The evidences of deep melting processes in xenolith bearing mafic rocks in Southern Thrace region: The new insights for peridotite and the pyroxenite source melting

   

The evidences of deep melting processes in xenolith bearing mafic rocks in Southern Thrace region: The new insights for peridotite and the pyroxenite source melting

       Xenolith bearing mafic rocks with late Miocene age are widely distributed in southern Thrace region. Primitive mantle - normalised multi-element diagrams of these mafic rocks display OIB signature and specific incompatible element ratios such as Nb/La (1.65-2.05) Nb/U (37.81 -48.74), Zr/Ba (0.45-0.72) further indicate that mafic rocks were originated from the OIB-like component. Re content of xenoliths range between 0.09 – 0.44 and similar with fertile mantle values (0.26 ppb) suggested by Morgan (1986), besides, xenoliths (0.1191-.0.1379) and the host rocks (0.1279-0.1439) have the similar   ¹⁸⁷Os/¹⁸⁸Os isotopic compositions.

        Geothermobarometric analyses of clinopyroxene (Putirka, 2008) from host basalts express that the melting source resides at an estimated depth of around 85 km. In addition, Gd/Yb ratios span between 0.97-3.3 in xenoliths and also span between 3.92-5.24 in basaltic rocks, suggest melting from a deep source.The mafic lavas of Thrace region with high Tb/Yb(N) values (2.33 – 3.16) seem to be derived from garnet bearing peridotite (Tb/Yb(N) >1.8 Wang et al., 2002) and these ratios also gain significant support from Dy/Yb values that range between 2-2.43 for xenoliths and 1.98-3.27 for host rocks. High Nb/U, Gd/Yb ratios, Re-Os isotopic compositions, and the REE-based melting model starting from the primitive xenoliths (from study region) and pyroxenite source (Van Nostrand, 2015) reveal that single source melting is not capable of producing   the mafic lavas, instead, these rocks appear to originate from the melting of the deeper part of the mantle rather than shallow asthenosphere.