Farzaneh Arzhangnezhad; Abbas Moradian; Zeinab Keshtkar
Volume 6, Issue 24 , January 2016, , Pages 151-170
Abstract
Subvolcanic masses of Shah khairollah and Madvar located in the southeast of Urumieh-Dokhtar magmatic belt and northwest of Dehaj-Sardoieh belt, north and southeast of Shahr-e Babak ...
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Subvolcanic masses of Shah khairollah and Madvar located in the southeast of Urumieh-Dokhtar magmatic belt and northwest of Dehaj-Sardoieh belt, north and southeast of Shahr-e Babak city. Generally, these subvolcanic masses contain dacite, rhyodacite and rhyolite lavas. Mineralogically, they consist of plagioclase, amphibole, alkali feldspar, biotite and quartz and the dominant texture of the studied rocks are porphyritic. Based on Microscopic studies plagioclases show resorption and zoning and opaticitization is observed in the mafic minerals. Geochemical investigations show that the Madvar and the Shah khairollah masses are acidic in composition and all the rock samples fall in the field of calc-alkaline magmatic series, originated in an active continental margin arc setting. Chemical compositions of the studied rocks in spider diagrams show the significant enrichment in LREE rather than HREE, as well as Sr, K. The depletion of Pb, P, Pr, Zr, Y, Nb and Ti in those rocks are observed. The negative anomalies of Ta, Nb and Ti in the rocks studied is similar to those of the subducted rocks series. The values of MgO, Na2O , Ni, Cr and Mg#, depletion of Y and high ratios of LREE/HREE, Sr/Y (Ave. 137.26), La/Yb (Ave. 50) in the studied rocks are similar to those of adakites which have derived from partial melting of young oceanic crust. Geochemical characteristics of these two masses indicate the partial melting of oceanic crust prior to hydration and the low concentrations of Yb, Y, HREE, TiO2, is consistent with the partial melting of subducted oceanic crust slab under amphibolite facies conditions in the depth of 35 km.
