Petrology & Geochemistry of paleogene volcanic rocks in HERIS( Eastern Azarbaidjan - NW of Iran)
The study area is located in east of Heris, NW of Iran, and is a part of structural zone of Western Alborz - Azarbaidjan. It has middle Eocene volcanic and pyroclastic rocks intruded by early Oligocene intrusive bodies, varying in composition from andesite, trachy - andesite, pyroxene- andesite, andesi- basalt and so pyroclastic rocks (tuffs, agglomerate and ignimberite). These rocks contain phynocrystes of plagioclase (andesine), augite, biotite and hornblende set in the microlitic matrix generally displaying porphyritic, microlitic- porphyritic and hyalo- microlitic textures. Features such as selective alteration, composite and distorted twinning, sieve texture, reverse and oscillatory zoning in plagioclase, presence of opacitic biotite and hornblende, presence of acicular apatite indicate that magma mixing process was the main factor in generation of parent magma for the volcanic rocks in the area. These rocks tectonically belong to the post- collision arc setting corresponding with closure of Neotethys ocean and with collision of Arabian plate and central Iran block, and with post- collision evolutionary processes. Post- collision extentional stresses in Paleogene (especially in Eocene) caused for generation of hybrid melts and eruption of numerous and sporadic volcanoes in Weatern Alborz- Azarbaidjan zone.?