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

Abstract

AbstractPaleo‐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°± 1.5° 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.