Structural and thermal evolution of high-grade areas in the northwestern parts of the Iberian massif

Composite dome structures are a common feature of the European Hercynide foldbelt in areas of all metamorphic grades. Where a dome is superimposed on an older nappe structure, the dominant foliation is inherited from the nappe and is refolded consistent with the domal shape. Where a dome is simply the result of refolding of an older anticline with steeply dipping axial surface the dominant foliation does not so clearly outline the domal shape. In the high-grade areas, thermal domes nearly coincide with structural antiforms or domes. The youngest mineral assemblages in the pelites are of low-pressure type such as andalusite-cordierite-sillimanite and are closely related to S-type granites, but an older, higher pressure event is recorded in relict garnet-staurolite-(kyanite) assemblages. An uplift P-T trajectory from about 750°C at more than 7 kb down to 690° to 750°C at about 6 to 5 kb has been deduced from thermobarometric estimates. Considering the P-T conditions as Upper Namurian on the basis of radiometric ages of synmetamorphic intrusions, an average uplift rate between 0.6 and 1.3 mm/yr can be calculated for the high-grade dome cores during the last stages of their history in the Namurian and Westphalian. -from Authors