Magmatism in the evolution of the South China Sea: Geophysical characterization

Song, Xiaoxiao; Li, Chun‐Feng; Yao, Yongjian; Hu, Shi

doi:10.1016/j.margeo.2017.07.021

Cited by 53 publications

(38 citation statements)

References 66 publications

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“…Yan et al () found that post‐seafloor spreading volcanic activities include discontinuously volcanic zone along the northern margin, seamounts in the oceanic basins and volcanoes around the SCS by compiling observations of magmatism in/around the SCS. On comparison to the number of volcanoes found in the hyper‐extended continental slopes and massive intrusions nearby the Dongsha uplift region in the northern SCS margin (Fan et al, ; Gao et al, ; Lüdmann & Wong, ; Song, Li, Yao, & Shi, ; Sun et al, ; Yan et al, ), the post‐seafloor spreading magmatism in the Xisha uplift region of the northwestern SCS appears to be similarly active (Wang, Zhao, Wu, Wang, & Wang, ; Zhang et al, ). However, magmatism of the Xisha uplift especially Xisha Islands region which includes nearshore and offshore areas surrounded by the islands and constitutes the main part of the Xisha uplift, is poorly studied by comparison to the Dongsha uplift, largely because of the complex topography and limited bathymetry coverage in the shallow waters surrounding the Xisha Islands.…”

Section: Introductionmentioning

confidence: 99%

Post‐seafloor spreading magmatism and associated magmatic hydrothermal systems in the Xisha uplift region, northwestern South China Sea

Gao

Bangs

et al. 2019

Basin Research

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Submarine magmatism and associated hydrothermal fluid flows has significant feedback influence on the petroleum geology of sedimentary basins. This study uses new seismic profiles and multibeam bathymetric data to examine the morphology and internal architecture of post-seafloor spreading magmatic structures, especially volcanoes of the Xisha uplift, in extensive detail. We discover for the first time hydrothermal systems derived from magmatism in the northwestern South China Sea. Numerous solitary volcanoes and volcanic groups occur in the Xisha uplift and produce distinct seismic reflections together with plutons. Sills and other localized amplitude anomalies were fed by extrusions/intrusions and associated fluid flow through fractures and sedimentary layers that may act as conduits for magma and fluid flows transport. Hydrothermal structures such as pipes and pockmarks mainly occur in the proximity of volcanoes or accompany volcanic groups. Pipes, pockmarks and localized amplitude anomalies mainly constitute the magmatic hydrothermal systems, which are probably driven by post-seafloor spreading volcanoes/plutons. The hydrothermal fluid flows released by magma degassing or/and related boiling of pore fluids/metamorphic dehydration reactions in sediments produced local overpressures, which drove upward flow of fluid or horizontal flow into the sediments or even seafloor. Results show that post-seafloor spreading magmatic activity is more intense during a 5.5 Ma event than one in 2.6 Ma, whereas the hydrothermal activities are more active during 2.6 Ma than in 5.5 Ma. Our analysis indicates that post-seafloor spreading magmatism may have a significant effect on hydrocarbon maturation and gas hydrate formation in the Xisha uplift and adjacent petroliferous basins. Consequently the study presented here improves our understanding of hydrocarbon exploration in the northwestern South China Sea. K E Y W O R D S hydrothermal fluid flows, NW South China Sea, post-seafloor spreading magmatism, Xisha uplift | 689 EAGE GAO et Al. 692 | EAGE GAO et Al. the top of the Huangliu formation, is the boundary of late Miocene and Pliocene (about 5.5 Ma).

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Section: Introductionmentioning

confidence: 99%

Post‐seafloor spreading magmatism and associated magmatic hydrothermal systems in the Xisha uplift region, northwestern South China Sea

Gao

Bangs

et al. 2019

Basin Research

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“…The magmatic activities were not strong before and during the SCS rifting and seafloor spreading and no high‐velocity anomaly was found onland South China (Yin ZX et al, ). Post‐spreading magmatic activities became more active, and more seamounts developed parallel to the faults in this stage (Ru K and Pigott, ; Song XX et al, ). Therefore, we infer that the high‐velocity anomalies may have been formed by magmatic underplating after the cessation of seafloor spreading.…”

Section: Discussionmentioning

confidence: 99%

“…We further argue that the anomalies could be formed after the spreading stopped because significant episodic extensions (~15.2 Ma and 5.2 Ma) may have thinned the lithosphere, leading to high heat flow (He LJ et al, ; Shi XB et al, ). Thermal contraction in the oceanic lithosphere may also trigger extension and decompressive melting along weak zones in the continental slope and the oceanic basin (Song XX et al, ). As a consequence, high‐ temperature melting would increase the Mg content at the expense of Fe (White et al, ) and reduced the V P / V S ratio.…”

Section: Discussionmentioning

confidence: 99%

“…Seismic data and geochemical studies reveal that the magmatic activities in the northeastern SCS continental margin were not strong during the incipient rifting and spreading (66–26 Ma) (e.g.,Song XX et al, ; Fan CY et al, ; Xia SH et al, ). Based on magnetic data analysis, Li C‐F et al () found that the full spreading rate of the East Subbasin was higher (~70 km/) at the beginning of seafloor spreading from ~32 to ~29 Ma, and dropped to ~25 km/ on average from ~29 to ~26 Ma.…”

Section: Discussionmentioning

confidence: 99%

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Crustal S-wave velocity structure across the northeastern South China Sea continental margin: implications for lithology and mantle exhumation

Hou

Wan

et al. 2019

Earth and Planetary Physics

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The northeastern margin of the South China Sea (SCS), developed from continental rifting and breakup, is usually thought of as a non‐volcanic margin. However, post‐spreading volcanism is massive and lower crustal high‐velocity anomalies are widespread, which complicate the nature of the margin here. To better understand crustal seismic velocities, lithology, and geophysical properties, we present an S‐wave velocity (V S) model and a V P/V S model for the northeastern margin by using an existing P‐wave velocity (V P) model as the starting model for 2‐D kinematic S‐wave forward ray tracing. The Mesozoic sedimentary sequence has lower V P/V S ratios than the Cenozoic sequence; in between is a main interface of P‐S conversion. Two isolated high‐velocity zones (HVZ) are found in the lower crust of the continental slope, showing S‐wave velocities of 4.0–4.2 km/s andV P/V S ratios of 1.73–1.78. These values indicate a mafic composition, most likely of amphibolite facies. Also, aV P/V S versus V P plot indicates a magnesium‐rich gabbro facies from post‐spreading mantle melting at temperatures higher than normal. A third high‐velocity zone (V P : 7.0–7.8 km/s;V P/V S: 1.85–1.96), 70‐km wide and 4‐km thick in the continent‐ocean transition zone, is most likely to be a consequence of serpentinization of upwelled upper mantle. Seismic velocity structures and also gravity anomalies indicate that mantle upwelling/ serpentinization could be the most severe in the northeasternmost continent‐ocean boundary of the SCS. Empirical relationships between seismic velocity and degree of serpentinization suggest that serpentinite content decreases with depth, from 43% in the lower crust to 37% into the mantle.

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“…In the SCS and its adjacent areas, Cenozoic magmatism is relatively active, and Cenozoic igneous rocks are widely distributed. The Cenozoic igneous rocks are mainly characterized by basaltic rocks, volcanic clastic rocks, and intermediate-acid extrusive rocks [1][2][3][4][5][6]. For a long time, domestic and foreign scholars performed a lot of research on the Cenozoic basalts of the SCS.…”

Section: Introductionmentioning

confidence: 99%

LA-ICP-MS Analysis of Clinopyroxenes in Basaltic Pyroclastic Rocks from the Xisha Islands, Northwestern South China Sea

Zhang

Qian

2018

Minerals

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Cenozoic volcanic rocks were recently discovered during full-coring kilometer-scale major scientific drilling in the Xisha Islands, northwestern South China Sea. A systematic mineralogical study of these samples was performed for this paper. The results show that the volcanic rock samples are basaltic pyroclastic. The major elements demonstrate that the clinopyroxenes are diopside and fassaite, which contain high Al 2 O 3 (5.33-11.2 wt. %), TiO 2 (2.13-4.78 wt. %) and wt. %). Clinopyroxenes have high REE abundances (104-215 ppm) and are strongly enriched in LREE (LREE/HREE = 3.56-5.14, La/Yb N = 2.61-5.1). Large-ion lithophile elements show depleted characteristics. Nb/Ta shows obvious fractionation features: Nb is lightly enriched, relative to primitive mantle, but Ta is heavily depleted, relative to primitive mantle. The parental magma of the basaltic pyroclastic rocks belongs to a silica-undersaturated alkaline series, characterized by a high temperature, low pressure, and low oxygen fugacity. The Al IV content increases with decreasing Si concentration. The Si-unsaturated state causes Si-Al isomorphic replacement during the formation of clinopyroxene. The electric charge imbalance caused by the replacement of Si by Al is mainly compensated by Fe 3+ . The clinopyroxene discrimination diagrams show that the parental magma formed in an intraplate tectonic setting environment.The mineral composition of igneous rocks depends on the chemical composition and crystallization environment of magma. Changes in mineral composition and structure are direct evidence of changes in the diagenetic environment and material composition. Therefore, the characteristics of mineral composition can be used to explore mineral petrogenesis and the magma evolution mechanism [18]. Clinopyroxene is one of the main rock-forming minerals of mafic-ultramafic rocks and plays a major role in the generation and subsequent differentiation of magma [16,[19][20][21][22][23][24]. Clinopyroxene composition mainly depends on primary magma characteristics, the crystallization environment, and the tectonic setting of magmatism [25][26][27][28][29][30][31][32]. Relative to other minerals in mafic-ultramafic rocks, clinopyroxene is considered to be the main carrier for most trace elements and holds a unique further record of magma history [33,34]. The mineral chemistry of relict clinopyroxene in igneous rocks can reflect the characteristics of the primary magma well and has been widely used to study the nature of the original magma and complicated processes that have affected the lithospheric mantle [21,[35][36][37][38][39][40][41][42]. Furthermore, clinopyroxenes in altered basalts are of interest, because they often survive in a relatively pristine form, after the matrix and other minerals have been converted to secondary minerals. The major-and minor-element geochemistry of clinopyroxene is varied and provides a filtered view of the composition of the magma from which the clinopyroxene crystallized, lending it the potential to provide insight into t...

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Magmatism in the evolution of the South China Sea: Geophysical characterization

Cited by 53 publications

References 66 publications

Post‐seafloor spreading magmatism and associated magmatic hydrothermal systems in the Xisha uplift region, northwestern South China Sea

Post‐seafloor spreading magmatism and associated magmatic hydrothermal systems in the Xisha uplift region, northwestern South China Sea

Crustal S-wave velocity structure across the northeastern South China Sea continental margin: implications for lithology and mantle exhumation

LA-ICP-MS Analysis of Clinopyroxenes in Basaltic Pyroclastic Rocks from the Xisha Islands, Northwestern South China Sea

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