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Oligo-Miocene time is a critical tectonic period for western Anatolia, showing a drastic tectonic change from E-W trending compression to N-S trending extensional regime due to western movement of Anatolian Block. The rate of western movement has reduced and Simav, Gediz, Byk Menderes and Kçk Menderes grabens were formed in the Aegean Region. Magmatic evolution patterns are also associated with the geodynamic evolution of the region. To clarify these relationships between tectonic settings and magma series of Oligo-Miocene period, whole-rock geochemistry of Oligo-Miocene igneous activities around Simav Graben are documented. Based on major and trace element compositions, two distinct magma series have been described, as calc-alkaline (granitic, dacitic, andesitic) and alkaline (K-rich basaltic and lamproitic) series. In terms of the available geochronological data, it appears that alkaline series are younger (Early-Middle Miocene) than calc-alkaline series (Oligocene-Early Miocene). Calc-alkaline, silica-saturated to over-saturated; magmas are most probably related to relaxation phase of last stage of collision. The younger alkaline series are characterized by the high K/Na, MgO, Cr, Ni, Sc, V, Ba, Sr and Zr contents, reflecting to effect of an enriched mantle on their source domains. On the basis of magmatic geochemical signatures and related-tectonic regimes, we suggested that K-rich basaltic and lamproitic magmas with alkaline affinity may be an indicator for the initiation time of extensional regime and mantle melting in crust-mantle system, following the emplacement of the late-syn-collisional calc-alkaline magma series.
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