Structural analysis of compressional and extensional deformation within the Wood River and Milligen Formations, south-central, Idaho
- Univ. of Idaho, Moscow, ID (United States). Dept. of Geology and Geological Engineering
The Pennsylvanian to Permian Wood River Formation consists of calcareous and siliciclastic rocks that were deposited unconformably on argillaceous rocks of the Devonian Milligen Formation. The original depositional contact between the two formations is preserved locally; however, the contact was also mapped as a thrust, a normal fault, a reactivated thrust with a normal sense of movement, and as a sheared unconformity with an indeterminate sense of movement. Early reverse movement with northeast tectonic transport along the Milligen-Wood River contact is documented by mesoscopic and microscopic field evidence, including Riedel shears, drag folds, angular relations of cleavage in the fault plane, and oriented thin sections. Faults that separate middle Wood River in the upper plate from upper Wood River in the lower plate are also associated with this early phase of thrusting. Tertiary extensional deformation resulted in high-angle and low-angle normal faulting with some reactivation of Mesozoic thrusts. High-angle fault have normal, dip-slip or normal, obliquie-slip movements. Low-angle normal faults with north-west to southwest tectonic transport cut the Milligen and Wood River Formations, as well as units within the Tertiary Challis Volcanics. The movement sense on the normal faults in documented by drag folds, the angular relation of extension joints relative to the fault plane, shear steps, and oriented thin sections. Faults that separate younger sequences of the Wood River in the upper plate from older sequences in the lower plate are also associated with this phase of normal faulting.
- OSTI ID:
- 5024844
- 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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