40Ar/39Ar thermochronology of the Sulu terrane: Late Triassic exhumation of high- and ultrahigh-pressure rocks and implications for Mesozoic tectonics in East Asia

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. 40Ar/39Ar ages from K-bearing phases record recrystallization and cooling through amphiboliteand 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 40Ar/39Ar 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 40Ar/39Ar data is consistent with mid to Late Cretaceous deformation associated with the Tan-Lu fault. In total, the data reveal that highpressure 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 40Ar/39Ar 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.