Crustal thinning and extension in the northwestern continental margin of the South China Sea

Abstract

Multichannel seismic data on the continental shelf have been used to image the rift‐related shallow structural units of the Pearl River Mouth Basin across the northwestern margin of the South China Sea. The Hainan Uplift, Zhu 3 Depression and Shenhu‐Ansha Uplift zones are bounded by normal faults or listric‐normal faults, which suggest lithospheric extension on the continental shelf. Graben structures 10–15 km wide are imaged on the Wanshan Uplift and Northern Fault Terrace from the reflection data. The thinned continental crust and anomaly rift‐related crust in the depression zone and the transitional crust indicated by the wide‐angle OBS velocity model dominate the crustal structure of the continental shelf in the continental margin of the South China Sea. The different total crustal stretching factors in different shallow structural units suggest that non‐uniform horizontal stretching controls the crustal thinning. The total crustal stretching factor is ca. 1.4–1.6 at the coast area, ca. 1.67–1.8 in the rift‐depression zone and ca. 1.7–1.75 in the transitional crustal domain. Pure‐shear crustal thinning controls the crustal extension in the rift‐depression zone. The high heat flow anomaly in the vicinity of the seismic lines and anomaly rift‐depression velocity structure suggest that the crustal thinning on the continental shelf of the South China Sea can be produced by lateral mantle flow within the hotter regional lithospheric background. Copyright © 2015 John Wiley & Sons, Ltd.

Crustal structure and rifting of the northern South China Sea margin: Evidence from shoreline‐crossing seismic investigations

“…The Hainan Rise (uplift) was previously recognized in seismic reflection data of the PRMB (Li & Rao, ; Wang, ; Wu, ; Yu, ). A high heat flow (95 Mw/m 2 ) was found in the Hainan Rise (Wang, ; Xu, He, He, & Gong, ) and may be related to the crustal thinning in this area (Zhu et al, ). From north to south in the PRMB, three successive depressions (Zhu 1, Zhu 2, and Zhu 3) are separated by uplift zones (Figure S1).…”

“…The terrestrial deposition of the Shenhu, Wenchang, and Enping formations controls the sedimentary history of the PRMB since 65 to 28 Ma (Gong, Jin, Qiu, Wang, & Meng, ). The Zhuhai, Zhujiang, Hanjiang, Yuehai, Wanshan, and Quaternary formations indicate block faulting, slight folding and erosion, and frequent magmatic activity (Gong et al, ; Yan et al, ; Zhu et al, ). Based on the distribution of the Cenozoic igneous rocks around the SCS, the weak and limited magmatism was proposed during the rifting and sea‐floor spreading in this region (Yan, Deng, Liu, Zhang, & Jiang, ).…”

“…The shallow configuration of the oil-and gas-bearing PRMB, which is located above the continental crust and transitional crust (Li, 1984;Li & Rao, 1994;Yu, 1990), consists of a series of uplift zones and depressions (Li & Rao, 1994;Wang, 1982;Wu, 1988;Yu, 1990;Zhu et al, 2012;Zhu, Li, Sun, & Li, 2016; Figure S1). The Hainan Rise (uplift) was previously recognized in seismic reflection data of the PRMB (Li & Rao, 1994;Wang, 1982;Wu, 1988;Yu, 1990).…”

Fault interaction and evolution during two‐phase rifting in the Xijiang Sag, Pearl River Mouth Basin, northern South China Sea

“…The Xijiang Sag is a large offshore oil‐bearing Cenozoic sedimentary basin in the north‐west part of the PRMB (Ding et al, ; Huang, Peng, & Liu, ). The study area has undergone multiple rifting phases during the Palaeocene to the early Oligocene (He et al, ; Tang et al, ), which are associated with the rifting processes in the Chinese south‐east continental margin (Franke et al, ; Zhong et al, ; Zhu, Li, Sun, & Li, ). The rift stage of the PRMB can be divided into two phases of successive extension with different directions (Cullen, Reemst, Henstra, Gozzard, & Ray, ; Hu et al, ; Li et al, ; Li, Lei, Zheng, Duan, & Yan, ; Li & Rao, ; Ru, ; Wu, Hu, & Zhong, ; Zhou et al, ; Zhu et al, ), which resulted in the Wenchang and Enping formations.…”

“…phases during the Palaeocene to the early Oligocene (He et al, 2017;Tang et al, 2017), which are associated with the rifting processes in the Chinese south-east continental margin (Franke et al, 2014;Zhong et al, 2014;Zhu, Li, Sun, & Li, 2016). The rift stage of the PRMB can be divided into two phases of successive extension with different directions (Cullen, Reemst, Henstra, Gozzard, & Ray, 2010;Hu et al, 2016;Li et al, 2014;Li, Lei, Zheng, Duan, & Yan, 2015;Li & Rao, 1994;Ru, 1988;Wu, Hu, & Zhong, 2015;Zhou et al, 1995;Zhu et al, 2015), which resulted in the Wenchang and Enping formations.…”