Geochemistry, petrogenesis and tectonic setting of Kamarbon Theralitic, Teschenitic gabbroic intrusion (Central Alborz)

In the northern hillside of Central Alborz, south of Kamarbon village, there is an outcrop of alkaline gabbroic intrusion that its petrogenesis and tectonic environment have been studied in this research. The studied intrusion has fine grained theralite in the margins whichconverted to coarse grained teschenite toward the center. The Mg number is decreased from theralite towards teschenite. The occurrence of theralites in the fine grained margin can reveal early crystallization of the margins due to rapid fall of temperature. The studied rocks on the spider diagrams show the enrichment of LILE (Rb, Ba) and HFSE (Nb) and the depletion of P, K, HREE (Y, Yb). These trends are similar to those of interacontinental alkaline rocks. Low values (less than 1) of HFSE/LREE can represent the astenospheric mantle as the source of magma. The YbN<10, high values of (La/Yb)N (19.98-28.41) and high values of (Dy/Yb)N (1.39-1.68) may indicate the presence of garnet as residual phase in the mantle source of the magma that generated the Kamarbon gabbroic alkaline rocks. In gabbro classification diagrams, the studied rocks are located in the field of interacontinental rift gabbros. The development of this gabbroic intrusion can be related to the plutonism of interacontinental rift that had been activated in late Triassic time in Central Alborz.