206Pb/204Pb ratios than the whole rocks. (b) Samples 93–490 and 93–505, which are offset to higher (87Sr/86Sr)i at a given (143Nd/144Nd)i (Figure 11), have higher ( 207Pb/204Pb)i at a given ( 206Pb/204Pb)i. Plagioclase data are not shown in Figure 12b because of large uncertainties in 207Pb/204Pb ratios. Figure 13. (Sr/Nd)PM versus initial ( 206Pb/204Pb)i for Upper Transitional Group lavas from Mt. Capitole. (Sr/Nd)PM broadly increases with abundance of plagi- oclase phenocrysts; the exception, sample 93–472, has abundant microphenocrysts of plagioclase. The correla- tion indicates that plagioclase with high Sr/Nd ratio (Table 6) has radiogenic Pb isotopic ratios. Two sigma errors for (Sr/Nd)PM and ( 206Pb/204Pb)i are ±3% and the in-run uncertainties, respectively. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 26 of 34 low 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb and high 87Sr/86Sr in some archipelago lavas. [41] Some lower continental crust, especially of Archean age, has very unradiogenic Pb isotopic ratios [e.g., Dickin, 1981; Huang et al., 1995]. Moreover, Archean cratons (India, South Africa, Antarctica and Australia) surround the Indian Ocean. Therefore we evaluate evidence for lower continental crust as a component that contributed to Kerguelen Archipelago lavas. On the basis of oxygen isotopic ratios, the proportion of lower continental crust in Kerguelen Archipelago lavas is small. For example, the few d18O measurements of olivine phenocrysts from the Kerguelen and Heard Islands lavas are within the range of upper mantle peridotite and MORB sources [Eiler et al., 1997]. If lower continental crust has d18O of 8.1% [Simon and Lécuyer, 2005], the absence of anomalous d18O in Kerguelen Archipelago and Heard Island basalt limits lower continental crust to less than 14%; i.e., larger amounts of these com- ponents would result in d18O greater than that found in upper mantle peridotite and MORB sour- ces which range from 5.0 – 5.4% [Eiler et al., 1997]. [42] We have previously argued that the absence of relative depletion in Nb and Ta abundance is inconsistent with a continental component contrib- uting to Kerguelen Archipelago lavas [e.g., Yang et al., 1998; Doucet et al., 2002; Frey et al., 2002a]. Specifically, Kerguelen Archipelago lavas lack the marked relative depletion in Nb, i.e., (La/Nb)PM and (Th/Nb)PM 1.5 (PM indicates primitive man- tle from Sun and McDonough [1989]), found in Cretaceous basalt forming the Kerguelen Plateau at ODP Sites 738, 747 and 1137 (Figure 17a). Such plateau basalt is interpreted to be plume-derived basalt that assimilated continental crust [Mahoney et al., 1995; Weis et al., 2001; Ingle et al., 2002; Frey et al., 2003]. Mt. Capitole lavas in the Lower Transitional and Low-Silica Groups range from only 0.75 to 1 in (La/Nb)PM and (Th/Nb)PM, but these ratios are positively correlated (Figures 17a and 17b). Although low degree of melting (<6%) can change La/Nb and Th/Nb ratios, the melting trend leads to more variable La/Nb than Th/Nb (Figure 17b). Two samples (93–490 and 93–505) from the Lower Transitional Group which are offset to higher 87Sr/86Sr at a given 143Nd/144Nd and offset to higher 207Pb/204Pb at a given 206Pb/204Pb have the lowest 206Pb/204Pb and relatively high Th/Nb ratios (Figures 11a, 12b, and 17b). These characteristics are consistent with the involvement of a continental component in these samples. Figure 17b shows mixing trends for two estimates of lower continental crust compositions. We note that these amounts of lower continental crust, 6–20%, are maximum values because the lower continental crust of stable, mature continents (i.e., Archean cratons) may be silicic, e.g., the Lewisian in Scotland [Rudnick and Gao, 2004; Willbold and Stracke, 2006]. Such lower continen- tal crust is readily partially melted by basaltic magma; consequently lower proportions of incom- patible element rich melt would be required. Figure 14. Al2O3 versus MgO (wt.%) showing that lavas from the flood basalt sections in the Northern Kerguelen Archipelago define broad trends consistent with initial olivine fractionation (negative Al2O3 - MgO trend) followed by segregation of a plagioclase-rich assemblage (positive Al2O3 - MgO trend). In contrast, the younger, 24–25 Ma flood basalt from the eastern archipelago (Mt. Crozier and Ravin Jaune and du Charbon) defines a steep inverse Al2O3 - MgO trend that dominantly reflects high-pressure clinopyroxene fractionation [Damasceno et al., 2002; Scoates et al., 2006]. Mt. Capitole lavas (symbols as in Figure 12) show two trends; the uppermost lavas, Upper Transi- tional Group, define a negative Al2O3 versus MgO trend, but in this case, the trend reflects plagioclase accumulation. In contrast, the Low-Silica and Lower Transitional Groups define a positive Al2O3 versus MgO trend that is consistent with plagioclase fractiona- tion. Inset shows the fractionation/accumulation trends of different phase assemblages; using the measured plagioclase core and clinopyroxene compositions in Mt. Capitole lavas (Table 2), the vectors for plagioclase addition and clinopyroxene fractionation are similar. Data sources are the same as Figure 5. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 27 of 34 [43] Compared to oceanic basalt, lower continental crust has distinctive incompatible trace element ratios that involve Nb and Pb (Table 7). For example, lower continental crust has Ce/Pb and Nb/U ratios of 5 and 25, respectively [Rudnick and Gao, 2004], whereas fresh ocean island basalt (OIB) has Ce/Pb and Nb/U ratio of 25 ± 5 and 47 ± 10, respectively [Hofmann et al., 1986]. Mt Capitole lavas have average Ce/Pb (24 ± 2.7) and Nb/U (45 ± 9.5 for lavas with LOI <2.5%). Although these averages for Mt. Capitole lavas overlap those of OIB, Mt. Capitole lavas define a weak correlation between Ce/Pb, Nb/U and (Th/ Nb)PM (e.g., Figure 17c). Mass balance calcula- Figure 15. Geochemical parameters controlled by plagioclase: (a) (Sr/Nd)PM versus Eu/Eu*, (b and c) (Sr/Nd)PM and (Ba/Th)PM versus MgO content (wt%), and (d and e) Th abundance and Al2O3/TiO2 versus (Sr/Nd)PM. Eu* is Eu abundance interpolated from chondrite-normalized abundances of Sm and Gd, and subscript ‘‘PM’’ designates normalized to primitive mantle estimate [Sun and McDonough, 1989]. Ten of 16 Upper Transitional Group lavas have more than (or equal to) 10 vol% plagioclase phenocrysts (Table 1), which is consistent with their (Sr/Nd)PM and Eu/Eu* greater than 1, and relatively high (Ba/Th)PM and Al2O3/TiO2. These are all characteristics of plagioclase accumulation. All other Mt. Capitole lavas define trends of decreasing (Sr/Nd)PM and Eu/Eu* with decreasing MgO and increasing Th. These characteristics reflect plagioclase fractionation. Dashed and solid lines in Figure 15d are plagioclase accumulation/fractionation trends starting from aphyric sample 93–467 (An76 (solid line) and An52 (dashed line); tick marks are 5% intervals). Partition coefficients (Sr and Nd) for plagioclase are from Bindeman et al. [1998], and DTh = 0.05. For Upper Transitional Group, plagioclase accumulation is the major process, and for other Mt. Capitole lavas, plagioclase fractionation is required, but in detail clinopyroxene (±olivine) fractionation is also required. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 28 of 34 tions shows that addition of 18% lower continental crust of Rudnick and Gao [2004] or 6% lower continental crust of Shaw et al. [1994] decreases Ce/Pb from 23.5 to 18.5 and 21, and Nb/U from 43.5 to 42.3 and 41.3, respectively. [44] Lavas related to the Kerguelen hot spot that have high (La/Nb)PM also have distinctive radio- genic isotopic ratios. For example, Kerguelen Pla- teau lavas with high (La/Nb)PM have high 208Pb/204Pb at a given 206Pb/204Pb [Frey et al., 2003, Figure 10]. In Figure 17d we show that as in Figure 16, Site 1140 lavas define a mixing line between SEIR MORB and the plume, whereas the Big Ben Series of Heard Island and the Upper Miocene Series from Southeast Province in the Kerguelen Archipelago define a trend between the plume and lower continental crust. 6. Summary [45] Geochemical and petrographic characteristics define three distinct basalt types in the Mt. Capitole section. The Lower Transitional Group, tholeiitic/ transitional lavas, is compositionally distinct from the overlying Low-Silica Group, transitional to alkalic lavas. This upward transition from tholeiitic to alkalic composition is also observed at nearby Mt. Tourmente and is analogous to the 30 to 24 Ma compositional change of the flood basalt form- ing the bulk of the Kerguelen Archipelago. In Figure 16 Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 29 of 34 contrast the uppermost lavas, Upper Transitional Group, are distinguished by abundant plagioclase xenocrysts that show evidence for magma mixing. [46] Mt. Capitole lavas define trends in 206Pb/204Pb versus 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf and 208Pb/204Pb that do not extrapolate to the field of SEIR N-MORB (Figure 16). These trends cannot be explained by plume-MORB mixing. We pro- pose a two-step mixing process for forming the 29–25 Ma flood basalt of the Kerguelen Archi- pelago; that is mixing of MORB-like and plume- related components followed by variable addition of a continental-related component with high 87Sr/86Sr and low 143Nd/144Nd, 176Hf/177Hf and 206Pb/204Pb. This temporal sequence of events explains the slopes of arrays for the Mt. Capitole lavas and lavas from Mt. des Ruches and Fontaine (Figure 16). Our mixing scenario schematically illustrated in Figure 16e is similar to that proposed by Doucet et al. [2005]. Mixing trend 1 involves the Kerguelen plume- and MORB-like components (thick black curve in Figure 16e). Mixing trend 2 involves addition of a continental component, probably lower continental crust, to a Kerguelen plume-derived magma (thick red curve in Figure 16e) or to mixtures of the plume- and MORB-like components (thin red curves in Figure 16e). The first mixing event is best represented by NKP Site 1140 lavas and the second mixing event is consis- Figure 16. Initial 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, and 208Pb/204Pb versus 206Pb/204Pb. All data are age- corrected except for Pb data for Mt. Tourmente and SE Charbon/Jaune lavas, which lack U and Pb abundance data. Red squares indicate Mt. Capitole data. The 2s uncertainties are less than the size of the symbol. (a) The field for SEIR N-MORB is at relatively low 87Sr/86Sr and 206Pb/204Pb, whereas the inferred ratios for the Kerguelen mantle plume are at relatively high 87Sr/86Sr and 206Pb/204Pb. The average (K. Plume) and radiogenic (rad. K. Plume in Figures 16d and 16e) Kerguelen plume compositions are from Table 3 of Weis and Frey [2002] for 87Sr/86Sr, 143Nd/144Nd, and 206Pb/204Pb and from Mattielli et al. [2002] for 176Hf/177Hf. Other data fields are as in Figure 11. Note that samples 41 and 42 from Mt. des Ruches are distinct from other lavas in this section. Lavas from the Northern Kerguelen Plateau, Site 1140, are an example of binary mixing between plume and MORB-like components [Weis and Frey, 2002], but the elongated trends defined by the groups of Kerguelen and Heard basalt require components with relatively high 87Sr/86Sr and low 206Pb/204Pb. (b and c) 143Nd/144Nd and 176Hf/177Hf versus 206Pb/204Pb. In contrast to the trends in Figure 16a, the slopes for archipelago groups are positive because 87Sr/86Sr is inversely correlated with 143Nd/144Nd and 176Hf/177Hf. Fields defined by data from the same references as in Figure 11 plus Chauvel and Blichert-Toft [2001], Hanan et al. [2004], and Graham et al. [2006]. (d) (206Pb/204Pb)i versus (208Pb/204Pb)i showing Mt. Capitole data and fields for various sections of the Kerguelen Archipelago and Heard Island lavas. Lavas from NKP Site 1140 and Group D lavas from Mt. Bureau and Rabouillère define trends that extrapolate toward the SEIR N-MORB field; these trends were attributed to the mixing of Kerguelen plume and SEIR MORB–like components (thick black lines) [Yang et al., 1998; Doucet et al., 2002; Weis and Frey, 2002], but several sections of lavas from Kerguelen Archipelago (Mt. Capitole, Mt. des Ruches and Fontaine, Mt. Bureau and Rabouillère (Group P), and SE Charbon/Jaune) and Big Ben Series lavas from Heard Island define trends toward higher 208Pb/204Pb at a given 206Pb/204Pb than the field for SEIR N-MORB. Also shown is a field for continental- related clasts in a conglomerate intercalated with basalt from ODP Site 1137 on the Kerguelen Plateau [Ingle et al., 2002]; none of the Kerguelen Archipelago or Heard Island fields extrapolate toward this field. (e) A schematic diagram showing two mixing events. Triangles are data for Site 1140 lavas. The green field schematically shows that although lower continental crust (LCC) is isotopically heterogeneous, a distinguishing characteristic of many LCC samples is unusually low 206Pb/204Pb and variable 87Sr/86Sr [e.g., Huang et al., 1995; Downes et al., 2001; Liu et al., 2004; Lustrino, 2005]. The field for ODP Site 747 lavas from the Central Kerguelen Plateau (CKP) is an example of inferred LCC contamination in the Cretaceous basalt forming the Kerguelen Plateau [Frey et al., 2002b]. Note that MORB-plume mixing could be either solid-solid mixing or mixing of melts. The MORB-plume mixing trajectory is for melt mixing, whereas the addition of LCC assumes bulk assimilation of LCC, i.e., a maximum estimate (see Table 7 for parameters used for mixing end-members). Mixing curves between Kerguelen plume and LCC are near linear because Sr/Pb ratios for Kerguelen plume and average LCC are similar. The isotopic variation of Mt. Capitole lavas can be explained by mixing of Kerguelen plume primary melt with 50% SEIR MORB followed by 6% LCC addition using the modeling parameters in Table 7. The ticks on the red line are a proportion of LCC at 1% intervals. The proportions for MORB are indicated next to the black line. Triangles stand for Site 1140 lavas. Two geographically separate Pleistocene/Holocene lava groups from Heard Island have been studied: Big Ben Series and Laurens Peninsula Series (LPS) [Barling et al., 1994]. Like some lavas from the Kerguelen Archipelago, Big Ben Series lavas (x) extend to low 206Pb/204Pb and high 87Sr/86Sr. In contrast, the LPS lavas (open circle) with high 3He/4He (16.2–18.3 R/Ra [Hilton et al., 1995]) have lower 87Sr/86Sr and higher 206Pb/204Pb than proposed for the Kerguelen plume, perhaps reflecting plume heterogeneity. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 30 of 34 Figure 17. (a) Abundance ratio of (Th/Nb)PM versus (La/Nb)PM showing the field for Kerguelen Archipelago lavas and Mt. Capitole data for the Low-Silica and Lower Transitional Group (red squares). Subscript PM indicates ratios normalized to primitive mantle ratios [Sun and McDonough, 1989]. Also shown is average lower continent crust (LCC) from Rudnick and Gao [2004]. Shown for comparison are data points for oceanic basalt inferred to contain a component derived from continental crust; i.e., Kerguelen Plateau Sites 738, 747, and 1137 [Mahoney et al., 1995; Frey et al., 2002b; Ingle et al., 2002] and Pitcairn Island [Eisele et al., 2002; Honda and Woodhead, 2005]. (b) Expanded scale of Figure 17a showing the positive trend for Mt. Capitole lavas in the Lower Transitional Group (red squares) and Low-Silica Group (blue circles). Upper Transitional Group lavas from Mt. Capitole which have accumulated plagioclase, not plotted in Figure 17a, are shown as a field because accumulation of plagioclase creates higher La/Nb ratios at a given Th/Nb [Bindeman et al., 1998]. Lower Transitional Group lavas 93–490 and 93–505 with relatively high 87Sr/86Sr and 207Pb/204Pb at a given 143Nd/144Nd and 206Pb/204Pb, respectively, have relatively high Th/Nb and La/Nb ratios. These characteristics are consistent with involvement of LCC and inconsistent with partial melting trend. Using the average lower continental crust composition of Rudnick and Gao [2004], 20% LCC is needed to explain the maximum variation of Th/Nb and La/Nb ratios in Mt. Capitole lavas. However, if the Shaw et al. [1994] estimate of lower continental crust is used, then only 6% LCC is needed. These are maximum values of LCC (see text). Since SEIR N-MORB has low Th/Nb but relatively high La/Nb ratios, the Kerguelen plume composition has to be slightly offset from the trend defined by Mt. Capitole lavas. We note that the average Heard Island LPS (filled large pink triangle) which may represent the extreme Kerguelen plume composition has such La/ Nb and Th/Nb ratios. Trace element compositions for Kerguelen plume, SEIR N-MORB, and LCC are in Table 7. The 2s uncertainties shown in Figure 17b are ±3%. (c) Ce/Pb versus (Th/Nb)PM for Mt. Capitole lavas (symbols as in Figure 5). Incorporation of LCC into oceanic basalt creates an inverse correlation. Error bars indicate ±3% 2s uncertainties. Sample 93–483 and 93–510 are outliers; 93–483 is offset to high Pb in Figure 8, possibly because of Pb contamination, and 93–510 is the most evolved sample (Figures 7 and 8). (d) Initial 87Sr/86Sr versus (La/Nb)PM showing that the Kerguelen Plateau Site 1140 data are consistent with mixing of MORB- and plume-related components, whereas the Heard Island Big Ben Series (BBS) and the Upper Miocene Series from the southeast Kerguelen Archipelago (SE UPMS) define a trend between plume and LCC-related components. The Mt. Capitole data define a trend emanating from the MORB-Plume mixing line toward a LCC component. Geochemistry Geophysics Geosystems G3 xu et al.: flood basalts in kerguelen archipelago 10.1029/2007GC001608 31 of 34 tent with the trend of Mt. Capitole lavas. Since Cretaceous Kerguelen Plateau may underlie the Cenozoic Kerguelen Archipelago, and some basalt forming the plateau has assimilated continental crust [e.g., Mahoney et al., 1995; Frey et al., 2002b], it is possible that the continental crust signature evident in some archipelago lavas was acquired by assimilation of plateau lavas that were contaminated by lower continental crust [Ingle et al., 2003]. Acknowledgments [47] G.X. thanks M. Lo Cascio, Stephanie Ingle, and Sonia Doucet for assistance during sample preparation in Brussels, B. Kieffer and J. Barling for help in acquisition of the whole rock isotopic data, F. Dudas and S. Bowring for advice and assistance during plagioclase separation and acquisition of isotopic data, B. Grant and R. Kayser for their assistance with ICP-MS analyses, and P. Ila for her assistance in obtaining INAA data. N. Chatterjee, T. L. Grove, E. Medard, and J. Barr are thanked for their assistance in obtaining mineral compo- sition data. Each of these individuals plus M. Lustrino and T. Plank are thanked for helpful discussions. This study was supported by National Science Foundation grants to F.F. and NSERC Discovery grants to D.W. and J.S. We thank M. Regelous and A. Saunders for their review comments and the editor, V. Salters, for his comments and suggestions. References Annell, H., D. Weis, J. Scoates, and A. Giret (2004), Evidence for a depleted mantle component in mildly alkalic high-MgO basalts from Mt. Marion Dufresne, Kerguelen Archipelago, southern Indian Ocean, Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract V31B-1436. Annell, H., S. J. Scoates, D. Weis, and A. Giret (2007), Petrol- ogy and phenocryst mineral chemistry in flood basalts from the tholeiitic-alkalic transition, Mt. Marion Dufresne, Ker- guelen Archipelago, southern Indian Ocean, Can. Mineral, in press. Barling, J., S. L. Goldstein, and I. A. 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