壳-幔动力学与活化构造(地洼)理论

壳-幔动力学是地球内部物理学和大地构造演化的重要研究方向之一。本文从地球物理角度出发,以物理概念和数学描述相结合的定量方式,对陈国达院士生前所创建的活化构造(地洼)理论研究中的某些地球深部动力学问题进行了较系统的综合评述和探讨。主要论题包括岩石圈的性质与物理学、地幔流变学、重力与均衡理论、地球的温度和热传递,诸如热传导、物质的物理运动所引起的热传输、地球内部的热对流及地幔柱的形成和作用等。作者特别强调了构造演化的定量分析问题,如热时间常数、热应力与其它力源、水平运动与垂直运动的关系,以及地壳断裂作用。岩石圈的构造作用与演化是与深部热运动有关的水平 (压缩和扩张)应力和由地壳厚度差异所导致的垂直应力差的共同结果。热应力的构造意义主要表现为短时间尺度的脆性断裂或柔性应变松弛过程。局部对流机制对活化构造(地洼)研究值得重视。

CRUST-MANTLE DYNAMICS AND ACTIVATED TECTONICS (DIWA) THEORY

Crust-mantle dynamics is an essential research direction in physics of the Earth's interior and geotectonic evolution. Some geodynamic issues concerned in activated tectonics (Diwa) theory, initialized by Academician Chen Guoda in 1950's, are systematically reviewed and discussed in this paper to celebrate and rememorize his outstanding contribution and achievement in Earth Sciences. Main topics discussed here, purely from geophysical viewpoints, involve the nature and physics of lithosphere, mantle rheology, gravity and isostasy, temperature of the Earth and heat transfer including heat conduction, advection and thermal convection. Key topics of practical significance in quantitative geotectonics are particularly studied, such as thermal stress, heat response time (thermal constant), horizontal and vertical crustal movements, potential energy and roles of plume, as well as crustal faulting. A physical and quantitative approach is followed in stating the problems and solutions, which is necessary for better understanding and attacking some of the most difficult issues in mantle and crustal dynamics that is also an important component of the activated tectonics (Diwa) theory. Tectonic Processing and dynamic evolution of the lithosphere (crustobody, as termed by Chen Guoda) is caused by a combination of horizontal (compressive and extensional) forces, associated with thermal movement in the mantle, and the vertical differential forces due to variations of crustal thickness. Thermal stress is most likely associated with a short time scale (less than Maxwell time, say 10~3 year) in which it may be released by brittle fracture or ductile relaxation of strain. Due to the non renewable nature of thermal stress, its long term geotectonic role, with the mantle viscous time scale (greater than Maxwell time), seems to be of uncertainty. Local and small scale mantle convection may be a causative mechanism of activated tectonics (Diwa) that is worthy of further studying.