South China Sea documents the transition from wide continental rift to continental break up

Abstract

During extension, the continental lithosphere thins and breaks up, forming either wide or narrow rifts depending on the thermo-mechanical state of the extending lithosphere. Wide continental rifts, which can reach 1,000 km across, have been extensively studied in the North American Cordillera and in the Aegean domain. Yet, the evolutionary process from wide continental rift to continental breakup remains enigmatic due to the lack of seismically resolvable data on the distal passive margin and an absence of onshore natural exposures. Here, we show that Eocene extension across the northern margin of the South China Sea records the transition between a wide continental rift and highly extended (<15 km) continental margin. On the basis of high-resolution seismic data, we document the presence of dome structures, a corrugated and grooved detachment fault, and subdetachment deformation involving crustal-scale nappe folds and magmatic intrusions, which are coeval with supradetachment basins. The thermal and mechanical weakening of this broad continental domain allowed for the formation of metamorphic core complexes, boudinage of the upper crust and exhumation of middle/lower crust through detachment faulting. The structural architecture of the northern South China Sea continental margin is strikingly similar to the broad continental rifts in the North American Cordillera and in the Aegean domain, and reflects the transition from wide rift to continental breakup.

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

“…The rift parallel structures may also be shown in the enlarged topography map of the Zhongsha Trough (Figure 8), where two parallel ridges of ∼30 km in length are separated by ∼12 km. If this is supposed as the corrugation structures, the aspect ratio of ∼2.5 is highly consistent with the value of the Liwan detachment fault (Deng et al, 2020). However, the nature and origin of these ridges still remain unclear, as the seismic profile obliquely crosses the structures and high-resolution seismic surveys are lacking for this zone.…”

“…In all profiles, the seaward dipping detachment faults are recognized along the basement highs, beneath which the crust is stretched to be ∼10 km and the crust above 6.0 km/s is highly stretched or dismantled. The large-scale detachment fault, featuring exhumed middle/lower crust and extension-al-parallel corrugation, has also been documented in the northern SCS margin (Liwan detachment fault, in Deng et al, 2020). The rift parallel structures may also be shown in the enlarged topography map of the Zhongsha Trough (Figure 8), where two parallel ridges of ∼30 km in length are separated by ∼12 km.…”

Seismic Imaging of an Intracrustal Deformation in the Northwestern Margin of the South China Sea: The Role of a Ductile Layer in the Crust

“…The rift parallel structures may also be shown in the enlarged topography map of the Zhongsha Trough (Figure 8), where two parallel ridges of ∼30 km in length are separated by ∼12 km. If this is supposed as the corrugation structures, the aspect ratio of ∼2.5 is highly consistent with the value of the Liwan detachment fault (Deng et al., 2020). However, the nature and origin of these ridges still remain unclear, as the seismic profile obliquely crosses the structures and high‐resolution seismic surveys are lacking for this zone.…”

“…In all profiles, the seaward dipping detachment faults are recognized along the basement highs, beneath which the crust is stretched to be ∼10 km and the crust above 6.0 km/s is highly stretched or dismantled. The large‐scale detachment fault, featuring exhumed middle/lower crust and extensional‐parallel corrugation, has also been documented in the northern SCS margin (Liwan detachment fault, in Deng et al., 2020). The rift parallel structures may also be shown in the enlarged topography map of the Zhongsha Trough (Figure 8), where two parallel ridges of ∼30 km in length are separated by ∼12 km.…”

Evidence of Lithospheric Boudinage in the Grand Banks of Newfoundland from Geophysical Observations

“…Following this, the spectra of gravity and magnetic data are analyzed to determine the dominant wavelengths present in the regional structures, in order to establish the periodic nature of these wavelengths perpendicular to the rift axis. Moreover, there are a number of well-studied examples of rift margin evolution with demonstrated and analogous boudinage mechanisms such as in the Norwegian Shelf and the South China Sea [7][8][9].…”