Paleo-stress analysis of Koleh Sangi region- northern Zahedan- Sistan suture zone

Understanding regional tectonics and characterizing local processes greatly benefit from local measurements of paleo-stress direction. Mathematical techniques based on the inversion of fault slip data are one of the frequently used techniques for detecting the direction of the paleo-stress (Balansa et al., 2022; Zhang et al., 2020; Angelier 1994; Jentzer et al., 2017). The deformed area of Koleh-Sangi is situated structurally in the centert of the Sistan Suture Zone, north of Zahedan. Sistan Suture Zone is a most intricate structural regions that several research have been conducted to comprehend the past deformation of this area. Given that the studied region has several faults and fractures, the orientation of paleo-tectonic stresses has mostly been dependent on the orientation of faults and the relative movement along them, and the results of structural analysis and paleo-stress investigations were ignored. Therefore, it is essential to conduct this research, and its findings may contribute to a better knowledge of the Sistan Suture Zone.

A kinematic process results in slickenside and movement along the fault. For many years, structural investigations have employed the kinematic study index to identify several types of paleo-stress, including fault lines, shear zones, veins, and stylolites. The slickenside fault planes can be employed as movement or kinematic markers (Hancock 1985; Roberts 1996; Roberts and Michetti 2004). The range of structural components, such as slickenside, have been considered in the reconstruction techniques for paleo-stress. The four stress tensor parameters are based on the amount and direction of slide on the fault plane (Angelier, 1989; 1991). These parameters, which include the principal stress axes σ1≥σ2≥σ3, are introduced in the form of the following equation with the title R, which is the same as the ratio of the magnitude of the stress ellipse. These parameters depend on the ratio of the magnitude of the intermediate stress σ2, the maximum σ1, and the minimum σ3 principal stresses.

It was attempted to take the spatial features of faults and their related structures from four sites with varied ages of deformed rocks to calculate the paleo-stress parameters in the different area (areas A, B, C and D). According to the main goal of the article, it has been tried to take into account the early and late geological events. The properties of the fault planes, the slickenside, as well as the fault's Cross-cutting relationships and movement, were collected during the field surveys. The stress ratio (φ) has been fluctuating between 0.3 and 0.9 based on observations made and the interpretation of the data acquired in the MIM software from four areas with varying rock ages. The maximum and minimum trend and plunge of the computed axes were drawn on the contour diagram for each range to produce a specific pattern to estimate the orientation of the stress axes, and the most compatible planes for the axes were identified on the diagram.

The earliest rock formations in the area, were impacted by a compressional phase that occurred at an N84°E.The second phase of progressive deformation indicates the N59°E.Its compressional direction has been determined to be N10°. This compressional direction is consistent with both the compressional trend determined by GPS (Vernant et al, 2004) and the trend obtained for the major faults in this region,) such as the Zahedan dextral strike-slip fault, the Nosratabad dextral strike-slip fault and reverse faults with a north-northwest strike (Berberian et al., 2000; Walker and Khatib, 2006). According to the available data and earlier investigations, this deformation phase occurred during or after the Eocene and has persisted up to the current day.A transtension regime is visible in the youngest phase in Paleocene and Oligocene-Miocene outcrops. This phase may be brought on by normal faults along fold axes, on the hanging wall of thrust faults and associated with north-south strike-slip faults. The latest stage of deformation in the area may be explained by the presence of the Zahedan strike-slip fault, which has a significant amount of displacement throughout its length.