Monazite LA-ICP-MS U-Pb Dating to Constrain the Metamorphic Age of the Muzidian Gneiss Complex in the Northern Dabie Orogen

The Muzidian gneiss complex (MGC) in the Northern Dabie Orogen is the oldest exposed rock formation in the South China block. However, there is still a lack of research on its metamorphic age and tectonic implications. LA-ICP-MS in situ U-Pb dating and trace element analysis of monazite were carried out on two gneiss samples from the MGC. The results show that most monazite grains exhibit homogeneous features with no zoning, evident depletion of HREEs and negative Eu anomalies, suggesting that they may be of metamorphic origin. The monazite U-Pb ages of the two gneiss samples are 129±1Ma and 130±1Ma, respectively, which represent the time of metamorphism of the MGC. These ages are broadly consistent with the emplacement age of the early Cretaceous granitoids in the Muzidian area, as well as the large amount of exposed migmatites in the Northern Dabie Orogen. Our study shows that the extensional collapse of the thickened continental crust and the delamination of the orogenic crustal root during the early Cretaceous of the Dabie Orogen caused contemporaneous metamorphism, migmatation, and magmatism, which constrained the tectonic regime switch time of the Northern Dabie Orogen from compression to extension to ~130Ma. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202403050032.