2011 Annual Science Report
Arizona State University Reporting | SEP 2010 – AUG 2011
Habitability of Water-Rich Environments, Task 4: Evaluate the Habitability of Ancient Aqueous Solutions on Mars
Field, laboratory, and numerical modeling studies have been performed to understand the chemical processes and mineralogy relevant to low- and high-temperature aqueous alteration processes on ancient Mars. Results show that significant amounts of aqueous solutions could have been involved in the formation of secondary minerals (silica, clays) observed on Mars, with important implications for its past habitability.
As a context for evaluating the recent discovery of high silica deposits at Home Plate, Columbia Hills, Farmer’s group documented systematic changes in the mineralogy and microtexture of modern siliceous hot spring deposits, along gradients in temperature, pH and flow velocity. Study sites included active acidic (pH 2-5) and alkaline-neutral (pH 7-10) springs in Yellowstone National Park (YNP). In the field, we measured pH, temperature and flow velocity. In the lab, mineralogy was determined by X-ray powder diffraction (XRPD), thermal infrared spectroscopy (TIR); sinter microtextures were determined by thin section petrography. We used clay separation and glycolization methods combined with high resolution XRPD, to identify phyllosilicates. Results showed that early diagenetic ordering of silica phases (opal-A to cristobalite and quartz) was more rapid in acidic springs and that kaolin family minerals occurred over the entire pH range. We observed systematic trends in the temperature distribution of clays, with: 1) Dickite being abundant in high temperature (near-vent) microfacies, 2) kaolinite dominating mid-temperature outflow channels, slope and upper distal apron microfacies, and 3) halloysite being restricted to lower distal apron-marsh microfacies transitions.
A stratigraphic sequence of clay minerals have been reported in martian Mawrth Vallis region based on the orbital infrared spectroscopy. Drs. Zolotov and Mironenko used numerical models to explore a formation of these rocks through alteration of a basaltic material by a downward percolation of acid fluids. The most advanced models consider kinetics of mineral dissolution. All models closely reproduce the observed silica-kaolinite-montmorillonite-smectite sequence. These models also lead to evaluation of temporal evolution of pH (neutralization) and chemical composition of groundwater. The results imply a large-scale aqueous alteration of martian rocks by acidic fluids and a development of thick weathering crusts with contrast pH and redox environments. Some of these weathering crusts could have been habitable.