Timing of collision of the Sino-Korean and Yangtse cratons: U-Pb zircon dating of coesite-bearing eclogites

The suture zone between the Sino-Korean and Yangtse cratons in central China is marked by a series of fault-bounded belts composed of crustal protoliths. In the Dabie Mountains some of these blocks contain coesite and diamond, indicating subduction to minimum depths of ∼120 km as a result of continental collision. The blocks range from the structurally lowest ultrahigh-pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest, low greenschist facies belt. Furthermore, the faults mark large contrasts in metamorphic grade. These features form a structure that is similar to metamorphic core complexes, indicating extension as part of the exhumation process. Timing of the continental collision has previously been inferred as Late Triassic, from regional geologic relations, or Caledonian, from ⁴⁰Ar/³⁹Ar dating of the adjacent and possibly related Qinling metamorphic belt. U-Pb dating of zircon from ultra-high-pressure eclogites yields a metamorphic age of 209 ±2 Ma. This age coincides with later stages of collision and is therefore a minimum estimate of the time of collision.