SHRIMP U-Pb zircon age, geochemistry and Nd-Hf isotope of Neoproterozoic mafic dyke swarms in western Sichuan: Petrogenesis and tectonic significance

摘要

Neoproterozoic magmatic rocks are widespread in the western margin of the Yangtze block, and their origin and genesis have significant implications for understanding the evolution of the Rodinia super-continent. However, there are currently two opposing interpretations for their petrogenesis and tectonic setting: mantle plume-related and island arc origin. To further verify these two competing models, SHRIMP U-Pb zircon age determinations and geochemical and Nd-Hf isotopic analyses are conducted" on the mafic dykes in the Kangdian Rift, western Sichuan. U-Pb dating suggests that these mafic dykes were emplaced at 780—760 Ma, spatially and temporally coeval with the Kangding granitoid complex. The parental magmas of these dykes were derived from a depleted asthenosphere mantle source likely triggered by an anomalously-hot mantle plume. Despite some arc-geochemical features caused by variable degrees of contamination of young island arc crust during magma ascending and emplacement, they show general geochemical and Nd-Hf isotopic features similar to those of the intraplate basalts. Our results support the reconstruction model of Rodinia in which the South China block was located between Australia and Laurentia.