Large-scale replacement of ancient mantle lithosphere during supercontinent assembly: Evidence from the South China Craton

Abstract

The modification and destruction of the sub-continental lithospheric mantle (SCLM) has been identified in numerous studies. However, what principally controls the susceptibility and extent of destruction of the SCLM and how this leads to the corresponding variation of the overlying crust remain long-standing issues. Here we provide an integrated study of petrology, mineralogy, and geochemistry, including highly siderophile element (HSE) abundances and whole-rock and/or mineral Os-Hf-Sr-Nd isotopic compositions of mantle peridotite xenoliths from Hainan Island, together with a compiled dataset from the eastern South China Craton (SCC) to investigate the mechanism and timing of replacement and destruction of the SCLM. The mantle xenoliths from the eastern SCC are overall more fertile than cratonic lithospheric mantle, and have generally experienced various extents of metasomatic enrichment, including carbonate and silicate melt metasomatism. In addition, the absence of Archean ages and compositional or temporal stratification of the SCLM beneath the eastern SCC indicates that the Archean lithospheric mantle may have been replaced/reworked and has essentially vanished, hence the present underlying lithospheric mantle is a relatively new and young lithospheric mantle. The formation time of the SCLM underneath Hainan Island constrained by both the ReOs and LuHf isotopic systems is late Mesoproterozoic (∼1.2 Ga), largely consistent with the Meso- to Neoproterozoic peak of whole-rock TRD ages (0.9–1.3 Ga) of the refractory mantle peridotites in the compiled dataset. This age distribution can be reconciled with the assembly time of the Rodinia supercontinent, indicating a close linkage between the replacement of large-scale lithospheric mantle via mantle convection erosion and regional continental amalgamation. Meanwhile, the relative location to the plate margins influences the preservation of the cratonic mantle. The SCLM located at the plate margin (e.g., eastern SCC compared to western SCC), where destructive processes frequently occur, is susceptible to destruction, whereas that within the plate interior is likely to remain relatively intact.