Assessment the role of tectonics in the outcrops of the Zagros area salt domes

Introduction :

The Zagros fold-thrust belt belongs to the part of the Alpine-Himalayan system, represented by the southern Zagros-Dinaride branch of the orogenic belt. This is an orogenic segment NW-SE trending to a distance of nearly 2000 km and structurally consists of many synclines and anticlines. However, as basement faults are hidden from view under the more recent sedimentary units scarcely reach the surface. As a consequence, the identification and study of basement faults has mostly relied on indirect information such as anomalies in topography. Within the Zagros fold-thrust belt, there are many pierced salt plugs that are known as Hormoz series. Hormoz Salt Basin includes many diapirs of Cambrian salt that have risen through the Permian to Recent sediments. The aim of this paper is identification of basement faults in the Zagros fold-thrust belt using interpretation of satellite images, and determination of relationship between basement faults and salt plugs of Hormoz series using Geographical Information System (GIS) techniques such as the weights of evidence modeling. 

Methodology:

 In this research, we examined many techniques of remote sensing for the recognition of faults, and then we did field checking to determination of the accuracy of the work. Remotely sensed data, including Landsat Enhanced Thematic Mapper plus (ETM+) images, were used to obtain information on structural features and for deriving lineaments of the study area by production of color composite images and applying some filters, such as Laplacian and Sobel and also some directional filler. Usually, the basement faults are hidden by sedimentary cover, and their location is uncertain, but there is some evidence for identification of them, such as deflections in trends of fold axes, offset markers and alignments of salt diapirs. In the study area, most of the folds have a general east-west trend that some detachment folds are cut by basement faults. There are deflection in general trend of folds and have been classically interpreted as the effect on the cover of strike-slip movement along underlying basement trends. Some conceptual models for the evolution of the fold structures affected by basement faults, offered by Leturmy et al. that in this research are confirmed.

 Results and discussion:

 In the studied area, 34 normal and strike slip faults were recognized. Some of these basement faults could have an important role for salt uplifting. Fault No.1 is strike-slip fault with 26o azimuth crosses Larak salt plug and Hormoz salt plug and caused deviation and sinistral displacement of east of Namak anticlinal axes. Based on this fault activity, some minor faults formed parallel to the major fault. Fault No. 2 the strike-slip fault with 129o azimuth caused a deviation of the Faraghon and Namak anticline axes. This fault crosses Darbast, Takhu, Kushk kuh-West, and Gahkum salt plugs. In some tectonics text, this fault is known as Oman line. Fault No.3 This fault is known as a Minab fault, the trend of the Minab anticline and the deviation of that axis can be considered as this fault's function. The fault has a 165o azimuth. However some of the mentioned basement faults, such as fault numbers 1, 9, 11, 13, 15, 16, 17, 18, 19, 23, 24, 26, 28 and 33 may already identified, but the influence of them on the salt diapirism in the Zagros region have not been discussed. Based on the result of weights of modeling method, there is positive spatial association between the Basement faults and the salt diapirs as indicated by the contrasts C. So, findings of this research to be consistent with the aim of the plan. The positive spatial relationship is statistically considerable within 1000 to 10000 m; so, following to the highest Studentised C, it is optimal within 1000 m.

 Conclusion:

 The interpretation of satellite images based on remote sensing techniques such as shaded-relief images analysis, filtering, and deflections in trends of fold axes, shows that some structures have a character of regional photolineaments (especially NNW-SSE and NE-SW trending. Such structures were considered to be main fault systems of the study area. Finally, 34 basement faults have been identified that among them 14 faults are introduced as the first time. Also, there is a rectilinear pattern of salt diapir emplacements. These implicit lines of weakness are approximately indeed related to basement structural trends, based on weights of evidence method; pierced salt diapirs are associated spatially with basement faults within a distance of 1 km. Also among 123 detected salt diapirs in the region, forty-five of them, 36 percent, have a maximum relationship with basement faults. So, tectonic condition is an important factor in the exposure of salt diapirs in the study area.