The Petrology and Geochemistry of Basaltic lavas fromQorveh-Bijar volcanic belt, north western Iran, Kurdistan

Quaternary syn-collusional magmatism in Kurdistan, western Iran, is one of the expressions of the Arabian-Eurasian collusions. After this continental collusion, dozens of centers have been manifested from Eastern Turkey (Anatoly) to western Iran during late Miocene to Quaternary. studied rocks have located between Qorveh and Bijar cities , 47° 46′ - 47° 59′ E and 35° 18′ - 35° 30′ N , parallel to Zagros fault in the Sanandaj Sirjan Zone (SaSZ), these basaltic rocks have erupted over a particular geographical area (NW-SE trend) during a limited time. Volcanic products in Qorveh-Bijar area were composed of lava flows, scoria, lapilli tuff, and bombs with a thickness of several tens of meters. The studied samples showed porphyric, glomeroporphiitic, and microlithic textures. These samples were described by the phenocryst and microphenocryst contents (35–45 vol. %) and ground mass which consist of microlites ( 35 vol. %) and glass ( 20 vol. %). The groundmass textures of the samples were composed of clinopyroxene, acicular plagioclase as microlites and opaque minerals oxides (titanomagnetite). In the nomenclature diagram of Nb/Y vs. Zr/TiO2_0.0001, the study volcanic rocks were characterized as trachyandesite/alkali basalts (Fig.4).Petrographic observation (Quartzes and K-feldspar xenoliths) along with major and isotopic variation (The rough positive correlation between (87Sr/86 Sr)i and SiO2 ,besides the obvious positive correlation between ɛNd and Sm/Nd),coupled with trace element enrichment((LILE); Cs, 1.11-3.61; Sr, 1177- 2690; Pb,6-23.23 and 50 (La/Yb) N 108) suggested that these alkali basalts underwent some degree of crustal contamination. LILE enrichment and the presence of negative HFSE (particularly, Nb and Ta) anomalies in the trace element patterns of the studied volcanic rocks indicated some similarities with the magmas generated in the subduction-related regions. This feature could cause by a widespread contamination with continental crust, however high degree of contamination in this area is impossible. the presence of a subduction component in the source region of the parental magma could also resulted in highly enrichment in LILE and Nb-Ta trough which observed studied samples trace element diagrams, so we assumed that the northward subduction of the Neotethys Oceanic crust under the southern margin of Eurasia during Mesozoic times can be responsible. The small positive ɛNd coupled with light REE enrichment in these rocks mentioned to the depleted mantle source which has only recently become enriched and melted to originate magma. Refer to the occurrence of subduction in this are one of the possible explanation for this enrichment would be incorporation of melt from subducted oceanic crust with mantle source which can cause these features. Modeling of REE (the diagram of La/Sm versus Sm/Yb) suggest that they could formed by low degrees of partial melting ((around 0.5%) from an enriched mantle source in garnet stable field. We proposed that the presence of a thick crust and burial of the contaminated and metasomatized mantle affected by the subducted component have triggered partial melting of the garnet peridotite and resulted in the formation of the basaltic magmas in the western Iran.