Sediment Characteristics And Provenance Forward Modeling Of Detrital Zircon In The Beida River System,North Qilian

Source analysis is a necessary part of basin mountain coupling analysis,paleogeographic reconstruction,and tectonic background tracing.With the advancement of modern analytical methods,source analysis has gradually developed into a form of analysis that combines multiple methods and technologies.Although the methods of source analysis are becoming increasingly diverse,there is still room for breakthroughs in accurate and reliable quantitative analysis of sources.Traditional source analysis mostly involves inversion of the source,which involves simple correspondence between the sink and source regions.However,the inherent limitations of the source analysis method,as well as the material changes that occur during sediment transportation,as well as the impact of factors such as terrain elevation,parent rock lithology,erosion intensity,and climate conditions on the erosion,transportation,and sorting of different debris,will increase the difficulty of source inversion analysis.In response to the challenges faced by quantitative analysis of sediment sources,forward modeling analysis of sediment sources in rivers is gradually being carried out.The formation,uplift and denudation of the North Qilian Mountain is an important part of the study of tectonics evolution and collision response in the northern margin of the Tibetan Plateau.The complex tectonic evolution has led to the widespread development of rivers and basins in the North Qilian Mountain,making it an ideal place to study the source sink system of material transport.There has been detailed research on the stratigraphic composition,structural evolution,and river sediment characteristics in this area.Each source element has a rich reserve of zircon dating data,providing a good foundation for conducting forward research on sediment source analysis in the Beida River.From the perspective of forward source analysis,this article uses river sand as a medium to understand the source sink system and conducts forward modeling research on modern river sediment characteristics and detrital zircon sources.By conducting gravel statistics,heavy mineral analysis,and U-Pb dating of detrital sediments from the Beida River,the significance of different detrital sediments as indicators of provenance is discussed.Simultaneously utilizing the morphological characteristics of zircon and U-Pb dating results of detrital zircon,combined with recycled zirconα-dose calculation and DZmix source forward modeling explored the transport process,sorting conditions,and contribution mechanism of sediment from source to sink from the perspective of source forward modeling.The main insights are as follows:The results of the Beida River detrital sediment show that different sediments have different emphasis on reflecting the source of matter.The composition of gravel is influenced by the lithology,area,flow range,and fault zone of adjacent exposed strata.Heavy minerals are more sensitive to the reflection of iron ore in the watershed,and the ZTR index can be used as an effective indicator to determine the transportation distance.The detrital zircon comes from the comprehensive contribution of the source end element in the source area,and the proportion of zircon has a good positive correlation with the comprehensive contribution of the age peak of the source end element.Therefore,the relative content Di of the detrital component in the sink area can be regarded as the comprehensive contribution of the detrital component in the source area Pj（Di=₁ⁿPj×Cj）,where Cj represents the contribution rate of various detrital components,and the contribution rate of fractured and loose rock layers is higher.The CL images and morphological features of detrital zircons also contain a lot of source information,and their comprehensive application can provide good indicators for source supplementation,source mixing,and source distance along the way.The vertical height difference and the transportation and sorting of flowing water have a significant impact on the roundness of zircon.The change in integrity can indicate whether there are new sources of sediment supplementation during transportation.The variation trend of the Di value of detrital zircon can reflect the source distance under certain conditions,but it should be carefully combined with the geological background around the sampling point to discuss the relationship between the recycling of zircon and the distance from the source.The forward modeling results of zircon U-Pb age spectrum confirm that the DZmix model can accurately fit the distribution of complex source ages,but the contribution rate of the obtained source strata largely depends on the selection of source end elements,and there is no positive correlation with the area of source end elements/source drainage basin.In addition to the area of the source end elements,factors that affect the contribution of zircon in different source end elements should also be considered,and appropriate weights should be given to their contribution rate to the source end elements.Further integrating various influencing factors（source area,lithology,tectonics,elevation and slope,precipitation,etc.）and conducting numerical simulation will obtain more accurate source forward results,providing a basis for improving the quantitative analysis method of source.