Petrography and mineral chemistry of Tarom plutonic complex, NE Zanjan


1 Department of Geology, School of Basic Sciences, Tarbiat Modares University, Tehran, Iran

2 Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran


Tarom plutonic complex is located in northeast of Zanjan and in the Alborz-Azerbaijan zone with northwest-southeast trending. The Eocene Tarom plutons include Zanjan (quartz monzodiorite), Zaker (quartz monzonite), Morvarid (monzogranite to syenogranite) and Kuh Tabar (porphyry microquartz diorite) which intruded within the volcanic and volcanoclastic rocks of Karaj Formation. The EPMA analyses of plagioclase, alkali feldspar, pyroxene and chlorite indicate that the core of plagioclase crystals is more calcic than their rim suggesting normal zoning in these minerals. The pyroxenes are mostly clinopyroxene with minor amount of orthopyroxene that belongs to Fe-Mg-Ca pyroxenes. The pyroxenes of these plutons show augite-diopside composition. The chlorites are Mg-bearing chlorite and classified as the picnochlorite, diabanite and talc chlorite. Based on the composition of pyroxenes, the Tarom plutonic complex crystallized from sub-alkaline magmas which formed in a subduction tectonic setting. Barometric studies exhibit that the clinopyroxenes crystallized in pressures lower than 5 Kbar. Pyroxene thermometry in these plutons indicate that the pyroxenes crystallized in temperatures ranging of 700-850 ˚C in the quartz monzodioritic, 600-700 ˚C in the quartz monzonitic pluton and 800-900 ˚C in the porphyry micro quartz dioritic pluton. Moreover, plagioclase thermometry shows that the crystallization temperatures of plagioclases in the Tarom area range from 550 to 900 ˚C.