Olivine-Carbonate Mineralogy of the Jezero Crater Region

A well-preserved, ancient delta deposit, in combination with ample exposures of carbonate outcrops, makes Jezero Crater in Nili Fossae a compelling astrobiological site. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) observations to characterize the surface mineralogy of the crater and surrounding watershed. Previous studies have documented the occurrence of olivine and carbonates in the Nili Fossae region. We focus on correlations between these two well-studied lithologies in the Jezero crater watershed. We map the position and shape of the olivine 1 μm absorption band and find that carbonates are found in association with olivine which displays a 1 μm band shifted to long wavelengths. We then use Thermal Emission Imaging Spectrometer (THEMIS) coverage of Nili Fossae and perform tests to investigate whether the long wavelength shifted (redshifted) olivine signature is correlated with high thermal inertia outcrops. We find that there is no consistent correlation between thermal inertia and the unique olivine signature. We discuss a range of formation scenarios for the olivine and carbonate associations, including the possibility that these lithologies are products of serpentinization reactions on early Mars. These lithologies provide an opportunity for deepening our understanding of early Mars and, given their antiquity, may provide a framework to study the timing of valley networks and the thermal history of the Martian crust and interior from the early Noachian to today.
Plain Language Summary We used Martian orbital data from a hyperspectral instrument on the spacecraft Mars Reconnaissance Orbiter (MRO) to assess the minerals on the surface of Mars at the future landing site of the Mars2020 rover. We found correlations between the minerals olivine and carbonate which are of interest to planetary scientists due to often being associated with volcanic activity (olivine) and life (carbonates). We used spectra of these minerals to infer the likely composition and grain size range of the olivine unit, and we document our new approach. We use our curve fitting approach to identify for the first time a special group of olivine-bearing rocks at Nili Fossae that show the most extremely redshifted absorption bands, and we show herein that these special olivines are not spatially associated with carbonates or clay rocks.