海南地幔柱P波有限频层析成像研究

HAINAN MANTLE PLUME FROM P WAVE FINITE FREQUENCY TOMOGRAPHY

陈云鹏

11849157

硕士

力学

陈永顺

2020-05-20

2020-07-20

哈尔滨工业大学

深圳

海南及邻近地区位于欧亚、印度-澳大利亚和太平洋-菲律宾海板块的交汇处，受板块之间运动的影响，该地区发育了深大断裂和板内火山，形成了独特而复杂的地质构造。海南热点位于海南岛，火山活动从始新世开始一直持续到全新世，在周围区域内覆盖超过7000 km2的玄武质熔岩流，前人研究将其归因于地幔柱的影响。岩石学、地球化学和地球物理学的研究都为海南地幔柱的存在提供了证据，研究海南地幔柱的起源、形态特征和影响范围等对于理解海南地幔柱的形成机制和板内火山的深部动力学过程有重要的科学意义，为该地区构造性质、资源效应等问题的研究提供了参考。本次研究选取2016至2018年布设在海南、广东和广西三省的81个宽频带密集地震台站记录的走时数据，采用P波有限频层析成像对该区域内的上地幔速度结构进行了研究，对比基于射线理论的走时层析成像，有限频层析成像考虑了地震波的波前愈合效应、散射波等问题，将地震记录分频段处理，可以获得更加真实的地下速度结构。基于对海南及邻区的文献调研和P波有限频层析成像结果，主要得到以下几点认识：海南地幔柱主要位于海南岛东北部，从上地幔顶部延伸到地下300 km，其特征是直径约200 km垂直上升的柱状低速异常，可以认为该处是岩浆最强上涌的中心，并且在到达岩石圈底部后有明显的水平运动；海南地幔柱的异常幅值和分布情况随深度的变化而变化，大致可以分为三个阶段，异常中心在海南岛东部和东北部进行转移，可能与该地区上地幔各向异性和热化学结构有关；海南地幔柱的与该地区构造活动分布有很好的对应关系，滨海深大断裂可能为岩浆上涌提供了重要通道，海南地幔柱为板内构造活动提供了物质和能量来源。

Hainan and its adjacent areas are located at the junction of Eurasian, Indo-Australian and Pacific-Philippine Sea plates, which are affected by the relatively movement between plates. The region has developed deep large faults and intraplate volcanism, forming unique and complex geological structures. Hainan hotspot is located on Hainan Island, the volcanic activity began from the Early Eocene and continued to the Holocene, resulting in more than 7000 km2 of basaltic lava flow. The Hainan hotspot has commonly been attributed to the mantle plume. Numerous petrological, geochemical and geophysical studies all provide evidence for the existence of Hainan mantle plume. The study of the origin, morphological characteristics, and influence range of Hainan mantle plume is essential for understanding the formation m and deep dynamic processes of intraplate volcanism.In this study, we use seismic data recorded by 81 broadband seismic stations from 2016 to 2018, which belongs to Guangdong, and Guangxi, and Hainan province networks. We picked P wave travel-time at three frequency band using cross-correlation and finite frequency tomography was used to construct high resolution 3D upper mantle velocity model in this region. Compared with the ray theory travel time tomography, finite frequency tomography considers wave front healing effect, scattering wave and significantly improves resolution. P wave velocity model of Hainan and its adjacent regions from P wave finite frequency tomography shows that:A columnar-shaped low velocity zone (LVZ) with a diameter of ~ 200 km is observed to the northeast of Hainan Island, extending from the uppermost mantle to 300km depth. We suggest that this observation provides seismic evidence for the deep welling of the Hainan plume and the LVZ to the northeast of the Hainan Island can be considered as the current upwelling center of the Hainan plume. In the uppermost mantle, the low velocities horizontally spread to the west of the upwelling center. The distribution of Hainan mantle plume varies with depth, which can be roughly divided into three stages, and the upwelling center shifts in the east and northeast of Hainan Island. The location of the present upwelling center of the Hainan mantle plume is closely related to the Littoral fault zone in the northern South China Sea. We suggest that these deep-penetrated fault zones provide pathway for the magma transportation, and the Hainan plume is the main cause for intraplate geological phenomena, such as volcanic activities.

地震 海南地幔柱 有限频理论 层析成像 上地幔结构

seismology Hainan mantle plume theory of finite-frequency tomography structure of upper mantle

中文

联合培养

南方科技大学

陈云鹏. 海南地幔柱P波有限频层析成像研究[D]. 深圳. 哈尔滨工业大学,2020.