Estimates of Late Cenozoic extension, east-central Idaho
- Utah State Univ., Logan, UT (United States). Dept. of Geology
Late Cenozoic normal faults define the southwest flanks of the Lost River, Lemhi and Beaverhead Ranges in east-central Idaho. Cross sections and structural analysis suggest that throws along the central parts of the Lost River and Lemhi faults range from about 2 to 5 km. If the Beaverhead fault has a similar throw, then Miocene to Recent extension of east-central Idaho ranged 5 to 15%. However, three additional Late Cenozoic normal faults (the Hawley Mountain, Goldburg and Barney faults) bound a NW-trending horst between the Lost River and Lemhi Ranges in the Hawley Mountain and Donkey Hills area. The horst-bounding normal faults are inferred to have formed during Late Cenozoic time because: (1) the faults parallel the NW to NNW strike of Late Cenozoic normal faults in the region, (2) scattered Quaternary fault scarps coincide with the Barney fault, (3) steep topographic fronts define parts of the Goldburg and Hawley Mountain faults, (4) the Hawley Mountain fault displaces two Eocene normal faults, and (5) gravity lows are present in the hanging walls of the Barney and Goldburg faults. Left-lateral separation across the inferred NE-dipping Barney fault suggests 2--3 km of throw, assuming dip-slip displacement. Throw across the Goldburg fault, which uplifts Oligocene basin-fill deposits in its footwall, is at least 500 m. Although two of the horst-bounding normal faults have not offset Quaternary surficial deposits, estimated slip across these faults have not offset Quaternary surficial deposits, estimated slip across these faults is similar to slip across the prominent range-front faults in the region. Therefore, estimated Late Cenozoic extension of east-central Idaho along a NE-SW cross section through the Hawley-Goldburg horst is about 10 to 20%.
- OSTI ID:
- 5022760
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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