Neoproterozoic subduction-related active rifting in the South China Craton: insights from geochemical and zircon Hf isotopic data

Active and passive continental rifts are generally attributed to plume and subduction mechanisms, respectively. However, controversy surrounding the role of the two mechanisms continues, especially for the mid-Neoproterozoic rifts in the South China Craton. Here, we use geochemical and zircon Hf isotope data from the craton's rift successions to examine the mechanism of rifting. The compiled geochemical data support the existence of subduction-related magmatic belts along the Jiangnan Orogen and western Yangtze margin of the craton during the mid-Neoproterozoic, consistent with a conventional subduction-related passive rift mechanism. But evidence of asthenospheric upwelling and subsequent lithospheric uplift, metamorphism, volcanism and magma-rich rift infill indicate rifting was active. Compiled zircon epsilon Hf(t) values and crustal incubation times suggest a ca. 830-780 Ma transition from advancing to retreating subduction that coincides with rifting across the craton. We therefore propose a subduction-related active rifting model in which the onset of transitionalsubduction triggered mantle convection and plume activity that led to the mid-Neoproterozoic initiation of active rifting in the South China Craton. This suggests a mixed mechanism for rifting rather than two distinct end-members.