Regional crustal-scale structures as conduits for deep geothermal upflow

Siler, Drew L.; Kennedy, B. Mack

doi:10.1016/j.geothermics.2015.10.007

Cited by 18 publications

(8 citation statements)

References 75 publications

(147 reference statements)

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“…Eraifej (2006) measured high 3 He/ 4 He ratios of samples collected from wells and springs along the DST and close to the eastern part of the DSB. Anomalously high 3 He/ 4 He in geothermal fluids indicate that these geothermal systems are associated with more rapid upwelling of mantle derived fluids (Siler & Kennedy 2016). More recently, Schaeffer & Sass (2014) investigated thermal water samples from the eastern side of the Dead Sea valley and suggested that the high geothermal gradient could be best explained if water of deep origin invaded the hydrothermal system of the DSB.…”

Section: Discussion O F T H E 2 -D E L E C T R I C a L C O Nmentioning

confidence: 99%

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

et al. 2016

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S U M M A R YWe report on a study to explore the deep electrical conductivity structure of the Dead Sea Basin (DSB) using magnetotelluric (MT) data collected along a transect across the DSB where the left lateral strike-slip Dead Sea transform (DST) fault splits into two fault strands forming one of the largest pull-apart basins of the world. A very pronounced feature of our 2-D inversion model is a deep, subvertical conductive zone beneath the DSB. The conductor extends through the entire crust and is sandwiched between highly resistive structures associated with Precambrian rocks of the basin flanks. The high electrical conductivity could be attributed to fluids released by dehydration of the uppermost mantle beneath the DSB, possibly in combination with fluids released by mid-to low-grade metamorphism in the lower crust and generation of hydrous minerals in the middle crust through retrograde metamorphism. Similar high conductivity zones associated with fluids have been reported from other large fault systems. The presence of fluids and hydrous minerals in the middle and lower crust could explain the required low friction coefficient of the DST along the eastern boundary of the DSB and the high subsidence rate of basin sediments. 3-D inversion models confirm the existence of a subvertical high conductivity structure underneath the DSB but its expression is far less pronounced. Instead, the 3-D inversion model suggests a deepening of the conductive DSB sediments off-profile towards the south, reaching a maximum depth of approximately 12 km, which is consistent with other geophysical observations. At shallower levels, the 3-D inversion model reveals salt diapirism as an upwelling of highly resistive structures, localized underneath the Al-Lisan Peninsula. The 3-D model furthermore contains an E-W elongated conductive structure to the northeast of the DSB. More MT data with better spatial coverage are required, however, to fully constrain the robustness of the above-mentioned off-profile features.

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Section: Discussion O F T H E 2 -D E L E C T R I C a L C O Nmentioning

confidence: 99%

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

et al. 2016

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“…It is interpreted as underplating because of likely temperatures and oxidation state, and because existing seismic studies (COCORP, PASSCAL) resolved VP attenuation, high VP underplate and high reflectivity there (Catchings and Mooney, 1991;Wannamaker et al, 2007;2008). Mantle sourced 3 He anomalies corroborate this (Kennedy and van Soest, 2007;Siler and Kennedy, 2016), and the situation fits into the general deep hydrological/magmatic paradigm of Crossey and Karlstrom (2012) (Figure 1). An important factor in bringing exploitable fluids surfaceward at Dixie Valley is the intersection of N-S and NE-SW fault trends (Faulds et al, 2011), also resolved in 3D MT surveying (Wannamaker et al, 2013).…”

Section: Technical Approach and Objectivesmentioning

confidence: 56%

“…R/Ra values ranged from 0.35-0.49 in 36-10 fluids to 0.41-0.57 in 28-10 fluids. While these do not rival the high magmatic values seen at Coso or some Cascades volcanoes, they are significantly above the Great Basin background value of ~0.1 van Soest, 2006, 2007;Siler and Kennedy, 2016), signifying that, like the van Soest, 2006, 2007). However, this amount may differ from the long term average depending upon deformation and seismicity, as exemplified in the Mammoth Hot Springs district (Sorey et al, 1998).…”

Section: Production Fluids and Soil Gas Geochemistrymentioning

confidence: 70%

“…Reconnaissance MT surveys show that the onset of low resistivity in the deep crust generated by active magmatic underplating and fluid release may come to remarkably shallow depths in areas of high rates of recent extension (Wannamaker et al, 2006(Wannamaker et al, , 2011Siler et al, 2014;Dobson, 2016). Commonly, steep crustal-scale fault zones connect this deep conductor to high temperature geothermal systems near the surface (Wannamaker et al, 2011;Siler and Kennedy, 2016). As structural analyses have accumulated, systems are increasingly recognized to form in zones of structural complexity and dilatancy of various possible types, including horsetailing fault terminations, step overs (or relay ramps), and accommodation zones (Faulds and Hinz, 2015).…”

Section: Introductionmentioning

confidence: 99%

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Integrating Magnetotellurics, Soil Gas Geochemistry and Structural Analysis to Identify Hidden, High Enthalpy, Extensional Geothermal Systems

Wannamaker

Faulds

Kennedy

et al. 2017

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We applied magnetotellurics (MT), diagnostic structural affiliations, soil gas flux, and fluid geochemistry to assist in identifying hidden, high-enthalpy geothermal systems in extensional regimes of the U.S. Great Basin. We are specifically looking for high-angle, lowresistivity zones and dilatant geologic structures that can carry fluids from magmatic or high-grade metamorphic conditions in the deep crust upward to exploitable depths, and to verify the nature of the deep sources through soil gas and fluid compositions. The project was motivated by prior MT transect coverage of western and central Nevada centered upon the Dixie Valley producing geothermal system where such favorable indicators were first recognized. The high-angle MT structures are taken to be fluidized fault zones connecting deep magmatic/metamorphic activity with the geothermal system, but the concept required verification by testing at other systems.The project was set up with a two-phased organization. Phase I was carried out at the McGinness Hills system, central Nevada, where Ormat Inc flagship power facility is located and a considerable amount of pre-existing data were available. Transect MT data also showed a strong low-resistivity upwelling originating from interpreted deep crustal magmatic underplating. Controlling structures on production as indicated by Ormat data and our new mapping were favorable to dilatancy, comprising an accommodation zone between major normal faults of opposing dip. A 3D MT survey and inversion confirmed the existence of the steep low-resistivity zone dipping ESE toward the deep crust and placed N-S bounds upon the feature. In cooperation with Ormat personnel, we sampled well fluids from production intervals for He isotope composition. Elevated 3 He was verified through mass spectrometry analysis confirming a magmatic connection into the producing system. High CO2 soil gas flux including possibly metamorphic 13 C and 14 C component was measured over the area of dilatant structures. Hence, the triad of indicators posed above was confirmed in Phase I.Subsequently, Phase II of the project proceeded in the greenfield Kumiva-Blackrock Desert district of northwestern Nevada to see if a new system could be identified. Transect MT data also showed a strong low-resistivity upwelling originating from interpreted deep crustal magmatic underplating. An areal MT survey of 131 sites was imaged through 3D inversion using the in-house, DOE-supported finite element algorithm. Particular MT low resistivity upwellings that received followup study occurred under the flanks of the Seven Troughs Range, under Kumiva Playa immediately west of the Blue Wing Mountains, and under northern Granite Springs Valley. Structural assessment of the project area by Co-I J. Faulds at UNR provided numerous favorable Quaternary fault settings, which were correlated to the MT upwelling structures. Soil CO2 gas flux anomalies generally were not large but did show correlation with MT upwelling structure and favorable geological structures. Isotope ana...

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“…Hydrogeologists and geologists want to understand the nature, origin, and role of fluids in such fundamental geological processes as hydrothermal systems [3], deep geothermal systems [4,5], ore deposition [6,7], hydrocarbon maturation, migration and entrapment [8], seismicity [9], and metamorphism [10][11][12]. In sedimentary rocks, fluid pathways include connected rock porosity and lithological changes.…”

Section: Introductionmentioning

confidence: 99%

Reconstructing Paleofluid Circulation at the Hercynian Basement/Mesozoic Sedimentary Cover Interface in the Upper Rhine Graben

Dezayes

Lerouge

2019

Geofluids

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In this paper, we focus on paleocirculation at the Hercynian basement/sedimentary cover interface in the tectonic environment of the Upper Rhine graben. The goal is to increase our understanding of the behavior of the fracture-fault network and the origin of the hydrothermal fluids. We studied orientations, mineral fillings, and fluid origins of fractures that crosscut the Hercynian granitic basement and the Permo-Triassic formations in relation to the major tectonic events. Because the Mesozoic formations and the Hercynian basement on the graben flanks and inside the graben do not have the same evolution after uplift, our study includes 20 outcrops on both graben flanks and cores of the Soultz-sous-Forêts geothermal wells located inside the graben. The Hercynian granitic basement and Permo-Triassic formations were affected by several brittle phases associated with fluid circulation pulses related to graben formation during the Tertiary. We distinguished at least four stages: (1) reactivation of Hercynian structures associated with pre-rift tectonics during the early Eocene and descending meteoric waters, characterized by shearing/cataclasis textures and precipitation of illite and microquartz; (2) initiation of convective circulation of deep hot brines mixed with descending meteoric waters at the Hercynian basement/sedimentary cover interface during this first stage of Eocene rifting, characterized by dolomite and barite fillings in reactivated Hercynian fractures; (3) N-S tension fractures associated with rift tectonics just prior to uplift of the graben shoulders during Oligocene extension and descending meteoric waters, characterized by cataclastic textures and precipitation of quartz, illite, hematite, and barite; and (4) current convective circulation of deep hot brines mixed with descending meteoric waters at the Hercynian basement/sedimentary cover interface, characterized by calcite and barite fillings within the graben. This convective circulation is today present in deep geothermal wells in the western part of the Rhine graben.

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Regional crustal-scale structures as conduits for deep geothermal upflow

Cited by 18 publications

References 75 publications

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

Integrating Magnetotellurics, Soil Gas Geochemistry and Structural Analysis to Identify Hidden, High Enthalpy, Extensional Geothermal Systems

Reconstructing Paleofluid Circulation at the Hercynian Basement/Mesozoic Sedimentary Cover Interface in the Upper Rhine Graben

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