有关青藏高原东北缘晚新生代扩展与隆升的讨论*

青藏高原晚新生代的扩展和隆升对周边环境演变产生重大影响,确定扩展和隆升的起始年代是一个重要的科学问题。近年来在六盘山、积石山和祁连山及其相邻盆地的研究表明,青藏高原东北缘晚新生代(5~10MaB.P. 或约8MaB.P. )发生了准同期、影响深远的构造变形,导致了沉积盆地的消亡和山脉的隆起。青藏高原北缘的阿尔金山和东缘的岷山、龙门山及川滇高原也在该时段发生了构造活动的加速和构造隆升。所有这些准同期的事件反映了约8MaB.P. 前后青藏高原向周边的扩展,扩展的方式是通过一系列逆冲断裂、褶皱变形、左旋走滑及其伴随的山脉隆起和盆地消亡而实现的。该时期青藏高原的扩展导致了周边的环境变化,奠定了今日环境的格局。

DISCUSSION ON LATE CENOZOIC GROWTH AND RISE OF NORTHEASTERN MARGIN OF THE TIBETAN PLATEAU

The Tibetan Plateau provides an outstanding field laboratory for studies of lithospheric dynamics and of the effects of large-scale topography on the earths atmosphere and, by extension, on climate. On a regional scale, the warming of air over Tibet is commonly interpreted to be a major factor that makes the Indian Monsoon the model for monsoonal circulations. Conversely, suggestions of a strengthening of the monsoon at ca.8MaB.P. have been used as arguments for an abrupt ca.1000-m rise of Tibets surface elevation, and therefore as support for proposed deeper mantle processes. Northeastern Tibet offers both a missing link in our understanding of Tibets overall growth and an ideal field laboratory in itself for studies of both how and why high, regionally extensive plateaux grow and how such terrains affect regional climate. We summarize recent studies of Late Cenozoic tectonic deformation in the Liupan Shan, Jishi Shan, Qilian Shan as well as their adjacent basins, to show that approximate coeval deformation occurred during 5~10MaB.P. or near 8MaB.P. in northeastern margin of the Tibetan Plateau. This tectonic event poses profound impacts on geomorphology, paleoclimate, and environment around the Tibetan Plateau. The tectonic acceleration and mountain uplift also occur during this time interval in the Altyn Tagh along Tibets northern boundary, and the Longmen Shan and Sichuan-Yunnan Plateau. All of these coeval events are manifestations of outward growth of the Tibetan Plateau near ca.8MaB.P. The outward growth is tectonically characterized by north northeastward convergence thrust faulting, folding, strike-slip faulting, and associated mountain uplift and sedimentary basin extinction. It is also this outward growth that set up the modern pattern of environments in and around the Tibetan Plateau.