geology and petrology of tertiary volcanic rocks of sarbisheh perlite mine area (eastern iran) and industrial applications

the study area is located at northwest of sarbisheh in south khorasan province and eastern border of lut block. in this area, tertiary (eocene-oligocene to pliocene) volcanic rocks consisting of basaltic andesite, dacite, rhyodacite, vitreous rhyolite (perlitic in some parts), tuff and ignimbrite are exposed. in the daghar mountain, a, b and c perlite layers with thicknesses of 102, 7 and 58 meters respectively, occur alternatively with volcanic-pyroclastic rocks. zoning, sieve texture and embayment of plagioclase and roundness of minerals in the lavas indicate disequilibrium conditions during magma crystallization. chemically, these are meta-aluminous, medium to high-k calc-alkaline, enriched in lile and negative anomaly for nb and ti. chondrite-normalized rare earth elements (ree) plots indicate enrichment of light ree in comparison with heavy ree, (la/yb)n of 9.14-12.64, low negative anomaly for eu in basaltic andesite (eu/eu*=0.91) and dacite (eu/eu*=0.78-0.87) and strong negative anomaly for eu in the rhyolites (eu/eu*=0.18-0.35). negative anomaly for eu indicates calc-alkaline nature for these rocks. on the basis of chemical characteristics and magnetic susceptibility, these are i-type. tectonically, the rocks belong to subduction zone and active continental margin and their parental magma originated from partial melting of enriched mantle and then crustal contamination during differentiation process. dacites have an initial 87sr/86sr between 0.7048 and 0.7050 (average 0.7049) that confirm mantle source for the magma. volcanic glasses of rhyolitic composition altered by hydration (likely meteoric water) and formed perlite. physical tests and chemical analyses show that perlite of sarbisheh is suitable as raw material for production of expanded perlite.