现今全球岩石圈水平速度矢量场及其在地史时期的代表性

PRESENT-DAY HORIZONTAL VELOCITY VECTOR FIELD OF LITHOSPHERE AND ITS REPRESENTATIVITY IN GEOLOGICAL HISTORY STAGES

空间测量与地球物理资料分别揭示出十年尺度与百万年尺度的全球岩石圈现今绝对水平速度矢量场的基本特征,说明现今全球岩石圈存在显著的总体西向圈层运动。北半球岩石圈现今绝对水平速度矢量以西向为主。南半球岩石圈现今水平运动方向呈现规律性变化,南美大陆一西大西洋岩石圈速度矢量以西向为主,形成西向流;而东大西洋岩石圈速度矢量以东向为主,形成东向流;西向流与东向流在东经45°～160°的澳大利亚一北印度洋区域汇聚,形成全球唯一的强大岩石圈北向流。将全球主要岩石圈块体的现今速度矢量与依据海底磁条带、热点迁移及大陆古地磁资料所确定的一定地质历史时期内的古速度矢量进行综合对比分析与一定的统计分析,发现岩石圈古、今速度矢量场高度相似。主要岩石圈块体的古、今速度矢量,无论其速率大小、还是矢量方向,都非常相近。说明全球岩石圈现今速度矢量场在一定地质历史时期内有其代表性,基本反映了白垩纪以来全球岩石圈的稳态水平运动规律,可能适用于整个中生代。

Geodetic ranging and geophysical survey provide present-day absolute horizontal velocity vector field of lithosphere in scales of ten years and million years respectively, and illustrate well the evident westward motion of lithosphere. Present westward velocity vectors are prevailling for lithosphere in north hemisphere while the horizontal motion direction changes regularly for lithosphere in south hemisphere. The velocity vectors are mainly westward or near westward in South America and southwest Atlantic ocean, forming westward lithospheric current. The major velocity vectors are eastward or near eastward in east Atlantic ocean and its eastern adjacent area, forming eastward lithospheric current. The eastward current and westward current converged in Australia-North Indian ocean of east 45°— 160° longitude, forming the only one powerful northward lithospheric current in the whole earth. Palaeo-velocity vectors of lithosphere in geological historical stages are derived from sea-floor magnetic anomalies, hotspot migrations and continental paleomagnetic data. By comparing the palaeo-velocity vectors and present-day velocity vectors of major lithospheric blocks, it is discovered that high similarities of horizontal velocity vector fields exist between geological history and present-day. For most lithospheric blocks, their ancient and present velocity vectors are very similar or almost equal both in rate and vector direction. These clearly illustrate the representativity of present-day horizontal velocity vector fields in geological history, especially in Cretaceous-Cenozoic era. Some data even suggest that present- day velocity vector field of lithosphere may be used in the whole Mesozoic era.