Coeval calcalkaline, adakitic, and ultrapotassic Eocene magmatism in Central-Eastern Anatolia: Implications for the syn- to post-collisional tectonics in the region

The central-eastern Anatolian region includes a wide range of syn- to post-collisional Paleocene to Eocene magmatic rocks. On a regional scale, these rocks are here grouped as (1) the post-collisional Eocene magmatic rocks that occur along the Pontides, (2) the syn- to post-collisional Paleocene-Eocene magmatic rocks associated with the foreland basins developed along the İzmir-Ankara and Inner Tauride suture zones, (3) the Eocene magmatic rocks associated with the Maden Basin to the southeast, (4) the small outcrops of Eocene granitoid plutons and volcanic rocks developed in an N-S trend along the Sivas and Malatya regions which is the main scope of this study. In this study, we focused on the (2) and (4) group rocks.

The Eocene magmatic rocks between the Sivas and Malatya comprise (1) basaltic volcanics and gabbroic to dioritic plutons derived from subduction-modified mantle sources, (2) andesitic rocks that have differentiated from the basaltic magmas via crystal fractionation and mixing processes, (3) adakitic rhyolites produced by the melting of lower crustal lithologies possibly in response tobasic underplating. The basaltic rocks were derived from the shallow melting of depleted lithospheric mantle sources, which were metasomatised by subduction-related components. This N-S trending Eocene magmatism may have originated from a zone of weakness inherited from the transform fault-related deformations in the upper plate, which was related to the Subduction-Transform Edge Propagator (STEP) faulting at the western margin of the Late Cretaceous Baskil-Hınıs arc.

The Eocene ultrapotassic rocks exposed in the Ulukışla and Sivas basins along the Inner Tauride suture zone, however, were derived from more fertile and deeper mantle sources with contributions from the asthenosphere, which have been highly contaminated by subduction-related processes, possibly by the Late Cretaceous continental subduction. This magmatic activity was related to slab-break-off processes developed shortly after the latest Cretaceous collision.