GARDEN CITY: A COMPLEX VEIN SYSTEM OBSERVED BY THE CURIOSITY ROVER AT PAHRUMP HILLS, GALE CRATER, MARS

Over the last 1000+ sols, the Mars Science Laboratory (MSL) Curiosity rover has observed a variety of diagenetic features, including nodules, raised ridges, dendritic/lenticular crystals, and veins. Veins, or mineral-filled fractures, have been the most ubiquitous diagenetic feature present in Gale crater rocks, and have been described in almost all stratigraphic units encountered by MSL.

On sol 753, Curiosity entered the Pahrump Hills region, which represents the first outcrops associated with Lower Mount Sharp. Upon entering Pahrump, the nature of veins changed dramatically in both the number of generations, as well as their size, density, and complexity. We’ve observed a drastic change from the uniformly small, light-toned calcium sulfate veins seen at Yellowknife Bay and along Curiosity’s traverse to what appears to be multiple generations of vein material, each with distinct textural and chemical signatures. Curiosity spent ~20 sols observing the vein rich outcrop named Garden City. Extensive Mastcam and MAHLI imaging was conducted across the outcrop. Additionally, Curiosity collected geochemical data on 17 ChemCam targets and 7 APXS targets, shedding light on the composition and provenance of vein fluids at Garden City.

Veins at Garden City range from mm- to cm-scale and are dominated by light-toned mineral fill. Textures in these white veins vary over local distances and range from smooth and massive/homogeneous to pitted and rough. The largest veins are brecciated and in multiple locations entrain host rock and darker vein material within their matrix. At Garden City, grey-toned material is observed along fracture walls, and is commonly bisected by a later stage of calcium sulfate mineralization. An additional generation of dark-toned vein material occurs in the form of erosionally-resistant thin fins. These fins are oriented in 3-dimensions and are commonly observed in float. These three distinct vein generations (light-toned/white, dark-toned/grey, and thin fins) are interpreted to reflect separate diagenetic fluid events, and have implications in constraining the duration of liquid water and potential habitability on Mars.