Deconvolution of distinct lithology chemistry through oversampling with the Mars Science Laboratory Alpha Particle X‐Ray Spectrometer

Abstract

aThe Alpha Particle X-Ray Spectrometer (APXS) determines the chemical composition of Martian rocks and soils on-board both active National Aeronautics and Space Administration (NASA) rovers using X-ray emission spectroscopy through complementary particle-induced X-ray emission (PIXE) and X-ray fluorescence (XRF) excitation methods. A single APXS spectrum represents the sum of the signals from within the instrument's field of view (FOV). In the past, features smaller than the FOV have been investigated through repeated measurements with stepwise lateral offsets. These lateral offsets allow for empirically extracting, through elemental correlations, distinct compositions of different features. Here, we present a novel analytical method for deconvolving the endmember chemistry of visually distinct components through oversampling and the integrated analysis of the elemental data and supporting images. We discuss specifically the method's application to three targets investigated by the Mars Science Laboratory rover Curiosity during its traverse, as well as the added information that can be gained from this method in the future.

Zinc and germanium in the sedimentary rocks of Gale Crater on Mars indicate hydrothermal enrichment followed by diagenetic fractionation

“…Widespread white sulfate veins and concretions (Mavor class) have been investigated throughout most units by the APXS in Gale [ McLennan et al ., ; Nachon et al ., ; VanBommel et al ., , ]. The veins crosscut bedding planes and thus represent late diagenetic fluids.…”

“…The veins crosscut bedding planes and thus represent late diagenetic fluids. Rasters over these features show that they are Ca and S rich, with 1:1 stoichiometric Ca‐S variation consistent with pure Ca sulfate [ VanBommel et al ., ]. Vein targets are typically small with respect to the ~1.5 cm APXS field of view (some veins are thicker but were not measured by the APXS).…”

“…A deconvolution of the five point raster on the target Sayunei (sol 165) using the method of VanBommel et al . [] yields effectively zero Zn and Ge in the pure Ca sulfate veins. All other white veins similarly do not contain evidence of trace element enrichments (Ni, Zn, and Ge).…”

“…Because the two phases were small with respect to the APXS field of view (~1.5 cm), an APXS and MAHLI raster of seven spots was conducted to enable deconvolution of the compositions using the method of VanBommel et al . []. In the raster, the white phase exhibits a 1:1 molar variation of Ca and S, consistent with the nearly pure Ca sulfates common in veins in Gale.…”

“…An analysis of rasters over concretions by VanBommel et al . [] demonstrated 1:1 stoichiometric Mg‐S variation, indicating Mg sulfates. Unlike the Ca sulfates, these concretions are not pure; they are a mixture of ~10% Ni, Mg sulfate, and the host bedrock.…”