Phyllosilicates in fluvial-lacustrine sediments in Gale Crater as revealed by the Curiosity rover.
Phyllosilicates in fluvial-lacustrine sediments in Gale Crater as revealed by the Curiosity rover.
Previously Published Material: Some of the mission results have been presented in papers by Vaniman et al. (2013), Léveillé et al. (2014) and in LPSC abstracts. This presentation summarizes some of the specific findings on phyllosilicates and adresses new questions related to cements and habitability.
Abstract ID#: 35930
English Abstract:
The Mars Science Laboratory (MSL) rover Curiosity has encountered diverse sedimentary rocks within Gale Crater. These rocks provide an opportunity to understand weathering and diagenesis on early Mars and to assess past habitable conditions. Determining the chemical and mineralogical composition of rocks involves the coordinated interpretation of data from multiple instruments on Curiosity. CheMin X-ray diffraction results for the Yellowknife Bay mudstone (Cumberland, John Klein) and the Windjana sandstone established the presence of significant amounts of poorly crystalline phyllosilicates. The XRD features are most consistent with ferromagnesian smectites with and without collapsed interlayers. The Windjana sandstone also contains a high abundance of magnetite and K-feldspar. The Confidence Hills target in the Pahrump sandstone contains a lesser amount of a 1.0 nm phyllosilicate (10%), but more iron oxides, dominantly hematite. An amorphous component, present in all rocks analysed by CheMin so far, is likely Fe-rich. In the Yellowknife Bay lacustrine mudstone, fine-scale analyses by ChemCam of sub-cm diagenetic raised-ridges suggests the presence of Fe-Mg-phyllosilicates. As fluids deposited these clays in fractures, they may also have influenced pre-existing neoformed clay minerals in the mudstone. Geochemical modelling, using data from CheMin, ChemCam and APXS suggests that brackish, near-neutral pH fluids existed at moderate temperatures in a shallow near-surface environment. Analyses of elemental composition and mineralogy in Gale Crater are consistent with alteration of basaltic material with Fe and Mg mobility and the possible presence of nanophase Fe-oxide or Fe-Mg phyllosilicate cements. Rocks at Pahrump show evidence for greater chemical alteration; some phyllosilicates may have been removed or altered further by circulating fluids. As Curiosity is now exploring the base of Mt. Sharp, more Fe-Mg-bearing phyllosilicates are expected to be found based on orbital observations.