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.

Abstract The Qinling-Tongbai-Hong’an-Dabie Shan area is an about 2000 km long Triassic Indosinian orogenic belt produced by the collision between the Sino-Korean and the Yangtze cratons ( Fig. 1 ). Its eastern extension, the Sulu area, occupies the southeastern side of the Shandong Peninsula, and is considered to be displaced about 500 km by the NE-SW trending left lateral Tan-Lu Fault after the Mesozoic ( Fig. 1 ). Among these areas, most of the UHP rocks were found from Hong’an, Dabie Shan and Sulu areas, suggesting that these areas represent the most extensive UHP metamorphic belt in the world. Their UHP peak is dated around 220-230 Ma ( e.g. Ames et al. , 1993 , 1996 ; Li et al. , 1993 ; Hacker & Wang, 1995 ; Hacker et al. , 1996 ; Rowley et al. , 1997 ) and these UHP terrains are considered to be formed chiefly by attempted north-directed subduction of the Yangtze craton or a microcontinent beneath the Sino-Korean craton ( e.g. Hacker et al. , 1996 ).