U-Pb zircon and K-Ar geochronology reveal the emplacement and cooling history of the Late Cretaceous Beypazari granitoid, central Anatolia, Turkey

The Beypazari granitoid has been studied with respect to multi-radiometric dating and oxygen isotopic geothermometry. Radiometric dating of the granitoid yields zircon U-Pb isochron ages ranging from 72.5 +/- 12.6 to 78.6 +/- 4.7, and K-Ar ages of 71.4 +/- 2.8 to 74.9 +/- 2.9 and 59.5 +/- 2.2 to 75.4 +/- 2.9 Ma for hornblende and biotite, respectively. Oxygen isotope thermometry for the granitoid gives temperatures of 550 +/- 25 degrees C to 605 +/- 30, 390 +/- 15 to 540 +/- 25 degrees C, and 481 +/- 5 to 675 +/- 10 degrees C, for hornblende, biotite, and K-feldspar, respectively, when paired with quartz. The systematic differences among ages according to different techniques used on different minerals are used to reconstruct the cooling history of the granite. The results yield rapid cooling rates of 33.3 degrees C/Ma from 800 degrees C to 550 degrees C, and slow cooling rates of about 15 +/- 0.5 C/Ma from 550 to 300 degrees C. Rapid subsolidus cooling between 600 degrees C and 550 degrees C is documented by Ar-40/Ar-39 ages on amphibole and biotite between 71.4 +/- 2.8 and 75.4 +/- 2.9 Ma. Younger ages on biotites from two samples (59.5 +/- 2.2 and 64.4 +/- 2.5) are probably caused by loss of Ar. The reason for this possible Ar loss can be interpreted as slower subsolidus cooling (+/- 375 degrees C) ages. There is an apparent spatial and temporal relationship between the intrusion-cooling of the Beypazari granitoid and the evolution of the Izmir-Ankara-Erzincan ocean belonging to the northern Neo-Tethyan ocean domain