Thermo-mechanical role of a Cambro-Ordovician paleorift during the Variscan collision: the NE margin of the Bohemian Massif

The Stare Mesto (SM) belt (NE margin of the Bohemian Massif) represents a p reserved example of an intracontinental Cambro-Ordovician rift that has bee n shortened during the Variscan orogeny. The rifted sequence consists of ga bbroic intrusions and a leptyno-amphibolite complex of Cambro-Ordovician pr otolith age. The latter suffered medium pressure, granulite facies, Cambro- Ordovician metamorphism associated with extension in a continental protorif t, The Variscan tectonometamorphic event is manifested by convergent orogen esis with syn-convergent intrusion of a Carboniferous tonalitic sill, high temperature-medium pressure compressional deformation of gabbros and high t emperature: metamorphism of peridotites, Numerical thermal and theological modelling suggests that the SM paleorift after 140 Ma of cooling represented a stiff heterogeneity between an easter ly situated Cadomian continent and a westerly lying Variscan orogenic root zone. Carboniferous underplating of the paleorift by tonalitic magma was pr obably responsible for the thermal weakening of both the upper mantle and t he mafic lower crust, and the subsequent uplift of the remaining rigid part of the Cambro-Ordovician crust, All the units were later deformed in trans pressional heterogeneous greenschist facies regime at a supracrustal level. (C) 2001 Elsevier Science B,V. All rights reserved.