Abstract

The mafi c rocks outcrops exposed in the South of Gorgan, northeastern of Iran. These gabbroic rocks are intruded into the Middle–Upper Paleozoic sedimentary rocks and Gorgan schist units representing a part of the north Gondwana province. Petrography studies of these rocks show medium to coarse grained sizes and the texture varies from ophitic to intergranular under polarized microscope. The mineralogical composition of mafi c dykes is dominated by large crystals of clinopyroxene + orthopyroxene + plagioclase and hornblende. These rocks can be classifi ed as gabbroic rock. Geochemical studies show that these rocks have low to medium K2O contents. The trace element data shows low La/Nb ratios and LREE enrichment (La/Yb 10–21.4). The high LREE/ HREE ratios and low Y content corresponding high Ti/Y ratios of the gabbros suggest that they could be derived from melt fractions of a garnet stable source. Considering that the REE plot and tectonic diagrams of the region’s gabbro are similar to that of OIB (Ocean island basalt), the former’s origin is the same as that of OIB magmas.

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