中国东北地区北部上地幔各向异性及其动力学意义

doi:10.6038/cjg20151010

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摘要

中国东北地区广泛发育新生代板内火山,晚中生代以来岩石圈遭受过多期拉张作用.作为中国唯一的深震孕育区,中国东北地区受到太平洋板块的西向俯冲,使得其成为研究岩石圈变形、板块俯冲和板内火山成因及其相互作用关系的天然实验室.通过分析架设在中国东北地区北部的147个流动和固定台站的SKS波形数据,共计得到了377对各向异性参数和251个无效分裂结果.结果表明,中国东北地区东西两侧具有不同的各向异性分布:西部地区各向异性方向变化范围为N143-199°E,平均N169°E,与晚中生代岩石圈伸展方向一致;其各向异性延迟时间平均值约为0.8 s,说明来自地幔的各向异性比较微弱,主要由残留在岩石圈中的古老变形所引起.同时,在松辽盆地和佳木斯地块部分区域,观测到延迟时间较小的各向异性(~0.4 s),可能是由于岩石圈的拆沉和热地幔物质的上涌侵蚀了保留在岩石圈的古老形变所致.在研究区东部,NNW-SSE朝向的各向异性被观测到,并伴随较大的延迟时间(大于1.0 s),可能与太平洋板块撕裂回撤而产生的地幔流动有关.此外,近W-E方向的各向异性只在佳木斯地块被观测到,而太平洋板块在地幔过渡带中的俯冲可能是其产生的主要成因.

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	强正阳
	吴庆举

关键词 ：中国东北, 剪切波分裂, 地震各向异性, SKS震相

Abstract：

Northeast China located in the eastern part of the Central Asian Orogenic Belt (CAOB), one of the largest Paleozoic orogens on Earth. Surrounded by the Siberian craton, North China plate and the Pacific plate, northeast China is characterized by widespread Cenozoic intraplate volcanism and lithospheric deformation caused by multiepisode extension since Late Mesozoic.As the only area developing deep earthquake in China, northeast China has suffered the subduction of the Pacific plate, which makes it become the natural laboratory of studying the lithospheric deformation, subduction and intraplate volcanos and also their interaction relationship.
Seismic anisotropy determined by the splitting of shear waves, especially the core-refracted phases like SKS, is one of the most direct and effective ways to image the structure and deformation in the interior of the Earth. We measure the shear wave splitting parameters,the fast polarization direction (φ) and the splitting time between the fast and slow waves (δt), using the SplitLab analysis software package which combine both the rotation-correlation (RC) method and the transverse minimum energy (SC) method. A quality factor (good, fair, or poor) is assigned to all the shear wave splitting measurements,according to the signal to noise ratio of the initial phase, the rectilinear polarization of the particle motion after correction, and well-defined extreme value of contour plot.Only the measurements marked as 'good’ or 'fair’ are retained in the subsequent analysis and discussion, and the delay times less than 0.4 s will be marked as null measurements based on measurement error consideration.
A total of 377 pair of SKS splitting measurements obtained at 147 temporary and permanent seismic stations in northeast China are used to infer the upper mantle structure of this area. The shear wave splitting results at most of stations in western part of our study area are characterized by homogeneously oriented fast directions trending N143°E to N199°E with an average close to N169°E, in agreement with the extensional orientation of the Late Mesozoic lithosphere. Additionally, the delay times vary from 0.4 s to 1.6 s with a mean value of 0.85±0.23 s and correspond to a 98±26 km thick layer if 4% anisotropy is assumed, suggesting the anisotropy mainly reside in the lithosphere. Several anisotropy with small delay times (~0.4 s) are observed in the Songliao basin and Jiamusi massif which are probably caused by the lithosphere delamination or the hot mantle upwelling that partially eroded the ancient deformation frozen within lithosphere.While in the eastern part, NNW-SSE trending fast directions with large delay times (larger than 1.0 s) are observed. As the missing of the deep seismicity of this area, we speculate that there exist a slab tear at the end of Pacific plate, whose roll-back may induce NW trending mantle flow. In addition, nearly W-E fast splitting directions are observed in Jiamusi massif only, which can be best explain by the LPO of metastable olivine within the Pacific slab.

Key words： Northeast China Shear-wave splitting Seismic anisotropy SKS phase

收稿日期: 2015-08-11

PACS:

P315

基金资助:

国家自然科学基金(41474074、90814013)和国土资源部探测技术与实验研究专项(SinoProb-02-03)联合资助.

通讯作者: 吴庆举,男,1966年生,研究员,主要从事地震学、地球内部结构以及动力学研究.E-mail:wuqj@cea-igp.ac.cn E-mail: wuqj@cea-igp.ac.cn

作者简介: 强正阳,男1988年生,在读博士生,主要从事地震各向异性及动力学方面的研究.E-mail:qmail@aliyun.com

链接本文:

http://www.geophy.cn/CN/10.6038/cjg20151010 或 http://www.geophy.cn/CN/Y2015/V58/I10/3540

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