Alm Ku 0099M 14701 DATA 1.Pdf
Total Page:16
File Type:pdf, Size:1020Kb
A Geological and Geophysical Investigation into the Evolution and Potential Exploitation of a Geothermal Resource at the Dixie Valley Training Range, Naval Air Station Fallon. BY Steve Allen Alm Jr. Submitted to the graduate degree program in Geology and the Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the degree of Master of Arts Advisory Committee ___________________________ J. Douglas Walker, Chair ___________________________ Michael H. Taylor ___________________________ George Tsoflias Date Defended: May 12, 2016 The Thesis Committee for Steve Allen Alm Jr certifies that this is the approved version of the following thesis: A Geological and Geophysical Investigation into the Evolution and Potential Exploitation of a Geothermal Resource at the Dixie Valley Training Range, Naval Air Station Fallon. ___________________________ J. Douglas Walker, Chair Date Approved: May 12, 2016 ii Abstract This study examines the geological and geophysical controls on geothermal fluid migration in two discrete geothermal systems in the highly-extended region of the central Great Basin. Active right-lateral oblique slip of the Fairview Peak-Louderback Mountain fault zone is transferred to similarly active normal dip-slip movement in the Dixie Valley-La Plata-Sand Springs fault zone across a buried accommodation structure in southern Dixie Valley and northern Fairview Valley, central Nevada. This accommodation zone coincides with the potentially exploitable geothermal systems known as Pirouette Mountain and Elevenmile Canyon. Similar to many other Great Basin geothermal systems the translation of geothermal fluids near to the surface is related to a structural configuration that promotes fluid flow through fracture permeability. An interpretation of this relationship as it applies to these geothermal systems was completed through a combination of detailed geologic mapping, Ar- geochronology, interpretation of geophysical data (aeromagnetics, gravity, and 2D-seismic), and structural analysis. The geophysical data was critical in understanding the geometry of structures not expressed at the surface. The structural analysis included an examination of available fault kinematic data that was resolved into paleostress orientations applied to an analysis of slip and dilation tendency for all mapped structures in the study area, including 3D planes generated from the 2D-sesimic interpretation. The results indicate that the Pirouette Mountain geothermal system is associated with a concealed oblique anticlinal accommodation zone that is bound by structures that are poorly oriented for slip and dilation and act as fluid barrier to southward fluid migration in basement stratigraphy. Fault intersections with the iii steeply dipping, dilation prone, northern continuation of the Louderback Mountains fault appear to be critical to geothermal fluid migration in the system. The results also characterize the Elevenmile Canyon geothermal system as a discrete upwelling of geothermal fluids along faults well oriented for slip and dilation that terminate into the Elevenmile Canyon caldera margin within a broader structural setting that can be characterized as a major stepover from the Sand Springs Range frontal fault system to the Stillwater Range frontal fault system. The results of this study are meant to inspire renewed interest in further exploration and delineation of geothermal systems in Southern Dixie Valley in addition to generating new discussion on the application of these methods and others in the best practice of identifying, exploring, and exploiting additional geothermal systems in the Great Basin and beyond iv Acknowledgements This work was financially supported by the US Navy Geothermal Program Office located at the Naval Air Weapons Station in China Lake, CA, a Graduate Research Fellowship from Chevron, and a Teaching assistantship from the University of Kansas. A special thanks to Dr. J. Douglas Walker, Dr. George Tsoflias, and Dr. Michael Taylor for sponsoring this work and always being available for discussion and inspiration. Thanks to Dr. Joseph Andrew for letting me sit next to you and ask questions to no end. Thanks to Satish Pullammanappallil at Optim llc for the acquisition and processing of the 2D-seismic data. Thanks to Andrew Tiedeman for helping me collect rock samples in the hot Nevada sun. Thanks to Jerry Whistler for providing GIS support. Thanks to Alan Morris at the Southwest Research Institute for developing and supporting 3D- Stress. And so much appreciation to all the people who contributed their expertise along the way: Dr. Andrew Sabin, Dr. Ross Black, Dr. Chris Henry, Dr. John Bell, Dr. John Caskey, Nick Hinz, Josh Feldman, Michael Lazaro, Kelly Blake, Jeff Shoffner, and Dr. Drew Siler. Thanks to all my friends and family for their endearing support and constant inspiration. v Dedication This work is dedicated to my family, without whom this project would not have been possible. Monica, my wife and partner in life, who has stood with me through this and all other challenges, who never questions our ability to achieve great things, and to whom I am forever grateful. To my daughter Victoria and my son Axel I hope that someday you find the great happiness I have found in you, you mean the world to me. vi Contents Introduction...................................................................................................................... 1 1.1 Background ............................................................................................................... 1 1.2 Purpose ................................................................................................................... 18 Geologic Setting ............................................................................................................. 20 2.1 Physiographic and Tectonic Setting ........................................................................ 20 2.2 Stratigraphic Framework ........................................................................................ 22 2.3 Structural Framework (Oligocene to present) ........................................................ 28 2.4 Neotectonics ........................................................................................................... 33 Methods ......................................................................................................................... 38 3.1 Detailed Geologic Mapping .................................................................................... 38 3.2 Fault Kinematic data ............................................................................................... 41 3.3 Ar/Ar Geochronology .............................................................................................. 42 3.4 2D-seismic acquisition and interpretation ............................................................. 46 3.5 Gravity and Magnetic Data ..................................................................................... 47 3.6 Structural Model ..................................................................................................... 54 Results ............................................................................................................................ 54 4.1 Seismic interpretation ............................................................................................. 54 vii 4.2 Geologic Mapping ................................................................................................... 71 4.3 Timing of deformation ............................................................................................ 75 4.4 Geometry of Faulting .............................................................................................. 78 4.5 Slip and Dilation Tendency Analysis ....................................................................... 82 Discussion ....................................................................................................................... 89 5.1 Timing of Deformation ............................................................................................ 89 5.2 3D Structural Model ................................................................................................ 89 5.3 Structural Controls on Geothermal Activity ........................................................... 97 Conclusions................................................................................................................... 102 6.1 Recommendations for further exploration: ........................................................ 105 References .................................................................................................................... 106 APPENDIX A: 40Ar/39Ar GEOCRONOLOGY ..................................................................... 114 APPENDIX B: 2D-SEICMIC IMAGES ............................................................................... 130 APPENDIX C: GEOLOGIC MAP OF LA PLATA CANYON AREA CHURCHILL COUNTY, NEVADA 142 viii LIST OF FIGURES Figure 1.1. Rate of deformation mapped from the second invariant of strain .............................. 3 Figure 1.2. Annotated model of a basic, conceptual geothermal system ...................................... 5 Figure 1.3. From Faulds et al. (2011). Four illustrations of favorable structural settings for geothermal systems. ............................................................................................................... 8 Figure 1.4. Distribution