Sill swarms and hydrothermal vents in the Qiongdongnan Basin, northern South China Sea

Abstract

Sills and hydrothermal vents are commonly observed in sedimentary basins. However, not all sills could generate overlying hydrothermal vents, and whether a sill generates a hydrothermal vent or not is still poorly constrained. In this study, a large number of sills and hydrothermal vents are observed, using high-resolution reflection seismic data in the Qiongdongnan Basin of northern South China Sea. These sills are characterized by saucer or linear shapes and present as isolated sills or sill swarms, roughly being larger with buried depth increase. More importantly, the hydrothermal vents are mainly related to the underlying sills intruding into the shallow strata (buried depth <1.4 km), which suggests that magma intrusion depth (from paleo-seabed to the tip of sill) plays an important role on the formation of hydrothermal vents. The duration of magmatism lasted for ∼5 Ma from ∼11.6 Ma to ∼5.7 Ma with peak occurring at ∼8.2 Ma, judging from the spans of hydrothermal vents in the sedimentary strata. This study reports the intense magmatism in the eastern Qiongdongnan Basin for the first time, which extends the distribution of post-rift magmatism in the South China Sea and benefits to explore the mysterious origin of post-rift magmatism. The intense magmatism would also influence the maturity of source rock and hydrocarbon migration in such a petroliferous basin. Moreover, this study also highlights that shallow emplacement of sill is advantageous for the occurrence of hydrothermal vents due to the heating of unconsolidated/less consolidated strata by magmatic sills.

Keywords

• Sill swarm
• Hydrothermal vent
• Sill
• Pathway
• Magmatism
• Qiongdongnan basin