Rapid eruption of the Ningwu volcanics in eastern China: Response to Cretaceous subduction of the Pacific plate

Abstract

The relationship between lithospheric evolution of eastern Eurasia and subduction of the Pacific plate has long been debated. However, the timing and implications of subduction on the tectonics of eastern China are not well constrained. Here we present new zircon U-Pb ages and Hf isotopes, elemental and Sr-Nd-Pb isotopic data on Cretaceous volcanic rocks from the Ningwu basin, eastern China to further address this issue. Our age data reveal rapid eruption of the volcanic rocks within a short duration from 133 to 130 Ma. The rocks, mostly characterized by shoshonitic and high-K calc-alkaline signatures, display light rare earth element and Pb enrichment, Nb, Ta and Ti depletion, highly radiogenic Sr-Pb isotopic ratios and variable ε Hf (t) (+1.8 to -10), suggesting derivation from an enriched lithospheric mantle metasomatized by marine sediments. The early lavas (133.3 ± 1.1 Ma) show stronger subduction-related signatures than the late lavas (130.1 ± 1.0 Ma), which we interpret to reflect consumption of a significant volume of fusible subducted components in the early melting phase. The large ε Hf (t) variation of late lavas suggests greater involvement of asthenospheric melts and lower crust in their petrogenesis. The youngest age (130 Ma) appears to coincide with an inferred change in the direction of Pacific-Eurasia convergence, manifested as a change from extension to transpression in eastern China. The narrow window of eruption may signify a rapid change of the tectonic regime in the Early Cretaceous. ©2013. American Geophysical Union. All Rights Reserved.