黄海及其邻近地区的Pn波速度与各向异性   总被引：12，自引：9，他引：3       下载免费PDF全文

胥颐  李志伟  刘劲松  郝天珧 《地球物理学报》2008,51(5):1444-1450

利用中国东部地震台网和ISC 报告1980~2004年的地震走时数据,反演了黄海及其邻近地区的Pn波速度和各向异性,根据岩石层地幔的横向非均匀性分析了区域地质构造的深部特点.Pn波速度的变化与区域地质构造有一定的对应关系,黄海地区上地幔顶部的P波平均速度较高,没有发现明显的低速异常,表明上地幔顶部不存在大范围的地幔扰动.速度异常的分布表明,南黄海东部和西部有可能分属于不同的构造块体,其间的分界大致对应于南北走向的黄海东部断裂带,具有相对较低的Pn波速度.边界东、西两侧的Pn波各向异性存在明显的差异：南黄海西部Pn波的快波方向以北东—北北东方向为主,反映了海区内部扬子块体向北运动产生的构造变形;南黄海东部Pn波的快波方向为南北方向,与黄海东部断裂带的走向基本一致,说明黄海东部和西部之间存在一个深达岩石层地幔的南北向转换边界.结合相关资料估计黄海东部断裂带在中生代时期发生了右旋走滑运动,以响应中国东部郯庐断裂带的大规模左旋剪切以及南黄海扬子块体的向北嵌入.  相似文献   

Insight into craton evolution: Constraints from shear wave splitting in the North China Craton   总被引：7，自引：0，他引：7  

Liang Zhao  Tianyu Zheng  Gang Lü 《Physics of the Earth and Planetary Interiors》2008,168(3-4):153-162

The multi-episodic tectonic activities from the Precambrian to Cenozoic, including nucleus formation, cratonic amalgamation, and rejuvenation, make the North China Craton (NCC) an ideal natural laboratory for studying craton evolution. Spatial change in the upper deformation records is an important aspect for understanding cratonic formation and rejuvenation. In this study, we performed seismic shear wave splitting analysis using SKS phases from 50 portable stations. Two different methodologies, shear wave splitting measurement and amplitude analysis of transverse/radial components, produced mutually consistent splitting results. These results showed that the seismic anisotropy beneath the Ordos Block can be divided into three subgroups reflecting the tectonic control. Combining these results with those from previous splitting studies in the eastern NCC, we suggest that the Proterozoic amalgamation generated the seismic anisotropy in the boundary zone between the Ordos Block and the Trans-North China Orogen, while the anisotropy in the eastern Trans-North China Orogen and eastern NCC were possibly associated with the lithospheric rejuvenation during the Late Mesozoic to Cenozoic.  相似文献   

中国青藏高原地球物理研究的第一批重大成果其发展导向与核心科学问题的认识和思考   总被引：1，自引：0，他引：1       下载免费PDF全文

滕吉文 《地球物理学进展》2008,23(2):301-318

青藏高原的地球物理研究是深化认识高原本体和东亚壳、幔结构、隆升机制与大陆动力学响应的基础,故为中、外地球科学家们所瞩目.为此本文主要讨论以下4个方面问题:(1)问题的提出与背景;(2)率先进行青藏高原深部地球物理研究取得的第一批重要成果与进程;(3)青藏高原地球物理研究中的开创性研究成果和得到的启迪与国际影响;(4)当今青藏高原地球物理研究中的核心科学问题与当前青藏高原地球物理学要做些什么与思考.研究结果表明:(1)在青藏高原地球物理研究中只有在清晰思路指导下,取得高分辨率的数据才能反演,并刻画其壳、幔介质的精细结构;(2)青藏高原地壳巨厚、岩石圈相对较薄的层块结构与壳、幔结构分区特征,特别是存在地壳低速层和地幔低速层及其不均匀展布;(3)在多维力系作用下、深部物质重新分展、调整、运移和在多要素约束下的物理-数学模拟及陆-陆碰撞动力学响应;(4)当今在青藏高原地球物理研究的核心问题是地球内部物质和能量的交换、圈层耦合及其深层动力过程.中国地球科学家们应当清晰地认识到,青藏高原地球物理研究乃是中国地球科学家摘取"桂冠"的一个契机,故必须走自主创新之路,以建立起具有特色中国地球科学的理论和和运动学与与学模型.  相似文献   

K‐ and Si‐rich glasses in harzburgite from Damaping,north China     

Yongfeng Zhu 《Island Arc》2008,17(4):560-576

A study of potassium‐ and silica‐rich glass (SiO₂ = 65.3–67.4%, K₂O = 7.1–9.8%, Na₂O = 4.4–6.5%) in spongy clinopyroxene rims from anhydrous spinel harzburgite, collected from Damaping (Hannuoba, north China), is reported here. The corroded surface of clinopyroxene along with clear chemical zonation (homogeneous core and partially melted rim) suggests that incongruent melting of primary clinopyroxene is responsible for generating the Si‐rich glass in clinopyroxene rims. The degree of clinopyroxene melting is estimated to be higher than 15%. In order to generate glass with K₂O contents of 7.0 to 9.8% by clinopyroxene melting at a degree of 15% in a closed system, K₂O contents in the primary clinopyroxene should be greater than 1.0 wt%, suggesting a very deep origin for the Damaping harzburgite.  相似文献   

Reconciling strong slab pull and weak plate bending: The plate motion constraint on the strength of mantle slabs     

Benjun Wu  Clinton P. Conrad  Arnauld Heuret  Carolina Lithgow-Bertelloni  Serge Lallemand 《Earth and Planetary Science Letters》2008,272(1-2):412-421

Although subducting slabs undergo a bending deformation that resists tectonic plate motions, the magnitude of this resistance is not known because of poor constraints on slab strength. However, because slab bending slows the relatively rapid motions of oceanic plates, observed plate motions constrain the importance of bending. We estimated the slab pull force and the bending resistance globally for 207 subduction zone transects using new measurements of the bending curvature determined from slab seismicity. Predicting plate motions using a global mantle flow model, we constrain the viscosity of the bending slab to be at most ~ 300 times more viscous than the upper mantle; stronger slabs are intolerably slowed by the bending deformation. Weaker slabs, however, cannot transmit a pull force sufficient to explain rapid trenchward plate motions unless slabs stretch faster than seismically observed rates of ~ 10^− 15 s^− 1. The constrained bending viscosity (~ 2 × 10²³ Pa s) is larger than previous estimates that yielded similar or larger bending resistance (here ~ 25% of forces). This apparent discrepancy occurs because slabs bend more gently than previously thought, with an average radius of curvature of 390 km that permits subduction of strong slabs. This gentle bending may ultimately permit plate tectonics on Earth.  相似文献   

Deformation and seismic anisotropy of the lithospheric mantle in the southeastern Carpathians inferred from the study of mantle xenoliths   总被引：1，自引：0，他引：1  

Gyrgy Falus  Andrea Tommasi  Jannick Ingrin  Csaba Szab 《Earth and Planetary Science Letters》2008,272(1-2):50-64

Peridotite xenoliths with a broad range of textures provides evidence for consistent microstructural evolution in a vertical transect of the shallow lithospheric mantle (35–55 km depth) beneath the Persani Mountains, SE Carpathians, Romania, due to ongoing plate convergence in the Carpathian Arc nearby. The recrystallized grain size, crystal preferred orientations strength, and resulting seismic anisotropy vary continuously and display a strong correlation to equilibrium temperatures, suggesting a continuous change in deformation conditions with depth. The shallowmost xenoliths have microstructures typical of high stress deformation, marked by strong recrystallization to fine grain sizes, which results in weak crystal preferred orientations and anisotropy. The deepest xenoliths have coarse-grained porphyroclastic microstructures and strong crystal preferred orientations. Replacive orthopyroxene structures, consuming olivine, and high H₂O concentrations in the pyroxenes are observed in some xenoliths indicating limited percolation of fluids or volatile-rich melts. Despite the high stress deformation and high H₂O contents in some of the studied xenoliths, analysis of olivine crystallographic orientations indicates that [100] slip systems, rather than “wet” [001] accommodate most of the deformation in all samples. Seismic anisotropy estimated from the measured olivine and pyroxene crystal preferred orientations suggests that the strike-parallel fast SKS polarization directions and ~ 1 s delay times measured in the SE Carpathians are likely the consequence of convergence-driven belt-parallel flow in the lithospheric mantle.  相似文献   

Attenuation of multiple ScS in various parts of the world   总被引：1，自引：0，他引：1  

W. Winston Chan  Zoltan A. Der 《Geophysical Journal International》1988,92(2):303-314

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Lateral variation of upper mantle structure beneath New Caledonia determined from P-wave receiver function: evidence for a fossil subduction zone   总被引：2，自引：0，他引：2  

Marc Regnier 《Geophysical Journal International》1988,95(3):561-577

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The interaction of the S-wavefield with upper mantle heterogeneity     

G. Nolet  B.L.N. Kennett 《Geophysical Journal International》1990,101(3):751-762

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Group velocity distribution of Rayleigh waves and crustal and upper mantle velocity structure of the Chinese mainland and its vicinity   总被引：7，自引：6，他引：1  

何正勤  丁志峰  叶太兰  孙为国  张乃铃 《地震学报(英文版)》2002,15(3):269-275

Introduction A lot of results have been achieved on the study of crust and upper mantle structure in Chinese mainland by the surface wave dispersion. The seismometer can be classified into three types based on the development from the analog to digital instrument. FENG, et al (1981) measured the dispersion curves of group and phase velocity along 28 paths, with 19 earthquakes recorded by 15 base analog seismic stations, subdivided the Chinese mainland into 5 blocks and obtained the average c…  相似文献