Mesozoic and Cenozoic tectonic evolution of the Longmenshan fault belt |
| |
Authors: | ErChie Wang QingRen Meng |
| |
Institution: | (1) Institute of Geology and Geophysics, State Key Laboratory of Lithospheric Evolution, Chinese Academy of Sciences, Beijing, 100029, China |
| |
Abstract: | The giant earthquake (M
s=8.0) in Wenchuan on May 12, 2008 was triggered by oblique convergence between the Tibetan Plateau and the South China along
the Longmenshan fault belt. The Longmenshan fault belt marks an important component of the tectonic and geomorphological boundary
between the eastern and western part of China and has a protracted tectonic history. It was first formed as an intracontinental
transfer fault, patitioning the differential deformation between the Pacific and Tethys tectonic domains, initiated in late
Paleozoic-early Mesozoic time, then served as the eastern boundary of the Tibetan Plateau to accommodate the growth of the
plateau in Cenozoic. Its current geological and geomorphological frameworks are the result of superimposition of these two
tectonic events. In Late Triassic, the Longmenshan underwent left-slip oblique NW-SE shortening due to the clockwise rotation
of the Yangtze Block, which led to the flexural subsidence of the Sichuan foreland basin, but after that, the subsidence of
the Sichuan Basin seems no longer controlled by the tectonic activity of the Longmenshan fault belt. The Meosozoic tectonic
evolution of the Songpan-Ganzi fold belt differs significantly compared with that of the Yangtze Platform, featured by intensive
northeast and southwest shortening and resulted in the close of the Paleo-Tethys. Aerial photos taken immediately after main
shock of the giant May 12, 2008 earthquake have documented extensive rock fall and landslides that represent one of the most
destructive aspects of the earthquake. Both rock avalanches and landslides delivered a huge volume of debris into the middle
part of the Minjiang River, and formed many dammed lakes. Breaching of these natural dams can be catastrophic, as occurred
in the Diexi area along the upstream of the Minjiang River in the year of 1933 that led to devastating floodings. The resultant
flood following the breaching of these dams flowed through and out of the Longmenshan belt into the Chengdu Plain, bringing
a huge volume of sediments. The oldest alluvial deposits within the Chengdu Plain are estimated to be Late Miocene (8–13 Ma).
We suggest that the flooding that transported the course-grained sediments into the Chengdu Plain occurred in late Cenozoic,
resulted from both the climate and the historical earthquakes similar to the May 12 earthquake. Estimated age of the sediments
related to earthquakes and coeval shortening across the Chengdu Plain indicate that the eastern margin of the plateau became
seismically and tectonically active in Late Miocene.
Supported by Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KZCX2-YW-12), National Natural Science
Foundation of China (Grant Nos. 40672151, 40721003, 40472121 and 40830314) and PetroChina Company Limited |
| |
Keywords: | Wenchuan earthquake Longmenshan landslide flooding Chengdu Plain |
本文献已被 CNKI SpringerLink 等数据库收录! |
|