The Tertiary Thrace basin of SE Bulgaria and NE Greece: a review of petrological and mineralogical data of sedimentary sequences

Sandstone petrology and detrital heavy mineral geochemistry have been widely used to investigate the post-collisional magmatism that followed the closure of the Vardar Ocean, the Alpine deformation and the orogenic collapse of the Rhodopian terranes, and its influence during the deposition of Upper Eocene-Oligocene sediments of the north and western portions of the Thrace basin. Beside the important amount of clastic sediments eroded from the Rhodope and Circum Rhodope terranes, volcanoclastic sediments are well represented in the area and offer a good opportunity to constrain the evolution of Thrace basin. Petrography of sediments allows discriminating among three distinct petrofacies reflecting multiple provenance from different tectonic settings as they evolve from quartzolithic to quartzofeldspathic to volcanoclastic compositions, corresponding to collisional orogen, crustal block uplift, and volcanic arc settings, respectively. Beside of the deposition of siliciclastic material, volcanic contributions from both, basic-intermediate and acid products represent an important source of sediments in the area. Despite of dominant intermediate to acid volcanic products, volcanic lithic fragments in sandstones (microlithic, lathwork and brown vitric textures) indicate main inputs from intermediate and basic products. Detrital amphibole and pyroxene chemistry is used to characterize the supply of volcanic material and understand the role played by basic and felsic volcanism in the infill of the north and western Thrace basin. This study demonstrates how Tertiary sandstone compositional shifts in the Thrace basin in NE Greece and SE Bulgaria are strictly related to various geodynamic stages of the Rhodope region.