The Triassic age for oceanic eclogites in the Dabie orogen: Entrainment of oceanic fragments in the continental subduction

Low-temperature and high-pressure eclogites with an oceanic affinity in the western part of the Dabie orogen have been investigated with combined Lu-Hf and U-Pb geochronology. These eclogites formed over a range of temperatures (482-565 degrees C and 1.9-22 GPa) Three eclogites, which were sampled from the Gaoqiao country, yielded Lu-Hf ages of 240.7 +/- 1.2 Ma, 243 3 +/- 4.1 Ma and 238.3 +/- 1.2 Ma, with a corresponding lower-intercept U-Pb zircon age of 232 +/- 26 Ma Despite the well-preserved prograde major- and trace-element zoning in garnets, these Lu-Hf ages mostly reflect the high-pressure eclogite-facies metamorphism instead of representing the early phase of garnet growth due to the occurrence of omphacite inclusions from core to rim and the shell effect. An upper-Intercept zircon U-Pb age of 765 +/- 24 Ma is defined for the Gaoqiao eclogite, which is consistent with the weighted-mean age of 768 +/- 21 Ma for the country gneiss However, the gneiss has not been subjected to successive high-pressure metamorphism The new Triassic ages are likely an estimate of the involvement of oceanic fragments in the continental subduction (C) 2010 Elsevier B V All rights reserved