Thermal histories of Cenozoic southern Marmara granitoids from emplacement to exhumation: Implications for tectono-thermal evolution of NW Anatolia (Türkiye)

We investigated the thermal history of the southern Marmara granitoids (Northern Kap & imath;dag, Southern Kap & imath;dag and Avs,a Plutons), from the crystallization cooling to exhumation cooling, by using multiple geothermochronology methods that included zircon U-Pb, biotite 40Ar/39Ar, apatite and zircon (U-Th)/He dating as well as geothermobarometry calculations. The geothermobarometry calculations and zircon U-Pb dating indicate that they were emplaced into mid-crustal levels (13.5 to 8.8 km) during the middle to late Eocene (48-37 Ma). The integrated multiple geo-thermochronological dataset yields similar t-T paths for each pluton, which were divided into three distinct intervals: Interval I: high to mid temperatures (800-350 degrees C), Interval II: mid to mid-low temperatures (350-180 degrees C), and Interval III: mid-low to low temperatures (180-60 degrees C). Interval I is characterized by steep t-T paths showing that the plutons reached mid-temperature levels by rapid cooling during the middle to late Eocene (48-35 Ma). Interval II, on the other hand, is distinguished by skewed t-T paths along the mid- to low temperatures, implying a deceleration in the cooling rates. Finally, in Interval III, the t-T paths steepen again, indicating rapid exhumation in the early Oligocene (32-28 Ma). We infer that the Eocene rapid cooling was most likely induced by bottom-up extension (slab break-off or convective removal of the lithosphere) while the early Oligocene rapid exhumation of NW Anatolia was triggered by the back-arc extension resulting from the rollback of the subducting African slab along the Hellenic trench system, which has migrated southward in time.