Abstract

Agkand area is located in 50 km north of Zanjan at 37º 04´ 30˝ N and 48º 20´ 13˝ E. This area is a part of Hashtjin geological map in 100000 scales and located in the Alborz geostructural zone. This area composed of basalt- andesitic basalt and trachy-basalt lavas and dark color basic tuffs (Eocene), rhyolite-rhyodacite lava, perlite, pitchstone, ignimbrite and rhyolitic-rhyodacitic tuffs (Oligocene). Rhyolites-rhyodacites have porphyritic, microlitic porphyry, vesicular and amygdaloidal textures in which plagioclase, biotite and some sanidine phenocrysts located within the fine grained to microlitic matrix. Cavities and vesicles have been filled by amorphous silica (opal and chalcedony), quartz and chlorite. Perlites have hyalophyric and perlitic textures with plagioclase, sanidine and biotite phenocrysts in the glassy matrix with rounded fractures. Pitchstones have oriented fractures in the glassy matrix and rounded fractures don’t present in these rocks. Ignimbrites have eutaxitic and porphyroclastic texture with flow structures. These rocks composed of plagioclase, sanidine, quartz and opaque minerals together with lithic fragments with porphyritic texture and shards. Basalts-andesitic basalts have porphyritic texture composed of plagioclase and clinopyroxene phenocrysts within the cholritized and epidotized fine grained matrix. Some plagioclase crystals indicate sieve texture, and mainly altered to epidote and calcite. Some of the clinopyroxene phenocrysts have undergone epidote, calcite, chlorite and quartz alteration. Perlites in Aqkand area present as masses at the foothills of rhyolitic-rhyodacitic domes and can be classified as granular and classic perlites.