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

Abstract

We investigated the thermal history of the southern Marmara granitoids (Northern Kapıdağ, Southern Kapıdağ and Avşa Plutons), from the crystallization cooling to exhumation cooling, by using multiple geo-thermochronology 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 °C), Interval II: mid to mid-low temperatures (350–180 °C), and Interval III: mid-low to low temperatures (180–60 °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.