GRANULITE-FACIES METAMORPHISM IN THE ANATECTIC COMPLEX OF TOLEDO, SPAIN - LATE-HERCYNIAN TECTONIC EVOLUTION BY CRUSTAL EXTENSION

The Anatectic Complex of Toledo consists of a heterogeneous suite of high-grade metamorphic rocks, mainly granulitic migmatites of pelitic composition and orthogneisses, and different types of syn-orogenic granitoids with minor associated basic rocks. None of the metamorphic rock types records evidence of the early prograde history, and only the peak and retrograde P-T conditions can be estimated. The intrusion of the syn-orogenic granitoids is either slightly before or synchronous with the metamorphic climax. These rock types thus can be used to make P-T estimates of the peak and retrograde conditions. Microtextural analysis of reaction textures in conjunction with a petrogenetic grid, has enabled construction of an incomplete ''clockwise'' P-T path that is characterized by an isothermal decompression after or during the metamorphic peak temperatures. The peak estimates from different geothermobarometers are 800 degrees +/- 50 degrees C and 4-6 Kbar, the highest temperatures recorded in this part of the Iberian Hercynian Belt. It is proposed that this high-T/low-P metamorphism is at least partially related to an extensional process, possibly due to gravitational collapse of previously thickened crust.