Geodynamic significance of the Mesozoic volcanism of southeastern China

Abstract

The late Mesozoic geologic development of southeastern China was marked by two main magmatic episodes during the Yenshanian cycle, separated by an important tectonic event. The first spisode, late Jurassic-middle Cretaceous, led to intrusion and extrusion of mainly acidic to intermediate rocks, with abundant ignimbrites interlayered with red continental clastites. Petrologically and geochemically, these rocks belong to three different suites, including K-rich calc-alkaline series. During the second episode in the late Cretaceous, a bimodal suite of continental tholeiitic basalts and acidic rocks was erupted. The tectonic event separating these magmatic sequences is marked by an angular unconformity, over the deformed lower Cretaceous or older rocks. The following geodynamic evolution is proposed: subduction of the Izanagi plate beneath an east Asian Andean-type continental margin until middle Cretaceous, collision with the West Philippines Block around the early-late Cretaceous boundary, post-collisional crustal extension and onset of rifting during the late Cretaceous, prior to the India-Asia indentation process. This suggests that several mechanisms operated during the opening of the South China Sea.