The petrography and geochemistry of volcanic rocks of Ghaflankuh, Myaneh (NW Iran)

The study area is a part of the western Alborz-Azarbaijan magmatic belt. The main outcrops in Ghaflankuh are including alternative andesite lava, andesite-basalt, trachy-andesite and related tuffs. This sequence is coverd by acidic domes and in some areas by acidic lavas and ignimbrites. Olivine, clinopyroxene, hornblende, biotite, plagioclase, quartz and sanidin are the major minerals of the studied rocks, displaying hyalo-porphyric, microlithic and porphyry and glomero-porphyry textures. The mafic to intermediate lavas have andesi-basalt and felsic rocks have rhyolithic composition. The mafic to intermediate magmas are low-K and metaluminous with significant enrichment in LREE in compare to HREE, as well as Sr, K and display depletion in Pb, P, Pr, Zr, Y, Nb and Ti. The negative anomaly of Ta, Nb, and Ti in these rocks is similar to subduction related rocks. These lavas are produced from differentiation of magma derived from enriched- mantle with 1-5 precent partial melting of garnet-lehrzolite. The variations of Rb/Sr, Nb/Th imply for the presence of phologopite (glimeritic veins) in the source. The high ratios of K/P (6.5-43) and La/Nb (1.7-2.8) point to contamination of magma with crustal materials. This sequence is evolved in an active continental arc environment.