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Home , Dar al Gani, Koga (crater), Meteorite classification

& Planetary Science 1–13 (2016) doi: 10.1111/maps.12624

Constraints on the water, chlorine, and fluorine content of the mantle

1* 2,3 4 Justin FILIBERTO , Juliane GROSS , and Francis M. MCCubbin

1Department of Geology, Southern Illinois University, 1259 Lincoln Dr, MC 4324, Carbondale, Illinois 62901, USA 2Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854, USA 3Department of Earth and Planetary Sciences, The American Museum of Natural History, New York, New York 10024, USA 4NASA Johnson Space Center, Mail Code XI2, 2101 NASA Parkway, Houston, Texas 77058, USA *Corresponding author. E-mail: fi[email protected] (Received 30 July 2015; revision accepted 22 January 2016)

Abstract–Previous estimates of the volatile contents of Martian basalts, and hence their source regions, ranged from nearly volatile-free through estimates similar to those found in terrestrial subduction zones. Here, we use the bulk chemistry of Martian , along with Martian apatite and amphibole chemistry, to constrain the volatile contents of the Martian interior. Our estimates show that the volatile content of the source region for the Martian meteorites is similar to the terrestrial Mid-Ocean-Ridge Mantle source. Chlorine is enriched compared with the depleted terrestrial mantle but is similar to the terrestrial enriched source region; fluorine is similar to the terrestrial primitive mantle; and water is consistent with the terrestrial mantle. Our results show that Martian magmas were not volatile saturated; had water/chlorine and water/fluorine ratios ~0.4–18; and are most similar, in terms of , to terrestrial MORBs. Presumably, there are variations in volatile content in the Martian interior as suggested by apatite compositions, but more bulk chemical data, especially for fluorine and water, are required to investigate these variations. Finally, the Martian interior, as exemplified by surface basalts and NWA 7034, may have had higher volatile contents.

INTRODUCTION et al. 2013). However, Martian magmas may have partly degassed upon eruption and lost water and/or There is considerable debate about the pre-eruptive halogens to the surface (e.g., McSween and Harvey magmatic volatile (H2O, F, and Cl) contents of Martian 1993) and because of this uncertainty, estimates of the basalts and hence their source regions (see Filiberto pre-eruptive water contents of Martian magmas range et al. Forthcoming). The bulk water contents of the from essentially dry to 2 wt% H2O (e.g., Dann et al. Martian meteorites are rather low compared to 2001; 2004; Nekvasil et al. 2007; McCubbin terrestrial basalts (<350 ppm H2O released at et al. 2010a, 2012; Usui et al. 2012, 2015; Giesting et al. T > 350 °C [e.g., Leshin et al. 1996]), as are the 2015). Experimental studies suggest that up to 2 wt% magmatic water contents of glassy -hosted melt H2O may be required to reproduce the mineralogy and inclusions in primitive basaltic shergottites (<251 ppm temperatures of crystallization of shergotittes and H2O [Usui et al. 2012, 2015]). Comparable terrestrial chassignites (Dann et al. 2001; Nekvasil et al. 2007, basaltic rocks typically contain much higher 2009; Filiberto 2008). Further, studies of Li, Be, and B concentrations of H2O(~2000–20,000 ppm [e.g., zoning in pyroxenes and lithium isotopes, which are Johnson et al. 1994; Dixon and Clague 2001; Saal et al. thought to be geochemical proxies for fluid movement, 2002]). Bulk fluorine and chlorine contents of the have revealed conflicting results (e.g., Herd et al. 2004; unaltered Martian basalts are similar to those of Beck et al. 2006b; Magna et al. 2006, 2015; Seitz et al. terrestrial tholeiites (29–41 ppm F and 14–137 ppm Cl; 2006; Treiman et al. 2006; Filiberto et al. 2012a; Udry Dreibus and Wanke€ 1987; Bogard et al. 2010; Burgess et al. 2016). These studies have suggested degassing of

1 © The , 2016. 2 J. Filiberto et al.

potentially hydrous magmas (Lentz et al. 2001; (or at least codominant with H2O; e.g., Filiberto and McSween et al. 2001; Beck et al. 2004; Herd et al. 2005; Treiman 2009b). Further, recent investigations of Udry et al. 2016), but bulk Li isotopes are not apatite in lunar rocks showed that apatite is not a consistent with degassing for many of the Martian robust hygrometer if it forms as a result of fractional meteorites (Magna et al. 2006; Seitz et al. 2006; crystallization, and using the F:Cl:OH ratio of such Filiberto et al. 2012a) and many shergottites and apatite to calculate the parental magma volatile have been affected by post-crystallization concentration may overestimate the H2O content of the diffusion of Li, complicating the use of Li to constrain parental magma (Boyce et al. 2014). degassing (e.g., Beck et al. 2006b; Treiman et al. 2006; There has been much less focus given to amphibole Udry et al. 2016). Results from geochemical modeling in Martian meteorites and there are few direct analyses studies also suggest that water may be required to of water in Martian amphiboles (Watson et al. 1994b; explain Martian bulk chemistry, mineralogy, McCubbin et al. 2010a; Giesting et al. 2015). and temperatures of crystallization (McSween et al. Kaersutitic amphibole in has 0.1 wt% Cl and 2001; McCubbin et al. 2010a, 2012; Balta and McSween 0.5 wt% F from EMP (electron microprobe) analyses, 2013; He et al. 2013). However, recent experimental but SIMS (secondary ion mass spectrometry) analyses work (Filiberto and Treiman 2009a; Filiberto et al. have yielded two distinctly different results for water 2012b, 2014a; Giehl et al. 2014; Farcy et al. content: 0.1–0.2 wt% H2O and 0.41–0.74 wt% H2O Forthcoming) has shown that chlorine and fluorine (Watson et al. 1994b; McCubbin et al. 2010a; Giesting affect crystallization temperatures of magmas in similar et al. 2015). Kaersutitic amphibole in the chassignite ways to water. Thus, the observed mineralogy and NWA 2737 has F and Cl concentrations (0.45–0.58 and crystallization temperatures of the Martian meteorites 0.09–0.13 wt% by EMP) that are similar to those in may not be due to water alone, which would lower the Chassigny, and ~0.1 wt% H2O measured by SIMS required dissolved water concentrations. Therefore, (Beck et al. 2006a; Treiman et al. 2007; Giesting et al. there is an unresolved debate about the pre-eruptive 2015) but may have been affected by shock water, chlorine, and fluorine bulk contents of Martian dehydrogenation (Giesting et al. 2015). Kaersutitic magmas and hence their source regions. Here we use amphiboles in Zagami and Shergotty have ~0.1–0.2 the bulk chemistry of Martian meteorites along with wt% H2O measured by SIMS but <0.1 wt% F and Cl parental magma compositions calculated from apatite measured by EMP (Treiman 1985; Watson et al. 1994a). and amphibole chemistry, to calculate the average volatile content of the mantle source METHODS FOR CALCULATING VOLATILE region. ABUNDANCES OF PARENTAL MAGMAS TO AMPHIBOLE AND APATITE MARTIAN APATITE AND AMPHIBOLE CHEMISTRY Volatile-bearing minerals can be used to calculate volatile ratios (F/OH, Cl/OH, and F/Cl) of their Many studies have focused on using the OH- parental magma (e.g., Patino~ Douce and Roden 2006; bearing phases amphibole and apatite to constrain the Patino~ Douce et al. 2011; Giesting and Filiberto 2014; Martian igneous volatile history and budget (e.g., McCubbin et al. 2014, McCubbin et al. 2015b, Greenwood et al. 2003; Patino~ Douce and Roden 2006; Forthcoming). Patino~ Douce and Roden (2006), Patino~ Filiberto and Treiman 2009b; Patino~ Douce et al. 2011; Douce et al. (2011), Gross et al. (2013), and Howarth McCubbin et al. 2012; Giesting et al. 2015; Giesting et al. (2015) used thermodynamic calculations to show and Filiberto, Forthcoming; McCubbin et al. that volatile fugacity ratios of parental magmas can be Forthcoming). Apatite in Martian meteorites range calculated from apatite analyses and then compared on a from OH-bearing, F-apatite to almost pure endmember global and planetary basis. However, calculating exact Cl-apatite, which suggests a range in volatile contents of parental magma volatile concentrations requires primary magmas with some being potentially rich in partition coefficients relevant to planetary compositions. H2O (e.g., McCubbin et al. 2012; Gross et al. 2013). Recently, McCubbin et al. (2015b) provided experimental However, the majority of Martian apatite are chlorine- F-Cl-OH apatite-melt partition coefficients for a rich and typically plot in or near the field of chlorine- shergottite bulk composition, which will be used in this ~ dominant parental magmas (Patino Douce and Roden work to calculate the H2O/Cl and Cl/F ratio of magmas 2006; Filiberto and Treiman 2009b; McCubbin et al. parental to the Martian meteorites, rather than relying 2013; Howarth et al. 2015), suggesting that the majority on the volatile fugacity ratios as has previously been of magmas that crystallized apatite are chlorine-rich and done. Giesting and Filiberto (Forthcoming) provide a some may even have chlorine as the dominant volatile regression equation for volatile element partitioning Constraints on the volatile content of the Martian mantle 3 between amphibole and basaltic glass, which has been the Earth (Bogard et al. 2010; Burgess et al. 2013). used to calculate the Cl/OH ratio of magmas parental to However, in order to compare bulk compositions of the chassignites (Giesting et al. 2015). We will use these different planetary bodies, it is not enough to compare values in our modeling below. concentrations of elements. Instead, we must compare ratios of similarly incompatible elements, which PARENTAL MAGMA COMPOSITIONS accounts for differences in magmatic processes such as partial melting and fractional crystallization, as well as Estimates of Martian magma compositions range degassing and secondary alteration (e.g., Dreibus and from drier than terrestrial magmas to similar water Wanke€ 1987). We use the Cl/La ratio which has contents found in terrestrial subduction zone magmas previously been used (Dreibus and Wanke€ 1985, 1987; (e.g., Dann et al. 2001; Jones 2004; Nekvasil et al. 2007; Filiberto and Treiman 2009b). Both chlorine and McCubbin et al. 2010a, 2012; Usui et al. 2012, 2015; lanthanum are incompatible elements, and therefore, Giesting et al. 2015). Estimates for Martian magma should track each other during magmatic processes such volatile contents in this volume are similar to terrestrial as partial melting and fractional crystallization. Mid-Ocean Ridge Basalts and Ocean Island basalts However, chlorine is a volatile lithophile element that is and not subduction zone magmas and suggest fluid mobile during degassing and low-temperature heterogeneities in the shergottite mantle source region alteration, while lanthanum is a refractory lithophile (e.g., Mane et al. Forthcoming; McCubbin et al. element; therefore, any deviations from a constant Cl/ Forthcoming). McCubbin et al. (Forthcoming) La can be explained by degassing (low Cl/La values) specifically calculates the H2O and Cl contents of and/or alteration (high Cl/La values). parental magmas to the enriched and depleted Figure 1 shows the Cl/La values for different classes shergottite source regions. Important for this work, of Martian meteorites. Six meteorites have significantly McCubbin et al. (Forthcoming) calculates H2O/Cl higher Cl/La ratios than the rest of the Martian ratios of the parental magmas at the time of apatite meteorites: Nakhla, SAU005, DaG476, NWA 7034, crystallization of 2.5–17.9 for enriched, and 3.5–13.1 for Y98, and QUE. Nakhla, SAU005, DaG476, and NWA depleted shergottite magmas based on new apatite-melt 7034 have experienced alteration (Bridges and Grady volatile element exchange coefficients in McCubbin 1999; Bridges et al. 2001; Wadhwa et al. 2001; Gnos et al. (2015b). Giesting et al. (2015) calculate 0.5–4.0 et al. 2002; Crozaz et al. 2003; Treiman 2005; H2O/Cl ratio for the parental magma to the chassignites Mohapatra et al. 2009; Muttik et al. 2014), which can from amphibole-melt pairs (before H loss due to either explain the high Cl contents. Nakhlites contain degassing or shock). We calculate 0.7–4.2 H2O/Cl ratio phyllosilicates, carbonates, Cl-scapolite, and halite that for the parental magma to the chassignites from apatite- are purportedly Martian in origin (Bridges and Grady melt pairs using data from McCubbin and Nekvasil 1999; Bridges et al. 2001; Treiman 2005; Filiberto et al. (2008) and apatite-melt exchange coefficients from 2014b), while SAU005 and DaG476 contain significant McCubbin et al. (2015b), which agrees well with the evidence for terrestrial alteration (Wadhwa et al. 2001; estimates based on amphibole-melt chemistry from Gnos et al. 2002; Crozaz et al. 2003; Mohapatra et al. Giesting et al. (2015). From McCubbin et al. (2013), we 2009). Regolith NWA 7034 also contains calculate an H2O/Cl ratio of 0.6–0.9 for the nakhlites extensive evidence for alteration and fluid mobility (e.g., based on apatite analyses and new apatite-melt Muttik et al. 2014). Therefore, we will ignore those for exchange coefficients from McCubbin et al. (2015b). In the rest of this discussion. Interestingly, depleted the next section, we will use these calculated volatile shergottites, Y98 and QUE, have higher Cl/La ratios ratios of the parent magmas combined with the bulk (342 Æ 116) than the rest of the shergottites and values chlorine and fluorine composition of the Martian as high as some of the altered meteorites, which meteorites to calculate the volatile concentration of suggests that the depleted source region may have Martian magmas and their source regions. higher Cl than the average mantle. One sample, NWA 1068, has significantly lower Cl/La ratio compared to BULK CHEMISTRY the rest of the Martian meteorites. This can be explained by preferential loss of Cl to La either by Chlorine volcanic degassing during eruption and emplacement or by a shock process (Fig. 2). The Cl content in NWA Bulk chlorine contents of the unaltered Martian 1068 was analyzed using Ar noble gas measurements, basalts are similar to those of terrestrial tholeiites which can be subject to loss. The rest of the Martian (Table 1), which have been used to suggest that the basalts fall along a trend line and by filtering the data Martian interior has bulk halogen contents similar to to only those data that have not experienced Cl loss or 4 J. Filiberto et al.

Table 1. Meteorite bulk Cl, F, and La concentrations. 10000 F Cl La Meteorite (ppm) (ppm) (ppm) Reference Shergottites 1000 Depleted shergottites QUE 94201 40 91 0.35 1 Yamato-980459 86 60.7 0.143 2 100 DaG 476 840 0.13 3 Depleted Shergottites

SAU 005 56 143 0.11 4 Cl (ppm) Enriched Shergottites Intermediate shergottites Intermediate Shergottites 10 Chassigny NWA 6234 59 0.96 5 Nakhlites EETA79001 39 26 0.37 6 ALHA 84001 NWA 7034 Lithology A EETA79001 31 48 0.8 6 1 Lithology B 0.01 0.1 1 10 100 EETA79001 glass 35 0.3 6 La (ppm) ALHA 77005 22 14 0.32 6 LEW 88516 27 29 0.314 9 Fig. 1. Cl/La abundances of Martian meteorites based on Enriched shergottites meteorite classification. Data sources as in Table 1. Shergottites — Zagami 41 137 3.2 6 are shown by boxes depleted (yellow), intermediate (), Shergotty 41.6 108 2.44 6 and enriched (blue); chassignites are shown as pink diamonds, nakhlites (altered and unaltered) are shown as red circles; NWA 1068 13 2.25 7 ALH 84001 as a cyan circle; and breccia NWA 7034 as black LosAngeles 131 4.06 7 stars. Nakhlites Nakhla 268 2.14 7 Nakhla 57.1 1145 2.14 6 gas data, may represent the Martian interior (Ott 1988), Nakhla 105 2.14 8 MIL 03346 164 4.3 8 suggesting that our Cl/La ratio may represent the MIL 03346 210 4.3 7 average Martian meteorite source region. Yamato 00593 87 2.79 7 Comparing the Cl/La ratio of Martian basalts to Lafayette 65 1.86 9 terrestrial basalts (Fig. 2) shows that Martian basalts Chassignites have slightly lower Cl and La concentrations to Chassigny 14.7 34 0.59 6 terrestrial basalts, which is consistent with higher Chassigny 38 0.53 7 degrees of partial melting and/or smaller amounts of fractional crystallization. For the Earth, we calculate a ALHA84001 8 0.19 9 Cl/La ratio of 21 Æ 6. Comparing these ratios, we Regolith breccia calculate that has a Cl/La ratio 2.5 (Æ1.0) times NWA 7034 whole rock 2200 13.66 10 that of the Earth consistent with previous notions that NWA 7034 whole rock 8.03 11 Mars is ~2–3 times as enriched in Cl as the Earth NWA 7034 bulk matrix 1600 8.4 12 € NWA 7034 protobreccia 1260 13 12 (Dreibus and Wanke 1985, 1987; Filiberto and Treiman clast 2009b). We can now use this comparison to calculate the Cl Fluorine and chlorine data from: 1. Dreibus et al. (1996); 2. Dreibus et al. (2003), Shirai and Ebihara (2004); 3. Zipfel et al. (2000), 4 concentration of the source region of the Martian Dreibus et al. (2000); 5. Burgess et al. (2013); 6. Dreibus and meteorites. Assuming a bulk mantle La value of 0.48 Wanke€ (1985, 1987); 7. Bogard et al. (2010); 8. Cartwright et al. ppm (Dreibus et al. 1982), we estimate a bulk Cl (2013); 9. Lodders (1998); 10 Agee et al. (2013); 11. Nyquist et al. abundance of 25 Æ 8 (ppm) (Table 2), which is (Forthcoming); and 12. McCubbin et al. (2015a). Lanthanum data significantly lower than the bulk Mars Cl abundance from Lodders (1998), Filiberto et al. (2012a), and Meyer (2014). calculated based on the crustal Cl/K ratio (390 ppm; Taylor et al. 2010), and slightly lower than previous gain (through chlorine-loss by degassing or chlorine- estimates based on the Martian meteorites 44 ppm addition by alteration), plus the depleted shergottites (Dreibus and Wanke€ 1985) and based on the Th/Cl that have a higher Cl/La ratio, we calculate a Cl/La bulk Mars abundance of 32 Æ 9ppm (Taylor 2013). ratio for Martian basalts of 51 Æ 17; however, there Interestingly, our new estimate is similar to estimates may be source regions with different Cl/La ratios for the terrestrial enriched mantle (30 ppm) but an (Fig. 1). Importantly, Chassigny has a Cl/La ratio order of magnitude higher than estimates for the consistent with the Mars trend line and, based on noble terrestrial depleted mantle (1 ppm) (Michael and Constraints on the volatile content of the Martian mantle 5

10000 10000, Basalts

Gusev Basalts "ratted" surface 1000 Alteration 1000

Mars 100 100 F (ppm)

Cl (ppm) Earth 10 10 Degassing Mars Earth 1 1 0.01 0.1 1 10 100 1 10 100 1000 10000 La (ppm) Cl (ppm) Fig. 3. Cl/F abundances of Martian meteorites (red circles) Fig. 2. Cl/La ratio of Martian meteorites compared with and terrestrial basalts (blue circles). A 1:1 line is shown for terrestrial basalts updated and modified from Filiberto and comparison. Data for Martian meteorites as in Table 1. Treiman (2009b). Bulk chlorine and lanthanum abundances in Terrestrial data from Yoshida et al. (1971) and Nogami et al. Martian basaltic meteorites (red circles) and terrestrial basaltic (2006). rocks (blue squares). Data sources for meteorite data as in Table 1. Terrestrial samples are the same from Filiberto and Treiman (2009b) and were chosen for this study to represent shergottites combined with terrestrial basalts to make magmas and xenoliths that are relatively un-degassed (Dreibus up for the paucity of data. Shergottites and terrestrial € and Wanke 1985, 1987; Simons et al. 2002). Arrows show how basalts combined have a Cl/F ratio of 0.80 Æ 0.40 alteration (high Cl/La) and degassing (low Cl/La) affect the Cl/La ratio. Also plotted for comparison is Cl concentration (Fig. 3). The deviation from a Cl/F ratio of 1 reflects of Class basalts (dark red box; Gellert degassing and alteration in some of the analyzed rocks et al. 2006) after removal of all surface coatings and alteration instead of igneous processing. F and Cl are both products by rock abrasion tool (“ratted” surface) and the similarly incompatible during mantle melting and average Cl concentration of basaltic rocks in Gale Crater igneous crystallization and therefore igneous processes (dark red box; et al. 2014); La was not measured in these rocks (Gellert et al. 2006; Schmidt et al. 2014). The high should not affect the Cl/F ratio (e.g., Fuge 1977; Cl concentrations of the rocks in Gale Crater is presumably Aiuppa et al. 2009; Dalou et al. 2012), but Cl readily due to alteration, as these rocks have not been abraded to degasses from a basaltic magma while F is compatible remove surface coatings. with a magma (e.g., Carroll and Webster 1994; Webster and Rebbert 1998; Webster 2004; Aiuppa 2009; Pyle Cornell 1998; Saal et al. 2002; Kendrick et al. 2012). and Mather 2009). Therefore, degassing of the magma This suggests a source region for the Martian meteorites before crystallization causes the Cl/F ratio to be lower with a chlorine content similar to the terrestrial enriched than the initial value (assumed to be less than 1). MORB source. Further, alteration will causes the Cl/F ratio to be higher than the initial value (again assumed to be 1) Fluorine because Cl is more soluble in aqueous fluids (e.g., Pyle and Mather 2009; Anazawa et al. 2011). Therefore, if Similar to chlorine, bulk fluorine contents of the we assume a ~1:1 correlation to calculate the Martian Martian meteorites are also similar to terrestrial basalts, mantle F concentration, we calculate a bulk F but there are few analyses of fluorine in Martian abundance of the source of 25 (ppm) (Table 2); meteorites (Table 1) (Dreibus and Wanke€ 1985, 1987; however, the error on this calculation is significantly Treiman 2003). Because of this paucity of data, there higher than for our Cl calculation and we assume an has been no calculation of the bulk F content of the error of 13 ppm based on the uncertainty in the data Martian interior (see Dreibus and Wanke€ 1985, 1987; (Fig. 3). A Martian mantle with 25 ppm F is, within Treiman 2003). Here we calculate the F content of the error, the same as estimates for the primitive terrestrial Martian mantle by using the Cl/F ratio of Martian mantle of 25 ppm F (McDonough and Sun 1995), and 6 J. Filiberto et al.

Table 2. Calculated F, Cl, and H2O as high as 126.7 and as low as ~0 (McCubbin et al. contents of the Martian interior with Forthcoming). Similar to the comparison of Cl and F, Cl representative uncertainty. and H2O are both incompatible during igneous processes Cl (ppm) 25 Æ 8 (melting and crystallization) as long as no hydrous phase F (ppm) 25 Æ 13 fractionates (e.g., Aiuppa et al. 2009; Pyle and Mather Æ H2O (ppm) 56 71 2009). Therefore, we will assume the magma H2O/Cl ratio is the same as the mantle H2O/Cl ratio, and using the calculated chlorine content of the Martian source slightly higher than the terrestrial depleted mantle of 16 region of 25 Æ 8 ppm, we calculate an average H2O ppm F (Saal et al. 2002). content of the source region to the Martian meteorites. Interestingly, magma compositions calculated from Using a parental magma H2O/Cl of 2.7 Æ 4.4 based on Martian apatite suggest a parental magma with a Cl/F amphibole and apatite in chassignites and apatite in ratio of 2.1–40, which is significantly higher than the nakhlites, we calculate 68 Æ 113 ppm H2O in the source bulk rock analyses of Martian meteorites and terrestrial region. Based on melt inclusions in shergottites LAR and basalts. Depleted shergottites have the lowest calculated Y98 H2O/Cl ratio of 2.3 Æ 3, we calculate 56 Æ 71 ppm Cl/F compositions, while enriched shergottites have the H2O in the source region (Table 2). Apatite in highest calculated Cl/F ratios. This can be explained by shergottites have a much larger range in H2O/Cl ratios two different processes to elevate the Cl/F ratio (1) a (Figure 4, Table 3, McCubbin et al. Forthcoming) and source region with elevated Cl/F, depleted in F and/or therefore uncertainty in our calculation (21 Æ 37); we enriched in Cl above terrestrial values; (2) the apatites calculate an H2O content of the source region of analyzed in the Martian meteorites formed by fractional 540 Æ 940 ppm. The large uncertainty in our calculation crystallization and the early-formed F-rich apatite is not likely reflects heterogeneities in the Martian interior (such typically sampled. If we assume that the calculated as the depleted, intermediate, and enriched source parental magma Cl/F ratio from apatite represents the regions, as well as the chassignite- source region), igneous compositions, we calculate a mantle source but in order to resolve those differences we would need composition of 1 Æ 1 ppm F, which would suggest a more data to constrain whether or not the apatite Martian interior that is an order of magnitude depleted compositions reflect primary igneous crystallization, in F compared with the terrestrial mantle (McDonough fractionational crystallization, degassing, and/or shock and Sun 1995; Saal et al. 2002). affects. Interestingly, our calculated H2O contents of the Water Martian interior for the chassignite and nakhlite source region, as well as the source region for Yamato-980459 To calculate the water content of the Martian and LAR 06319 are similar to the depleted terrestrial interior, we rely on the calculated H2O/Cl concentration MORB source of 100–180 ppm (Michael 1988) or for Martian magmas from apatite and amphibole 142 Æ 82 ppm (Saal et al. 2002). This is different than analyses and direct measurements of H2O/Cl the F and Cl contents which are similar to the enriched concentrations in glass melt inclusions (Table 3). terrestrial MORB-source region. A MORB-like source- Figure 4 shows the calculated H2O/Cl ratios of Martian region water content, has been previously suggested for magmas by meteorite subgroup. Amphibole-melt pairs in the source region to the SNC meteorites based on NWA 2737 and Chassigny give a parental magma H2O/ apatite analyses in NWA 6234 and shergotty (e.g., Cl ratio of 0.5–4.0 (Giesting et al. 2015), and apatite-melt McCubbin et al. 2012; Gross et al. 2013). However, this pairs from Chassigny give a parental magma H2O/Cl of does not rule out an ancient mantle with significantly 0.7–4.2. Consistent with the chassignite results, the H2O/ higher volatile contents that lost volatiles during the Cl ratio of the glassy melt inclusions in Yamato-980459 Magma Ocean and subsequent basalt genesis (Medard and LAR 06319 are 0.4–6.7 (Usui et al. 2012, 2015). and Grove 2006; Elkins-Tanton 2008). Nakhlite magmas at time of apatite crystallization have a H2O/Cl ratio of 0.6–0.9 based on apatite chemistry CONCLUSIONS (McCubbin et al. 2013) consistent with a parental magma that has Cl > H2O (Filiberto et al. 2014b); however, this Using the bulk chlorine content of Martian low H2O/Cl ratio may be the result of crustal meteorites, along with apatite and amphibole chemistry, contamination in the nakhlites (Franz et al. 2014; we calculate the water, fluorine, and chlorine content of Williams et al. Forthcoming). Enriched, intermediate, the Martian interior. Our calculations suggest a Martian and depleted shergottites have average H2O/Cl ratios of interior that is similar to the terrestrial MORB source 1.6–17.9 based on apatite chemistry with values reaching and has water/chlorine ratios ~0.4–18. Melting of such a Table 3. Apatite compositions form Martian meteorites and calculated melt volatile ratios assuming apatites are magmatic in origin. Apatite data cited in table are from previously published literature (Boctor et al. 2003; Greenwood et al. 2008; Gross et al. 2013; Hallis et al. 2012; Leshin 2000; McCubbin and Nekvasil 2008; McCubbin et al. 2012, 2013, Forthcoming) Average apatite Apatite composition composition StDev Based on apatite and apatite melt exchange Kd Average StDev Max Min Average Ap Ap Ap Ap Ap Ap melt (H2O/ (H2O/ (H2O/ Median melt StDev Max Min Median Meteorite (F) (Cl) (OH) (F) (Cl) (OH) (H2O/Cl) Cl) Cl) Cl) (H2O/Cl) (Cl/F) (Cl/F) (Cl/F (Cl/F) (Cl/F) Shergottites Depleted shergottites

QUE 94201 0.364 0.243 0.394 0.108 0.059 0.054 7.4 1.3 9.8 5.9 7.3 6.3 7 2.5 9.3 1.8 6.4 mantle Martian the of content volatile the on Constraints NWA 1195 0.475 0.169 0.356 0.088 0.084 0.132 13.1 10.4 36.9 2.5 11.4 3.1 1.8 8.0 1.3 2.8 DaG 476c 0.708 0.268 0.024 N/A 3.3 (OH below detectiona) LAR 12095c 0.662 0.188 0.151 3.5 2.4 Intermediate shergottites NWA 6234 0.332 0.261 0.407 0.133 0.156 0.100 14.2 24.4 126.7 1.4 8.8 10.0 10.1 34.4 0.2 5.4 NWA 1950 0.488 0.491 0.021 0.061 0.045 0.021 N/A 8.9 2.0 11.9 7.0 7.8 (OH below detectiona) EETA79001 0.132 0.641 0.227 0.032 0.056 0.056 1.6 0.5 2.8 0.9 1.5 44.8 13.7 68.6 28.3 40.4 Lithology B Enriched shergottites Zagami 0.463 0.249 0.288 0.166 0.071 0.122 5.2 2.2 10.4 1.0 4.5 6.2 5.3 25.4 2.3 3.8 Shergotty 0.256 0.360 0.383 0.160 0.184 0.119 6.0 4.2 26.7 0.2 5.5 45.7 100.7 442.6 1.4 7.6 Los Angeles 0.041 0.442 0.517 0.034 0.107 0.102 5.6 2.3 9.8 2.5 5.6 146 116 549 18 101 NWA 2986 0.218 0.511 0.271 0.054 0.094 0.069 2.5 0.8 4.0 0.1 2.5 22.9 13.0 77.4 9.3 19.1 RBT 04261 0.453 0.335 0.212 0.109 0.153 0.100 14.0 32.2 113.2 0.9 2.2 7.3 4.7 17.5 0.2 6.8 LAR 06319 0.306 0.250 0.444 0.122 0.135 0.126 17.8 26.3 98.4 1.6 7.4 9.6 8.9 42.0 0.6 5.9 NWA 3171 0.236 0.293 0.471 0.067 0.107 0.058 8.1 3.4 14.6 2.9 7.4 13.3 11.0 41.7 3.6 9.9 Nakhlites NWA 998 0.416 0.492 0.093 0.067 0.041 0.073 0.86 0.80 3.67 0.00 0.63 10.5 2.1 15.7 6.9 10.3 Nakhla 0.486 0.459 0.0559b 0.224 0.172 0.60 0.22 1.02 0.33 0.56 14.1 15.8 53.8 2.7 6.9 Lafayette 0.444 0.526 0.030 0.186 0.182 0.041 N/A 16.1 17.6 68.8 3.7 10.2 (OH below detectiona) Governador 0.576 0.388 0.037 0.221 0.213 0.083 N/A 8.7 9.0 39.5 0.9 6.5 Valaderas (OH below detectiona) NWA 817 0.774 0.219 0.008 0.060 0.060 0.021 N/A 2.5 0.8 3.5 1.4 2.4 (OH below detectiona) .Flbroe al. et Filiberto J. 8

Table 3. Continued. Apatite compositions form Martian meteorites and calculated melt volatile ratios assuming apatites are magmatic in origin. Apatite data cited in table are from previously published literature (Boctor et al. 2003; Greenwood et al. 2008; Gross et al. 2013; Hallis et al. 2012; Leshin 2000; McCubbin and Nekvasil 2008; McCubbin et al. 2012, 2013, Forthcoming). Average apatite Apatite composition composition StDev Based on apatite and apatite melt exchange Kd Average StDev Max Min Average Ap Ap Ap Ap Ap Ap melt (H2O/ (H2O/ (H2O/ Median melt StDev Max Min Median Meteorite (F) (Cl) (OH) (F) (Cl) (OH) (H2O/Cl) Cl) Cl) Cl) (H2O/Cl) (Cl/F) (Cl/F) (Cl/F (Cl/F) (Cl/F) MIL 03346 0.811 0.189 0.000 0.043 0.043 N/A 2.0 0.6 3.2 0.9 2.0 (OH below detectiona) NWA 5790 0.788 0.198 0.014 0.042 0.059 0.031 N/A 2.2 0.8 3.0 1.3 2.2 (OH below detectiona) Chassignites Chassigny MI 0.753 0.142 0.1173b 0.065 0.062 4.2 3.0 14.7 2.0 3.0 1.7 0.8 3.0 0.3 1.7 Chassigny 0.471 0.460 0.0726b 0.091 0.080 0.67 0.12 0.96 0.50 0.64 9.0 3.1 15.1 4.6 8.6 Interstitial NWA 2737 0.592 0.365 0.043 0.079 0.057 0.043 N/A 5.5 1.4 7.4 3.0 5.5 (OH below detectiona) Regolith breccia NWA 7034 0.167 0.660 0.172 0.045 0.077 0.065 1.2 0.6 2.6 0.3 1.0 37.0 13.5 83.9 12.9 33.8 aThe detection limit for an OH component in apatite from F and Cl EPMA data is approximately 0.08 sfu (McCubbin et al. 2010b). bMinimum value measured by SIMS (Nakhla from Hallis et al. 2012; Chassigny from Boctor et al. 2003). cOnly 1 analysis has been reported, so statistical analysis was not possible. Constraints on the volatile content of the Martian mantle 9

1000 In situ and orbital studies of rocks on the surface of Mars can provide information about bulk chlorine (e.g., McSween et al. 2004; Keller et al. 2006; Schmidt et al. 100 2009; Taylor et al. 2010), but this is only useful if the analyses are of an unaltered rock. In order to truly resolve whether the Noachian mantle had higher

O/Cl 10 volatile contents, bulk unaltered samples of ancient 2

H Mars are needed.

1 Acknowledgements—The authors thank Tomo Usui and Hap McSween as well as the Guest AE Walter Kiefer 0.1 for their constructive reviews, which greatly improved the manuscript. This work was supported by NASA Mars Fundamental Research Program grant Y98 LAR # NNX13AG35G to JF and JG. FMM acknowledges support from NASA’s Mars Fundamental Research Nakhlites Program grant NNX13AG44G.

Editorial Handling—Dr. Walter Kiefer

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