Geologic mapping has revealed that the Myrick Spring-Eagle Crags area of the northern Mojave Dese... more Geologic mapping has revealed that the Myrick Spring-Eagle Crags area of the northern Mojave Desert is an intermediate to silicic volcanic center covering nearly 100 square km. A complex series of flows, tuffs, dikes, sills and flow breccias ranging in composition from calc-alkaline basalt to high slica rhyolite were extruded through at least three different types of NW- to W-trending
Exploration for utility-grade geothermal resources has mostly relied on identifying obvious surfa... more Exploration for utility-grade geothermal resources has mostly relied on identifying obvious surface manifestations of possible geothermal activity, e.g., locating and working near steaming ground or hot springs. This approach has lead to the development of over 130 resources worldwide, but geothermal exploration done in this manner is akin to locating hydrocarbon plays by searching for oil seeps. Confining exploration to areas with such features will clearly not discover a blind resource, that is, one that does not have surface expression. Blind resources, however, constitute the vast majority of hydrocarbon plays; this may be the case for geothermal resources as well. We propose a geothermal exploration strategy for finding blind systems that is based on an understanding of the geologic processes that transfer heat from the mantle to the upper crust and foster the conditions for hydrothermal circulation or enhanced geothermal exploration. The strategy employs a genetically based sc...
Journal of Volcanology and Geothermal Research, 2014
Extensional-type geothermal systems are complicated by the interrelation between footwall advecti... more Extensional-type geothermal systems are complicated by the interrelation between footwall advection during exhumation, and the subsequent redistribution of heat by migrating hydrothermal fluids in the hanging wall. The southern Wassuk Range (WR) hanging wall hosts a moderate-temperature, extensional-type geothermal system and is ideal for studying this duality by analyzing a suite of apatite (AHe) and zircon (ZHe) helium samples from the footwall and hanging wall of the southern WR. Young (~3-4 Ma) AHe ages along the WR front are concentrated along the SE corners of segmented footwall blocks, marking the location of focused Mio-Pliocene transtension, fracture dilation, and advection. Hydrothermally reset AHe ages along the footwall range front suggest that the Hawthorne geothermal system (85°-135°C) is long lived and has resided at a prominent structural boundary in the WR footwall marked by localized advection and range-front deformation. In contrast, the presence of both hydrothermally reset and non-reset AHe ages from a~1.4 km deep borehole in the hanging-wall basin probably indicate that the geothermal plumbing system and current manifestation as a thermal anomaly (~113°C) are juvenile and are controlled by the generation of newly formed faults in the hanging wall. AHe ages have been shown here to greatly enhance the focusing of regional-scale geothermal exploration efforts, and for the first time have been used to identify and estimate the temperature of unseen hydrothermal fluids.
Abstract This study assesses the relative importance of deeply circulating meteoric water and dir... more Abstract This study assesses the relative importance of deeply circulating meteoric water and direct mantle fluid inputs on near-surface 3 He/4 He anomalies reported at the Coso and Beowawe geothermal fields of the western United States. The depth of meteoric fluid ...
The Cudahy Camp Formation, located in the El Paso basin, east-central California, consists of a 3... more The Cudahy Camp Formation, located in the El Paso basin, east-central California, consists of a 350-m-thick volcanic and sedimentary sequence of early Miocene age. Previous investigators determined from paleocurrent indicators that the source for these rocks was to the south and southeast, but failed to suggest a specific location for that source. Restoration of 64 km of left slip on the Garlock fault places Cudahy Camp rocks north and northwest of the early Miocene Eagle Crags volcanic field. The unique geochemical nature of basalts found in both locations, coincident ages of volcanic rocks, identical clast content of volcanic tuffs, and identical stratigraphic sequence indicate that the source for the Cudahy Camp Formation was the Eagle Crags volcanic field. This is the first documented occurrence of Miocene rocks offset by the Garlock fault. Because the Cudahy Camp rocks and their sources appear to be offset by the full displacement on the Garlock fault, we conclude that movement on the Garlock started after earliest middle Miocene time. Further constraining initiation of movement on the Garlock fault adds significantly to fully understanding the evolution of the western North American plate boundary in the middle to late Cenozoic. Figure 1. Map of study area showing locations of key sites. AM-Avawatz Mountains, BM-Black Mountain, CV-Cantil Valley, DVFZ-Death Valley fault zone, MS-Myrick Spring, PKV-Pilot Knob Valley, SAFZ-San Andreas fault zone, SR-Slate Range, and SNF-Sierra Nevada front. Dot pattern denotes outcrops of Cudahy Camp formation. Brick pattern denotes outcrops of Paleozoic metamorphic rocks. Area marked with v pattern denotes outcrops of Eagle Crags volcanic rocks that are 17 Ma or older. Letters in circles indicate geologic markers that have been used to determine offset along Garlock fault zone. A-A' are from Smith et al. (1968), B-B' are from Smith (1962), and C-C' are from Smith and Ketner (1970).
ABSTRACT We are investigating the plumbing of the Coso geothermal system and the nearby Coso Hot ... more ABSTRACT We are investigating the plumbing of the Coso geothermal system and the nearby Coso Hot Springs using finite element models of single-phase, variable-density fluid flow, conductive-convective heat transfer, fluid-rock isotope exchange, and groundwater residence times. Using detailed seismic reflection data and geologic mapping, we constructed a regional cross-sectional model that extends laterally from the Sierra Nevada to Wildhorse Mesa, west of the Argus Range. The base of the model terminates at the brittle-ductile transition zone. A sensitivity study was conducted using the model to explore the interaction between local and mountain front recharge, the effects of spatial variations in heat flow, and the role of permeable faults in controlling fluid circulation patterns. The model is constrained by present day bore hole temperature surveys, fluid inclusion temperatures, fluid-rock isotopic alteration patterns, and hot spring activity. While the results are non-unique, the analysis permits us to bracket the likely ranges of permeabilities and heat flow conditions that are consistent with observed data. Our findings suggest that active faults and seismogenic zones in and around the Coso geothermal area have much higher permeability and reactive surface areas than far field crustal rocks such as those in the Sierra Nevada. The Coso Wash fault zone must extend down to brittle- ductile transition zone depths of about 4 km in order for modeled results to match the observed hot spring activity.
ABSTRACT The Coso Hot Springs are located almost two miles from the Coso geothermal field within ... more ABSTRACT The Coso Hot Springs are located almost two miles from the Coso geothermal field within the China Lake Naval Air Weapons Station, China Lake, California. The hot springs are about 16 m above the adjacent valley floor and because of their position are not believed to be in good hydrologic connection with the regional groundwater water table. Shortly after the onset of geothermal production in 1987, both water levels and temperatures within the South Pool of Coso Hot Springs increased. Although water levels appeared to be stable by 1989-1990, temperatures continued to rise until about 1993. We postulate that Coso hot springs are a condensate fed geothermal feature associated with vapor flux emanating from the Coso Wash Fault. We developed a suite of generic and site specific numerical models using FEHM to test whether these measured changes in the hot springs might be due to the removal of fluids associated with production from the Coso geothermal field. The idealized models were based on observed conditions including the locations of faults and geologic framework as well as temperature/pressure/production history of the geothermal field. The model results suggest that pressure declines associated with geothermal production led to an expanded steam cap which resulted in an enhanced vapor flux up the Coso Wash Fault zone.
Geologic mapping has revealed that the Myrick Spring-Eagle Crags area of the northern Mojave Dese... more Geologic mapping has revealed that the Myrick Spring-Eagle Crags area of the northern Mojave Desert is an intermediate to silicic volcanic center covering nearly 100 square km. A complex series of flows, tuffs, dikes, sills and flow breccias ranging in composition from calc-alkaline basalt to high slica rhyolite were extruded through at least three different types of NW- to W-trending
Exploration for utility-grade geothermal resources has mostly relied on identifying obvious surfa... more Exploration for utility-grade geothermal resources has mostly relied on identifying obvious surface manifestations of possible geothermal activity, e.g., locating and working near steaming ground or hot springs. This approach has lead to the development of over 130 resources worldwide, but geothermal exploration done in this manner is akin to locating hydrocarbon plays by searching for oil seeps. Confining exploration to areas with such features will clearly not discover a blind resource, that is, one that does not have surface expression. Blind resources, however, constitute the vast majority of hydrocarbon plays; this may be the case for geothermal resources as well. We propose a geothermal exploration strategy for finding blind systems that is based on an understanding of the geologic processes that transfer heat from the mantle to the upper crust and foster the conditions for hydrothermal circulation or enhanced geothermal exploration. The strategy employs a genetically based sc...
Journal of Volcanology and Geothermal Research, 2014
Extensional-type geothermal systems are complicated by the interrelation between footwall advecti... more Extensional-type geothermal systems are complicated by the interrelation between footwall advection during exhumation, and the subsequent redistribution of heat by migrating hydrothermal fluids in the hanging wall. The southern Wassuk Range (WR) hanging wall hosts a moderate-temperature, extensional-type geothermal system and is ideal for studying this duality by analyzing a suite of apatite (AHe) and zircon (ZHe) helium samples from the footwall and hanging wall of the southern WR. Young (~3-4 Ma) AHe ages along the WR front are concentrated along the SE corners of segmented footwall blocks, marking the location of focused Mio-Pliocene transtension, fracture dilation, and advection. Hydrothermally reset AHe ages along the footwall range front suggest that the Hawthorne geothermal system (85°-135°C) is long lived and has resided at a prominent structural boundary in the WR footwall marked by localized advection and range-front deformation. In contrast, the presence of both hydrothermally reset and non-reset AHe ages from a~1.4 km deep borehole in the hanging-wall basin probably indicate that the geothermal plumbing system and current manifestation as a thermal anomaly (~113°C) are juvenile and are controlled by the generation of newly formed faults in the hanging wall. AHe ages have been shown here to greatly enhance the focusing of regional-scale geothermal exploration efforts, and for the first time have been used to identify and estimate the temperature of unseen hydrothermal fluids.
Abstract This study assesses the relative importance of deeply circulating meteoric water and dir... more Abstract This study assesses the relative importance of deeply circulating meteoric water and direct mantle fluid inputs on near-surface 3 He/4 He anomalies reported at the Coso and Beowawe geothermal fields of the western United States. The depth of meteoric fluid ...
The Cudahy Camp Formation, located in the El Paso basin, east-central California, consists of a 3... more The Cudahy Camp Formation, located in the El Paso basin, east-central California, consists of a 350-m-thick volcanic and sedimentary sequence of early Miocene age. Previous investigators determined from paleocurrent indicators that the source for these rocks was to the south and southeast, but failed to suggest a specific location for that source. Restoration of 64 km of left slip on the Garlock fault places Cudahy Camp rocks north and northwest of the early Miocene Eagle Crags volcanic field. The unique geochemical nature of basalts found in both locations, coincident ages of volcanic rocks, identical clast content of volcanic tuffs, and identical stratigraphic sequence indicate that the source for the Cudahy Camp Formation was the Eagle Crags volcanic field. This is the first documented occurrence of Miocene rocks offset by the Garlock fault. Because the Cudahy Camp rocks and their sources appear to be offset by the full displacement on the Garlock fault, we conclude that movement on the Garlock started after earliest middle Miocene time. Further constraining initiation of movement on the Garlock fault adds significantly to fully understanding the evolution of the western North American plate boundary in the middle to late Cenozoic. Figure 1. Map of study area showing locations of key sites. AM-Avawatz Mountains, BM-Black Mountain, CV-Cantil Valley, DVFZ-Death Valley fault zone, MS-Myrick Spring, PKV-Pilot Knob Valley, SAFZ-San Andreas fault zone, SR-Slate Range, and SNF-Sierra Nevada front. Dot pattern denotes outcrops of Cudahy Camp formation. Brick pattern denotes outcrops of Paleozoic metamorphic rocks. Area marked with v pattern denotes outcrops of Eagle Crags volcanic rocks that are 17 Ma or older. Letters in circles indicate geologic markers that have been used to determine offset along Garlock fault zone. A-A' are from Smith et al. (1968), B-B' are from Smith (1962), and C-C' are from Smith and Ketner (1970).
ABSTRACT We are investigating the plumbing of the Coso geothermal system and the nearby Coso Hot ... more ABSTRACT We are investigating the plumbing of the Coso geothermal system and the nearby Coso Hot Springs using finite element models of single-phase, variable-density fluid flow, conductive-convective heat transfer, fluid-rock isotope exchange, and groundwater residence times. Using detailed seismic reflection data and geologic mapping, we constructed a regional cross-sectional model that extends laterally from the Sierra Nevada to Wildhorse Mesa, west of the Argus Range. The base of the model terminates at the brittle-ductile transition zone. A sensitivity study was conducted using the model to explore the interaction between local and mountain front recharge, the effects of spatial variations in heat flow, and the role of permeable faults in controlling fluid circulation patterns. The model is constrained by present day bore hole temperature surveys, fluid inclusion temperatures, fluid-rock isotopic alteration patterns, and hot spring activity. While the results are non-unique, the analysis permits us to bracket the likely ranges of permeabilities and heat flow conditions that are consistent with observed data. Our findings suggest that active faults and seismogenic zones in and around the Coso geothermal area have much higher permeability and reactive surface areas than far field crustal rocks such as those in the Sierra Nevada. The Coso Wash fault zone must extend down to brittle- ductile transition zone depths of about 4 km in order for modeled results to match the observed hot spring activity.
ABSTRACT The Coso Hot Springs are located almost two miles from the Coso geothermal field within ... more ABSTRACT The Coso Hot Springs are located almost two miles from the Coso geothermal field within the China Lake Naval Air Weapons Station, China Lake, California. The hot springs are about 16 m above the adjacent valley floor and because of their position are not believed to be in good hydrologic connection with the regional groundwater water table. Shortly after the onset of geothermal production in 1987, both water levels and temperatures within the South Pool of Coso Hot Springs increased. Although water levels appeared to be stable by 1989-1990, temperatures continued to rise until about 1993. We postulate that Coso hot springs are a condensate fed geothermal feature associated with vapor flux emanating from the Coso Wash Fault. We developed a suite of generic and site specific numerical models using FEHM to test whether these measured changes in the hot springs might be due to the removal of fluids associated with production from the Coso geothermal field. The idealized models were based on observed conditions including the locations of faults and geologic framework as well as temperature/pressure/production history of the geothermal field. The model results suggest that pressure declines associated with geothermal production led to an expanded steam cap which resulted in an enhanced vapor flux up the Coso Wash Fault zone.
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