Petrology and geodynamic setting of metagabbroic rocks within Tokat meta-morphic massif (Amasya, NE Turkey)

The Eastern Black Sea Mountain Belt geographically corresponds to the northeastern part of Turkey and constitutes one of the essential parts of the Alpine-Himalayan Belt. Its Pre-Jurassic geodynamic evolution is still controversial due to lack of systematical geological, geochemical and geochronological data. This study focuses on the petrology and geodynamic setting of the Pre-Jurassic metagabbroic bodies cutting Tokat metamorphic massif exposed in the southern part of Amasya that is situated in the southwestern corner of the Eastern Black Sea Mountain Belt and presents new geological, petrographical and whole rock geochemical data from these metagabbroic rocks. The studied bodies occur as small-scaled intrusions within the Tokat metamorphic massif. Contact metamorphism and forcefull injection traces are common in wall rocks. They can be divided into two main subgroups as amphibole-rich and pyroxene-rich metagabbros. However, both groups display very similar geochemical characteristics to each other, indicating that they were derived from same magma source. Metagabbroic rocks are characterized by high concentrations of TiO2 (3.53-6.52 wt.%), Na2O (1.4-5.45 wt.%), Zr (230-442 ppm), Nb (42.1-104 ppm) and also light rare earth elements. Their primitive mantle and chondrite-normalized trace and rare earth element distribution diagrams are consistent with OIB-type basalts, suggesting an ocean island basalt-like magma source in their petrogenetic evolution. Considering all geological, petrographical and geochemical data, it is clear that the studied metagabbroic rocks were generated from an ocean island basalt-like asthenospheric mantle source in the back-arc region of Eastern Black Sea Mountain Belt during the Late Permian-Early Triassic.