Hainan Mantle Plume From P Wave Finite Frequency Tomography

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 300 km 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.