Reinitiation of modern-style plate tectonics in the Early Neoproterozoic: Evidence from a ∼930 Ma blueschist-facies terrane in South China

Abstract

When and how plate tectonics operated throughout Earth’s history remain a matter of debate. The absence of low-temperature/high-pressure metamorphic rocks during Earth’s middle age (∼1.8–0.8 Ga) leads to some arguing for a temporary shutdown or change of modern-style plate tectonics throughout the Mesoproterozoic and Early Neoproterozoic. Here we report the first discovery of ∼930 Ma blueschist-facies metamorphic rocks (Tianli Schist) from the Jiangnan Orogen, South China. Peak pressure–temperature conditions of ∼425–475 ℃ and ∼0.8–1.1 GPa recorded by these units represent an average geothermal gradient of ∼14 ℃/km, characteristic of cold subduction zones. Available geologic and geochronologic constraints indicate that the Tianli Schist protolith was deposited in the southeast margin of the Yangtze Block and subsequently experienced blueschist-facies metamorphism during ocean closure at ∼930 Ma. Combined with the global metamorphic record, our results suggest that modern-style plate tectonics did not operate continuously since initiation in the Early Paleoproterozoic, but was inhibited in the Mesoproterozoic and restarted again at the end of Earth’s middle age.