Petrology, Geochemistry and Tectonic setting of Javaherdasht Cretaceous gabbro in the north part of Alborz Mountains, East of Guilan, North of Iran: A part of ophiolite sequence or intra-continental rift?

The Cretaceous gabbros located in Javaherdasht area in the northern part of Alborz Mountains, south of Guilan province. These gabbros show layered structure at the bottom and the isotropic structure at the top. From the mineralogical point of view, they have plagioclase, augite, olivine, biotite and magnetite. Geochemically, they belong to transitional magmatic series. Positive anomaly of Pb, K, Th, Rb and negative anomaly of Ba, Zr, Nb and P indicate contamination with continental crust. Tectonic setting diagrams of these gabbros suggest a continental intraplate environment, also the value of (Nb/Nb*)pm ~0.89 in the studied gabbros is similar to intra-continental rift basalts with crustal contamination. The REE pattern of the studied gabbros is also similar to transitional-sub alkalic intracontinental rift basalts and the values of (Ce/Yb)N ~3.9 and (Dy/Yb)N ~1.3 indicate the presence of spinel in their mantle source. The high ratio of Th/Nb and Nb>0 prove that the magma is derived from MORB mantle plumes (P-MORB) which has been contaminated with continental crust.