THE FEATURES OF CONTEMPORARY GLOBAL TECTONICS AND ITS DYNAMIC EXPLANATION
Ma Zongjin Gao Xianglin Ren Jinwei (Institute of Geology, State Seismological Bureau)
Structural geology, geotectonics and global tectonics are three research fields in different dimensions with mutual interaction and their own emphases. Global tectonics can be divided into two branches: historical global tectonics and contemporary global tectonics. The basic tectonic forms of the contemporary lithosphere include lithospheric plate and strip, slab structure, oceanic ridge structure, detachment structure with variable dipping angles and nets of shear faulting within continental plates. The following three tectonic systems represent the global-order, contemporary lithospheric structures: the slab structural system of the Circum-Pacific subduction zones, the oceanic ridge structural system of the oceanic growth zones and the orogenic structural system of continental collision. They are characterized by the antisymmetrical relationship of hemisphere-order (north/south, 0°/180° longitude) with regard to the structural form, physical background and dynamic state in the spherical coordinate system. There are also east/west antisymmetrical relationship in each tectonic system. Dynamically, orientation of relatively westward drift of the lithosphere and eastward motion of the mantle may show the directive action of the change of the Earth's rotation, which determines the antisymmetry of multi-orders on the both sides of the longitudinal tectonic zone. The north/south antisymmetry may be attributed to southward deviation of the thermal center and northward deviation of the mass center within the mantle demonstrated by seismic tomography. It is suggested that the structural thermal apwelling caused by the layered mantle and weak material under the tectonic extention might be the mechanism of the lithospheric movement. By using this model we can explain the apparent convection on the surface, jumping displacement and pattern-changing of the tectonic movement as well as the origin of the antisymmetry.