ژئوشيمي و پتروژنز سنگ هاي آتشفشاني شمال شرق اردستان

Geochemistry and Petrogenesis of Volcanic Rocks in North-East of Ardestan

consists of intermittent of lava flows (mainly basaltic andesite, andesite, dacite, rhyodacite and rhyolite) and pyroclastics (tuff, ignimbrite and agglomerate). These lavas are composed essentially of quartz, plagioclase, kfeldspar, amphibole, biotite, clinopyroxene and olivine, set in a matrix of the same minerals associated with apatite, zircon and opaque mineral. The study of volcanic rocks shows a selective enrichment of large ion lithophile elements (eg., K, Rb, Ba) and a depletion in elements having high field strength (HFSE) as Nb, Ti , Ta compared to chondrites and primitive mantle. Based on the geochemical data, trace and REE element diagrams, these rocks are high potassium calc-alkaline and shoshonite. Trace element patterns show similarities with volcanic arc magma. Therefore, volcanic rocks of north-east of Ardesten are products of volcanism of metasomatized mantle.