THE CHARACTERISTICS AND DISTRIBUTION OF THE MOHO REFLECTIONS IN THE SOUTH CHINA SEA OCEANIC BASIN

Abstract

The distribution and the characteristics of the Moho reflections (M-reflections) in oceanic basins record the seafloor spreading process and provide crucial insights into the formation and evolution of the oceanic basins. Approximately 20000 km of multi-channel seismic reflection sections (MCS) are used to characterize the M-reflections and the crustal structures in the South China Sea (SCS) oceanic sub-basins. The identified M-reflections are mainly distributed in the Northwest Sub-basin, the East Sub-basin and the northern and southern flanks of the Southwest Sub-basin. They exhibit a banded distribution pattern in two-way travel time along the north-south direction, with shallower depths observed in the central region and gradually deepening towards the northern and southern sides. Additionally, the M-reflection amplitudes generally weaken, the reflection events become less-continuous as the igneous oceanic crust thins along with the seafloor spreading prior to the second ridge jump event. Ultimately, the M-reflection become indistinguishable in proximity to fossil spreading centers. These observations suggest a decreasing magma supply towards the cessation of the spreading. Despite the significance of Moho interface imaging at the crust-mantle boundary, the distinct M-reflections are absent in the Southwest Sub-basin and in the vicinity of the Zhenbei-Huangyan Seamounts Chain, which are attributed to several factors, especially the vague nature of Moho interfaces.