川滇地块东南部新生代构造与地貌过程的构造热年代学与盆地物源分析

The southeastern margin of the Tibetan Plateau is an important avenue for plateau outward expansion and mass transportation. The knowledge of how the tectonics and landscape have evolved during Cenozoic is fundamental to address the mechanism of lateral plateau growth and the geodynamics of intracontinent deformation. The Sichuan-Yunnan block lies in the core of the expanding southeast Tibetan Plateau. Well-constrained link between the Cenozoic tectonics and landscape development of this area in space and time are key to understand the processes and mechanism of the growth of the southeast Tibetan Plateau, and even the Tibetan Plateau as a whole. In this project, we will target the southeastern Sichuan-Yunnan block, where previous tectono-termochronology work is relatively weak. On the basis of the analyses on the critical Cenozoic structures relevant to the plateau expansion, multiple thermochronometers will be applied to decipher how the Cenozoic structures developed and controlled differential rock exhumation and uplift. Meanwhile, the state-of-the-art approaches will be used to trace the source of the sediments in major Cenozoic basins in the study area. The comparison of provenance changes between these basins will be useful to reveal how regional fluvial system has evolved and reorganized. To sum up, based on the analysis of the interaction between tectonic and surface process, we hope to elucidate how the plateau expansion has shaped regional structures and drainages, and build multi-stage geodynamic models for Cenozoic tectonic and landscape evolution of the southeastern Tibetan Plateau.

青藏高原东南缘是新生代高原向外扩展和内部物质外运的重要通道，其新生代构造与地貌过程的精细约束是探索和揭示高原东南缘侧向扩展机理的基础，对正确理解大陆内部变形机制具有重要意义。川滇地块作为高原东南部侧向扩展的核心区域，其新生代构造与地貌过程时空关联的精细约束是高原东南缘乃至整个青藏高原扩展过程及机制研究的关键场所。本研究选择新生代构造热年代学研究相对薄弱的川滇地块东南部作为重点研究区域，在对系列新生代构造剖析的基础上，对与高原隆升扩展相关的关键构造开展针对性的构造热年代学研究，刻画控制差异抬升剥露的新生代构造发育的精细过程；同时，借助沉积盆地物源分析手段，通过川滇地块东南部主要新生代沉积盆地物源变化的对比，探寻新生代宏观地貌水系格局的演替规律。通过构造与地貌过程的综合分析，建立新生代构造发育与地貌水系格局演变和高原扩展之间的联系，探寻新生代构造—地貌演化的分阶段动力学模型。

揭示青藏高原东南缘新生代构造地貌过程是正确理解高原东南缘侧向扩展机理及大陆内部变形机制的重要基础。川滇地块作为高原东南部侧向扩展的核心区，其新生代构造地貌过程的精细约束成为关键。本研究选择川滇地块作为重点研究区，对与高原隆升扩展相关的关键构造开展针对性的构造热年代学剖析；基于主要新生代盆地沉积物源变化，探寻新生代宏观地貌水系格局的演替规律，建立高原东南缘构造-地貌-水系格局演变与高原扩展之间的联系。通过四年的探索，总体完成既定目标，重要成果体现在：1.运用数字高程分析技术，揭示川滇地块受玉龙-木里逆冲断裂和金河-箐河逆冲断裂控制的台阶式宏观构造地貌结构。2.运用构造热年代学技术，约束控制高原东南部第一、二级台阶地貌边界的玉龙-木里断裂和金河-箐河断裂分别形成于~28-20 Ma和20-15 Ma，反映高原东南缘向南东方向的台阶式前展逆冲扩展方式。3.通过对剑川盆地及邻区地质填图、构造年代学和沉积学研究，界定出鲁甸-中合江褶皱逆冲断裂带为控制川滇地块西部新生代早期盆山地貌边界，断裂于~50-37 Ma的逆冲活动控制了具有类前陆盆地性质的剑川盆地的发育及南流的古金沙江水系。4.新生代代表性沉积盆地发育时限及物源分析刻画了响应宏观地貌格局变革的水系路径演变：始新世,南流的古金沙江水系可能经过思茅盆地汇入古南海，古红河为局部水系；晚渐新世-早中新世发生，古红河发生大规模溯源侵蚀，袭夺了汇入南海的古金沙江，形成汇入南海的古金沙江–红河水系和红河谷地；中新世中晚期，走滑断裂系统引起的局部强侵蚀作用导致东流长江水系袭夺南流古金沙江-红河水系，红河断头，现代长江贯通。5.综合围限川滇地块的系列断裂活动时限及古高程、古地貌水系演化等信息，构建了川滇地块新生代多阶段断裂活动控制的构造地貌演化模型，揭示高原东南缘新生代以断裂活动为主控因素的构造地貌演化和侧向扩展过程，不支持下地壳流动机制。