Garden City Vein Complex, Gale Crater, Mars: Implications for Late Diagenetic Fluid Flow

Abstract:

Calcium sulfate filled fractures are observed in nearly all stratigraphic units encountered by the Mars Science Laboratory (MSL) Curiosity rover. The mm-scale of veins, however, provides little evidence for emplacement style. From sols 924-949, Curiosity observed a vein rich outcrop called Garden City, which shows variation in both thickness and complexity of veins. Extensive Mastcam and MAHLI imaging was conducted across the outcrop to provide textural detail that can be related to emplacement mechanisms. Additionally, Curiosity collected geochemical data on 17 ChemCam targets and 7 APXS targets, shedding light on the composition and variety of potential vein fluids.

The Garden City vein system records (1) the presence of distinct dark-toned and light-toned (calcium sulfate) mineralization, and (2) the presence of laminated, epitaxial, and brecciated fabrics that suggest multiple emplacement modes. Dark-toned mineralization is observed as erosionally resistant ridges predominantly along fracture walls. Although erosional resistance may reflect the permeability of host rock to fracture-borne fluids, at Garden City, laminated textures suggest that at least some mineralization may have occurred as fracture-fill. Light-toned mineralization often bisects dark-toned material, indicating re-use of fluid pathways. Light-toned veinlets permeate fracture walls, and the largest veins entrain host rock and dark-toned material within calcium sulfate matrix. Such brecciation indicates high forces associated with fluid expulsion. Elsewhere, linear patterns occur broadly perpendicular to fracture walls, and are interpreted to represent epitaxial crystal growth, suggesting lower flow rates and fluid flow pressures within the fracture system. Together these observations indicate multiple episodes of fluid flow in the Gale Crater system.