U-Pb SIMS dating of synkinematic granites: timing of core-complex formation in the northern Anatolide belt of western Turkey

摘要

Secondary ion mass spectrometry (SIMS) U-Th-Pb dating of magmatic zircon from the synkinematic Egrigoz and Koyunoba granites and a leucogranite dyke dates core-complex formation in the northern Anatolide belt of western Turkey at 24-19 Ma. The granites intrude into the footwall of the Simav detachment and are strongly elongated in the NNE direction parallel to tectonic transport on the detachment. Although large parts of the granites are undeformed, localized mylonitic to ultramylonitic deformation occurs directly beneath the Simav detachment and preserves evidence of progressive deformation from ductile to brittle conditions. Oscillatory zoned rims of long-prismatic zircon from the Egrigoz and Koyunoba granites yield identical and well-constrained intrusion ages of 20.7 ± 0.6 Ma and 21.0 ± 0.2 Ma, whereas inherited grains range from Palaeoproterozoic (2972 ± 13 Ma) to Neoproterozoic (653 ± 6 Ma to 500 ± 5 Ma) in age. A leucogranite dyke yields an intrusion age of 24.4 ± 0.3 Ma, with inherited Neoproterozoic (640 ± 7 Ma to 511 ± 6 Ma) grains. Our data, in conjunction with published ~(40)Ar/~(39)Ar biotite ages, indicate very rapid cooling (greater than c. 200 ℃ Ma~(-1)) for the granites during and after synkinematic emplacement.