Neogene igneous intrusions in the northern South China Sea: Evidence from high-resolution three dimensional seismic data

• Large scale igneous intrusions are identified in the study area for the first time.
• The igneous intrusions are bounded within the Early Miocene strata.
• The igneous intrusions emplaced at the early of Middle Miocene.
• The igneous bodies could serve as fluid pathways.

Igneous intrusions emplaced within the prospective intervals of sedimentary basins can exert a significant impact on petroleum systems and hence are of considerable interest particularly when risking exploration plays. A number of discordant high amplitude seismic anomalies (DSAs) with a range of geometries are documented in high resolution 3D seismic data in the northern South China Sea. Their distribution and seismic characteristics are analysed and compared with similar seismic anomalies documented within sedimentary basins in the Atlantic margins and other locations. The DSAs occur mainly within Early Miocene strata and are interpreted as igneous intrusions that were emplaced close to the palaeo-seabed and are dated as early Middle Miocene using seismic-stratigraphic methods. A number of vents are also identified above the intrusions within early Middle Miocene strata. Several geometrical forms are observed, referred to here as saucer-shaped, lensoid-shaped, stacked and composite intrusions. The seismic expression of these is increasing complex towards the palaeo-seabed, with a tendency for the saucer-shaped sills to be the deepest intrusive forms. The igneous intrusions observed in this study only could be identified using 3D seismic data and they are important for the future evaluations of petroleum systems, basin evolution and tectonic analysis in the Pearl River Mouth Basin.