Construction of a Structural Model for Harir Anticline within Zagros Fold-Thrust belt, Kurdistan of Iraq

Abstract

Abstract The study area is considered to be a part of Arabian plate, located within High Folded Zone of the Zagros Fold-Thrust Belt in the Iraqi Kurdistan Region. This area consists of a major anticline called Harir anticline. The study of this structure was conducted along five traversal sections through 57 field stations in order to understand the geometry and elucidate structural model for generation and propagation of this fold. Thirteen formations were exposed covering this anticline, ranging in age from Early Cretaceous up to the Pleistocene. Geometrical analysis of Harir fold indicates that this fold is asymmetrical double plunging anticline, gentle to open and non-cylindrical, curvi-planar anticlinal structure. Due to presence of three strike slip-faults cross cutting this anticline, it segmented into four transversal blocks which are namely Batas, Harir, Sheikh-Mamudian and Ashkafta blocks. Each block has its own structural, sedimentlogical, and morphological properties making it different from the other blocks. Detailed balanced and retro-deformable cross sections in the studied area reveal that the shortening increases gradually from northwest toward middle part and decreases towards southeastern part of Harir Anticline. The calculated shortening consecutively is 6.76%, 14.30% and 14.31 % 10.52%, 5.48% from northwestern plunging area to the southeastern plunge. The depth to detachment surface has been calculated, ranging between 10-10.5km below the regional level of Bekhme Formation. This depth coincides with surface of the Upper Paleozoic Ora shale formation, which indicates this anticline is generated from this depth and propagated upwards. Structural model is constructed for this anticline taking into consideration the two mechanisms informing this structure; one is the occurrence of slipping along detachment surface and second is the effect of the strike-slip faults (Tear faults) cross cutting Harir structure. These two mechanisms acted synchronously and beginning at least from Late Cretaceous to the end of the Tertiary.