A Model for Mesozoic Crustal Melting and Tectonic Deformation in Southeast China

Abstract

In relation to an in-situ melting model to explain the origin and distribution of Mesozoic granite in Southeast China, this paper proposes a subduction-related source of heat responsible for melt production in upper crustal rocks. Seven Late Triassic-Late Cretaceous compressional deformation episodes show a close time-space relationship with granite production and are correlated with northwest subduction of the paleo-Pacific (Kula) plate over ~130 Ma. This is characterized by periods of prolonged extension and transient compression caused by alternate accelerated and decelerated subduction (possibly accompanied with varying subduction angle, e.g., tectonic switching), respectively. Increasing intracrustal temperature during periods of accelerated subduction results in melting of the upper crustal rocks and formation of a granitic melt layer. Thinning and softening of the remaining solid crust after formation of the melt layer reduces the continental resistance to the lateral pressure exerted by the subductive plate, leading to a crustal compression (tectonic episode) accompanied by crystallization and deformation of the granitic melt layer. Temporal fluctuation of the melt interface generates multiple granite layers with younger granite superposed by old granite, and is responsible for the formation of composite granite bodies that are widely distributed in Southeast China and for the southeast younging of the Mesozoic granite belts.