THE TRANSITION FROM NEUTRAL TO ACIDIC ALTERATION AT MAWRTH VALLIS AS OBSERVED FROM THE MINERALOGICAL RECORD
The mineralogical record at Mawrth Vallis documents a region where water was present long-term and geochemical processes were active and changing over time. Acidic alteration of the Fe/Mg-smectite-rich rock appears to have taken place following formation of that unit and either prior to or coincident with deposition of jarosite, hydrated silica, montmorillonite and kaolinite. The patches of acid-altered smectite and jarosite are typically 100-500 meters across. Identification of these unique materials has benefitted from recent advances in processing of CRISM images as MTRDR files and in the creation of new spectral parameters. We have recently developed a method of overlaying 5 different geologic units identified using CRISM over newly generated HRSC stereo mosaics. This has enabled us to trace the stratigraphy of the acid alteration unit across broader areas and has revealed a similar geochemical history throughout the aqueous outcrops in the Mawrth Vallis region.