Calc-alkaline I-type plutons in the eastern Pontides, NE Turkey: U-Pb zircon ages, geochemical and Sr-Nd isotopic compositions

Abstract

The Koprubasi intrusion from the eastern Pontides of NE Turkey consists of granodiorite and monzogranite, and contains a number of mafic microgranular enclaves (MMEs). We report here U-Pb zircon age, geochemical and Sr-Nd isotopic data for these rocks in order to determining magma sources and magma production processes. On the basis of U-Pb zircon sensitive high-resolution ion microprobe dating (SHRIMP), the magma emplacement age of the granodiorite is 79.3 +/- 1.4 Ma. The rocks of the pluton are calc-alkaline, metaluminous to peraluminous characteristics, and display features of I-type granites. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) with negative Eu anomalies (Eu/Eu* = 0.60-0.76), but are depleted in high field strength elements (HFSE). They have small range of Sr-87/Sr-86((i)) (0.7067-0.7070) and epsilon(Nd(i)) (-3.2 to -4.4) values. Fractionation of plagioclase, hornblende and Fe-Ti oxides played an important role in the evolution of the Koprubasi intrusion. A relatively shallow intrusion depth (similar to 2-8 km) was estimated from the Al-in-hornblende geobarometry. All these characteristics, combined with the low values of K2O/Na2O, SiO2, Al2O3/(FeOT + MgO + TiO2) and (Na2O + K2O)/(FeOT + MgO + TiO2), suggest an origin by dehydration melting from a metabasaltic lower crustal source. (C) 2010 Elsevier GmbH. All rights reserved.