New constraints on P-T-t path of high-T eclogites in the Dabie orogen, China

Deciphering the P-T-t path of ultrahigh-pressure (UHP) rocks is crucial for reconstructing the evolution of continental crustal terranes involved in very deep subduction followed by exhumation. Achievieng this goal is especially challenging for UHP terranes which experienced protracted high/ultrahigh temperature (high-T/UHT) exhumation histories, because the widespread anatexis associated to retrograde re-equilibration often obliterate the evidence of UHP metamorphism. In the Dabie-Sulu orogenic belt of central-eastern China, which is the largest UHP terrane in the world, the migmatitic North Dabie complex Zone (NDZ) is the archetype of such UHP terranes experiencing a "slow and hot" exhumation. The NDZ stands out for the widespread anatexis that widely overprinted the traces of eclogite-facies metamorphism, hampering a precise reconstruction of its P-T-(t) evolution. This paper presents the results of a multidisciplinary study integrating P-T pseudosection of phase equilibrium modeling, conventional geothermometry and zircon U-Pb dating with trace element analysis applied on the high-T UHP eclogites from the NDZ. The studied eclogites underwent a multistage metamorphic evolution including post-peak granulite-facies overprinting and subsequent amphibolite-facies retrogression. P-T conditions of the granulite-facies overprinting and the amphibolite-facie retrogression have been estimated at >830 °C, 7-12 kbar and 560-880 °C, 4.3-8.9 kbar, respectively. New zircon U-Pb dating, mineral inclusion and trace element analysis, combined with modeled plagioclase modal variation by pseudosection approach, allowed constraining the ages of prograde metamorphism, eclogite-facies metamorphism, granulite-facies overprinting and amphibolite-facies retrogression of the eclogites at 247-230 Ma, 226-219 Ma, 217-212 Ma and 214-198 Ma, respectively. These results provide new P-T-t estimates and age data for the multiple metamorphic stages during continental collision, contributing to precisely reconstruct the whole P-T-t path of the NDZ.