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Hematite (U-Th)/He thermochronometry detects asperity flash heating during laboratory earthquakes

Gabriele Calzolari, Alexis K. Ault, Greg Hirth and Robert G. McDermott
Hematite (U-Th)/He thermochronometry detects asperity flash heating during laboratory earthquakes
Geology (Boulder) (March 2020) 48 (5): 514-518

Abstract

Evidence for coseismic temperature rise that induces dynamic weakening is challenging to directly observe and quantify in natural and experimental fault rocks. Hematite (U-Th)/He (hematite He) thermochronometry may serve as a fault-slip thermometer, sensitive to transient high temperatures associated with earthquakes. We test this hypothesis with hematite deformation experiments at seismic slip rates, using a rotary-shear geometry with an annular ring of silicon carbide (SiC) sliding against a specular hematite slab. Hematite is characterized before and after sliding via textural and hematite He analyses to quantify He loss over variable experimental conditions. Experiments yield slip surfaces localized in an approximately 5-30-mu m-thick layer of hematite gouge with <300-mu m-diameter fault mirror (FM) zones made of sintered nanoparticles. Hematite He analyses of undeformed starting material are compared with those of FM and gouge run products from high-slip-velocity experiments, showing >71%+ or -1% (1sigma ) and 18%+ or -3% He loss, respectively. Documented He loss requires short-duration, high temperatures during slip. The spatial heterogeneity and enhanced He loss from FM zones are consistent with asperity flash heating (AFH). Asperities >200-300 mu m in diameter, producing temperatures >900 degrees C for approximately 1 ms, can explain observed He loss. Results provide new empirical evidence describing AFH and the role of coseismic temperature rise in FM formation. Hematite He thermochronometry can detect AFH and thus seismicity on natural FMs and other thin slip surfaces in the upper seismogenic zone of Earth's crust.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 48
Serial Issue: 5
Title: Hematite (U-Th)/He thermochronometry detects asperity flash heating during laboratory earthquakes
Affiliation: Utah State University, Department of Geosciences, Logan, UT, United States
Pages: 514-518
Published: 20200318
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 32
Accession Number: 2020-030422
Categories: GeochronologySeismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Respository item 2020148
Illustration Description: illus.
Secondary Affiliation: Brown University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 2020
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