GROWTH PATTERNS AND EMPLACEMENT OF THE SILICIC LAVA DOMES IN SOUTHWEST OF ARDABIL, IRAN

11th International Multidisciplinary Scientific GeoConference SGEM2011, www.sgem.org, SGEM2011 Conference Proceedings/ ISSN 1314-2704, June 20-25, 2011, Vol. 1, 147-152 pp

ABSTRACT

The area under study is located in east Azerbaijan and southwest of Ardabil. In this area
the volcanic rocks are placed over the Oligocene and lower Miocene clastic sedimentary
rocks and under lower Pliocene epiclastic sediments. Therefore, their age is middle and
upper Miocene. These volcanic rocks have been extruded in dome shape from the
fissures of an eruptive caldera. These domes are rich in silica. From the boundary to the
center of caldera, these domes are categorized into three types with regard to their
formation mechanism. First, there are the domes located towards the edge. They have
dacitic composition and have been extruded in a single stage. Different parts of these
domes are similar in general. Second, there are the domes located between the edge and
center of the caldera. These domes are rhyodacitic in composition and have extruded in
multiple stages and are layered. Generally, the layers of these domes are similar. The
third types are placed in the center of the caldera, have rhyolitic composition and, like
the previous type, have been extruded in several stages and are layered. However, the
layers are quite different from each other. Field evidence and geochemical studies are
suggestive of the existence of a genetic association between the magma of these domes.
Differentiation has triggered the variety in the chemical composition and consequently
the extrusion mechanism in different parts of the caldera. Chemical composition,
viscosity, temperature, the amount of volatile materials in magma and the difference in
density of magma and the surrounding rocks are among the most significant factors
which determine extrusion mechanism and formation of silicic domes in the area.

Keywords: silicic dome, eruptive caldera, formation mechanism, miocene, Ardabil