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.
Highlights
Previous studies paid more attention to the rift basins that evolved through multiple phases of rifting, yet the characteristics of extensional structures developing after a period of compressional event, such as the reactivation mode of pre-existing thrust faults, the growth patterns of lowangle normal faults, and their interactions with high-angle normal faults, still lack investigation
The mechanics of low-angle normal fault development have been debated for decades, with key questions concerning about whether a given fault was initiated at low dip and whether the fault was active at low dip
This study aims to investigate how basement thrust faults evolve, how they influence the development of rift systems and normal faults during subsequent rifting, and what enlightenments that influence can provide about the subsequent basin structure and syn-rift stratigraphic sequence
Summary
Reactivation of pre-existing basement faults or shear zones and their influence on the growth of newly formed normal faults have been recognised in many multiphase rift basins, such as the NW shelf of Australia (e.g. Frankowicz and Mcclay, 2010), Gulf of Thailand (e.g. Morley et al, 2004, 2007), Gulf of Aden (e.g. Lepvrier et al, 2002; Bellahsen et al, 2006), northern North Sea (e.g. Badley et al, 1988; Færseth, 1996; Færseth et al, 1997; Odinsen et al, 2000; Whipp et al, 2014; Duffy et al, 2015; Deng et al, 2017a; Fazlikhani et al, 2017), and East African Rift (Le Turdu et al, 1999; Lezzar et al, 2002; Corti, 2009; Muirhead and Kattenhorn, 2017). Reactivation of pre-existing basement faults or shear zones and their influence on the growth of newly formed normal faults have been recognised in many multiphase rift basins, such as the NW shelf of Australia Previous research has suggested that pre-existing basement faults or shear zones originating from an earlier tectonic event were prone to reactivate, interact, and link with newly formed normal faults during a later rifting stage and result in some special structural styles, e.g. non-collinear fault arrays, various styles of fault interactions, and gradual changes in fault geometries with increased depth The influence of pre-existing basement structures on the rift basin evolution of the northern South China Sea has already been reported by previous researchers. How do pre-existing thrust faults reactivate and grow as low-angle normal faults during the subsequent rifting? How do pre-existing thrust faults control the development of newly formed normal faults and rift basins? Answering these questions will help to improve our understanding of the structural style and rift development over preexisting basement thrusting structures in general
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