Sedimentary basement structure of the Southwest Sub-basin of the East Vietnam Sea by 3D direct gravity inversion

Abstract

In this paper, we present a procedure based on Parker’s three-dimensional direct gravity inversion to determine the sedimentary basement depth rapidly and objectively. In the foregoing procedure, the Bouguer gravity anomaly is continued downward near the seabed before inversion, and the mean depth of the basement is constrained by the power density spectrum of the gravity anomaly. The bulk density of sediment and basalt rocks are also constrained by the logging data obtained from Expedition 349 Scientists (Expedition 349 Scientists, in: International Ocean Discovery Program Preliminary Report, 349, (2014). doi:10.14379/iodp.pr.349.2014). The sedimentary basement depth of the Southwest Sub-basin (SWSB) of the East Vietnam Sea (South China Sea) derived from the inversion of the downward continued Bouguer anomalies has more detail and accuracy than the sediment basement depth inverted from Bouguer anomaly at the sea level. The calculated basement depth and the sedimentary thickness in the SWSB vary from 4.0 to 6.5 km and from 0.5 to 2.0 km, respectively. The crustal thickness beneath the SWSB ranges from 4.0 to 7.5 km. Our model is consistent with sedimentary basin structure where spreading ridge valley is presented as the deepest points in the sedimentary basement and the terrain along the two banks of the valley is elevated. In addition, the SWSB is divided into four structure domains that are useful for the geodynamic and tectonic implications of the SWSB and surrounding area.