291-8 Crystal Chemistry of Igneous Minerals in Jezero Crater, Mars from the First 100 PIXL Scans of Abraded Rocks on the Mars 2020 Mission

Session: Mineralogy in the Solar System

Presenting Author:

Eleanor Moreland

Authors:

Moreland, Eleanor Louise¹, Siebach, Kirsten Leigh², Jones, Michael³, Treiman, Allan H.⁴

(1) Earth, Environmental, and Planetary Science, Rice University, Houston, TX, USA, (2) Earth, Environmental, and Planetary Science, Rice University, Houston, TX, , (3) Queensland University of Technology, Brisbane, Australia, (4) Lunar & Planetary Institute, Houston, TX, ,

Abstract:

The Perseverance rover has traversed a wide range and age of terrains during its exploration of Jezero crater, Mars. This includes relatively young cumulate lava flows, ancient Noahcian-aged rocks, crater rim impactites, altered and largely unaltered igneous terrains, and fluviodeltaic sedimentary rocks from conglomerates to mudstones. Deciphering the history of the complex geology in Jezero crater, Mars, requires an understanding of mineralogy, as minerals record conditions of surface and subsurface formation environments.

 

Perseverance does not have a dedicated instrument for determining silicate mineralogy, but it does obtain high-resolution ~120 micron spot size geochemistry with the Planetary Instrument for X-ray Lithochemistry (PIXL) instrument, an X-ray fluorescence spectrometer. Throughout the mission, Perseverance has abraded, or ground away, the surfaces of rocks along its traverse to expose fresh material for characterization. PIXL retrieves one to three geochemical maps, typically ~3 mm x ~5 mm, on each of these abraded rocks. Here, we focus on the first 100 scans PIXL retrieved of abraded rocks through 1855 sols (Mars days of the mission), comprising over 200,000 individual geochemical analyses.

 

We use a four-step procedure to identify coarse, crystalline, silicate mineral grain candidates. We then extract mineral chemistry to assess the igneous conditions of mineral formation and correlate mineral sources across the traverse. We focus primarily on mineral species in feldspar, olivine, and pyroxene groups. Our procedure includes: 1) use the Mineral Identification by Stoichiometry (MIST) algorithm to filter for stoichiometric mineral compositions, 2) propagate analytical uncertainty via Monte Carlo to assess confidence, 3) use K-nearest neighbors to isolate spatial clusters, 4) correlate PIXL diffraction to confirm crystalline material. We find that about one-third of the rocks abraded by Perseverance and scanned by PIXL have at least one coarse igneous mineral for which we can derive precise crystal chemistry. These crystal chemistries and their spatial distribution allow us to interpret differences in igneous formation conditions and shifts in mineral provenance along the traverse.

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