Petrology, geochemistry and tectonic setting of intrusives around omam (east of guilan)

Abstract

Intrusives around Omam (East of Guilan) with gabbro, monzo-gabbro-porphyry, syenite and granite compositions have intruded to upper Cretaceous lavas, sedimentary and pyroclastic rocks. The geochemical data of the mentioned intrusives on the variation diagrams show that these rocks are categorized into mafic and felsic groups and in terms of magmatic series, they are often from alkaline one. Relative continuity between most intrusive mafic rocks data on the variation diagrams and the parallel feature of their rare earth elements patterns clearly show the derivation of this group from a common origin. Based on the severity of changes in strongly compatible elements versus the strongly incompatible elements, the dominant process governing the magmatic evolution for mafic rocks is fractional crystallization. REE patterns for different types of mafic rocks are in parallel with each other and have a uniform and downward slope, while the slope of felsic varieties patterns for LREE is steep and descending and flat for HREE. Based on the La/Sm ratio, it seems that the melts forming mafic rocks are derived from the enriched mantle with spinel lherzolite composition and partial melting degree of 4 to 10 percent. On the tectonic setting discrimination diagrams, the intrusive rocks of the studied area are categorized in the territory of intracontinental rifts.