UNDERSTANDING FRACTURE FORMATION CONDITIONS IN GALE CRATER, MARS

Hydrofracture veins are important indicators of post-depositional fluid flow within a stratigraphic package. Vein chemistry can elucidate diagenetic fluid composition, and vein behavior can provide constraints on the conditions under which they formed. Conditions of formation (burial depth, fluid pressure) depend strongly on the intrinsic material properties of the host rock, such as rock strength, Young’s modulus, grain size, permeability, layer thickness, and potential heterogeneities. Here we utilize a variety of physical parameters and computational modeling to shed light on the formation of specific vein-host rock relationships in the basal Murray formation, Gale crater, Mars. Exploring the development of these vein networks will allow for a broader understanding of the overall burial and exhumation history of the Murray formation.

Veins have been consistent features of the rocks observed by NASA’s Curiosity rover in Gale crater, Mars. The Pahrump Hills member of the Murray formation represents the lowermost unit of Mount Sharp and contains abundant multigenerational veins throughout the ~13 meters of stratigraphic section. High-resolution images and geochemical instruments onboard Curiosity allow us to resolve the crystal growth mode and chemistry of vein-forming fluids, yet the mechanics of fracture formation are poorly understood. At Pahrump Hills, we focus first on two distinct vein-host rock relationships: (1) vein aperture (thickness) increasing up-section as veins approach the Salsberry Peak capping unit, and (2) veins penetrating the boundary between the Murray mudstone and the overlying Salsberry Peak caprock.

To simulate the formation of these veins at Pahrump Hills, we will utilize a two-step approach. First, analog samples were collected to simulate the Pahrump Hills mudstone and capping sandstone lithologies; rock strength and fracture properties will be derived from mechanical testing methods. Second, we apply COMSOL Multiphysics modeling software to replicate vein behavior and propagation under various conditions.