GLOBAL-SCALE SEMI-AUTOMATED MAPPING OF HYDROTHERMAL AND LOW-GRADE METAMORPHIC MINERALS ON MARS

Since the late 2000s, high resolution optical imagery and shortwave infrared spectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) have been collected from orbit and interpreted to identify widespread occurrences of potential hydrothermal and metamorphic activity. Hydrothermal and low-grade metamorphic minerals are sensitive recorders of geochemical and thermal conditions and thus provide valuable evidence for environmental conditions and astrobiological potential during formation. Thus, understanding Mars as a system and its potential for harboring life throughout its formation and evolution requires having a clear understanding of the distribution of these phases throughout exposed Martian stratigraphy. Despite relevant minerals having been identified in several regional and site-specific studies, at present, a full synthesis of locations of hydrothermal and low-grade metamorphic mineral occurrences does not exist.

We will present a global, semi-automated mapping effort focused on identifying and differentiating key hydrothermal and low-grade metamorphic phases which define boundaries in basaltic metamorphic facies, or better constrain pH and pCO₂ conditions during formation. The mapping effort utilizes a new processing pipeline focused on targeted, high spatial resolution CRISM images. Through newly developed automatic spectral-ratioing methods, mineral-class specific spectral parameters, and explicit treatment of systematic and stochastic noise, we have successfully differentiated and automatically spatially mapped phases which have previously been mapped as poorly constrained mixtures. This includes the separation of iron-rich chlorite, prehnite, and epidote from both each other, and the much more common iron-magnesium smectites which make up most of the known aqueous alteration on Mars.

We are currently developing methods to map occurrences of analcime, iron chlorite/pumpellyite, epidote/clinozoisite, prehnite, serpentine, actinolite, and talc as well as several other carbonates, phyllosilicates, and zeolites. We will show both positive and negative results from a wide range of images including locations such as Nili Fossae, Terra Sirenum, Argyre Basin, Vallis Marineris, and Jezero Crater.