Thrace Basin-An Oligocene Clastic Basin Formed During the Exhumation of the Rhodope Complex

Some orogenic sedimentary basins are difficult to assign to a particular category. An example is the hydrocarbon-bearing Thrace Basin in the northern Aegean. It has more than 9-km-thick Cenozoic clastic sediment, and is spatially associated with the Rhodope metamorphic core complex in the west, and with the Tethyan subduction-accretion complexes in the south, and is cut by the North Anatolian Fault and its precursors. It has been interpreted variously as an intramontane, a forearc, or an orogenic collapse basin. Here, we provide new geochronological and biostratigraphic data to constrain the tectonic evolution of the Thrace Basin. The new data indicate that as an individual depocenter the Thrace Basin has a short age span (late Eocene-Oligocene, 36-28 Ma) and more than 90% of the basin fill consists of early Oligocene (34-28 Ma) siliciclastic turbidites, deposited at rates of 1.0 km/my. Paleocurrents and new detrital zircon U-Pb ages show that the Rhodope Complex was the main sediment source. The exhumation of the northern Rhodope Complex (36-28 Ma) was coeval with the main subsidence in the Thrace Basin (34-28 Ma), and involved clockwise crustal rotation in the northern Aegean and possibly crustal flow from underneath the Thrace Basin. Crustal rotation is indicated by the paleomagnetic data, regional stretching lineations in the Rhodope Complex, and the triangular shape of the Thrace Basin. The rotating crustal block must have been bounded in the south by a sinistral fault zone; the location of which corresponds largely with the present day North Anatolian Fault.