Styles Of Extension Offshore Mid-norway And Implications For Mechanisms Of Crustal Thinning At Passive Margins

摘要

Eocene magmatic breakup along the mid-Norway rifted margin was preceded by extreme Jurassic-Cretaceous crustal thinning in a magma-poor environment. Along the SE borders of the rift, "top basement" detachment faults with heaves on the order of 15-40 km evolved in at least two stages to become the boundaries between moderately thinned (20-30 km thick) crust and a 100-200 km wide, highly extended area with crustal thicknesses generally between 2 and 12 km under the present-day More and V0ring basins. In the footwalls of the basin flank detachments, lower and middle crust was exhumed in extensional domes that became incised by a younger set of normal faults. Under the most highly thinned areas, a more distal set of deep-seated (basin floor) detachments incised and extended remnant crust and, probably, the upper mantle, leaving as little as <5 km of continental crust to be preserved under thick synrift and postrift deposits. We suggest that basin flank detachments such as the ones described above hold the potential to reduce the crustal thickness down to the critical value required for embrittlement of continental crust. Thus, they prepare the ground for incision by the basin floor detachments, which may become responsible for exhumation of deep crust or continental mantle if extension is allowed to proceed.