Two Mechanisms Generating Intraplate Volcanism in Southeast Asia: Insights From Mantle Transition Zone Discontinuities

Shang, Zhengtao1,2; Yang, Ting1,2,3; Jiang, Ming2; Le, Ba Manh4; Zhou, Yong5; Chen, Yongshun1; Morgan, Jason P.1

2024-08-01

10.1029/2024JB029090

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   影响因子和分区

2169-9313

2169-9356

["Determining the mechanisms responsible for intraplate volcanism - such as slab devolatilization melting versus active mantle plumes - remains a challenge. The greater South China Sea (SCS) region has experienced extensive intraplate Cenozoic volcanism across areas including Hainan, Southeast Indochina, northern Borneo, the northern SCS, and the post-spreading SCS basin. The prevalence of volcanism distributed widely across this region prompts fundamental questions about the key geodynamic processes driving such diverse magmatic activities. In this study, we elucidate the mantle transition zone (MTZ) discontinuities in this region using SS precursors, which helps to overcome the sparse seismic coverage due to its predominantly oceanic setting. We collected over 16,000 high-quality seismograms that sample the upper mantle and MTZ beneath this region from global earthquakes and stations. After correcting for the effects of shallow crustal variations and upper mantle heterogeneity on traveltimes of SS phases and their precursors, we unveil lateral variations in the MTZ boundaries (d410 and d660) and intricate features of the mid-MTZ reflectors (S520S). Significant MTZ thinning and normal S520S waveforms beneath Hainan provide compelling evidence for mantle upwelling through the MTZ. Conversely, the evident splitting of S520S beneath the northern SCS, Southeast Indochina, and northern Borneo, all characterized by stagnant subducted slabs, indicates that the volcanism in these regions likely originated from a mechanism distinct from the active upwelling beneath Hainan. Dehydration melting attributed to devolatilizing stagnant slabs in the MTZ is a potential cause for Cenozoic volcanism in these regions.","Determining the causes of volcanic activity far from tectonic plate boundaries remains a challenge. The greater South China Sea region experienced widespread volcanism during the Cenozoic era, prompting questions about the driving geological processes behind this phenomenon. This study investigated the boundaries of the mantle transition zone (MTZ) beneath the region using seismic wave analysis of over 16,000 seismic recordings. By analyzing the travel times of signals reflected from the MTZ boundaries and internal reflectors, lateral variations in the structure of the MTZ boundaries and internal features were revealed. Beneath Hainan, thinning of the MTZ and normal waveforms of the internal MTZ reflector suggest upwelling of hot mantle material through the MTZ, likely causing the surface volcanism. In contrast, beneath the northern South China Sea, Southeast Indochina, and northern Borneo, the distorted waveforms of signals from the internal MTZ reflector indicate a different mechanism. These latter regions contain ancient, subducted slabs present in their MTZs. Dehydration melting, caused by the release of water from these stagnant slabs within the MTZ, is a potential cause of the Cenozoic volcanism in these areas, distinct from the mantle upwelling observed beneath Hainan.","SS precursors from the mantle transition zone (MTZ), notably the S520S, provide insights into mantle dynamics beneath the greater South China Sea (SCS) region Evidence of MTZ thinning and normal S520S waveform beneath Hainan suggests active mantle upwelling through the MTZ The S520S splitting beneath areas with stagnant subducted slabs indicates a possible magmatic origin through flux melting"]

intraplate volcanism mantle transition zone subduction zone mantle plume SS precursors

SCI

英语

第一 ; 通讯

National Natural Science Foundation of China (NSFC)["92058209","92058212","42327804","41890814","42104104"] ; Shenzhen Science and Technology Program[KQTD20170810111725321] ; High Level Special Fund of SUSTech[G03050K001] ; Vietnam Academy of Sci. and Tech. (VAST)[THTETN.06/24-25]

Geochemistry & Geophysics

Geochemistry & Geophysics

WOS:001284849300001

AMER GEOPHYSICAL UNION

GEOSCIENCES

Web of Science

1.Southern Univ Sci & Technol, Dept Ocean Sci & Engn, OBS Lab, Shenzhen, Peoples R China
2.Peng Cheng Lab, Shenzhen, Peoples R China
3.Shanghai Sheshan Natl Geophys Observ, Shanghai, Peoples R China
4.Vietnam Acad Sci & Technol VAST, Inst Geophys IGP, Hanoi, Vietnam
5.Chinese Acad Sci, South China Sea Inst Oceanol, Key Lab Ocean & Marginal Sea Geol, Guangzhou, Peoples R China

Shang, Zhengtao,Yang, Ting,Jiang, Ming,et al. Two Mechanisms Generating Intraplate Volcanism in Southeast Asia: Insights From Mantle Transition Zone Discontinuities[J]. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH,2024,129(8).

Shang, Zhengtao.,Yang, Ting.,Jiang, Ming.,Le, Ba Manh.,Zhou, Yong.,...&Morgan, Jason P..(2024).Two Mechanisms Generating Intraplate Volcanism in Southeast Asia: Insights From Mantle Transition Zone Discontinuities.JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH,129(8).

Shang, Zhengtao,et al."Two Mechanisms Generating Intraplate Volcanism in Southeast Asia: Insights From Mantle Transition Zone Discontinuities".JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 129.8(2024).