Study of petrography and chemistry of volcanic rocks minerals belonging to the Palaeogene of Alamut region

The region under study is structurally belonging to the tectonic range of the central Alborz. According to microscopic studies, the petrological study of the rocks on the region composed of olivine basalt, basaltic andesite, andesite, and basalt. Based on the geochemical diagrams, the chemical composition of most rocks is in the alkaline range. From the perspective of the texture, most rocks are porphyry with microlithic paste or porphyry with medium grain paste. In particle decomposition of minerals, clinopyroxene has diopside to wollastonite composition range. Also, the plagioclase composition is in the range of anthritis to beyonite. Study of thermobarometer results indicates that clinopyroxenes of the region consist of 0.9 to 3 wt% TiO2 in the compressive range of 5-10 kbar and temperatures between 500 and 1200° C. Furthermore, plagioclases are composed at a pressure of 10 kbar at a temperature between 750 and 950° C. The chemical data of clinopyroxene is an indicator of magma with the alkaline basaltic composition. Regarding their tectonic and magma state, the rocks bed in the inner continent rift zones, where the formation of these rocks can be attributed to the effects of intercontinental tensile phases associated with deep faults during the Alpine oceanic phases during the Eocene period.

Keywords:

Thermobarometery , Alkaline Basalt , Central Alborz , Petrography.