青藏高原东缘龙门山山系构造隆起的地貌表现  

MORPHOLOGICAL APPEARANCE OF THE LONGMENSHAN TECTONIC UPLIFT ON THE EASTERN MARGIN OF TIBETAN PLATEAU

作　　者：张世民[1] 丁锐[1] 毛昌伟[1] 吕志强[1] 

机构地区：[1]中国地震局地壳应力研究所,北京100085

出　　处：《第四纪研究》2010年第4期791-802,共12页Quaternary Sciences

基　　金：中央级公益性科研院所基本科研业务专项项目(批准号:ZDJ2009-1);国家自然科学基金项目(批准号:40972143)共同资助

摘　　要：龙门山山系是青藏高原东缘新生代造山作用的体现,是理解青藏高原向东扩展动力学过程的窗口。龙门山隆升机制研究因而成为青藏高原地学领域的热点问题之一,并形成了地壳缩短与下地壳管道流两种截然不同的观点,进一步的讨论期待着对龙门山隆升特征作出更深入地认识。夷平面与河流地貌忠实地记录了山地隆升的过程,其形态能够客观地反映山地隆升的几何特征。文章通过数字高程资料分析了龙门山地区的第三纪夷平面,并沿横穿龙门山的大渡河流域测量了河流阶地、山麓剥蚀面及其同期宽谷地貌。夷平面、宽谷地貌与河流阶地的变形特征显示,晚新生代以来,龙门山山系一方面相对东侧四川盆地发生显著的冲断式隆升,隆起幅度达4500m左右;同时相对青藏高原腹地发生了一定的挠曲式隆升,挠曲的枢纽大致沿龙日坝断裂带展布,隆起幅度为500m至1000m,即龙门山山系的构造隆升由东翼的冲断作用与西翼的挠曲作用联合完成,龙门山山系因而构成了青藏高原与四川盆地之间的一道地形屏障。文章最后讨论了导致龙门山山系拱曲冲断作用的可能因素,包括上地壳的断弯褶皱作用、下地壳物质上涌作用和地表侵蚀导致的重力均衡效应。鉴于沿龙门山隆升带东西两翼发现了纵向逆冲断裂或逆走滑断裂,而没有发现纵向张性构造,推断断弯褶皱可能为主导因素。The Longmenshan Moutains are a vivid manifestation of the Cenozoic orogenesis on the eastern margin of the Tibetan Plateau,and a key to understand the geodynamics of eastward extending of the plateau. Thus the uplift mechanism of the Longmenshan Mountains became a hot spot issue of geosciences concerned about the Tibetan Plateau. Two entirely different hypotheses were put forward： crustal shorting and lower crustal channel flow, but the solution is open. Further discussion needs our deeper understanding of the uplifting features of the Longmenshan Mountains. Fortunately,the uplifting processes were recorded objectively by peneplains and river landforms. In this paper,the Tertiary planation surface of the Longmenshan Mountains area was analyzed on the basis of elevation data,terraces, pediments, and straths of the Dadu River across the mountains were surveyed, geometric features of Cenozoic uplifting were studied, and the possible mechanisms for the uplifting were discussed. In the study area,planation could begin in Early Cenozoic time but end at Late Miocene. In that period,the height differences between mountains and valleys were possibly less than one kilometer. The Daduhe River incised into the planation surface and resulted in more than ten levels of terraces. The highest terrace occurred as a strath which corresponded to the pediplane formed in Late Pliocene or in Early Pleistocene. Because of their originally flat feature,the planation surface and the strath can be used as the datum planes for judging neotectonic deformations. Since Late Miocene,the southeastern side of the Longmenshan Mountains has been dominated by thrust-faulting with a total vertical displacement of about 4500m against the Sichuan Basin,while the northwest side has maintained an arch uplifting： the long axis of the arch uplifting approximately followed the Longriba fault and the uplift height was about 500m to 1000m. As a landform barrier between the Tibetan plateau and the Sichuan Basin, the Longmenshan Mountains has been fo

关 键 词：青藏高原 龙门山 夷平面 宽谷 河流阶地 拱曲 冲断 

分 类 号：P542[天文地球—构造地质学] P941.74[天文地球—地质学]