An Experimental Study of Water in Nominally AnhydrousMineralsintheUpperMantlenear the Water-saturated Solidus

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1 JOURNAL OF PETROLOGY VOLUME 53 NUMBER10 PAGES 2067^ doi: /petrology/egs044 An Experimental Study of Water in Nominally AnhydrousMineralsintheUpperMantlenear the Water-saturated Solidus ISTVA NKOVA CS 1,2 *, DAVID H. GREEN 1,3, ANJA ROSENTHAL 1 y, JO «RG HERMANN 1, HUGH ST. C. O NEILL 1,WILLIAM O. HIBBERSON 1 AND BEATRIX UDVARDI 2,4 1 RESEARCH SCHOOL OF EARTH SCIENCES, THE AUSTRALIAN NATIONAL UNIVERSITY, MILLS ROAD, BUILDING 61, CANBERRA, ACT 0200, AUSTRALIA 2 DEPARTMENT OF DATA MANAGEMENT, GEOLOGICAL AND GEOPHYSICAL INSTITUTE OF HUNGARY, COLUMBUS U T 17^23, 1145, BUDAPEST, HUNGARY 3 SCHOOL OF EARTH SCIENCES AND CENTRE FOR ORE DEPOSIT STUDIES, UNIVERSITY OF TASMANIA, PTE. BAG 79, HOBART, TASMANIA 7001, AUSTRALIA 4 LITHOSPHERE FLUID RESEARCH LAB, EO«TVO«SUNIVERSITY,PA ZMA NY PE TER SE TA NY 1/C, 1117, BUDAPEST, HUNGARY RECEIVED JULY 30, 2011; ACCEPTED JUNE 4, 2012 ADVANCE ACCESS PUBLICATION SEPTEMBER 2, 2012 The incorporation of water in olivine and pyroxenes interlayered within fertile lherzolite compositions was explored experimentally near the wet solidus of lherzolite at 2 5 and 4 GPa. The concentrations and activities of water were varied to establish the partitioning of water between nominally anhydrous minerals (NAMs) and the hydrous minerals pargasite and phlogopite. The water content in NAMs was determined by Fourier-transform infrared (FTIR) spectroscopy. The main absorption bands in NAMs from these experiments are very similar to those generally found in natural upper mantle peridotites. Olivine, orthopyroxene and clinopyroxene contain 32^190, 290^320 and 910^980 ppm of water under the studied conditions. The partition coefficients between coexisting clinopyroxene and orthopyroxene (D cpx/opx )are and at2 5 and 4 GPa respectively, whereas values for coexisting orthopyroxene and olivine (D opx/ol )are6 7 2and , at 2 5 and 4 GPa respectively.the storage capacity in NAMs in a model mantle composition close to the vapour-saturated solidus (water-rich vapour) is 190 ppm at both 2 5 and 4 GPa. Pargasite is the most important phase accommodating significant amounts of water in the uppermost mantle. Its breakdown with increasing pressure at 3 GPa at the vapour-saturated solidus (which is at 10258C at 2 5 GPa) results in a sharp drop in the water storage capacity of peridotite from 1000 ppm to 190 ppm H 2 O. At pressures 43 GPa, melting in fertile lherzolite begins at the vapour-saturated solidus if the bulk H 2 O concentration exceeds 190 ppm. KEY WORDS: upper mantle; partial melting; water; infrared spectroscopy; nominally anhydrous minerals; pargasite; phlogopite INTRODUCTION The identification of water (i.e. H 2 O, OH,H þ )asa trace element at defect sites in nominally anhydrous minerals (NAMs) has modified our understanding of water storage in the mantle (Smyth et al., 1991; Bell & Rossman, 1992). It is now well appreciated that water in the NAMs of the Earth s mantle has a major impact on the mantle s physical and chemical properties such as *Corresponding author: kovacs.istvan.janos@mfgi.hu ypresent address: Department of Earth Sciences, University of Minnesota,108 Pillsbury Hall, Minneapolis, MN 55455, USA. ß The Author Published by Oxford University Press. All rights reserved. For Permissions, please journals.permissions@ oup.com

2 JOURNAL OF PETROLOGY VOLUME 53 NUMBER 10 OCTOBER 2012 melting temperature, viscosity, rheology, deformation pattern, elasticity and electrical conductivity. For instance, the presence of water lowers the melting temperature of mantle peridotite (e.g. Bowen, 1928; Kushiro et al., 1968; Green, 1973; Milhollen et al., 1974; Wyllie, 1978; Falloon & Danyushevsky, 2000). However, there is disagreement as to how the solidus changes in the presence of varying amounts of water for water-saturated peridotite at changing pressure and temperature at uppermost mantle conditions owing to differences in experimental approaches and interpretations of the experimental observations (Kushiro et al., 1968; Green, 1973; Milhollen et al., 1974; Mysen & Boettcher, 1975; Green, 1976; Wendlandt & Eggler, 1980; Mengel & Green, 1989; Wallace & Green, 1991; Niida & Green, 1999; Grove et al., 2006; Green et al., 2010, 2012). Water also lowers the viscosity of the mantle, facilitating its deformation and convection (Dixon et al., 2004). The deformation patterns of mantle rocks change with changing water concentration as different slip systems are activated at different concentrations (i.e. Karato et al., 1986; Karato & Wu, 1993; Kaminski, 2002). It has been argued by using a rheological modeling approach that water plays a substantial role in the initiation of subduction and global plate tectonics (Regenauer-Lieb et al., 2001; Regenauer-Lieb & Kohl, 2003; Li et al., 2008; Peslier et al., 2008). Water concentration in NAMs seems to have a relatively minor effect on both P and S seismic velocities (Karato, 1995; Jacobsen et al., 2004), but a larger effect on seismic wave attenuation at seismic frequencies 51 Hz (Jackson et al., 2002; Karato, 2006; Aizawa et al., 2008). The electrical conductivity of the mantle also depends on water concentration (Karato, 1990, 2011; Wang et al., 2008), and this property is seen by many as complementing the inferences derived from seismic methods in examining the structure of the lower crust and upper mantle (Gatzemeier & Moorkamp, 2005; Tommasi et al., 2006). Although it is evident that water plays a fundamental role in mantle processes, it has been difficult to assess the mechanisms by which water is incorporated in mantle minerals, and consequently how much water may be accommodated. The direct measurement of water in NAMs from mantle xenoliths (e.g. Bell & Rossman, 1992; Grant et al., 2007a; Peslier, 2010) carries the ambiguity of whether the original mantle H 2 O contents are preserved (Demouchy et al., 2006; Ingrin & Blanchard, 2006; Peslier & Luhr, 2006; Peslier et al., 2008; Sundvall, 2010; Yang et al., 2008). The fundamental problem is that the minerals of xenoliths undergo subsolidus re-equilibration and are in addition often metasomatized, so they do not carry direct information on the water content of the typical mantle at near-solidus conditions, which is a matter more appropriately addressed by experiment. Experiments in peridotitic NAMs and chemically simple systems (e.g. Kohlstedt et al., 1996; Rauch & Keppler, 2002; Stalder & Skogby, 2002; Berry et al., 2005, 2007; Bromiley et al., 2004; Smyth et al., 2006; Grant et al., 2007b) are able to constrain the incorporation mechanisms of water in NAMs. Water incorporation in NAMs in peridotitic system has also been studied by determining the partitioning between olivine, orthopyroxene, clinopyroxene and a hydrous basaltic melt in natural analogue starting compositions, using secondary ion-mass spectrometry (SIMS) (e.g. Koga et al., 2003; Aubaud et al., 2004; Hauri et al., 2006; Tenner et al., 2009). However, these experiments do not answer the allimportant question of how much water is held in the NAMs of a given peridotitic mantle composition at saturation with a hydrous phase such as pargasitic amphibole or phlogopite, or at the vapour-absent solidus. For example, although it is experimentally possible to measure the water content of olivine at 2 5GPa,12008C in the presence of a water-rich vapour, under these conditions a lherzolite would be partially molten, and a vapour phase would not be present except at extremely high bulk H 2 O contents (45 wt %) (Green, 1973; Niida & Green, 1999; Green et al., 2010, 2012; Fig. 1). There is no evidence that such large concentrations of water occur in mantle rocks, nor any compelling reasons to hypothesize that they might. Maximum petrogenetic information is obtained from melting experiments when a low degree of thermodynamic Pressure (GPa) water saturated solidus from Green (1973) solid+vapour solid+melt Temperature ( o C) Fig. 1. Experimental P^T conditions for model lherzolite compositions with mineral (i.e. NAMs) layers. 2068

3 KOVA CS et al. WATER IN NOMINALLY ANHYDROUS MINERALS variance is achieved and the chemical potentials of all major components are constrained. For mantle melting under hydrous conditions, the minimum variance condition is at the wet peridotite solidus where the four anhydrous phases of normal peridotite (i.e. olivine þ orthopyroxene þ clinopyroxene plus an aluminous phase, plagioclase, spinel or garnet, depending on pressure), hydrous phases such as pargasite and/or phlogopite, melt and vapour may all coexist. In this most interesting area there were no experimental studies before the recent work of Green et al. (2010, 2011) owing to the technical and analytical difficulties in measuring the water contents of NAMs in equilibrated peridotitic bulk compositions under controlled pressure, temperature and water conditions in tiny experimental run products. Here we introduce a new approach to the measurement of partitioning of water between melts, hydrous minerals and NAMs in equilibrium (i.e. in terms of major elements and water) within peridotite under controlled pressure, temperature and bulk water concentration, using Fourier transform infrared (FTIR) spectroscopy. Under the pressure^temperature conditions of the upper mantle, the solubility of other components (i.e. Na 2 O, K 2 O and SiO 2 ) in an aqueous vapour phase reduces the water fugacity in the vapour phase relative to pure water at the same conditions (e.g. Bowen & Tuttle, 1949; Newton & Manning, 2002; Dolejs & Manning, 2010). Furthermore, in high-pressure peridotitic melting experiments, the partitioning of the alkali components Na 2 O and K 2 O into such a vapour phase obviously depletes them in the other phases of the system, particularly clinopyroxene, and, at high water/rock ratios, may destabilize hydrous phases such as pargasite or phlogopite (Green et al., 2010, 2011). These changed phase compositions and stabilities alter the melting behaviour of mantle lherzolite in ways that depend on the amount of excess H 2 O, which explains the apparent discrepancies between determinations of the wet solidus of mantle peridotite from different laboratories (see Green, 1973; Grove et al., 2006; Green et al., 2010, 2011, 2012; Till et al., 2011). In this study we use FTIR spectroscopy to determine how the concentration of water in NAMs changes through the water-saturated solidus at 2 5 and 4 GPa in fertile lherzolite compositions under controlled pressure, temperature and bulk water concentrations. We also determine the type of defects in which the water is stored. The method uses layers of target phases placed in the experimental charge to act as water sensors. The mineral grains formed in the layers are large enough (minimum 30^50 mm) for FTIR analysis, and sufficient randomly oriented grains are available to make the statistical approach of Kova cs et al. (2008) and Sambridge et al. (2008) feasible. Green et al. (2010,2011,2012) clarified the roles of solute-rich aqueous vapour, water-rich silicate melt, and pargasite and phlogopite stability fields in a model mantle composition. Green et al. (2010, 2011) found that the vapour-saturated solidus (water-rich vapour) of the lherzolite model mantle composition is 10108C at 2 5 GPa, 12108C at 4 GPa, and 13758C at 6 GPa. Inthis study, the technique of using melt-- traps (layers of polycrystalline olivine and pyroxenes) facilitates the identification of solid phases quenched from hydrous silicate melt and the distinction between hydrous silicate melts and water-rich vapour. EXPERIMENTAL AND ANALYTICAL METHODS General approach Determining water contents of NAMs by FTIR spectroscopy has the advantage that the mechanism of water substitution may be identified from the spectra (e.g. Berry et al., 2005), but quantification is dependent on calibrating extinction coefficients for each substitution mechanism, mineral composition and wavenumber (Paterson, 1982; Bell et al., 1995, 2003; Libowitzky & Rossman, 1997; Sambridge et al., 2008; Kova cs et al., 2008, 2010). Alternative techniques such as secondary ionization mass spectrometry (SIMS) determine the totals from all mechanisms of water substitution but also unfortunately from any fluid inclusions present (i.e. Hauri et al., 2002; Koga et al., 2003; Aubaud et al., 2007). Water in NAMs can be quantified by analyzing 10^20 randomly oriented grains using unpolarized IR light (Kova cs et al., 2008; Sambridge et al., 2008). It is not necessary to use large, oriented crystals, which may be difficult to equilibrate with the matrix (i.e. Bai & Kohlstedt, 1992; Zhao et al., 2004). Instead, crystals generated in the experiments can be utilized, although IR spectroscopy requires grain sizes of 20^100 mm, which are generally not achieved in experimental subsolidus or near-solidus runs. We have overcome this problem by using sensor layers of olivine (Tables 1 and 2), which are small enough to equilibrate completely with the neighbouring peridotite matrix during the experimental run but large enough to be analysed by IR spectroscopy. An additional advantage of using such monomineralic sensor layers is that contamination of spectra by fluid inclusions or water-rich phases can be avoided. The experiments in which layers of olivine or discs of single-crystal olivine were used as melt or vapour traps (Table 2, Fig. 2) are from Green et al. (2010, 2011). The addition of olivine layers to the lherzolite composition does not change the relative proportions of the key oxides such as CaO, Al 2 O 3,TiO 2, Na 2 O, K 2 O and H 2 O but may slightly alter Mg# [100Mg/(Mg þ Fe)] if the Mg# of the added olivine differs from that of the lherzolite (Green et al., 2010). Additional experiments were performed specifically for this study in which polycrystalline orthopyroxene and clinopyroxene were added as layers either with or 2069

4 JOURNAL OF PETROLOGY VOLUME 53 NUMBER 10 OCTOBER 2012 Table 1: Starting composition (wt %) of lherzolite mixes and pyroxenes HZ1 HZ2 HZ1 þ 5 wt % dry phl Al-poor Al-rich enstatite chrome-diopside enstatite diopside DTP 1 1 D E D SiO TiO Al 2 O FeO* Fe 2 O 3 n.a. n.a. n.a MnO MgO CaO Na 2 O K 2 O P 2 O 5 n.a. n.a. n.a n.a. n.a. Cr 2 O NiO n.a. n.a. n.a. n.a. H 2 O (ppm) 3 n.a. n.a. n.a Total Mg# *For HZ1 and HZ2 mix iron expressed as total iron in FeO. 1 A. J. Easton s analysis (1963). 2 From Green (1964). 3 Water content is determined by FTIR using the calibration factors of Bell et al. (1995). The analytical uncertainty is c. 30%. n.a., not analysed. without olivine (Table 2, Fig. 2; Green et al., 2010), to quantify the amounts of water stored in these phases at the multiply saturated solidus. Pyroxenes have significant SiO 2, CaO, Al 2 O 3,TiO 2 and Na 2 O contents and these components exchanged readily with the lherzolite layer. Thus these experiments were not used by Green et al. (2010, 2011) to determine the phase equilibria of the lherzolite (HZ composition). Experimental procedures Details of experimental methods have been given by Green et al. (2010). Here we focus on the experimental and analytical procedures used to quantify water incorporation and substitution mechanism in peridotitic NAMs. Two lherzolitic compositions were investigated, one matching the upper mantle composition of Hart & Zindler (1986), with Mg#¼ 89 9 (HZ1, Table 1), and the other being more magnesian (Mg# ¼ 94 5; HZ2, Table 1), with approximately half the FeO content of HZ1. Each composition was prepared in duplicate as described by Green et al. (2010), both as an anhydrous mix, using fired oxides including MgO, and as a hydrous mix by substituting Mg(OH) 2 for the MgO, giving water contents of 0 and 14 5wt % H 2 O respectively. These end-member compositions were combined in appropriate proportions to give starting mixes with water contents of 2 9, 1 45 and wt %. The roles of K 2 O and phlogopite were investigated by adding 5 wt % of a dry phlogopite component to the HZ1 composition; that is, HZ1 þ5 wt % dry phlogopite (Table 1). In addition to the experiments with controlled water contents, two dry experiments were conducted below the solidus, one at 2 5GPa without, and one at 4 0 GPa with, the 5 wt % dry phlogopite component. The mixes were loaded in silver, gold or, in one experiment, gold^palladium (Au 25 Pd 75 ) capsules, with polycrystalline layers of crushed natural crystals of olivine, orthopyroxene or clinopyroxene at the top and bottom of the capsules (Table 2). Five kinds of crystals were used: Al-rich orthopyroxene (E2554) and clinopyroxene (D2554) from the primary assemblage of the Lizard Peridotite, Cornwall (Green, 1964); Al-poor chromediopside clinopyroxene (D2501) from a garnet lherzolite from Almklovdalen, Western Norway; Al-poor orthopyroxene (enstatite, DTP1) from a garnet harzburgite xenolith 2070

5 KOVA CS et al. WATER IN NOMINALLY ANHYDROUS MINERALS Table 2: Experimental conditions and results on HZ1, HZ2 and 95% HZ1 þ5% dry phlogopite compositions Run no. Mount no. T (8C) Time (days) wt % H 2 O Capsule Top L Bottom L Phase assemblage (with OL þ OPX þ CPX þ GA) Water in OL (ppm) Water in OPX (ppm) Water in CPX (ppm) PHL PAR Melt Vap HZ1 peridotite at 2 5 GPa D968 P DRY Au OL(SC) Lo-Al Opx PAR D897 O Ag OL(SC) OL(SC) PAR Vap 67 D937 P Au Hi-Al Opx Hi-Al Cpx Vap D944 P Au Lo-Al Opx Lo-Al Cpx Vap C2936 O Ag OL(SC) OL(SC) Melt Vap 71 C2930 O Ag OL(SC) OL(SC) Melt 68 HZ2 peridotite at 2 5 GPa C2888 O Ag OL-Disc PAR Vap 35 C2886 O Ag OL(SC) OL(SC) PAR Vap 31 C2887 O Ag OL(SC) OL(SC) Melt 52 95% HZ1þ 5% anhydrous phlogopite at 2 5 GPa D949 P Au OL(SC) Lo-Al Opx PHL PAR D948 P Au OL(SC) Lo-Al Opx PHL PAR Vap HZ1 peridotite at 4 0 GPa C2987 O Au OL(SC) OL(SC) Vap 110 C2942 O Au OL(SC) OL(SC) Vap 188 C3005 P Au Hi-Al Opx Hi-Al Cpx Vap C3010 P Au Lo-Al Opx Lo-Al Cpx Vap C2950 O Au OL(SC) OL(SC) Vap 115 C2899 O98/ AuPd OL(SC) OL(SC) Melt 30 HZ2 peridotite at 4 0 GPa C2889 O Ag Ol-Disc Vap 80 C2928 O Ag OL(SC) OL(SC) Vap 62 95% HZ1þ 5% anhydrous phlogopite at 4 0 GPa C3087 P DRY Au OL(SC) Lo-Al Opx PHL C3029 P Au OL(SC) Lo-Al Opx PHL C3024 P Au OL(SC) Lo-Al Opx PHL Vap C3014 P Au OL(SC) Lo-Al Opx Melt OL(SC), olivine (San Carlos); OPX, orthopyroxene; CPX, clinopyroxene; GA, garnet; PAR, pargasite; PHL, phlogopite; Vap, vapour; L, Layer; Lo-Al OPX, low-alumina orthopyroxene; Hi-Al OPX, high-alumina orthopyroxene; AuPd, AuPd double capsule. The maximum uncertainty in the reported concentrations is 30%. in the Dutoitspan kimberlite, South Africa; San Carlos olivine (Fig. 3). Major element analyses of these pyroxenes are given intable 1. We deployed four configurations: configuration 1, San Carlos olivine (SC) layers at the top and bottom, using HZ1 or HZ2 bulk compositions; configuration 2, Al-rich clinopyroxene (D2554) at the top and Al-rich orthopyroxene (E2554) at the bottom, using fertile HZ1 lherzolite bulk composition; configuration 3, Al-poor clinopyroxene (D2501) at the top and Al-poor orthopyroxene (DTP1) at the bottom, using fertile HZ1 lherzolite bulk composition; configuration 4, San Carlos olivine (SC) at the top and Al-poor orthopyroxene (DTP1) at the bottom, using fertile HZ1 lherzolite or HZ1 þ5 wt % dry phlogopite bulk compositions (Fig. 2, Table 2). Two experiments (O60, O61, Table 2) were carried out at the start of the campaign with single-crystal discs of San Carlos olivine within the lherzolite-filled capsule, but because the recovered crystals contained many fluid inclusions along healed fractures, which dominated the FTIR spectra, this approach was not continued, and crushed minerals were used instead. The olivine-disc experiments nevertheless served to 2071

6 JOURNAL OF PETROLOGY VOLUME 53 NUMBER 10 OCTOBER 2012 San Carlos olivine layer ol ol ol 3.5 mm Ol(SC) layer Lo-Al Opx (DTP1) layer OL(SC) HZ1 + 5 wt % dry phl Lo-Al opx (DTP1) HZ1 fertile lherzolite layer + 5 wt % dry phl Lo-Al orthopyroxene (DTP1) layer 500 µm 500 µm opx 500 µm Fig. 2. Photomicrograph of the P12 experimental charge with San Carlos olivine (SC) and Al-poor orthopyroxene (DTP1) layers in the K-enriched HZ1 fertile lherzolite mix. The images are taken in plane-polarized light. Al-poor orthopyroxene (DTP1) Al-poor clinopyroxene (D2501) San Carlos olivine Wavenumber (cm -1 ) 3000 opx Al-rich orthopyroxene (E2554) Al-rich clinopyroxene (D2554) Wavenumber (cm -1 ) Fig. 3. Average unpolarized IR spectra for the original pyroxenes and San Carlos olivine, normalized to 1cm thickness, used as starting minerals interlayered within model lherzolite compositions. Dashed lines represent the spectra of original sensor minerals. Continuous lines indicate the spectra of the respective sensor minerals in some experiments at 4 GPa and 11008C. (See Figs 4^6 and text for details.) Spectra are stacked for clarity Absorbance/cm 2072

7 KOVA CS et al. WATER IN NOMINALLY ANHYDROUS MINERALS demonstrate the presence of vapour rather than silicate melt and the ability of the vapour phase to react with olivine along microfractures within the olivine discs (Experiment O89, Table 5) (Green et al., 2010). Experiments were conducted in end-loaded pistoncylinder apparatuses at 2 5 and 4 GPa and temperatures of 1000^10508C and 1100^12258C respectively (Table 2; Green et al., 2010). The Au, Ag or Au 25 Pd 75 capsules were placed within NaCl^Pyrex sleeves, a cylindrical graphite furnace, and internal spacers of crushable MgO. Oxygen fugacity is not buffered and may vary in experiments, as it is a function of H 2 O activity, furnace assembly components, any Fe loss to the capsules, and the starting material. Oxygen fugacity, however, is inferred to lie between the fayalite^magnetite^quartz (FMQ) and iron^wu«stite (IW) buffers based on the results of Niida & Green (1999) using similar furnace assemblies, and calculation of fo 2 from spinel stoichiometry. In higher temperature experiments where it was necessary to use AuPd double capsules, the mineralogy indicates higher oxidation state (see below). Pressure was calculated from the direct conversion of load to pressure (no friction correction) and is accurate to 0 1GPa. The experiments ran from 1 to 7 days, with longer durations used in particular for lower temperature and nominally dry runs to promote the attainment of equilibrium. Temperature was controlled to an estimated accuracy of 108C and precision of 28C, using a Eurotherm 904 controller affixed to type-b thermocouple (Pt 94 Rh 6 /Pt 70 Rh 30 ). The recovered samples were mounted in epoxy and polished after exposure of a representative section. Analytical methods The phase compositions, phase relations and grain sizes were determined by energy-dispersive spectrometry (EDS) using a JEOL 6400 scanning electron microscope (SEM), and additional analyses and imaging were performed using a Hitachi 4300 field emission SEM (FESEM), both operating at 15 kv and a beam current of 1 na. All facilities are housed in the Electron Microscopy Unit (EMU) of the ANU. Mineral standards produced by Astimex Scientific Limited were used to standardize mineral and glass analyses. Detection limits are 0 10 wt % for K 2 O, TiO 2 and MnO, 0 15 wt % for Cr 2 O 3, and 0 15 wt % for Na 2 O. Analyses by EDS^SEM have advantages in comparison with wavelength-dispersive spectrometry (WDS)^microprobe in allowing analysis of fine-grained experimental run products at low beam current (minimizing element volatilization, particularly Na) and simultaneous rather than sequential analyses for the selected elements. The accuracy of the EDS^SEM methods used in this and similar studies from ANU, relative to the WDS^microprobe methods has been demonstrated (Spandler et al., 2010) with multiple analyses of garnet, clinopyroxene and plagioclase. After SEM analysis, doubly polished thin-sections were made for FTIR analysis, with thicknesses from 37 to 124 mm (Tables 3 and 4). The thickness of the doubly polished section was measured with a Mitotuyo analogue micrometer, which is nominally accurate to within 2 mm. A Bruker IFS-28 IR spectrometer mounted with an A590 Bruker IR microscope, supplied with a nitrogen-cooled MCT detector, and a KBr beam splitter was used for IR analysis (see Berry et al., 2005; Kova cs et al. 2008, 2010, for further details). Spectra were recorded in the range 600^5000 cm 1. The spectra have a resolution of 2 cm 1. Analyses were made with a circular aperture of 30^100mm diameter (depending on the target grain s size) while the microscope stage was continuously flushed with nitrogen. Spectra were processed using the OPUS Õ software (Bruker Inc.). For background subtraction the interactive concave rubberband correction (ICRC) tool within the OPUS Õ software was used where there was a relatively smooth background, but it was drawn manually where it was irregular owing to water vapour, fluid inclusions, etc. The alternative background correction routines provide similar integrated areas within 5%. The integrated intensities of the main absorption bands were obtained with the Integration tool of the OPUS Õ software using the integration limits given in Electronic Appendix Table EA1 (available for downloading at The total absorbance was calculated from the average unpolarized spectra. The precision in the total integrated transmittance, and also, absorbance [i.e. as theoretically shown by Sambridge et al. (2008) and tested by Kova cs et al. (2008)], normalized to unit thickness, which is simply proportional to water content, is subject to (1) uncertainty in the measured integrated absorbance from each spectrum, and in the thickness of the sample, and (2) uncertainty in the estimation of the total absorbance, which depends on the number of grains analysed for the average unpolarized absorbance (e.g. Sambridge et al., 2008). Here we have at least nine grains, suggesting that this error should be510 %. In addition (see below for further details), the calibration factors also introduce an error, thought to be less than 15% (Bell et al., 1995; Kova cset al., 2010). If all of these factors are considered, a maximum error of 30% in each datum appears to be realistic, but should typically be lower than this. There are major substitution mechanisms for water in olivine, associated with (1) Si vacancies, (2) Mg vacancies, (3) octahedral Ti, and (4) trivalent cations compensated by H bound to oxygens at the tips of the vacancies, which hereafter we label as [Si] (3450^3630 cm 1 ), [Mg] (3100^3300 cm 1 ), [Ti] (3525 and 3572 cm 1 ) and [triv] (3300^3400 cm 1 ), respectively (Berry et al., 2005, 2007; Walker et al., 2007; Kova cs et al., 2010; Balan et al., 2011). 2073

8 JOURNAL OF PETROLOGY VOLUME 53 NUMBER 10 OCTOBER 2012 Table 3: Infrared characteristics of olivine in chemically complex experiments t (mm) n.o.a. [Si þ Ti] [triv] H 2 O (ppm) Bands (cm 1 ): 3613 þ 3598 [Si] 3572 [Ti] 3525 [Ti] 3480 [Si] 3450 [Si] 3354 þ 3329 [triv] K* B O61 75(5) O76 83(2) O80 77(2) O92 124(5) O81 71(5) O98 77(4) Bands (cm 1 ): 3611 [Si] 3597 þ 3588 [Si] Quantifying water contents from IR absorption spectra requires the use of calibration factors, and Kova cs et al. (2010) pointed out that these four common substitution mechanisms for water in olivine each requires its own calibration factor: k [Si] ¼ , k [Ti] ¼ , k [triv] ¼ , and k [Mg] ¼ Recently, Balan et al. (2011) provided additional theoretical support for the different substitution mechanisms requiring different calibration factors. 3567y [Ti] 3546 [Si] 3526 [Ti] 3480 [Si] 3448 [Si] 3354 þ 3329 [triv] O60 70(5) O85 83(3) O52 73(5) O79 71(2) O53 63(5) O77 80(5) Bands (cm 1 ): 3613 [Si] 3596 þ 3587 [Si] 3568y [Ti] 3545 [Si] 3525 [Ti] 3480 [Si] 3450 [Si] 3354 þ 3329 [triv] P8 74(9) P11 65(2) P12 70(3) P9 60(2) P10 67(4) P32 81(5) P30 72(5) Absorbances are in integrated total absorbance normalized to 1 cm thickness. t, thickness, with standard deviation given in parentheses. n.o.a., number of analyses; [Si], silica-vacancy substitution; [Ti], Ti-clinohumite substitution; [triv], trivalent cation-related substitution (see text for details). ythese bands more likely represent [Ti] peaks or a combination of [Ti] and [Si] bands. K, Kovács et al. (2010); B, Bell et al. (2003). k ¼ *Calibration factors of 0 572, 0 182, and are applied to [Si], [Ti] and [trivalent] bands respectively (see Kovács et al., 2010). The challenge is to resolve accurately the contribution of the [Ti] and [Si] bands between 3500 and 3600 cm 1. The [Ti] mechanism can be identified by two major bands at 3572 and 3525 cm 1 and where these were visible we used the calibration factor for this mechanism, as the amounts of water associated with [Si] are probably low at the relative high silica activity of the experiments. For the sake of comparison, the water concentrations for olivine calculated by the Bell et al. (2003) calibration are also 2074

9 KOVA CS et al. WATER IN NOMINALLY ANHYDROUS MINERALS Table 4: Infrared characteristics and parameters for orthopyroxene and clinopyroxene Sample Thickness (mm) n.o.a. A tot /cm H 2 O (ppm) Bell et al. (1995) Orthopyroxene Configurations 2 and 3 P3 60(2) P4 67(4) P6 53(3) P7 37(4) Configuration 4 P8 74(9) P9 65(2) P10 70(3) P11 60(2) P12 67(4) P30 81(5) P32 72(5) E (13) DTP1 161(21) Clinopyroxene Configurations 2 and 3 P3 60(2) P4 67(4) P6 53(3) P7 37(4) D (2) D (20) Values in parentheses are standard deviations. The absorbances are given in integrated total absorbance normalized to 1 cm thickness. n.o.a., number of unpolarized FTIR analyses. reported in Table 3, and these usually give lower values than the Kova cs et al. (2010) calibration, especially when the contribution of the [Si] bands is significant. For the pyroxenes the calibration factors of Bell et al. (1995) were applied. The mechanism by which water substitutes in both orthopyroxene and clinopyroxene is less variable than in olivine, producing spectra with roughly the same absorption characteristics in all experiments. These spectra are similar to those in the samples used for calibration by Bell et al. (1995), showing mainly high wavenumber bands at cm 1 ; hence the calibration factors of Bell et al. (1995) were taken to be applicable. RESULTS Achievement of equilibrium Analyzing the NAM sensor crystals before and after experiments both for major elements and water allows us to check whether they approached equilibrium in both respects. The original San Carlos olivine has Mg# 90 5 according to Galer & O Nions (1989) although samples display a small variation in colour. Olivine grains are 70^120 mm in diameter in the layers and chemically homogeneous in each run, with the Mg# varying from 90 to 91 3 for olivine coexisting with the HZ1 composition (Table 5). However, the interlayered olivine becomes more magnesian (Mg# ¼ 91 5^93 2) in the HZ2 lherzolite mix (Table 5). The absorption characteristics of O^H vibration bands of San Carlos olivine also changed as [triv] (3329 and 3354 cm 1 ) and [Si] (3598 and 3612 cm 1 ) bands appeared in addition to or replacing the original [Ti] bands (3525 and 3572 cm 1 ) in all studied experimental configurations (Fig. 3). Inhomogeneity of water concentration was not detected in the sensor minerals before and after the experiments (no diffusion profiles could be observed). Pyroxenes of configurations 2, 3 and 4 changed their chemical composition by exsolving an aluminous phase (garnet), which lowers their Al 2 O 3 content with respect to the starting pyroxenes by adjusting to the new bulk compositions (Table 5; Green et al., 2010; see below for details). In the IR spectra of pyroxenes, both the position and contribution of the original bands changed with respect to the starting pyroxenes (Fig. 3). The original Al-rich orthopyroxene (E2554) has three major absorption bands at 3565, 3525 and 3420 cm 1 contributing 110 ppm of water (Fig. 3, Table 1). The original Al-poor orthopyroxene (DTP1), in contrast, has its major absorption band at 3600 cm 1 with a smaller one at 3420 cm 1, and only 49 ppm water (Fig. 3, Table 1). The spectra of newly formed orthopyroxene in both configuration 2 and 3 experiments all have major, broad bands at 3600, 3530 and 3420 cm 1 clearly differing from the original orthopyroxene (Fig. 3). The original Al-rich clinopyroxene (D2554) has 1180 ppm of water, with three major absorption bands at 3565, 3525 and 3420 cm 1 and a broad band at 3675 cm 1 (Fig. 3, Table 1). The broad band at 3675 cm 1 is typical of hydrous minerals such as amphibole. The original Al-poor clinopyroxene (D2501), in contrast, has a much lower concentration of water (83 ppm) and two major bands at 3540 and 3450 cm 1 (Fig. 3, Table 1). The re-equilibrated clinopyroxene in all configuration 2 and 3 experiments has two broad bands at 3640 and 3450 cm 1 and a smaller one at 3360 cm 1 (Fig. 3) regardless of whether the starting clinopyroxene was Al-rich or Al-poor, indicating that equilibrium was approached in the experiments for the water substitutions. There is no evidence that significant water defects are inherited from the original sensor crystals (Fig. 3). Instead, new substitution mechanisms formed (i.e. additional bands appeared) and the original bands decreased in intensity, broadened, narrowed or vanished during the experiments (Fig. 3). 2075

10 JOURNAL OF PETROLOGY VOLUME 53 NUMBER 10 OCTOBER 2012 Table 5: Major element composition of minerals in the sensor layers and the lherzolite mix Phase n SiO 2 1s TiO 2 1s Al 2 O 3 1s Cr 2 O 3 1s NiO 1s FeO 1s MgO 1s CaO 1s Na 2 O 1s K 2 O 1s Total Mg# [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] HZ2 Peridotite at 2.5 GPa Run O-60 (10008C, 2 9% H2O)* OL Lhz bdl bdl bdl bdl bdl bdl Run O-89 (10008C, 7 25% H 2 O)* OL Lhz bdl bdl bdl bdl bdl bdl OL disc (central) bdl bdl bdl bdl bdl bdl OL disc (edge) bdl bdl bdl bdl bdl bdl Run O-52 (10258C, 1 45% H 2 O) OL Lhz bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl Run O-53 (10508C, 1 45% H2O) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl HZ2 Peridotite at 4 0 GPa Run O-61 (11008C, 2 9% H2O)* OL Lhz bdl bdl bdl bdl bdl bdl OL disc-edge bdl bdl bdl bdl bdl Run O-76 (11508C, 1 45% H2O) OL Lhz bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl HZ1 Peridotite at 2 5 GPa Run P-30 (10008C, dry) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl OPX Lhz bdl bdl bdl bdl OPX-L bdl bdl bdl bdl Run O-85 (10008C, 1 45% H2O) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl Run P-4 (10008C, 1 45% H2O) OPX Lhz bdl OPX-L bdl bdl bdl CPX Lhz bdl CPX-L bdl bdl Run P-7 (10008C, 1 45% H2O) OPX Lhz bdl bdl bdl OPX-L bdl bdl bdl bdl CPX Lhz bdl bdl CPX-L bdl bdl Run O-79 (10258C, 1 45% H 2 O) OL Lhz bdl bdl bdl bdl bdl Run O-77 (10508C, 1 45% H2O) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl HZ1 Peridotite at 4 0 GPa Run O-92 (11008C, 0 145% H 2 O) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl Run O-80 (11008C, 1 45% H 2 O) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl Run P-3 (11508C, 1 45% H 2 O) OPX Lhz bdl bdl bdl bdl (continued) 2076

11 KOVA CS et al. WATER IN NOMINALLY ANHYDROUS MINERALS Table 5: Continued Phase n SiO2 1s TiO2 1s Al2O3 1s Cr2O3 1s NiO 1s FeO 1s MgO 1s CaO 1s Na2O 1s K2O 1s Total Mg# [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] [wt%] OPX-L bdl bdl bdl bdl CPX Lhz bdl bdl CPX-L bdl bdl Run P-6 (11508C, 1 45% H2O) OPX Lhz bdl bdl bdl OPX-L bdl bdl bdl CPX Lhz bdl bdl CPX-L bdl bdl Run O-81 (12008C, 1 45% H2O) Ol Lhz bdl bdl bdl bdl bdl bdl Run O-98/99 (12258C, 1 45% H 2 O) OL Lhz bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl % HZ 1þ 5% anhydrous phlogopite at 2 5 GPa Run P-10 (10008C, 0 145% H 2 O) Ol Lhz bdl bdl bdl bdl bdl OPX Lhz bdl bdl OPX-L bdl bdl bdl Run P-9 (10008C, 1 45% H 2 O) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl OPX Lhz bdl bdl bdl OPX-L bdl bdl bdl % HZ 1þ 5% anhydrous phlogopite at 4 0 GPa Run P-12 (11008C, 0 145% H2O) OL Lhz bdl bdl bdl bdl bdl bdl OPX Lhz bdl bdl bdl bdl OPX-L bdl bdl bdl bdl Run P-11 (11008C, 1 45% H2O); CPX** ¼ (50 11 wt%k2o) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl OPX Lhz bdl bdl OPX-L bdl bdl bdl bdl Run P-8 (11508C, 1 45% H 2 O) OL Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl OPX Lhz bdl bdl bdl OPX-L bdl bdl bdl bdl Run P-32 (11758C, dry) Ol Lhz bdl bdl bdl bdl bdl bdl OL-L bdl bdl bdl bdl bdl bdl OPX Lhz bdl bdl bdl OPX-L bdl bdl Three experiments [O60, O61, O89; Green et al. (2010, supplementary tables 3 & 4 therein)] used olivine discs inserted in the capsule and surrounded by HZ2 Lherzolite mix. The three discs were cut from the same olivine crystal (San Carlos olivine) and the reaction between the HZ2 Lherzolite mix and the olivine disc was examined in O89. Olivine analyses located 410 microns from the margin of the disc or from a fracture decorated with clinopyroxene (Fig. S1f of Green et al., 2010) have Mg# Olivine within the lherzolite mix averages Mg# ¼ 93 9 and olivine within 10 microns of the margin or of the clinopyroxene within the fracture averages Mg# ¼ Our data show that the olivine disc composition (Mg#) relevant to the FTIR measurements is that of the original San Carlos olivine and that only the margins (to approx 10 microns) of the olivine has re-equilibrated in Mg# with the more magnesian lherzolite HZ2. The data for O89 are tabulated under O60 as no additional internal disc compositions were determined in this experiment. In the remainder of the experiments with HZ2 Lherzolite and olivine layers, the observation that the starting material included many grains 520 microns diameter and samples clearly showed grain growth is consistent with olivine-in-layer compositions of Mg#¼ 91 5 (O53); 92 4 (O76); 92 6 (O52); 93 2 (O81) i.e. transitional between initial composition of Mg# ¼ and HZ2 Lherzolite composition Mg# 94. For experiments with HZ1 composition the San Carlos olivine composition of Mg# ¼ is very close to that within the lherzolite layer and this is apparent in this Table. Lhz ¼ lherzolite layer, -L ¼ sensor mineral layer, disc ¼ sensor discs, bdl ¼ below detection limit 2077

12 JOURNAL OF PETROLOGY VOLUME 53 NUMBER 10 OCTOBER 2012 Phase relations and chemical compositions Experimental conditions and phase relations (Table 2) are from Green et al. (2010). In the experiments with San Carlos olivine layers (configuration 1) olivine, orthopyroxene, clinopyroxene, garnet, pargasite and vapour were present in the lherzolite below the solidus at 2 5 GPa, with pargasite and aqueous vapour replaced by melt ( vapour) above the solidus (Table 2). Phase relations at 4 GPa were similar except that pargasite is missing from the assemblage (Table 2). It is important that addition of olivine to the lherzolite composition does not alter the phase assemblage (other than increasing the modal olivine content in the bulk charge) except to modify the Mg# of phases in the HZ2 composition towards lower values. For the HZ1 and HZ1 þphlogopite compositions with Mg# 90, the addition of layers of olivine (Mg# ¼ 90) has no effect. The experiments with Al-rich orthopyroxene and clinopyroxene layers (configuration 2) were conducted below the solidus and with 1 45 wt % H 2 O. They produced olivine, orthopyroxene, clinopyroxene and garnet present with vapour in the lherzolite layer at both 2 5 and 4 GPa. Pargasite is absent at 2 5 GPa because the increased modal clinopyroxene in the charge, owing to the clinopyroxene layer, lowers the Na 2 O content of clinopyroxene (i.e. the activity of Na 2 O in the charge) below that necessary for pargasite stability (Table 2). In the mineral layers the clinopyroxene grains are 30^60 mm in size, whereas the orthopyroxene is 50^150 mm after the experiments. The Al-rich orthopyroxene layer contained 6 3wt % of Al 2 O 3 before the experiments, but this decreased to mean compositions of 1 4 and 2 8 wt % at 4 and 2 5 GPa respectively, as Al 2 O 3 exsolved to form garnet in the mineral layer (Table 5). Similarly, the Al-rich clinopyroxene lost most of its original Al 2 O 3 (6 8 wt %) with mean compositions of 2 0 and 3 7 wt % at 4 and 2 5 GPa, respectively (Table 5). The recrystallized pyroxenes are not homogeneous, as relict Al-rich cores were found. The composition of orthopyroxene in the originally monomineralic layers is on average more aluminous and has greater variability than that in the lherzolite layers (Table 5). The decrease in alumina is a consequence of exsolution of garnet and is more marked at higher pressures. In the experiments with Al-poor pyroxenes (configuration 3), the orthopyroxene lost some of its Al 2 O 3 to form garnet at 4 GPa, but there is little change at 2 5 GPa (Table 5). Al-poor clinopyroxene has similar Al 2 O 3 content (2 6 wt %) at both pressures (Table 5). The resulting compositions are more homogeneous than those from the Al-rich pyroxenes of configuration 2, with minor variations only for Na 2 OandAl 2 O 3 in the Al-poor clinopyroxene at 2 5GPa. Comparisons of clinopyroxene and orthopyroxene analyses between experiments with olivine layers and those with pyroxene layers show that there is incomplete equilibration of the pyroxenes throughout the charge, but as already pointed out, there is sufficient exchange of major elements between the lherzolite mix and the sensor layers at 2 5 GPa to decrease the Na content of clinopyroxene in the lherzolite layer and consequently to destabilize pargasite. The direction of reaction in configuration 2 (high-alumina pyroxenes) is to strongly decrease the Al solubility in pyroxene by formation of garnet, and also to decrease the Ca content of orthopyroxene and increase the Ca content and Na content of the high-alumina clinopyroxene starting material. Collectively, the data show that the experiments using low-alumina pyroxene layers (configuration 3) or olivine þ low-alumina orthopyroxene (configuration 4) yield products closest to the pyroxene compositions in experiments with HZ1 or HZ1 þ Phlogopite lherzolite, in which there were olivine-only layers (configuration 1) or no layers at all. In interpreting the phase relations, particularly pargasite stability and solidus temperature, Green et al. (2010, 2011) emphasized that only those experiments without monomineralic layers or with olivine only (configuration 1) were used to define the phase relations and solidus temperatures of HZ1 and HZ2 lherzolites. This is because of the participation of the pyroxene layers in reaction with the lherzolite. With respect to interpreting the FTIR data and water solubility in pyroxenes and olivine, the spectra obtained are specific to the phases as analysed. Because the OH solubility in orthopyroxene and clinopyroxene is positively correlated with AlAlMg 1 Si 1 (Tschermak s substitution; e.g. Stalder, 2004), the presence of relict alumina-rich cores in P4 and P3 (at 2 5 and 4 GPa respectively) will bias water contents to higher values than appropriate for the equilibrated lherzolite composition (Table 2). Thus experiments using configuration 3 (P6, P7) or configuration 4 (P8^P12, P32) are preferred for deducing the contents of the lherzolite assemblage at the P, Tof the experiments. The experiments with San Carlos olivine and Al-poor orthopyroxene layers (configuration 4) (i.e. HZ1 þ5 wt % dry phlogopite) and with 1 45 wt % H 2 O have olivine, orthopyroxene, clinopyroxene, garnet, phlogopite and vapor present at 4 GPa and 11008C (P11) (i.e. below the solidus), but above the solidus quenched melt is present and phlogopite absent at 11508C (P8, Table 2). The P12 experiment at 4 GPa and 11008C with0 145 wt % H 2 O has the same solid phases as in P11 (1 45 wt % H 2 O) but mass-balance calculations show that vapor is absent as all water is taken up by NAMs and phlogopite. At 2 5 GPa and 10008C (P9 and P10) pargasite is present in addition to the phlogopite and garnet lherzolite assemblage, and vapor is present with 1 45 wt % H 2 O (P9) but absent with wt % H 2 O (from mass-balance calculations, P10, Table 2). The olivine and orthopyroxene grains were 50^200 mm in the layers, and free of inclusions and impurities. Olivine has an Mg# of 90 6 at2 5 GPa (P9, P10) and 91 6 at4gpa 2078