摘要：AbstractThe subduction factories in convergent plate margins exert crucial control on recycling terrestrial components and returning to the overlying crust. The Nd and Hf isotopic systems provide potential tracers to evaluate these processes. Here we present a case where these isotopic systems are decoupled in a suite of granites from the Chinese Altai, showing a wide range ofεHf(t) values (from −4.7 to +10.8) in contrast to a limited range ofεNd(t) values (from −5.8 to −1.9). The zircon xenocrysts occurring frequently in these rocks show markedly negativeεHf(t) values (from −34.3 to −6.5) and positiveδ7Li values (from +12.5 to +18.2). We propose a model to explain the observed relationship between residual zircon and Nd–Hf isotope decoupling. We suggest that the Altai granites originated from partial melting of subducted slab components under relatively low temperature conditions which aided the residual zircon from oceanic sediments to inherit and retain a significant amount of177Hf in the source, thereby elevating the176Hf/177Hf ratio of the melt, and decoupling from the143Nd/144Nd ratio during the subsequent magmatic processes. Our study illustrates a case where sediment recycling in subduction zone contributes to decoupling of Nd and Hf isotopic systems, with former providing a more reliable estimate of the source characteristics of granitic magmas.Graphical abstractDisplay OmittedHighlights•We first report zircon Li isotope data in CAOB.•Nd–Hf decoupling inherited from disequilibrium melting processes.•Role of oceanic sediments recycling during accretion of the Chinese Altai.
关键词：KeywordsenNd and Hf isotope systematicsSubduction tectonicsOceanic sediment meltingGeochemical recyclingChinese Altai
