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چکیده
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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# (42.6e60.1), 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 (87Sr/86Sr)I ratios ranging from 0.70498 to 0.70591, positive εNd(t) values varying from +0.21 to +2.3, and TDM2 ranging from 760 to 909 Ma, which is consistent with that of associated mafic microgranular enclaves (87Sr/86Sr)i = 0.705111-0.705113, εNd(t)= +2.14 to +2.16, TDM2 =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
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