中国岩石圈三维结构雏型

A preliminary 3D model of lithospheric structure in China

根据岩石圈的流变习性,可以将中国岩石圈分成3层,即:弹性上地壳、塑性下地壳和岩石圈地幔。它们的构造各不相同,并且各层间呈现复杂的关系。在新疆地区,上地壳推覆叠置形成以三山四盆为特点的盆山构造,驮伏在一系列东西走向的条带状背型构造与向型构造的下地壳之上。在强烈隆升中的西藏地区,它的周边是差异隆升,但它的腹部地区的弹性上地壳完整未遭破坏。这是因为它的腹部的下地壳和岩石圈地幔发生局部熔融,上地壳被局部熔融的下地壳和岩石圈地幔顶托,以液压的方式整体抬升。华北地区,则是软流圈上升破坏了岩石圈地幔,形成新生地幔与残留地幔并存的蘑菇云岩石圈地幔构造。并由于软流圈的上升,使地壳拉张减薄形成裂谷盆地。中国大陆下除了东北吉辽地区太平洋板块向大陆俯冲外,东部其他地区都没有发现太平洋板块俯冲的证据。中生代以来中国东部发生的岩石圈巨变不是太平洋板块向中国大陆的俯冲而造成的,而是软流圈物质上涌的结果。因此,中国大陆当今的构造动力,是西部由印度板块俯冲推挤和东部东亚-西太平洋软流圈上升构成的二元系统。这两个动力系统的分界是南北地震带。在南北地震带以西整体处在压缩环境中;南北地震带以东,则处在拉张环境中。正是由于应力场由压缩转变成拉张产生的剪应力造成了南北地震带。华北地区所以成为地震活动地区是因为它的岩石圈地幔已被强烈的改造成为蘑菇云构造,热流上升,弹性层急剧减薄,弹性极限下降所致。

According to theological behaviors of the hthosphere, the authors have divided the lithosphere of China into three layers, i.e., elastic upper crust, plastic lower crust and lithospheric mantle, and pointed out that they have different structures and complicated relationships. In the Xinjiang area, four basins and three ranges were formed by thrusting and overlapping in the upper crust, overlain on a series of EW-striking antiforms and synforms of the lower crust. The uplifting of the central part of the Tibetan plateau was as a whole caused by the hydraulic pressure due to the partial melting of its lower crust and lithospheric mantle, but the uplifting of the border parts is of the differential nature. In North China, the upwelling of ashenosphere material destroyed lithospheric mantle and formed a mushroom cloud structure in which the new-born mantle and the residue mantle existed side by side, and grabens occurred in the elastic upper crust. There exists no evidence for the subduction of the Pacific plate under the continent of China, except for things in a limited area of northeast China. The violent deformation of eastern China was produced by the upwelling of ashenospheric materials instead of by the subduction of the Pacific plate. So the tectonic forces nowadays in China constitute a dual system which includes the subduction of the Indian plate in the west and the uplifting of the ashenosphere in the east. The boundary of the two different tectonic forces is the north-south seismic belt. To the west of the north- south seismic belt, the lithosphere is under a compression regime, whereas to the east of the north-south seismic belt, the lithosphere is under an extensional regime. The reason for the seismicity of North China is that the elastic crust of this area was thinned by strong geothermal activity, which resulted in the considerable lowering of the elastic limit.