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 ± 8 Ma, 238 ± 3 Ma, and 232 ± 7 Ma, respectively, which are considered to be the peak metamorphic ages. A much younger age (218 ± 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.

The Haiyangsuo area of the NE Sulu ultrahigh-pressure terrane, eastern China, consists of gneisses with minor granulite and amphibolite layers, metagabbros, and granitic dikes. The peak-stage assemblages of the granulites (garnet + orthopyroxene + clinopyroxene + plagioclase ± pargasite ± biotite ± quartz) formed at >750 °C and 9–11 kbar and were overprinted by amphibolite-facies phases characterized by well-developed corona layers of | garnet | amphibolite + quartz | at contacts between plagioclase and clinopyroxene or orthopyroxene, as well as by the exsolution of (orthopyroxene + ilmenite + amphibole) from clinopyroxene. These textures indicate a near-isobaric cooling history of the granulite-bearing gneiss terrane. The metagabbro preserves a relict igneous assemblage (orthopyroxene + clinopyroxene + plagioclase + pargasite ± ilmenite ± quartz) in its core, but in its margins has a metamorphic corona texture similar to the granulite that formed at ∼600–700 °C and 7–10 kbar. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb dating of zircons indicates that the protolith age of the garnetbiotite gneiss is older than 2500 Ma, whereas the granulite-facies metamorphism (the first regional metamorphic event) occurred at 1846 ± 26 Ma. Gabbro intrusion took place at 1734 ± 5 Ma, and the formation of amphibolite assemblages in both metagabbro and granulite occurred at ca. 340–370 Ma. Both gneiss and metagabbro were intruded by granitic dikes, with one dated at 158 ± 3 Ma. These data, together with a lack of eclogitic assemblages, suggest that this granulite-amphibolite–facies complex is exotic relative to the Triassic Sulu high-pressure–ultrahigh-pressure terrane; juxtaposition took place in Jurassic time.