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Regional Variations in Structural Controls on Geothermal Systems in the Great Basin

Structural settings of geothermal systems in the Great Basin are known (e.g., Faulds et al. 2004, 2006, 2011), but regional variations in structural controls have not been systematically studied. There are several types of Quaternary faults in the Great Basin, including major north-striking normal fault systems along the east and west boundaries of the Basin and Range province, NNE-striking normal faults throughout the Basin and Range province, and several structural domains of strike-slip faults in the Walker Lane (e.g., Stewart, 1988; Faulds and Henry, 2008). These Quaternary faults are superimposed on different ages and styles of pre-existing rocks and structures, both of which may also influence the structural control of geothermal systems. Analysis of data from four geologically distinct areas in the Great Basin reveals systematic differences in ages and orientations of faults. The dominant structural controls on geothermal systems differ between study areas, suggesting guidelines for geothermal exploration. Faults related to geothermal systems in southeastern Oregon preferentially strike northwest (an anomaly true only of this study area); step-overs and fault intersections are the most common structural controls. The Basin and Range of central Nevada has the strongest preferred fault orientation, NNE, and structural controls (step-overs, fault terminations and accommodation zones, in that order) are consistent with a dominant set of sub-parallel faults. Faults related to geothermal systems in western Utah have a N to NE preferred orientation, but there are subsidiary faults at a high angle to these. Fault intersections are the most common structural control in Utah, and are more prevalent here than in any of the other study areas; however, step-overs, fault terminations and accommodation zones are also relatively well represented. The Walker Lane of western Nevada exhibits the most diverse range of fault orientations and of structural controls on geothermal systems. Pull-aparts are the most common, and are unique to this study area; fault intersections and fault terminations are second in abundance. In summary, these preliminary results suggest that an improved understanding of regional variations in structural control will lead to region-specific exploration strategies for geothermal systems.