Late Triassic acidic volcanic clasts in different Neotethyan sedimentary mélanges: paleogeographic and geodynamic implications

Abstract

U/Pb zircon dating and trace element geochemical analysis were performed on rhyolite clasts of different Middle Jurassic sedimentary mélanges from the Western Carpathian and Dinaric orogen. These igneous clast-bearing sedimentary successions were deposited on the westernmost passive margin of the Neotethys Ocean. During the latest Jurassic and Cretaceous, they became parts of different nappe stacks forming now the Inner Western Carpathians and some inselbergs within the Pannonian Basin. The Meliata nappe was stacked on the northern passive margin, while the Telekesoldal and Mónosbél nappes were part of the imbricated western–southwestern margin. U/Pb dating of the 100 m-sized rhyolite blocks and redeposited smaller clasts within the mélange, and fine-grained sediments formed two age groups: 222.6 ± 6.7 and 209.0 ± 9 Ma. Trace element geochemistry suggested within-plate continental volcanism as magma source. However, the measured ages are definitely younger than the classic, rift-related Anisian–Ladinian (238–242 Ma) magmatism, which was wide-spread along the western and southwestern margin of the Neotethys Ocean (e.g., Dolomites and different Dinaridic units). On the other hand, similarly, Late Triassic ages are reported from tuff intercalations from the Outer Dinarides and Western Carpathians, along with even more sparse effusive rocks of the Slovenian Trough. Trace element (incl. rare-earth element) analysis showed positive correlation between the mélange clasts and the in situ Late Triassic rhyolites of the Slovenian Trough. This newly established link between the mélange nappes in NE Hungary and the in situ Late Triassic rhyolites in the Slovenian Trough make a good opportunity to reconsider both Middle Jurassic paleogeography, and later tectonic deformations, which led to the separation of the source area and the redeposited clasts.