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长江中下游地区浅部成矿带分布与深部壳幔速度结构之间的关系

发布时间:2018-02-24 15:04

  本文关键词: 长江中下游成矿带 壳幔速度结构 背景噪声成像 双平面波成像 出处:《中国地质大学(北京)》2015年硕士论文 论文类型:学位论文


【摘要】:长江中下游地区主要包括华北克拉通的东南部、大别-苏鲁造山带、扬子克拉通的中东部以及华夏板块的东北部。长江中下游成矿带位于研究区域的中心,它是我国东部重要的多金属成矿带和矿物资源基地,由7个大型矿集区,约200多个大中型矿床组成。为什么在如此狭窄的弧形带内集中产出了众多的大型、超大型矿床?其深部动力学背景是什么?深部结构和浅部矿床之间是否存在一定关联?因而探测长江中下游地区地壳和上地幔速度结构,对于加深我们对成矿带的深部构造背景和岩浆活动机制的了解有重要意义。但由于长江中下游地区地震活动性较低,传统的地震成像法比较难获取该地区高分辨的壳幔速度结构,因此该地区一直缺乏高精度的壳幔速度结构模型。本文首次利用背景噪声和双平面波层析成像方法联合反演了长江中下游地区的地壳和上地幔剪切波速度结构。研究中所用数据包括从2012年7月至2013年8月共14个月的连续背景噪声数据以及219个远震数据,这些数据是由中国地震局区域数字地震台网和中国地质大学(北京)布设的流动宽频地震台站所记录到的。通过背景噪声层析成像,获得了5 s到42 s的瑞利波群速度和相速度。然后,对远震瑞利波数据进行了双平面波层析成像,获得了20-143 s的瑞利波相速度频散。通过将这两种方法的频散结果联合起来,反演了5-143 s的瑞利波速度结果,得到了长江中下游地区从地表到250 km深度范围内的三维剪切波速度结构。研究结果表明:在6 km深度,盆地地区均表现为低速特征,且河淮、苏北和江汉盆地表现出比南阳和合肥盆地更低的速度,这可能是由于南阳和合肥盆地具有相对较薄的沉积层;大别-苏鲁造山带和华南褶皱带表现为高速特征,这些高速可能是由于这些地区广泛存在中生代岩浆岩和非常浅的基底而导致的;在上地幔,长江中下游成矿带下方100 km到200 km深度范围内存在一个明显的低速区。该低速区可能代表由于古太平洋板块部分熔融或者古太平洋的西向俯冲引起的地幔部分熔融而产生的热的上地幔物质,然后这些幔源岩浆上涌从而导致了在长江中下游成矿带形成大量的花岗岩和丰富的矿床。
[Abstract]:The middle and lower reaches of the Yangtze River mainly include the southeastern part of the North China Craton, the Dabie Sulu orogenic belt, the east-central Yangtze craton and the northeast of the Huaxia plate. It is an important polymetallic metallogenic belt and mineral resource base in the east of China. It is composed of seven large ore concentration areas and about 200 large and medium-sized deposits. Why are there so many large and super large deposits concentrated in such a narrow arc belt? What is the deep dynamic background? Is there a relationship between the deep structure and the shallow deposits? Therefore, it is important to probe the velocity structure of crust and upper mantle in the middle and lower reaches of the Yangtze River to deepen our understanding of the deep tectonic background and the mechanism of magmatic activity in the metallogenic belt, but because of the low seismicity in the middle and lower reaches of the Yangtze River, The traditional seismic imaging method is more difficult to obtain the high resolution crust-mantle velocity structure in this area. Therefore, there has been a lack of accurate crust-mantle velocity structure model in this area. In this paper, the crust and upper mantle shear wave velocity structures in the middle and lower reaches of the Yangtze River are retrieved by using background noise and biplane wave tomography for the first time. The data used in the study included 14 months of continuous background noise data from July 2012 to August 2013 and 219 teleseismic data. These data were recorded by the regional digital seismograph network of the China Seismological Bureau and the mobile broadband seismic stations set up by the China University of Geosciences (Beijing). The Rayleigh wave group velocities and phase velocities of 5 s to 42 s are obtained. Then, the Rayleigh wave data of distant earthquakes are computed by biplane wave tomography, and the dispersion of Rayleigh wave phase velocities of 20-143 s is obtained. By combining the dispersion results of the two methods, The Rayleigh wave velocity of 5-143s is inversed, and the 3-D shear wave velocity structure is obtained in the middle and lower reaches of the Yangtze River from the surface to the depth of 250 km. The results show that at the depth of 6 km, the basin is characterized by low velocity and river and Huaihe River. The north Jiangsu and Jianghan basins show lower velocities than the Nanyang and Hefei basins, which may be due to the relatively thin sedimentary layers in the Nanyang and Hefei basins, while the Dabie Sulu orogenic belt and the southern China fold belt are characterized by high speed. These high speeds may be due to the widespread presence of Mesozoic magmatic rocks and very shallow basements in these areas; in the upper mantle, There is an obvious low velocity zone between 100 km and 200 km below the metallogenic belt in the middle and lower reaches of the Yangtze River. This low speed zone may represent the partial melting of the mantle due to partial melting of the paleo-Pacific plate or westward subduction of the paleo-Pacific Ocean. The hot upper mantle material that melts, Then these mantle magma upwelling resulted in the formation of a large number of granite and rich deposits in the middle and lower reaches of the Yangtze River metallogenic belt.
【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】:2015
【分类号】:P617;P542.5

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