MODELING AN ACTIVE HYDROTHERMAL SYSTEM IN A VOLCANIC, BASEMENT RIDGE STEP-OVER: FIRST STEPS IN A MULTI-DISCIPLINE APPROACH, SOUTHERN DIXIE VALLEY, NEVADA

This study uses a new 2D seismic reflection dataset to image a buried structural transition zone that links active right-lateral oblique slip of the Fairview Peak-Louderback Mountain fault zone to active normal dip-slip movement in the Dixie Valley-La Plata-Sand Springs Fault zone of Central Nevada. The reflection survey was designed with long line lengths for greater offsets and was processed using a first arrival velocity optimization and prestack depth migration for imaging steeply dipping, complex structures. In a region with sparse subsurface well control this work provides new insight on the local fault geometry and kinematics. As a direct analog to the subsurface data, we use new mapping of an adjacent tilted Miocene basin, eruptive ages of Miocene andesites, and other unpublished geophysical data (gravity, magnetic, and magnetotelluric data) to construct a geologic history model. We use this model to propose a fault-controlled mechanism for the translation of hydrothermal fluids near to the surface. Aspects of the conceptual model derive, in part, from previous studies of the geology of Dixie Valley and surrounding ranges. Our conceptual model presents a framework for the period of post-caldera collapse (from ca. 25 to 21Ma) to present tectonic, volcanic, and stratigraphic evolution of internally draining extensional basins and the active structural transition zone that links the modern basins. Combined with previous neotectonic studies and geologic mapping, our observations and interpretations demonstrate a complex origin for the formation, propagation, linkage, and termination of faults, minor folding, and vertical axis rotation that accommodates extension and minor amounts of transtension. The model honors the details of relevant studies for the subsurface fault geometries in the structural transition zone. In this zone, a basement ridge is actively being breached and deformed through a variety of tectonic processes. These processes create favorable conditions for the circulation of hydrothermal fluids near to the surface potentially exploitable for geothermal production.