藏南雅鲁藏布江现代河流砂碎屑锆石U-Pb定年和Hf同位素分析

论文摘要

为限定当前藏南雅鲁藏布江水系物源特点以及沉积物搬运过程对物源特点的影响,我们对采自雅鲁藏布江及其流经拉萨地体不同物源区域的二级河流的10个河流砂样品开展了同时的U-Pb定年和Hf同位素分析。我们也引用早期工作中的四个样品来补充这次研究的结果。拉萨河与其流域内基岩之间U-Pb年龄谱和εHf（t）值的的详细对比证实除基岩类型及其相应的出露面积外,差异风化和埋藏历史对二级河流搬运源区某些特征有重要作用。尽管部分北拉萨地体位于藏南雅鲁藏布江的流域内,但是我们结果表明雅鲁藏布江主干携带的碎屑物质主要来自南拉萨地体和喜玛拉雅造山带,并且南拉萨地体的U-Pb年龄谱和相应的εHf（t）值侧向发生变化。此外,随着远离相应的物源区域,雅鲁藏布江的搬运作用系统地稀释了特征物源的信号强度。因此,我们认为侧向变化的物源以及搬运过程的稀释作用共同决定最终搬运到喜玛拉雅前陆盆地的碎屑物质的特征。结合东喜玛拉雅前陆盆地新近纪砂岩的早期结果,我们发现Itanagar地区的Dafla组和Bhalukpong地区的Subansiri组中存在来自贡嘎和加查之间南拉萨地体和雅拉香波附近年轻喜玛拉雅岩浆岩的物质,而Itanagar地区的Subansiri和Kimin组的碎屑物质和现在的香河携带的碎屑物质相似。同时考虑搬运过程的作用,我们倾向于认为：在当前雅江-布拉马普特河流轮廓确定之前,由于藏南雅江受冰川坝或南北向裂谷的阻挡作用,古雅江和古布拉马普特河之间曾通过古苏班西里河短期相连。

论文目录

• 摘要
• Abstract
• CHAPTER 1 INTRODUCTION
• 1.1 Fundamental Questions
• 1.2 Study Contents
• 1.3 Completed Work
• CHAPTER 2 REGIONAL GEOLOGY
• 2.1 Lhasa Terrane
• 2.2 Himalayan Orogen
• 2.3 Models for the Evolution of the Yalu River system
• 2.3.1 Stationary River Configuration
• 2.3.2 Eastern Option
• 2.3.3 Capture of the Longitudinal Rivers by Transverse Rivers
• 2.3.4 Diversion of Longitudinal Rivers into Transverse Rivers due to Damming
• CHAPTER 3 AGES AND HF ISOTOPE VALUES OF BEDROCKS
• 3.1 Lhasa Terrane
• 3.1.1 The Northern Lhasa Terrane
• 3.1.2 The Southern Lhasa Terrane
• 3.1.3 Bomi-Chayu Igneous Belt
• 3.2 Himalayan Orogen
• CHAPTER 4 SAMPLLE COLLECTION AND ANALYTICAL METHODS
• 4.1 Sampling Strategy and Sample Sites
• 4.2 Analytical Methods
• 4.2.1 Petrographic Study by the Gazzi-Dickinson Point-counting Method
• 4.2.2 LA-ICP-MS U-Pb Dating and Lu-Hf isotopic Analysis of Detrital Zircon
• CHAPTER 5 PETROGRAPIC OBSERVATION AND DATA RESULTS
• 5.1 Petrograpic observation
• 5.1.1 Short Rivers Transversing the Sourthern Lhasa Terrane
• 5.1.2 Long Rivers Traversing the Northern and Southern Lhasa Terrane
• 5.1.3 Main Trunk of the Yalu River
• 5.2 Results of U-Pb detrital zircon dating
• 5.2.1 Short Rivers Traversing the Southern Lhasa Terrane
• 5.2.2 Long Rivers Traversing the Northern and Southern Lhasa Terrane
• 5.2.3 Main Trunk of the Yalu River
• 5.3 Hf Isotopic values of Detrital Zircon
• 5.3.1 Short Rivers Traversing the Southern Lhasa Terrane
• 5.3.2 Long Rivers Traversing the Northern and Southern Lhasa Terrane
• 5.3.3 Main Trunk of the Yalu River
• CHAPTER 6 DISCUSSION
• 6.1 Comparison between Bedrock and Modern Sand:The Role of Differential Weathering
• 6.1.1 Short Rivers North of the Yalu River
• 6.1.2 Long Rivers North of the Yalu River
• 6.1.3 An Example:the Lhasa River
• 6.2 Variation of Age Spectra along the Yalu River:The Role of Laterally Varying Provenance and Sediment-transport Processes
• 6.3 Late Cenozoic Drainage Evolution in the Eastern Himalayan Orogen
• CONCLUSION
• ACKNOWLEDGEMENTS
• REFERENCE
• CURRICULUM VITAE
• APPENDIX DATA A
• APPENDIX DATA B
• APPENDIX DATA C