INVESTIGATING THE GEOMETRY OF THRUST STRUCTURES IN THE PRE-EXTENSIONAL GREAT BASIN

The Great Basin lies in a tectonically complex location within the North American Cordillera: it forms the hinterland of the east-directed Mesozoic Sevier thrust belt, the back arc of the Sierran magmatic arc, and it has undergone significant Cenozoic Basin and Range extension. It is arguably a key area in the tectonics of the Cordillera: Mesozoic crustal thickening reached a maximum in this region; it is likely that it formed a high plateau analogous to the present day Altiplano; and it served as a mediator between high velocity oceanic subduction on the western margin of the Cordillera and retro-arc thrusting at a rate nearly two orders of magnitude slower along the eastern margin. High magnitude, regionally pervasive Cenozoic extension has overprinted the Mesozoic contractional structures, which as a result are poorly understood. This project focuses on constraining the geometry and magnitude of these contractional structures. We use thermometry from Laser Raman spectroscopy of carbonaceous material (LRCM) to estimate the depths to which large thrust sheets were buried, as well as the locations, and potentially the displacements, of major thrust faults. LRCM allows for the determination of the maximum temperature to which a given package of rocks has been heated between ~50-650°C. This is useful for determining the maximum depth to which a thrust sheet could have been buried, and it can also be used as a tool for constraining fault location if the temperature difference across the fault is greater than the method’s uncertainty (~20°C). We will use low temperature thermochronology to check whether the temperatures derived from LRCM have been overprinted by heating associated with Tertiary magmatism. Significant sample collection and preliminary LRCM data have been conducted, and the early findings will allow for further focus onto key areas in the Great Basin.