# Crustal structure, structural style, and tectonostratigraphy of the Northeast South China Sea rifted margin

Mateus Rodrigues de Vargas, Geoffroy Mohn, Julie Tugend, Nick Kusznir, Andrew Lin, Liang-Fu Lin

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## To cite this version:

Mateus Rodrigues de Vargas, Geoffroy Mohn, Julie Tugend, Nick Kusznir, Andrew Lin, et al., Crustal structure, structural style, and tectonostratigraphy of the Northeast South China Sea rifted margin. EGU General Assembly 2025, Apr 2025, Vienne, Austria. 10.5194/egusphere-egu25-17640. hal-05132705

HAL Id: hal-05132705

https://hal.science/hal-05132705v1

Submitted on 27 Jun 2025

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# Crustal structure, structural style, and tectonostratigraphy of the Northeast South China Sea rifted margin

**Mateus Rodrigues de Vargas<fnref n="1" />, Geoffroy Mohn<fnref n="1" />, Julie Tugend<fnref n="1" />, Nick Kusznir<fnref n="2" />, Andrew Lin<fnref n="3" />, and Liang-Fu Lin<fnref n="4" />**

The South China Marginal Sea (SCS) is a Marginal Sea Basin characterized by several failed continental rifts preceding continental break-up and subsequent seafloor spreading. The oldest phase of rift propagation is located in the northeast South China Sea (NE SCS). We present new work constraining the tectonostratigraphic evolution and crustal structure of this NE SCS margin, which we compare with that of the adjacent Pearl River Mouth Margin (PRMM). To achieve this, subsurface mapping from reflection seismic data was used together with crustal thickness determined from gravity inversion to identify multiple stages of deformation, crustal domains, and related depositional environments on the NE SCS rifted margin.

Within the NE SCS margin, from north to south, four crustal domains were interpreted: (i) the proximal (i.e., Northern Rift System and Penghu-Peikang High), (ii) narrow necking (i.e., Tainan Basin, Central High, and its southern vicinities), (iii) wide distal (i.e., Southern Rift System, Southern High, and narrow continent-ocean transition – COT), and (iv) oceanic. On the heterogeneous continental crust, three main Cenozoic tectonosedimentary stages took place: (1) rift (Late Paleocene to Early Oligocene); (2) post-rift (Early Oligocene to Late Miocene), and (3) foreland (Late Miocene to Early Oligocene).

Rifting was synchronous throughout the NE SCS, following an NE-SW structural trend. Syn-rift sedimentation patterns and seismic facies analysis suggest deltaic to marine environments in the proximal domain and a sediment-starved deep marine setting in the distal domain. During post-rift punctual structural reactivation occurred in the Penghu-Peikang and Central highs, controlling paleo-reliefs only flooded during maximum transgressive periods. Shelf-dominated deposition prevailed north of the Central High, while deep marine is observed to its south. This pattern persisted during the foreland stage.

The crustal structure of the NE SCS strikingly differs from that of the PRMM. Although PRMM crustal architecture results from widespread crustal boudinage, the narrow necking and sparseness of faulting in the Southern High of the adjacent NE SCS suggest that parts of its crust are showing different initial rheologies. This distinct crustal structure is related to the inherited

<footnote n="1">¹CY Cergy Paris Université, Sorbonne Université, Institut des Sciences de la Terre de Paris, ISTeP, Neuville-sur-Oise, France</footnote>

<footnote n="2">²Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom</footnote>

<footnote n="3">³Department of Earth Sciences & Institute of Geophysics National Central University, Taoyuan, Taiwan</footnote>

<footnote n="4">⁴Ocean Center, National Taiwan University, Taipei, Taiwan</footnote>
Mesozoic history of the region: the PRMM Cenozoic history evolved on a magmatic arc, while the NE SCS records not only the remnants of this arc (proximal domain) but also an accretionary prism (Southern Rift System) resultant of the docking of an allochthonous tectonic block (the Southern High) to the south.

The Cenozoic sedimentary infilling of PRMM and NE SCS shows an interplay between paleogeography and eustatic variations. The syn-rift sedimentary thickness variations are directly related to the proximity of the sink area with emerged portions of the Eurasia continent, such as in Penghu, Baiyun, and Liwan Basins. Subordinately, the proximity and subaerial exposure of structural highs (e.g., Penghu, Central, and Yunli High) also affected syn-rift sedimentary thickness. During the syn-rift stage, PRMM sediments were predominantly deposited in lacustrine environments, while sedimentation in the NE SCS was fully marine. Post-rift sedimentation is similar in both margins.