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Structures controlling geothermal circulation identified through gravity and magnetic transects, Surprise Valley, California, Northwestern Great Basin
Abstract
Combined geological and geophysical investigations are used to characterize intra-basin and basin-bounding faults, constrain basin geometry, study fault interactions, and ultimately to identify areas favorable to hydrothermal flow in the geothermal system in Surprise Valley, California. We utilize high-resolution gravity and ground-magnetometer data collected along several detailed transects within Surprise Valley to identify intra-basin structures. Our data show two types of structures whose magnetic signatures differ markedly: N-S-trending normal faults and NW-SE-trending fracture zones that accommodate little offset. The geothermal system is concentrated at the intersections of these two contrasting structural trends, implying that the fracture system facilitating hydrothermal flow to hot springs in Surprise Valley is more complex than typically envisioned for Basin and Range extensional geothermal systems. Our results suggest that there are potentially many pathways for fluid flow, offering new targets for geothermal exploration.
... A ground magnetic survey totaling 300 line-km using Geometrics G858 and G859 cesium vapor magnetometers was conducted to identify subsurface faults and areas of hydrothermal alteration. Magnetic lows can be associated with geothermal activity due to the alteration of rocks by hydrothermal processes (e.g., Glen et al., 2008Glen et al., , 2018Orenstein et al., 2015;Schwering et al., 2012). Corrections were applied for variations in the local magnetic field . ...
This study assessed the potential for a high-temperature blind geothermal system in southeastern Gabbs Valley, an area with no previous geothermal exploration, by utilizing geothermal play fairway analysis. Gabbs Valley is a structurally complex, tectonically active basin occupying a transtensional displacement transfer zone. Multiple lines of evidence suggest the presence of a blind geothermal system, including collocated intersecting gravity gradients, magnetic-low, low-resistivity, 2 m temperature anomaly, and 130–140 °C geothermometers obtained from nearby agricultural wells. Six 150 m-deep temperature-gradient holes were drilled to target the geophysical and thermal anomalies. Two holes produced bottom-hole temperatures of 114.5 °C and 124.9 °C. Drilling results establish the discovery of a blind geothermal system. Power estimates based on resource conceptual models of the geothermal system suggest a median (P50) capacity of ∼16 MWe.
... Non-invasive magnetics methods are often appropriate for locating blind structures (e.g. Glen et al., 2008). During the last five decades, a variety of methods based on vertical and horizontal gradients of magnetic potential-field anomalies have been developed and implemented for the determination of geologic boundaries, such as lithological contacts and faults, hence these methods are also valuable for the exploration of geothermal resources (Nabighian, 1972(Nabighian, , 1974Keating and Pilkington, 1990;Ferreira et al., 2013;Mazzoldi et al., 2020). ...
In this study, three geophysical techniques
were used to identify, localize, and characterize
a partly blind fault in the Llano Grande
basin within the Agua Fría Graben. This
tectonic basin is located in the Los Azufres
Volcanic Complex, one of the major silicic
volcanic centers in the Trans-Mexican Volcanic
Belt. The 1 km wide Agua Fría graben
could be considered as an analogous of the
larger graben structures bounded by the
Morelia-Acambay Fault System. Since it is
filled by recent sediments, it represents a challenge
for the recognition and characterization
of active faults that lack clear surface expression.
Newly collected magnetic data led to
the identification of lineaments interpreted
as structural discontinuities. Ground penetrating
radar and seismic refraction surveys
were carried out across one of these magnetic
lineaments crossing the basin to characterize
the nature and geometry of the inferred
discontinuity. The ground penetrating radar
profiles allowed the identification of buried
deformational structures interpreted as the
northern segment of the Agua Fría fault. The
subsurface reflectors displaced 1 to 1.5 m by
the fault indicate that this structure is potentially
active. The opening of trenches based
on these results makes it possible to confirm
the interpretation of the geophysical profiles,
to discuss the precision of the data and to
validate their use for such studies. On seismic
refraction profiles, the deformation zones are
related to low P-wave velocity zones. These
geophysical studies demonstrate the potential
of such techniques to locate faults in the
subsurface, partially characterize the width
of the fault zone and the associated displacement
within the uppermost of the subsurface.
Our results may be applied to define ideal
sites for paleoseismic excavations which are
essential for the identification and description
of historical and prehistoric earthquakes,
and thus, for the characterization of the local
seismic hazard.
... Non-invasive potential methods -such as gravity and magnetics -are often appropriate for locating structures (e.g. Glen et al., 2008) and in the general characterization of an underground (geothermal) system, aiming to its exploitation (Pipan et al., 2010;Kipsang, 2015). During the last five decades, a variety of methods based on the use of vertical and horizontal gradients of potential-field anomalies have been developed and implemented for the determination of geologic boundaries, such as contacts and faults -hence also valuable for the exploration of geothermal resources (Nabighian, 1972(Nabighian, , 1974Keating and Pilkington, 1990;Ferreira et al., 2013). ...
Para el desarrollo de un campo geotérmico, el conocimiento de la distribución de fracturas, la hidrología y la evolución tectónica del sitio a través de la caracterización estructural del sistema natural es un requisito previo a la perforación de pozos exploratorios. Fallas y fracturas representan vías preferenciales por el flujo de fluidos en el subsuelo y pueden ser detectadas mediante investigaciones geológicas en la superficie y geofísicas en el subsuelo. Una anomalía magnética positiva y de forma sub-circular en planta se encuentra en el medio del lago Cuitzeo, México. A través de un levantamiento geomagnético dentro y alrededor del área que comprende la anomalía tratamos caracterizar el reservorio geotérmico que, al sur del lago, está notificado por manifestaciones hidrotermales. Utilizando filtros computacionales basados sobre el uso de operaciones con las derivadas de valores de campo a los datos magnéticos grabados, hemos puesto en luz algunas de las estructuras que influencian la circulación de los fluidos en el sistema geotermal. Nuestra atención se focalizó sobre fallas ~N-S and E-W, pertenecientes respectivamente a la tectónica Básin & Range (B&R) y a la del Cinturón Volcánico Mexicano (CVM). Según nuestra interpretación, la interacción de dos o mas estructuras de diferentes orígenes (B&R y CVM), además del entorno geodinámico específico (subducción de zona de fracturas), facilitó el surgimiento de cuerpos magmáticos básicos del profundo que, bloqueados por la capa argilosa de sedimentación lacustre del Cuitzeo, dieron lugar, enfriándose lentamente, al sistema geotermal y contribuyeron a la formación de la anomalía magnética.
doi: https://doi.org/10.22201/igeof.00167169p.2020.59.2.2084
... Non-invasive potential methods -such as gravity and magnetics -are often appropriate for locating structures (e.g. Glen et al., 2008) and in the general characterization of an underground (geothermal) system, aiming to its exploitation (Pipan et al., 2010;Kipsang, 2015). During the last five decades, a variety of methods based on the use of vertical and horizontal gradients of potential-field anomalies have been developed and implemented for the determination of geologic boundaries, such as contacts and faults -hence also valuable for the exploration of geothermal resources (Nabighian, 1972(Nabighian, , 1974Keating and Pilkington, 1990;Ferreira et al., 2013). ...
For the development of a geothermal field, the understanding of fracture distribution, hydrology and tectonic evolution of the site through structural characterization of the natural system is a prerequisite to the drilling of exploratory wells. In order to image the underground shape of approximately planar, relatively permeable, geologic features (fractured rock-volumes around fault planes) and to detect hot rock volumes, geologic and geophysical surveying is carried out. A strong positive magnetic anomaly, nearly circular in 2D, characterizes the middle of Cuitzéo lake, Michoacán, Mexico, apparently not related with a volcanic structure on the surface. It may instead be associated to the geothermal system in the area which yields at present hot springs at the southern shore of the lake, at boiling temperatures. In this study, we conducted a ground magnetic survey within and around Lake Cuitzeo with the aim of characterizing this anomaly, following one-kilometer-spaced survey-lines and covering an area of approximately 100 km2. To enhance interpretability, we applied computational filters based on directional derivatives (vertical and horizontal) to our reduced-to-pole magnetic-field raw data-illuminating underground faults and other permeable pathways for fluids and delineating contacts between differently magnetized rocks, through maxima and minima on maps. While most filters used were able to define the basic configuration of the system, we found that computational filters working with ratios of derivatives (vertical and horizontal) were able to better account for the depth of a magnetic source. Also, faults were more clearly imaged on maps. We could mainly highlight ~E-W and ~N-S striking fault-systems, respectively belonging to the ~N-S Trans-Mexican Volcanic Belt extensional tectonics and to the ~E-W Basin & Range, both with lateral movements and still active today. We interpret the magnetic source as a magma body (related to the volcanism of Michoacán-Guanajuato Volcanic Field) that remained trapped during its ascent under Cuitzeo lacustrine sedimentation, during the last 500 ka, forming the once stronger geothermal system.
... Regional gravity and magnetic data along with several detailed transects are available for Surprise Valley ). Many studies have utilized this data to access geothermal potential and to map subsurface structures within the basin Lerch et al., 2006;Glen et al., 2008). Rock properties are well measured and defined for the region, which helps in potential field modeling Ponce et al., 2009). ...
Using mapped paleoshoreline features with high-resolution topographic data and obtained radiocarbon dates on paleoshoreline tufas, I documented precise fault offsets of dated features over the last 25 ka along the Surprise Valley Fault (SVF). Fault offset measured in three lake sections within Surprise Valley ranged from 3.6 m in the southern section to 14.4 m in the central section. The offset paleoshorelines are dated to the late Pleistocene (<22 >ka) and were formed during the latest impoundment of pluvial Lake Surprise since the last glacial maximum. Slip rates vary along strike, assuming a fault dip of 68° with 0.25 ± 0.02 mm/yr in the northern section, 1.07 ± 0.10 mm/yr in the central section, and 0.36 ± 0.04 mm/yr in the southern lake section. Potential field modeling of profiles drawn through detailed, gridded gravity and magnetic data, suggest that the surficial scarps continue at depth, where they may accommodate greater offset. These results refine the time-averaged slip rate along the SVF and show variability spatially and temporally, allowing for correlations with changes in paleolake levels. This study suggest iv complex relation between pluvial lakes and their proximal faults that show that the lake likely influenced earthquake recurrence and slip rate along the SVF.
... In addition to exploration drilling, several geophysical and geologic studies have been conducted to evaluate geologic and structural controls on subsurface geothermal fluid flow in Surprise Valley using high-quality gravity, magnetic, and audio magnetotelluric measurements (Glen et al., 2008;Kell-Hills et al., 2009;Lerch et al., 2010;Glen et al., 2013;Hawkes et al., 2013;Egger et al., 2014;Athens et al., 2016;Tanner et al., 2016). These studies show a close association of hot springs with faults in Surprise Valley, and support the contention of Duffield and Fournier (1974) that thermal fluid flow is structurally controlled . ...
Characterizing the geothermal system at Surprise Valley (SV), northeastern California, is important for determining the sustainability of the energy resource, and mitigating hazards associated with hydrothermal eruptions that last occurred in 1951. Previous geochemical studies of the area attempted to reconcile different hot spring compositions on the western and eastern sides of the valley using scenarios of dilution, equilibration at low temperatures, surface evaporation, and differences in rock type along flow paths. These models were primarily supported using classical geothermometry methods, and generally assumed that fluids in the Lake City mud volcano area on the western side of the valley best reflect the composition of a deep geothermal fluid. In this contribution, we address controls on hot spring compositions using a different suite of geochemical tools, including optimized multicomponent geochemistry (GeoT) models, hot spring fluid major and trace element measurements, mineralogical observations, and stable isotope measurements of hot spring fluids and precipitated carbonates. We synthesize the results into a conceptual geochemical model of the Surprise Valley geothermal system, and show that high-temperature (quartz, Na/K, Na/K/Ca) classical geothermometers fail to predict maximum subsurface temperatures because fluids re-equilibrated at progressively lower temperatures during outflow, including in the Lake City area. We propose a model where hot spring fluids originate as a mixture between a deep thermal brine and modern meteoric fluids, with a seasonally variable mixing ratio. The deep brine has deuterium values at least 3-4‰ lighter than any known groundwater or high-elevation snow previously measured in and adjacent to SV, suggesting it was recharged during the Pleistocene when meteoric fluids had lower deuterium values. The deuterium values and compositional characteristics of the deep brine have only been identified in thermal springs and groundwater samples collected in proximity to structures that transmit thermal fluids, suggesting the brine may be thermal in nature. On the western side of the valley at the Lake City mud volcano, the deep brine-meteoric water mixture subsequently boils in the shallow subsurface, precipitates calcite, and re-equilibrates at about 130 °C. On the eastern side of the valley, meteoric fluid mixes to a greater extent with the deep brine, cools conductively without boiling, and the composition is modified as dissolved elements are sequestered by secondary minerals that form along the cooling and outflow path at temperatures less than 130 °C. Re-equilibration of geothermal fluids at lower temperatures during outflow explains why subsurface temperature estimates based on classical geothermometry methods are highly variable, and fail to agree with temperature estimates based on dissolved sulfate-oxygen isotopes and results of classical and multicomponent geothermometry applied to reconstructed deep well fluids. The proposed model is compatible with the idea suggested by others that thermal fluids on the western and eastern side of the valley have a common source, and supports the hypothesis that low temperature re-equilibration during west to east flow is the major control on hot spring fluid compositions, rather than dilution, evaporation, or differences in rock type.
... The inferred "Lake City Fault Zone" (LCFZ) (Hedel, 1980(Hedel, , 1981(Hedel, , 1984Benoit et al., 2004;Egger et al., 2011) is a structure thought to run across the graben and connect the two range front faults ( Figure Figure 1: Map of the Surprise Valley geothermal region, showing water sample locations by region. 1), and has led to the proposition that the LCFZ controls west to east thermal fluid flow (Glen et al., 2008). Barring the emergence of hot springs at either end of the LCFZ, there is little evidence for the movement of fluids across this inferred conduit. ...
Despite the prevalence of hot springs and the drilling of several test wells, the Surprise Valley geothermal system remains relatively undeveloped. One reason for this is that the source and flow-path of geothermal waters within the subsurface remains enigmatic. Our study aims to determine this through a comprehensive investigation of the geochemistry of the Surprise Valley fluids. Our approach divides the valley into five regions that we believe to be operationally distinctive in their channeling and mixing of waters. We compiled and analyzed relationships between all of the available major element and isotopic geochemical data on thermal waters from within these regions. Chemical data were modeled Geochemists Workbench®. Initial results support the theory that discrete recharge sources and mechanisms are operating throughout the valley. Our geochemical modeling suggests that the hottest waters within the system originate at around 170° C, and may be diluted by cold waters from multiple sources. We believe this study may be useful in the context of emergent geophysical work that is investigating structures controlling fluid flow within the valley.
... A deep (~1500 m) geothermal exploration well (Phipps 2) was subsequently drilled near Lake City in the 1970's, and produced the hottest water found thus far in Surprise Valley at a temperature of~170 C. Following drilling of Phipps 2, geothermal exploration activities waned until about 2001, when several temperature gradient wells and core holes (Holes OH-1 and LCSH-5) were drilled near Lake City (Benoit et al., , 2005a(Benoit et al., , 2005b and later at Fort Bidwell (LaFleur et al., 2010). Since then, a number of structural and geophysical studies have been conducted in Surprise Valley to better understand the geology of this area, the relationship between structures and hydrothermal activity, and to further assess the potential for geothermal energy development in the valley (Glen et al., 2008;Kell-Hills et al., 2009;Egger et al., 2010;Egger and Miller, 2011;Glen et al., 2013;Egger et al., 2014). ...
Geothermal resource exploration is generally limited to areas with surface expressions of thermal activity (fumaroles and hot springs), or relies on expensive geophysical exploration techniques. In this study, the hidden subsurface distribution of geothermal fluids has been identified using a free and publicly available water quality dataset from agricultural and domestic water wells in Surprise Valley, northeastern California. Thermally evolved waters in Surprise Valley have element ratios that vary in response to Ca carbonate and Mg silicate mineral precipitation, and have elevated total dissolved solids (TDS). The arid climate in Surprise Valley leads to surface water evaporation in a closed basin, producing high TDS Na-Cl-CO3-SO4 brines in three ephemeral alkali lakes and in shallow groundwater under elevated soil CO2 conditions. Evaporated fluids in Surprise Valley follow a chemical divide that leads to Ca carbonate and Mg silicate mineral precipitation. Plots of dissolved element ratios can be used to distinguish groundwater affected by evaporation from water affected by thermal water-rock interaction, however it is challenging to select components for plotting that best illustrate different fluid evolution mechanisms. Here, we use a principal component analysis of centered log-ratio transformed data, coupled with geochemical models of fluid evaporation and thermal mixing pathways, to identify components to plot that distinguish between groundwater samples influenced by evaporation from those influenced by thermal processes. We find that groundwater samples with a thermal signature come from wells that define a coherent, linear geographical distribution that closely matches the location of known and inferred faults. Modification of the general approach employed here provides promise for identifying blind geothermal resources in other locations, by applying low-cost geochemical modeling and statistical techniques to areas where large groundwater quality geochemical datasets are available.
... Penelitian terkait eksplorasi geotermal menggunakan metoda geomagnet [1, 2, 3, 4, 5, 6] dapat menentukan prospek geotermal dengan mengkaji distribusi anomali geomagnetik. Penggunaan metoda geomagnet sangat efektif dan efisien untuk digunakan dalam eksplorasi geotermal karena dapat menentukan prospek geotermal dengan melihat distribusi secara horizontal [1,4,6] dan vertical [2, 3, 5]. ...
In 2012 the Geological Agency of Indonesia discovered 14 new geothermal sites in Indonesia, one of which is in the area Diloniyohu (now Bongongoayu) are included in the administrative area of the District Boliyohuto Gorontalo regency. Preliminary investigation geothermal area with geomagnetic methods used to determine the geothermal prospects. This study aimed to analyze the distribution of magnetic anomalies and determine the geothermal prospects based on the distribution of magnetic anomalies.
The magnetic survey carried out by the closed-loop system is the measurement starts and ends at the same point. The number of points is 224 points measuring geomagnetic measuring scattered on the 8 track measuring point. The total length of the measuring point is 5.4 Km. The distance between the measuring point is 25 m and the distance between tracks is 100 m. Value IGRF (International Geomagnetic Reference Field), inclination and declination obtained using NGDC Geomagnetic Calculators. By entering coordinates and elevation study site at NGDC Geomagnetic Calculators values obtained IGRF = 40633.97 nT, value Inclination = -14,75⁰ and declination = 0,79⁰ value. The results of the magnetic survey in the form of cross-section of the magnetic anomaly and magnetic anomaly distribution map.
Magnetization area which is indicative of reservoir is characterized by low magnetic anomaly (-400 to -150 nT) to moderate magnetic anomalous zone (-150 to 50 nT), which is at the center of the study area. Comprehensive prospecting area is > 320,000 m2 with a volume of 22.4 million m3 reservoir. Integrated investigations should be carried out to the west which is characterized by a moderate magnetic anomalies klosur opening and expanding research into the area of geothermal manifestations appearing more precisely in the area Talumopatu, District Paguyaman Mootilango and upstream watershed.
Keywords: Geothermal, Magnetic, Magnetic Anomali, Bongongoayu
... Penelitian terkait eksplorasi geotermal menggunakan metoda geomagnet [1, 2, 3, 4, 5, 6] dapat menentukan prospek geotermal dengan mengkaji distribusi anomali geomagnetik. Penggunaan metoda geomagnet sangat efektif dan efisien untuk digunakan dalam eksplorasi geotermal karena dapat menentukan prospek geotermal dengan melihat distribusi secara horizontal [1,4,6] dan vertical [2, 3, 5]. ...
Bongongoayu area is one of the areas in Gorontalo which is a place of geothermal manifestations (hot water pond) with a surface temperature of 43 ⁰C - 59 ⁰C. This research aimed to analyze sections of magnetic anomalies and electrical. The method used is quantitative research methods. Acquitition data was carried out in the field by using Proton Precission Magnetometer and Resistivity meter. The number of magnetic measuring points is 224 points while the number of electrical sounding is 2 points. Measurements of magnetic and electrical section is shown in the form of magnetic anomalies and electrical section. The results showed that the geological structure and litology in the area of Bongongoayu geothermal obtained by the magnetic anomaly sections. Indication of the geological structure and litology in the section of magnetic anomalies obtained by contrasting positive and negative anomalies values (> 300 nT). Negative magnetic anomalies on the L1 – L7 dominate the northwestern part of the track while the southeastern part of the track is dominated by positive magnetic anomalies. Based on the electrical section, the cap rock characterized by low resistivity values (<20 Ωm) and the very low resistivity (20-100 Ωm). Geothermal reservoir is characterized by high resistivity values (> 500 Ωm). Section of magnetic and electrical anomalies indicate that the geological structures (> 300 nT) are trending Northeast - Southwestern is a factor controlling of fluid in Bongongoayu geothermal area, Gorontalo.
... High-resolution gravity data must be collected at point locations on the ground. However, high-resolution magnetic data can be collected from the air and can provide continuous coverage (Glen et al., 2008). Prolonged low-altitude high-resolution manned aircraft surveys are dangerous, costly and relatively inflexible to changes in the survey specifications that may arise as data are collected. ...
Unmanned aircraft systems (UAS) are important assets for accessing high risk airspace and incorporate technologies for sensor coordination, onboard processing, tele-communication, unconventional flight control, and ground based monitoring and optimization. These capabilities permit adaptive mission management in the face of complex requirements and chaotic external influences. NASA Ames Research Center has led a number of Earth science remote sensing missions directed at the assessment of natural resources and here we describe two resource mapping problems having mission characteristics requiring a mission adaptive capability extensible to other resource assessment challenges.
One example involves the requirement for careful control over solar angle geometry for passive reflectance measurements. This constraint exists when collecting imaging spectroscopy data over vegetation for time series analysis or for the coastal ocean where solar angle combines with sea state to produce surface glint that can obscure the signal. Furthermore, the primary flight control imperative to minimize tracking error should compromise with the requirement to minimize aircraft motion artifacts in the spatial measurement distribution. A second example involves mapping of natural resources in the Earth’s crust using precision magnetometry. In this case the vehicle flight path must be oriented to optimize magnetic flux gradients over a spatial domain having continually emerging features, while optimizing the efficiency of the spatial mapping task.
These requirements were highlighted in recent Earth Science missions including the OCEANIA mission directed at improving the capability for spectral and radiometric reflectance measurements in the coastal ocean, and the Surprise Valley Mission directed at mapping sub-surface mineral composition and faults, using high-sensitivity magnetometry. This paper reports the development of specific aircraft control approaches to incorporate the unusual and demanding requirements to manage solar angle, aircraft attitude and flight path orientation, and efficient (directly geo-rectified) surface and sub-surface mapping, including the near-time optimization of these sometimes competing requirements.
In this study, we explore various fluid dilution and mixing scenarios that might explain the geochemical variability observed in the composition of Surprise Valley hot springs, NE California, with a particular focus on the Lake City area. Building on previous work by the lead authors, our approach involves applying various graphical and geochemical modeling techniques, including multicomponent geothermometry and reaction path computations, using available analyses of thermal and cold waters to infer reservoir temperatures as well as the compositions of potential end-member mixing fluids. This integrated approach is proving useful to estimate deep reservoir temperatures and unravel the chemical evolution of thermal fluids in systems that have undergone fluid mixing, boiling, and/or water-rock interaction along flow paths. Our investigations show that hot spring waters exhibit similar ratios of concentrations for many solutes, with compositions falling between those of cold groundwater and of a deep thermal component. Some thermal springs also appear to be impacted by interaction with alkali lake waters and/or minerals, although distinguishing this influence from that of a deep thermal component is difficult. Our results suggest that traditional geothermometry methods should be applied to Surprise Valley hot spring fluids with caution, as these estimates yield a wide range of reservoir temperatures. Integrated multicomponent geothermometry analyses, taking into account dilution and CO 2 loss in hot spring waters, suggest deep reservoir temperatures may reach up to 230°C in the Lake City area and also near Fort Bidwell, even though reported fluid temperatures measured in drill holes have yet to exceed 170°C.
Following a spectacular mud volcano eruption in 1951, the Lake City geothermal system has been intermittently explored for 44 years. A discovery well was drilled 30 years ago. The geothermal system is associated with a two mile-long, north-south trending, abnormally complex section of the active Surprise Valley fault zone that has uplifted the Warner Mountains by as much as 14,000' in the past 14 my. The known reservoir consists of a 337°F fractured production zone between depths of 4500 and 4946' in the Phipps #2 well, sited directly on the range-front fault. Production is from dacitic to rhyolitic Tertiary volcanic rocks. Temperature-gradient data show the natural heat loss of the geothermal field is comparable to the Soda Lake and Beowawe geothermal fields in Nevada currently producing between 12 and 16 megawatts of electricity.
We have estimated patterns and rates of crustal movement across 800 km of the Basin and Range at ~39° north latitude with Global Positioning System surveys in 1992, 1996, 1998, and 2002. The total rate of motion tangent to the small circle around the Pacific-North America pole of rotation is 10.4 +/- 1.0 mm/yr, and motion normal to this small circle is 3.9 +/- 0.9 mm/yr compared to the east end of our network. On the Colorado Plateau the east end of our network moves by ~1-2 mm/yr westerly with respect to North America. Transitions in strain rates delimit six major tectonic domains within the province. These deformation zones coincide with areas of modern seismicity and are, from east to west, (1) east-west extension in the Wasatch Fault zone, (2) low rate east-west extension centered near the Nevada-Utah border, (3) low rate east-west contraction between 114.7°W and 117.9°W, (4) extension normal to and strike-slip motion across the N10°E striking Central Nevada Seismic Zone, (5) right lateral simple shear oriented N13°W inside the Walker Lane Belt, and (6) shear plus extension near the Sierra Nevada frontal faults. Concentration of shear and dilatational deformation across the three westernmost zones suggests that the Walker Lane Belt lithosphere is rheologically weak. However, we show that linear gradients in viscosity and gravitational potential energy can also effectively concentrate deformation. In the Basin and Range, gradients in gravitational potential are spatially anticorrelated with dilatational strain rates, consistent with the presence of horizontal variations in viscosity of the lithosphere.
The horizontal‐gradient method has been used since 1982 to locate density or magnetic boundaries from gravity data (Cordell, 1979) or pseudogravity data (Cordell and Grauch, 1985). The method is based on the principle that a near‐vertical, fault‐like boundary produces a gravity anomaly whose horizontal gradient is largest directly over the top edge of the boundary. Magnetic data can be transformed to pseudogravity data using Fourier techniques (e.g., Hildenbrand, 1983) so that they behave like gravity data; thus the horizontal gradient of pseudogravity also has maximum magnitude directly over the boundary. The method normally is applied to gridded data rather than to profiles. The horizontal‐gradient magnitude is contoured and lines are drawn or calculated (Blakely and Simpson, 1986) along the contour ridges. These lines presumably mark the top edges of magnetic or density boundaries. However, horizontal‐gradient magnitude maxima (gradient maxima) can be offset from a position directly over the boundary for several reasons. Offsets occur when boundaries are not near‐vertical, or when several boundaries are close together. This note predicts these offsets. Many other factors also cause offsets, but they are less straightforward and usually are only significant in local studies; we discuss these factors only briefly.
A "nested graben" structural model, in which multiple faults successively displace rocks downward to the deepest part of the basin, is supported by recent field geologic analysis and correlation of results to geophysical data for Dixie Valley. Aerial photographic analysis and detailed field mapping provide strong evidence for a deep graben separated from the ranges to the east and west by multiple normal faults that affect the Tertiary/Quaternary basin-fill sediments. Correlation with seismic reflection and gravity surveys shows that some faults recognized by minor displacements at the surface produce significant stratigraphic offsets at depth in basin-fill sediments and help to explain gravity gradients displaced basin-ward from the range-front. The concept of a complex series of faults (both synthetic and antithetic) separating the Stillwater Range from Dixie Valley allows for the possibility that the geothermal circulation encompasses multiple faults both inboard and outboard of the range-front fault. This geometry increases the exploration potential of the area by providing additional possibilities for fault- controlled permeability and larger volumes of permeable rocks.
Paleomagneitic data from late Oligocene to early Miocene ash-flow tuffs at four localities in the northern Dixie Valley region, west-central Nevada, indicate that parts of the crust have rotated counterclockwise by at least 25° and perhaps significantly more in late Cenozoic time. Field relations in White Rock Canyon, Stillwater Range, suggest that rotation (1) was accommodated by right-lateral slip on northwest-trending faults, (2) spanned ash-flow tuff emplacement, and (3) probably ceased before eruption of overlying middle Miocene basalts. Accurate estimates of Cenozoic extension, as well as evaluation of earlier Mesozoic structures, must include the strain partitioned into rotation in the area.
The terracing operator works iteratively on gravity or magnetic data, using the sense of the measured field's local curvature, to produce a field comprised of uniform domains separated by abrupt domain boundaries. The result is crudely proportional to a physical-property function defined in one (profile case) or two (map case) horizontal dimensions. This result can be extended to a physical-property model if its behavior in the third (vertical) dimension is defined, either arbitrarily or on the basis of the local geologic situation. The terracing algorithm is computationally fast and appropriate to use with very large digital data sets. The terracing operator was applied separately to aeromagnetic and gravity data from a 136km x 123km area in eastern Kansas. Results provide a reasonable good physical representation of both the gravity and the aeromagnetic data. Superposition of the results from the two data sets shows many areas of agreement that can be referenced to geologic features within the buried Precambrian crystalline basement. -from Authors
Late Miocene-Pliocene (8-3 Ma) olivine basalt lavas, dated in this study by the 40Ar/39Ar method, have been faulted and tilted on both the east and west sides of the Warner Range of NE California, which is itself a tilted block rising to 2960 m at its crest that is composed of Miocene-Oligocene lavas and volcaniclastic rocks. The late Miocene-Pliocene lavas, distinctively poor in K2O and rich in MgO, are called low-K olivine tholeiites and have a different mantle source region than that of the older subduction-related lavas of the main Warner Range. Hays Canyon Range (max. elev. 2400 m) lies to the east of the Warner Range, and the broad Surprise Valley separates the two fault-bounded ranges. Middle Miocene (ca. 15 Ma) basic lavas, with a small easterly dip, cap the Hays Canyon Range and overlie Oligocene silicic ash-flow deposits and a basaltic andesite spatter volcano. Middle Miocene basic lavas also form the crest of the Warner Range and its westerly dip slope (∼15°). Nearly horizontal basic lavas of the same age are also found on both sides of the Warner Range, and it is a plausible conclusion that these middle Miocene basalts were a contiguous group before faulting and uplift of the Warner Range. Derived estimates of uplift rates (∼1 mm/yr) of the Warner Range indicate that uplift could have been initiated at ca. 4 Ma, a period of the most voluminous eruption of low-K olivine tholeiite lavas. If the slower Cretaceous exhumation rate of the Sierra Nevada (0.5-1.0 mm/yr) is applied to the total offset of the Warner Range (4270 m), and it did not vary with time, then the uplift of the Warner Range was initiated at ca. 8 Ma, which coincides with the age of the oldest low-K olivine tholeiite lava (8 Ma). Low-K olivine tholeiites require a hot shallow asthenospheric source, and it is the rise of this hot mantle that is presumed to have caused the uplift of the Warner Range. Whether or not the widespread eruption of small volumes of Pliocene low-K olivine tholeiites in central and eastern Oregon is associated with crustal uplift is unknown.
Paleomagnetic results from Cenozoic (62-12 Ma) volcanic rocks of the Cascade arc and adjacent indicate that moderate to large clockwise rotations are an important component of the tectonic history of the arc. Two mechanisms of rotation are suggested by the regional pattern of paleomagnetic rotations. The progressive increase in rotation toward the coast in arc and forearc rocks results from distributed dextral shear, which is likely driven by oblique subduction of oceanic plates to the west. Simple shear rotation is accommodated in the upper crust by strike-slip faulting. The right-lateral Mount St. Helens seismic zone may be an active manifestation of this process. Dextral shear probably obscures a subequal contribution to arc and forearc rotation that is driven by intraarc or backarc extension. This rotation is suggested by the average southward increase in continental margin rotations into the region outboard of the Basin and Range. The southward increase in rotation parallels a change in the arc tectonic regime from largely compressional in northern Washington to extensional in Oregon. Concomitant with this change is a southward increase in the volume of eruptive rocks and the number of basaltic vents in the arc. A progressive eastward shift of the arc volcanic front with time in the rotated arc terrane is the result of the westward pivoting of the arc block in front of a zone of extension since Eocene time. Westward migration of bimodal Basin and Range volcanism since at least 16 Ma is tracking westward rotation of the frontal arc block and growth of the Basin and Range in its wake.
All normal-fault systems must terminate both along and orthogonal to strike. As many as four terminations may be associated with a single culmination. Most normalfault systems terminate in either transfer zones or accommodation zones. In the nongenetic classification proposed here, transfer zones are defined as discrete zones of strike-slip and oblique-slip faulting that generally trend parallel to the extension direction and typically facilitate a transfer of strain between extended domains arranged in an en echelon pattern. Accommodation zones are belts of overlapping fault terminations and can separate either systems of uniformly dipping normal faults or adjacent domains of oppositely dipping normal faults. They can trend parallel, perpendicular, or oblique to the extension direction. A review of variously extended continental provinces and passive continental margins reveals that the style of deformation within transfer and accommodation zones is independent of the magnitude of extension. Strike-slip and oblique-slip faults within transfer zones are closely linked kinematically with major normal faults within the extended terranes. Transfer zones linking spatially separated loci of extension display along-strike variations in both magnitude and sense of motion, whereas local normal and reverse faults may develop in the vicinity of releasing and restraining fault bends. Strain within accommodation zones is transmitted directly between normal-fault systems, geometries being controlled by the amount of overlap between and relative dip direction of competing sets of normal faults. Antithetic accommodation zones develop between oppositely dipping normal-fault systems, whereas synthetic accommodation zones occur between similarly dipping systems. In the synthetic zone, relay ramps commonly connect the hanging wall of one fault to the footwall of another fault and trend obliquely in zones that have significantly overlapping normal faults but transversely (parallel to extension direction) in zones that have minimal overlap. Antithetic zones exhibit a wider variety of geometries, including (1) strike-parallel (parallel to trend of rift) anticlines and synclines between normal-fault systems having complete overlap that dip toward and away from one another, respectively, (2) obliquely trending anticlines and synclines in areas of partial fault overlap, and (3) transverse zones between minimally overlapping fault systems. The distinction between the strike-parallel and transverse accommodation zones is scale dependent; large strike-parallel segments are characterized by finescale offsets of hingelines along small transverse segments, and large transverse zones commonly contain small anticlinal and synclinal segments. The anticlines and synclines are manifestations of extensional strain, as opposed to localized shortening. Accommodation zones are essentially regional rupture barriers to normal-fault systems and are critical for evaluating seismic hazards in contemporary rifts and kinematic models of continental extension. The minimal displacements on normal faults suggest that accommodation zones in actively extending orogens are relatively low risk regions for major surface-rupture displacements. In addition, magmatism is commonly focused along the zones, suggesting that subjacent plutons and batholiths inhibit the lateral propagation of normal-fault systems. Accommodation and transfer zones provide topographic frameworks and depositional settings in which sand-rich, potentially permeable rocks entering grabens near fault terminations can laterally interfinger with organic-rich, fine-grained rocks accumulating within hanging-wall depocenters developed near fault displacement maxima. Related facies changes, stratigraphic pinchouts, and onlap relations associated with the termination of half grabens generate abundant stratigraphic traps for migrating fluids. Potential structural traps include anticlines and intersecting conjugate normal faults. Dense fracture networks that characterize these zones may enhance permeability and promote hydrocarbon and ground-water accumulation.
Footwall rocks of the 1954 rupture segment of the Dixie Valley Fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events. Hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages. The P-T path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics. The path includes a lithostatic fluid pressure at 305°C and 1570 bars. Hydrothermal alteration product minerals, fluid temperatures, pressures, and compositions in the footwall of the Dixie Valley Fault constrain minimum fault age to 20 to 25 Ma, displacement to 6km with about 3km of pre-10 to 13 Ma and 3km of post-10 Ma uplift. From fluid compositions and P-T data a mechanism for rupture initiation and arrest is presented. -from Authors
The GPS-derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ∼2500-km-long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ∼1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ∼100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth-averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ∼1000 km from the major plate boundaries.
During the night of March 1 and 2, 1951, an inconspicuous group of hot springs and small mud volcanoes in northeastern California burst into spectacular eruption, unequalled by other known mud volcanoes. The eruption cloud of steam, gases, and mud particles rose several thousand feet in the air and distributed fine debris to the southeast for a distance of at least 4 miles. More than 20 acres of the hot-spring area was intensely disturbed and greatly modified by the eruption, estimated to involve at least 6 million cubic feet or 300,000 tons of mud. Several days after the eruption, the area was barely active. The eruption appears to be unique in the history of the springs. The hot-spring system is in deep fine-grained clastic sediments immediately east of the Surprise Valley fault bounding the Warner Range. The sediments of the spring area are saturated with near-neutral hot saline water. Previous temperatures and geothermal gradient of the area were probably high. Mud volcanoes exist in similar physical environment near Gerlach in Washoe County, Nevada, and on the southeast shore of Salton Sea, Imperial County, California. Other mud volcanoes occur in acid thermal areas and are characterized by abundant volcanic gases and near-surface alteration by sulfuric acid; their eruptions involve only surficial material and not underlying competent bedrock. Eruptions in deep fine-grained basin sediments are attribured to unstable or metastable temperature-depth relations existing in many high-energy thermal systems. Vapor pressure at depth may equalor exceed hydrostatic pressure. Great energy is stored in a thermal system of this type, but ordinarily is released slowly. A mud-volcano origin is possible for some eruption deposits classed as phreatic or cryptovolcanic. Although near-boiling hot springs are considered phases of volcanism, true volcanic eruptions are distinct from mud-volcano eruptions. The former derive their energy directly from new volcanic rocks or magma, but the latter are caused by sudden release of energy stored in near-surface hydrothermal systems and do not involve direct release of energy from new volcanic magma. The energy of true volcanic eruptions, however, may be increased by release of energy from previously existing hydrothermal systems, for example in the Rotomahana phase of the great Tarawera eruption of 1886 in New Zealand.
1] We use geodetic velocities obtained with the Global Positioning System (GPS) to quantify tectonic deformation of the northwest Basin and Range province of the western United States. The results are based on GPS data collected in 1999 and 2003 across five new quasi-linear networks in northern Nevada, northeast California, and southeast Oregon. The velocities show 3.5 mm/yr and is possibly influenced by the approximately eastward motion of the Juan de Fuca plate. These results disagree with secular northwest trenchward motion of the Oregon forearc inferred from paleomagnetic rotations. South of latitude 43°, however, trenchward motion exists and is consistent with block rotations, approximately east-west Basin and Range extension, and northwest Sierra Nevada translation.
Principal facts and preliminary interpretation for gravity profiles and continuous magnetometer profiles in Surprise Valley
- A Griscom
- A Conradi
Griscom, A., and A. Conradi, 1976, Principal facts and preliminary interpretation for gravity
profiles and continuous magnetometer profiles in Surprise Valley, California: U. S.
Geological Survey Open-File Report 76-0260, 21 pp.
Map showing geothermal resources of the Lake City-Surprise Valley known geothermal resource area
- C W Hedel
Hedel, C. W., 1981, Map showing geothermal resources of the Lake City-Surprise Valley known
geothermal resource area, Modoc County, California, Miscellaneous Field Studies Map MF-1299, Reston, VA, U. S. Geological Survey.
Maps showing geomorphic and geologic evidence for late Quaternary displacement along the Surprise Valley and associated faults
- C W Hedel
Hedel, C. W., 1984, Maps showing geomorphic and geologic evidence for late Quaternary
displacement along the Surprise Valley and associated faults, Modoc County, California,
Miscellaneous Field Studies Map MF-1429, Reston, VA, U. S. Geological Survey.
Selected data for hydrothermal convection systems in the United States with estimated temperatures + or -90 degrees
- R H Mariner
- C A Brook
- J R Swanson
- D R Mabey
Mariner, R. H., C. A. Brook, J. R. Swanson, and D. R. Mabey, 1978, Selected data for
hydrothermal convection systems in the United States with estimated temperatures + or -90
degrees, 460 pp.
Logs and scarp data from a paleoseismic investigation of the Surprise Valley fault zone
- S F Personius
- A J Crone
- M N Machette
- D J Lidke
- L.-A Bradley
- S A Mahan
Personius, S. F., A. J. Crone, M. N. Machette, D. J. Lidke, L.-A. Bradley, and S. A. Mahan,
2007, Logs and scarp data from a paleoseismic investigation of the Surprise Valley fault
zone, Modoc County, California, U.S. Geological Survey Scientific Investigations Map SIM-2983, 2 sheets.