U-Pb SHRIMP Zircon Ages, Geochemical and Sr-Nd Isotopic Compositions of the Late Cretaceous I-type Sariosman Pluton, Eastern Pontides, NE Turkey

Abstract

The petrogenesis and U-Pb SHRIMP zircon ages of the Late Cretaceous Sariosman pluton in the Eastern Pontides is investigated by means of whole-rock Sr-Nd isotope data with field, petrographic and whole-rock geochemical studies. The bulk of the I-type Sariosman pluton consists of biotite-hornblende monzogranite, with minor quantities of porphyritic hornblende-biotite monzogranite. The biotite-hornblende monzogranite contains a number of mafic microgranular enclaves (MMEs) of quartz monzodiorite composition. U-Pb zircon sensitive high-resolution ion microprobe dating ( SHRIMP) dates the magma emplacement age of the biotite-hornblende monzogranite at 82.7 +/- 1.5 Ma. The rocks of the pluton show high-K calc-alkaline, metaluminous to slightly peraluminous characteristics, and are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE), thus displaying features of arc-related granitoids. Chondrite-normalised rare earth-element (REE) patterns have concave upward shapes (La-cn/Lu-cn = 10.1-17.4) with pronounced negative Eu anomalies (Eu/Eu*= 0.61-0.80). Initial epsilon(Nd) values vary between -3.0 and -4.1 and initial Sr-87/Sr-86 values between 0.7062 and 0.707. The MMEs are characterised by higher Mg-numbers (27-29) and lower values of both SiO2 (56-58 wt%) and aluminium saturation index (0.9-1.0), compared to the monzogranites. Fractionation of plagioclase, hornblende and Fe-Ti oxides played an important role in the evolution of the Sariosman pluton. The crystallisation temperatures of the melts ranged from 700 to 800 C and a relatively shallow intrusion depth (similar to 2 to 7 km) is estimated from the Al-in-homblende geobarometry. The geochemical and isotopic compositions of the Sariosman pluton suggest an origin through dehydration melting of mafic lower crustal source rocks.