A 3D Snapshot of Crustal Breakup Deduced From Seismic Analysis of the Tip of the NW South China Sea

Abstract

Based on a high‐resolution seismic reflection data set, we describe and map rift domains at the tip of the V‐shaped NW‐South China Sea (NW‐SCS) Basin. We compare our rift domain map with seismic refraction, magnetic and gravity field data, and previously mapped Continent‐Ocean Boundaries (COB). We also define and map syn‐breakup sedimentary and magmatic sequences across the sediment‐rich NW‐SCS, which enables us to reconstruct the tectono‐stratigraphic evolution of the area. This work enables us to describe and discuss the 3D architecture and nature of the crust at the tip of the NW‐SCS, investigate how extensional and magmatic processes interacted during the breakup, and propose a kinematic model for late rifting, breakup, and finally stalling of the seafloor spreading system. This study provides exceptionally well‐documented insights into the spatial and temporal evolution at the tip of a so‐called “rift propagator,” and enables us to show that breakup in the NW‐SCS may rather correspond to a “retrogrador,” in which the extension zone retreats due to the reorganization of a failing rift system.

Stratigraphic record of continental breakup, offshore NW Australia—Discussion

“…Recent data from West Iberia, Newfoundland and the South China Sea reveal the pinching‐out, onlapping and eventual lateral disappearance of the Breakup Sequence towards the loci of continental breakup, where oceanic crust is first formed, as the main seismic‐stratigraphic feature marking continental breakup—see Figure 1c,d in Alves and Cunha (2018), figure 10 in Lei et al (2019), figures 7 and 9 in Zhang et al (2021) and figure 8 in Chao et al (2022). The stratigraphic pinch‐out of Breakup Sequences towards the loci of continental breakup can be gradual or abrupt but is usually difficult to identify when approaching the continental slope.…”

“…Recent IODP drilling at the loci of contine nta l breakup of the northern South China Sea, has also demonstrated that single seismic markers (breakup-related unconformities) associated with contine nta l breakup comprise local stratigraphic features, cannot be linked to the protracted opening of the South China Sea, and are relative ly older in the basins located inboard of the IODP drilling sites (Zhao et al, 2016;Lei et al, 2019;Zhang et al, 2021;Chao et al, 2022).…”

“…Thus, seismic-stratigraphic boundaries identified on the proximal margin, as those boundaries defined in Reeve et al (2022), cannot necessarily be tied to what are essentially protracted geodynamic processes happening near the loci of continental breakup. Recent IODP drilling at the loci of continental breakup of the northern South China Sea has also demonstrated that single seismic markers (breakup-related unconformities) associated with continental breakup comprise local stratigraphic features, cannot be linked to the protracted opening of the South China Sea and are relatively older in the basins located inboard of the IODP drilling sites (Chao et al, 2022;Lei et al, 2019;Zhang et al, 2021;Zhao et al, 2016).…”

“…d inAlves and Cunha (2018), figure10inLei et al (2019), figures 7 and 9 inZhang et al (2021) and figure8inChao et al (2022). The stratigraphic pinch-out of Breakup Sequences towards the loci of continental breakup can be gradual or abrupt but is usually difficult to identify when approaching the continental slope.…”

3D Crustal Architecture and Along‐Strike Variation in the Mid‐Northern South China Sea Rifted Margin

“…In addition, 18 exploration wells, sampling the syn‐rift Paleogene strata and locally reaching the top basement, have been tied to the seismic images (Figures 1b and 2) through synthetic seismograms produced by the China National Offshore Oil Corporation (CNOOC). Previous seismic stratigraphy interpretation in the northern SCS was based on CNOOC's age calibration (Zhou et al., 2018; Hao et al., 2022; Zhao et al., 2021; Chao et al., 2022; Ye et al., 2022).…”