Submarine volcanic mounds in the Pearl River Mouth Basin, northern South China Sea

• A volcanic mound and sill system occurs in the Pearl River Mouth Basin.
• The volcanic system formed during the Early Miocene.
• Faults and basement structures controlled the emplacement of this volcanic system.

A number of enigmatic, km-scale mound structures have been discovered in the Baiyun Sag of the Pearl River Mouth Basin using high-resolution 2D and 3D seismic data combined with multi-beam bathymetry. Based on detailed seismic characterization, we interpret these as sill-fed volcanic mounds. Associated structures include igneous sills, trans-tensional faults, lava flows and compactional drape folds. The igneous intrusions and associated mounds were emplaced in the late Early Miocene (c. 18.5 Ma or shortly thereafter), constrained by the onlap relationship between the mounds and their overburden. The volcanic mounds are preferentially developed above or adjacent to basement highs, indicating a structural control on the igneous plumbing system. We propose that the fractures and tectonic faults above the raised basement follow pre-existing zones of weakness and may have acted as feeding conduits for the magmatic material. The discovery of the Early Miocene igneous province has important implications for the understanding of the evolution of the Pearl River Mouth Basin and for regional hydrocarbon prospectivity.