Distribution and variation of plagioclase compositions on Mars

This study presents the first global compositional maps of plagioclase, the most abundant mineral in the Martian crust. Linear deconvolutions of spectra from the Thermal Emission Spectrometer (TES) allowed calculation of average plagioclase compositions for dust-free areas on Mars 60 of the equator (approximately 40% of the surface for this range of latitudes). As a whole, surface type 1 and 2 terrains are virtually identical with respect to their average plagioclase compositions, ∼An₆₀. The majority of TES observations were modeled as labradorite and bytownite (between An₅₀ and An₉₀), while fewer observations were modeled with other plagioclase compositions that did not correlate with specific geologic terrains. The lack of diversity in average plagioclase compositions across multiple geologic units may represent an upper Martian crust with minimal variation in plagioclase compositions. Alternatively, aeolian, fluvial, and/or impact activity may have redistributed heterogeneous crustal material forming a relatively homogeneous, global surface layer.