Provenance of the Beihuaiyang lower-grade metamorphic zone of the Dabie ultrahigh-pressure collisional orogen, China: evidence from zircon ages

摘要

The Beihuaiyang zone of the Dabie ultrahigh-pressure collisional belt, which was formed by the Early Mesozoic collision of the North and South China (Yangtze) Blocks, is diversely interpreted as an active or a passive sedimentary sequence. It comprises the Luzhenguan and Foziling complexes. Six granitoid rocks of the Luzhenguan complex are dated at 770 Ma to 720 Ma and one schist sample also contains detrital zircons of 760 Ma to 720 Ma. These data indicate that this complex was of the South China affinity and probably originated from the northern Yangtze Block. Two quartzite samples of the Foziling complex contain abundant detrital zircons of Archean to Paleozoic ages, clustering around 2.5 Ga, 1.9-1.8 Ga, 1.0-0.7 Ga, and 0.5-0.4 Ga. This age spectrum demonstrates a mixed source of these two blocks. The youngest zircons suggest a Paleozoic deposition along an active continental margin south of the North China Block, while these Late Proterozoic zircons are characterized for the Yangtze Block. Subsequently, it is suggested that a terrain drifted from the northern Yangtze Block in Early Paleozoic must have been situated to the southern margin of the North China Block to provide material source prior to the final collision in Early Mesozoic.