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In central and eastern Anatolia, volcanism related to continental collision occurred in Neogene to Quaternary times. Major-and trace-element compositions,87Sr86/Sr and K-Ar ages were determined for volcanic rocks from selected volcanoes in this region.87Sr86/Sr for basalts from Erciyes volcano in the eastern part of central Anatolia, as well as Ararat, Nemrut and Karacadag volcanoes in eastern Anatolia are in the range 0.7035–0.7040. These ratios are higher than those of N-type MORB but overlap arc volcanic rock values. This suggests that the mantle source, which was possibly contaminated by fluids and melts with higher87Sr86/Sr during the pre-collisional events, has similar Sr isotopic compositions in wide areas of the eastern part of central Anatolia and eastern Anatolia, even across the collision plate boundary. In addition, chemical compositions of the mantle source are not homogeneous with respect to HFS element contents, indicating that the slab-derived components resulting from past subductions are not homogeneously distributed. The mantle source beneath the western part of central Anatolia, which corresponds to the transitional region from collision tectonics in the east to subduction tectonics in the west, has different chemical and Sr isotopic signatures from other parts of Anatolia. In the western part of central Anatolia, the87Sr86/Sr of basaltic rocks from three regions characterized by monogenetic volcanoes are in the range 0.70427 to 0.70581 and differ from region to region, in spite of indistinguishable chemical compositions. This indicates either source heterogeneity on a small scale, or different contributions of local crustal contaminants. Calc-alkaline lavas from Ararat and Kars in eastern Anatolia have chemical compositions with subduction signatures inherited from pre-collision subduction events. In contrast, the chemical and Sr isotopic features of volcanic rocks from Erciyes volcano in central Anatolia indicate that the combined process of fractional crystallization of basaltic magma and crustal assimilation, without injection of slab-derived components, is the dominant process generating calc-alkaline andesite, under the collision tectonics regime operating in this region. |
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