Writers : Emami.M.H and Irannejadi.M.R
Refference : Geosciences Scientific Quarterly Journal,No.:7,P.:3

Abstract :

The Stratovolcano of Damavand has been built up in Quaternary by alternation of explosive and effusive phases.It covers an area of about 400 km 2with mainly Mesozoic sediments as its basement. The volcanic rocks of Damavand can be divided into basic, intermediate and acidic facies including alkali olivine basalt, trachybasalt, trachyandesite, trachyte and related pyroclastic rocks.The basic rocks eruped during the earlier phases of Damavand activity and the trachytic rocks originated from differentiation of magma, at its later stages. Trachyandesite is the most dominent rock of Damavand stratovolcano. Geochemical data shows that all the volcanic rocks of Damavand belong to alkalic series. There is a compositional continuum from alkali basalt to trachyte. The latter are the products of the differentiation of a primary basaltic magma. The fugacity of oxygen has been high and there is no enrichment of iron(Fenner Trend), during magmatic differentiation. The decrease of Mg.Ni and rapid increase of alkali metals are pronounced. This study shows that the primary magma of Damavand was originally sodic alkali basalt which became more potassic during differentiation. Geodynamically, this magmatism is comparable to intraplate alkaline magmatism,developing in platform areas during the post orogenic events. The magma seems to have originated from fertile layer of upper mantle and the deep- seated faults of the region have facilitated the eruption of magma in an extentional phase.

Subject List : volcanic rocks