Global Mineralogic and Petrologic Mapping of Mars: The Past, the Present, and the Future

Fifty years ago Mars was a point in the sky that we knew was red. Thirty years ago we suspected it had mafic minerals. Today we think of Mars as a real geologic place, with a remarkably complex history and a broad diversity of igneous, aqueous, impact, and alteration processes. The key to this explosion in our understanding has been the combination of global reconnaissance of the mineralogy and petrology of the surface, together with in situ exploration of a few critical sites. Global mineral mapping began with the Phobos mission, and has continued with visible and infrared spectrometers on Mars Global Surveyor, Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. These global data have provided the context for the igneous, sedimentary, and chemical alteration processes that have occurred. This mineralogic information has shown that Mars is fundamentally a volcanic planet dominated by basalt, but it exhibits a broad range of compositions that vary from ultra-mafic basalts to andesites, dacites, and granitoids. Low- and high-Ca pyroxenes, olivine, plagioclase feldspar and high-silica phases vary spatially, suggesting spatial/temporal differences in fractional crystallization, assimilation, and source region composition. Superimposed on this volcanic background are rare, but significant, deposits of sedimentary and chemical precipitate rocks containing sulfates, phyllosilicates, crystalline iron oxides, and chlorides. Carbonate minerals have been found, but as a minor component of the martian dust that likely formed through interaction with the martian atmosphere. Taken together, the global mapping has discovered a large, and still growing, suite of minerals, discovered a major early phase of phyllosilicate alteration, mapped widespread salt deposits, discovered ancient olivine-bearing rock layers that extend over 1,000's of km, placed bedrock compositional units into their geologic context, and played the major role in selecting future landing sites by creating a global context for interpreting martian geologic history.