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Decoupling of fluids and fluid-mobile elements during shallow subduction: Evidence from halogen-rich andesite melt inclusions from the Izu arc volcanic front

Susanne M. Straub

GEOMAR Forschungszentrum an der Christian-Albrechts Universita¨t zu Kiel, Wischhofstrasse 1 – 3, 24148 Kiel, Federal Republic of Germany

Now at Lamont Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, New York 10964, USA.

(smstraub@ldeo.columbia.edu)

Graham D. Layne

Woods Hole Oceanographic Institution, MS 23, Clark 114A, Woods Hole, Massachusetts 02543, USA

[1] Very rare, halogen-rich andesite melt inclusions (HRA) in bytownitic plagioclase phenocrysts (An89 – 90) from tephra fallout of the Izu arc volcanic front (Izu VF) provide new insights into the processes of fluid release from slab trenchward to the volcanic front in a cool subduction zone. These HRA are markedly enriched in Cl, F and Li - by factors of up to 8 (Cl, F) and 1.5 (Li) - but indistinguishable with respect to the fluid-mobile large-ion lithophile elements (LILE; K, Sr, Rb, Cs, Ba, Pb, U), rare earths (REE) or high field strength elements (HFSE) from the low-K tholeiitic magmas of the Izu VF. We suggest that the chemical signature of the HRA reflects the presence of a fluid in the mantle source that originated from the serpentinized mantle peridotite above the metacrust. This ‘‘wedge serpentinite’’ presumably formed by fluid infiltration beneath the forearc and was subsequently down-dragged with the slab to arc front depths.

The combined evidence from the Izu VF (110 km above slab) and the outer forearc serpentinite seamounts (25 to 30 km above slab) suggests that the slab flux of B and Cl is highest beneath the forearc, and decreases with increasing slab depths. In contrast, the slab flux of Li is minor beneath the forearc, but increases with depth. Fluorine may behave similarly to Li, whereas the fluid-mobile LILE appear to be largely retained in the slab trenchward from the Izu VF. Consequently, the chemical signatures of both Izu trench sediments and basaltic rocks appear preserved until arc front depths.

Components: 14,241 words, 10 figures, 5 tables.

Keywords: Izu volcanic arc; slab devolatilization; fluid-mobile elements; fractionation.

Index Terms: 1030 Geochemistry: Geochemical cycles (0330); 1065 Geochemistry: Trace elements (3670); 3640 Mineralogy, Petrology, and Mineral Physics: Igneous petrology.

Received22 March 2002;Revised9 April 2003;Accepted23 April 2003;Published8 July 2003.

Straub, S. M., and G. D. Layne, Decoupling of fluids and fluid-mobile elements during shallow subduction: Evidence from halogen-rich andesite melt inclusions from the Izu arc volcanic front,Geochem. Geophys. Geosyst.,4(7), 9003,

doi:10.1029/2002GC000349, 2003.

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Theme: Trench to Subarc: Diagenetic and Metamorphic Mass Flux in Subduction Zones Guest Editors:Gray Bebout and Tim Elliot

Published by AGU and the Geochemical Society AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES

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1. Introduction

[²] During shallow subduction (trenchward from the volcanic front), the descending lithosphere releases large amounts of water and carbon dioxide [e.g., Kerrick and Connolly, 1998; Wallmann, 2001]. Since water is a primary transport agent for many fluid-mobile elements (e.g.,, Li, B, Cl, Cs, Pb), these elements might be lost from slab during early subduction as well, implying that the composition of the subducted material changes significantly prior to reaching arc front depths [e.g., Bebout et al., 1999; Class et al., 2000].

Unfortunately, the critical region for early slab devolatilization (<110 km depth) cannot be directly observed at active convergent margins since there is no concomitant volcanism. To date, the most comprehensive information on the early chemical evolution of the subducting slab derives from studies of uplifted, metamorphosed slab fragments [e.g.,Bebout et al., 1999;Scambelluri et al., 2001].

In active settings, however, information on the composition of the shallow fluids can only be obtained from serpentinite seamounts, located 20– 25 km above slab on the outer trench slope [Fryer et al., 1999; Benton et al., 2001], or from the volcanic arc, located110 km above slab [e.g., Taylor and Nesbitt, 1998; Hochstaedter et al., 2001].

[³] In this study, we present data on the Cl, F and Li contents of both matrix glasses and plagioclase melt inclusions from fallout tephra of the Izu arc volcanic front (Izu VF). These tephra glasses are an excellent proxy to Izu VF magma compositions (e.g., S. M. Straub, G. D. Layne, A. Schmidt and C. H. Langmuir, The recycling of fluids and sediment melts in volcanic arcs, manuscript submitted to Geochemisty Geophysics Geosystems, 2003, hereinafter referred to as Straub et al., submitted manuscript, 2003). Cl, F and Li are enriched in the subducting slab, owing to contributions from seawater, sediments, and basaltic oceanic crust [e.g., Ryan and Langmuir, 1987; Decitre et al., 2002].

Since Cl, F and Li are also highly mobile in hydrothermal fluids [e.g., Schilling et al., 1978;

Ryan and Langmuir, 1987; Seyfried and Ding, 1995], they should become readily entrained in

fluids during early subduction. The data show that Cl, F and Li display a much wider range in composition than the other recycled, fluid-mobile large-ion lithophile elements (LILE; K, Sr, Rb, Cs, Ba, Pb, U) in the Izu VF magmas. In combination with existing data from the outer forearc seamounts, our results provide new insights into the sequential release of fluid-mobile elements during shallow subduction.

2. Geological Setting

[⁴] The evolution and structure of the intraoceanic Izu Bonin Mariana arc/backarc system (IBM; NW Pacific) has been described in detail elsewhere [Taylor, 1992; Hochstaedter et al., 2001]. In summary, volcanism in the Izu and Mariana arcs began at 49 Ma (middle Eocene), following the westerly subduction of the Mesozoic (130 Ma) Pacific plate beneath the Philippine plate. In the Oligocene (31 Ma) the Izu arc split along-strike.

During the Miocene (24 to 15 Ma), the Shikoku backarc basin formed. Volcanism at the Izu VF waned during backarc spreading, but rejuvenated 15 Ma ago, and has since been vigorous. A new period of intraarc rifting was initiated at2.8 Ma immediately west of the Izu VF (Figure 1). The Quaternary Izu VF is constructed on20 km thick crust [Suheyiro et al., 1996], and located about 100 –110 km above a well-defined Wadati-Beni- off zone [Katsumata and Sykes, 1969; Wicks and Richards, 1993]. The subducting crust is Creta- ceous in age, with the basaltic basement being similar in composition to the mid-ocean ridge basalts of the East Pacific Rise [Fisk and Kelley, 2002]. The sediment cover consists of 400 m thick Mesozoic and Cenozoic pelagic clays (39%), arc-derived ash (5%) and chert, nanno- fossil chalk and marls (56%) [Plank et al., 2000].

[5] The Izu VF is an informative setting to study, since it has a highly depleted subarc mantle wedge [Taylor and Nesbitt, 1998; Langmuir et al., 2003]

with no evidence of partial slab melts in the mantle source [Taylor and Nesbitt, 1998; Hochstaedter et al., 2000, 2001]. Against this background, the chemistry of slab-derived fluids is clearly recog-

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nizable. Moreover, the Izu Bonin is a classic example of a cool subduction zone, in which most of the fluid-mobile elements may be retained in the slab until arc front depths [e.g.,Bebout et al., 1999].

Comprehensive studies of major and trace elements, and radiogenic isotopes (Sr, Nd, Pb), have shown that (1) the composition of the mantle and slab sources have been homogenous during the last 15 million years and that (2) the Neogene Izu VF magma source is infiltrated by fluid components from both the subducting sediment (3.5% of total fluid) and the subducting basaltic crust (96.5% of total fluid) [e.g., Taylor and Nesbitt, 1998; Hoch- staedter et al., 2001; Straub et al., submitted manuscript, 2003]. Hydrated serpentinized peridotite, that provides additional fluid sources, is considered to be present either above [Straub and

Layne, 2002], or below, the slab [Peacock, 2001]

(Figure 1). For these reasons, the Izu VF volcanics are ideally suited for an investigation of the prov- enance and pathways of slab-derived fluids.

3. Samples and Methods

[⁶] Halogen and Li abundances of Izu VF magmas were determined from matrix shards and melt inclusions from fallout tephra. The tephra was recovered from sediments at ODP site 782A, locat- ed120 km trenchward of the Quaternary Izu VF (Figure 1). Site 782A contains numerous fallout tephras, which provide a highly resolved temporal record (one event per 0.12 Ma on average) of Izu VF volcanism. Most of the fallout tephra investigated is of Neogene age (0.55 –14.2 Ma); only a

Hachijojima Oshima

A.

Sumisujima My.

Mk.

Torishima Sofugan

Nis.

Iwo Jima

3000

7000

H o n s h u

136 140 144

26 30 34

N

E

442

443

444 ZR

DSDP/ODP drill sites Shikoku

Basin

Pacific Plate TrenchIzu

Bonin Is.

7 8 2 A

O l i g o c e n e - E o c e n e ( 7 5 m ) Q u a t e r n a r y - M i d - M i o c e n e ( 3 1 5 m )

Figure 1. Geological setting of the Izu-Bonin arc/backarc system with DSDP and ODP drill sites. ODP Site 782A is indicated. From East to West: Pacific Plate, Izu Trench, Izu Forearc, Izu Volcanic Front (stippled line), rift (grabens), rear arc (hatched) and the inactive Shikoku Backarc Basin. Depth contours are in meters. ZR, Zenisu Ridge (subaerial volcanoes Nijiima and Kozushima are not shown); Subaerial volcanoes (black triangles) unless labeled are My, Miyakejima; Mk, Mikurajima; A, Aogashima; Nis, Nishinoshima. BI, Bonin islands (uplifted Eocene forearc basement). Diagonal solid lines in rear arc region denote rear-arc volcanic chains. Stratigraphy of ODP Site 782A afterXu and Wise [1992].

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single Oligocene fallout tephra (29.6 Ma) was included. A comprehensive data set exists for the 782A fallout tephra. This includes bulk analyses of Sr, Nd and Pb isotopes [Schmidt, 2001], as well as major and trace elements, and B isotopes, by microanalytical methods on single glass shards [Straub and Layne, 2002, 2003; Straub et al., submitted manuscript, 2003]. A representative sub-set of the glasses has been analyzed for trace elements by laser ablation-ICP-MS (Straub et al., submitted manuscript, 2003). The Cl, F and Li determinations were performed, by electron microprobe (Cl) and ion microprobe (F, Li), on the same suite of matrix glasses and melt inclusions previ- ously analyzed for major elements (electron microprobe) and B isotopes (ion microprobe). The data relevant to this paper, and a short summary of the analytical procedures, is provided in Tables 1 –4 for easy reference. A detailed description of the analytical procedures is given in Straub et al.

(submitted manuscript, 2003) (major elements, B, Li), Straub and Layne [2002] (B isotopes) and Straub and Layne [2003] (Cl, F). None of these previous studies, however, addresses in detail the question of the origin of the halogen-rich andesite inclusions, and the potential implications for shallow slab devolatilization, which are the focus of this paper.

[⁷] The glasses from the Site 782A fallout tephras are mostly low-K basalts to rhyolites that are very similar in major element, trace element and isotope composition to the Quaternary Izu VF lavas. The single Oligocene tephra studied (sample 108), which was heavily disturbed by the drilling, has a subordinate population of medium-K glasses, which is not further considered here. With the exception of a single high-MgO Izu lava from the island of Hachijojima (MgO = 8.23 wt%; Mg# = 62), the tephra glasses and Izu arc front lavas have similar maximum MgO (6 wt%) and Mg# numb- ers [60; where Mg# = molar ratio Mg/(Mg + Fe²⁺)]. Basaltic through rhyolite lava and tephra series are indistinguishable in their Sr-, Nd-, Pb- and B isotope ratios, demonstrating that the series are co-genetic and originate from the same sources as the Izu VF lavas [Straub et al., submitted manuscript, 2002;Straub and Layne, 2002]. Further, no

evidence for post-eruptive alteration has been found. The glasses investigated are all clear, color- less to brown glass shards, or melt inclusions, without any telltale signs of birefringence under crossed polarizers or cloudiness indicative of incip- ient alteration. The consistency of glass and melt inclusion compositions, the apparently magmatic systematics of alteration-sensitive elements like Li and B (Figure 2), and the combination of high B (10– 40 ppm) withd¹¹B of +5%to +12%in the Izu glasses, all militate against the presence of any syn- or post-eruptive seawater alteration [Straub and Layne, 2002, 2003]. Thus the high B contents and high-d¹¹B values of the normal-group glasses and the HRA demonstrate the presence of a slab component in the Izu VF magma source and imply a slab origin for other fluid-mobile elements as well.

4. Results

4.1. Two Component Melts:

Normal-Group Glasses and HRA

[⁸] On the basis of their Cl, F and Li contents, the Izu glasses can be divided into two groups (Figure 2).

The majority of glasses and melt inclusions (termed

‘‘normal-group’’ glasses), contain 0.05 –0.40 wt%

Cl, 70 –400 ppm F and 4– 10 ppm Li. The normal- group glasses comprise matrix glasses, and melt inclusions in plagioclase, that range from basalt to rhyolite in composition. In this group, Cl, F and Li behave similarly to the fluid-mobile LILE. This means that Cl, F and Li vary by about a factor of two at a given MgO, and increase by a factor of three with decreasing MgO (Figure 2; in the context of this paper the term ‘‘fluid-mobile LILE’’ refers to Cs, Rb, Ba, U, K, B, Sr and Pb). In contrast, the second group of glasses (‘‘halogen-rich inclusions’’;

= HRA) consists of rare andesite melt inclusions in plagioclase (Figures 2– 4). The HRA are selectively enriched in the halogens Cl (0.70 –0.86 wt%), and F (700 –900 ppm) by about a factor of 8. The abun- dance of Li (15 ppm) is increased by about a factor of 1.5, excepting a single HRA melt inclusion that has a ‘normal’ Li content (Figure 2). The HRA were found in only three out of forty of the 782A tephras investigated. In these three tephras, the HRA are readily identified by their characteristic Cl enrich-

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Table1(RepresentativeSample).CompositionofMatrixGlassesFrom782AFalloutTephraa [ThefullTable1isavailableintheHTMLversionofthisarticle athttp:/www.g-cubed.org.] Sample11,6H-6-88-90, 1.94MadSample19,11X-3-0-1, 2.84MaSample22,13X-3-51- 53,3.26MaSample29,15X-3-9-10, 3.78MaSample34, 17X-1-56-58,4.99Ma GlassNo.b f2g1g2a1f119–719–319–819–219–919–11f5d5b1b2d2f1b1c2c134–234–334–1034–7 Shard/Incc gggggggggggggggggggggggg Abundancesinwt% SiO254.9656.3557.3058.6967.3152.7452.8053.0653.1653.9355.2754.7655.1855.2055.2951.7652.2752.2852.4552.4957.0557.3257.4257.52 TiO20.961.011.000.950.581.111.101.091.101.071.111.000.960.960.941.261.251.261.281.261.001.020.981.00 Al2O314.5814.8514.8714.5313.1414.9015.0715.1115.0515.0715.1115.2415.2815.3915.2614.7114.6914.6314.8814.8914.9214.8214.8715.10 FeO*11.3911.3610.9310.787.0412.3012.1712.2012.3112.0211.6010.9110.7511.1110.8613.9113.4212.9613.2313.2310.6510.5510.5910.89 MnO0.230.230.220.230.210.280.230.240.220.260.200.210.230.210.190.250.190.190.260.220.210.240.230.20 MgO3.603.553.502.761.154.464.324.424.204.133.763.823.743.843.794.714.614.484.614.603.453.313.293.51 CaO8.238.097.927.244.689.189.039.168.908.848.468.288.368.358.269.469.249.229.339.387.927.797.707.98 Na2O2.962.812.843.063.742.482.592.482.762.662.832.812.742.812.832.212.202.342.292.302.862.962.882.82 K2O0.360.390.390.470.720.210.200.190.220.220.260.380.300.370.370.340.390.380.360.400.350.340.340.38 P2O50.100.110.100.110.140.120.130.120.120.110.120.130.160.140.150.110.100.110.100.100.120.120.120.12 Total97.498.699.098.798.597.897.798.198.198.398.697.597.698.297.898.798.497.898.898.998.498.498.399.4 H2O(SD)2.81.41.01.31.52.32.52.01.91.81.42.62.41.82.21.41.82.31.31.31.61.61.70.6 H2O(SIMS)3.12.12.72.52.32.52.42.72.11.82.22.21.9 Abundancesinppm Cl176019371907229733101160119012271108122212481657117815631565109310501077111810471423123512531338 F164186196262287192211196233191236203195200215149158151159157204189196233 Li6.906.857.517.928.424.024.013.853.914.044.356.947.106.616.937.296.996.657.547.006.316.136.436.08 Be0.410.490.420.470.570.440.500.430.570.410.450.490.500.530.530.520.550.480.570.520.420.430.450.48 B18.719.920.722.336.99.79.59.79.610.211.317.217.617.017.523.923.722.326.324.018.417.819.017.9 d11 B---12.010.4-11.0------7.9-7.0-7.6---- a Majorelementoxides,Clandsummationdeficit(=100minussumofoxides;denotedbyH2O(SD))byelectronmicroprobe.H2O(SIMS)andothertraceelementdatabyionmicroprobe(SIMS)(see alsoStraubandLayne[2002]andStraubetal.(submittedmanuscript,2003)fordetaileddescriptionofanalyticalmethods.MajorelementsmeasuredbyelectronmicroprobeCamecaSX50attheGeomar andarenormalizedtothesamechipofbasaltglassJDF-D2.Precisions(onestandarddeviation)aretypically(inwt%):SiO2(0.26),TiO2(0.02),Al2O3(0.1),FeO*(0.11),MnO(0.02),MgO(0.06),CaO (0.06),Na2O(0.04),K2O(0.01),P2O5(0.01).TheelementsB,LiandFweremeasuredbyCamecaIMS3fionmicroprobeattheWoodsHoleOceanographicInstitution.ThereproducibilityofBisbetter than10%atB<10ppmandbetterthan5%athigherBcontents.ThereproducibilityofLiis4%(relative).ThereproducibilityFis±10%(relative).Boronisotopeanalyseswereperformedusingthe CamecaIMS1270ionmicroprobeatWoodsHoleOceanographicInstitution.Atypicalreproducibilityis±0.7%atthegivenlevelofabundances.Columnheadsareasfollows:samplecodes,ODPSample Number,andAgegiveninMa.The‘‘Samplecode’’(e.g.Sample11)isasusedintext. b ‘‘GlassNo.’’identifiesindividualglassormeltinclusionsinpolishedsection. c ‘‘Shard/Inc’’specifiesglasstypeanalyzed(g,matrixglass,cpx,opx,pl,meltinclusionsinclinopyroxene,orthopyroxeneandplagioclase). d NumericagesbasedoncalcareousbiostratigraphyofXuandWise[1992].

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Table2.CompositionofMatrixShardsandMeltInclusionsinFalloutTephraSample3(=782A-2H-4-113-114)a Glass No.

MatrixShards,0.55MaMeltInclusions,0.55Ma 91540444638C38A38B131A1B6B6C6D6E10A10B11A/J11E11H12A13A14B14C29B48A48D48E Shard/ Incgggggcpxcpxcpxopxplplplplplplplplplplplplplplplplplplpl SiO270.0273.1472.8359.6558.4052.7752.3552.9870.9670.3868.8870.4270.2271.8871.5673.6073.4068.8970.2472.0168.3272.1372.1471.2164.4469.4568.3672.57 TiO20.500.490.430.710.780.600.580.590.350.760.760.510.590.500.480.430.440.480.540.470.650.430.490.471.030.810.540.39 Al2O312.3512.6912.1815.0615.3516.1115.8416.2911.9212.5212.5212.7512.7812.6412.7511.8312.0512.2412.6812.5412.8211.8512.6013.2012.2912.2012.2511.83 FeO*3.733.363.278.589.289.189.199.113.144.115.383.753.923.403.572.492.663.513.993.374.742.653.133.156.755.034.812.61 MnO0.110.120.120.170.190.200.210.150.130.120.180.140.160.100.090.060.080.150.130.140.130.070.080.100.210.150.100.10 MgO0.520.380.322.793.095.976.235.870.280.620.950.530.560.480.510.420.440.490.670.510.790.490.430.421.210.670.660.32 CaO2.742.542.226.687.0811.2511.4310.852.212.843.132.872.922.542.722.152.302.562.812.533.122.142.512.943.773.042.992.13 Na2O4.013.954.063.573.412.062.112.063.924.454.503.613.783.763.743.713.843.573.813.763.753.593.913.833.703.713.614.12 K2O1.191.171.190.620.620.500.550.621.131.171.091.141.181.201.191.251.321.051.161.201.091.211.171.190.931.361.321.27 P2O50.070.090.060.140.150.150.150.120.00.130.140.120.130.090.090.070.080.100.120.070.210.070.090.080.110.140.060.01 Total95.197.996.697.998.298.798.498.594.197.097.595.896.196.496.696.096.593.096.096.695.494.696.496.594.396.394.895.4 H2O (SD)4.92.13.42.11.81.31.61.55.93.02.54.23.93.63.44.03.57.04.03.44.65.43.63.55.73.75.24.6 H2O (SIMS)1.61.61.4 Abundancesinppm Cl2532267027051553151711721192123221433482493333333518312832532350250029203289280639262478283424795857524754422942 F445444520299272214214189433607712572653505511382388589595487666460508496697554402413 Li12.6814.012.69.18.74.75.55.011.817.217.714.714.713.714.013.213.715.614.315.115.113.213.614.815.015.812.614.5 Be0.610.740.620.540.530.470.450.460.680.630.570.560.590.620.620.590.640.630.610.590.570.620.620.650.480.580.600.59 B62.7666435311718186283486158707466626263705060656144875765 d11B------------9.8-11.2--9.29.310.9-9.5-9.2---- a Thistablelists‘‘mixedrhyolite’’inclusionsandbasalticinclusionsonly.Halogen-richandesiteinclusions(HRA)fromthesamesamplearelistedinTable3.Capitallettersidentifymultiplemelt inclusionsinsinglephenocrysts.ForabbreviationsandanalyticalmethodsseeTable1.

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Table3.CompositionofMeltInclusions:Halogen-RichAndesites(Sample3)andNormalGroupGlasses(Samples45,80,108)ofthe782AFalloutTephraa Glass No.

3-halogen-richandesites,2H-4-113- 114,0.55MaSample45,19X-1-147-149, 6.03MaSample80,29X-5-13-15, 12.11MaSample108,39X-1-21- 23,29.61Ma 7A16A16B29C45B45C9A9B10A11B12B12C7B8B9A9B12A13A14A14B3A5A5B6A Shard/ Incplplplplplplplplplplplplplplplplplplplplplplplpl Abundancesinwt% SiO260.7460.2658.6761.4859.5458.8752.3752.1854.0554.9052.5153.8756.0654.5154.2053.4356.3956.0948.6147.8950.1851.7351.2753.12 TiO21.000.861.041.020.991.020.650.700.570.510.860.591.000.961.010.990.871.070.740.710.930.780.980.79 Al2O312.5412.0812.1112.2712.0611.9814.9315.0515.5515.4015.1715.5814.7814.6514.6014.8314.5514.8114.6515.0614.8613.5113.4715.44 FeO*10.688.9211.378.5710.7010.9410.8310.629.158.3810.409.749.7010.7411.1310.808.889.9511.3711.3511.4311.3013.2110.48 MnO0.290.230.270.210.160.270.230.190.210.210.170.200.230.240.260.240.250.250.220.240.220.230.280.22 MgO2.301.962.941.662.933.055.695.985.206.105.856.113.313.713.803.822.812.955.965.846.086.575.695.05 CaO4.704.575.174.305.014.9410.6310.7710.5810.4010.4210.637.437.918.058.047.037.2311.5311.6211.0910.439.4110.24 Na2O3.003.253.023.063.043.041.671.661.932.021.891.932.952.932.782.693.163.111.591.611.791.952.112.14 K2O0.720.840.620.800.700.690.230.210.190.170.230.190.420.380.370.370.480.410.160.200.250.280.280.27 P2O50.130.160.150.110.050.120.100.100.090.090.110.090.140.140.130.140.160.130.110.110.120.100.100.11 Total96.193.1395.3693.4895.1894.9297.3397.4697.5298.1897.6198.9396.0296.1796.3395.3594.589694.9494.6396.9596.8896.897.86 H2O (SD)3.906.874.646.524.825.082.672.542.481.822.391.073.983.833.674.655.424.005.065.373.053.123.202.14 H2O (SIMS)3.916.174.475.844.534.793.022.922.872.362.831.853.973.863.764.445.013.954.724.973.303.353.392.64 Abundancesinppm Cl77126888852872926687661750360852870893383812081412146213631303135354063574794313131003 F80678189977990683010289848182100152163191202163187837212320219894 Li15.315.214.59.914.414.97.77.64.94.45.56.06.76.56.96.68.87.54.04.15.16.76.76.1 Be0.480.540.470.510.480.500.450.370.480.430.440.490.480.420.440.520.480.520.440.420.330.320.340.44 B35373240323211119713918161616202010101491411 d11B-9.4--9.99.96.4-5.57.07.26.9-6.3-4.66.86.54.95.8---- a ForabbreviationsandanalyticalmethodsseeTable1.