SHRIMP U-Pb zircon dating of the Rongcheng Eclogite and associated peridotite; new constraints for ultrahigh-pressure metamorphism of mantle-derived mafic-ultramafic bodies from the Sulu Terrane

New sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages from eclogite and associated peridotite near Rongcheng, Sulu terrane, eastern China, indicate that eclogite within peridotite experienced Triassic metamorphism at the same time as the surrounding host gneiss. Cathodoluminescence (CL) images reveal that most of the zircons from two eclogites and one dunite have unzoned, homogeneous or slightly mottled patterns, typical of metamorphic zircons. Some zircons from eclogite sample CJ4C have distinct nonluminescent U-rich cores and luminescent U-poor rims, but similar ages were obtained from both domains. SHRIMP U-Pb zircon analyses of one dunite (MC5A) and two eclogites (CJ4A, 4C) yielded ages of 242+ or -8 Ma, 238+ or -3 Ma, and 232+ or -7 Ma, respectively, which are considered to be the peak metamorphic ages. A much younger age (218+ or -5 Ma) was obtained from eclogite CJ4D, but no petrological evidence for a retrograde event was found in this sample, and therefore this age is also considered to reflect eclogite-facies growth. Thus, new geochronological data confirm that these mantle-derived mafic-ultramafic bodies were emplaced into the subducting slab in the Triassic and experienced the ultrahigh-pressure metamorphism together with the adjacent supracrustal rocks.