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Episodic Dissolution, Precipitation, and Slip along the Heart Mountain Detachment, Wyoming

Swanson, Erika and Wernicke, Brian P. and Hauge, Thomas A. (2016) Episodic Dissolution, Precipitation, and Slip along the Heart Mountain Detachment, Wyoming. Journal of Geology, 124 (1). pp. 75-97. ISSN 0022-1376. http://resolver.caltech.edu/CaltechAUTHORS:20160415-074945846

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Abstract

The Heart Mountain allochthon is among the largest landslide masses in the rock record. The basal fault, the Heart Mountain detachment, is an archetype for the mechanical enigma of brittle fracture and subsequent frictional slip on low-angle faults, both of which appear to occur at ratios of shear stress to normal stress far below those predicted by laboratory experiments. The location of the detachment near the base of thick cratonic carbonates, rather than within subjacent shales, is particularly enigmatic for frictional slip. A broad array of potential mechanisms for failure on this rootless fault have been proposed, the majority of which invoke single-event, catastrophic emplacement of the allochthon. Here, we present field, petrographic, and geochemical evidence for multiple slip events, including cross-cutting clastic dikes and multiple brecciation and veining events. Cataclasites along the fault show abundant evidence of pressure solution creep. Banded grains, which have been cited as evidence for catastrophic emplacement, are associated with stylolitic surfaces and alteration textures that suggest formation through the relatively slow processes of dissolution and chemical alteration rather than dynamic suspension in a fluid. Temperatures of formation of fault-related rocks, as revealed by clumped isotope thermometry, are low and incompatible with models of catastrophic emplacement. We propose that displacement along the gently dipping detachment was initiated near the base of the carbonates as localized patches of viscous yielding, engendered by pressure solution. This yielding, which occurred at very low ratios of shear stress to normal stress, induced local subhorizontal tractions along the base of the allochthon, raising shear stress levels (i.e., locally rotating the stress field) to the point where brittle failure and subsequent slip occurred along the detachment. Iteration of this process over geological time produced the observed multikilometer displacements. This concept does not require conditions and materials that are commonly invoked to resolve the stress paradox for low-angle faults, such as near-lithostatic fluid pressures or relative weakness of phyllosilicates in the brittle regime. Cyclic interaction of viscous creep (here by pressure solution) and brittle failure may occur under any fluid pressure conditions and within any rock type, and as such it may be an attractive mechanism for slip on “misoriented” fault planes in general.


Item Type:Article
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http://dx.doi.org/10.1086/684253DOIArticle
http://www.journals.uchicago.edu/doi/10.1086/684253PublisherArticle
ORCID:
AuthorORCID
Wernicke, Brian P.0000-0002-7659-8358
Additional Information:© 2016 University of Chicago Press. Manuscript received October 31, 2014; accepted September 9, 2015; electronically published January 8, 2016. This research was supported by National Science Foundation grant EAR 12-50565 awarded to B. P. Wernicke and J. Eiler and by the Gordon and Betty Moore Foundation.
Funders:
Funding AgencyGrant Number
NSFEAR 12-50565
Gordon and Betty Moore FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20160415-074945846
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160415-074945846
Official Citation:Erika Swanson, Brian P. Wernicke, and Thomas A. Hauge, "Episodic Dissolution, Precipitation, and Slip along the Heart Mountain Detachment, Wyoming," The Journal of Geology 124, no. 1 (January 2016): 75-97. DOI: 10.1086/684253
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66201
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:16 Apr 2016 17:47
Last Modified:01 Feb 2017 00:54

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