Excision and the original low dip of the Miocene-Pliocene Bannock detachment system, SE Idaho: Northern cousin of the Sevier Desert detachment?

摘要: Geologic mapping and structural analysis in the Bannock Range, SE Idaho, indicate that bulk of Cenozoic extension southeast Idaho was accommodated by slip on low-angle detachment system. The system consists normal faults with a likely N–S extent >130 km. It active from ca. 10.3 Ma to 3–4 >15 km top-to-the-WSW extension. master fault cuts steeper, older extensional folds its hanging wall. Crosscutting relationships prior work show wall began as cohesive block later broke up along either sole into or are cut fault. After breakup began, folded isostatically NNW-trending anticline, Oxford Ridge anticline. folding produced new listric east anticline replace back-tilted portion This excised part wall, hanging-wall structures, served secondary breakaway for detachment. West initiated slipped at low angle, is youngest system, has not been rotated low-dip angle through time. exhumed although somewhat smaller, shorter lived, more disrupted younger Basin Range faults, similar buried Sevier Desert beneath central Utah. Both top-to-the-west systems formed near transition between thrust belt hinterland, collapsed broad thrust-related culminations eroded Cambrian rocks, paired partly coeval top-to-east metamorphic core complexes ∼100–160 west, lie major ramps, angles most extended exhibit translation phase deformation. late age have voluminous lacustrine synrift deposits record saline alkaline conditions during early Similar processes both systems.