MINERAL SPECTROSCOPY REVEALS THE EVOLUTION OF PLANETARY HABITABILITY ON MARS: A CASE STUDY OF SOUTHERN HIGHLANDS SULFATES AND CHLORIDES

The processes controlling Mars’ evolution and changes in habitability over billions of years can be deciphered from its mineralogy. Water-rock reactions in various environmental settings generate characteristic mineral assemblages, crucial to determining pH, redox potential, salinity, temperature, pressure, and other geochemical attributes of past waters. In this Gilbert award session, I am pleased to highlight Dr. Janice Bishop’s fundamental contributions on the spectroscopic signatures of the various forms of OH/H2O in minerals and the spectroscopic signatures of rocks from terrestrial environments that we now know to be chemically analogous to Mars. Dr. Bishop’s work has been essential for interpretation of orbiting infrared spectroscopic data from Mars, including for our recent Leask et al. (submitted) and Leask & Ehlmann (submitted) studies, because it has revealed how geological processes are recorded at the rock-level.

A regional study of Terra Sirenum, one of the few locations on Mars where nearly all classes of secondary minerals are found in regional-scale spatial proximity, reveals (1) ancient Fe/Mg smectites and carbonates in crater peaks and walls; (2) small amounts of Al-rich clays associated with sulfates in the western part of the study area (Eridania) and thick, finely layered kaolinite-bearing units throughout the northeastern Terra Sirenum that we interpret as a felsic ash unit, providing an Al source for the numerous alunite detections found in conjunction with this unit; (3) two post-dating chemically and spatially distinct sedimentary deposits. Sulfates are typically adjacent to or underneath volcanic morphologies, and almost always in deep crater basins, likely formed by upwelling groundwaters with magmatic contributions of S and acidity. Chloride deposits are related to saline chains of lakes that are present at most elevations throughout the region. Age dating to obtain oldest age bounds of 3.4-2.3 Ga reveals these are some of the youngest large-scale mineral deposits on Mars with evidence of flowing surface water extending into at least the early Amazonian.