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.

Structural and thermochronological data from the Sulu terrane of eastern China document the exhumation of high-pressure and ultrahigh-pressure (UHP) metamorphic rocks to upper-crustal depths by ca. 206 Ma. 40 Ar/ 39 Ar ages from K-bearing phases record recrystallization and cooling through amphibolite- and upper greenschist–facies conditions during top-to-the-NW noncoaxial shear and suggest cooling rates on the order of 55 °C/m.y. Integration of the 40 Ar/ 39 Ar data with U/Pb constraints on the timing of UHP metamorphism yields vertical exhumation rates of >6 mm yr −1 from mantle to upper-crustal depths. Qualitative thermal models of metamorphic K-feldspars suggest transient reheating in the Jurassic of a magnitude insufficient to reset mica ages. The Yantai-Qingdao-Wulian fault that currently delineates the boundary between the Yangtze and Sino-Korean cratons was active in the Early Cretaceous as a top-to-the-W extensional detachment fault. The youngest phase of deformation recorded by the 40 Ar/ 39 Ar data is consistent with mid to Late Cretaceous deformation associated with the Tan-Lu fault. In total, the data reveal that high-pressure and UHP rocks of the Sulu terrane reached and resided at higher structural levels by the end of the Late Triassic relative to the high-pressure and UHP rocks presently exposed in the Dabie Shan. Thus, our 40 Ar/ 39 Ar data from the Sulu terrane provide the tightest constraints thus far on the timing and rates of exhumation of high-pressure and UHP rocks to upper-crustal depths in the orogen.

Four structural-metamorphic zones separated by ductile shear zones comprise the Sulu high- to ultrahigh-pressure metamorphic terrane. From south to north, they are the southern high-pressure zone (0.2–0.4 GPa, 350–400 °C), the central very high-pressure zone (1.5–2.5 GPa, 500–600 °C), the northern ultrahigh-pressure (UHP) zone (>2.8 GPa, 650–800 °C) dominated by paragneiss, and the northern UHP zone dominated by granitic gneiss. Exhumation was associated with retrograde amphibolite- to greenschist-facies metamorphism and oblique southeastward ductile extrusion within the subduction channel. Geologic observations and seismic reflection profiles suggest an eroded asymmetric antiformal slab intruded by numerous Mesozoic granitic plutons. Zircon U/Pb ages indicate that peak metamorphism in the UHP zone occurred at 240–220 Ma, and 40 Ar/ 39 Ar thermochronology documents later exhumation at 220–200 Ma. In contrast, in the high-pressure zone, peak metamorphism and exhumation ages are older than 253 Ma and 253–240 Ma, respectively, by the same mineral. Together with previous results, these new data suggest that subduction and exhumation of different parts of the Yangtze slab occurred at different times, depending upon vertical variations in the physical properties of the subducted continental crust.