A New Crustal Thickness and VP/VS Model of the Indochina Peninsula

Abstract

Abstract The Indochina peninsula is formed by the collision of continental terranes, magmatic arcs, and suture zones due to the closure of the Palaeo-Tethys oceans during the Mesozoic and has experienced complex tectonic activities during the Cenozoic. Crustal thickness and VP/VS of the peninsula can help better understand its tectonics and formation, so we generate a new high-precision crust model for this region via the receiver function H−κ stacking method. The Khorat plateau has thicker crust (∼36.3 km) than other regions (∼32.4 km), whereas the elevation is similar (<500 m) or even lower. The poor correlation between crustal thickness and elevation suggests that there are other factors controlling the Khorat plateau elevation, for example, negative buoyancy of the lithosphere mantle. High crustal VP/VS (1.79–1.83) observed in southern Khorat plateau and southeastern Indochina Terrane indicates a mafic crustal composition that is consistent with extensive Late Cenozoic basaltic volcanism. Furthermore, our new model reveals high crustal VP/VS (1.81–1.95) in the east of the Nan suture and north of Khorat plateau, which could be interpreted as mafic–ultramafic intrusions in the continental back-arc basin east of the Sukhothai arc in the Late Palaeozoic. Our model does not support the existence of the eastward branch of the midlower crustal flow of the Tibetan plateau because a crustal weak layer would be too thin or too dispersed to flow.