三维地震波速结构约束下的变黏度地幔对流及其动力学意义

3-D lateral variable viscosity mantle convection constrained by seismic wave velocity and its geodynamic implications

建立了三维黏度扰动下的变黏度地幔对流模型,并提供了在引入地幔的三维地震波速度结构下相应的求解方法.依此反演了瑞利数Ra=106时,两种不同边界条件下的极、环型场对流图像,这有助于深化对地幔物质流动和大地构造运动的深部动力学过程的认识和理解.研究结果表明,不但地幔浅部的极型场对流图像显示出了与大地构造运动的相关性并揭示了其深部动力学过程,更重要的是,地幔浅部的环型场对流图像首次为我们认识和理解板块构造的水平与旋转运动提供了重要的信息:环型场速度剖面中在赤道附近存在一条大致南东东—北西西向的强对流条带,可能与环赤道附近大型剪切带的形成相关,进而表明可能是该带强震发生的深部动力学背景;在南北半球存在的旋转方向相反的对流环表明它们整体上可能存在差异旋转.

Mantle convection model with a 3-D lateral variable viscosity constrained by seismic wave velocity is developed and its corresponding solution is presented in this paper. The poloidal and toroidal convection patterns are presented at Rayleigh number Ra = 10^6 under two kinds of boundary conditions, respectively, which are helpful to further recognize and understand the behavior of mass motion in the mantle and the deep dynamic process of surface tectonic motion. Our results indicate that not only the poloidal convection patterns in uppermost mantle have good correlations to surface tectonic motion, but also the toroidal ones reveal important information of their horizontal motion and rotation for the first time. There is a SEE-NWW strong convection zone close to the equator in toroidal convection patterns, which probably correlates with the large-scale shear zone near the equator and is the deep dynamic background of strong earthquake occurrence in this zone. The opposite rotating large-scale convection rolls in the Southern and Northern hemispheres suggest that maybe there is differential rotation between them.