Dehe Bala granodioritic pluton with an E-W trend is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with diorite and quartz monzodiorite in composition. The ellipsoidal and rou
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Dehe Bala granodioritic pluton with an E-W trend is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with diorite and quartz monzodiorite in composition. The ellipsoidal and rounded enclaves with 2 to 30 cm in sizes have been scattered in host granodiorites. The enclaves commonly have a sharp contact with the host granodiorites. Textural evidence indicative of disequilibrium condition, include plagioclase with oscillatory zoning and repeated resorption surfaces, acicular apatite and quartz ocelli as chemical and/or thermal changes in the melt during crystal growth and as evidence for occurrence of magma mixing. The enclaves enriched in LILES and LREES and are depleted in HFSES. The SiO2 content of the granodiorite ranges from 64.2 to 66.9 wt%. They are high-k calc-alkaline in composition, displaying a metaluminous character (A/CNK<1.1). Enrichment of incompatible elements such as La, Ce, Rb, Th, K and Nd coupled with negative anomalies of Ti, Ba, Eu, Nb and P implying the role of the lower crust in the formation of the granodioritic magma, but relatively high content of Mg value (0.39 – 0.43) suggest that the granodiorites were generated by mixing of mantle-derived mafic magma with felsic melt derived by partial melting of lower crust. The MMEs are characterized by relatively low contents of SiO2 = 52.8–58.2 wt%, moderate K2O=1.4-3.8 and high Mg (0.4 -0.46). Geochemical features and values of Dy/Yb=1.6 – 1.8 in MMES suggest that enclave magmas were derived by partial melting of the mantle wedge in the spinel–garnet transition zone and they have partially evolved in contact with fusion of crust-derived felsic magmas.
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