Physico-chemical estimation of the formation and comparison of chemistry of biotite mineralization in igneous rocks south of Germi, northwest of Iran

abstract Northwest of Iran, especially Talesh zone, is one of the important Alkaline and Shoshonite magmatic activity area in the Cenozoic. Eocene - Oligocene Gabbroic rocks in the south of the city of Germi as part of the Talesh zone have penetrated the Eocene alkaline basalts. Alkaline basalts with hyalomicrolitic porphyrytic and glomerulophorphyric texture are composed of plagioclase and clinopyroxene with lower amounts of olivine minerals, dark minerals, black mica, amphibole and alkali feldspar. Gabbro masses have granular texture containing pyroxene minerals, plagioclase, black mica, amphibole and ± alkaline feldspar. Composition of all these rock outcrops are alkaline to shoshonite. The studied micaceous of south Germi, based on the chemical classification with Fe #> 0.33, have biotite composition at the interface between the two poles of sydrophyllite and stonitis, which, according to the evidence of petrography and chemical composition, coexist with amphibole. The chemical composition of these biotite is indicative of the nature of alkaline and magnesium host magma and have been crystallized from primary magma with respect to AlVI <1 values. In all studied samples, the amount of Mg # ranged from 53 to 67%, the Al Total value ranged from 2.4 to 2.58 and Fe # ranged from 0.33 to 0.47. The presence of Fe3 + in the structure of hic biotite from 1.73 to 2.23 indicates high fugacity values of 10-15 until10-17 for Ghafar Kandi gabbroic rocks and between 10-13 until 15-10 for Gabbro and basalts of Marallo with buffering of hematite and Magnetite. The studied biotites is chemically similar to the biotite samples of the Roman-type and the Marand Potassic rocks, indicating the dependence of the magma to the subduction environment.