Seismic Imaging Of an Intracrustal Deformation In the Northwestern Margin Of the South China Sea: the Role Of a Ductile Layer In the Crust

Abstract

Rifting and lithosphere thinning eventually lead to continental breakup and oceanic spreading. As many continental margins show similar behavior in rifting, simple models were proposed to explain the crustal extension. For example, the "pure-shear" extension model was established to describe symmetric and uniform rifting (McKenzie, 1978), while the "simple-shear" model takes asymmetry further into account (Wernicke, 1981). Today, additional geophysical data challenge the abovementioned models and indicate a depth-dependent extension which favors strong decoupling between intracrustal layers (Hopper

Understanding the 3D Formation of a Wide Rift: The Central South China Sea Rift System

“…On the northern rifted margin, we interpret a set of strong, subhorizontal, low‐frequency reflections at 8‐ to 10‐s TWT as the Moho (dark green dots in Figure 3). The TWT of these reflections is consistent with the crust‐mantle boundary modeled from coincident and nearby WAS data (dashed white line in Figs 3 and 5 from Qiu et al, 2001; pink dashed line in Figs 3 and 7 from Qiu et al, 2020). We extended the Moho interpretation throughout the entire line SO49‐23, mapping similar—albeit often weaker—reflections (green dots in Figure 3).…”

“…Dark green dots mark the interpreted Moho under the continental domain and blue dots under the oceanic domain from this work. Moho depth has been constrained from nearby or coincident WAS data (Qiu et al, 2001, dashed white line; Qiu et al, 2020, dashed pink line). The basement thickness is indicated at locations by green/blue vertical lines and corresponding values (in seconds TWT).…”

“…Numbered brown arrows locate the axis of the interpreted interboudin necks in Figures 3–8. See enclosed legend for additional information: (1) wide‐angle seismic profiles: (a) Ding et al (2011); (b) Guo et al (2016); (c) Lü et al (2016); (d) Pichot et al (2014); (e) Qiu et al (2001); (f) Qiu et al (2020); (g and h) Wei et al (2012, 2016); (i) Zhang et al (2016); (2) 2D and 3D MCS data: Ding et al (2015); Lei and Ren (2016); Qiu et al (2013); Steuer et al (2013); (3) magnetic anomalies from Barckhausen and Roeser (2004) and Barckhausen et al (2014); (4) boreholes used for stratigraphic calibration: In the northern margin, boreholes CC4‐1‐1 and CC1162 (Lei & Ren, 2016) projected in Figures 3 and 5; in the southern margin, boreholes Sampaguita‐1 and Aboabo A‐1x (Steuer et al, 2013) projected in Figure 4; (5) location of boreholes in the Paracel Islands used to time constraints (Yubo et al, 2011), see the text; (6) high thin‐crust regions reported by Huang et al (2005), Pang et al (2018), Wang et al (2018), Zhao et al (2015), and Zhou et al (2018); (7) study area in the Zhu‐3 Depression where detailed stratigraphic works constrained by ~30 boreholes (black dots) interpreted the end of the main extensional phase at ~23 Ma (Fengjun et al, 2001); (8) direction of opening of the CSB (Briais et al, 1993; Udo Barckhausen et al, 2014).…”