Aiotsdzor

This volcanic complex lies in the southwestern part of central Armenia within the Western Aiotsdzor district and extends over an area of about 150 km2. The volcanic rocks have a thickness of 500 to 700 m and in vertical sections three series can be distinguished (1) 220 to 300 m of andesitic basalts and tuff breccias, (2) 200 to 400 m of sanidine trachytes and tuffs and (3) about 100 m of dacitic lavas. In the lower part of the first series andesitic lavas and pyroclastics with fragments of trachy-liparite and sanidine crystals are predominant; in the upper part tuff breccias of andesitic basalt with fragments of alkaline trachyte, sometimes containing pseudomorphs of leucite in the groundmass, are common. Also found within the first series are leucite and hauyne tephrites and alkali basalts. In the second series, which is composed predominantly of tuffaceous and other fragmental formations, the rocks are essentially trachytic and represented by porphyritic sanidine trachy-liparites with a microlitic groundmass. In this series are concentrated subvolcanic bodies which are also of sanidine trachy-liparite. Age K-Ar determinations gave 21 to 24 Ma (Bagdasaryan and Meliksetyan, 1966)