MINERALIZED FRACTURES IN THE SICCAR POINT GROUP, GALE CRATER, MARS

Development of mineralized fracture fills is critical to understanding the persistence of fluid flow in the Martian subsurface. Within Gale crater, Mars, the Curiosity rover has documented evidence of both surficial fluids in the form of lacustrine mudstone deposits (Grotzinger et al., 2014, 2015), and subsurface fluids in the form of mineralized fractures (Nachon et al., 2014). Here we use HiRISE images to map mineralized fractures within portions of the Siccar Point group (cf. mound-skirting unit of Anderson and Bell, 2010) of Gale Crater to explore the nature and timing of fluid flow events.

The Siccar Point Group (SPg) contains an erosionally resistant, geologic layer that is best exposed in the northwest region of Gale Crater, between the low-albedo sands and the primary strata of Mount Sharp. The SPg is marked by relatively low albedo (depending on extent of dust cover) and high thermal inertia, and shows a cross-cutting relationships with underlying strata of the Murray formation, lower Mount Sharp (Kah et al. 2013). More detailed examination shows that the SPg is further characterized by three distinct stratigraphic intervals including a lower, fractured unit; a middle, ridged unit; and an upper, heavily cratered unit. Potential mineralized fractures within the MSU occur as linear, positive relief features that form polygonal networks that average up to 10m in diameter and do not penetrate beyond the lower portion of the SPg. Although there is some variation in the shape of individual polygons, which affects intersection angles of mineralized fractures, the size and density of fracture networks are surprisingly uniform across the mapped extent of the SPg. Together, these observations suggest (1) that subsurface fluids were active and potentially widespread in Gale crater after deposition and erosion of Mount Sharp; (2) that this portion of the SPg was sufficiently lithified to form an effective barrier to migration of subsurface fluids at the time of fracturing; and (3) was regionally homogeneous, resulting in uniform pattern of fracturing throughout the mapped region.