Influence of the Istranca-Rhodope Massifs and strands of the North Anatolian Fault on oil potential of Thrace Basin, NW Turkey

The Thrace Basin (NW Turkey) is an intermontane trough bounded to the north and west by the granitic and metamorphic rocks of the Istranca and Rhodope Massifs. Recent subsurface studies of the NW portion of the Thrace Basin h ave led to the identification of two trends in geothermal gradient, both of which are oriented approximately NW-SE (i.e. parallel to the depositional axis of the basin). Geological and geophysical data indicate that, due to t he thrust of the Istranca Massif upon the Rhodope Massif, the subsurface te mperature may have increased in the northern part of the basin. Other contr ols were wrench-fault activity of the Splays of the North Anatolian Fault ( SNAF) and continuing basinal subsidences. The thermal history of the southe rn part of the basin was affected by Miocene ophiolitic emplacement to the west in Greece. The presence of a belt of intrabasinal palaeotopography (ma inly Palaeozoic rocks) also contributed to increased geothermal gradients i n the southern part of the study area. The basin is divisible into northern and southern zones of subsidence, which are separated by the Kuleli-Babaes ki High. During the Oligocene, subsidence rates were highest in the norther n zone and in the western sector of the southern zone. Later, during the Mi ocene, basin subsidence was associated with intense tectonic activity of th e SNAF and with the emplacement of ophiolites to the west. A map of the top of the oil generation zone, based on TTI values calculated by the Lopatin method, indicates the presence of two maturation zones in the basin; these were separated by the Late Oligocene Kuleli-Babaeski High. Oil generation i n these zones was influenced by rapid subsidence, by a NW-SE oriented wrenc h fault system associated with the NAF and also by tectonic activity of the Istranca and Rhodope Massifs in the study area. (C) 2000 Elsevier Science B.V. All rights reserved.