Dark-Toned Halite-Enriched Veins Above the Marker Band Record a Drying Environment in Gale Crater

The Martian surface preserves evidence of a global climate transition from wetter to drier 29 conditions, but the nature of the fluids involved in this evolution remains poorly constrained. In 30 Gale crater, the clay-sulfate transition and presence of evaporite mineral assemblages can 31 provide insights into the properties of these fluids and the timing of environmental change. 32 While traversing though the Chenapau member of the sulfate-bearing unit in Gale crater, the 33 Curiosity rover encountered a set of dark-toned veins enriched in Na and Cl, suggestive of halite. 34 However, previous halite detections in Gale crater have been limited to occurrences along the 35 edges of Ca-sulfate veins or nodules, suggesting a unique origin for this set of veins. Here, we 36 hypothesize that these veins formed through the infiltration of saline fluids along hydraulically 37 induced fractures. These fluids permeated into the host rock beyond the primary fractures, 38 precipitating halite and cementing the fractures. Using Mastcam and ChemCam spectra, we 39 found that the veins display a downturn in the near-infrared wavelengths, consistent with the 40 presence of ferrous iron. Furthermore, textural analysis of the veins reveals host rock material 41 preserved within the veins. ChemCam laser-induced breakdown spectroscopy (LIBS) 42 observations also support the presence of a minor Fe component in the veins and halite 43 concentrated along the center of the fractures. Our results demonstrate that these veins represent 44 a distinct class of diagenetic features in Curiosity’s mission that record an important transition in 45 near-surface fluid chemistry consistent with a transition to a drier environment.