Implications Of Thrust And Detachment Faulting For The Structural Geology Of The Thermo Hot Springs Kgra Utah

This 23 page report is an initial investigation into the role that low-angle faulting may play in the formation of the Thermo Hot Springs Known Geothermal Area (KGRA), within the Sevier geothermal anomaly of southwestern Utah. The stratigraphy and structures exposed in the southern mineral mountains are used as an analog for studying the subsurface stratigraphy and the detachment fault within the Thermo Hot Springs KGRA.

Geologists have long grappled with understanding the mechanical origins of rock deformation. Stress regimes control the nucleation, growth and reactivation of faults and fractures; induce seismic activity; affect the transport of magma; and modulate structural permeability, thereby influencing the redistribution of hydrothermal and hydrocarbon fluids. Experimentalists endeavour to recreate deformation structures observed in nature under controlled stress conditions. Earth scientists studying earthquakes will attempt to monitor or deduce stress changes in the Earth as it actively deforms. All are building upon the pioneering research and concepts of Ernest Masson Anderson, dating back to the start of the twentieth century. This volume celebrates Anderson's legacy, with 14 original research papers that examine faulting and seismic hazard; structural inheritance; the role of local and regional stress fields; low angle faults and the role of pore fluids; supplemented by reviews of Andersonian approaches and a reprint of his classic paper of 1905--

Past exploration in low- and moderate-temperature systems of the Great Basin shows that the relatively small area associated with fluid upflow and elevated temperatures is often difficult to detect by drilling widely spaced temperature-gradient holes or by other methods. By studying the Newcastle geothermal system, we hoped to develop a basic understanding of the concealed hydrothemlal system as a tool for assessing other geothermal areas of the Great Basin. The emphasis of our work centered on determining (1) the distribution of subsurface heat and the movement of thermal fluid, (2) the location and geometry of bedrock structures that might control fluid movements, (3) the chemical character of the geothermal water, and (4) the geometry of the bedrock beneath the Escalante Desert. Field studies included: (1) drilling and monitoring temperatures in shallow themlal-gradient boreholes, (2) mapping geologic units and performing structural studies in the adjacent mountains, (3) conducting detailed gravity surveys, (4) conducting electrical resistivity and self-potential (SP) surveys, (5) collecting water samples for detennining major ions and light stable isotope analyses, and (6) mapping Quaternary units.

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This volume emphasizes the interaction of the Cordilleran thrust belt and Rocky Mountain foreland in studies of regional structural geology, geophysics, and sedimentology from west-central Montana to Arizona. The volume outlines how the nature of the Rocky mountain foreland and its deformation affect the geometry of the Cordilleran thrust belt. Many of the structural and geophysical studies reported in this volume also address the question of which structures - forland or thrust belt - developed first in a specific region and how early formed structures influenced later ones. Several chapters address the nature and style of foreland development.