A Subsurface 3D Model of Basin Geometry and Fault Architecture at the Dixie Meadows Geothermal Prospect Based On Potential Field Geophysical Data
Paul C. Schwering¹, Robert E. Karlin¹, Patricia H. Cashman¹,
Ashton N. McGill², and Wendy M. Calvin³
¹Department of Geological Sciences and Engineering, University of Nevada, Reno, NV, USA
²ARANZ Geo Limited, Christchurch, New Zealand
³Great Basin Center for Geothermal Energy, University of Nevada, Reno, NV, USA
The western Basin and Range province contains an abundance of geothermal systems that are structurally controlled; in many cases, the controlling faults have little or no surface expression (i.e., blind faults). 3D characterization of these faults is a crucial step in exploration and potential development of these resources. The Dixie Meadows geothermal prospect is located ~150 km east-northeast of Reno, Nevada, USA. It lies within an active, primarily north-northeast-trending, rangefront fault zone between the Stillwater Range to the west and Dixie Valley to the east. Geothermal surface expressions, consisting of advanced argillic alteration, fumaroles, and hot springs, are indicative of a potentially productive geothermal reservoir. Joint geophysical modeling of potential field data indicates that multiple normal faults of differing age and orientations, many of which are blind faults, are controlling geothermal fluid flow at depth.
Geological units exposed on the Stillwater Range footwall of the rangefront fault zone consist primarily of Oligocene ash-flow tuffs. The tuffs unconformably overlie magnetized Jurassic volcanic rocks that are tectonically intercalated with older Mesozoic sedimentary and metasedimentary basement. These units are down-dropped on the Dixie Valley hanging wall, and are covered by unconsolidated erosional basin fill.The relatively low density of the basin fill and relatively high magnetic susceptibility of the Jurassic volcanics are mappable with gravity and magnetic potential field techniques, respectively. This study comprises ~150 square kilometers of potential field data coverage from 80 aeromagnetic transects flown by the USGS in 2002, and from 516 gravity stations acquired in 2010 by Zonge Geosciences for Ormat Technologies. Reduced-to-pole (RTP) magnetic data reveal a distinct relative magnetic low, indicating an apparent discontinuity of the Jurassic volcanics. Complete Bouguer anomaly (CBA) gravity data, reduced to 2.35 g/cc, in the basin contain strongly linear horizontal gradients, suggesting that subsurface faults are present.
AAPG Search and Discovery Article #120140© 2014 AAPG Hedberg Conference 3D Structural Geologic Interpretation: Earth, Mind and Machine, June 23-27, 2013, Reno, Nevada