Melville Island's salt-based fold belt (Arctic Canada)

[摘要] Melville Island lies astride the Cambrian through Devonian Arctic Platform, correlative rocks of the Franklinian Mobile Belt and, unconformable post-Devonian cover of the Sverdrup Basin. Seismic profiles and a revised geology map provide insight into Melville Island bedrock structure spanning a billion years of earth history to depths exceeding 20 km. Structures at the deepest levels include possible ?Precambrian crystalline basement and three ?Proterozoic seismic successions deformed and eroded prior to unconformable overlap by ?Lower Cambrian strata. Over a south to north distance of 300 km, the ?Cambrian through Devonian shelf-marginal wedge increases from 1200 m to at least 12500 m in thickness. The overlying Devonian clastic wedge (3000 to 4600 m) represents the depositional record of the ancestral Ellesmerian Orogeny. deformation that eventually terminated lower Paleozoic sedimentation. This southerly-directed deformation produced large contractional features on the island, and a salt-based fold belt that dominates surface structure. The fold belt is continuous downwards with: a seismically-imaged, folded and thrust faulted interval with up to 28 km (15%) horizontal shortening; a basal detachment at 5 km, and; an array of southerly- and northerly-transported thrusts most of which fail to appear at surface. Elements of a younger Ellesmerian deformation phase, recognized in surface cross-fold axes, are also mapped within the folded sub-salt succession below 5 km. Ellesmerian deformation continues to the west where style is related to slip on a ?mid-Cambrian detachment. Thrusts that ramp up to the sub-salt decollement have produced large anticlinoria near the present margin of the Sverdrup Basin. These faults have been repeatedly reactivated since the ?Precambrian. Recognized phases include: a N40-10$spcirc$W-directed Late ?Proterozoic extension; mid-?Cambrian growth faulting; two phase sinistral transpressive inversion of these extensional structures during the Ellesmerian Orogeny; northerly-directed rifting of Sverdrup Basin in the Carboniferous; inversion of the rift zone during the mid-Permian; evaporite diapirism and magmatic activity in the Jurassic and pre-Albian Cretaceous; southwesterly-directed sinistral transpressive adjustments coeval with the mid-Tertiary Eurekan Orogeny, and; a final phase of uplift and continuing seismicity.

[发布机构] Rice University

[效力级别] Geophysics