Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
The study area is located in the northern part of Khusf in Southern Khorasan province which borders the Sistan suture zone and the Lut block. Tertiary volcanic lavas outcropped in this area contain andesite, quartz andesite, dacite and rhyolite. These rocks are dominated by porphyric and glomeroporphyric textures. The essential minerals in andesitic rocks are plagioclase, amphibole and pyroxene set in microlitic groundmass in some samples. Rock forming minerals in quartz andesite and dacite include of plagioclase, biotite, amphibole and quartz phenocrysts. Rhyolites are composed of quartz, alkali feldspar and plagioclase. The presence of sieve texture, zoning, regrowthing rim, synthetic twinning in plagioclase crystals, rounded and embayed quartz and reaction rim in amphibole crystals refers to non-equilibrium condition during magma crystallization. Geochemically, the studied rocks are calc-alkaline and medium to high-K that are characterized by enrichment in LILE, the negative anomaly of Nb, Ta, Ti which indicate magma relation to subduction zone and active continental margin. Chondrite- normalized pattern shows LREE enrichment relative to HREE suggestsing the parental magma could have generated from partial melting of metasomatized mantle by fluid related to subducted sediments.