Dynamic Evolution Of Drainage Divides And Their Correlation With Tectonic Activities

The evolution of landscape is jointly controlled by tectonic,lithological,and climatic conditions.This recognition provides a basis for reconstructing tectonic or climatic processes using topography.The fluvial landform is ubiquitous on the Earth’s surface,and its shape,structure,and evolution are controlled by the above factors,so it contains important information about the tectonic movement.As an important geomorphic unit in fluvial landforms,drainage divides also contain rich geological information in their morphology and dynamic evolution.Therefore,drainage divides have always been an important topic to geomorphologists,and have become a hot topic in geomorphological research in recent years.Describing the movement of drainage divides and analyzing the controlling factors of their dynamic evolution is not only the premise of reconstructing the past geological process through the Earth’s surface but also the basis for further understanding the interaction between the surface process and the Earth’s spheres.In addition,studying the“Dynamic evolution of drainage divide and its correlation with tectonic activity”can not only give new ideas for analyzing tectonic movements but also provide new techniques for the research of active structures and earthquake-geological hazards.The dynamic evolution of the drainage divides and its influencing factors have always been an important topic that draws the attention of geomorphologists,and has also become a hot topic in recent years.In recent years,a lot of progress has been made on this topic,but how tectonic movement controls the stable location of a drainage divide and whether the tectonic information can be extracted from the morphology of the drainage divide have not been fully answered.A recent study has given a quantitative relationship between the stable location of a drainage divide and the spatial distribution of uplift rate,and believes that the controlling factor of the drainage divide is the uplift gradient.However,this conclusion is also based on some assumptions,and how the tectonic movement controls the drainage divide’s location when the assumptions change has not yet been theoretically studied.To further explore the influence of tectonic movement on the drainage divide’s location,in Chapter 2,we give the quantitative relationship between the uplift rate and the stable location of a drainage divide.The results show that the uplift ratio is the key controlling factor of the drainage divide’s position.To verify the correctness of the formula,we construct 16 numerical models of landform evolution with different parameters.In addition,two nature examples（the Wula Shan and the Zhongtiao Shan）are given to demonstrate the application of the formula.Except for tectonic movements,previous studies about natural examples and numerical simulations have shown that a drainage divide’s location may also be affected by lithology and climate.According to the studies,drainage divides tend to move toward the region with lower precipitation or erodibility.Besides,the morphology of drainage basins may also affect the location of drainage divides.However,how the drainage divide will adjust in response to the perturbations in lithology,climate,base-level elevation,and drainage basin’s morphology is still an unresolved issue,which may bring uncertainties in the extracting of tectonic information from the morphology of drainage divides.To further explore the influence of the above factors,in Chapter 3,we construct a parameter C（cross-divide contrast index）to quantify the influence of lithology,climate,base-level elevation,drainage basin’s morphology,etc.,and establish a multi-factor control equation for a drainage divide’s location.This theory makes the relationship between the drainage divide’s location and the uplift rate more accurate and reduces the error in the extraction of tectonic information.To verify the correctness of the theory,we construct numerical landscape evolution models to test the influence of tectonic uplift,lithology,precipitation,and base-level elevation on the location of drainage divides.In addition,we also provide three nature examples to demonstrate the application of the formula in tectonic stable areas（e.g.,the Loess Plateau）,asymmetric uplift areas（e.g.,the Wula Shan）,and the drainage divide migration areas（e.g.,the Wutai Shan）.Except for the drainage divides at steady-state,many studies show that unstable drainage divides also widely exist in nature,and determining the motion of the drainage divides is a prerequisite for extracting tectonic information from fluvial landforms.Based on theχ-transform theory,determining the motion of drainage divides by comparing theχvalues on both sides of the drainage divides was proposed.However,this method is only applicable when there is no spatial difference in the uplift rate and erosion coefficient.When the above conditions are spatially different,theχvalues on both sides of a drainage divide may also be different,and in this case,theχcomparison method can no longer be used to determine the migration direction of the drainage divide.However,spatial differences in uplift rate,erosion coefficient,and base-level elevation are widespread phenomena in nature.Without the knowledge of how these factors affect theχvalue,the further application of theχcomparison method will be limited.To quantify the influence of the above factors onχvalue,we provide a multi-factor control equation on the cross-divideχratio at steady state in Chapter 4.Using the equation,the migration direction of the drainage divide can be determined when the spatial distribution of the uplift rate and erosion coefficient is known.Besides,the uplift rate or erosion coefficient can also be inverted from theχratio when the drainage divide is stable.To verify the reliability of the formula,we construct numerical landscape evolution models and compare the results of the models with those calculated by the formula.In addition,we also give two natural examples in the drainage divide stable（e.g.,the Wula Shan）and migration area（e.g.,the Xizhou Shan）to demonstrate the application of the formula.In addition to the determination of the drainage divide’s migration direction,the quantification of the migration rate is also an important issue.At present,the calculation of a drainage divide’s migration rate mainly relies on the catchment-wide cosmogenic nuclides(¹⁰Be)concentration measurements in river sediments.However,the results of this method are controlled by the sampling location.The samples collected from larger catchments often cannot represent the erosion rate near the drainage divide.Besides,if the sampling catchment is too small,the results are often disturbed by factors including landslides near the drainage divides.Except for that,the high cost of sample testing makes it very challenging to be used in an entire landscape.Therefore,it is necessary to have a quick and efficient geomorphological method for calculating the drainage divide’s migration rate.In Chapter 5,we explore the relationship between the erosion rates and theχvalues on both sides of a drainage divide and establish a method for calculating the migration rate in large-scale landforms,which greatly improves the efficiency and reduces the cost of acquiring migration rate data.We then apply this method to eastern Tibet and give the first drainage divide migration rate distribution map in this area.Besides,to improve the calculation accuracy for small-scale landforms,we also propose a method using the channel head parameters to calculate the migration rate in Chapter 6.We then apply the above two methods to calculate the migration rate of two drainage divide segments in the Loess Plateau and the Wutai Shan.After quantifying the influence of the factors including tectonic,lithology,precipitation,base-level,and drainage divide morphology on the stable location of a drainage divide（Chapters 2 and 3）,and establishing an appropriate geomorphological method to determine the movement of the drainage divide（Chapters 4 to 6）,and in Chapter 7,we establish the process of extracting tectonic information from drainage divides at different spatial scales and motion states.Because the drainage divides with different motion states need different methods to extract tectonic information,it is necessary to first determine the motion of the drainage divides according to Chapters 5and 6.For large-scale landforms,when the requirements of accuracy are relatively low,we can use the relatively simplified formula in Chapter 5 in combination with the open-source topographic data to calculate the migration rate.For small-scale landforms,when the requirements of accuracy are relatively high,we can use the formula in Chapter 6 combined with higher-resolution topographic data to calculate the migration rate.After determining the motion of the drainage divide,for the stable drainage divide,we can use the formula in Chapter 3 to extract the tectonic information.For the migrating drainage divide,we can use the formulas in Chapter 3 or Chapter 4 to constrain the range of regional uplift rates.This study reveals the relationship between tectonic uplift and drainage divide location,quantifies the influence of tectonic,lithology,precipitation,base-level elevation,and drainage divide morphology on drainage divide’s location,and establishes a method for extracting tectonic information from stable drainage divides.This study also quantifies the influence of the above factors on the cross-divideχratio,thereby the drainage divide migration direction can be determined through the comparison of the measured and calculatedχvalues.Besides,this study provides methods for calculating the drainage divide migration rate in large-scale and small-scale landforms,which improves the acquisition efficiency of migration rate data and reduces the cost.It is worth noting that this study provides a feasible method to give constraints of uplift rate when the drainage divide is unstable.This study makes an important and timely contribution to the research hotspot of“Dynamic evolution of drainage divide and its control mechanism”,and provides a new perspective for further understanding the interaction between surface processes and the Earth’s spheres.In addition,this study also provides new ideas for analyzing tectonic movements and gives new technical means for studying active tectonics and earthquake-geological hazards.