Petrgraphy, mineral chemistry, geochemistry and tectonic setting of Tertiary volcanic rocks in Shoushk area (east of Sarbisheh), Southern Khorasan

Tertiary volcanic rocks including andesite, trachydacite and rhyodacite with pyroclastic rocks cropped out in east of Sarbisheh at Southern Khorasan. The main minerals in andesites are plagioclase, pyroxene, amphibole and biotite and for acidic rocks include plagioclase, quartz, sanidine, amphibole and biotite. On the basis of microprobe analyses, the composition of plagioclases in andesites ranges from Ab62.7,An30.2to Ab35.5, An62.9and are andesine to labradorite. Pyroxenes are enstatite and have compositional range of En50.6-57.8, Fs39.8-47. Orthopyroxene thermometry represents temperature of 1050 to 1100oC with pressures of 1 to 10 Kbar. The studied rocks have medium to high-K calc-alkaline and shoshonitic nature. Geochemical characteristics, such as enrichment in LILE, depletion of HFSE and Zr/Y>3, indicate magma relation to subduction zone and active continental margin. Relatively low values of (La/Yb)N(7.17-11.68) and Dy/Yb(