Temporal and spatial distribution of Cenozoic igneous rocks in the South China Sea and its adjacent regions: implications for tectono‐magmatic evolution
Authors: Hui GeGe , Li Sanzhong , Li Xiyao , Guo LingLi , Suo YanHui , Somerville Ian D. , Zhao Shujuan , Hu Mengying , Lan Haoyuan , Zhang Jian 
Published: May 2016

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.