Fig. 1

Significant scientific experiments and key data acquired during this project. Circles and a triangle represent Ocean Bottom Seismometers (OBS) stations recording signals caused by active airgun-shooting and passive earthquakes, respectively, in (a). Circles in (b) indicate the Ocean Bottom ElectroMagnetometers (OBEM) stations; and the seismic line L1 corresponds to the multichannel reflection profile in Fig. 4"

Fig. 2

Velocity structure along the profile OBS2015-2. (a) and (b) showing the forward and inverted velocity structures, respectively. (c) and (d) are one-dimensional velocity structures beneath each OBS station, which was extracted from the forward (a) and inverse velocity structures (b), respectively"

Fig. 3

Continent-Ocean Boundaries in the northeastern continental margin of the South China Sea. (a) The bathymetry map in the northeastern SCS. (b) The free-air gravity map in the northeastern SCS. Grey lines indicate magnetic anomalies, and black lines with crosses in (b) indicate structural highs (elongated volcanic intrusions) referenced by Briais et al (1993), Hsu et al (2004), and Sibuet et al (2016)"

Fig. 4

Multi-channel seismic reflection profile (upper) and interpretation (lower) of accretionary prism of northern Manila subduction (after Gao et al, 2018). The location of this profile is shown in Fig. 1b"

Fig. 5

The whole oceanic crust domain when the SCS seafloor spreading stopped (15Ma); after Zhao et al (2019). The subducted SCS plate (dVP) is unfolded and restored on the surface of the Earth, and the plate extends 400-500 km east along the Manila trench. The green line is the current SCS domain (Sibuet et al, 2016), and the east part is the domain of subducted SCS oceanic crust. The grey shaded area (<100 km width) is probable artifacts. The SCS oceanic domain, characterized by N055°, N075° and N085° seafloor spreading directions, is delimited by pink, yellow and light blue areas, respectively. The red double dashed line indicates the extinct spreading ridge of the SCS (He et al, 2016), the red line indicates COB, and the circles indicate the location of IODP drilling sites"

Fig. 6

The kinematic evolution of the SCS and PSP since 15 Ma (after Zhao et al, 2019). (a) About 15 Ma, the oceanic crust of the SCS started to subduct along the left shear plate boundary to the bottom of the PSP. (b)The current location of the emplacement of the Philippine belt, the accretion of the western part of the Huatung Basin and the western Luzon arc. (c) A simplified diagram of profile AA’ and BB’ located in (a) and (b), respectively. Dark green: early Cretaceous HB; light green: current PSP; extension of the HB within the portion of PSP in light grey, which will subduct to be disappeared; yellow area: eastern extension of the SCS at the end of seafloor spreading; orange domain: part of East Asian Plate defined by Wu et al (2016); and pink domain: the northeastern extension of the Sulu Sea"