Jurassic-Cretaceous magmatic arcs in the Eastern Black Sea: Evidence from geophysical studies and 2D modeling

Abstract

The origin, tectonic development, and lithosphere structure of the East Black Sea Basin (EBSB) are governed by the evolution of the northern branch of the Tethys ocean. The most spectacular features of its evolution could retain their imprints in geophysical fields and models, which we used to constrain a geophysical transect for the crust and upper mantle crossing the EBSB and the Shatsky Ridge (SR) from the Eastern Pontides to the Northern Caucasus. 2D gravity and magnetic modeling, constrained by wide-angle seismic data, revealed thin high-density and high-velocity sub-oceanic crust of the EBSB with the Moho shallowing up ~20 km depth. A spectacular feature of the Black Sea magnetic field is the Alushta-Batumi anomaly (ABA) above the SR that could be an imprint of subduction-related Middle Jurassic magmatic arc, whereas the Cretaceous (in Eastern Pontides) magmatic arc manifests itself by a chain of magnetic anomalies on the southern shoreline of the Black Sea. The high-velocity heterogeneity, revealed by seismic tomography, could be an image of a slab due to Mesozoic (Middle Jurassic and Cretaceous) subduction of the northern branch of Neotethys ocean. It shows rather a flat subduction slab that plunges northwards from subcrustal depths south of Eastern Pontide to the depth of > 70–80 km below the SR. Middle Jurassic and Cretaceous subduction fronts are located closely in the region of Eastern Pontides, whereas the related magmatic arcs are spaced differently – over the SR for the Middle Jurassic arc and along the southern coastline for Cretaceous Eastern Pontide magmatic arc correspondingly. The latter could be caused by the opening of the EBSB in the Cretaceous that separated the eastern segment of the BS onto the Eastern Pontides – Arkhangelsky Ridge and the SR – Northern Caucasus domains.