Mg-Ba isotopes in arc magmas record lateral transport of sediments in a diachronous closure convergence zone

Sediments play an important role in the evolution of convergent plate margins. Thermo-mechanical models have proposed that sediments can laterally migrate, especially in a diachronous subduction zone; however, there are no known arc-magmatism records of the lateral transport of sediment. The thermo-mechanical models can best be exemplified within an ancient diachronous convergence zone accompanied by along-trench arc lavas. We report Mg-Ba-Sr-Nd isotope compositions for late Paleozoic mafic arc rocks along the northern margin of the North China craton because of their potential to trace the different origins of metasomatism components corresponding to the diachronous process of the Paleo-Asian Ocean closure. The studied samples have large variations in δ26Mg (−0.28‰ to −0.16‰) and δ138/134Ba (−0.1‰ to +0.33‰) values with highly variable Sr-Nd isotopic compositions compared with the primitive mantle. Shallow-level geological processes cannot explain such large isotopic variations. Instead, the geochemical features of our samples reveal the prominent differences in the contributions of subduction sediments. Modeling results indicate that, spatially, subduction sediment flux gradually increased toward the ongoing arc magmatism in the scissor-like Paleo-Asian Ocean−North China craton convergence zone, corresponding to lateral sediment migration. This process is not smooth and has the potential not only to control the diverse composition of arc magmatism but also to cause episodic production and migration of mantle-derived arc magmatism in diachronous convergence zones. Consequently, Mg-Ba isotopes are reasonably considered as powerful tools to trace lateral sediment transport and its effects on arc magmatism diversity in extinct subduction systems.