Discovery of a hidden Triassic Arc in the Southern South China Sea: Evidence for the breakaway of a ribbon continent with implications for the evolution of the Western Pacific margin

Paleo-Pacific subduction generated a prolonged active continental margin along the coast of the South China Block (SCB). A Triassic magmatic gap was argued to have occurred and was ascribed to flat-slab subduction of an oceanic plateau. We study for the first time a >330-m-long core of typical arc volcanics dated at ca. 218 Ma from the Meiji Atoll in the southern South China Sea (SCS). Paleomagnetism suggests 4.1 degrees +/- 1.5 degrees of post-eruption southward drift. These observations clearly support the existence of a Triassic arc in the SCB and imply that part of the arc later split off and drifted southward during the opening of the SCS in the Oligocene. Our results better constrain the lateral extent of the proposed flat-slab subduction along the margin of the SCB. Moreover, we provide direct evidence of how the breakaway of ribbon continents operated in active continental margins, a recurrent scenario that has been invoked for Phanerozoic tectonics and continental growth throughout Asia.

Automated summary

The study identifies a Triassic arc in the South China Sea, supporting the existence of an active continental margin in the region. Part of the arc later split off and drifted southward during the Oligocene opening of the South China Sea. The research results help to better understand the lateral extent of flat-slab subduction along the margin of the South China Block and the breakaway of arcs in active continental margins.