Investigating the geodynamic origin of tertiary volcanism in the north of Birjand
The area is situated between 59.00-59.20 to 32.55-33.00 degrees in north birjand mountains. According to petrographic studies ,extrusive Igneous rocks have a vast Composition form Dacite to rhyodacite. Andesitic- dacite , andesite and basitic andesite, that erupted during a 50 Ma period from end of cretaceous to early neogen. Based on Tectonomagmatic diagrams and spiderdiagrams studies , geodynamic location of this volcanic complex has been explained . Results show that this compositions be related on orogenic mechanism and continental margine calcoalkaline lavas. Increase of Zr component in this extrusive igneous rocks in strong probability resulted from mixing of parent magma with relatively thick crust materials . Follow evidences , Y/Nb and Ba/La ratios extraordinary distribution of pyroclastic components, considerable presence of amphibole phonocrysts, absence of linear relationship between Zr and TiO2 and exraordinary sufficiency of lithophyl elements with large ionic radiation , supported the results and reinforced the Idea of correlation between north birjand extrusive igneous rocks with active continental margines calcoalkaline lavas.