The evolution of Eastern Tornquist-Paleoasian Ocean and subsequent continental collisions: A case study from the Western Tatra Mountains, Central Western Carpathians (Poland)

The crystalline basement of the Tatra Mountains in the Central Western Carpathians, forms part of the European Variscides and contains fragments of Gondwanan provenance. Metabasite rocks of MORB affinity in the Tatra Mountains are represented by two suites of amphibolites present in two metamorphic units (the Ornak and Goryczkowa Units) intercalated with metapelitic rocks. They are interpreted as relics of ocean crust, with zircon delta O-18(VSMOW) values of 4.97-6.96 parts per thousand. Zircon REE patterns suggest oxidizing to strongly oxidizing conditions in the parent mantle-derived basaltic magma. LA-MC-ICP-MS U-Pb dating of magmatic zircon cores yields a crystallization age of c. 560 Ma, with inherited components at c. 600 Ma, corresponding to the Pannotia break-up event and to the formation of the Eastern Tornquist-Paleoasian Ocean. However, the zircon rims of both suites yield evidence for two different geological histories. Zircon rims from the Ornak amphibolites record two overgrowth phases. The older rims, dated at 387 +/- 8 Ma are interpreted as the result of an early stage of Variscan uplift while the younger rims dated at 342 +/- 9 Ma are attributed to late Variscan collisional processes. They are characterized by high delta O-18(VSMOW) values of 7.34-9.54 parts per thousand and are associated with migmatization related to the closure of the Rheic Ocean. Zircon rims from the Goryczkowa amphibolites yield evidence of metamorphism at 512 +/- 5 Ma, subsequent Caledonian metamorphism at 447 +/- 14 Ma, followed by two stages of Variscan metamorphism at 372 +/- 12 Ma and 339 +/- 7 Ma, the latter marking the final closure of the Rheic Ocean during late-Variscan collision. The presented data are the first direct dating of ocean crust formation in the eastern prolongation of the Tornquist Ocean, which formed a probable link to the Paleoasian Ocean. (C) 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.