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
Fatemeh Sarjoughian, Bahareh Zahedi, Hossein Azizi, Wenli Ling, David R. Lentz, Yoshihiro Asahara
Abstract
Abstract 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 SiO 2 ranging from 61.1 to 71.5 wt% and MgO from 0.8 to 3.3 wt%, with Na 2 O + K 2 O 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 87 Sr/ 86 Sr ratios (0.70440–0.70504) and notable positive ϵ 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.