Structural evolution of northwest-southeast trend in Hemmatabad area – East Iran

Northwest-southeast structural trend, is one of the dominant structural trends in the east of Iran. Dextral N-S striking Nehbandan fault system, is located between Sistan and Lut structural zones. The tectonic model and growth of northwest-southeast trends in the east of Iran will be introduced by deformation analysis in Hematabad region.

The rock units of the Sistan subzone include: Cretaceous ophiolitic and metamorphic units and flysch-pyroclastic units. Hematabad region includes: ophiolitic units extending in the northwest-southeast direction, volcanic rocks, and sandstone, shale, limestone units with metamorphism ranging from slate, phyllite to schist.The northwest plunging folds in the tertiary’s shale and sandstone units have steep forelimb on the southwest side, which indicates the southwest tectonic vergence. From northeast to southwest, ophiolite outcrops, folded cretaceous and tertiary sediments can be observed, which can be a reason for the growth of structures from northeast to southwest. North-south and northwest-southeast striking fault zones are dominated in this region. Geometric and kinematic analysis of mentioned fault zones, indicates the main axis of compression in the region has an average trend of N25E. The shear component is dominant in the north-south fault zones and the compressive component is dominant in the northwest-southeast ones. According to the geometrical analysis of the faults and their mechanisms, folds and the rock units outcrop, the activity of the faults in the northeastern part can be considered as older (earlier) faults. Therefore, they are a series of thrust faults that are growing from the northeast to the southwest.

Based on geomorphological evidences such as displaced rivers, shutter ridges and fault scarps in Hematabad region, fault zones migrate to the southwest. In addition, tectonic activity decreases from southeast toward the northwest. By asessement of the fault and folds, outcrop of the rock units and the morphotectonic features, the following structural model can be presented:The first stage: by NE component of compressive stress, the NW-SE striking Hematabad fault zone in which the pressure component is dominant, ophiolitic units was exposed.The second stage: a new fault the same as Hemmatabad fault zone (NW-SE) has been formed in its southwestern part with a reverse right-lateral mechanism. With the continuation of mentioned deformation, folding of Cretaceous and Paleocene-Eocene sedimentary rocks and displacement in rivers occurred.Third stage: Shutter ridges develop with the formation of new faults. In this model, the growth of the structures has been done from the northeast to the southwest.NE component of compressive stress, has caused folds with a northwest-southeast axial trace in the region. In north-south striking faults, the strike-slip component is dominant, but in northwest-southeast striking faults (such as Hematabad fault zone), the reverse component is dominant.The morphotectonic evidences indicate that the uplift of fault scarps is decreasing from the northeast to the southwest, and the deflection of rivers is decreasing from the southeast to the northwest. Therefore, the tectonic activity in the southeastern part is more than the northwestern part in this region.

The growth of structures in this area continues with the creation of NW-SE striking fault zones from the northeast to the southwest, which indicates the structural growth in the northwest-southeast trends in the east of Iran.