Metamorphic Evolution of Chloritoid-Bearing Micaschist from the Variscan Elstergebirge: Evidences for Stacking of High-Pressure Rocks in the Saxothuringian Zone of Central Europe

A chloritoid-garnet-bearing micaschist from the southern part of the Elstergebirge was studied to better understand the Variscan orogenic evolution in the Saxothuringian zone of the northwestern Bohemian Massif. Based on the textural relations and compositions of minerals, especially of zoned garnet and potassic white mica, a P-T path was reconstructed using contoured P-T pseudosections. The U-Th-Pb dating of monazite in the micaschist was undertaken with the electron microprobe. The micaschist experienced P-T conditions along a clockwise path between 16 kbar at 510 ℃ and 5 kbar at 555 ℃ followed by isobaric heating to about 600 ℃. Monazite ages range between 315 and 480 Ma with the most prominent maxima and side maxima at 346.0±1.1(2σ), 357.3±2.3, and 368.3±1.7 Ma. Ages older than 380 Ma were related to detrital monazite pointing to a Devonian sedimentary protolith. Other ages around 325 Ma were assigned to the isobaric heating by nearby post-tectonic granites. The high-pressure event, being the result of the collision of Laurussia and Gondwana after closure of the Rheic Ocean, occurred in the Late Devonian. The exhumation to 15-20 km(5 kbar) ended probably in the Early Carboniferous. The high-pressure micaschists from the Fichtelgebirge to the Erzgebirge crystalline complexes are suggested to represent a single nappe within a metamorphic nappe pile. This nappe is composed of metasedimentary slices, which experienced different peak pressures rather than representing a coherent crustal section.