Tectonic Switching of Southeast China in the Late Paleozoic

Abstract

AbstractThe identification of Late Carboniferous (317 ± 3 Ma) Daixi‐Wufenglou S‐type granites and Early Triassic (247 ± 2 Ma) Houzhang complex (comprising monzodiorite and monzogranite) in southeast China provides new insights into the bewildering tectonics of south China, before its final welding to the Eurasian continent. The Daixi‐Wufenglou granites have high K2O (4.01–6.54 wt%), A/CNK (1.02–1.34), high bulk initial 87Sr/86Sr (0.7094–0.7160) and low εNd(t) (−8.87 to −6.31), and low zircon εHf(t) (−8.1 to −1.9) and high δ18O (12.7–14.0‰), indicating derivation by partial melting of a Neoproterozoic basement as a result of the input of mantle‐derived heat in a back‐arc extensional setting, triggered by rollback of the Paleo‐Pacific plate subduction beneath the outboard proto‐Japan arc. The monzodiorites are shoshonitic, characterized by high K, Ni, Cr, and Mg#, and the monzogranites are adakitic, defined by high Sr/Y, (La/Yb)n and low Y, Yb. They have similar 87Sr/86Sr (0.7085–0.7087), εNd(t) (−5.92 to −5.34), and εHf(t) (−7.5 to −2.5), indicating their petrogenetic linkage. The monzodiorites and monzogranites represent early crystallization phases (cumulates) and residual melts of a mantle‐derived magma, generated from a metasomatically enriched mantle. Integrating these data with other geological information from south China and neighboring countries, we propose a new model for the tectonic evolution of the Late Paleozoic south China, which was controlled by the subduction of the Paleo‐Pacific Ocean plate. A distal continental back‐arc setting was produced by slab rollback in the early stages, and an active continental margin environment was produced by the accretion of the proto‐Japan arc in the later stages.