接收函数方法研究大同火山地壳精细结构

HIGH RESOLUTION CRUSTAL STRUCTURE OF DATONG VOLCANO FROM RECEIVER FUNCTION USING DENSE SEISMIC ARRAY

李凤英

11849211

硕士

力学

郭震

2020-05-20

2020-07-21

哈尔滨工业大学

深圳

华北克拉通是位于中国东部古老的克拉通。自中生代新生代以来遭遇了严重的破坏和改造，东部岩石圈厚度从200 Km减薄至100Km以下，但西部块体仍处于稳定状态。对于华北克拉通岩石圈是如何拉张减薄的、克拉通破坏的范围、以及克拉通破坏是否存在多期目前还存在争议。大同火山群位于华北克拉通中部的造山带，鄂尔多斯东北缘。大同火山区独特的地理位置引起地球物理学界、地球化学界科学家广泛的关注。众多学者通过P波层析成像、面波、大地电磁、背景噪声等手段发现大同火山区下方存在低速、低阻、高导的异常体。但对于大同火山群下方的异常体的深度、形态、大同火山区岩浆来源还存在有不同的争议。本文主要利用南方科技大学海洋科学与工程系在大同火山群布设的166台间距为5 Km的三分量短周期地震记录仪记录到的4个月的远震波形数据，并选取震中距在280 ~ 920，震级大于5.0级的211个远震事件进行研究。将记录得到的波形数据截取P波之前20 s，P波之后60 s的波形数据，在0.05 ~ 5Hz的范围内滤波，用时间域迭代反褶积提取接收函数，并人工筛选出4541条接收函数。最后，利用接收函数H-k叠加和可希霍夫偏移成像研究大同火山精细地壳结构。研究结果表明：以山西断陷为界，研究区域西部地壳厚，东部地壳薄；山西断陷区域内莫霍面深度在35 ~ 40 Km，莫霍整体隆起，局部地壳增厚，波速比数值高达2.0，根据山西断陷莫霍深度和波速比分布推测山西断陷并不是均匀拉张，部分区域存在基性岩浆底侵，造成地壳增厚，波速比增大；研究区域地壳厚度自北向南逐渐减薄，与地貌构造相吻合；接收函数可希霍夫偏移成像的研究结果表明大同火山下方地壳增厚，对应较高的平均地壳波速比1.85，且增厚区域主要在大同火山群的西面。该观测支持大地电磁和面波成像的结果，即大同火山下方的地幔上涌造成的底侵主要发生在大同火山群西部。

North China Craton (NCC) is one of the most ancient Archean cratons in China. Since the Mesozoic and Cenozoic, the lithosphere of NCC has experienced significant reworking, the eastern NCC has been thinned from over 200 km to less than 100 km, but the western NCC still keeps intact. There are still debates about how the lithosphere of the North China Craton been thinned, the extent, and origin time of the craton destruction. Datong volcanic group is located in the Trans-North China Orogen, the northeastern margin of Ordos.Numerous pervious work using magnetotelluric, P wave and surface wave tomography have found that there are low velocity and high conductivity bodies in the mid-to lower crust and uppermost mantle beneath the Datong volcano. But there are still controversies about the sources of magma that feeds the Datong volcano.In this study, we use seismic data recorded by a dense array deployed by SUSTech in Datong volcano. The The seismic array consists of 166 short-period seismometers, three-component seismometers spaced at 5 Km interval，which are operated for 4 months. We selected 211 well-recorded earthquakes at epicentral distances of 280 ~ 920, and earthquake magnitude greater than 5.0 to the seismic array.Waveforms from these events were bracketed from 20 s before the first P-wave arrival to 60 s after its arrival and then band-pass filtered between 0.05 and 5.0 Hz, then calculated receive function by Time domain iterative deconvolution, and selected 4541 receivefuntion.We obtain high resolution crustal structure of Datong volcano using H-k stacking and Kirchhoff imaging. The results show that: the crust is relatively thick beneath the western study area, which gradually thins to the east; The Moho depth is fluctuated between 35 and 40 km beneath the Shanxi rift with Vp/Vs ratio in the study area locally up to 2.0. We suggest that the high Vp/Vs ratio is likely caused by the mafic underplating, leading to the conclusion that the crust of the Shanxi rift is not uniformly extended;The thickness of crust gradually decreased from north to south of the study area; To the west of the Datong volcano, relatively thick crust is observed with high Vp/Vs ratio of 1.85. We therefore suggest that mafic underplating mainly exists to the west of the Datong volcano, which supports the hypothesis that the Datong volcano is fed by the asthenospheric upwelling from west.

山西断陷 大同火山 接收函数 H-k扫描 柯希霍夫成像

shanxi rift datong volcanoes receive function H-k Kirchhoff imaging

中文

联合培养

南方科技大学

李凤英. 接收函数方法研究大同火山地壳精细结构[D]. 深圳. 哈尔滨工业大学,2020.