Geochemical and isotopic signatures of the KurtogluMeta-Granite (Gümüshane)

Gümüşhane area is one of the locations where Variscan metamorphic basement rocks are cropped out. These metamorphic rocks, which expose in an area of ~0.3-3 km width and about 28 km long, extend from the vicinity of Kırıklı Village in the southwest direction to Tersun Mountain. They were metamorphosed under low to medium degrees of regional metamorphic conditions in the early-middle Carboniferous. The rocks that are termed Kurtoğlu Metamorphites consist of two tectonic units: (i) mica schist, gneiss and cros-cutting meta-granites, (ii) phillite and calc schist. The meta-granites, chosen as the topic of this study, were investigated in terms of petrographical, geochemical and geochronological characteristics. The rocks petrographically can be divided into two subgroups: mucovit meta-granite and biotite meta-granite. The ages obtained by U-Pb SHRIMP method in the zircons of the biotite meta-granite sample (KU-35) are vary from 511 Ma to 452 Ma (late Cambrian-late Ordovician). While the muscovit meta-granites are grouped at the felsic end of the compositional range (SiO2= % 72.8−77.8), the biotite meta-granites display relatively a large compositional range (SiO2= % 67.46−78.44). Except for the two biotite-meta-granite samples that have granodioritic composition, all the samples have granitic composition. The samples as a whole have strongly peraluminous geochemical character, a geochemical composition ranging from high K-calcalkaline to shoshonitic and include normative corundum varying between 1.02 and 4.41. Some of the biotite meta-granite samples comprise garnet and sillimanite that are typical for S-type granites/rhyolites. The samples have highly radiogenic Sr isotope ratios (0.712-0.745), negative εNd(t) values (-5.13 ̶ -8.55) and Pb isotope ratios, referring precisely to a source located in the continental crust. CaO/Na2O, Al2O3/TiO2, Rb/Sr and Rb/Ba ratios suggest that biotite and muscovite meta-granites were derived by partial melting of clay-poor and clay-rich sources respectively. Decreasing MgO, Fe2O3 and TiO2 contents against increasing SiO2 imply that fractional crystallization has played a significant role during the formation of the Kurtoğlu meta-granite and that muscovite meta-granites were evolved from a biotite meta-granitic melt through fractional crystallization. Despite the slightly right-side inclined rare earth element profiles, negative Nb, Ta, Ti and positive Pb anomalies imply subduction-related tectonic setting, tectonic setting discrimination diagrams commonly refer to the syn-collision and post-collision settings during their formation.