EVIDENCE for MAGMATIC-HYDROTHERMAL ACTIVITY on MARS from Cl-RICH SCAPOLITE in NAKHLA

45th Lunar and Planetary Science Conference (2014) 1620.pdf

EVIDENCE FOR MAGMATIC-HYDROTHERMAL ACTIVITY ON MARS FROM Cl-RICH SCAPOLITE IN NAKHLA. J. Filiberto1, C.A. Goodrich2, A.H. Treiman3, J. Gross4, and P.A. Giesting1, 1Southern Illinois University, Geology Dept, Carbondale, IL 62901 USA, [email protected], 2Planetary Science Institute, Tucson AZ 85719 USA. 3Lunar and Planetary Institute, Houston, TX 77058 USA, 4American Museum of Natural History, New York, NY USA.

Introduction: Scapolite is a common terrestrial The melt inclusion containing the Cl-scapolite (Fig. hydrothermal, metamorphic, and metasomatic mineral 1) is dominated by high-Ca pyroxene, K-feldspar and which forms by the reaction of plagioclase and a Cl- or K-rich glass, with minor chromite, Fe-sulfides, Fe-Ti CO2-rich fluid [1-3]. It is less common as a primary oxides, and alteration material [9]. The occurrence of igneous phase, but has been reported as megacrysts, the scapolite appears to be texturally equivalent to the phenocrysts, and oikocrysts in alkali-rich basaltic K-feldspar or the glass (i.e., interstitial to the pyrox- magmas [4-6]. Based on reflectance spectra, scapolite enes), and may therefore be replacing, or contempora- has also been suggested to exist on the surface of Mars neous with, one of these phases. It contains ~3.9 wt.%

as a possible alteration mineral [7]. Cl, and has the formula (Na2.8Ca0.7K0.3)3.9(Si8.3Al3.7)12ClO24. Scapolite has three main end member composi- It is almost pure end-member marialite with little tions: marialite (Na4Al3Si9O24Cl), meionite meionite component (Fig. 2). We did not analyze for C (Ca4Al6Si6O24CO3), and mizzonite or S, but the scapolite contains enough Cl to preclude (~NaCa3Al5Si7O24CO3) [e.g., 1]. Unlike other-chloride the presence of significant CO3 or SO4. bearing minerals (such as apatites, amphiboles, and micas), scapolite contains little to no OH. The chemistry of scapolite can therefore be used as a tracer of the Cl and CO2 contents of the fluid responsible for its formation, independent of fH2O [2-3, 8]. Here we report the first occurrence of Cl-scapolite in a martian meteorite – in a melt inclusion in olivine in Nakhla – and use terrestrial metamorphic experiments and modeling to constrain its origin. Sample: During a study of melt inclusions in Nak- hla [9], Cl-scapolite was found, as an ~100 m-long patch, within one large melt inclusion in olivine (Fig. 1). Following repolishing to remove beam damage caused by high-current X-ray mapping and grid analy- sis, the scapolite was analyzed using 15 KeV and 10 nA beam current [9]. Fig. 2. Range of natural terrestrial scapolite composi- tions (black symbols) distinguished by mode of occurrence. Terrestrial data and figure modified from Reb- bert and Rice [3]. Martian scapolite from this study is shown for comparison (red).

Martian vs terrestrial. Alteration materials found in the nakhlites are thought to be both martian and terrestrial in origin [10-13]. The scapolite is found within an olivine-hosted melt inclusion that shows minor to moderate evidence for fracturing. The scapolite occurs well within the melt inclusion and is not adjacent to any large fractures. It is adjacent to the alteration material (labeled “iddingsite”) which is thought to be martian in origin [11-13]. Cl- scapolite forms at conditions > 700 º C at 1 bar [8, 14-17], while terrestrial alteration would occur at surface tempera- Fig. 1. Melt inclusion NK12A1 in Nakhla, from [9]. tures and pressures. Therefore, based on textural and Combined potassium x-ray map (orange) and BEI. chemical arguments, we infer that the scapolite formed 45th Lunar and Planetary Science Conference (2014) 1620.pdf

in the martian crust and not as a product of terrestrial ture waters [20-23]. Mars Science Laboratory has al- alteration. ready found evidence for near-neutral pH water in an Cl-Scapolite Formation. Scapolite chemistry re- ancient stream bed and from hydrous minerals [24-25]. flects the formation conditions and fluid composition Alteration minerals in the nakhlites have also revealed (Fig 2.; [1-3]). We can use the chemistry of the mar- evidence for martian CO2-rich fluids at temperatures < tian scapolite, compared with terrestrial scapolite of 150-200 ºC [18]. Here we show that the fluid forming known origin, to constrain its formation conditions. scapolite in Nakhla was warmer than previous esti- The scapolite in Nakhla is almost pure end-member mates for martian fluids and was Cl-rich and not CO2- marialite. Terrestrial marialite typically forms by hy- rich. Any potential biologic activity would have to deal drothermal activity of a brine with a high mole fraction with high temperatures and saline fluids. of NaCl in the fluid [8] but it can also form as a late Conclusions: We report the first occurrence of Cl- stage igneous phase occurring in the mesostastis or rich scapolite in a martian meteorite. The Cl-rich sca- melt inclusions [4-6]. In terrestrial systems, the Cl may polite in Nakhla is consistent with formation from ei- have been original to the system or introduced from an ther a late stage Cl-rich, water-poor magma or mag- outside source through fluid migration [2]. From expe- matic Cl-rich hydrothermal brine at a minimum tem- rimental results and natural systems, it has been shown perature of 700 ºC. that marialite is stable at 700 – 850 ºC at 1bar [14]. References: [1] Goldsmith J.R. (1975) GSA Bulletin, Much more is known about the C- bearing scapolites, 87, 161-168. [2] Mora C.I. and Valley J.W. (1989) AmMin, which are stable to much higher temperatures and 74, 721-737. [3] Rebbert C.R. and Rice J.M. (1997) GCA, pressures and are consistent with hydrothermal to low- 61, 555-567. [4] Smith G.C. et al. (2008) Min Magazine, 72, grade metamorphic conditions [1]. Therefore, by anal- 1243-1259. [5] Vaggelli G. et al. (1992) European Journal of ogy to terrestrial scapolites, the Cl-rich scapolite in Min, 4, 1113-1124. [6] Vaggelli G. et al. (1993) J. Vol and Nakhla is consistent with formation during hydrother- Geothermal Res, 58, 367-376. [7] Clark R.N. et al. (1990) mal, and/or late-stage igneous, activity at a minimum JGR, 95, 14463-14480. [8] Ellis D.E. (1978) GCA, 42, temperature of 700 ºC. 1271-1281. [9] Goodrich C.A. et al. (2013) MaPS, 48, 2371- Conditions of Hydrothermal Alteration, Com- 2405. [10] Gooding J.L. et al. (1991) Meteoritics, 26, 135- parison with Alteration Mineralogy: We can com- 143. [11] Treiman A.H. (2005) Chemie der Erde- pare the temperature recorded by the scapolite with Geochemistry, 65, 203-270. [12] Changela H.G. and Bridges recent estimates for conditions of formation of other J.C. (2010), MaPS, 45, 1847-1867. [13] Bridges J.C. et al. alteration minerals in the Nakhla based on thermo- (2001) Chronology and Evolution of Mars, 365-392. [14] chemical modeling [18]. Bridges and Schwenzer [18] Eugster H. and Prostka H. (1960) Bull. Geol. Soc. Amer, 71, show that the Fe-rich carbonates precipitated from a 1858. [15] Vanko D. and Bishop F. (1980). Geol Soc Am CO2-rich brine at 150-200 ºC. The brine continued to Abstr Prog. [16] Rebbert C.R. (1995) PhD thesis, University cool until 50 ºC, at which point Fe-phyllosilicates pre- of Oregon. [17] Newton R.C. and Goldsmith J.R. (1976) cipitated. The temperature of hydrothermal activity Zeitschrift fur Kristallographie, 143, 333-353. [18] Bridges recorded by the Cl-scapolite is > 700 ºC, significantly J.C. and Schwenzer S.P. (2012), EPSL, 359–360, 117-123. higher than the temperatures recorded by the alteration [19] Cockell C.S. et al. (2012) Icarus, 217, 184-193. [20] minerals. Further, the alteration minerals record a CO2- Schwenzer S.P. and Kring D.A. (2009) Geology, 37, 1091- rich fluid, while the Cl-scapolite forms from a Cl-rich, 1094. [21] Tosca N.J. et al. (2008) Science, 320, 1204-1207. CO2-poor brine (otherwise we would have mizzinite or [22] Zolotov M.Y. and Mironenko M.V. (2007), JGR meonite instead of marialite). This could suggest that Planets, 112, E07006. [23] Filiberto J. and Schwenzer S.P. the phases are not related and may suggest a late stage (2013) MaPS, 48, 1937-1957. [24] Williams R.M.E. et al. igneous origin instead of hydrothermal origin for the (2013) Science, 340, 1068-1072. [25] Vaniman D.T. et al. scapolite. However, the alteration material is found (2013) Science. adjacent to the scapolite, suggesting that they may be related and the Cl-scapolite simply records a higher temperature stage of the alteration. Implications for Habitability: In order to evaluate the potential for habitability within the martian crust, it is vital to understand the temperature, duration, and composition of any fluids present [e.g., 19]. Orbiter and lander missions have revealed extensive evidence of hydrous minerals on the surface that precipitated from acidic to neutral pH and cold to warm tempera-