Petrology of Toveireh alkaline basalt an evidence of within-plate Oligocene volcanism in the northwest of Central-East Iranian Microcontinent, southwest of Jandaq

In the northwest of the Central-East Iranian Microcontinent (CEIM)، southwest of Jandaq، the Toveireh Oligocene alkaline basalt with NW-SE to W-E trend is outcropped. This alkaline basalt with porphyritic، poikilitic and microlithic porphyritic textures have olivine (chrysolite)، clinopyroxene (diopside and augite)، plagioclase (labradorite) and spinel as primary minerals and titanomagnetite، serpentine and zeolite as secondary phases. The rock in question is enriched in alkalies (Na2O+K2O)، TiO2، LILE (Cs، Rb and Ba)، HFSE (Ti، Nb، Hf and Zr) with high ratio of LREE/HREE (Light Rare Earth Elements/Heavy Rare Earth Element) (La/Yb=9. 64-12. 68). The chemical composition of theses rocks indicates that the primary magma of the Toveireh alkaline basalt is produced by partial melting of carbonated garnet lherzolite of asthenospheric mantle. The geological situation of the study area suggests that the subduction of oceanic crust along the Great Kavir Fault from the Triassic to the Eocene caused carbonate metasomatism and mantle enrichment. The presence of abundant xenoliths، xenocrysts and the reaction textures show fast magma rising. The activity of Great Kavir and the Toveireh faults in an extensional system in the NW of CEIM can be accounted for the Oligocene alkaline magmatism.