Writers : Dervishzadeh.A and Asiyabanha.A
Refference : Geosciences Scientific Quarterly Journal,No.:37-38,P.:48
Publishing Year : 1380

Abstract :
The Ab-e-Torsh volcanic district contains the Paleogene outcrops of trachyandesitic and dacitic lava flows and fall out pyroclastic deposits (equivalent to Karaj Formation) which have been hydrothermally altered. The ,abundant fractures and faults produced a cauldron subsidence. Subsequently, fissure eruptions occurred and later hydrothermal solutions were intruded through the country rocks.
One the basis of the formation of the sulfate mineral (alunite), it seems that the acidic solutions (e.g. H2 ! and H 2 SO 4) have beer formed by the interaction of hypogene volcanic vapours with hot solutions. Because of the interaction of the acidic solution with the countn rocks and their chemical leaching, silicic, allunitic, argillic and advanced argillic alteration zones were developed.
The high permeability and reactivity of the pyroclastic deposits with respect to the hydrothrmal fluids facilitated the chemical reaction!
and hence the alteration products have been well developed in the latter unit. However, due to the presence of fractures the other units (e.g trachyandesitic and dacitic lava flows) were also intruded by the solutions and altered.
Subject List : volcanic rocks