用接收函数研究云南省地壳上地幔结构

发布时间：2018-01-26 22:27

本文关键词： 云南接收函数地壳演化泊松比　出处：《武汉大学》2017年硕士论文　论文类型：学位论文

【摘要】：云南地处青藏高原东南缘,地震活动性强、断层分布广泛。中国大陆42.4%以上的6级以上地震发生在这里。此外在中国云南省西部的腾冲火山地区存在大量的第四纪火山活动的遗迹以及丰富的火山温泉。独特的地质和地球物理特征,长久以来受到全世界地球科学科学家们的关注。最近的研究认为云南地区现存两条以上从青藏高原中部逃逸的下地壳管道流,但是他们各自的结果间依然存在巨大的分歧,比如管道流通道位置以及相同深度的速度切片的速度值大小。我们注意到他们仅依据S波异常情况来描绘这一粘滞性流体在复杂研究区的拓展情况,以期获取这一假想流体的分布线索。不幸地是,在这样一个变形剧烈、裂隙极度发育的地区,单纯的S波速度结构并不能唯一来表征这一高温、软弱物质。我们使用H-κ方法获取地壳平均波速比来识别下地壳流的分布情况,以及共转换点叠加方法(CCP)获取研究区内地壳上地幔的精细剖面信息。同时我们做了几组不同参数下影响接收函数H-κ叠加效果的数值试验,目的是为了合理地解释之前类似研究中部分地区结果大相径庭的原因。研究结果表明:地壳泊松比分布具有明显的分区特点,高泊松比(0.28)主要分布在北纬26度以北,并且腾冲和楚雄火山地区有极高的泊松比(0.30),这些结果暗示地壳中可能存在部分熔融/铁镁质含量增加。我们发现沿着北纬26度的Moho面和下地壳组成变化剧烈,预示着这里可能存在一个转换带。CCP剖面的结果显示,在云南北部存在两个地壳上地幔隆起并且转换带附近的地壳界面较为脆弱,横向变化剧烈。有趣的是我们发现部分台站下方存在"阶梯状""双层" Moho结构,这可能与下地壳的拆沉有关。拆沉会导致低泊松比的出现并且系统性的低泊松比,通常认为是铁镁质层沉入上地幔的结果。本文结果显示在26°N存在一条低泊松比带,其将两边的正常---较高泊松比物质隔开。基于滇西北下地壳存在明显的物质转换,以及层析、S波分裂和SKS的结果在26°N的显著特征,我们推断下地壳流局限于转换带以北。火山地区地壳上地幔的隆升为缅甸和青藏高原东南缘的上地幔流定向运动所产生的结果。本研究中高泊松比区域与云南地区大陆热流值场数据吻合的非常好。
[Abstract]:Yunnan is located in the southeast margin of the Qinghai-Tibet Plateau and has strong seismicity. Faults are widely distributed. Earthquakes of magnitude 6 or above occurred here in mainland China. In addition, there are a large number of traces of Quaternary volcanic activity and abundant volcanoes in Tengchong volcanic area in western Yunnan Province, China. Hot springs. Unique geological and geophysical characteristics. Earth science scientists around the world have long been concerned. Recent studies suggest that there are more than two lower crustal pipeline flows that escape from the middle of the Qinghai-Tibet Plateau in Yunnan. But there are still huge differences between their respective outcomes. For example, the location of the channel and the velocity value of the velocity slice of the same depth. We note that they only describe the expansion of the viscous fluid in the complex study area based on the S-wave anomaly. Unfortunately, in such an area where the deformation is severe and the fracture is extremely developed, the simple S-wave velocity structure is not the only indication of this high temperature. Weak material. We use H- 魏 method to obtain the average velocity ratio of crustal wave to identify the distribution of lower crustal flow. And the common conversion point stacking method (CCPP) is used to obtain the fine profile information of the crust and upper mantle in the study area. At the same time, we have done several numerical experiments on the effect of H- 魏 stack on the receiving function under different parameters. The purpose of this study is to explain reasonably the reason why the results of some of the previous similar studies differ greatly. The results show that the distribution of the crustal Poisson's ratio has obvious zoning characteristics. The high Poisson ratio (0.28) is mainly distributed in the north of 26 ~ N, and has a very high Poisson's ratio (0.30) in Tengchong and Chuxiong volcanic areas. These results suggest that there may be an increase in partial melting / magnesia content in the crust. We found that the composition of the Moho surface and lower crust along the 26 ~ N latitude changed dramatically. The results show that there are two crustal upper mantle uplift in northern Yunnan and the crustal interface near the transition zone is relatively weak. It is interesting to find that there is a "ladder" "double layer" Moho structure under some stations. This may be related to the desubsidence of the lower crust, which leads to the emergence of low Poisson's ratio and systematic low Poisson's ratio. It is generally considered to be the result of the subsidence of the ferromagnesite layer into the upper mantle. The results show that there is a low Poisson ratio zone at 26 掳N. It separates the normal -high Poisson ratio material from both sides. It is based on the obvious material transformation in the lower crust of northwest Yunnan, and the obvious characteristics of S-wave splitting and SKS at 26 掳N. We infer that the lower crustal flow is confined to the north of the transition zone. The uplift of the upper mantle in the volcanic area is the result of the directional movement of the upper mantle flow in Myanmar and the southeastern margin of the Qinghai-Xizang Plateau. The data of the continental heat flux field are in good agreement with each other.
【学位授予单位】：武汉大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P315.2;P542.5

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