Mantle source characteristics of the Quaternary Alkali olivine basalts in Qorveh-Takab area

The quaternary alkali olivine basalts exposed in the east and northeast of Sanandaj in Qorveh, Takab and Bijar axis. These rocks are mainly olivine basalts with normative nepheline and olivine. The existence of gneissic xenolith, quartz xenocrysts and phenocrysts of biotite are evidences of crustal contamination. From geochemical point of view, negative anomaly of P, Zr, Nb, Ti and Pb positive anomaly as well as enrichment of LIL elements indicate crustal contamination. In tectonic setting diagrams, the samples plot in intra-plate alkali basalts. The low ratios of Y/Nb, Zr/Nb, high ratio (La/Yb)N 24 and the similarity of REE pattern with OIB, show that of magma generated in an enriched mantle. Also, geochemical studies indicate that the studied basalts are derived from enriched mantle OIB-like source with spinel facies in the pressure of 10-15 kbar, depth of less than 60 km and less than 15% partial melting.