Impact of Active Tectonics and Climate Change on Marvast Alluvial Fan Central Iran

Active tectonics and climate changes have important role in evolution of the alluvial fans in Central Iran. Climate change coupled with neotectonics of Marvast active faults have had significant role in creation and transformation of abnormal morphological patterns on the Marvast alluvial fan. In this research, have been imployed fieldworks, different software, digital elevation model, satellite images and results generalization of paleo-climatic changes studies related to Iran and adjacent areas to determine the evolution of Marvast alluvial fan. We considered all aspects of dispersion, distribution and landforms patterns to determined the mechanism of faulting, and then the development and evolution of the Marvast alluvial fans are analyzed. Perhaps, Initial formation of the Marvast alluvial fan could be attributed to the late Pleistocene, when the basin had cold and dry climate and poor vegetation cover and thunder rainfall, therefore existed large floods associated with high frequency. Following this period, with increasing of precipitation and wet period (15-10 million years ago), there were not much vegetation in the watershed, but water flow and sediment loads are increased dramatically, therefore the Marvast fan has reached its maximum expansion (950 Km2). With establishment of the wet period and dense vegetation in the basin, the sediment loads of the basin have been outclassed on basin water debit. These led to: the trenching of large fan, leaving the water flow from the abandonment fans (3 cone) on the hanging-wall of the Marvast fault, forming the new fan on foot-wall of fault (5-10 thousand previous year). The most important factor of changing of the Marvast fans, after conquering the dry climate conditions (since the early Holocene), is the active tectonic of the Marvast fault. It cased to forming a new alluvial fans in direct the Marvast fault. Although large amounts of sedimentation of dry-wet periods late Pleistocene had an important role in the Marvast alluvial fan, but available evidence suggests acceleration of the morphogenesis processes by tectonic activities. Deformation of tectonic landforms on Marvast fans, indicated displacement of about 1000 m of Pleistocene landforms, and offset the Holocene drainage systems as much as 30 meters, all of which imply an active tectonic fault Marvast, and possibly high seismic potential of faults in the future.