INTEGRATING CRISM AND TES DATA TO CONSTRAIN THE MODAL MINERALOGY OF HYDRATED MINERAL DEPOSITS ON MARS – A PAN-SPECTRAL APPROACH

Kashira crater (D=~60 km) in the Margaritifer Terra region of Mars has a volcanically resurfaced floor (VRF) and contains a ~480 km² light-toned mound deposit (LTM) that bears hydrous minerals. While the formation of the LTM is enigmatic, its size and composition present an excellent opportunity to quantify the modal mineralogy of this hydrated mineral deposit using visible to thermal infrared spectroscopy. We present analyses using a ‘pan-spectral’ approach integrating visible to near-infrared reflectance data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and thermal emissivity data from the Thermal Emission Spectrometer (TES).

CRISM observations of the LTM uniquely identify kaolinite, while observations of the VRF identify olivine and pyroxene. The LTM within Kashira crater is distinct from layered Al-phyllosilicate deposits elsewhere on Mars and is one of the largest surface exposures of kaolinite-bearing material, large enough to fully fill several TES pixels. To estimate mineral abundances within each unit, TES data from the LTM and VRF were linearly unmixed using standard methods and a starting endmember library of primary silicates (e.g. olivine, pyroxene) plus kaolinite. Linear unmixing of the LTM results in ~41±12% kaolinite, while the VRF lacks spectral contributions from kaolinite and requires primarily plagioclase, olivine and pyroxene (i.e. basalt).

In order to test the fidelity of these results, we ran an iterative unmixing algorithm using a base endmember library of primary silicates, plus a randomly selected group of alteration minerals (including kaolinite and smectite clay). Results from 10,000 trials show that kaolinite is modeled at >10% in 99.97% of trials for the LTM (mean abundance = ~25%, std. dev. = ~8%) indicating a robust identification, and ~13% of trials for the VRF, which we attribute to model error.

Using CRISM data to constrain the endmember library for TES linear unmixing results in an estimate of >~25% kaolinite for the LTM in Kashira crater, requiring a high degree of alteration at this site, potentially due to a large hydrothermal system. We plan to test this pan-spectral method in other areas on Mars with large exposures of alteration minerals (e.g. Nili Fossae, Mawrth Vallis) in an attempt to further understand the history of aqueous alteration on Mars.