عنوان مقاله [English]
Iran forms a relatively compact zone of active continental deformation resulted from the northward collision of Arabia with Eurasia during late Cenozoic times, which is continuing to the present-day at a rate of 25 mm/yrs (from GPS data). Evidences of active tectonic in different parts of Iran, has been studied and identified. The arid climate, low rates of erosion, and minimal vegetation cover across the majority of the country result in excellent preservation and exposure of surface deformation produced by active faults. Geomorphic indices are useful tools for evaluation of active tectonics because they can provide rapid insight concerning specific areas within a region which is undergoing adjustment to relatively rapid and even slow rates of active tectonics. Alluvial fans, river terraces, runoff anomaly and horizontal and vertical displacement of faults are the most important landforms that indicate active tectonics and active faults. Active tectonics play a very important role in deformations of the alluvial fans. Without continued tectonics, fans may become minor or short-lived features. Morphological evidence of different types of faults such as thrust faults and strike-slip faults can be determined in surface of quaternary landforms. For example, Late Quaternary activity on strike-slip faults can be determined from the lateral displacement of young landforms such as river terraces and alluvial fans, or from scarps introduced by slight dip-slip components of motion. In this study, the evidence and impacts of the active faults have been investigated in quaternary landforms such as river terraces, stream displacements and spatially alluvial fans morphometry and morphology located at the south part of the MishoDagh Mountain in northwest Iran.
Materials and Methods
The method is based on the obtained qualitative and quantitative data. The quantitative data includes satellite image interpretation and digital elevation models, alluvial fan morphometry, channel displacement and rate of sediments uplift. Longitudinal and cross profile and gradient analysis used to interpret the active fault effects on alluvial fans. Topography maps (1:25000), ETM, SPOT and Quickbird satellite images with 30, 15 and less than 3 m spatial resolution, geology maps (1:100000) and digital elevation models (10m pixel resolution) were applied in this study. For such interpretation, ArcGIS, ENVI and Freehand software were utilized. All of the maps were produced using freehand and ArcGIS software. The field works for investigation of the evidence of fault activities were performed. Field studies were performed for the identification and measurement of parameters such as the uplift of sediments, displacements of river, alluvial fans, and channel avulsion and river terraces. Finally, the data obtained during field studies are compared and analyzed through quantitative and descriptive methods. It was also attempted to estimate spatial development and effectiveness of active tectonics on quaternary landforms and alluvial fans.
Results and Discussion
The study area of this research is located in south part of MishoDagh Mountains, northwest Iran (north of Lake Urmia). Tabriz fault is located in east part of the study area. There are three main faults in this area. South Misho Fault (SMF) is located in mountain front and affects the apex of alluvial fans and river terraces. The faults of Shabestar, Daryan-Heris-Shanlan, and Sharafkhane are located far from the mountain front. South Misho Fault has caused displacement of the main channel in fan apex, and alluvial terrace sequence. This fault has elevated river terraces about 150m from river bed. while evidence of the activities of the two other faults are more, and has caused uplifting of terain, derelict of fan surface, change of intersection point, uplift of fan sediment and lateral change of fan surface channels. The slope of most alluvial fans is 3-5 percent. The Sis fan is the largest fan in the study area. This fan is combined from several quaternary surfaces elevated in response to fault activity. Sis fan are affected by the faults more than the others and reformated to present landform since quaternary. The faults of Shabestar, Sharafkhane and Heris-Daryan-Shanjan are strike-slip faults that have changed rivers and runoff laterally.
The findings show that the faults of Shabester, Sharafkhane, Heris-Daryan-Shanjan and South Misho were active in quaternary. The position and forms of alluvial fans are affected by the activities of these faults. The faults have had either lateral or vertical displacements. The findings have also indicated that the alluvial fan forms and their longitudinal and lateral profiles are affected by Shabester, Sharafkhane, Heris-Daryan-Shanjan faults. Investigations show that there is no statistical correlation among the variables that affect the alluvial fans. Generally, tectonic activities disrupt natural evolution of alluvial fans. Each fault has a different effect on alluvial fan evolution. South Misho fault has caused the displacement of the main channel and the formation of river terraces. Therefore, has increased slope of this part. Other faults have caused uplift of fan deposits, change in the intersection point and reconstruction of new alluvial fans in the lower part of this point. Remote sensing studies can provide a valuable first step in the identification and analysis of active faulting in actively deforming regions.