EPS Colloquium: Jeff Berger

Using the APXS on the Rover Curiosity to Constrain Ancient Geochemical Conditions in Gale Crater on Mars

Since landing in Gale Crater in 2012, the Mars rover Curiosity has deployed the Alpha Particle X-ray Spectrometer (APXS) more than 715 times to determine the elemental composition of Martian rocks, soils, and sand. Curiosity's 20km traverse has been upward toward Mt. Sharp through a sequence of sedimentary beds that record the geochemical conditions of ancient Gale Crater when it may have contained one or more lakes. Discoveries include alkalic and potassic rocks, silica-rich alteration haloes, ubiquitous Ca-sulfate cross-cutting veins, localized phosphorus and manganese enrichments, and nickel-rich Mg-sulfate nodules. I will focus on the remarkable discovery of widespread zinc and germanium enrichments, both of which are tens to hundreds of times greater than expected for average silicate Mars. The enrichment of the two elements indicates hydrothermal deposits in the sediment source region were dispersed in siliciclastic sediment during transport into the crater. Subsequent disgenetic mobilization and fractionation of zinc and germanium is evident in veins that are further enriched, as well as in bedrock that is variably enriched and depleted in zinc. The distribution of the two elements is consistent with fluid interaction of pH<<7, indicating acidic diagenetic conditions.