Zircon U-Pb ages, geochemistry and Sr-Nd isotopes of the Golshekanan granitoid, Urumieh-Dokhtar magmatic arc, Iran: evidence for partial melting of juvenile crust

The Golshekanan granitoid body is situated in the central part of the Urumieh-Dokhtar magmatic arc (UDMA) in central Iran, and includes granite and granodiorite with minor monzonite and diorite. Zircon U-Pb dating yields a late Eocene (Priabonian) crystallization age of 37.6 +/- 0.2 Ma. The body is calc-alkaline and metaluminous to weakly peraluminous (A/CNK <= 1.10) with SiO2 ranging from 61.1 to 71.5 wt% and MgO from 0.8 to 3.3 wt%, with Na2O + K2O of 4.0-8.5 wt%. Primitive mantle-normalized trace-element patterns display enrichments in the large-ion lithophile elements (LILE), such as Rb, Cs, Ba and K, and depletion from the high-field-strength elements (HFSEs), such as Nb, Ti, Ta and P. The rocks are enriched in LREEs relative to HREEs (average (La/Yb)(CN) = 4.3) and exhibit weak negative Eu anomalies (average Eu/Eu* = 0.75), revealing typical active continental margin arc affinity. The low initial Sr-87/Sr-86 ratios (0.70440-0.70504) and notable positive epsilon(Nd)(t) values (+4.0 to +5.2) indicate an origin by partial melting of juvenile rocks in the lower crust, possibly with some involvement of sub-continental lithospheric mantle beneath Central Iran. These processes probably occurred due to the Neo-Tethys oceanic slab retreat and (or) rollback during late Eocene time.