The tectonostatigraphic evolution of the Huronian basement and the subsequent basin fill: geological constraints on impact models of the Sudbury event

Abstract

Abstract Whereas both meteorite impact and volcanic mechanisms have been proposed to explain the rocks and associated ore deposits within the Sudbury structure (1.85 Ga), few models take into consideration the paleogeographic constraints implied by the history of the region before, and following the “Sudbury event”. Huronian depositional style south of the Sudbury structure appears to have been strongly influenced by the early development of transtensional extensional basins. These basins were initiated by sinistral strike-slip movement along part of a Paleoproterozoic continental margin, which later evolved into a passive margin. Transition from a rifted strike-slip margin to a passive margin was accompanied by major slope failure and soft sediment deformation south of the Murray Fault. Diabase dikes were intruded into unconsolidated sediments at considerable depth, producing round-stone breccias, which are texturally similar to Sudbury breccia. Minor compressional folding occurred prior to emplacement of the Nipissing Diabase Suite at around 2.2 Ga. The abundance of diabase intrusions near the Sudbury structure suggests that the area may have been a focal point for magma emplacement. The post “event” fill of the Paleoproterozoic Sudbury Basin reflects initial deposition in a deep-water, anoxic setting. There is no evidence to suggest that sedimentation was influenced by the steep-walls of an impact crater. Carbonate in the basal, Vermilion Member is of sedimentary-exhalative origin and was not derived from a shallow marine shelf. Turbidites in the Chelmsford Formation show no evidence of centripetal fill as might be expected from a restricted, circular basin. They appear to have been emplaced along the depositional axis of an elongate foreland basin developed in front of the rising Penokean mountain chain. Penokean deformation continued after the “Sudbury event” and influenced strata well into the Archean Craton. Deformation of Huronian strata in paleovalleys north and west of the Sudbury structure does not appear to be genetically related to the “Sudbury event”. If “superfaults” were generated around the Sudbury structure in response to compression and crustal rebound following a meteorite impact, these do not appear to have caused offset of pre-existing steeply dipping contacts between the Huronian and underlying Archean basement. A new model, consistent with these observations needs to be developed.