基于最小二乘配置模型探讨青藏高原巴彦喀拉块体的运动特征

Study on Movement Characteristic of Bayanhar Block in the Qinghai-Tibet Plateau Based on Least Squares Collocation Model

论述了块体刚性运动和最小二乘配置模型的原理及构建方法,并对青藏高原中部巴彦喀拉块体的运动趋势及内部形变进行了深入研究。基于最小二乘配置模型,通过建立推估点与观测点间的协方差矩阵,能够较好地区分块体整体刚性旋转及内部的弹性形变,削弱了点位分布对形变场构建产生的影响,从而准确描述区域地壳运动的趋势及应变场特征。结果表明:巴彦喀拉块体的地壳形变受到印度板块的俯冲挤压和青藏高原物质东移的双重作用,在欧亚框架下块体旋转的欧拉矢量为((0.45°±0.14°)/Ma,(-17.5°±5.93°)N,(-77.91°±12.9°)E);巴彦喀拉块体东部北向速率逐渐减小,东向速率逐渐加大。通过对巴彦喀拉块体应变率及面膨胀率的特征分析,发现龙门山断裂带前地壳挤压特征并不明显,说明其逆冲特性并非通过上地壳的缩短实现,应该受到下地壳低速体的作用。

The principle and structure method of block rigid movement and least squares collocation model were introduced,and the movement tendency and interior deformation of Bayanhar Block in the Qinghai-Tibet Plateau were discussed.Based on least squares collocation model,covariance matrixes between collocation points and measurement points were established to discriminate the rigid rotation and elastic deformation of the block,and weaken the influence of point distribution on constructing deformation field,so that the movement trend of regional crust and characteristic of strain field were accurately described.The results indicated that the crustal deformation of Bayanhar Block was influenced by subduction of Indian Plate and eastward movement of the Qinghai-Tibet Plateau,the Euler vector of block rotation was（（0.45°±0.14°）/Ma,（-17.5°±5.93°）N）,（-77.91°±12.9°）E）;velocity gradually decreased northward and increased eastward in the eastern of Bayanhar Block.According to the discussion on the characteristics of strain rate and superficial expansivity of Bayanhar Block,the crustal extrusion was not obvious in front of Longmenshan fault zone,so that the thrust characteristics were not accomplished by the supracrustal shortening,but influenced by lower crustal low-speed body.