Anatexis witnessed post-collisional evolution of the Dabie orogen, China

Crustal anatexis plays a significant role in the processes of orogenic evolution. We carried out a combined study of structure, U-Pb age and trace element on zircons from leucosome-based migmatites in the North Dabie zone to provide information on crustal anatexis during the evolution of the Dabie orogen. Protoliths of the migmatites are Middle Neoproterozoic (ca. 780-710 Ma) magmatic rocks that belong to the South China Block. They underwent a relatively low-T eclogite-facies metamorphism during the Middle to Late Triassic (235-225 Ma) continental subduction and collision. An over-thickened crustal root was formed and the Dabie orogen entered into the stage of post-collisional evolution after the Triassic. The earliest anatexis occurred at ca. 185 Ma; the anatexis in the Jurassic was weak and gentle due to episodic flow of metamorphic fluids with a prolonged interval. Nevertheless, it indicates that the crustal root started to become ductile and unstable at that time. Extensive epsodic anatexis occurred between ca. 160 Ma and 110 Ma. As the anatexis became stronger, more extensive and uninterrupted, the anatectic products changed gradually from low-degree migmatites to high degree migmatites. The beginning of extensive anatexis at similar to 160 Ma marks the beginning of orogenic activation. The duration of ca. 160-145 Ma corresponds to the orogenic activation when the collision-thickened crust still remained, whereas the period of ca. 145-110 Ma is in accordance with the orogenic collapse. The peak period of anatexis (ca. 145-125 Ma) was accompanied by plutonism, high-T granulite-facies metamorphism, extensional uplift and subsequent delamination of crustal root. After that, the anatexis trailed off until ca. 110 Ma. The long lasting multistage anatexis recorded in the migmatites has witnessed the evolution of the Dabie orogen in the postcollisional stage.