青藏高原地面抬升证据讨论

Discussion on Evidences for Surface Uplift of the Tibetan Plateau

当前学术界在青藏高原地面何时达到现代高度问题上存在着许多不同观点 ,概括起来主要有 3种 :14Ma前已达到高于现代的最大高度 ,8Ma前已达到或超过现代高度 ,距今 3.4 Ma来分阶段强烈上升并逐步达到现代高度 .之所以出现如此大的意见分歧 ,除高原面积广阔、研究程度不深和覆盖面不够的原因外 ,不同研究者所使用研究方法和证据的差异也是重要因素 .在分析了各种证据对高原地面上升的记录机理后 ,我们认为夷平面、河流阶地、山麓相砾岩和高原周围盆地物质堆积速率等证据较准确地记录了高原的地面抬升 ,今后必须加强这类证据的研究 ;断层活动、地层褶皱、火山喷发、岩体热演化、生物演化、气候变化等记录不是高原地面抬升的直接证据 ,但可以作为推断高原隆升的辅助资料 .

When has the Tibetan Plateau attained its present altitude? There are many hypotheses about it.They can be summed up into three groups. Firstly, it is suggested that the Tibetan Plateau reached its maximum height 14Ma ago and fell back a little bit after this age. This hypothesis is based on dating of normal fault on Himalayas. Secondly, some scientists propose that the plateau attained or exceeded its present altitude 8Ma ago, according to dating of normal fault and the strengthening of Indian Monsoon. The third viewpoint is that intense uplift started 3.4Ma ago and pushed the plateau up to the present elevation stage by stage, of which the evidences are deposition of conglomerate, planation surfaces, biological fossil and so on. Except for shortage in research area and degree, the different of evidences for plateau uplift are responsible for the rise debate. After analyzing recording mechanism of every evidence, we think that planation surfaces, river terraces, conglomerate and depositional rate in the surroundings of the Plateau are more important factors for surface uplift. Because of complicate causes of formation, fault, folding, volcano activity, thermal evolution of rock, biological evolution and climatic changes in the plateau and its surroundings uncertainly reflected the surface uplift. Therefore, dating paleosurfaces and conglomerate is more benefitcial to the reconstruction of height history of Tibet than dating faults.