Document Type : Original Research Paper


1 Department of Economic Geology, Tarbiat Modares University, Tehran, Iran

2 Department of Geology, University of Zanjan, Iran



The Tarom metallogenic belt of the Alborz magmatic belt in NW Iran is characterized by two alignments of intrusion in its northern and southern parts. The northern intrusion is younger than the southern one. Mineral chemistry investigations on the northern and southern intrusions characterize calc-alkaline magmatism. The northern intrusion consists mostly of quartz monzonite, and the southern intrusion comprises 1) gabbro - pyroxene quartz monzodiorite – quartz monzodiorite series and quartz syenite; 2) gabbro-diorite. Electron microprobe chemistries indicate that the northern plagioclases are An22 to An49 (oligoclase to labradorite). Plagioclases from the southern intrusion are An35 to An54 (andesine to labradorite) and gabbro-diorite plagioclases are An65 to An61 (labradorite). All pyroxenes correspond to the Quad (diopside, augite, and clinoenstatite) and crystallized at <2 to 5 kbar and H2O=10%. Formation temperatures of pyroxenes from the northern intrusion are in the range of 1100-1175°C. The northern feldspars show temperatures ~550°C. Formation temperatures for the clinopyroxene and feldspar from the southern intrusion are estimated at 1140-1185°C and 550-600°C, respectively. The Fe-rich biotite minerals from the northern intrusion suggest high oxygen fugacity magma. The northern and southern intrusions formed in an arc-related tectonic setting. The northern magma is sourced from the melting of a mixed mantle-crust in a subduction-related environment. The mineral composition of the northern intrusion implies magma fertility and porphyry mineralization which can be due to its high oxygen fugacity magma and lower crystallization pressure relative to those of the southern intrusion.