The significance of fault reactivation on the Wilson cycle undergone by the northern South China Sea area in the last 60 Myr

Fault reactivation is a process that has long been described in nature and modelled in the laboratory. Although many plate boundaries worldwide have undergone successive deformation events during one or more Wilson cycles, most often the influence of fault reactivation on mainly the last deformation event can be comprehensively estimated. The northern South China Sea area has undergone, in the last 60 Myr, an entire Wilson cycle associated with the opening and the ongoing closure of the South China Sea oceanic basin. The continental basement that underwent extension during the opening of the South China Sea was associated with at least two, well-defined, systems of faults inherited from the Cretaceous tectonic evolution of the area. Also, the ongoing closure of the northern South China Sea is partial as convergence is highly oblique and collision is very localized and confined to the Taiwan mountain belt, while in most of the Eurasian rifted margin the extensional structures related to the opening of the South China Sea are not yet overprinted. Both these conditions make the northern South China Sea area an ideal one for investigating the significance of fault reactivation throughout the Wilson cycle. In this article, we first review the tectonic history of the northern South China Sea area in the last 60 Myr focusing on how it is reflected on the northern South China Sea rifted margin and the Taiwan mountain belt. We then review the influence that fault reactivation has exerted in these two areas. We found that fault reactivation had a crucial role in accommodating deformation during both the divergence and convergence episodes of the Wilson cycle, and that the degree to which faults are reactivated as well as the style of fault reactivation can be shown to be associated with the angle that inherited faults form with the extension and shortening directions, respectively. Reactivation of faults involving significant remobilisation of basement rocks seems to have been promoted for faults that were forming a high angle with the extension and shortening directions. These results highlight not only the continuous significance that fault reactivation can have during the Wilson cycle undergone at a plate boundary, but also how the first-order, underlying, geometric controls on fault reactivation can display consistency throughout the cycle itself.