New U-Pb sensitive high-resolution ion microprobe (SHRIMP) dating of zircon from the ultrahigh-pressure Sulu terrane, eastern China, records three events in the evolution of the orogen. Peak ultrahigh-pressure and retrograde metamorphism in the Middle to Late Triassic (ca. 230–200 Ma) is recorded in zircon mantles and rims; cathodoluminescence imaging, grain morphology, and U-Th-Pb and rare earth element chemistry cannot distinguish between ultrahigh-pressure and retrograde zircon growth. Comparison of high-temperature thermochronology for the Sulu and Dabie–Hong'an areas suggests that peak ultrahigh-pressure metamorphism in Sulu took place at ca. 230 Ma, postdating Dabie–Hong'an by 10 m.y.; this age disparity has implications for collision-subduction-exhumation models for the entire Qinling–Hong'an–Dabie–Sulu orogen and suggests that Sulu was a separate ultrahigh-pressure slab that was never adjacent to Dabie. Relict zircon cores and mantles preserve protolith ages between 700 and 790 Ma, reflecting the Yangtze craton affinity of the Sulu terrane and supporting other evidence indicating that the suture between the Yangtze and Sino-Korean cratons lies along the Yantai-Qingdao-Wulian fault zone. Late Jurassic to Early Cretaceous ages from a pegmatite vein near the suture probably reflect early melting related to a widespread magmatic event that affected the northern margin of the Dabie-Sulu belt.

Abstract The conclusions of most previous studies on the eastward extension of the collision zone between the Sino-Korean and Yangtze Blocks can generally be divided into two categories: (1) the collision zone is connected to the Imjingang belt and crosses the Korean Peninsula; (2) the eastward extension of the collision zone does not enter the Korean Peninsula, nor is connected to the Imjingang belt. Recent geophysical studies on gravity and velocity tomography in the Yellow Sea and adjacent regions, respectively, have provided geophysical evidence for a nearly north–south-trading dextral strike-slip fault in the eastern margin of the Yellow Sea, which we have named the East Marginal Fault of the Yellow Sea (EMFYS). The geophysical evidence indicates that the EMFYS extends to great depth. It dips westward, and within 100 km depth the dip angle is very steep. The geophysical characteristics on its two sides show that they belong to different tectonic units. This fault is connected to the Wulian–Qingdao Fault in the north, and to the South Marginal Fault of Jeju Island (SMFJI) in the south (the SMFJI is a part of the collision zone). Therefore the EMFYS is considered as a part of the junction zone between the Sino-Korea and Yangtze Blocks, with the Korean Peninsula being part of the Sino-Korea Block. In the Late Triassic, it is inferred that dextral strike-slip movement took place on the EMFYS, and in the same geological period sinistral strike-slip took place on the Tan-Lu Fault Zone. Under north–south tectonic stress the Yangtze Block was translated northward and inserted into the Sino-Korea Block. Therefore the junction zone between the two blocks formed a gigantic Z-shaped tectonic belt. According to the gravity data and seismic tomography it is also inferred in this paper that the junction zone between the Yangtze and Cathaysia Blocks extends from the Jiangshao Fault eastward to the southern edge of the Hida Block, Japan.