New insight for genesis of megacorrugations in detachment fault: combined control of accommodation fault and magmatism
Authors: Guan Wei , Huang Lei , Liu Chi-yang , Wang Xu-dong , Zhang Li-li , Wu Zhe 
Published: February 2023

Detachment faults are developed in different tectonic settings and can record several important tectonic events, such as the rifting and breakup of continents and the spreading of mid-ocean ridges. Megacorrugation is a special structural feature of the detachment fault, characterized by gently domed, overall turtleback shape and prominent undulations of the fault surface that parallel the fault slip direction, corresponds to specific formation conditions. However, the formation mechanism of megacorrugation is still controversial.To date, there are many controversies regarding the formation mechanism of megacorrugations. Most of these existing models come from the analysis of submarine geomorphic data and onshore field outcrops, lacking direct observation of three-dimensional structures. Therefore, the limitation of adequate datasets might be the main reason for the controversial understanding of the genesis of megacorrugations.In this study, we finely image the detachment fault in the northern continental margin of the South China Sea using 3D seismic data. Typical megacorrugations are identified on the detachment fault surface. We find that megacorrugations are the result of the superposition of extension-parallel and extension-perpendicular uplifts, and these uplifts are successively controlled by two stages of magma during detachment fault activity. Meanwhile, several accommodation faults, as the key factor controlling the formation of megacorrugations, are discovered on the detachment fault surface for the first time. These accommodation faults control the distribution of early magma and determine the style of megacorrugations. Consequently, the megacorrugations have a formation mechanism dominated by both tectonism and multistage magmatism. This formation mechanism is consistent with the characteristics of the intermediate-type margin. The megacorrugations are the structural features of intermediate-type margins, which are different from the type of magma-poor and magma-rich margins, providing a new constraint for the classification of passive continental margins. Furthermore, we infer that accommodation faults may be widespread in the megacorrugations of mid-ocean ridges; thus, the formation mechanism proposed in this paper is likely common in megacorrugations.&#160;ReferencesBrun, J. P. et al. Crustal versus mantle core complexes. Tectonophysics 746, 22&#8211;45 (2018).Cannat, M., Sauter, D., Escart&#237;n, J., Lavier, L. & Picazo, S. Oceanic corrugated surfaces and the strength of the axial lithosphere at slow spreading ridges. Earth Planet. Sci. Lett. 288, 174&#8211;183 (2009).Gao, J. et al. The continent&#8211;ocean transition at the mid-northern margin of the South China Sea. Tectonophysics 654, 1&#8211;19 (2015).Lister, G., Etheridge, M. A. & Symonds, P. A. Detachment faulting and the evolution of passive continental margins. Geology 14, 246&#8211;250 (1986).Smith, D. K., Cann, J. R. & Escart&#237;n, J. Widespread active detachment faulting and core complex formation near 13&#176; N on the Mid-Atlantic Ridge. Nature 442, 440&#8211;443 (2006).Tucholke, B. E., Lin, J. & Kleinrock, M. C. Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge. J. Geophys. Res. 103, 9857&#8211;9866 (1998).Whitney D. L., Teyssier C., Rey P. & Buck W. R. Continental and oceanic core complexes. Geol. Soc. Am. Bull. 125, 273&#8211;298 (2013).Zhang, C. et al. Syn-rift magmatic characteristics and evolution at a sediment-rich margin: Insights from high-resolution seismic data from the South China Sea. Gondwana Res. 91, 81&#8211;96 (2021).