First U–Pb zircon and (U-Th)/He apatite ages of the Paleo-Tethys rocks in the Strandja Massif, NW Turkey: implications from newly identified serpentinite body

The Paleozoic evolution of the Paleo-Tethys (NW Turkey) remains unclear due to lack of sufficient geological and geochronological data from the Strandja Massif. In the present contribution, we provide new geological, petrographical, geochemical, and first zircon LA-ICP-MS (U–Pb) and apatite (U-Th)/He age data from the ultramafic and mafic metamorphic rocks, remnants of the Paleo-Tethys in the Strandja Massif. The ultramafic and mafic metamorphic rocks in the Karaçoban area (Lalapaşa, NW Thrace) are the host serpentinite body located in contact with the surrounding gneisses, and hornblend-hornfels, chloritite, and amphibolite bands as the blackwall-rocks of metasomatized mantle peridotite. Of these, the chloritite has unusually high zircon contents, which contrast with the usual lack of this mineral in ultramafic rocks. The LA-ICPMS zircon geochronology of chloritites gives clue for two main age clusters, dated at 360 ± 2.2 Ma and 316.6 ± 2.5 Ma, which most probably correspond to its magmatic crystallization and metamorphism. The application of Ti-in-zircon thermometer (T ZT ) reveals crystallization temperatures ranging from 696 to 852 °C for the chloritite. Seven apatite crystals of the chloritite yielded (U-Th)/He (AHe) ages from 33.3 ± 2.1 to 56.1 ± 5.6 Ma. The AHe ages are not scattered and tightly clustered with a weighted average of 46.4 ± 2.9 Ma. This age could be interpreted that the ultramafic and mafic metamorphic rocks of the Strandja Massif exhumed and cooled in the Lutetian time at ~ 65 to 70 °C. The studied ultramafic and mafic metamorphic rocks represent igneous protoliths in an oceanic ridge extensional setting associated with the Upper Paleozoic opening of the Paleo-Tethys.