Structure and generation mode of travertine fissure-ridges in Azarshahr area, Azarbaydjan, NW Iran

Fissure-ridge type travertines are exposed in extensive area in Azarshahr and eastern partof the Urmia Lake in Azarbaydjan, NW Iran. Some of the ridges are still active in the areaindicating active displacement along the faults in this region. Field observations indicatedthat abundant ridges up to 2 km long and 150 m height are generated in tow vein and layered types along the extension fractures in the area. Quaternary active Sahand volcaniccomplex close to the travertine ridges had reasonable influence on solution of the Jurassicand Cretaceous carbonates and stained travertine layers. Climate changes, strongly affectsthe amount of water supply in travertine ridges. This is well identified by inter-bedded paleo-soil bands sub-horizontal to the travertine layers and change of dip in travertine layers. Normal faults and steep extension fractures cut the travertine layers and indicate latter active extension in the area.Trends of fissures in the ridges have structural relation with the NW-SE oriented active faults in the area. Vertical veins in central fissures of the travertine ridges contain horizontally oriented aragonite and calcite fibers. These fibers are measured in the ridges to get the locally developed extension orientation in the travertine ridges. Structural evidence indicates that travertine ridges are generated in pull-apart basin of the active NW-SE oriented dextral strike-slip faults.