Metamorphic records for subduction erosion and subsequent underplating processes revealed by garnet‐staurolite‐muscovite schists in central Qiangtang, Tibet

Abstract

AbstractSubduction erosion is confirmed as a crucial geodynamic process of crustal recycling based on geological, geochemical, and geophysical observations at modern convergent plate margins. So far, not a single metamorphic record has been used for constraining a general tectonic evolution for subduction erosion. Here we first revealed metamorphic records for a subduction erosion process based on our study of the Late Paleozoic garnet‐staurolite‐muscovite schists in the central Qiangtang block, Tibet. Provenance analyses suggest that the protoliths of garnet‐staurolite‐muscovite schists have the Northern Qiangtang‐affinity and were deposited in an active continental margin setting. Mineral inclusion data show that the early metamorphic stage (M1) recorded blueschist facies pressure‐temperature (P‐T) conditions of 0.8–1.1 GPa and 402–441°C, indicating that a part of the material from the overriding plate had been abraded into the subduction channel and undergone high‐pressure/low‐temperature metamorphism. The peak metamorphic stage (M2) recorded amphibolite facies P‐T conditions of 0.3–0.5 GPa and 470–520°C. The 40Ar/39Ar cooling ages (263–259 Ma) yielded from muscovite suggest the amphibolite facies metamorphism (>263 Ma) occurred at oceanic subduction stage. The distinctly staged metamorphism defines a clockwise and warming decompression P‐T‐t path which reveals an underplating process following the early subduction erosion. During the tectonic process, the eroded low‐density material escaped from the cold subduction channel and rise upward into the warm middle‐lower crust of the upper plate, undergoing amphibolite facies metamorphism. Our new results revealed a complete evolutional process from the early subduction erosion to the subsequent underplating during the northward subduction of the Paleo‐Tethys Ocean.