Detachment fault and metamorphic core complex at the distal continental margin of the northern South China Sea

Deng, Dr Hongdan1, Ren, Jianye1, Rey, Patrice2, McClay, Ken3

1China University Of Geosciences, Wuhan, China, 2Earthbyte Research Group, Basin Genesis Hub, School of Geosciences, The University of Sydney, Sydney, Australia, 3Australian School of Petroleum, Adelaide University, Adelaide, Australia

Detachment fault and metamorphic core complex (MCC) are widely documented structures in extensional environment where continental lithosphere has been thermally weakened. The North American Cordillera and Aegean Sea have a widespread deformation of extension (up to 1000 km) and are regions that exemplify detachment fault and MCC development in natural exposures. However, how these structures evolve from wide extended terrane to continental break-up remains enigmatic because there are a few exposed continental margins that preserved these type of deformation. In addition, thick package of sedimentary units on the passive margin could obscure the imaging of low-angle fault and dome structures at depth. Here we use high-resolution 2D and 3D seismic data together with International Ocean Drilling Program (IODP) result and industry wells to show that Eocene extension across the northern margin of the South China Sea records large detachment fault (displacement >100 km) and MCCs at the highly extended (<15 km), distal continental margin. The South China Sea has wide continental margins that span a width of up to 1000 km and 500 km in the north and in the south. 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. On the distal continental margin, we conclude that 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 further indicates that detachment faulting and the development of metamorphic core complex play an important role in controlling continental break-up.


Biography

Hongdan Deng is a postdoc researcher at China University of Geosciences. His research has focused on fault-fold system evolution in orogenic belts and three-dimensional extensional structures and basins evolution on passive margins. This involves field and seismic studies integrated with analogue modelling of sedimentary basin structures.

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