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Fluid Flow, Brecciation, and Shear Heating on Faults: Insights from Carbonate Clumped-Isotope Thermometry

Swanson, E. M. and Wernicke, B. P. and Eiler, J. M. (2018) Fluid Flow, Brecciation, and Shear Heating on Faults: Insights from Carbonate Clumped-Isotope Thermometry. Tectonics, 37 (9). pp. 2938-2960. ISSN 0278-7407. doi:10.1029/2018TC004984.

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Slip on gently dipping detachments in the brittle crust has been enigmatic for decades, because fracture mechanics laws predict frictional resistance is too great for sliding to occur, except under rather unusual circumstances. The Miocene Mormon Peak detachment in Nevada and the Eocene Heart Mountain detachment in Wyoming are two well‐studied examples of upper crustal, carbonate‐hosted low‐angle detachments, with highly debated slip processes. Both low‐angle faults were active during regional magmatism, and a number of proposed slip mechanisms involve magmatic fluids, frictional heating, or both. To address the role that magmatic fluids and frictional heating may have played in reducing friction, we measured clumped‐isotope ratios on 137 carbonate samples from these faults. The majority of fault breccias and gouges on the detachment slip surface record temperatures that are colder than the host rock. Surprisingly, samples from within 5 m of the Heart Mountain detachment average just 65 °C, and not a single sample (out of 37 measurements, excluding metamorphosed host rock at White Mountain) records a temperature greater than 90 °C. Along both faults, most samples are depleted in δ^(18)O relative to the host rock, indicating that meteoric, not magmatic, fluids were present and interacting with the fault rock. However, a few samples preserve temperatures of over 160 °C, which, based on textural and geochemical criteria, are difficult to explain other than by frictional heating during slip. These temperatures are recorded in one sample directly on the Mormon Peak detachment slip surface and in two hanging wall localities above the Heart Mountain detachment.

Item Type:Article
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URLURL TypeDescription
Swanson, E. M.0000-0002-2238-010X
Wernicke, B. P.0000-0002-7659-8358
Additional Information:© 2018 American Geophysical Union. Received 7 FEB 2018; Accepted 4 AUG 2018; Accepted article online 17 AUG 2018; Published online 8 SEP 2018. We are indebted to two anonymous reviewers for comments that contributed substantially to the clarity of presentation. This research was supported by National Science Foundation grant EAR 12-50565 awarded to B. P. Wernicke and J. Eiler and by the Caltech Tectonics Observatory of the Gordon and Betty Moore Foundation. Data presented and discussed here are all in the tables and supplementary information presented in this manuscript.
Group:Caltech Tectonics Observatory
Funding AgencyGrant Number
NSFEAR 12-50565
Caltech Tectonics ObservatoryUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Issue or Number:9
Record Number:CaltechAUTHORS:20180820-083434380
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Official Citation:Swanson, E. M., Wernicke, B. P., & Eiler, J. M. (2018). Fluid flow, brecciation, and shear heating on faults: Insights from carbonate clumped‐isotope thermometry. Tectonics, 37, 2938–2960.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88945
Deposited By: Tony Diaz
Deposited On:20 Aug 2018 16:13
Last Modified:16 Nov 2021 00:31

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