Multiple phases of Tertiary extension and synextensional deposition of the Miocene–Pliocene Salt Lake Formation in an evolving supradetachment basin, Malad Range, southeast Idaho, U.S.A.

摘要: The extensional history of the Malad and Bannock ranges in southeast Idaho northern Utah involves multiple phases Tertiary normal faulting synextensional deposition. Detailed geologic mapping, structural stratigraphic analyses, geochronologic data from this study elucidate previously defined deformational events region, define two new episodes. The largest-magnitude extension took place along low-angle faults ∼10–4-Ma detachment system, with concurrent sedimentation Miocene–Pliocene Salt Lake Formation a regionally continuous supradetachment basin. This basin developed by ∼10.2 Ma, was preceded smaller-magnitude, aerially restricted sedimentation. In Henderson Creek quadrangle southern Range, earliest event involved ∼8% north–south during deposition Paleocene–Eocene Wasatch (?) Formation. conglomerate unit deposited an asymmetric, south-tilted half-graben bounded on south syntectonic Willow Spring fault. The next pre-detachment produced north-striking, east-tilted which Middle to Late Miocene Skyline Member (∼11.9–10.2 Ma) as ash-rich alluvial fan. is east Red Knoll Trail faults. Detrital zircon age tuffaceous sandstone bed suggest incorporation reworked zircons ∼12.5–15-Ma Owhyee-Humboldt volcanic field southwest 10.3-Ma glass. The inception regional system recorded breakup ∼16% west-southwest its hanging wall set north- north–northwest-striking These were associated Cache Valley (∼10.2− <9.2 regional-scale lake system. During deposition, northeast-dipping Steel Canyon fault accommodated uplift intrabasinal horst that shed wedge Third eastward into between ∼10.0 Ma. interfingers lake-margin tufa-bearing facies, changes deeper-water, micritic limestone-bearing facies. The most recent ∼9% east–west north-striking Pliocene–Quaternary fault. A segment boundary fault, consisting 2.5–3.5-km-wide relay ramp formed right-stepping en echelon segments, lies just north Idaho-Utah border. addition, broad, north–northwest-trending antiformal zone folds present half area interpreted double-rollover anticline progressively time above oppositely dipping listric