Abstracts Earth and Environmental Sciences

Using Travertine-Cemented Fault Breccias to Understand theArchitecture and History of the Gunnison Fault Zone, eastern Basinand Range, Utah

by Joel Main

In the easternmost Basin and Range Province (BRP) in central Utah, the east-west trending Dry Canyon Graben formed perpendicular to the Gunnison Fault, which bounds the San Pitch Mountains horst block. A detailed investigation of the Rock Canyon fault zone, bordering the northern side of the Dry Canyon Graben, using field mapping, structural kinematic analysis, textural analysis of fault rocks, and radiogenic dating, has helped reveal the linkages between the graben and regional Basin and Range structure. Discovery of both dip-slip and oblique-slip lineations on faults in both the Rock Canyon fault zone and the south Dry Canyon fault zone indicate at least two phases of displacement occurred along boundary faults of the Dry Canyon Graben. Rock Canyon fault zone is likely connected to the Gunnison Fault, and Dry Canyon Graben may be part of a complex accommodation zone between three overlapping segments of the Gunnison Fault. A precise U-series date of 346.95 + 0.000098 Ka documents late Pleistocene fault activity. This suggests that the Dry Canyon Graben is a Basin and Range structure that formed concurrent with the Gunnison fault up until at least 347 Ka before present. Rock Canyon Fault zone is associated with multiple phases of fault rupture and sealing, indicated by polyphase cement-rich chaotic breccias, juxtaposed layers of slickenfibers, and composite zones of alternating breccias and veins along faults. The main faulting process is dilational faulting and collapse of subsurface fault voids as indicated by the dominance of cement-rich clast-supported chaotic breccias. Repeated rupture in the same zone is indicative of a fault weakening system. The crystal textures, travertine forms and layered carbonate deposits in the fault zone point to a near-surface environment for the deformation processes, where low lithostatic pressures permit open space to form and remain open. CO2-rich fluids ascended through fracture conduits along the Gunnison and Rock Canyon zone faults, likely derived from the Navajo Sandstone reservoir in the subsurface Sanpete-Sevier Valley anticline.Tufa deposits along the Gunnison Fault trace at Birch Canyon are reinterpreted as cascade deposits draping over and depositing in-situ over a pre-existing escarpment on a segment of the Gunnison Fault. If the Birch Canyon escarpment marks a fault scarp related to the Gunnison Fault, then the last displacement on that fault strand must be older than ~3200 years, the oldest dated tufa deposited in the linked upper and lower alluvial fans. Advisors/Committee Members: Wilson, Terry (Advisor).