Granulite-facies metamorphism in the Anatectic Complex of Toledo, Spain: late Hercynian tectonic evolution by crustal extension

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Abstract
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 geo-thermobarometers are 800° ± 50 °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.