Metamorphic evolution and protolith formation age of metasedimentary rocks in the Dabie orogenic belt

The Dabie orogen has been primarily studied through metaigneous rocks, whereas metasedimentary rocks remain poorly constrained in metamorphic evolution and protolith ages. This study presents petrography, mineral chemistry, phase equilibrium modelling, and geochronology of two representative metasedimentary rocks. Jadeite quartzite records four metamorphic stages (M1, M2, M3, and M4) with pressure and temperature (P-T) of 3.25–3.33 GPa/595–647 °C; 2.51–2.73 GPa/493–543 °C; 1.0–1.1 GPa/629–691 °C; and <0.8 GPa/317 ± 43 °C, respectively. However, the epidote-biotite-plagioclase gneiss records only retrograde metamorphism. Zircon and rutile U-Pb dating yields two age clusters: 234–225 Ma for ultrahigh-pressure metamorphism (UHPM) and 204–203 Ma for retrogression. Detrital zircon age spectra, with a youngest population at ~440 Ma, indicate Paleozoic deposition. Integrated with protolith ages of the Susong Complex and Foziling Group, these metasedimentary rocks of the Dabie orogen are interpreted as Paleozoic sediments deposited along the northern passive margin of the Yangtze Plate. Compared with P-T-t paths of UHPM rocks, the studied units record a complex exhumation path marked by initial decompression with cooling, subsequent decompressional heating, and late-stage decompressional cooling, highlighting the critical role of metasedimentary rocks in resolving the tectonic architecture of the Dabie orogen.