Sarah Brown | West Virginia University (original) (raw)

Papers by Sarah Brown

Geological Society of America Abstracts with Programs, 2017

Long-lived intra-oceanic arcs of Izu-Bonin-Marianas (IBM)-type are built on thick, granodioritic ... more Long-lived intra-oceanic arcs of Izu-Bonin-Marianas (IBM)-type are built on thick, granodioritic crust formed in the absence of pre-existing continental crust. International Ocean Discovery Program Expedition 350, Site U1437, explored the IBM rear arc to better understand continental crust formation in arcs. Detailed petrochronological (U–Pb geochronology combined with trace elements, oxygen and hafnium isotopes) characterizations of zircon from Site U1437 were carried out, taking care to exclude potential contaminants by (1) comparison of zircon ages with ship-board palaeomagnetic and biostratigraphic ages and ⁴⁰Ar/³⁹Ar geochronology, (2) analysing zircon from drill muds for comparison, (3) selectively carrying out <i>in situ</i> analysis in petrographic thin sections, and (4) minimizing potential laboratory contamination through using pristine equipment during mineral separation. The youngest zircon ages in Site U1437 are c...

The core of the Cretaceous (?) proto-Kern Canyon Fault (KCF) is exposed continuously for 1.25 km ... more The core of the Cretaceous (?) proto-Kern Canyon Fault (KCF) is exposed continuously for 1.25 km along Engineers Point at Lake Isabella, Kern County, California. The proto-KCF is notable for (1) its long and complex history within, and perhaps preceding the Sierra Nevada batholith, and (2) hosting the Quaternary Kern Canyon Fault, an active fault that threatens the integrity of the Lake Isabella auxiliary dam and surrounding communities. We are investigating the internal architecture of the proto-KCF to explore its control on the likely behavior of the modern KCF. The proto-KCF is developed in the Alta Sierra biotite-granodiorite pluton. A traverse across Engineers Point, perpendicular to the proto-KCF trace, reveals gradational increases in fracture density, fracture length, bulk alteration, and decreases in fracture spacing and grain size toward the fault core. Mapping of the fault core reveals two prominent and laterally extensive zones: (1) continuous foliated blastomylonitic gr...

Lunar and Planetary Science Conference, Mar 1, 2021

The Review of scientific instruments, 2018

Fluid flow in the subsurface is not well understood in the context of "impermeable" geo... more Fluid flow in the subsurface is not well understood in the context of "impermeable" geologic media. This is especially true of formations that have undergone significant stress fluctuations due to injection or withdrawal of fluids that alters the localized pressure regime. When the pressure regime is altered, these formations, which are often already fractured, move via shear to reduce the imbalance in the stress state. While this process is known to happen, the evolution of these fractures and their effects on fluid transport are still relatively unknown. Numerous simulation and several experimental studies have been performed that characterize the relationship between shearing and permeability in fractures; while many of these studies utilize measurements of fluid flow or the starting and ending geometries of the fracture to characterize shear, they do not characterize the intermediate stages during shear. We present an experimental apparatus based on slight modification...

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International Journal of Rock Mechanics and Mining Sciences, 2021

Abstract Flow in fractures is of critical importance to fluid flow in low-permeability shales, pa... more Abstract Flow in fractures is of critical importance to fluid flow in low-permeability shales, particularly when they restrict vertical migration from reservoirs. The Mt. Simon Sandstone is a target for geologic CO 2 sequestration and the overlying Eau Claire Formation is the sealing formation capping this reservoir. The lower Eau Claire, a primary barrier to upward migration of CO2 from the Mt. Simon, is lithologically heterogenous with a mixture of sandstone and shale. We use a series of flow-through experiments on fractured samples from the Eau Claire to document the morphological changes taking place in the fracture and surrounding rock as it is sheared in a stepwise fashion. The samples were imaged using computed tomography after each shearing episode and flow resistance was calculated based on the pressure differential across each core. We found that gouge accumulations in the fracture plane led to specific instances of self-sealing behavior despite the fact that most samples increased in average fracture aperture and transmissivity . Gouge limited the increase or, in some cases, decreased flow through these samples. Fractures adjacent to shale-rich zones and concordant with bedding were more likely to show evidence of self-sealing, while increased sandstone content and fracture orientation perpendicular to bedding planes was more likely to result in fracture dilation and fracture permeability increases. Reactivation and shearing of vertical fractures in lithologically heterogenous caprocks is more likely to pose risks to long term CO 2 storage scenarios.

Lithosphere, 2016

The distribution of tectonic superstructure across the Shuswap metamorphic complex of southern Br... more The distribution of tectonic superstructure across the Shuswap metamorphic complex of southern British Columbia is explained by east-westtrending corrugations of the Okanagan Valley shear zone detachment. Geological mapping along the southern Okanagan Valley shear zone has identified 100-m-scale to kilometer-scale corrugations parallel to the extension direction, where synformal troughs hosting upper-plate units are juxtaposed between antiformal ridges of crystalline lower-plate rocks. Analysis of available structural data and published geological maps of the Okanagan Valley shear zone confirms the presence of ≤40-km-wavelength corrugations, which strongly influence the surface trace of the detachment system, forming spatially extensive salients and reentrants. The largest reentrant is a semicontinuous belt of late Paleozoic to Mesozoic upper-plate rocks that link stratigraphy on either side of the Shuswap metamorphic complex. Previously, these belts were considered by some to be autochthonous, implying minimal motion on the Okanagan Valley shear zone (≤12 km); conversely, our results suggest that they are allochthonous (with as much as 30-90 km displacement). Corrugations extend the Okanagan Valley shear zone much farther east than previously recognized and allow for hitherto separate gneiss domes and detachments to be reconstructed together to form a single, areally extensive Okanagan Valley shear zone across the Shuswap metamorphic complex. If this correlation is correct, the Okanagan Valley shear zone may have enveloped the entire Shuswap metamorphic complex as far east as the east-vergent Columbia River-Slocan Lake fault zones.

AGU Fall Meeting Abstracts, Dec 1, 2020

Proceedings of the 6th Unconventional Resources Technology Conference, 2018

Geosphere, 2022

Combined Hf-O isotopic analyses of zircons from tuffs and lavas within the Sierra Madre Occidenta... more Combined Hf-O isotopic analyses of zircons from tuffs and lavas within the Sierra Madre Occidental (SMO) silicic large igneous province are probes of petrogenetic processes in the lower and upper crust. Existing petrogenetic and tectonomagmatic models diverge, having either emphasized significant crustal reworking of hydrated continental lithosphere in an arc above the retreating Farallon slab or significant input of juvenile mantle melts through a slab window into an actively stretching continental lithosphere. New isotopic data are remarkably uniform within and between erupted units across the spatial and temporal extent of the SMO, consistent with homogeneous melt production and evolution. Isotopic values are consistent with enriched mantle magmas (80%) that assimilated Proterozoic paragneisses (~20%) from the lower crust. 18Ozircon values are consistent with fractionation of mafic magma and not with assimilation of hydrothermally altered upper crust, suggesting that the silicic ...

Sample details, U-Pb geochronology data, EarthChem Database references, Lu-Hf data, oxygen isotop... more Sample details, U-Pb geochronology data, EarthChem Database references, Lu-Hf data, oxygen isotope data, zircon saturation temperature data, and assimilation–fractional crystallization modeling

Geological Society of America Abstracts with Programs, 2020

Geological Society of America Abstracts with Programs, 2020

Geological Society of America Abstracts with Programs, 2017

Long-lived intra-oceanic arcs of Izu-Bonin-Marianas (IBM)-type are built on thick, granodioritic ... more Long-lived intra-oceanic arcs of Izu-Bonin-Marianas (IBM)-type are built on thick, granodioritic crust formed in the absence of pre-existing continental crust. International Ocean Discovery Program Expedition 350, Site U1437, explored the IBM rear arc to better understand continental crust formation in arcs. Detailed petrochronological (U–Pb geochronology combined with trace elements, oxygen and hafnium isotopes) characterizations of zircon from Site U1437 were carried out, taking care to exclude potential contaminants by (1) comparison of zircon ages with ship-board palaeomagnetic and biostratigraphic ages and ⁴⁰Ar/³⁹Ar geochronology, (2) analysing zircon from drill muds for comparison, (3) selectively carrying out <i>in situ</i> analysis in petrographic thin sections, and (4) minimizing potential laboratory contamination through using pristine equipment during mineral separation. The youngest zircon ages in Site U1437 are c...

The core of the Cretaceous (?) proto-Kern Canyon Fault (KCF) is exposed continuously for 1.25 km ... more The core of the Cretaceous (?) proto-Kern Canyon Fault (KCF) is exposed continuously for 1.25 km along Engineers Point at Lake Isabella, Kern County, California. The proto-KCF is notable for (1) its long and complex history within, and perhaps preceding the Sierra Nevada batholith, and (2) hosting the Quaternary Kern Canyon Fault, an active fault that threatens the integrity of the Lake Isabella auxiliary dam and surrounding communities. We are investigating the internal architecture of the proto-KCF to explore its control on the likely behavior of the modern KCF. The proto-KCF is developed in the Alta Sierra biotite-granodiorite pluton. A traverse across Engineers Point, perpendicular to the proto-KCF trace, reveals gradational increases in fracture density, fracture length, bulk alteration, and decreases in fracture spacing and grain size toward the fault core. Mapping of the fault core reveals two prominent and laterally extensive zones: (1) continuous foliated blastomylonitic gr...

Lunar and Planetary Science Conference, Mar 1, 2021

The Review of scientific instruments, 2018

Fluid flow in the subsurface is not well understood in the context of "impermeable" geo... more Fluid flow in the subsurface is not well understood in the context of "impermeable" geologic media. This is especially true of formations that have undergone significant stress fluctuations due to injection or withdrawal of fluids that alters the localized pressure regime. When the pressure regime is altered, these formations, which are often already fractured, move via shear to reduce the imbalance in the stress state. While this process is known to happen, the evolution of these fractures and their effects on fluid transport are still relatively unknown. Numerous simulation and several experimental studies have been performed that characterize the relationship between shearing and permeability in fractures; while many of these studies utilize measurements of fluid flow or the starting and ending geometries of the fracture to characterize shear, they do not characterize the intermediate stages during shear. We present an experimental apparatus based on slight modification...

.................................................................................................... more ...................................................................................................................................1

International Journal of Rock Mechanics and Mining Sciences, 2021

Abstract Flow in fractures is of critical importance to fluid flow in low-permeability shales, pa... more Abstract Flow in fractures is of critical importance to fluid flow in low-permeability shales, particularly when they restrict vertical migration from reservoirs. The Mt. Simon Sandstone is a target for geologic CO 2 sequestration and the overlying Eau Claire Formation is the sealing formation capping this reservoir. The lower Eau Claire, a primary barrier to upward migration of CO2 from the Mt. Simon, is lithologically heterogenous with a mixture of sandstone and shale. We use a series of flow-through experiments on fractured samples from the Eau Claire to document the morphological changes taking place in the fracture and surrounding rock as it is sheared in a stepwise fashion. The samples were imaged using computed tomography after each shearing episode and flow resistance was calculated based on the pressure differential across each core. We found that gouge accumulations in the fracture plane led to specific instances of self-sealing behavior despite the fact that most samples increased in average fracture aperture and transmissivity . Gouge limited the increase or, in some cases, decreased flow through these samples. Fractures adjacent to shale-rich zones and concordant with bedding were more likely to show evidence of self-sealing, while increased sandstone content and fracture orientation perpendicular to bedding planes was more likely to result in fracture dilation and fracture permeability increases. Reactivation and shearing of vertical fractures in lithologically heterogenous caprocks is more likely to pose risks to long term CO 2 storage scenarios.

Lithosphere, 2016

The distribution of tectonic superstructure across the Shuswap metamorphic complex of southern Br... more The distribution of tectonic superstructure across the Shuswap metamorphic complex of southern British Columbia is explained by east-westtrending corrugations of the Okanagan Valley shear zone detachment. Geological mapping along the southern Okanagan Valley shear zone has identified 100-m-scale to kilometer-scale corrugations parallel to the extension direction, where synformal troughs hosting upper-plate units are juxtaposed between antiformal ridges of crystalline lower-plate rocks. Analysis of available structural data and published geological maps of the Okanagan Valley shear zone confirms the presence of ≤40-km-wavelength corrugations, which strongly influence the surface trace of the detachment system, forming spatially extensive salients and reentrants. The largest reentrant is a semicontinuous belt of late Paleozoic to Mesozoic upper-plate rocks that link stratigraphy on either side of the Shuswap metamorphic complex. Previously, these belts were considered by some to be autochthonous, implying minimal motion on the Okanagan Valley shear zone (≤12 km); conversely, our results suggest that they are allochthonous (with as much as 30-90 km displacement). Corrugations extend the Okanagan Valley shear zone much farther east than previously recognized and allow for hitherto separate gneiss domes and detachments to be reconstructed together to form a single, areally extensive Okanagan Valley shear zone across the Shuswap metamorphic complex. If this correlation is correct, the Okanagan Valley shear zone may have enveloped the entire Shuswap metamorphic complex as far east as the east-vergent Columbia River-Slocan Lake fault zones.

AGU Fall Meeting Abstracts, Dec 1, 2020

Proceedings of the 6th Unconventional Resources Technology Conference, 2018

Geosphere, 2022

Combined Hf-O isotopic analyses of zircons from tuffs and lavas within the Sierra Madre Occidenta... more Combined Hf-O isotopic analyses of zircons from tuffs and lavas within the Sierra Madre Occidental (SMO) silicic large igneous province are probes of petrogenetic processes in the lower and upper crust. Existing petrogenetic and tectonomagmatic models diverge, having either emphasized significant crustal reworking of hydrated continental lithosphere in an arc above the retreating Farallon slab or significant input of juvenile mantle melts through a slab window into an actively stretching continental lithosphere. New isotopic data are remarkably uniform within and between erupted units across the spatial and temporal extent of the SMO, consistent with homogeneous melt production and evolution. Isotopic values are consistent with enriched mantle magmas (80%) that assimilated Proterozoic paragneisses (~20%) from the lower crust. 18Ozircon values are consistent with fractionation of mafic magma and not with assimilation of hydrothermally altered upper crust, suggesting that the silicic ...

Sample details, U-Pb geochronology data, EarthChem Database references, Lu-Hf data, oxygen isotop... more Sample details, U-Pb geochronology data, EarthChem Database references, Lu-Hf data, oxygen isotope data, zircon saturation temperature data, and assimilation–fractional crystallization modeling

Geological Society of America Abstracts with Programs, 2020

Geological Society of America Abstracts with Programs, 2020