Petrology and geochemistry of volcanic rocks of Cheshmeh Khuri and Shekasteh Sabz areas, Khur, northwest of Birjand

Khur area is located in east of Iran and northwest of Birjand. The area comprises outcrops of Eocene to Oligocene volcanics with basaltic andesite to rhyolite composition¡ which were intruded by subvolcanic and intrusive bodies of granodiorite to gabbro. In the present work¡ petrogenesis of volcanic units in Cheshmeh Khuri and Shekasteh Sabz areas was studied¡ which are located in Khur area and these volcanics have most widespread in them. Rhyolite¡ dacite¡ andesite¡ trachyandesite and basaltic andesite units in Cheshmeh Khuri and trachyandesite unit in Shekasteh Sabz were identified. The main textures of these units are porphyritic¡ hialoporphyritic and microlitic and plagioclase¡ pyroxene¡ K-feldspar¡ hornblende¡ biotite and quartz are the main minerals. Volcanic units of Cheshmeh Khuri have characteristic of high-K Calc-alkaline. Enrichment of LREE relative to HREE and LILE to HFSE are important evidences that magma was formed in a magmatic belt of a subduction zone. Based on the initial 87Sr/86Sr of andesite and dacite¡ their magma has originated from partial melting of an enriched mantle and contaminated with the crust through its differentiation. Trachyandesites of Shekaste Sabz have characteristic of shoshonitic nature. These units are characterized by high FeOt/FeOt㈃¡ K2O/Na2O and Zr>360 ppm¡ Y>39 ppm¡ and Ce> 100 ppm. Also¡ they are enrichment in REE particularly in LREE¡ depletion of Eu¡ strong enrichment in HFSE¡ and depletion in Ba and Sr. Therefore¡ trachyandesites of Shekaste Sabz belong to post collision volcanics.