关键词: 大别造山带, 韧性剪切带, 石英组构, 超高压变质岩, 折返

Abstract: Exhumation processes of ultrahigh-pressure (UHP) metamorphic rocks are critical for evolution of continental collision
boundaries. The south-dipping Hualiangting-Mituo shear zone is the boundary between the South Dabie low-temperature/UHP zone and
the Central Dabie mid-temperature/UHP zone. It is characterized by SE-trending stretching lineation, and nearly equal thrust and strike
slip components. The lattice-preferred orientation of quartz from the Hualiangting-Mituo shear zone was determined using the electronic
backscatter diffraction (EBSD) technique. Most samples show the top-to-NW shear sense due to the fast SE-ward exhumation of the
Central Dabie mid-temperature/UHP zone. However, some samples developed the top-to-SE shear sense because of intrusion of granitic
domes and regional extension in the Early Cretaceous. A summary of petrological and geochronological data in the Dabie Mountains
reveals the decreasing U-Pb zircon ages of the prograde metamorphism and UHP peak metamorphism from south to north. The South
and Central Dabie UHP zones experienced coeval high-pressure eclogite facies metamorphism at 215~225 Ma and greenschist facies
metamorphism at 191~195 Ma. The relatively younger 40Ar/39Ar ages of muscovite and biotite near the Tanlu fault may be affected by
ductile activation of the Tanlu fault. The isobaric and isothermal contours of the peak metamorphism in the South and Central Dabie
UHP zones are oblique to the trend of the Hualiangting-Mituo shear zone, suggesting oblique exhumation of UHP rocks. We proposed
that the South Dabie low-temperature/UHP zone was first exhumed towards SE as a tectonic slice at ~236 Ma, which was followed by fast
exhumation of the Central and North Dabie UHP zones. The relative motion (i.e., different exhumation rates and oblique exhumation
angels) between these UHP metamorphic slices was adjusted by ductile shear zones.

Key words: Dabie orogenic belt, ductile shear zone, quartz fabric, ultrahigh-pressure metamorphic rocks, exhumation