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喜马拉雅东构造结及周边地区上地幔各向异性

DOI: 10.1007/s11430-015-5098-2, PP. 577-588

Keywords: 喜马拉雅东构造结,横波分裂,各向异性,岩石圈变形

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Abstract:

?收集了喜马拉雅东构造结地震台阵17个宽频带流动地震台站,以及东构造结周边地区布设的32个宽频带流动台站和中国地震台网10个宽频带固定台站的远震波形资料,并对这共计59个台站所记录的XKS(SKS,SKKS和PKS)波形资料作偏振分析,采用最小切向能量的网格搜索法和叠加分析方法求得每一个台站的XKS波的快波偏振方向和快、慢波的时间延迟,并结合其他研究在该区域取得的各向异性参数结果,获得了喜马拉雅东构造结及周边地区上地幔各向异性图像.从得到的结果来看,喜马拉雅东构造结的上地幔快波方向基本为NE-SW方向,其周边地区的快波方向自西向东呈现出NE-SW方向到E-W方向,然后到NW-SE方向,最后为N-S方向的逐步变化,其周边地区的快波方向表现出围绕东构造结顺时针旋转的变化特征.通过该区域快波方向与地表构造走向和运动速度场变化特征的对比分析,喜马拉雅东构造结及周边地区的快波方向与该区域地表构造走向和由GPS得到地表运动速度场运动趋势相一致,说明该区域地表变形特征与深部上地幔变形特征是一致的,其岩石圈变形是一种垂直连贯变形模式.喜马拉雅东构造结的快波方向为NE方向,与印度板块向青藏高原下NE方向的俯冲一致,说明稳定坚硬的印度块体向NE方向俯冲到青藏高原下方是引起该区域岩石圈变形的主要原因.围绕喜马拉雅东构造结的周边地区的快波方向呈现出顺时针旋转的环形变化特征,我们推测稳定坚硬的印度板块对青藏高原NE方向的俯冲作用,又由于缅甸块体下俯冲板片的东向俯冲和西向后撤对缅甸弧后的岩石圈产生了被动的西向拖曳力作用,使得绕喜马拉雅东构造结周边地区岩石圈产生了顺时针旋转的环形变形,进而形成了快波方向绕喜马拉雅东构造结顺时针旋转的各向异性特征.

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