Paleostress Analysis of the Northeastern Limb of Pulkhana Anticline /NE Iraq: Implications for Arabian Plate Tectonic Evolution

Abstract

Pulkhana anticline is located in Tuzhurmatu area, about 50 km SE of Kirkuk city. The study area forms a part of the Zagros Folded Zone which is situated in the unstable shelf of Iraq within the physiographic zone called Foothill Zone (in the middle of Hemrin- Makhul subzone). The north eastern limb of the anticline reaches to 50ᵒ and the dip of the south western limb reaches to 70ᵒ. The core of the structure comprises the rocks of Fat’ha Formation surrounded by rocks of Injana and Mukdadiya Formations, whereas Bai-Hasan Formation forms the slopes of the low hills surrounding the anticline. These Formations range in age from Middle Miocene to Pliocene. More than 761 readings of joint planes were collected from 20 stations within 5 traverses in the study area. The study of joint sets and system was within Injana and Mukhdadiya formations, along traverses with 3-5 stations for each travers track. The results showed the presence of two sets of tension joints (bc, ac) and five sets of shear joints, through defining the maximum stress axis (σ1) and acute angle dividers for these conjugate joints. It was determined that two directions of Paleostress are present in the area, which are NE-SW and NW-SE. The direction of the first major stress (NE-SW) is orthogonal with, or normal to, the fold axis in the study area, which can be considered as a horizontal component which resulted from oblique collision of Arabian and Eurasian Plates. This old compressive stress is the reason behind the formation of the tension joint (ac) and shear joints, where the sets (ac) and system are perpendicular-semi perpendicular to the bedding plane, as they were formed at an early stage of folding. Also, the ) joint was formed in five tectonic stages with different time intervals. Joints formed in different tectonic stages, in the study area, are attributed to oblique collision of Arabian and Eurasian plates and counter clockwise rotation of Arabian plate relative to Eruasian plate.

Extractions Morphotectonic Features Using Satellite Data Processing and DEM-Derived Spatial Models

“…The morphotectonic features inferred from the analysis of the Shireen Anticline indicate that they are caused by the asymmetric movement on both sides of shallow structural faults in a northwest-southeast direction within the sedimentary cover (Ramthan et al, 2021), as well as variation of tectonic stresses is affecting the shape of the folds in northern Iraq (AL-Hachem, 2020). However, the previous studies concerning the analysis of tectonic stress indicated that the magnitude of the greatest compressive stress was in the direction of northeast-southwest and the perpendicularity of the greater tensile stress to it in the early stages of folding as a result of the oblique collision between the Arabian Plate and the Eurasian Plate, as well as the rotation of the Arabian Plate counterclockwise (Agard et al, 2005;Othman and Jadda, 2020). This results in a differential motion that can be theoretically illustrated by Fig.…”

“…The current study involved extracting the morphotectonic features using the digital processing of Landsat image as well as the derivation of certain models from the DEM that covers the Shireen anticline. Because of the collision of the Arabian Plate with the Eurasian Plate (Numan, 2001;Agard et al, 2005;Othman and Jadda, 2020), the Shireen anticline showed certain morphotectonic properties due to the influence of different horizontal compressive stresses from the north and northeast. The results of the morphotectonic analysis revealed that there are several faults in the southwestern limb that have contributed to a clear displacement in the layers as well as an increase in the effect of tectonic uplift in this part of the anticline, which may have indicated that this limb has suffered extreme stresses relative to the northeastern limb.…”

“…Morphotectonic features represent major elements in high relief and tectonically active regions; hence, they demand sufficient detection and extraction to estimate the impact of tectonic activity on the landforms. According to (Mahmood et al, 2014;Hamdoon et al, 2021), morphotectonic features are controlled by some factors in the mountainous region; this includes the relative tectonic uplift rates, translational, and upright motions (Agard et al, 2005;Othman and Jadda, 2020;Znad et al, 2020). These factors specify the essential relationship of stream incision with the rock resistance to erosion (Anderson and MacGregor, 1998).…”