Orbital Identification of Carbonate-Bearing Rocks on Mars

Department of Geological Sciences, Brown University, Providence, RI02912, USA.
Science (Impact Factor: 33.61). 01/2009; 322(5909):1828-32. DOI: 10.1126/science.1164759
Source: PubMed


Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously
been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral
characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely
associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian
era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well
as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering,
proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.

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    • "Salts found in Martian soils have broad implications for the aqueous history and habitability of Mars because salts often form via aqueous processes and their composition indicates critical habitability parameters such as pH and water activity (a w ). Orbital spectra and in situ measurements by rovers have identified a variety of salts on Mars, including chlorides (Osterloo et al., 2008; Ruesch et al., 2012), sulfates (Gendrin et al., 2005; Langevin et al., 2005; Murchie et al., 2009; Bish et al., 2013), and carbonates (Bandfield et al., 2003; Ehlmann et al., 2008; Morris et al., 2010; Niles et al., 2013). "
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    ABSTRACT: The Wet Chemistry Laboratory (WCL) on the Mars Phoenix Lander measured ions in a soil-water extraction and found Na+, K+, H+ (pH), Ca2+, Mg2+, SO42-, ClO4-, and Cl-. Equilibrium models offer insights into salt phases that were originally present in the Phoenix soil, which dissolved to form the measured WCL solution; however, there are few experimental datasets for single cation perchlorates (ClO4-), and none for mixed perchlorates, at low temperatures, which are needed to build models. In this study, we measure ice and salt solubilities in binary and ternary solutions in the Na-Ca-Mg-ClO4 system, and then use this data, along with existing data, to construct a low-temperature Pitzer model for perchlorate brines. We then apply our model to a nominal WCL solution. Previous studies have modeled either freezing of a WCL solution or evaporation at a single temperature. For the first time, we model evaporation at subzero temperatures, which is relevant for dehydration conditions that might occur at the Phoenix site. Our model indicates that a freezing WCL solution will form ice, KClO4, hydromagnesite (3MgCO3·Mg(OH)2·3H2O), calcite (CaCO3), meridianiite (MgSO4·11H2O), MgCl2·12H2O, NaClO4·2H2O, and Mg(ClO4)2·6H2O at the eutectic (209 K). The total water held in hydrated salt phases at the eutectic is ∼1.2 wt.%, which is much greater than hydrated water contents when evaporation is modeled at 298.15 K (∼0.3 wt.%). Evaporation of WCL solutions at lower temperatures (down to 210 K) results in lower water activities and the formation of more dehydrated minerals, e.g. kieserite (MgSO4·H2O) instead of meridianiite. Potentially habitable brines, with water activity aw 〉 0.6, can occur when soil temperatures are above 220 K and when the soil liquid water content is greater than 0.4 wt.% (100 ×gH2Ogsoil-1). In general, modeling indicates that mineral assemblages derived from WCL-type solutions are characteristic of the soil temperature, water content, and water activity conditions under which they formed, and are useful indicators of past environmental conditions.
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    • "These are also water-bearing and form, or are stable, under specific physicochemical conditions. 3) carbonates such as calcite, siderite, and magnesite (e.g., Bandfield et al., 2003; Ehlmann et al., 2008; Boynton et al., 2009; Palomba et al., 2009; Michalski and Niles, 2010; Morris et al., 2010). While not all water-bearing, these minerals are generally associated with formation in hydrous environments, and are indicative of environmental conditions. "

    Planetary and Space Science 09/2015; DOI:10.1016/j.pss.2015.09.001 · 1.88 Impact Factor
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    • "face reduces the spectral information from minerals beyond the range of 2 . 6 lm wavelength . The contribution of ther - mal emissions and the lower signal - to - noise ratio of the detector have also been found around 3 lm and can also diminish impor - tant information from spectral signatures ( Wagner and Schade , 1996 ; Murchie et al . , 2007 ; Ehlmann et al . , 2008 ) . Therefore , in general , limited spectral range up to 2 . 6 lm was used in the pres - ent study to avoid the effect of the thermal emission of the surface and low signal - to - noise ratio of the detector . However , since some aqueous minerals such as hydrous silicates and carbonates also have diagnostic absorptions between the ran"
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    ABSTRACT: Spectral reflectance data from the MRO-CRISM (Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars) of Capri Chasma, a large canyon within Valles Marineris on Mars, have been studied. Results of this analysis reveal the presence of minerals, such as, phyllosilicates (illite, smectite (montmorillonite)) and carbonates (ankerite and manganocalcite). These minerals hint of the aqueous history of Noachian time on Mars. Phyllosilicates are products of chemical weathering of igneous rocks, whereas carbonates could have formed from local aqueous alteration of olivine and other igneous minerals. Four different locations within the Capri Chasma region were studied for spectral reflectance based mineral detection. The study area also shows the spectral signatures of iron-bearing minerals, e.g. olivine with carbonate, indicating partial weathering of parent rocks primarily rich in ferrous mineral. The present study shows that the minerals of Capri Chasma are characterized by the presence of prominent spectral absorption features at 2.31 μm, 2.33 μm, 2.22 μm, 2.48 μm and 2.52 μm wavelength regions, indicating the existence of hydrous minerals, i.e., carbonates and phyllosilicates. The occurrence of carbonates and phyllosilicates in the study area suggests the presence of alkaline environment during the period of their formation. Results of the study are important to understand the formation processes of these mineral assemblages on Mars, which may help in understanding the evolutionary history of the planet.
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