Detrital Zircon Geochronology and Provenance of Metasedimentary Rocks from the Susong Complex Zone in the Dabie Orogen

The Susong complex zone is a relatively low-grade metamorphic unit located in the southern part of the Dabie orogen and preserves a variety of metasedimentary rocks, mostly with epidote-amphibolite facies. However, their depositional age, provenance and tectonic setting of sedimentary protolith remain controversial due to the lack of fossils, precise dating and integrated geochemical investigation. This study has conducted whole-rock elemental, and zircon U-Pb SHRIMP dating and Lu-Hf isotope analyses on three types of representative metasedimentary rocks including garnet-bearing mica-quartz schist, graphite-muscovite-quartz schist and dolomitic marble from the Susong complex zone. The U-Pb SHRIMP dating data indicate that the sedimentary protolith of these rocks have the maximum depositional ages of less than 840-750 Ma and have various sedimentary provenances. In combination with zircon Lu-Hf isotope compositions, the provenance of the metasedimentary rocks in the region is for the first time documented to be mainly derived from four groups of magmatic rocks formed at similar to 2.5 Ga, similar to 2.0 Ga, similar to 1.4 Ga and similar to 0.8 Ga in response to four episodes of igneous activity in the northeastern margin of the Yangtze Block. The conventional geothermobarometry combined with rare metamorphic zircon ages indicate that the studied rocks underwent the Late Triassic continental subduction-related metamorphism with peak epidote-amphibolite facies conditions at P = 0.34-0.91 GPa and T = 427-532 degrees C. In addition, results of the elemental contents (i.e., La, Ce, Th and sigma REE) and ratios (i.e., Eu/Eu* and LaN/YbN) suggest that the protoliths of the metasedimentary rocks were mainly shales, wackes and limestones, most probably related to the Rodinia supercontinent rifting along the northern margin of the Yangtze Block during the Neoproterozoic. image