LITHOS, vol.119, pp.501-511, 2010 (SCI-Expanded)
Subduction/accretion complexes provide unique insight into the tectonic assembly of continental margins and oceanic basins, as they record the tectonic stacking and juxtaposition of materials derived from distinct tectonic environments. The Karakaya Complex, exposed throughout northern Turkey, is a good example of an ancient subduction/accretion complex that includes a number of pre-Liassic units that characterize the closure of Palaeotethys. Defining the components of this complex is of crucial importance to understanding the geodynamic evolution of Palaeotethys in the Eastern Mediterranean region. In this study, we explore the geochemistry of metabasic rocks within the Karakaya Complex, redefining and evaluating one of its main constituents, known as "the Nilufer Unit". New geochemical results combined with previously published data suggest that the Nilufer Unit is dominated by oceanic-island basalt (OIB)- and enriched mid-ocean ridge basalt (E-MORB)-type metabasic rocks which are variably enriched in the most highly incompatible elements relative to normal MORB (N-MORB). Associated alkaline OIB-type basalts are characterized by highly fractionated and variable rare earth element (REE) patterns ([La/Yb](N)=4.8-16.2), suggesting melting across the garnet spinel transition, derivation from a heterogeneous mantle source, and/or dynamic melting of a homogeneous source. Similar Nb/Y-Zr/Y systematics of spatially associated OIB- and E-MORB-type samples may indicate involvement of a shared enriched mantle source(s). Combining both geological and geochemical evidence, we suggest that the OIB- and E-MORB-type assemblages defining the Nilufer Unit represent seamounts and oceanic islands formed on Palaeotethyan oceanic crust, which was finally incorporated into a forearc accretionary prism during latest Triassic and became a component of the Karakaya Complex. (C) 2010 Elsevier B.V. All rights reserved.