scholarly journals Constraining Mantle Heterogeneity beneath the South China Sea: A New Perspective on Magma Water Content

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 410 ◽  
Author(s):  
Wei Wang ◽  
Fengyou Chu ◽  
Xichang Wu ◽  
Zhenggang Li ◽  
Ling Chen ◽  
...  
Keyword(s):  
South China Sea ◽  
Water Content ◽  
South China ◽  
Mantle Source ◽  
Melt Inclusions ◽  
The South China Sea ◽  
Spreading Ridge ◽  
Mantle Heterogeneity ◽  
The South ◽  
China Sea

The nature of upper mantle is important to understand the evolution of the South China Sea (SCS); thus, we need better constrains on its mantle heterogeneity. Magma water concentration is a good indicator, but few data have been reported. However, the rarity of glass and melt inclusions and the special genesis for phenocrysts in SCS basalts present challenges to analyzing magmatic water content. Therefore, it is possible to estimate the water variations through the characteristics of partial melting and magma crystallization. We evaluated variations in Fe depletion, degree of melt fractions, and mantle source composition along the fossil spreading ridge (FSR) using SCS basalt data from published papers. We found that lava from the FSR 116.2° E, FSR 117.7° E, and non-FSR regions can be considered normal lava with normal water content; in contrast, lava from the FSR 117° E-carbonatite and 114.9–115.0° E basalts have higher water content and show evidence of strong Fe depletion during the fractional crystallization after elimination of the effects of plagioclase oversaturation. The enriched water in the 117° E-carbonatite basalts is contained in carbonated silicate melts, and that in the 114.9–115.0° E basalts results from mantle contamination with the lower continental crust. The lava from the 117° E-normal basalt has much lower water content because of the lesser influence of the Hainan plume. Therefore, there must be a mantle source compositional transition area between the southwestern and eastern sub-basins of the SCS, which have different mantle evolution histories. The mantle in the west is more affected by contamination with continental materials, while that in the east is more affected by the Hainan mantle plume.

scholarly journals Coexistence of Hainan Plume and Stagnant Slab in the Mantle Transition Zone beneath the South China Sea Spreading Ridge: Constraints from Volcanic Glasses and Seismic Tomography

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 2) ◽  
Author(s):  
Shuang-Shuang Chen ◽  
Rui Gao ◽  
Zewei Wang ◽  
Tong Hou ◽  
Jie Liao ◽  
...  
Keyword(s):  
South China Sea ◽  
Oceanic Crust ◽  
Mantle Plume ◽  
South China ◽  
The South China Sea ◽  
Spreading Ridge ◽  
The South ◽  
China Sea ◽  
Volcanic Glasses ◽  
Hainan Mantle Plume

Abstract The influence of Hainan mantle plume and subducting recycled oceanic crust beneath the spreading ridge of the South China Sea (SCS) have been widely proposed recently, but still controversial and ambiguous. Here, we present seismic tomographic evidence, new major and trace element, and Pb isotopic compositions of volcanic glasses from one International Ocean Drilling Program drill core (Site U1434) in the SCS spreading ridge. The volcanic glasses are relatively enriched in alkalis and light rare earth elements (LREEs) and depleted in heavy REEs (HREEs), exhibit slightly positive anomalies in Nb, Ta, Zr, and Hf as well as a positive Nb relative to La and Th, and show relatively high 207Pb/206Pb and 208Pb/206Pb isotopic ratios, suggesting ocean island basalt- (OIB-) type and enriched mantle 2- (EM2-) type geochemical features likely related to a mantle plume. These geochemical features are consistent with those of late Cenozoic volcanic rocks in Hainan and surrounding areas associated with a mantle plume, likely providing the influence of Hainan mantle plume beneath the spreading ridge of the SCS. The SCS primary-melt and volcanic glasses indicate that the source mantle involved 18.5% eclogite (dense, recycled oceanic crust from the stagnant subducted slab) and 46.1% garnet pyroxenite (produced by the reaction between the peridotite melt and recycled oceanic crust). The existence of Hainan mantle plume and stagnant subducted slab is further supported by geophysical evidence from a recent three-dimensional P-wave seismic tomographic model.

scholarly journals Potential role of strike-slip faults in opening up the South China Sea

2019 ◽  
Vol 6 (5) ◽  
pp. 891-901 ◽  
Author(s):  
Chi-Yue Huang ◽  
Pinxian Wang ◽  
Mengming Yu ◽  
Chen-Feng You ◽  
Char-Shine Liu ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Strike Slip ◽  
The South China Sea ◽  
Strike Slip Fault ◽  
Spreading Ridge ◽  
The South ◽  
Regional Geology ◽  
Late Mesozoic ◽  
China Sea

Abstract Radiometric dates of key rock units indicate that a remnant Late Mesozoic ocean of the Huatung Basin is still preserved today east of the South China Sea (SCS). We integrate regional geology with a Cretaceous oceanic basement in the vicinity of the Huatung Basin to reconstruct the Huatung Plate east of the Eurasian continent. Results of geophysical investigations, four expeditions of deep-sea drilling and a renaissance of regional geology allow us to propose a hypothesis that the mechanism responsible for the SCS opening was raised from strike-slip fault on the east. The hypothesis suggests that the SCS opening could highly relate to the strike-slip faults inherited from Late Mesozoic structures onshore–offshore the SE Cathaysia Block to develop rhombic-shaped extensional basins en echelon on the thinned Eurasian continental crust in the Early Cenozoic. It was followed by sinistral strike-slip movements along the boundary between the Eurasian Plate and the Huatung Plate driven by oblique subduction of the Huatung Plate to the northwest coupled with slab-pull force by southward subduction of the Proto-SCS to open up the triangle-shaped oceanic East Sub-basin in the Early Oligocene (33/34 Ma). The spreading ridge then propagated southwestward in the step-over segment between the Zhongnan-Lile and the Red River strike-slip fault systems to open the triangle-shaped oceanic Southwest Sub-basin by 23 Ma. The plate boundary fault was subsequently converted into the Manila Trench when the Eocene Sierra Madre arc of the Huatung Plate had moved from the south to its present latitude by the Middle Miocene.

Age and tectonic setting of the East Taiwan Ophiolite: implications for the growth and development of the South China Sea

2016 ◽  
Vol 154 (3) ◽  
pp. 441-455 ◽  
Author(s):  
ROBERT B.-J. HSIEH ◽  
J. GREGORY SHELLNUTT ◽  
MENG-WAN YEH
Keyword(s):  
South China Sea ◽  
South China ◽  
Tectonic Setting ◽  
The South China Sea ◽  
Spreading Ridge ◽  
The South ◽  
China Sea ◽  
Marginal Seas ◽  
Icp Ms ◽  
T Values

AbstractThe South China Sea is one of the youngest marginal seas and understanding its development is important for reconstructing the tectonic evolution of Southeast Asia. The South China Sea is thought to have been actively spreading between 32 Ma and 15.5 Ma. The East Taiwan Ophiolite (ETO) is one of the few preserved remnants of the South China Sea on land and provides an opportunity to investigate the age and the tectonic setting of the accreted easternmost portion. The age of the ETO was obtained by LA-ICP-MSin situzircon U–Pb methods and yielded a mean206Pb–238U age of 14.1±0.4 Ma, suggesting that magmatic activity in the South China Sea continued ~1.5 million years beyond current estimates. Cr-spinel data (Cr no. = 42–54) and depleted εNd(t) values (i.e. +9.1 to +11.4) from the serpentinized peridotites and gabbros and the light rare earth element depleted patterns (La/Yb ≤ 1) of the ETO mafic rocks are consistent with a ridge setting (i.e. N-MORB composition). Therefore, the ETO likely represents the terminal portion of the South China Sea spreading ridge that was sheared off during the northward translation of the Luzon arc.

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