1 Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

2 Geological Survey of Iran, Tehran, Iran


Volcanic and volcaniclastic rocks with Cenozoic age are widespread at Bozghush Mountain, south of Sarab, northwest of Iran. The composition of the studied rocks is trachybasalts, trachyandesites and megaporphyritic andesites with probable middle Eocene age(?). The main texture of these rocks is porphyritic. Plagioclase, clino-pyroxene and sanidine are the main minerals in these volcanic rocks. All volcanic sequences show similar trace element and REE patterns, with troughs in Nb, Zr, strong enrichments in Rb, Ba, Th, La and depletions in Ti, Yb, Y, relative to N-MORB, indicating a subduction-metasomatized lithospheric mantle as their melt source. On the basis of Sm/La versus Th/La diagram and Ba/Nb (>49) and Ba/Ta (>900) ratios, the influence of slab-derived sediments and fluids on the genesis of these rocks is obvious. It seems that the lithospheric mantle source beneath the Bozghush Mountain was metasomatized by subducted NeoTethys oceanic lithosphere derived fluids and subsequent slab break, delamination of the mantle lithosphere and tectonic extension due to the roll-back of the subducting Tethyan lithosphere which gave rise to decompression melting of the subduction-metasomatized lithospheric mantle and the generation of the studied rocks at Bozghush Mountain.