Elsevier

Gondwana Research

Volume 120, August 2023, Pages 31-46
Gondwana Research

Three-stage extension in the Cenozoic Pearl River Mouth Basin triggering onset of the South China Sea spreading

https://doi.org/10.1016/j.gr.2022.05.023Get rights and content

Highlights

  • Three-stage Cenozoic extension is identified in the PRMB.

  • The second-third stage extension led to a dextral transtensional fault system.

  • This fault system resulted in the scissor-type SCS opening during Oligocene.

Abstract

In the Cenozoic, the East Asian Continental Margin developed intense rifting, producing massive rift basins and marginal seas. Among these, the South China Sea (SCS) and adjacent continental margin have attracted attention due to the obscure opening mechanism and strong lithospheric thinning. Based on the seismic sections and fault architecture data in this paper, we perform a delicate study of fault geometry, kinematics, and dynamics in the Pearl River Mouth Basin (PRMB). Three-stage Cenozoic extension is identified in the PRMB. The earliest NNW-SSE-directed extension occurred as early as the Paleocene, resulting in the NE- and ENE-trending faulting with dextral oblique extension to continue until the Middle Eocene. The second extension in the N-S direction resulted in NE-trending dextral transtension in the Late Eocene to Early Oligocene. Subsequently, the latest extension with the NNW-SSE direction occurred during the Late Oligocene, resulting in the sinistral strike-slip of a large number of WNW-trending faults. This second-third extension produced a NE-striking transtensional fault system with dextral right-stepping characteristics. In the Oligocene, this fault system resulted in the N-S directed scissor-type opening of the SCS with a progressively westward younging oceanic crust. During the Early Miocene, the dextral transtensional fault system disappeared due to the Pacific Plate subduction eastward retreat and the cease of the RRF sinistral strike-slipping. At this time, the SCS ridge spreading was controlled only by the NW-SE-oriented slab-pull linked to the proto-SCS.

Introduction

The East Asian Continent Margin developed a series of rift basins and marginal seas in the Cenozoic (Clift et al., 2002, Ren et al., 2002, Zhou et al., 2002, Yin, 2010, Zhu et al., 2012, Li et al., 2012a, Li et al., 2012b, Suo et al., 2015; Liu et al., 2016; Zhu et al., 2018, Wang et al., 2019, Sun et al., 2022, Zhou et al., 2023), such as the South China Sea (SCS), the Japan Sea and the Okhotsk Sea (Fig. 1). Among these, the SCS straddles the boundary between the Indochina Block to the west and the Pacific-Philippine Sea plates to the east, recording the interaction among multiple surrounding plates (Fig. 1). In the last 40 years, diverse models have been proposed for the opening mechanism of the SCS which include the concepts of strike-slip faulting and pull-apart basin (Yin, 2010). This view establishes a linkage between the Pacific Plate subduction and the SCS opening. An alternate model was proposed for extrusion tectonics (Molnar and Tapponnier, 1977) or mantle extrusion (Jolivet et al., 2018), linked to the Indo-Eurasian collision that triggered the SCS opening. The third school of thought considers that the driving force of the SCS opening is a combined effect between the subduction retreat of the Pacific Plate and the far-field Indo-Eurasian collision. According to this view, the westward-subducting Pacific Plate witnessed multiple changes in subduction direction during Cenozoic, resulting in multiple-phase back-arc rifting (Wang et al., 2021). Simultaneously, the Indian-Eurasian convergence occurred that induced the formation and rise of the Tibet Plateau (Torsvik et al., 2008). The interaction between two tectonic domains led to the SCS opening (Jolivet et al., 2018, Zhou et al., 2002, Xu et al., 2014). However, the origin of SCS remains obscure.

It is difficult to clearly reveal the dynamics of the SCS opening only based on the study of spreading ridges, magnetic lineations, and lithospheric structures. The processes of faulting and rifting among adjacent rift basins record critical information about the tectonic evolution of the SCS spreading. Thus, in this paper, we focus on the Pearl River Mouth Basin (PRMB), which is located in the midst of the northern SCS margin (Fig. 2), and try to investigate the geometry, kinematics, and dynamics of Cenozoic faulting in the rifted PRMB basin and to obtain insights on the origins of the SCS opening.

Section snippets

Tectonic setting

The northern SCS margin is bounded by the Indochina Block to the west, the South China Block to the north, the Manila Trench to the east, and Borneo to the south (Fig. 1). During the Early Mesozoic, a large number of WNW-, E-W, and ENE-oriented thrust nappe structures developed in the northern SCS margin, resulting from the Indosinian collision of the Indochina Block and South China Block (Wang et al., 2016a). The Indosinian suture with ENE orientation was located to the south of the PRMB (

Fault classifications during the Cenozoic

In the PRMB, abundant NE- and ENE-striking faults occur. The seismic profiles suggest that NE-striking faults in the PRMB are characterized by long-term extension process. In the syn-rift stage, the NE-, ENE- and WNW-trending faults dominated the sedimentation of different evolutionary stages in the PRMB. The faults with NE- or ENE strikes are finally cut through by an array of WNW-trending faults (Fig. 2). This study focuses on the Zhu III, Zhu Ⅱ, and Zhu Ⅰ depressions and we use the seismic

Structural characteristics of the three-stage extension

During the period of the earliest extension, the active faults extend along the ENE- and NE- trending. These faults display listric-like or domino-like patterns on seismic sections (faults marked in black in Fig. 5, Fig. 8, Fig. 10), and controlled the wedge-shaped deposition. In the plan view, most of these faults displayed simple parallel or linear alignment with NE or ENE orientations, whereas other faults exhibit some left-stepping en echelon alignments (black faults in Fig. 11), suggesting

Dynamics of three-stage faulting: Plate tectonic control

To the west of the PRMB, the Indian Plate and the Eurasian Plate started to collide in ∼55 Ma, resulting in intense compressive stress, uplift, and metamorphism of the Tibet Plateau (Ding et al., 2016b). Subsequently, the Indo-Eurasian collision resulted from lateral lithospheric creeping and collapse of the Tibetan Plateau, the post-collisional extension began to affect the Tibet Plateau and its adjacent domains since ∼45 Ma (Guo et al., 2018), accompanying by potassic magmatism during 34 Ma

Conclusions

Based on a detailed structural analysis of the PRMB, we arrive at the following conclusions.

  • (1)

    The analysis of basin structures in profile and fault patterns in plan view reveals that there are three-stage Cenozoic extensions. The earliest extension took place at the beginning of the Cenozoic to the Middle Eocene, producing NE- and ENE- trending faults. These faults with dextral oblique extensional characteristics display simple linear or left-stepping en echelon alignments.

  • (2)

    The second-stage

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was funded by the NSFC project (Grants 42002220, 42121005, 91958214, 41976054, 42072235), the Fundamental Research Funds for the Central Universities (202072015, 202172003), the Natural Science Foundation of Shandong Province (ZR202102180314), the Taishan Scholars (TS20190918, TSPD20210305), the Qingdao Leading Innovation Talents (19-3-2-19-ZHC) and Shenzhen Branch of CNOOC for 2019SZPS0167. Many thanks to the editors and reviewers for detailed and great reviews that helped us to

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