Tectonic Control On The Migration Of The Main Drainage Divide Of A Mountain Belt

The main drainage divide that spreads along the ridgeline,is one of the most important topographic features of a mountain range.The migration of the main drainage divide has a crucial impact on landscape evolution,precipitation,sediment transport and deposition,the occurrence of geologic hazards,land use,and biodiversity.Meanwhile,these processes,in turn,affect divide migration.Therefore,the study of divide migration has a significant impact on geomorphology,climatology,disaster science,sedimentology,and biology.Thus,it can promote the cross integration of these disciplines.Geomorphologists have studied the migration of the main drainage divide through a variety of methods.However,because divide migration is controlled by many factors,there are still some major scientific questions: How do tectonic uplift and horizontal advection affect divide migration? How do tectonic movement and surface erosion influence divide migration? How does tectonic uplift that varies along the mountain belt affect divide mobility? What is the indication of the main drainage divide on tectonic movement?Based on the above scientific questions,in this thesis,research is described through numerical simulations,geomorphological analyses,and mathematical derivations.First,numerical simulation and mathematical derivation are combined to study the control of the tectonic uplift gradient and advection velocity on the position of the main drainage divide.Then,the mechanism of joint control of tectonic movement and erosion on divide migration is explored.Accordingly,a method of constraining tectonic uplift and advection through the main drainage divide is established.The method is applied to Wulashan mountains in Inner Mongolia,Sicily island in Italy,and Taiwan island.In addition,numerical simulations are used to explore the response of the main drainage divide to normal fault linkage.The results of the simulations are applied to Langshan mountains in Inner Mongolia.The innovative results are: 1)Mountain asymmetry,depending on the location of the main drainage divide,increases with uplift gradient and advection velocity;2)Tectonic movement and erosion compete with each other and jointly influence the migration of the main drainage divide.When the contribution of tectonics and erosion to divide migration is equal and opposite,the divide will no longer move and the mountain belt will reach a topographic steady state;3)Using the tectonic information constraint method developed by this thesis,the uplift rate of the fault in the southern piedmont of Wulashan mountains is 0.14 mm/year higher than that in the northern piedmont.The tectonic activity in northeastern Sicily is relatively stable or slightly changed.Advection and differential uplift in southern Taiwan island are the main factors controlling divide migration,and differential precipitation is the secondary factor.Under current conditions,the main divide of southern Taiwan island should be stabilized closer to the southeast coast than its current location.The first possible reason for this difference is that the uplift gradient and advection velocity are overestimated.The second reason is that the tectonic activity of southern Taiwan island has increased;4)The main drainage divide evolves from an ‘M' shape before normal fault linkage to a ‘bow' shape after fault linkage;5)The topography of Langshan mountains has not reached a steady state and is responding to the fault linkage.This thesis systematically studies the migration of the main drainage divide,and establishes a new method for constraining tectonic uplift and advection.Four case studies provide more information about the local tectonic movement.The new method can be applied to other mountain belts in nature.Therefore,this thesis has high theoretical and practical significance.