Two-Stage Felsic Volcanism in the Western Part of the Southeastern Anatolian Orogen: Petrologic and Geodynamic Implications

摘要

We describe the petrogenesis of three phases of Late Oligocene to Middle Miocene felsic volcanism that occurred in the western part of the southeastern Anatolian orogen. All units are calc-alkaline. The S-type character of these volcanic rocks is supported by their peraluminous natures (A/CNK 1.11-3.14) and high (up to 9.89 percent) normative corundum contents. Elevated Rb/Sr ratios and low MgO and Fe_2o_(3total) of the first phase suggest that it might represent melts lacking entrained Fe-Mg-rich crystals, and that the magma developed by muscovite-dehydration melting. Relatively lower Rb/Sr ratios and higher Ba, Sr and Eu concentrations, and high zircon-saturation temperatures of the last two phases, indicate that these melts formed by water-saturated melting. The felsic volcanism of Southeast Anatolia wqs initiated during continental collision as a result of convergence between the Eurasian and Arabian plates, and occurred during both collisional and post-collisional periods. During the former, volcanism (the first phase) occurred by anatexis of the muscovite-bearing Piitiirge metamorphic rocks as a result of imbricate crustal thickening during the Late Oligocene-Early Miocene. In the Middle Miocene, continental exhumation and lithospheric fracturing caused partial fusion of the mantle beneath the Anatolian crust. Emplacement of hot, mantle-derived mafic melts in Anatolian lower crustal levels caused heating that led to partial melting, yielding felsic magmas of the second stage of volcanism (the last two phases).