Identification of hydrated silicate minerals on Mars using MRO‐CRISM: Geologic context near Nili Fossae and implications for aqueous alteration

Abstract

[1] The Noachian terrain west of the Isidis basin hosts a diverse collection of alteration minerals in rocks comprising varied geomorphic units within a 100,000 km 2 region in and near the Nili Fossae. Prior investigations in this region by the Observatoire pour l'Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) instrument on Mars Express revealed large exposures of both mafic minerals and iron magnesium phyllosilicates in stratigraphic context. Expanding on the discoveries of OMEGA, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has found more spatially widespread and mineralogically diverse alteration minerals than previously realized, which represent multiple aqueous environments. Using CRISM near-infrared spectral data, we detail the basis for identification of iron and magnesium smectites (including both nontronite and more Mg-rich varieties), chlorite, prehnite, serpentine, kaolinite, potassium mica (illite or muscovite), hydrated (opaline) silica, the sodium zeolite analcime, and magnesium carbonate. The detection of serpentine and analcime on Mars is reported here for the first time. We detail the geomorphic context of these minerals using data from high-resolution imagers onboard MRO in conjunction with CRISM. We find that the distribution of alteration minerals is not homogeneous; rather, they occur in provinces with distinctive assemblages of alteration minerals. Key findings are (1) a distinctive stratigraphy, in and around the Nili Fossae, of kaolinite and magnesium carbonate in bedrock units always overlying Fe/Mg smectites and (2) evidence for mineral phases and assemblages indicative of low-grade metamorphic or hydrothermal aqueous alteration in cratered terrains. The alteration minerals around the Nili Fossae are more typical of those resulting from neutral to alkaline conditions rather than acidic conditions, which appear to have dominated much of Mars. Moreover, the mineralogic diversity and geologic context of alteration minerals found in the region around the Nili Fossae indicates several episodes of aqueous activity in multiple distinct environments.

New evidence for a magmatic influence on the origin of Valles Marineris, Mars

“…Though we do not match the spectrum in the CRISM image of Claritas rise (FRT0000634B) in Fig. 13 to a particular phyllosilicate, Ehlmann et al (2009a) recently identified it as 'serpentine', along with further identifications of serpentine in the Nili Fossae region (Ehlmann et al, 2009b).…”

The science process for selecting the landing site for the 2011 Mars Science Laboratory

“…A northward traverse would cross the boundary between distinct, diverse units exposing Hesperian and Noachian-aged sequences with hydrated and phyllosilicate mineral signatures (Bibring et al, , 2006Ehlmann et al, 2010;Mustard et al, 2008Mustard et al, , 2010Poulet et al, 2007). Many of the mineral signatures may comprise evidence for past habitable environments (Farmer and Des Marais, 1999).…”

“…With these guidelines in mind, seven new candidate sites were submitted by the science community and discussed by the Steering Committee in December 2009 (Tables 4 and 5, Fig. 3): 1) Nili Fossae carbonate plains (Ehlmann et al, 2008b) including ultramafic, phyllosilicate-bearing, and carbonate-bearing outcrops (21.7 N, 78.8E), 2) a diverse assemblage of minerals straddling the Noachian-Hesperian boundary in northeast Syrtis Major (16.71N,76.91E) with an ellipse to the north of the previous Syrtis sites (e.g., Bibring et al, 2005Bibring et al, , 2006Ehlmann et al, 2010;Mustard et al, 2008Mustard et al, , 2010Poulet et al, 2007), 3) a delta deposit Fig. 4.…”

Lassen Volcanic Fumaroles and Hot Springs: Analog for Mars

“…Farmer et al, 1996), and potential hydrothermal mineral assemblages identified from orbit (e.g. Ehlmann et al, 2009). Chojnacki & Hynek (2008) attribute some of the widespread Valles Marineris sulfate deposits to high temperature basalt alteration.…”

“…Yen et al, 2008), and through remote sensing from the Mars Reconnaissance Orbiter (MRO, e.g. Ehlmann et al, 2009). …”