Investigation of Northeast Extension and Geological Evolution of the Sulu-Dabie High-Pressure Metamorphic Belt

Abstract

The Qianliyan Island locates at the northern Yellow Ocean about 80 km east from Qingdao, which develops lenses and layers of eclogite. The Qianliyan Island has been considered as the marine extension of the Dabie-Sulu orogen by comparing these two geological settings, especially their eclogites characteristics, such as mineral assemblages and compositions, temperature and pressure conditions, P-T path and geochronology. Based on textures and mineral compositions, three metamorphic stages were distinguished. The first stage is symbolized by the peak metamorphic assemblage of Grt-Omp-Ph-Rt in ecologite, T = 775˚C, P = 2.6 GPa. The second stage is represented by the retrograde assemblage amphibole + albite which form the symplectites around omphacite in eclogite, T = 740˚C~790˚C, P = 1.60~1.75 GPa. The third stage is symbolized by the actinolite appearing as a symbol of greenschist facies. The metamorphic age of the Qianliyan eclogite is documented at the age of the late Triassic ~222 Ma, consistent with those from Dabie-Sulu eclogites. It is proposed that the Qianliyan Island not only is the marine extension of the Dabie-Sulu orogen, but also may be the connecting part between Hongsong, South Korea, and the Dabie-Sulu orogen of China.