Early Mesozoic rift basins of eastern North America and their gravity anomalies: The role of detachments during extension (original) (raw)

Two end-member models of extension involving detachments have been developed. One model incorporates a fault that soles at midcrustal level overlying a broad region of pure shear in the lower crest. The second, referred to as the simple shear model, includes a detachment continuing through the entire crest and terminating in a region of concentrated extension in the lower crest. Both models predict basins with no localized thermal effect. With the inclusion of flexural isostasy, both models predict footwall uplift whose amplitude and wavelength are controlled by the detachment geometry and the lithospheric strength. A gravity anomaly over the hanging wall block distinguishes the simple shear model from the intracmstal detachment model. The early Mesozoic basins of the eastern North America, believed to have formed as the result of the normal-slip reactivation of a Paleozoic thrust system as the Atlantic opened, are associated with distinctive hanging wall gravity highs. These gravity highs, the basin geometry, the lack of a thermal subsidence phase in the rift basins, and the presence of a highly extended and heated region to the east, suggest that the simple shear model may be