Role of pre-rift rheology in kinematics of extensional basin formation: constraints from thermomechanical models of Mediterranean and intracratonic basins

Abstract

The role of pre-rift rheology on the kinematics of extensional basin formation is examined. Constraints obtained on the effective elastic thickness and level of necking, inferred from forward modelling of a number of Alpine/Mediterranean basins (including the Gulf of Lion margin, the Valencia Trough, the Tyrrhenian Sea and the Pannonian Basin), are interpreted in terms of the pre-rift rheology of the lithosphere underlying these basins. The Gulf of Lion/Tyrrhenian Sea basins and the Pannonian Basin appear to be end-members in terms of the inferred depth levels of necking. The models support the existence of spatial variations in crustal and lithospheric strength, as inferred from previous rheological modelling for other segments of the European lithosphere, and provide constraints on the ratio of crustal and subcrustal strength during extension. The results of these studies are compared with predictions on the kinematics of extension for a number of intracratonic basins, including the Black Sea basins, the Transantarctic Mountains/Ross Sea and Saudi Arabian Red Sea margins, and the Baikal and East African rifts. The kinematics of extension appears to be largely controlled by the (transient) thermal regime of the pre-rift lithosphere and the crustal thickness distribution. These usually result from orogenic processes operating on the lithosphere before extensional basin formation. Predictions are made for the level of external forces required to initiate rifting in intracratonic and Alpine/Mediterranean settings. The models also shed light on the relative parts played by far-field versus near-field stresses and inferred variations in strain rate during the evolution of these basins.