Petrogenesis of Middle-Eocene granitoids and their Mafic microgranular enclaves in central Urmia-Dokhtar Magmatic Arc (Iran): Evidence for interaction between felsic and mafic magmas

Whole rock major and trace element geochemistry together with zircon U-Pb ages and Sr-Nd isotope compositions for the Middle Eocene intrusive rocks in the Haji Abad region are presented. The granitoid hosts, including granodiorite and diorite, yielded zircon U-Pb ages with a weighted mean value of 40.0 +/- 0.7 Ma for the granodiorite phase. Mafic microgranular enclaves (MMEs) are common in these plutons, and have relatively low SiO2 contents (53.04-57.08 wt.%) and high Mg# (42.6-60.1), probably reflecting a mantle-derived origin. The host rocks are metaluminous (A/CNK = 0.69-1.03), arc-related calc-alkaline, and I-type in composition, possessing higher SiO2 contents (59.7-66.77 wt.%) and lower Mg# (38.6-52.2); they are considered a product of partial melting of the mafic lower crust. Chondrite-normalized REE patterns of the MMEs and granitoid hosts are characterized by LREE enrichment and show slight negative Eu anomalies (Eu/Eu* = 0.60-0.93). The host granodiorite samples yield (Sr-87/Sr-86)(i) ratios ranging from 0.70498 to 0.70591, positive epsilon(Nd)(t) values varying from +0.21 to +2.3, and T-DM2 ranging from 760 to 909 Ma, which is consistent with that of associated mafic microgranular enclaves (Sr-87/Sr-86)(i) = 0.705111-0.705113, epsilon(Nd)(t) = +2.14 to +2.16, T-DM2 = 697-785 Ma). Petrographic and geochemical characterization together with bulk rock Nd-Sr isotopic data suggest that host rocks and associated enclaves originated by interaction between basaltic lower crust-derived felsic and mantle-derived mafic magmas in an active continental margin arc environment. (C) 2018, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.