Abstract
Evolution of contractional structures in northern Idaho; Part 1, Constraints from regional restorable sections
Abstracts with programs - Geological Society of America, Vol.32(5), p.35
Geological Society of America, Rocky Mountain Section, 52nd annual meeting
03/2000
Abstract
Seismic profiles, structural sections, and regional geologic relations allow the trajectory of the basal decollement dipping west beneath the northern Rocky Mountain orogen to be estimated. Sections normal to the Rocky Mountain front suggest a significant difference in depth to the basal decollement north and south of the Lewis-Clark Shear Zone (LCSZ). Strike-sections through the LCSZ point to a west-northwest oblique ramp system that steps the decollement down to the southwest. North of the LCSZ, the basal decollement reaches depths of 12 to 15 km in northern Idaho and eastern Washington. The decollement is overlain by imbricated Belt Supergroup and Paleozoic rocks of low metamorphic grade in the east and extends west beneath high-grade metamorphic tectonites. The metamorphic rocks were uplifted from mid- to lower-crustal depths during Late Cretaceous contraction and exhumed during Eocene extension. South of the LCSZ, the decollement reaches mid-crustal depths 100 to 200 km farther east than comparable structures to the north. Metamorphic tectonites formed at mid- to lower-crustal depths and plutonic rocks of the Bitterroot lobe of the Idaho batholith were uplifted during regional shortening in the Late Cretaceous and were involved in Eocene extension along their eastern margin. The north to south increase in depth to the basal decollement is marked by the west-southwesterly dipping basement ramp which may have a surface expression corresponding to the Trans-Idaho discontinuity. North of the basement ramp, the hanging-wall geometry is complicated and forms a large-scale duplex. The duplex has a lower plate assemblage composed of imbricated metamorphic tectonites overlain by a north-dipping upper plate consisting of imbricated metasedimentary rocks. The upper- and lower-plate assemblages of the duplex are deformed in superposed northerly and west-northwest trending folds, related to easterly tectonic transport across the oblique-ramp system. The geometry and juxtaposition of rocks of different rheologic properties in the duplex apparently controlled the nucleation of younger structures relaying extensional displacement between the Priest River and Bitterroot extensional complexes.
Details
- Title: Subtitle
- Evolution of contractional structures in northern Idaho; Part 1, Constraints from regional restorable sections
- Creators
- J. S Oldow - University of IdahoWilliam C McClelland
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.32(5), p.35
- Conference
- Geological Society of America, Rocky Mountain Section, 52nd annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, Rocky Mountain Section, 52nd annual meeting
- Language
- English
- Date published
- 03/2000
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240907002771
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