Geochronological and geochemical investigations on high-pressure rocks and their host rocks from the Odenwald-Spessart and Erzgebirge basement, Variscides

• Applicant: Professor Dr. Thomas Michael Will, Ph.D.
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 443033070

The focus of this project is to determine the age of metamorphic and igneous rocks from two high-pressure basement areas in the Saxothuringian Zone of the Variscan Orogen in Germany: (i) the Odenwald-Spessart basement, which is part of the Mid-German Crystalline Zone and, (ii) the Erzgebirge basement. Despite the importance of the two basement areas for the reconstruction of the geodynamic evolution prior to and during the Variscan orogeny, the age of high-pressure metamorphism in both areas is currently only poorly known and ranges from c. 360 to 330 Ma in the Odenwald-Spessart and c. 380 to 330 Ma in the Erzgebirge. The planned study aims to resolve this uncertainty by determining U-Pb isotope data of zircon, rutile and monazite from different lithologies of the two basement areas. The data should provide more precise information about the timing of peak metamorphism and possibly also about the cooling history of the rocks. In addition, zircon Lu-Hf data, together with whole rock Sm-Nd isotope data, can be used to determine the provenance of the samples (either Baltica- or Gondwana-derived) and may help to better locate the position of the Rheic Suture within the Mid-German Crystalline Zone, whose position in currently debated. Furthermore, a petrological, geochemical and isotope geochemical study of felsic and mafic igneous rocks is planned to characterize the source region and the tectonic setting in which the precursor melts of these rocks formed. In addition, zircon oxygen isotope data will also be determined towards achieving this aim. The Odenwald-Spessart and Erzgebirge basement areas are characterized by large volumes of late-orogenic felsic to intermediate igneous rocks. It is to be expected that the igneous rocks formed as a result of a large thermal anomaly. However, the origin of this anomaly is entirely unclear and may have been caused by a plume head or may have been related to slab break-off during the final amalgamation of the Variscan orogen. Our new data may help to shed some light on the cause of these large volumes of melts.

• DFG Programme: Research Grants
• International Connection: China
• Cooperation Partners: Professor Dr. Xianhua Li; Professor Dr. Qiuli Li; Dr. Xiaoxiao Ling