Nanoscale Textural and Chemical Evolution of Silica Fault Mirrors in the Wasatch Fault Damage Zone, Utah, USA

Houser, Leah M.; Ault, Alexis K.; Newell, Dennis L.; Evans, James P.; Shen, Fen‐Ann; Devener, Brian Van

doi:10.1029/2020gc009368

Cited by 4 publications

(3 citation statements)

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“…has performed multiple analyses of tectonic lamellae and, notably, never observed amorphous silica associated with tectonic lamellae in quartz grains [40][41][42][43][44]. In addition, Houser et al [45] described finding tectonically-formed, nano-to micro-scale amorphous silica particles and nanofilms along active fault planes, but they reported no quartz grains with fractures containing amorphous silica. Multiple studies have observed amorphous silica within fractures, but only in impact-related shocked quartz and not in tectonic deformation lamellae [9,14,19].…”

Section: Key Analytical Studies Of Shock Fracturesmentioning

confidence: 99%

Microstructures in shocked quartz: linking nuclear airbursts and meteorite impacts

Hermes,

Wenk,

Kennett

et al. 2023

Airbursts and Cratering Impacts

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Many studies of hypervelocity impact craters have described the characteristics of quartz grains shock-metamorphosed at high pressures of >10 GPa. In contrast, few studies have investigated shock metamorphism at lower shock pressures. In this study, we test the hypothesis that low-pressure shock metamorphism occurs in near-surface nuclear airbursts and that this process shares essential characteristics with crater-forming impact events. To investigate low-grade shock microstructures, we compared quartz grains from Meteor Crater, a 1.2-km-wide impact crater, to those from near-surface nuclear airbursts at the Alamogordo Bombing Range, New Mexico in 1945 and Kazakhstan in 1949/1953. This investigation utilized a comprehensive analytical suite of high-resolution techniques, including transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Meteor Crater and the nuclear test sites all exhibit quartz grains with closely spaced, sub-micron-wide fractures that appear to have formed at low shock pressures. Significantly, these micro-fractures are closely associated with Dauphiné twins and are filled with amorphous silica (glass), widely considered a classic indicator of shock metamorphism. Thus, this study confirms that glass-filled shock fractures in quartz form during near-surface nuclear airbursts, as well as crater-forming impact events, and by extension, it suggests that they may form in any near-surface cosmic airbursts in which the shockwave is coupled to Earth’s surface, as has been proposed. The robust characterization of such events is crucial because of their potential catastrophic effects on the Earth’s environmental and biotic systems.

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Section: Key Analytical Studies Of Shock Fracturesmentioning

confidence: 99%

Microstructures in shocked quartz: linking nuclear airbursts and meteorite impacts

Hermes,

Wenk,

Kennett

et al. 2023

Airbursts and Cratering Impacts

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“…The active trace of the WFZ is expressed within Quaternary sediments (Figure 1b), but a ∼300–400 m‐wide fault damage zone crops out within the footwall of the southern Brigham City segment. This damage zone hosts chlorite breccia and phyllonite, rare gouge, Fe‐oxide rich cataclasite a few to tens of millimeters in thickness, disseminated Fe‐oxide alteration, abundant ∼mm‐thick specular hematite (specularite) veins and FMs (Evans & Langrock, 1994), and silica‐rich FMs (Houser et al., 2021). Hematite FMs and veins are observed as principally distributed in the damage zones of mesoscale normal faults subsidiary to the trace of the active WFZ (McDermott et al., 2017).…”

Section: Wasatch Fault Zone and Hematite Fault Mirrorsmentioning

confidence: 99%

Microscale Spatial Variations in Coseismic Temperature Rise on Hematite Fault Mirrors in the Wasatch Fault Damage Zone

et al. 2023

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Coseismic temperature rise activates fault dynamic weakening that promotes earthquake rupture propagation. The spatial scales over which peak temperatures vary on slip surfaces are challenging to identify in the rock record. We present microstructural observations and electron backscatter diffraction data from three small‐displacement hematite‐coated fault mirrors (FMs) in the Wasatch fault damage zone, Utah, to evaluate relations between fault properties, strain localization, temperature rise, and weakening mechanisms during FM development. Millimeter‐ to cm‐thick, matrix‐supported, hematite‐cemented breccia is cut by ∼25–200 μm‐thick, texturally heterogeneous veins that form the hematite FM volume (FMV). Grain morphologies and textures vary with FMV thickness over μm to mm lengthscales. Cataclasite grades to ultracataclasite where FMV thickness is greatest. Thinner FMVs and geometric asperities are characterized by particles with subgrains, serrated grain boundaries, and(or) low‐strain polygonal grains that increase in size with proximity to the FM surface. Comparison to prior hematite deformation experiments suggests FM temperatures broadly range from ≥400°C to ≥800–1100°C, compatible with observed coeval brittle and plastic deformation mechanisms, over sub‐mm scales on individual slip surfaces during seismic slip. We present a model of FM development by episodic hematite precipitation, fault reactivation, and strain localization, where the thickness of hematite veins controls the width of the deforming zones during subsequent fault slip, facilitating temperature rise and thermally activated weakening. Our data document intrasample coseismic temperatures, resultant deformation and dynamic weakening mechanisms, and the length scales over which these vary on slip surfaces.

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“…These high-gloss, light-reflective slip surfaces are composed of layered nano particles to micro particles that can form at seismic to subseismic slip rates (e.g., Siman-Tov et al, 2013;Verberne et al, 2013;Pozzi et al, 2018). Fault mirrors have been observed in a variety of rock types, including carbonate, siliciclastics, basalt, granite, hematite, and chert, and they occur at a variety of scales (square millimeter to greater than square meter surface area; Power and Tullis, 1989;Fondriest et al, 2013;Evans et al, 2014;Kuo et al, 2016;Borhara and Onasch, 2020;Houser et al, 2021). Some processes invoked for generating fault mirrors include thermal decomposition, melting, gel lubrication, frictional grinding and nanoparticle lubrication, crystal plastic deformation and recrystallization, and/or asperity flash heating (e.g., Collettini et al, 2013;Kirkpatrick et al, 2013;Smith et al, 2013;Pozzi et al, 2018;Ault et al, 2019;Han et al, 2011;De Paola et al, 2011).…”

Section: ■ Introductionmentioning

confidence: 99%

Seismicity recorded in hematite fault mirrors in the Rio Grande rift

et al. 2021

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Exhumed fault rocks provide a textural and chemical record of how fault zone composition and architecture control coseismic temperature rise and earthquake mechanics. We integrated field, microstructural, and hematite (U-Th)/He (He) thermochronometry analyses of exhumed minor (square-centimeter-scale surface area) hematite fault mirrors that crosscut the ca. 1400 Ma Sandia granite in two localities along the eastern flank of the central Rio Grande rift, New Mexico. We used these data to characterize fault slip textures; evaluate relationships among fault zone composition, thickness, and inferred magnitude of friction-generated heat; and document the timing of fault slip. Hematite fault mirrors are collocated with and crosscut specular hematite veins and hematite-cemented cataclasite. Observed fault mirror microstructures reflect fault reactivation and strain localization within the comparatively weaker hematite relative to the granite. The fault mirror volume of some slip surfaces exhibits polygonal, sintered hematite nanoparticles likely created during coseismic temperature rise. Individual fault mirror hematite He dates range from ca. 97 to 5 Ma, and ~80% of dates from fault mirror volume aliquots with high-temperature crystal morphologies are ca. 25–10 Ma. These aliquots have grain-size–dependent closure temperatures of ~75–108 °C. A new mean apatite He date of 13.6 ± 2.6 Ma from the Sandia granite is consistent with prior low-temperature thermochronometry data and reflects rapid, Miocene rift flank exhumation. Comparisons of thermal history models and hematite He data patterns, together with field and microstructural observations, indicate that seismicity along the fault mirrors at ~2–4 km depth was coeval with rift flank exhumation. The prevalence and distribution of high-temperature hematite grain morphologies on different slip surfaces correspond with thinner deforming zones and higher proportions of quartz and feldspar derived from the granite that impacted the bulk strength of the deforming zone. Thus, these exhumed fault mirrors illustrate how evolving fault material properties reflect but also govern coseismic temperature rise and associated dynamic weakening mechanisms on minor faults at the upper end of the seismogenic zone.

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Nanoscale Textural and Chemical Evolution of Silica Fault Mirrors in the Wasatch Fault Damage Zone, Utah, USA

Abstract: Earthquake nucleation and propagation involves a dramatic reduction in dynamic fault strength (e.g., Scholz, 1998). Fault weakening mechanisms identified in natural rocks and deformation experiments include mineral decomposition and dehydration (

Cited by 4 publications

References 79 publications

Microstructures in shocked quartz: linking nuclear airbursts and meteorite impacts

Microstructures in shocked quartz: linking nuclear airbursts and meteorite impacts

Microscale Spatial Variations in Coseismic Temperature Rise on Hematite Fault Mirrors in the Wasatch Fault Damage Zone

Seismicity recorded in hematite fault mirrors in the Rio Grande rift

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