Geochemistry and U–Pb zircon geochronology of metagranites in Istranca (Strandja) Zone, NW Pontides, Turkey: Implications for the geodynamic evolution of Cadomian orogeny

Abstract

New zircon U–Pb dating and whole-rock geochemical analysis were carried out on meta-intrusive rocks (Çatalca and İhsaniye metagranites) of the Istranca Zone, Western Pontides, with the aim of constraining the magmatic evolution of the Cadomian orogeny of the northern Gondwana margin during Late Precambrian–Early Paleozoic times. The Istranca zone is composed of metamorphic basement intruded by large granitic bodies and overlain by a Paleozoic–Mesozoic meta-sedimentary cover. The metamorphic rocks of the Istranca zone extend from Bulgaria, Istranca Mountains to NW Turkey and reach the area near Istanbul (Çatalca region).The Çatalca and İhsaniye metagranites have a subalkaline, high-K calc-alkaline and peraluminous character. Trace element geochemistry displays decreasing normalized concentrations from large-ion lithophile (LIL) elements to high field strength (HFSE) elements and from light (LREE) to heavy rare earth elements (HREE). A negative Eu anomaly is both types of metagranites. On tectonic discrimination diagrams, the samples from both metagranites plot in the subduction-related fields.The SHRIMP-II U–Pb zircon ages of the Çatalca metagranite range from 534.5±4.7Ma to 546.0±3.9Ma and LA-ICP-MS U–Pb zircon dating yields 535.5±3.6Ma age for the İhsaniye metagranite. The new ages together with the geochemical constraints allow a new geodynamic interpretation for the Istranca zone and we compare these metagranites with other Upper Ediacaran to Lower Cambrian granitoids of Turkey and Alpine–Himalayan orogenic belt. We deduce an origin of these elements from the northern Gondwana-Land margin.