Wyoming Geological Association: 1982 Luncheon Meetings Casper, Wyoming: Abstracts of Papers

The current models of the Belt Basin have evolved largely from prevailing interpretations of western Montana as a static craton margin receiving seidments in a slowly subsiding trough from 1450 to 850 mybp (Harrison, 1972; 1974; 1980; McMannis, 1965; Mudge, 1970). Seidmentation and subsidence were in perfect balance for 600 my. A model is presented for the structural evolution of the Belt Basin in a dynamic plate-tectonic setting. Deposition of Belt sediments was initiated in an aulacogen created during the rifting of Panamberia (1500-1450 mybp). A westward shift in the spreading zone created a remnant basement block, the Purcell Platform. A subduction zone developed along the western craton margin (1200-1100 mybp) as the eastern margin converged with the Grenville terrane. Attendant vulcanism resulted in the Purcell lava deposition. The Kootenay arch was accreted by rafting as a tectonostratigraphic terrane (1000-900 mybp). New rifting (850 mybp) resulted in Windermere deposition. A Phanerozoic wedge of mostly carbonate rocks was deposited on the Belt rocks. Compressive events resulted from the collision of tectonostratigraphic terranes rafted during middle and late Phanerozoic subduction. Deformation included thrusting of Belt over Phanerozoic strata, creating potential oil and gas reservoirs beneath a thrust belt, which must be extended west at least to the Montana/Idaho border.