Neogene and Quaternary volcanism in Western Anatolia: Magma sources and geodynamic evolution

The Western Anatolia Miocene-to-Present Day magmatism evolved from calc-alkaline and shoshonitic rocks (21-16 Ma) to lamproites (16-14 Ma), and eventually into OIB-type magmas (2-0 Ma) represented by the Kula volcanics. In the calc-alkaline and shoshonitic association, Sr and Nd isotopic ratios and trace element variations suggest that the interaction with the crust was moderate, so that the geochemistry of these rocks is considered to reflect the heterogeneous chemical nature of their mantle source. The ultrapotassic and lamproitic rocks are characterised by a high Sr and low Nd isotopic composition and are strongly enriched in K and Rb with respect to Ba, indicating a phlogopite-bearing lithospheric source. Low Sr and high Nd isotopic compositions, together with low LILE/HFSE ratios, reveal the OIB-type nature of the Kula volcanics. Therefore, the products switch from supra-subduction orogenic suites to volcanics coming from sub-slab astenospheric mantle. The evolution is interpreted as being due to a 'horizontal' stretching of the slab (no slab pull break-off) generated by different velocities in the subduction hangingwall lithosphere. This triggered the extensional movement between Greece and Turkey and the stretching into two slabs of the NE-directed African subduction, due to the faster southwestward slab rollback of Africa underneath Greece relative to the slab segment below Cyprus and Anatolia.