The geochemistry and petrogenesis of Hossein abad Tertiary volcanic rocks (southwest of Birjand, East of Iran)

The study area is located 50 km southwest of Birjand, in the northwest margin of Sistan suture zone. In Hosseinabad area, the Tertiary volcanic rocks cross-cut the upper Cretaceous ophiolitic sequences. These rocks are andesite and display porphyric and glomeroporphyric textures. Plagioclase, hornblende, augite and biotite are the main phenocrysts. Sieve texture and selective alteration in plagioclase, opacitization of hornblende and the presence of mica-schist and amphibolitic enclaves are very common in these rocks. High ratio of LREE/HREE, Sr/Y (average: 38.55) and SiO2 (average: 59.09), and lack of Eu negative anomalies indicate that these rocks are similar to silica-rich adakites suggesting that this magma could have been originated from a garnet amphibolite source, resulting from metamorphism of thickened lower crust.