The ocean–continent transition/conjunction zone is a mysterious and significant region in global tectonics and geodynamic evolution. The South China Sea (SCS) is one of the largest marginal basins in the Western Pacific with significant Cenozoic magmatic activities. The relationship between the tectono‐magmatic evolution and the tectonic setting of these Cenozoic igneous rocks is still controversial. In this study, the interpretation of gravity data, magnetic observation and seismic profiles is combined to identify the Cenozoic igneous rocks in the SCS and adjacent regions, and more than 70 magmatic activities have been discerned. We also show how the tectonic movements control the lithology and distribution of these magmatic activities. These Cenozoic magmatic rocks are related to the pre‐spreading, syn‐spreading and post‐spreading of the SCS. We suggest a geodynamic evolution of the SCS according to the temporal and spatial distribution of the igneous rocks. (1) An early period of bimodal volcanism (>32 Ma ago) mainly happened in the Paleogene basins at the northern margin of the SCS. This earlier volcanism happened under a trans‐extensional regime, which resulted from the collision between the Indian and the Eurasian plates since the early Cenozoic. The magmatic rocks may be related to the NNE‐trending right‐stepping dextral strike‐slip faults and the syn‐kinematic pull‐apart basins. These igneous rocks are mostly NNE trending. It is consistent with the Cenozoic dextral trans‐extensional tectonic setting in the East Asian Continental Margin. (2) Syn‐spreading igneous rocks first formed in the Northwest Sub‐basin of the SCS, and then later in the Central and Southwest sub‐basins. The mechanism of the magmatic emplacement results from the NNE‐trending right‐stepping dextral strike‐slip pull‐apart tectonic activity. (3) The spatial alignment of the Quaternary post‐spreading basalts is nearly E–W‐trending, and the different magmatic zones are segmented by NNE‐trending strike‐slip faulting. These volcanics are under an extrusion regime, which resulted from the arc–continent collision between the Luzon–Taiwan Arc and the Eurasian Plate due to the continuously WNW‐directed indentation of the Philippine Sea Plate during the period 9–6 Ma ago. In addition, the nascent NNE trending and dextral Changle–Nanao Fault may have played a significant role in the southward extrusion of the Taiwan Island Arc and the southeast SCS, resulting in an E–W‐trending distribution or strike of the volcanics and normal faults. In Indochina and the Malay Peninsula, widespread Cenozoic extensional post‐spreading granitic plutons are possibly derived from the mantle plume. Magnetic anomaly interpretation and tectonic analysis on these mafic rocks suggest that they were controlled by the Ailaoshan Red River left‐lateral ductile strike‐slip fault zone. Copyright © 2016 John Wiley & Sons, Ltd.

No abstract

The East China Sea Shelf Basin (ECSSB), the Pearl River Mouth Basin (PRMB) and the Taixinan Basin (TXNB) in the northern continental margin of the South China Sea (SCS) are important oil‐ and gas‐bearing basins on the Western Pacific Continental Margin. During the Paleocene to Late Miocene, their strata can be compared, and the lithofacies were continuous from the TXNB, via the Taixi Basin (TXB) to the ECSSB. The lithologies mainly consist of interbedded shale, sandstone and mudstone layers. In addition, these basins have similar tectonic and sedimentation features. The three basins had similar marine‐terrigenous facies in the Paleocene and marine–lacustrine–fluvial facies during the Eocene and Late Miocene. The basins experienced several coeval tectonic movements and episodes, and they developed a series of NE‐ and NNE‐trending faults during the Paleocene and Eocene, which controlled the structure of the basins. During the Early Oligocene and Middle Miocene, they developed a series of NW‐ and WNW‐trending strike‐slip faults, reverse folds and flower‐like strike‐slip faults. However, there were obvious differences in sedimentary and tectonic evolution since the Late Miocene. The TXNB and TXB developed marine facies after the Late Miocene, while in the Quaternary, open marine facies replaced the Pliocene terrigenous facies in the ECSSB. Since the Late Miocene, the south of the ECSSB developed into a subsidence stage, and fault activity stopped. The TXB and TXNB developed some inverse structures and then developed into a thermal subsidence episode after the Dongsha Movement. Thus, this paper proposes that the ECSSB and the Cenozoic basins in the SCS were originally a unified basin and then subsequently separated into two basins as a result of the indentation of the Philippine Sea Plate (PSP) and the arc–continent collision between the Luzon Arc and the Eurasian Plate. Copyright © 2016 John Wiley & Sons, Ltd.

No abstract

No abstract

No abstract

The ocean floor is leaky because it has numerous faults, cracks and joints upon formation and during the process of seafloor spreading. In time, these fractures are often closed after ocean floor cooling, hydrothermal circulation, and vein filling. The crack-seal mechanism of fractures of the oceanic crust is thus important for understanding its kinematics, kinetics and evolution. Coring and log data from IODP Expedition 324 reveal that the Shatsky Rise, an oceanic plateau in the NW Pacific Ocean, developed abundant joints and veins, and some veins formed along previous joints. We use log data from the Formation Micro-scanner Scanner (FMS) to reconstruct the original dip and dip direction of these structural elements. Using FMS microstructural analyses, the dip directions of joints and arrangement of solid inclusions in fibrous veins were examined for Holes U1347A, U1348A and U1349A. We found two types of veins, non-fibrous and fibrous, based on their physical appearance and mineralogical composition. Common to all samples is a straight fibrous inclusion fabric, associated with bands oriented parallel to the vein wall and trails typically at high angles to the vein wall. Cross-cutting relationships between the bands and the straight fibrous inclusions imply that inclusion bands reflect simple crack-seal increments. In the veins, inclusion bands are a sufficient criterion to infer the crack-seal mechanism. Further evidence for solid inclusions formed by the classic crack-seal mechanism is given by inclusion bands in carbon crystals grown in basalts. During incorporation, solid inclusions can remain undeformed, depending on their orientation with respect to the opening and spreading direction of mid-oceanic ridges. Simple displacement fields within the veins are recorded by straight crystal fibres, which track the opening direction. Based on the arrangement of solid inclusions within the veins, we suggest that the veins grew continuously during post-tectonic vein formation. Solid inclusions formed by steady adhesion at the vein wall interface during crack sealing and growth of a few veins were driven by the force of crystallization and extension of mid-oceanic ridges. Based on these two lines of evidence, we conclude that the formation of the Tamu Massif is consistent with the seafloor spreading history revealed by magnetic lineations, possibly accompanied with an interaction to the mantle plume head. In contrast, the formation of the Ori Massif, off the mid-ocean ridge, has no obvious preferred stress field, deduced to be related to a mantle plume tail with interaction to the mid-oceanic ridge.

No abstract