RECORDS OF THE EVOLUTION OF MAGMATISM IN THE BIGA PENINSULA, WESTERN TURKEY

Turkey is an amalgamation of crustal fragments separated by large-scale suture zones due to the closure of branches of two ancient Tethyan realms. The Biga Peninsula in western Turkey exemplifies this complex geology, as it is a “tectonic mosaic”, comprised of crustal fragments and oceanic assemblages of different ages and origins .The Biga Peninsula is located north of the Izmir-Ankara suture zone, which, in general, marks the separation between units belonging to Gondwana to the south from those of Laurasia. The Peninsula is located within the Pontide orogenic belt, a ~1500 km section of the Alpine-Himalayan mountain chain that accumulated oceanic and continental units during the progressive closure of the Paleotethys during the Cimmeride Orogeny and from the closure of the Neotethys during the Alpide Orogeny. Biga Peninsula granites have been studied for their geochemistry and ages for decades and some of the bodies have well-constrained K-Ar and Rb-Sr ages and information about their volcanic-arc source. We seek to refine the understanding of the evolution of magmatism in the Biga Peninsula and elsewhere in the Aegean region by applying in thin section ion microprobe zircon and monazite geochronology coupled with detailed imaging of individual dated mineral grains and of entire rock thin sections. These methods shed significant insight into the magmatic history of these rocks and the meaning of their ages. We obtained ages from 3 plutons in the Biga region: the Kestanbolu, Eybek, and Kozak. Many of the granites have ages inconsistent a single population. We found ages of the Eybek pluton range from 34.3±4.8 Ma to 21.2±1.7 Ma. However, zircons from the Kestanbolu granite range from 28.4±3.2 to 12.5±3.6 Ma, with many Miocene results. The Kozak pluton is largely thought to be Oligo-Miocene, but this granite yields the widest range of ages, with Permian (287±26 Ma), Eocene (37.8±5.4 Ma), Oligocene (24.0±2.8 Ma), Miocene (19.6±1.5) to Late Miocene (10.3±2.4 Ma) zircons. The range of ages is consistent with CL images that show many fluid-induced textures. We suggest the methods applied here would be useful in understanding the role of magmatism in driving or recording extensional processes in the Aegean Region.