Provenance and magmatic-metamorphic evolution of a Variscan island-arc complex: constraints from U-Pb dating, petrology, and geospeedometry of the Kyffhauser crystalline complex, central Germany

The Kyffhäuser Crystalline Complex, Central Germany, forms part of the Mid-German Crystalline Rise, which is assumed to represent the Variscan collision zone between the East Avalonian terrane and the Armorican terrane assemblage. High-precision U–Pb zircon and monazite dating indicates that sedimentary rocks of the Kyffhäuser Crystalline Complex are younger than c. 470 Ma and were intruded by gabbros and diorites between 345 ± 4 and 340 ± 1 Ma. These intrusions had magmatic temperatures between 850 and 900°C, and caused a contact metamorphic overprint of the sediments at P–T conditions of 690–750°C and 5–7 kbar, corresponding to an intrusion depth of 19–25 km. At 337 ± 1 Ma the magmatic–metamorphic suite was intruded by granites, syenites and diorites at a shallow crustal level of some 7–11 km. This is inferred from a diorite, and conforms to P–T paths obtained from the metasediments, indicating a nearly isothermal decompression from 5–7 to 2–4 kbar at 690–750°C. Subsequently, the metamorphic–magmatic sequence underwent accelerated cooling to below 400°C, as constrained by garnet geospeedometry and a previously published K–Ar muscovite age of 333 ± 7 Ma. With respect to P–T–D–t data from surrounding units, rapid exhumation of the KCC can be interpreted to result from NW-directed crustal shortening during the Viséan.

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