Compositional and Mineralogical Diversity of Jezero Western Fan, Mars, Revealed by Elemental Observations

The NASA Mars 2020 Mission Perseverance rover has conducted a four-Martian-year scientific campaign in the Jezero western fan, a typical fluvial–deltaic–lacustrine system on Mars. Equipped with the Planetary Instrument for X-ray Lithochemistry (PIXL) and SuperCam, the rover has collected high-resolution elemental data from abraded rock outcrops, providing a detailed geochemical and mineralogical characterization of key stratigraphic units. This work presents a systematic analysis of these targets, revealing distinct geochemical trends. Rocks from the delta front, upper fan, and margin units are enriched in Mg and Fe (e.g., mafic to ultramafic lithologies) and are depleted in Si, Al, Na, and Ca. These units share comparable mineral parageneses and exhibit pervasive alteration textures, in contrast to the more limited alteration observed in crater floor targets. Despite this, we also discussed insights derived from elemental data: (1) Low to medium chemical index of alteration (CIA) and modified index of alteration (MIA) values indicate limited silicate weathering. (2) Localized enrichments in Cl and Br suggest episodic mobilization of brines. (3) The presence of high-silica phases near the margin unit further points to hydrothermal processes. These observations suggest that sedimentation and diagenesis in the Jezero western delta were shaped by a complex interplay of fluvial, lacustrine, and localized hydrothermal processes.