Geology, mineralogy and evolution of iron skarn deposits in the Zanjan district, NW Iran: Constraints from U-Pb dating, Hf and O isotope analyses of zircons and stable isotope geochemistry

摘要

The Zanjan iron skarn deposits are located in the northwest Central Iranian terrane, along the Soltaniyeh mountains. The deposits are hosted by late Proterozoic to late Cambrian carbonate rocks (Soltaniyeh, and Mila Formations) and by Permian (Ruteh Formations), intruded by the Arjin granite, the Khakriz granodiorite and the Inche-Rahbari quartzmonzonite (53 1 Ma to 55 +/- 0.4 Ma, early Eocene). These granitoids show high-K calc-alkaline, metaluminous affinity and have similar geochemical features, including strong enrichment of LILE5 and LREEs, and depletion in high field strength elements (HFSEs) and HREE. The Arjin, Khakriz and Inche-Rahbari granitoid samples show zircon epsilon Hf-(t) values of 0.7 to +5.8 (T-DM2 = 1052-1640 Ma) and delta O-18 values of +5.55%. to +7.42%. suggesting partial melting of older crustal material then mixing with juvenile mantle-derived melts. The thermal anomaly induced by underplating mafic melts resulted in partial melting of continental crust and formation of Arjin, Khakriz and Inche-Rahbari magmas emplaced during several magmatic pulses at 53-55 Ma.