Evolution Of South China Sea Research Articles

Strontium isotope stratigraphy and LA-ICP-MS U-Pb carbonate age constraints on the Cenozoic tectonic evolution of the southern South China Sea

Abstract The tectonic evolution of the South China Sea is closely associated with multiple subduction-collision processes in Southeast Asia. When the collision of the Dangerous Grounds terrane with Sabah-Palawan Islands terminated is debated due to poor age constraints at the southern margin of South China Sea. A deep well drilled on Meiji Atoll penetrates Cenozoic carbonate strata in central Dangerous Grounds. Robust strontium isotope ages and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb dates provide critical chronological constraints on the Cenozoic evolution of the southern South China Sea. A middle Miocene hiatus spanning 9 m.y. on Meiji Atoll is thought to be mainly caused by tectonic uplift in the central Dangerous Grounds. The uplift in the central Dangerous Grounds was accompanied by underthrusting beneath the southern Palawan margin and orogenic uplifting in north Borneo during the middle Miocene. Data interpretation indicates an active collision in the southern South China Sea during the middle Miocene. The regrowth of the Meiji Atoll above the middle Miocene hiatus represents the end of this collision event in the southern South China Sea at ca. 11 Ma, after the cessation of seafloor spreading, which occurred at ca. 15 Ma.

Evolution of South China Sea and East Asian monsoon from spring to summer by the progression of daily weather types

AbstractThe monsoon development in the early rainy season in East Asia is analysed by the evolution of daily weather types (WTs). The WTs are classified by a k‐means clustering analysis based on 850 hPa winds from April 1 to July 31 in the 40‐year period of 1979–2018. Five WTs are identified, typifying the progression of weather regimes in the monsoonal evolution. WTs 1 and 2, with easterly winds in the South China Sea (SCS), occurs mostly in April and early May, corresponding to typical WTs before the SCS monsoon onset. In WT3, winds in the SCS turns westerly, and a rain band emerges in South China, extending east‐northeastward to the Pacific Ocean south of Japan, which signifies the May–June Mei‐yu in South China. Then, with the rain band moved to Yangtze River Valley (YRV) in WT4, this WT corresponds to the June–July Mei‐Yu in central and eastern China along the YRV. Finally, WT5 occurs more frequently towards the end of July, and corresponds to the post‐Mei‐Yu WT, indicating the ending of the early summer rainfall season in East Asia. The evolution of the WTs is gradual but intermittent, representing the weather‐within‐climate information. Each WT likely persists to itself. But WT1 and WT2 also progress to each other. The long persistence of WT3 and WT4 up to several weeks indicates the quasi‐stationary Mei‐Yu in South China and the YRV, respectively. The year‐to‐year variability of the WTs is also evident in the WTs. The El Niño–Southern Oscillation (ENSO) impact on the precipitation in the East Asian region is analysed for three types of ENSO: Eastern Pacific, Central Pacific, and mixed El Niño and La Niña. The seasonal mean precipitation anomalies can be interpreted by the frequencies of the daily WTs under different ENSO conditions.

Geochemistry of late miocene-pleistocene basalts in the Phu Quy island area (East Vietnam Sea): Implication for mantle source feature and melt generation

Geochemistry of late miocene-pleistocene basalts in the Phu Quy island area (East Vietnam Sea): Implication for mantle source feature and melt generation

Study of the permeability in melting zone of South China Sea based on percolation theory

Oceanic crust is formed at mid-ocean ridges. The melting zone extends up to several hundreds of km laterally, the upwelling area at the spreading axis is confined to a narrow belt of only 2–3 km width. Whereas the parameter of permeability that magma ascending from the mantle beneath mid-ocean ridges is still poorly understood, despite the important role of the process for the formation of crust. Based on continuum percolation, we build the random fracture network as magma migration channels of South China Sea; with momentum equation, we deduced the dynamic pressure distribution with passive corner flow. After which, the permeability of melting zone is calculated with finite element method. Numerical simulation results indicate that there exists a power law relationship between the permeability and magma migration channels. The simulated result is consistent with that calculated by fractal method. The discovery of the ruler provides sound theoretical basis for the formation and evolution of oceanic crust, and may help us better understanding the formation and evolution of South China Sea.

Comparison of Inversion Method of Wide Angle Ocean Bottom Seismometer Profile: A Case Study of Profile OBS973‐2 Across Liyue Bank in the South China Sea

AbstractDeep crust structure of the wide angle seismic profile OBS973‐2, which crosses the central sea basin and Liyue bank in the southern of South China Sea (SCS), represents one of the direct evidences for conjugate spreading and evolution of SCS. For this reason, we remodeled the data by using both forward and inversion methods for a detailed crustal velocity structure, and also compared results with depth profile of multi‐channel seismic (MCS) close to OBS973‐2 for more reliable crust thickness. Comparing to former works, and according to the new velocity models, we divided the profile to three parts of continental crust (0∼200 km in the profile), continent and ocean transition (COT, 200∼280 km in the profile) and ocean crust (280∼370 km in the profile). And their crust structures are obviously different. Sediment layer in the continental crust shows a feature of horizontal variations in both thickness and velocity, and total crust thickness in continental part is thick (about 20 km). In the COT, both thickness and velocity are horizontally smooth, and the total thickness of crust is thinner (about 8 km). And in the ocean crust, the crust thickness thins to 6 km. There are two main conclusions, (1) the method of using data collected by wide angle seismic and multi‐channel seismic and using both forward and inversion software in modeling will obtain more reliable information of crust structure, (2) the new insights on the crust structure are as follows. (a) We get the seaward thinning of Moho and its depth of about 12∼18 km below the sea level in COT from both wide angle and multi‐channel seismic profiles. (b) No high velocity layer was found beneath COT, which represents non volcanic passive continental margin and its conjugate spreading point is Zhongsha massif. (c) Heavy extension occurred in upper crust of continental part, which shows horizontal velocity anomalies and low velocity zone in the velocity model and a large number of normal faults in the multi‐channel seismic profile.

Sedimentary Evolution in the Northern Slope of the South China Sea Since the Oligocene and Its Response to Tectonics

AbstractThe sedimentary evolution of the South China Sea (SCS) since the Oligocene and its response to tectonics was reconstructed based on a multi‐proxies approach including monomineralic quartz oxygen isotope ratios (δ18O), terrigenous grain‐size and accumulation rate, and scanning electron microscopy (SEM) observation of isolated quartz in sediments from Ocean Drilling Program (ODP) Site 1148 in the northern SCS. The sedimentary evolution of SCS could be divided into five stages: initial expansion (34~28.5 Ma), intense tectonic activity (28.5~23 Ma), reduced tectonic activity (23~16.5 Ma), thermal subsidence (16.5~3.5 Ma), and Taiwan uplift (3.5 Ma to present). Significant variations of the composition of terrigenous minerals and oxygen isotope values of quartz between 28.5 Ma and 23 Ma suggest a change in sediments provenance, which may be related to the strongest tectonic activity of the SCS in the Oligocene. Terrigenous materials at the study site were mainly originated from the southern source (presumptively from Palawan) during the early spreading period of the SCS. With the extensive spreading of the SCS, especially when the spreading axis of the SCS jumped southwards during 25~23 Ma, the Palawan continental block moved away from the study site. Moreover, the northern sources (South China) were not significant because of low topography at that time. Therefore, the terrigenous mass accumulation rate (MAR) was very low. Because of the rapid uplift of the Qinghai‐Tibet Plateau, Pearl River developed gradually and thus South China became the main source of ODP Site 1148. With the formation of the Taiwan island since 3.5 Ma, Taiwan contributed significant terrigenous materials to the northern SCS. The hiatus in sediments at ODP Site 1148 in the late Oligocene possibly resulted from the influence of low terrigenous materials supply, rising sea level and relatively stronger currents during provenance change.

Eastern South China Sea Basin Expansion Numerical Simulation

AbstractThe formation and evolution of South China Sea has been one of the hot spot of attention at home and abroad. The expansion of the South China Sea happened in early Oligocene‐early Miocene, and the expansion of South China Sea includes ridge transition once at least. This paper uses a model of rising divergent mantle flow and convection coupling to simulate the expansion of eastern sea basin of the South China Sea, the ridge jump, and the process of lithosphere thermal structure evolution and melting of magma after expansion. Numerical simulation results indicate that a ridge jump is an important process of the South China Sea expansion. Ridge jump forms a magma chamber between the two ridges, and the existence of the magma chamber makes the submarine volcanoes relatively more and the terrain relatively high between the ridges. At the same time, it also leads to the terrain of both sides of south side ridge and the distribution of submarine volcano asymmetric, which in turn can demonstrate the reasonability of ridge jump model.

Mesozoic paleogeography and tectonic evolution of South China Sea and adjacent areas in the context of Tethyan and Paleo‐Pacific interconnections

Abstract During the Mesozoic era, the South China Sea and its environs were located at the south‐eastern margin of the Eurasian continent. There has been hot debate on the influences of Tethyan and Paleo‐Pacific tectonics to the Mesozoic evolution of the area. This paper compiles lithofacies maps of six time slices and discusses the paleogeographic and tectonic evolution of the area based on this compilation and other data on structural deformation and magmatism. In the Early Triassic, the Paleotethys Ocean extended eastward to the study area through the Song Da passage. Then a significant east–west differential evolution began. In the Late Triassic, the western area uplifted as a result of the collision between the Indosinian and South China blocks during the Indosinian orogeny, and the Song Da passage has closed since then. Meanwhile, a transgression of Paleo‐Pacific waters occurred in the eastern and south‐eastern portions of the area, forming the ‘East Guangdong–North‐west Borneo Sea’. In the Early Jurassic, seawater transgression was even more pronounced, resulting into the connection of this sea with the Mesotethys Ocean to the west. Large quantities of Tethyan water carrying Tethyan organisms entered the area. In the Middle Jurassic, a short‐lived transgression occurred in the eastern Mesotethys and resulted in the formation of the ‘Yunnan–Burma Sea’. The Late Jurassic to Early Cretaceous was the climax of the subduction of both the Mesotethys and Paleo‐Pacific towards the Eurasian continent. This led to the formation of the great ‘Circum South‐east Asia Subduction–Accretion Zone’ in the Middle or Late Cretaceous. This paper also presents various lines of evidence for a newly recognized segment of this Mesozoic subduction–accretion zone buried under Cenozoic sediments in the north‐eastern South China Sea.

Distribution and identification of the low-velocity layer in the northern South China Sea

The low-velocity layer (LVL), closely related with tectonic activities and dynamic settings, has always been a hot topic in the deep crustal structure studies. The deep seismic (OBS/OBH) and onshore-offshore experiments have been extensively implemented in the northern South China Sea (SCS) since the 1990s. Six seismic profiles were finished on the northern margin of SCS by domestic and international cooperations. The features of crustal structures were revealed and five velocity-inversion layers were discovered. Among them three LVLs with 3.0–3.5 km·s−1 velocity are located in the sedimentary structure (2.0–6.0km in depth and 2.0–4.6 km in thickness) of the Yinggehai Basin and Pearl River Mouth Basin. They were identified by the reflective and refractive phases for their shallow depth. The other two LVLs with 5.5–6.0 km·s−1 velocity generally existed in the middle crust (7.0–18.0 km in depth) with an about 2.5–6.0 km thickness in the transitional crustal structure of the northeastern and northwestern SCS. They were detected by the refractive phase from their overlain and underlying layers. We explored the possible tectonic formation mechanisms combining with previously reported results, which provided evidence for the formation and evolution of SCS.

Characteristics of Cenozoic sedimentary formation and tectonic evolution of South China Sea

The Cenozoic sedimentary formation of South China Sea can be classified into three types, namely the stable, substable and unstable types, and two cycles, the Lower (E1-E2) and Upper (Q-E3) cycles by the unconformity of Late Mid-Eocene. In the North and South Continental Margins two sedimentation cycles developed but only the upper one developed in the Central Ocean Basin. By analyses of the sedimentary formation, it is suggested that Lower Cycle was fill sediment, and mainly fluvial-lacustrine facies; the Upper Cycle was onlap sediment, and was mainly shallow marine or deep ocean. It indicates that the Central Ocean Basin formed after Mid-Oligocene, and the nappe and obduction of Philippines Island-Arc and the counter-clockwise rotation of Kalimantan resulted in the gradual closing of Paleo-South China Sea.

The geophysical characteristics and evolution of northern and southern margins of the South China Sea

Data of about 40,000 km gravity and magnetic measurements, 10,000 km multichannel seismic lines, 20 sonobuoy refraction seismic stations, and 5 heatflow stations have been obtained by our institute in the South China Sea (SCS) during the passed ten years. Based on these and other data, the present paper discusses the tectono-geophysical characteristics and evolution of SCS and put forward some new ideas. On the northern margin of SCS, five parallel structure zones have been recognized and named as, from the north to the south, the Littoral Fault Zone, Northern Depression Zone, Central Uplift Zone, Southern Depression Zone, and Slope Fault Zone. The basement of the margin is the extension of that inland Southeast China and consists of the Hercynian fold belt in the east and the Caledonian fold belt in the west. Both belts were extensively disturbed by Yanshanian magmatic emplacements. Based on gravity data, the crustal thickness is 25-26 km for the Northern Depression Zone, greater than 29 km for the Central Uplift zone, and 20-22 km for the Southern Depression Zone. A gradient belt of Moho surface is observed along the Slope Fault Zone. A belt of high magnetic anomalies is found extending from the Dongsha Uplift NE-ward to the Penghu Islands, and a magnetic quiet zone extending along the lower slope. The former is interpreted as the manifestation of a basalt belt of 1-3 km in depth. These were intraplate eruptions and indicate the Cenozoic extension. The Slope Fault Zone is represented by a northward dipping lithospheric fault that penetrates the basement down to the Moho. We prefer the interpretation of the fault as a segment of the Mesozoic East Asia subduction zone. The I-type granites (76-130 Ma) and associated volcanic rocks in the basement of the continental shelf might be the associated magmatic arc, while the thickened crust in the Central Uplift Zone might be the accretional wedge. The magnetic quiet zone might indicate the remains of the Paleo-Pacific oceanic crust. In the southern margin of SCS three seismic sequences have been identified. In particular, a thick Paleogene sequence consists of neritic clastics with clear stratification and widespread distribution. This sequence was strongly deformed into asymmetric folds and eroded in the western Nansha Block. Based on the correlation with limited and distant wells, this compressional event, called as the Nansha Movement, is tentatively dated as Late Eocene, which was contemporaneous with the first phase of the Zhu-Qong movement in the northern margin of SCS, but under totally different stress regime. Unconformably overlying Neogene sequence is thin and mainly as fillings of small and discrete half grabens in the Dangerous Grounds, but thick and continuous on the Liyue Bank and the NW Palawan shelf (1.5 to over 2 km), and even thicker in the Zengmu Basin (the Great Sarawak Basin) and to the west. This indicates that the Dangerous Grounds have stayed mainly in the uplift state since the Nansha Movement, different from the shelf area to the east, south, and southwest. In light of the above-mentioned findings, we suggest that this block collided with Paleo-Borneo and uplifted in Late Eocene time, long before the start of the opening of SCS. Before the collision, most areas of the Nansha block was the shallow sea bordering the Paleo South China continent, where marginal rifting had been continuing since the Late Cretaceous. Not until the Late Oligocene the extension extended southward to the Nansha Block and became strong enough to open the SCS. Later in the Early Miocene, Borneo rotated counterclockwisely, probably about a pole near the center of Borneo rather than to the west. The narrow Nansha Trough Basin was formed by the elastic downwarP under the load of the NW-ward overthrusting Sabah nappe, while the Zengmu Basin was formed by the extension west of the pole of rotation.

North Palawan Block, Philippines--Its Relation to Asian Mainland and Role in Evolution of South China Sea: DISCUSSION

North Palawan Block, Philippines--Its Relation to Asian Mainland and Role in Evolution of South China Sea: DISCUSSION

North Palawan Block, Philippines--Its Relation to Asian Mainland and Role in Evolution of South China Sea

The Island of Mindoro, the northern part of Palawan Island, and the Reed Bank area (southwestern Philippines) together constitute a continental fragment, the North Palawan block, lying within an island arc-oceanic setting. The Permian to Paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the Philippine Archipelago. These rocks also suggest that the North Palawan block once occupied a pre-drift position contiguous with the south China mainland. Four prominent pre-Neogene regional unconformities are recognized both onshore and offshore the China mainland, in Taiwan, and in the North Palawan block. The synchrony of these unconformities and the facies relation of the unconformity-bounded sedimentary units strongly suggest a common pre-Neogene history for all these areas. By contrast, an important regional unconformity, occurring at the top of the middle Miocene throughout the Palawan area, is absent from the Asian mainland. Extension in the South China Sea basin since the Mesozoic, which has separated the North Palawan block from the Asian mainland, has been approximately uniform from west to east. However, there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea-floor spreading. From the foregoing observations and using the most recent magnetic spreading anomaly data for the South China Sea, a suite of palinspastic reconstructions has been prepared, which shows the evolution of the South China Sea area from the Late Triassic to the Pliocene. The reconstructions illustrate (1) the convergent continental margin setting of the North Palawan block during much of the Jurassic and Cretaceous; (2) the Late Cretaceous inception of the Philippine island-arc system; (3) the subsequent counter-clockwise rotation of the arc system from the late Eocene onward; (4) the Paleocene to middle Miocene opening of the South China Sea; and (5) the early to middle Miocene collision between the North Palawan block and the Palawan subduction system.