长江中下游成矿带远震P波各向异性层析成像研究

发布时间：2018-02-21 10:05

本文关键词： 远震各向异性 P波长江中下游成矿带流动方向板块俯冲　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：长江中下游地区分布着我国重要的多金属成矿带。190～230 Ma年前,长江中下游成矿带岩浆-矿化作用强烈,形成了重要的内生金属矿藏。研究区范围为东经115°～122°,北纬28°～36°,主要涵盖安徽、江苏、江西和浙江等四省,处于中下扬子地块,而且西侧的深大断裂带—郯庐断裂带被认为是岩浆上涌的通道。已有的研究结果表明长江中下游成矿带下方上地幔内存在明显的低速异常体,这似乎与中生代岩石圈拆沉相关。为了深入讨论该地区的深部动力学过程,本文采用远震P波各向异性层析成像方法,通过挑选从中国地震台网获取的103个固定台站及野外布设的72个流动台站中所记录的300个震级大于5.5的远震事件数据,利用我们改进的多道互相关技术(MMCC),从远震波形资料计算得到22800个P波相对走时残差数据。通过以上数据反演了研究区域上地幔三维速度结构和各向异性分布情况,尝试给出地幔深部上涌的软流圈流体流动方向的直接证据,尝试解释不同深度各向异性产生的原因。研究上地幔各向异性对于地震预测、软流圈对流动力学过程、岩石圈拆沉理论的完善有着重要意义。在网格剖分时,在水平方向上,由于分辨率原因,在300km以上深度采用1°×1°水平网格,在400 km以下深度采用2°×2°;在垂直方向上,分辨率为50～100 km不等。各向同性速度研究结果表明,研究区内上地幔顶部100km以上深度,西侧显示为低的速度异常,东侧显示为高的速度异常。而深度范围为200～400 km深度范围中,西侧出现高速异常。这一变化被认为是由于岩石圈部分拆沉所引起。各向异性反演结果显示出,在100km以上深度内地震波速度快轴方向与地表的构造背景一致,为NE、NNE、NNW方向;从100 km往下,随着深度加深,最快速度方向逐渐转变为近水平向,并且当地震波遇到西侧高速异常体时,各向异性方位有拐弯的迹象,这可能指示地幔深部流体在上涌过程中的具体的流动方向。本文认为在地质解释和构建深部动力学模型时,在300 km以上深度,地震波快轴方向主要受控于低速异常体的蠕动或上涌状态,即地幔热物质的运移方向是南北向的;而在400km以下深度,太平洋板块的俯冲作用则发挥一定影响。
[Abstract]:An important polymetallic metallogenic belt distributed in the middle and lower reaches of the Yangtze River. 230 Ma ago, magma mineralization was strong in the metallogenic belt of the middle and lower reaches of the Yangtze River, forming an important endogenic metal deposit. The study area was 115 掳/ 122 掳E and 28 掳N / 36 掳N, mainly covering Anhui Province. Jiangsu, Jiangxi and Zhejiang provinces are in the middle and lower Yangtze block. Moreover, the deep fault zone in the west is considered to be a channel of magmatic upwelling. The results show that there are obvious low velocity anomalies in the upper mantle beneath the middle and lower reaches of the Yangtze River metallogenic belt. This seems to be related to the Mesozoic lithospheric desubsidence. In order to discuss the deep dynamic process in this area, a method of P-wave anisotropic tomography is used in this paper. By selecting 300 teleseismic events with magnitude greater than 5.5 recorded from 103 fixed stations and 72 mobile stations deployed in the field from the China Seismic Network, By using our improved multichannel cross-correlation technique, MMCC, 22800 P-wave relative travel time residuals are obtained from the remote seismic waveform data. The 3-D velocity structure and anisotropic distribution of the upper mantle in the studied area are inversed from the above data. This paper attempts to give direct evidence of the direction of flow of asthenosphere fluid in deep mantle upwelling, and try to explain the causes of anisotropy at different depths. It is of great significance to perfect the theory of lithospheric desubsidence. In the horizontal direction, for the reason of resolution, 1 掳脳 1 掳horizontal grid is used in the depth above 300 km, 2 掳脳 2 掳in the depth below 400 km, and in the vertical direction, when the meshes are divided into meshes, the depth is 1 掳脳 1 掳and the depth below 400 km is 2 掳脳 2 掳. The resolution varies from 50 to 100 km. The results of isotropic velocities show that the depth of the upper mantle is more than 100 km in the study area, the velocity anomaly in the west is low and the velocity anomaly in the east is high, while the depth range is 200 ~ 400 km. A high speed anomaly appears on the west side. This change is believed to be caused by the partial desubsidence of the lithosphere. The anisotropic inversion results show that the fast axis direction of seismic wave velocity is consistent with the tectonic background of the surface in the depth of more than 100 km, which is the NNE NW direction. From 100 km down, along with the depth deepening, the fastest velocity direction gradually changes to the near horizontal direction, and when the seismic wave meets the high-speed anomaly body on the west side, the anisotropic azimuth shows the sign of turning. This may indicate the specific flow direction of deep mantle fluids during upwelling. The fast axis direction of the seismic wave is mainly controlled by the creep or upwelling state of the low-velocity anomaly, that is, the direction of the mantle thermal material migration is north-south, but the subduction of the Pacific plate plays a certain role in the depth below 400km.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.4

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