【作者】 武岩；

【导师】 丁志峰； 朱露培；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理， 2011， 博士

【摘要】 华北克拉通的“去根”作用是克拉通活化的代表。研究其内部动力学对于了解华北克拉通的“去根”方式有着十分重要的意义。本文回顾了全球范围内的地幔动力学模式以及前人对于华北克拉通的地质、岩石圈、各向异性以及地幔过渡带等研究结果,以及通过层析成像和各向异性的研究结果所推测出的华北克拉通的动力学模式,介绍了接收函数以及其波形模拟、H－盯的叠加以及CCP叠加方法的基本原理。本文利用布设在华北克拉通的东部和中部地区以及西部陆块部分地区的200个呈密集面状分布的台站记录的近二三年的远震数据,采用接收函数波形模拟方法获得华北克拉通盆地地区的沉积层结构,根据接收函数的H－K叠加方法以及CCP叠加方法获取华北克拉通的地壳以及上地幔结构,以期通过对华北克拉通各圈层结构的研究,探讨华北克拉通的深部动力学模式。本文的研究结果表明：1)华北克拉通内的盆地,渤海湾盆地和大同盆地在结构和形成方式上略有不同：虽同为新生代裂陷盆地,但渤海湾盆地的结构更为复杂,盆地内不同块体的沉降程度不同,块体内沿断层方向东西两侧不对称,东侧的沉积层厚度大于西侧的沉积层厚度,体现了地垒(半地垒)－地堑(半地堑)的构造模式,目且沉积层厚度与老第三系地层的厚度相关。盆地内形成隆起带和坳陷带相间排列的格局。沉积层S波的平均速度与盆地厚度成正对应关系,波速比与盆地厚度成反对应关系。推测与老第三系地层较高的波速和较低的波速比有关。地热分布地区与局部高波速比有很好的对应关系；大同盆地则是以下窝寨和后所两个地区为中心进行沉降,中间厚周边溥,且沉积层较厚地区的波速比也较高,推测为地幔物质上涌地壳扩张形成的盆地。2)华北地区地壳厚度西厚东薄,泊松比与地壳厚度存在较为复杂的对应关系：中部陆块的泊松比与地壳厚度呈负线性关系,而渤海湾盆地周围的台站则与地壳厚度的关系较为复杂,其受地壳厚度的影响大于中部陆块,即随着地壳厚度的减薄,泊松比快速增加。说明克拉通东部地区的减薄是由拉伸作用造成的,且地幔底部没有地幔高铁镁物质的补充,中部造山带地区地壳减薄过程中存在地幔高铁镁物质的补充,使得其泊松比升高速度小于东部地区,推测重力梯度带区域内地壳快速减溥地区存在部分熔融和上地幔物质上涌。3)太平洋俯冲板块的停滞板块的边缘可以延伸到重力梯度带附近,且停滞板块对过渡带下界面的影响远远大于对上界面的影响。繁峙附近和研究区域西北侧过渡带厚度较薄,推测分别由向东的地幔上升流和破碎下沉的停滞板块造成的地幔上升流造成的。SEE方向的地幔上升流最终导致了华北克拉通东部陆块的拉伸和大同盆地的扩张。更多还原

【Abstract】 Lithosphere "de-rooting" beneath the North China Craton (NCC) is a representative phenomenon of reactivation of the craton. Studying the dynamics of the NCC can help to understand the mechanism of de-rooting.In this thesis, I start with a introduction to models of mantle dynamics and previous studies of the NCC geology, lithosphere, upper mantle anisotropy, the transition zone, and mantle convection models from seismic tomography. I then describe the basic principles of receiver function analysis and waveform modeling, and the H-κstacking and CCP stacking methods.Receiver functions are calculated from teleseismic waveform data recorded by 200 broad-band seismic sensors deployed in the eastern, central, and part of the western NCC. They are used to reveal structures of sedimentary basins by waveform inversion. The H-κstacking and the CCP stacking methods are used to obtain crustal and upper mantle structures. The goal is to understand mantle dynamic mechanism through studying structure beneath the NCC.The results show that:1) The structures and the evolution of the two basins in the NCC—the Bohai Bay Basin (BBB) and the Datong basin (DB) are different. Though both are the rift basins, the structure of the BBB is more complex. The subsidence is different from one block to another in the basin. The western and eastern sides across the fault in the basin are not symmetric; the sedimentary thickness of the eastern side is much thicker than the western side, which shows the characteristic of horst (half horst)-graben (half graben) pattern. The uplifts and depressions alternate in the BBB. Thick sedimentary layers always have high average S velocity with low Vp/Vs ratios. This may be caused the Palaeogene strata of higher S velocities and lower Vp/Vs ratios than the newer strata. There is a good correlation between the distribution of geothermal areas and high Vp/Vs ratios. In contrast, the DB has two depositional centers, one in Xiawozhai and another in Housuo. The sedimentary thicknesses near the centers are much thicker than the areas around. And thick sedimentary areas have high Vp/Vs ratios, suggesting that the DB was formed by stretching caused by upwelling of mantle.2) The crustal thickness of NCC is thicker in the western part than the eastern part. The relationship between the crustal Poisson ratio and thickness is very complex. In the central part the Poisson ratio is negatively linear proportional to crustal thickness while the relationship around the BBB is more complex. There the Poisson ratio increases rapidly with the decrease of crustal thickness. This suggests that the thinning of NCC in the eastern part is caused by stretching without underplating of mafic mantle material. There was underplating of mafic magmas from partially molten upper mantle in the central block.3) The stagnant of subducting Pacific slab reaches the bottom of the transition zone beneath the north-south gravity lineament. The transition thickness around Fanshi is very thin, which may be caused by the upwelling mantle material generated by the crack of the stagnant slab down to the lower mantle. The upwelling of the mantle material in the direction SEE caused the extension of the BBB and the expansion of the DB.更多还原