Geodynamics of Late Paleozoic to Early Mesozoic Magmatism in South China: Insights from the Genesis of the Late Permian S-Type Granites in the Yunkai Massif

Late Paleozoic granites have rarely been reported in South China. We present the first detailed zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating and in situ Hf isotopic and whole-rock element geochemical and Sr-Nd isotopic data for two late Permian granitic plutons (Napeng and Shicun) recently identified in the Yunkai massif, South China. In addition, we assess their origin and relationship to the geodynamics of late Paleozoic to early Mesozoic magmatism in South China. The Napeng pluton consists of cordierite- and/or garnet-bearing biotite granites, and the Shicun pluton is composed of two-mica granites and muscovite granites. Detailed LA-ICP-MS zircon U-Pb dating shows that both plutons were emplaced in the late Permian and contain abundant inherited zircons with a spread of ages, including Neoarchean-Paleoproterozoic, Neoproterozoic-Cambrian, Ordovician-Silurian, Devonian, Carboniferous, and early Permian. The cordierite- and/or garnet-bearing biotite granites are strongly peraluminous and have higher maficity than experimental melts of metasedimentary rocks. Both the two-mica and muscovite granites are also strongly peraluminous but have similar maficity to experimental melts of metasedimentary rocks. All the granites have high initial Sr-87/Sr-86, negative epsilon(Nd)(t), and epsilon(Hf)(t) (in situ zircon). Detailed petrographic and geochemical characteristics of the studied granites suggest that they are S-type granites and were formed by partial melting of subducted oceanic sediments of the eastern Paleo-Tethys Ocean within the depth of mantle region to normal lower crust in the continental collision zone. Our new data suggest that the origin of the Napeng and Shicun granites might mark the onset of the continental collision between the Indochina and South China Blocks with the initial closure of the eastern Paleo-Tethys Ocean at the beginning of the late Permian.