lut block

Galleh Chah area is located in the 1:100000 geological map of Ayesk, in the northwestern part of the Lut zone, in a sub-shear zone (the Galehchah shear zone) along the northwest-southeast direction. By studying satellite images along with field observations and drawing rose diagrams, fractures in the region are placed in three groups in order of occurrence time. 1. Almost north-south faults that are dextral strike-slip with a reverse component that are cut by other faults. These faults lack mineralization. 2. Northwest-southeast faults as dextral strike-slip with reverse component. These main shear zone faults (Y) and conjugate faults that have a smaller angle with the shear zone (R and P) have provided conduits for the rise and deposition of ores. 3. The northeast-southwest faults are left-lateral with a normal component that cut off the previous two groups. The paleostress patterns indicates two evolutionary stages in the Galleh Chah region. In the first stage, the stress in the northeast-southwest direction has caused the creation of an almost north-south shear zone with dextral strike-slip faults with a reverse component. In this stage, folds with a northwest-southeast axial trend have been created. Then, as a result of a local stress in the direction of north to northwest-south to southeast, Galleh Chah shear zone with northwest-southeast trend and with dextral strike-slip faults with reverse component has been formed. With the continued activity of Galleh Chah shear zone, antithetic Riddle fractures with the northeastsouthwest trend have caused the displacement of previous faults and mineralization veins.

Adjacent to the northern border of the Sistan suture zone and the Lut block, north of the Qayen, the Paleocene-Eocene volcano-sedimentary sequence represents an interference pattern of folding. Crescent structures indicate the type 2 of superimposed folding. The axial plan of the first generation of the large-scale folds is generally east-west trended, but along their strike, they are obviously curved to the north and south. A linear dioritic-andesitic dyke swarm, is intruded on this sequence with a radial pattern, and cut the axial plane of the first generation and is affected by the second generation of folding. In order to date this tectono-magmatic event, U-Pb dating is performed on the zircon crystals of these dykes, and an age of ~40 Ma is yielded as the cooling age. The consistency between the dykes’ strikes and the curvature of the first-generation folding axial plane (in response to the second folding event) gave a redial pattern with 30o declination to this dyke swarm. This may indicate the intruding and cooling of the dykes coincide with the second folding generation. Acceptable adaptation of the declination of these dykes to that of the curved axial plane of the first folding episode on the linear regression diagram can be a new method for testing the bends that originally have been linear. Our structural analyses on the Qayen area indicate that Achani structure is a clear example of a larger oroclinal buckling in the region, during the Eocene, coinciding with the formation of the Eastern Iranian Orocline.

SE trending (S62E) and NE dipping (80NE) mylonitic foliation is the main structural feature developed in ~557-561Ma Deh-Zaman mylonitic granite in the N70˚E trending Kuh-e-Sarhangi shear zone at the northwest of the Lut Block. 35˚ plunge of the stretching lineation on this mylonitic foliation in combined with microstructural evidence, especially on feldspar crystals confirmed dominant sinistral shear with the little compressional component. Sinistral shear proposed to initiate after emplacement of the granitic body and deformed it at ~300-500˚C during Early Cambrian. Our new and detailed microstructural analysis indicates considerable overprinting of dextral shear on the former older sinistral shear in the Deh-Zaman mylonitic granite. There is no radiometric age constraint on the timing of the shearing shift from sinistral to dextral kinematics; however, based on the structural and stratigraphic evidence, we propose post-Late Cretaceous- Paleocene age of the kinematic change. This shear sense change matches with Structural evolution of the Kuh-e-Sarhangi region in which sense of shear has been changed several times during its evolution.