基于热点参考系的板块绝对运动模型

An absolute plate motion model based on hotspot reference frame

本文在最新一代板块相对运动模型(MORVEL模型)的基础上,通过最小二乘反演观测热点方向数据建立板块绝对运动模型.经过对前人用于约束板块绝对运动模型的所有热点数据与MORVEL模型的一致性作系统的统计学检验,发现存在离群数据.相应地,提出两种系统剔除离群数据的新方法:逐一剔除法和全局搜索法.结合对总残差的卡方检验和对残差频率分布的正态检验,逐步筛选最优模型,最终得到一个基于热点参考系的板块绝对运动新模型(T87模型).该模型能够合理拟合全球分布的87个热点方向数据,而模型预测的板块绝对运动速率比观测热点火山的迁移速率系统偏小,最大偏差达到4 cm·a^(-1).这样的偏差可由观测热点速率的系统误差或地幔返回流造成的热点间运动解释.不论是哪种解释成立,本文结果表明热点方向数据能够独立、有效地定义全球热点参考系.这样定义的热点参考系可方便地应用于板块绝对运动、地幔对流及真极移的研究.

On the basis of the new generation model of relative plate motions, the MORVEL model, an absolute plate motion model is determined in terms of the least squares inversion of the observed hotspot trend data in this paper. A systematic test for the consistency between the MORVEL model and all the available hotspot data adopted by previous studies of absolute plate motion models shows there are outliers in the data set. Accordingly, two new methods for outlier rejection, viz., step-wise rejection and global search rejection, are proposed. Combined with the chi-square test for the total residual and the normal test for the residual frequency distribution, the best model is selected step by step, and a new model, the T87 model, for absolute plate motion based on hotspot reference frame is eventually obtained. This model provides reasonable fitting to globally distributed 87 hotspot trends, but the predicted plate velocities are systematically lower than the observed rates of volcanic migration along hotspot tracks, and the deviation is up to 4 cm·a-1. Such a deviation may be explained as a consequence of systematic errors possibly associated with the observed hotspot rate data, or due to relative motions between hotspots caused by mantle return flow. For either case, however, the results of this study demonstrate that the hotspot trend data are capable of defining a global hotspot reference frame, which could be conveniently applied to studies on absolute plate motion, mantle convection and true polar wander.