Medicine Lodge thrust system, east-central Idaho and southwest Montana

Ruppel, E.T.

doi:10.3133/ofr76366

Cited by 17 publications

(62 citation statements)

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“…First, Cretaceous thrusting dismantled the original crater and transported the fragment now exposed some distance to the east (Skipp, 1988;Ruppel, 1978 (Magloughlin and Spray, 1992). These fault surfaces are commonly oriented in relation to major structural features in the area (e.g., Magloughlin, 1989).…”

Section: Impact or Tectonic Pseudotachylites?mentioning

confidence: 99%

Pseudotachylites of the Beaverhead impact structure: Geochemicaly geochronological, petrographic, and field investigations

Fiske¹,

Hargraves²,

Onstott³

et al. 1992

Geological Society of America Special Papers

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Dikes and pods of pseudotachylite up to one meter thick have been found over an area >50 km 2 in the same area as shatter cones and other possible features of shock metamorphism in the Beaverhead and Tendoy Mountains in southwestern Montana, defining the allochthonous remains of the Beaverhead impact structure (see also Hargraves et al., Chapter 19, this volume). They are not associated with any tectonic feature in the area and have several features uncommon in pseudotachylites formed by tectonic processes (large size, vesicles, pseudotachylite clasts within pseudotachylite), but which have been documented in pseudotachylites from other impact structures. Rare single sets of planar deformation features (PDFs) are found in quartz grains in the pseudotachylites with crystallographic orientations similar to those found in shocked quartz from other impact structures. The major and trace element chemistry of the pseudotachylites is similar to their host rocks, but with some enrichments (Al, Mg, Fe, K, volatiles) and depletions (Si, Na) indicating low-grade metasomatic alteration. 40 Ar/ 39 Ar laser microprobe analyses of pseudotachylites from three localities show a wide spectrum of ages, from Precambrian to Tertiary. The distribution of ages suggests two isotopic signatures, one of Precambrian age (although younger than the age of the protoliths), and the other of Cretaceous age. 29 Si Magic angle spinning (MAS) nuclear magnetic resonance (NMR) studies of the pseudotachylite failed to detect the presence of highpressure polymorphs of quartz.The evidence suggests that these pseudotachylites were formed by the same event that formed the shatter cones. Related work (see Hargraves et al., Chapter 19, this volume) suggests that the original crater was at least 75 km in diameter and was formed in the late Proterozoic to Cambrian, 20 to 150 km to the west of the present location.

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Section: Impact or Tectonic Pseudotachylites?mentioning

confidence: 99%

Pseudotachylites of the Beaverhead impact structure: Geochemicaly geochronological, petrographic, and field investigations

Fiske¹,

Hargraves²,

Onstott³

et al. 1992

Geological Society of America Special Papers

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“…These faults bound the west side of eastward-tilted Paleozoic fault block (Ruppel, 1982;Scott et al, 1985) and the east side of half-gaben structures (Anders et al , 1989). The footwall of the faults consists of allochthonous paleozoic and Precambrian rocks that were transported east to northeastward on gently dipping thrust faults, from as early as the early Cretaceous and continued into the early Eocene (Ross, 1947;Skipp and Hait, 1977;Ruppel, 1978). Thrust faulting was followed by Eocene and Oligocene volcanism and the development of northeast-striking late Cenozoic normal faults (Baldwin, 1951).…”

Section: Northern Basin and Range Provincementioning

confidence: 99%

Site-specific probabilistic seismic hazard analyses for the Idaho National Engineering Laboratory. Volume 1: Final report

1996

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“…The potential for hydrocarbon reserves in eastcentral Idaho and southwestern Montana has been reviewed by Scholten (1967), Ruppel (1978), Skipp (1979), Perry and others (1981), and Perry and others (1983), and is considered low to moderate. The oil and gas potential for the Italian Peak Roadless Areas is considered low for the reasons discussed below.…”

Section: Oil and Gasmentioning

confidence: 99%

Mineral resource potential map of the Italian Peak and Italian Peak Middle Roadless Areas, Beaverhead County, Montana, and Clark and Lemhi counties, Idaho

Skipp¹,

Antweiler²,

Kulik³

et al. 1983

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Medicine Lodge thrust system, east-central Idaho and southwest Montana

Cited by 17 publications

References 0 publications

Pseudotachylites of the Beaverhead impact structure: Geochemicaly geochronological, petrographic, and field investigations

Pseudotachylites of the Beaverhead impact structure: Geochemicaly geochronological, petrographic, and field investigations

Site-specific probabilistic seismic hazard analyses for the Idaho National Engineering Laboratory. Volume 1: Final report

Mineral resource potential map of the Italian Peak and Italian Peak Middle Roadless Areas, Beaverhead County, Montana, and Clark and Lemhi counties, Idaho

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