Delamination Magmatism in Eastern Anatolia: A Geochemical Perspective

The Sr-Nd-Hf-Pb isotope geochemistry of the Late Miocene Tunceli Volcanics suggests that they are the products of mixed asthenospheric and lithospheric mantle melts. The combined elemental and mineral chemistry data additionally indicate that a pyroxenite component of lithospheric origin is involved in their genesis. Calculations favor melting depths of ∼2 GPa for the Tunceli lavas, that is, deeper than the current lithosphere-asthenosphere boundary beneath Eastern Anatolia. Geochemical data suggest that during regional Neo-Tethyan subduction, dense (i.e., pyroxenite-bearing) domains formed by progressive melt intrusion into the lower lithosphere resulted in gravitational instabilities. This unstable density configuration eventually led to the foundering of the eastern Anatolian lithosphere in the Late Miocene, resulting in progressive melting of fusible pyroxenite-bearing domains at asthenospheric depths. We demonstrate that these pyroxenitic melts mixed with ambient asthenospheric melts and generated the Tunceli lavas.