• 研究论文 •

### 青藏高原东南缘地貌边界性质的界定及其对高原东南缘扩展模式的启示

1. 1. 中国地质大学(武汉), 地球科学学院, 武汉 430074;
2. 中国地质大学(武汉), 地质过程与矿产资源国家重点实验室, 全球构造研究中心, 武汉 430074
• 收稿日期:2018-11-15 修回日期:2018-12-25 出版日期:2019-04-20 发布日期:2019-05-21
• 通讯作者: 王国灿,男,1963年生,教授,博士生导师,长期从事区域地质、构造地质学教学与研究,E-mail:wgcan@cug.edu.cn
• 作者简介:吴贵灵,男,1992年生,中国地质大学(武汉)构造地质学专业在读硕士研究生,主要从事青藏高原东南缘构造地貌研究,电话:17671462008,E-mail:1289037880@qq.com。
• 基金资助:
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（41672195）资助

### DEMARCATION OF THE GEOMORPHOLOGICAL BOUNDARIES OF SOUTHEASTERN TIBET: IMPLICATIONS FOR EXPANSION MECHANISMS OF THE PLATEAU EDGE

1. 1. Center for Global Tectonics, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;
2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China
• Received:2018-11-15 Revised:2018-12-25 Online:2019-04-20 Published:2019-05-21

Abstract: The geomorphologic structure in the southeastern Tibetan Plateau is one of the important indexes for the expansion and deep dynamic process of Tibet. There are two different understandings for the geomorphologic structure in the southeastern Tibetan Plateau, i.e. gradual change and abrupt change. The gradient model suggests a gradual topographic reduction towards southeast which is an important evidence for the lower crust channel flow. The abrupt model considers that the southeast boundary of the plateau shows an abrupt change of topography in a zone of 50~200km wide which is controlled by the Yarlung-Yulong fault system. Here, we describe the morphotectonic feature in detail of the Sichuan-Yunnan block on the southeast edge of the plateau through the digital elevation model(DEM)analysis, further review the structural controls on the geomorphologic structure by combining the tectono-thermochronology analysis, and evaluate the southeastward spreading mode of the plateau.
The topographic arithmetic progression ranking by using the DEM of the Sichuan-Yunnan block reveals three geomorphologic steps gradually lowering from the northwest to southeast. The switching of hypsometric integral(HI)value and the anomaly of SL/K value(where SL is stream length-gradient index and K is altitude of the profile)of river systems all occur on the edge of terraces. The high terrace is located on the north of Muli-Yulong with average elevation~4 200m; the secondary level of terrace extends to the Yanyuan-Lijiang area with average elevation~3 000m; and the third level is the region between the Jinhe-Qinghe and Anninghe with average elevation~1 800m.
Structure investigation reveals that all the topographic boundaries between different terraces are consistent with regional major faults. The Muli thrust fault and Yulong thrust fault control the southeast edge of the high terrace, the Jinhe-Qinghe thrust fault separates the second and third level of terrace. The coincidence between topography boundaries and faults suggests that the formation of the stepped geomorphology on the southeast edge of the plateau were induced by the fault activities, reflecting the fault-controlled southeastward stepped-expanding mode of the plateau.
The fission-track(FT)dating of the granites at the hanging wall of the Yuling-Muli Fault reveals fast uplift during~27~22Ma BP, reflecting the major thrusting along the Yulong-Muli Fault, which is consistent with the early-stage activity (~30~25Ma BP) of the Longmenshan Fault. Therefore, the high terrace was formed during the Oligocene to early Miocene with the thrusting of the Yulong-Muli Fault. Tectono-thermochronology analysis also reveals the major thrusting of the Jinhe-Qinghe Fault occurred during~18~11Ma BP, indicating the middle terrace was formed in the middle Miocene, which also could correspond to the middle Miocene(~15~10Ma BP) activity of the Longmenshan Fault.
Therefore, the thrusting faults controlled stepped terrace geomorphologic structure and the stepwise expanding mode under combined movements of large-scale thrusts and strike-slip faults at the southeast edge of Tibetan Plateau during the late Cenozoic do not support the lower crust channel flow model.