The tectonic implications of a rare metamorphic event in eastern China during the Earth's “middle age”

Abstract

The Mesoproterozoic Era has long been considered a relatively stable, silent, and even "boring" period in Earth's history, during which the lithosphere was tectonically inactive. However, an increasing amount of evidence suggests that metamorphism and magmatism were much more widespread and intense than previously thought, implying that this period was dynamic. Here we report metamorphism around ca. 1.4 Ga along the southeastern margin of the North China Craton, eastern China. We conduct TIMA, EMPA, and zircon SHRIMP and LA-ICP-MS U-Pb dating on garnet amphibolites and their country rocks. The detailed mineral composition of a representive garnet amphibolite sample is identified and determined by TIMA. Phase equilibria modelling using pseudosections combined with EMPA data indicates the peak metamorphism stage (M 2 ) of the garnet amphibolites at a P-T condition of 10.6-11.2 kbar/820 ℃. SHRIMP Zircon U-Pb analysis yields an age of 1366 ± 17 Ma for the garnet amphibolites, which is slightly younger than that of its country rock schist (1376 ± 22 Ma). Integrating the metamorphic event with geochemical signatures, magmatic records, and sedimentation patterns in analogous geological settings on other continents, our findings collectively demonstrate a protracted and pervasive orogenic process along the periphery of the Columbia supercontinent.