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The granitoid suites encountered by drilling in the northern South China Sea (SCS) remain important for understanding the evolution of the late Mesozoic Southeast Asian continental margin. They comprise a range of rock types including diorite, tonalite, granodiorite, monzogranite and syenogranite with SiO2spanning 56.4–76.8%. Newly acquired secondary ion mass spectrometry (SIMS) U–Pb ages of samples from 14 boreholes indicate two key magmatic episodes: Late Jurassic (161.6–148.2 Ma) and Early Cretaceous (136.5–101.7 Ma). Jurassic magmatism probably began in late Middle Jurassic time, documented by the dates of inherited zircons. The granitoids are dominated by metaluminous to weakly peraluminous I-type granites, are transitional between magnesian and ferroan, and encompass calc-alkaline, high-K calc-alkaline, and shoshonitic series. The geochemical signatures suggest that these granitoids were mostly generated in a normal continental arc environment. Notable features of the I-type samples are well-defined negative Nb–Ta–Ti anomalies typical of arc-related magmas. Taken together, the late Mesozoic arc granites of the SCS, the accretionary wedge of the Palawan terrane to the southeast, and the zone of lithospheric extension north of the SCS throughout Southeast China, define a southeast-to-northwest trench-arc-backarc architecture for the late Mesozoic Southeast Asian continental margin whose geodynamic setting is related to subduction of the Palaeo-Pacific slab beneath the Asian continent. Two key subduction episodes are recognized, one in Late Jurassic and the other in Early Cretaceous time. [ABSTRACT FROM PUBLISHER]

In response to various environmental factors in offshore South China Sea, a group of microstructures of the screw dislocation are assembled in multiphase screw dislocations on the surface of the nacreous layer of Pteria penguin from the coastal waters of Hainan Island, China. The results of the transmission and scanning electronic microscope testing show that organic matter periodically secreted by epithelial histology of mantle of Pteria penguin pre-forms the original screw dislocation growth template in the form of film, along with its function to select, identify, and adhere to the amorphous calcium carbonate particles as the fine organic venations diffused in the epitaxial screw growth area. With the inducement and screw modulation of the organic film and venations, the amorphous calcium carbonate particles gradually evolve into the pseudohexagonal self. aragonite microsheet with long-range order and screw dislocation structure by location-selecting tropism and screw dislocation growth. Numerous micron-scale aragonite microsheets join in the cluster's interactive movement and screw dislocation self-assembly of the organic film, stacking forward along the axis C spirally and forming the nacreous layer with screw dislocation structure. [ABSTRACT FROM AUTHOR]

Abstract: The northeastern South China Sea continental margin holds the key to understanding Late Mesozoic tectonics and evaluating hydrocarbon potentials in Mesozoic tectonic and stratigraphic structures offshore southeast China. With newly obtained and processed seismic data, and new drilling and logging data, we correlate regional Mesozoic stratigraphy and analyze major Mesozoic tectonic events and structures. In particular, we focus our study on the three major tectonic units in the area, the Chaoshan Depression, the Tainan Basin, and the Dongsha–Penghu Uplift, which are separated by basement high, thrust fold, and (or) faults. Stratigraphic correlations suggest a major phase of southeastward regression, spanning in time from the late Early Jurassic (∼180Ma) to the Early Cretaceous (∼120Ma). Seismic data reveal two major tectonic events, with the first one in the Late Jurassic to the Early Cretaceous, contemporary with the regression, and the second one in the Late Cretaceous. Regional magnetic anomaly map after the reduction to the pole clearly reveals the boundary between the Dongsha–Penghu Uplift and the Chaoshan–Tainan depositional system. The seismic and magnetic data also suggest that, while the Dongsha–Penghu Uplift has highly magnetized sources buried mostly in the upper crust at depths from about 2km to about 20km, the Chaoshan–Tainan depositional system has thick Mesozoic sediments of low magnetization. [Copyright &y& Elsevier]

Compared to the northern South China Sea continental margin, the deep structures and tectonic evolution of the Palawan and Sulu Sea and ambient regions are not well understood so far. However, this part of the southern continental margin and adjacent areas embed critical information on the opening of the South China Sea (SCS). In this paper, we carry out geophysical investigations using regional magnetic, gravity and reflection seismic data. Analytical signal amplitudes (ASA) of magnetic anomalies are calculated to depict the boundaries of different tectonic units. Curie-point depths are estimated from magnetic anomalies using a windowed wavenumber-domain algorithm. Application of the Parker–Oldenburg algorithm to Bouguer gravity anomalies yields a 3D Moho topography. The Palawan Continental Block (PCB) is defined by quiet magnetic anomalies, low ASA, moderate depths to the top and bottom of the magnetic layer, and its northern boundary is further constrained by reflection seismic data and Moho interpretation. The PCB is found to be a favorable area for hydrocarbon exploration. However, the continent–ocean transition zone between the PCB and the SCS is characterized by hyper-extended continental crust intruded with magmatic bodies. The NW Sulu Sea is interpreted as a relict oceanic slice and the geometry and position of extinct trench of the Proto South China Sea (PSCS) is further constrained. With additional age constraints from inverted Moho and Curie-point depths, we confirm that the spreading of the SE Sulu Sea started in the Early Oligocene/Late Eocene due to the subduction of the PSCS, and terminated in the Middle Miocene by the obduction of the NW Sulu Sea onto the PCB. [ABSTRACT FROM AUTHOR]

Abstract: The hydrography of the South China Sea (SCS) is characterized by a south–north (S–N) thermocline gradient in the upper water column from the northern margin of the western Pacific warm Pool (WPWP) to the sea area largely controlled by the East Asian monsoon. Here we examine the records of planktonic foraminifers from Ocean Drilling Program (ODP) Sites 1143 and 1146 in the southern and northern parts of the SCS, respectively, that identify three stages of evolution of the S–N hydrographic gradient in the SCS since the middle Miocene: first, the S–N thermocline gradient possibly occurred in the SCS for the first time during the period 11.5∼10.6 Ma, reflected by an opposite change in the relative abundance of deep-dwelling planktonic foraminiferal species in the south and north; next, the S–N thermocline gradient weakened or even disappeared during the period 10.6∼4.0 Ma, indicated by similar changes in the relative abundance of deep-dwelling species in the south and north; last, the S–N thermocline gradient substantially increased from about 4.0∼3.2 Ma, marked by a major increase in abundance of deep-dwelling species in the northern SCS and a decrease in the southern SCS. Based on the results of oceanic and coupled ocean–atmosphere model experiments and previous studies on planktonic foraminifers in the Pacific Ocean, it is inferred that the initial WPWP was probably formed during the period of 11.5∼10.6 Ma in response to the closure of the Indonesian seaway; The WPWP then weakened or became extremely unstable, before developing its present expression about 4.0–3.2 Ma, induced by the emergence of the Isthmus of Panama. Our observations and model experiments support the argument that the stages in evolution of the WPWP are linked to tectonic changes in ocean gateways. [Copyright &y& Elsevier]