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Abstract
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Mafic microgranular (microgranitoid) enclaves (MMEs), with fine to medium-grain–size igneous microstructures arecommon in the granodiorites from the Gheshlagh-Aftabrow pluton in the central part of Urumieh-Dokhtar magmatic arc (UDMA), Iran. They are mainly quartz diorite and gabbro in composition with SiO2 contents ranging from 50.5 to 55 wt.%. The mafic enclaves are mainly composed of hornblende, pyroxene, plagioclase, K-feldspar, quartz similar to the mineral assemblages of their host granitoids, but contain more abundant plagioclase and pyroxene, and slightly less abundant quartz and K-feldspar. Their aluminum saturation index (A/CNK values of 0.77-0.94) suggest that they are metaluminous in character. The mafic enclaves have lower K2O contents (0.47-1.22 wt.%) and higher Na2O (4.04-5.49 wt.%) than granitoid hosts, belonging to the medium-K calc-alkaline series. The field occurrence and textures including ellipsoidal and spherical shapes, chilled margins, the presence of acicular apatite, felsic vein, K-feldspar and plagioclase megacrysts in the microgranular enclaves, indicate that the magma hybridization process involve in the generation of the pluton. The MMEs display a moderate enrichment in light rare earth elements (LREEs), flat heavy rare earth elements (HREEs) with a (La/Yb)N varying from 2.13 to 4.17 and (Gd/Yb)N ranges from 0.86 to1.26 in these rocks. All samples show a weakly negative Eu anomaly with δEu varying from 0.75 to 0.90 in the enclaves, similar to those of host rocks indicating crust–mantle-derived magma interaction during their petrogenesis. This interpretation is furthermore supported by whole-rock Sr-Nd isotopic data of the enclaves and their host rocks. The MME samples have (87Sr/86Sr)i ratios ranging from 0.704997 to 0.705170, positive εNd(t) values varying from +2.15 to + 2.17, and TDM1 ranging from 874 to 980 Ma at an age of 40 Ma, which is consistent with that of host granitoids. The TDM1 values indicate that Neoproterozoic (TDM ages
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