The petrology of granitoids in the southeast Pertek (Tunceli)

The granitoid outcropping in the Pertek region, located to the North of Elazığ city. The Keban metamorphic rocks thrusted onto the granitoid and bothare unconcofmably overlain by Middle Eocene Kırkgeçit Formation It comprises a felsic to mafic range of rock tupes belonging to two sub-units: (1) a gabbroic dioritic sub-units and (2) a granitic sub-unit. The granitic sub-unit consists of tonalite, granodiorite and monzo-granite, while the gabbroic-dioritic sub-unit consists of gabbro, diorite, monzodiorite and quarzt monzodiorite. The granitic sub-unit have intruded into the gabbroic-dioritic sub-unit. The Pertek Granitoid comprises mafic microgranular enclaves. Holocrystalline and hypidiomorphic are charactersitic textures of the granitoid, but porphyritic, pertitic and graphic tectures are also shown. Whole rock major element contents are charesterized by SiO2 and K2O contents ranging from 47.61 to 76.03 wt% and 0.05 to 5.17 wt% respectively. Morever, Na2O and CaO contents renge of 1.61 to 5.56 wt% and 0.25 to 14.78 wt% respectively. There are negative correlations between SiO2 and CaO Al2O3 and Sr which suggest plagioclase fractionation or accumulation. MgO and FeO decrease with increasing SiO2 implying fractionation of ferromagnesian minerals such as biotitee and magnetite. Geochemically, the Pertek Granitoid is calc-alcaline, peraluminous and I type. A primitive mantle normalized multi element diagram displays a subduction zone magmatic signature for Pertek granitoid. A negative anomaly of some HFSE is revealedbypronounced troughs for Nb, Ta and Ti in the patterns. Likewise, the spike in Th reveals the enrichment of this element relative to HFSE such as Nb and Ta. Sr indicates a slight positive or negative anomaly which could be interpreted analogous to the Eu variations indicating plagioclase accumulation and fractionation. Low Dy/Yb ratio requires residual spinel in the source of the magma and indicates interaction of granitoid melts with spinel-amphibole lherzolite and spinel lherzolite thus origin from the spinel peridotite stability field. The trace element data of the Pertek Granitoid suggest a volcanic arc tectonic setting. The possible mechanism of Pertek Granitoid is the northdipping subduction of Neo-Tethyan southern branch during Late Cretaceous.