Impact of basement thrust faults on low-angle normal faults and rift basin evolution: a case study in the Enping sag, Pearl River Basin

Abstract

Abstract. Reactivation of pre-existing structures and their influence on subsequent rift evolution have been extensively analysed in previous research on rifts that experienced multiple phases of rifting, where pre-existing structures were deemed to affect nucleation, density, strike orientation, and displacement of newly formed normal faults during later rifting stages. However, previous studies paid less attention to the extensional structures superimposing onto an earlier compressional background, leading to a lack of understanding of, e.g. the reactivation and growth pattern of pre-existing thrust faults as low-angle normal faults and the impact of pre-existing thrust faults on newly formed high-angle faults and subsequent rift structures. This study investigating the spatial relationship between intra-basement thrust and rift-related faults in the Enping sag, in the northern South China Sea, indicates that the rift system is built on the previously deformed basement with pervasive thrusting structures and that the low-angle major fault of the study area results from reactivation of intra-basement thrust faults. It also implies that the reactivation mode of basement thrust faults is dependent on the overall strain distribution across rifts, the scale of basement thrust faults, and the strain shadow zone. In addition, reactivated basement thrust faults influence the nucleation, dip, and displacement of nearby new faults, causing them to nucleate at or merge into downwards it, which is representative of the coupled and decoupled growth models of reactivated thrust faults and nearby new faults. This work not only provides insights into the growth pattern of rift-related faults interacting with reactivated low-angle faults but also has broader implications for how basement thrust faults influence rift structures, normal fault evolution, and syn-rift stratigraphy.

Extensional fault geometry and evolution within rifted margin hyper-extended continental crust leading to mantle exhumation and allochthon formation

“…This value is consistent with Andersonian extensional fault mechanics (Anderson, 1905) and also the value of 55-60°d etermined for initial surface fault dip by Lymer et al (2019) from their analysis of 3D seismic reflection data on the SW Galicia Bank margin. Note that our RIFTER modelling results shown in this paper, using high initial fault angles, do not apply to low-angle extensionally reactivated thrusts (Morley, 2009;Deng et al, 2021).…”

Interactions between pre‐existing structures and rift faults: Implications for basin geometry in the northern South China Sea

“…The SCS evolved from a Mesozoic convergent margin formed by the subduction of the Paleo‐Pacific plate to a Cenozoic rifting‐dominated margin during the Cenozoic with the opening of the SCS (Figure 2; e.g. Camanni & Ye, 2022; Deng et al, 2021; Suo et al, 2022; Ye et al, 2020). During the Mesozoic, the convergent margin was formed in the northern SCS by the subduction of the paleo‐Pacific plate and underwent a complicated transition from an Andean‐type margin (Jurassic to the Early Cretaceous) to a Western Pacific‐type margin (Late Cretaceous; Figure 2; Cui et al, 2021; Ye, Mei, Shi, Camanni, et al, 2018).…”

“…Wei et al, 2022; Xu et al, 2013, 2017; Ye, Mei, Shi, Camanni, et al, 2018; Zhou et al, 2006). Therefore, we interpret sub‐horizontal SR2 and SR1 (Figure 3a) to represent the basal décollement and splay southward branch thrusts formed by the NW‐ward subduction of the paleo‐Pacific plate (Deng et al, 2021; Faure et al, 1996; Ren et al, 2002; Shu et al, 2009). Late Jurassic thrusts are also recorded in the onshore NE‐trending Lianhuashan fault zone in the South China Block, which is closely adjacent to the study area (Jahn et al, 1976; Li et al, 2020).…”

“…The SCS is the largest marginal sea of the western Pacific and is tectonically surrounded by the Pacific, Indo‐Australian and Eurasian plates (Figure 1a; Camanni & Ye, 2022; Deng et al, 2021; Suo et al, 2022; Ye et al, 2020). The Baiyun sub‐basin, the main study area in this paper, is located within the Pearl River Mouth Basin, which is the largest Cenozoic rift basin in the northern SCS margin (Figure 1b).…”

“…Huang et al, 2020; Peacock & Banks, 2020; Wiest et al, 2020); thus, the study of basement highs can also reveal the features of pre‐existing structures and their interactions with late rift structures. We choose the basement highs around the Baiyun sub‐basin (Figure 1c) for the following reasons: (1) These basement highs are located in the necking zone of the northern SCS margin, where Mesozoic and Cenozoic structural interactions are more obvious, reflecting not only the structural inheritance but also the late modification characteristics of the pre‐existing structure (Camanni & Ye, 2022; Deng et al, 2021; Suo et al, 2022; Yan et al, 2014). (2) Basement highs, which are significantly higher than the surrounding areas, are commonly unconformably overlain by younger condensed depositional sequences (Peacock & Banks, 2020), and more pre‐existing structures (e.g., faults and folds) are recorded (Ye, Mei, Shi, Camanni, et al, 2018).…”