The Hart Mountain Overthrust and Associated Structures in Park County, Wyoming

Dake, C. L.

doi:10.1086/622560

Cited by 14 publications

(6 citation statements)

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“…1) was first recognized by Eldridge (1894) and was described again by Fisher (1906). Further study revealed more apparent klippen to the west with similar structural characteristics, leading Dake (1918) to suggest emplacement by thrust faulting. The observation that the hanging-wall structure primarily reflects horizontal extension led Bucher (1947) to suggest that the allochthon, comprising Paleozoic blocks, was emplaced rapidly as discontinuous "individual fragments," perhaps in response to seismic activity antecedent to volcanism.…”

Section: Introductionmentioning

confidence: 84%

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

Swanson

Wernicke

Hauge³

2016

The Journal of Geology

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A B S T R A C TThe 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 crosscutting 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 faultrelated 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.

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Section: Introductionmentioning

confidence: 84%

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

Swanson

Wernicke

Hauge³

2016

The Journal of Geology

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“…General features of the Heart Mountain fault have been described by Dake (1918), Hewett (1920), Bucher (1933Bucher ( , 1940, Pierce (1941Pierce ( , 1957Pierce ( ,1960, Voight (1974), and Prostka (1978); detailed mapping of the fault and of the areal extent of the upper plate have been pub lished (see fig. 1 for references).…”

Section: Introductionmentioning

confidence: 98%

Clastic dikes of Heart Mountain fault breccia, northwestern Wyoming, and their significance

Pierce¹

1979

Professional Paper

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Description of dikes at specific sites-Continued Introduction ___________________________________ 1 Area 3, north of Republic Mountain ______________13 General features of the Heart Mountain fault____________ 3 Area 4, south of Pilot Creek __________________13 Clastic dikes of fault breccia_-_-__-________________ 3 Area 5, north of Jim Smith Peak_________________15 General features of clastic dikes in upper-plate Area 6, near White Mountain _ _____ ____ _______17 carbonate rocks_____________________________ 4 Area 7, west of Trout Creek __________________18 General features of clastic dikes in volcanic rocks ______ 4 Other sites of clastic dikes._____________________20 Description of dikes at specific sites _______________ 5 Breccia and brecciation produced by the Heart Mountain fault __20 Area 1, south of Silver Gate, Mont. _______________ 5 Mechanism of dike injection ____________________21 Calcibreccia dikes in Paleozoic rocks of Geologic significance of the clastic dikes __ _________ _23 the upper plate _________________________ 5 Summary __________________________________24 Calcibreccia dikes in the Wapiti Formation-______ 6 Acknowledgments _________________________-24 Area 2, southeast of Silver Gate, Mont.______________10 References cited _________________________24 Formation. Thus, calcibreccia dikes in the Cathedral Cliffs and Lamar River Formations show a sharp contact because the country rock solidified prior to fault movement, whereas calcibreccia dikes in the Wapiti Formation in many instances show a transitional or semifluid contact because the country rock was still unconsolidated or semifluid at the time of dike injection.

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“…The very long runout of the HML over an extremely shallow dipping slope is a physical enigma that seemingly violates simple mechanistic considerations of a block sliding down a tilted slope. For this reason probably, despite early discovery of the upper plate block structures by Dake [1918], their identification as erosional remnants of a much larger gravity‐driven slide structure was made only later by Pierce [1957].…”

Section: Introductionmentioning

confidence: 99%

The long runout of the Heart Mountain landslide: Heating, pressurization, and carbonate decomposition

2010

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[1] The Heart Mountain landslide of northwestern Wyoming is the largest subaerial landslide known. This Eocene age slide slid ∼50 km along a shallow 2°slope, posing a long-standing enigma regarding its emplacement mechanism. We suggest here a mechanism for the catastrophic emplacement of the Heart Mountain landslide that is independent of slide triggering. The mechanism is a feedback between shear heating, thermal pressurization, and thermal decomposition of carbonates at the slide shear zone. Such a feedback arises when a porous, fluid-filled shear zone heats up because of frictional sliding. If the shear zone is confined, the generated heat leads to pore pressure rise, which in turn reduces frictional resistance to sliding, leading to acceleration. Temperatures at the shear zone quickly reach the decomposition temperature of carbonates. Since the shear zone of the Heart Mountain slide is located within a dolomite layer, it is expected that thermal decomposition of dolomite occurred within the Heart Mountain shear zone. This prediction is supported by ample field evidence for carbonate decomposition during the emplacement. Simulation of the sliding dynamics of the Heart Mountain block, accounting for feedback between shear heating, thermal pressurization, and thermal decomposition of carbonates, successfully reproduce the travel distance of the Heart Mountain block. The simulation results also predict that the maximum sliding velocity ranged between tens of meters per second to more than 100 m s −1 (depending on model assumptions) and that the duration of sliding was of the order of a few tens of minutes, in agreement with previous assessments.

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The Hart Mountain Overthrust and Associated Structures in Park County, Wyoming

Cited by 14 publications

References 0 publications

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

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

Clastic dikes of Heart Mountain fault breccia, northwestern Wyoming, and their significance

The long runout of the Heart Mountain landslide: Heating, pressurization, and carbonate decomposition

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