TY - JOUR
T1 - Thermochronometric and textural evidence for seismicity via asperity flash heating on exhumed hematite fault mirrors, Wasatch fault zone, UT, USA
AU - McDermott, Robert G.
AU - Ault, Alexis K.
AU - Evans, James P.
AU - Reiners, Peter W.
N1 - Funding Information:
This work was supported by NSF-EAR 1419828 to AKA, JPE, and PWR. RGM, AKA, and JPE acknowledge support from the Utah State University Presidential Doctoral Research Fellowship and a field scholarship from the Tobacco Root Geological Society. We thank Fen Ann Shen and Uttam Chowdhury for analytical assistance, Tony Lowry and Ravi Kanda for helpful discussions during computer code development, and Dennis Newell for providing comments on an earlier version of the manuscript. We thank Dr. Richard Ketcham, an anonymous reviewer, and editor An Yin for comments that greatly improved the clarity of the manuscript.
Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2017/8/1
Y1 - 2017/8/1
N2 - Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U–Th)/He data patterns from these surfaces and host rock apatite (U–Th)/He data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time–temperature histories. Temperatures of >∼700–1200 °C, depending on asperity size, are sufficient to induce 85–100% He loss from hematite within 200 μm of the fault surface. Spatially-isolated, high-temperature microtextures imply spatially-variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (Mw≈−3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes.
AB - Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U–Th)/He data patterns from these surfaces and host rock apatite (U–Th)/He data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time–temperature histories. Temperatures of >∼700–1200 °C, depending on asperity size, are sufficient to induce 85–100% He loss from hematite within 200 μm of the fault surface. Spatially-isolated, high-temperature microtextures imply spatially-variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (Mw≈−3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes.
KW - Hematite (U–Th)/He thermochronometry
KW - Wasatch fault
KW - dynamic weakening
KW - earthquakes
KW - fault mirrors
KW - hematite microtextures
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U2 - 10.1016/j.epsl.2017.04.020
DO - 10.1016/j.epsl.2017.04.020
M3 - Article
AN - SCOPUS:85018934463
SN - 0012-821X
VL - 471
SP - 85
EP - 93
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -