Paleostress Analysis from Fractures in Kalosh Anticline, Kurdistan Region, North‒East of Iraq

Abstract

Fractures analysis carried out throughout traverses across Kalosh anticline. The anticline is located ~30 km south of Sulaimaniyah city, Kurdistan region, NE Iraq. It extends NW‒SE for ~17 km within the high folded zone of the northwestern segment of the Zagros Foreland Fold Thrust Belt. The aim of this work is for unraveling the tectonic history and detecting tectonic episodes responded for the initiation and development of the anticlinal structure. More than 450 fracture planes were classified into sets and systems according to their relations with three mutually perpendicular geometric axes (tectonic axes). Tension sets are ac and bc, the first one formed by extension along fold axis accompanying direct compression perpendicular to fold trend, whereas the second is the product of relaxation that motivated the primary compression. The shear systems are hk0, h0l and 0kl developed successively during direct compression and subsequent relaxation episodes of each tectonic force. Field observations and paleostress analysis indicate that the area was subjected to four stress phases. First is primary compressive tectonic phase in the directions NE‒SW. The second compressive tectonic stress in the direction NW–SE considered as a secondary phase. Third was extension tectonic phase in the direction NE–SW which developed during the final uplift stage of folding is normal to the major fold trend. The fourth is NW–SE extension face considerate as extension stress related to the primary NE‒SW compressive stress.