CONTEMPORARY TECTONIC STRAIN RATE FIELD OF CHINESE CONTINENT AND ITS GEODYNAMIC IMPLICATIONS
CONTEMPORARY TECTONIC STRAIN RATE FIELD OF CHINESE CONTINENT AND ITS GEODYNAMIC IMPLICATIONS
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作者：
Zheng-kang Shen
通过分析GPS速度场推断的地壳运动，我们得到了中国大陆的当代构造应变率。我们的研究结果表明，在印度板块向北凹陷的推动下，青藏高原及其邻近地区发生了广泛的变形，而不是集中在划定高原边界的少数大型走滑断层的狭窄变形带上；这种变形场广泛分布在高原内，不同地区的驱动机制可能不同。藏南应变率场表现为南北向压缩和东西向拉伸，两个分量的应变率约为2×10 -8 a -1 。这可能是地壳增厚和岩石圈拆沉的结果，导致上地壳与上地幔脱钩。这可能会响应印度板块向北的挤压，在下地壳中产生东向的延性流，导致上地壳东西向的张力。西藏中部羌塘地区的应变率场也显示出大约等量的NNE压缩和NWW拉伸。 2×10 -8 a -1 ，反映了一组北东向和西北向共轭走滑断层的活动断层活动，可能是软流圈南北向挤压和东向延性流作用的结果。柴达木盆地及其邻近地区存在东北方向约2×10 -8 a -1 压缩和西北方向约(0~1)×10 -8 a -1 伸展的应变率场。这种模式表明地壳增厚引起的地壳温度升高不足以引起上下地壳之间的完全脱钩，因此通过东西伸展来适应南北缩短的效率较低。 （即下地壳中的延性流动）而不是通过沿着断层的褶皱和逆冲（即沿着狭窄的薄弱带变形）。结论认为,青藏高原当代变形场是由南向北递进构造发展的结果,造成区域岩石圈结构的系统性差异,进而影响地壳变形的驱动机制。
We obtain contemporary tectonic strain rates of Chinese continent from analyzing crustal motion inferred from GPS velocity field. Our result shows that driven by the northward indentation of the Indian plate, the Tibetan plateau and its vicinity areas undergo extensive deformation, rather than concentrated along narrow deformation zones of a few large-scale strike-slip faults delineating the plateau boundaries; this deformation field is broadly distributed within the plateau, driven by possibly different mechanisms from region to region. The strain rate field in southern Tibet appears to be north-south compression and east-west extension, at the rate of about 2×10 -8 a -1 for both components. This could be the result of crustal thickening and lithospheric delamination, resulting in decoupling of the upper crust from the upper mantle.This could produce eastward ductile flow in the lower crust responding to the northward compression from the Indian plate, causing east-west tension in the upper crust.The strain rate field in the Qiangtang region, central Tibet, also shows nearly equal amount of NNE compression and NWW extension at about 2×10 -8 a -1 , reflecting active faulting along a group of conjugate strike-slip faults oriented northeasterly and northwesterly, possibly resulted from the north-south compression and eastward ductile flow in the asthenosphere. The Qaidam basin and its vicinity have a strain rate field of about 2×10 -8 a -1 compression in northeast direction and (0~1)×10 -8 a -1 extension in northwest direction.This pattern suggests that a temperature increase in the crust resulted from crustal thickening is not enough to cause full decoupling between the upper and lower crust, thus it is less efficient to accommodate the north-south shortening through east-west extension (i.e. ductile flow in the lower crust) than through folding and thrusting along faults (i.e. deformation along narrow weak zones). We conclude that contemporary deformation field of the Tibetan plateau has been the result of progressive tectonic development from south to north, causing systematic differences in regional lithospheric structures,which affect the driving mechanisms of crustal deformation consequently.