U-Pb zircon ages of granitoid rocks in the North Dabie Complex, eastern Dabie Shan, China

The North Dabie Complex (NDC) comprises a high-temperature metamorphic suite dominated by amphibolite-facies granitoid orthogneiss intruded by voluminous granites. U-Pb zircon dating on these rocks yields the following new results: (1) Two of the granitoid orthogneiss samples have Early Cretaceous protolith emplacement ages of 133.7 +/- 2.3 Ma and 134.0 +/- 2.8 Ma. (2) An undeformed granodiorite intrusive into granitoid gneiss yields an emplacement age at 125.6 +/- 0.3 Ma. These Early Cretaceous ages entirely post-date Late Triassic-Early Turassic continental subduction and exhumation evident in the neighboring ultrahigh and high-pressure metamorphic terrains to the south in the Dabie Shan; hence they do not support previous tectonic models that infer Paleozoic or Triassic protolith emplacement ages for these granitoid orthogneisses. (3) A mylonitic granite from the northern boundary of the NDC yields a concordant age of 756.6 +/- 0.8 Ma, which is interpreted as magma emplacement age. The concordance of this Late Proterozoic age suggests that the U-Pb systematics have not been disturbed by any significant thermal overprint since emplacement, implying that the northern extent of the deeply subducted Yangtze Block lies south of this locality.