Spatiotemporal distribution and mechanism of Mesozoic magmatism in the South China Sea and its adjacent areas: insights from seismic, geochemical, and geochronological data

Mesozoic igneous rocks are widely distributed in the South China Sea (SCS) and its adjacent areas and are exposed in the SCS, South China, Hainan, Indochina, Taiwan, the Philippines, and Borneo; these rocks are mostly dominated by granitoids. This paper presents a complete map of the Mesozoic igneous rocks of the SCS and its adjacent areas. This paper also presents an analysis of geological survey and published data in terms of seismic profiles, ages, geochemistry and isotopic systematics of the Mesozoic igneous complexes of the SCS and its adjacent areas. Three periods of igneous activity can be distinguished: (1) Permian – Triassic that spans from 250–201 Ma; (2) Jurassic (201–145 Ma); and (3) Latest Jurassic/Cretaceous to Maastrichtian (145–66 Ma), of which the Cretaceous is the best preserved and could possibly be the most widespread. Triassic igneous rocks are distributed in the northwestern and southern SCS (Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, the Dangerous Grounds, and the Reed Bank); Jurassic igneous rocks are distributed in the northern and southern SCS (Pearl River Mouth Basin, Qiongdongnan Basin, Yinggehai-Song Hong Basin, Beibu Gulf Basin, and the Reed Bank); and Cretaceous igneous rocks are distributed in the northern, western and southern SCS. The igneous activity of the SCS is mostly distributed in the continent slope. Mesozoic igneous rocks of the SCS include at least 350 rock masses: the smallest being 0.182 km2, the largest being 5,5,502 km2, and the total area covering 688,539 km2. Mesozoic magmatism in the SCS and its adjacent areas migrated oceanward (southeastward). Our new seismic profiles and the wells from the literature highlight that Jurassic granites occur not only inland of South China but also in coastal South China and the northern and southern SCS. The YING6 well in the northern SCS encountered andesite with an age of 68.24 Ma, which is the youngest age found for the SCS Mesozoic volcanic rocks. The XY1 well in the western SCS encountered granite with an age of 68.9 Ma, which is the youngest age found for the SCS Mesozoic intrusive rocks. The WZ12-3-1 well in the northern SCS encountered granite with an age of 243.3 Ma, which is the oldest age found for the SCS Mesozoic intrusive rocks. The encountered dacite ages (219.1 ± 1.4 Ma) of the NK-1 well in the southern SCS were the oldest ages found for the SCS Mesozoic volcanic rocks. The thickest Mesozoic igneous rocks (>1022.5 m) were encountered in the NK-1 well. Igneous rocks in the SCS and its adjacent areas are closely related to tectonic movements such as faults, plate movement, and mantle-derived igneous fluid ascent. They are controlled by the subduction of the Tethys lithospheric and Paleo-Pacific domains.