Global-Scale Semi-Automated Mapping of Hydrothermal and Low-Grade Metamorphic Minerals on Mars

Since the late 2000s, high resolution, shortwave infrared spectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), collected from orbit, have been interpreted to identify occurrences of diagenesis and hydrothermal and metamorphic activity. Understanding Mars as a system, the nature of its changing habitats, and its potential for harboring life throughout its formation and evolution requires having a clear understanding of the distribution of hydrothermal and low-grade metamorphic mineral 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 that define the temperatures and geochemistries of waters altering basaltic facies or better constrain pH and pCO₂ conditions during formation. The mapping effort focuses on targeted, high spatial resolution CRISM images and utilizes a new processing pipeline which employs 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, including the separation of magnesium-rich and iron-rich chlorite, prehnite, and epidote/clinozoisite from each other, and the much more common iron-magnesium smectites that make up most of the known aqueous alteration on Mars. We have evaluated differentiating chlorite-smectite mixed layer clays from smectites and chlorites. We are currently further developing methods to map occurrences of analcime, serpentine, actinolite, talc, and carbonates. 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 as we work toward creation of a global map of hydrothermal and metamorphic facies on Mars.