^1,2Yang Liu,¹Timothy D. Glotch,^1,3Noel A. Scudder,^1,4Meredith L. Kraner,¹Thomas Condus,⁵Raymond E. Arvidson,⁵Edward A. Guinness,⁶Michael J. Wolff,⁷Michael D. Smith
Journal of Geophysical Research Planets Link to Article [DOI: 10.1002/2016JE005028]
¹Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
²Southwest Research Institute, San Antonio, TX, USA
³Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
⁴Nevada Geodetic Laboratory, University of Nevada Reno, Reno, NV, USA
⁵Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri, USA
⁶Space Science Institute, Boulder, CO, USA
⁷NASA Goddard Spaceflight Center, Greenbelt, MD, USA
Published by arrangement with John Wiley & Sons

We present spectral unmixing results over the southwest Melas Chasma region, where a variety of hydrated minerals were identified. We use the DISORT radiative transfer model to simultaneously model Mars atmospheric gases, aerosols, and surface scattering and retrieve the single scattering albedos (SSAs) modeled by the Hapke bidirectional scattering function from CRISM data. We employ a spectral unmixing algorithm to quantitatively analyze the mineral abundances by modeling the atmospherically corrected CRISM SSAs using a non-negative least squares (NNLS) linear deconvolution algorithm. To build the spectral library used for spectral unmixing, we use the factor analysis and target transformation (FATT) technique to recover spectral end-members within the CRISM scenes. We investigate several distinct geologic units, including an interbedded poly- and monohydrated sulfate unit (interbedded unit 1) and an interbedded phyllosilicate-sulfate unit (interbedded unit 2). Our spectral unmixing results indicate that, polyhydrated sulfates in the interbedded unit 1 have a much lower abundance (~10%) than that of the surrounding unit (~20%) and thus may have been partially dehydrated into kieserite to form the interbedded strata, supporting a two-staged precipitation-dehydration formation hypothesis. In the interbedded unit 2 phyllosilicates have an abundance of ~40% and are interbedded with ~20% sulfates. The results, in combination with thermodynamic calculations performed previously, suggest that the interbedded phyllosilicates and sulfates likely formed through coupled basalt weathering and evaporation. The methodology developed in this study provides a powerful tool to derive the mineral abundances, aiming to better constrain the formation processes of minerals and past aqueous environment on Mars.