Investigations into fracture and vein systems in Gale crater, Mars

Rock fractures and veins are among the most common structural features in the Earth’s crust and provide information regarding the stress and deformation of a geologic succession. Assessment of fracture morphology and host rock properties can inform the conditions under which fracturing occurred. The chapters in this dissertation investigate fractures within Gale crater, Mars, to understand the nature and timing of post-depositional fluid events and the formation mechanisms driving fracture formation. Chapter 1 focuses on veins using the instruments of the Curiosity rover. Since 2012 Curiosity has been exploring sedimentary environments of Gale crater. Although veins have been observed since the early days of the mission, analysis of the Pahrump Hills site revealed an increase in the size, complexity, and range in composition of veins. Analysis of vein color, morphology, texture, and chemistry indicate at least three distinct events of post-depositional fluid flow. Observation of the relationships between veins and host rock, discrete mineral signatures, and mineral microtextures support hydrofracture as the primary formation mechanism. Chapter 2 focuses on observations of an extensive polygonal fracture network that is visible in orbital images. Relatively young strata in Gale crater contain a regionally extensive network of erosionally resistant polygonal ridges. Polygonal fractures exhibit relatively uniform size and shape, indicating uniform stress fields during formation. Intersection angles of polygons further indicate that fractures formed during repetitive contraction-expansion events that were later modified by diagenetic fluids. The considerable amount of time between fracture and cementation indicates a protracted history of fluid stability near the surface in Gale crater. Chapter 3 focuses on laboratory observation and analysis of Mars analog materials as a potential mechanism to better understand planetary surface materials. Information regarding mechanical rock properties are critical in informing the conditions required for fracture propagation. Utilizing a rock mechanics and engineering approach, analog rocks were selected to represent specific lithologies within Gale crater and experimentally tested to determine a variety of mechanical properties. Finite element models were then used to validate our understanding of, and ability to predict, rock properties.