Characterizing Hydration Carrier Phases in Altered Rocks of Jezero Crater Fan and Floor Geologic Units with SHERLOC on Mars 2020

The Mars 2020 Perseverance rover has explored fluvio-lacustrine sedimentary rocks within Jezero crater. Prior work showed that igneous crater floor Séítah and Máaz formations have mafic mineralogy with alteration phases that indicate multiple episodes of aqueous alteration. In this work, we extend the analyses of hydration to targets in the Jezero western fan, using data from the SHERLOC Raman spectrometer. Spectral features, e.g., sulfate and hydration peak positions and shapes, vary within and across the crater floor and western fan. The proportion of targets with hydration associated with sulfates were approximately equal in the crater floor (3/8 targets) and the western fan (6/17 targets). All hydrated targets in the crater floor and upper fan showed bimodal hydration peaks at ~3200 and ~3400 cm-1. The sulfate SO4 symmetric stretch at ~1000 cm-1 coupled with a hydration peak at ~3400 cm-1 indicate that MgSO4 • nH2O (2< n <5) is a likely hydration carrier phase in all units, perhaps paired with low-hydration (n ≤ 1) amorphous Mg-sulfates, indicated by the ~3200 cm-1 peak. Mg-sulfates of lower hydration degree (n = 1-2) are present at higher counts in the fan, and hydrated targets in the fan front only had one peak at ~3400 cm-1. While anhydrite co-occurs with hydrated Mg-sulfates in the crater floor and fan front, hydrated Ca-sulfates are observed instead at the top of the upper fan. Variable cation composition and degree of hydration of sulfates of the crater floor and fan indicates changing fluid chemistries, and/or multiple events across time and space at Jezero crater.