Geochemistry and zircon U-Pb dating and its implications of the Yukahe HP/UHP terrane, the North Qaidam, NW China

The Yukahe eclogite-gneiss section in the western segment of the North Qaidam HP/UHP belt, NW China occurs two types of eclogites as lenses or layers in both granitic and pelitic gneisses. Zircon in situ LA-ICP-MS U-Th-Pb and trace element analyzes, combined with cathodoluminescence images yield metamorphic ages of 431 +/- 4 to 436 +/- 3 and 431 +/- 3 to 432 +/- 19 Ma for eclogites and gneisses, respectively. These nearly identical metamorphic ages suggest that the eclogites and host gneisses underwent coeval early Paleozoic HP/UHP metamorphism. A few inherited zircon cores of eclogites have magmatic characters of high REE and HREE abundance, HREE-enriched REE pattern and Th/U > 0.4, and yield protolith ages of >750 Ma. Geochemical data show that the Yukahe eclogite has alkali basaltic protoliths with high TiO2 and K2O + Na2O contents and Nb/Y ratios, REE patterns and trace element contents similar to those of within plate basalts (WPB). Nd isotope analyzes give epsilon Nd ranges from -5.34 to +4.47, suggesting an enriched mantle source. These characteristics together with the geochronological results conclude that the Yukahe eclogite protoliths likely formed in a Neoproterozoic continental rift setting, and have subjected to HP/UHP metamorphism during early Paleozoic continental subduction. (C) 2009 Elsevier Ltd. All rights reserved.