中国科学院南京地质古生物研究所机构知识库

The Great Unconformity that separates the early Cambrian sandstones from the Proterozoic metamorphosed sedimentary rocks has been recognized in many blocks on Earth. However, whether it represents a globally synchronous event or a composite of a series of diachronous events, and its formation mechanism remain largely unknown. In this study, we carry out detrital zircon U-Pb analyses for seven samples collected from the Paleopmterozoic Quanji Group and the overlying Neoproterozoic strata in the Olongbuluke terrane (OLT) of Northwest China. The results show that apart from age populations of similar to 1.8-2.0 Ga and similar to 2.2-2.5 Ga for all samples, additional similar to 1.55-1.65 Ga age population occurs in sample from the Zhoujieshan Formation, and more scattered age populations ranging from similar to 0.75 to similar to 1.7 Ga are present in samples from the Heitupo and Hongtiegou formations. The similar to 1.8-2.0 Ga and similar to 2.2-2.5 Ga zircons correlate well with the magmatic and metamorphic events in the OLT basement, indicating their local provenances, while other zircons were possibly derived from the North China craton (NCC) or other adjacent blocks. Combined with published paleontological, stratigraphic, and geochronological data, the present study supports previous inference that the OLT had a close paleogeographic affinity to the NCC during late Paleoproterozoic to Neopmterozoic. New zircon U-Pb ages indicate that the Heitupo Formation was deposited later than similar to 750 Ma, and the underlying Hongzaoshan Formation was deposited at similar to 1.66 Ga, implying a huge break between them. Whereas the duration of the sedimentary break between the Heitupo Formation and the overlying Hongtiegou Formation is uncertain, biostratigraphic data suggest that a break of similar to 30 Myr may exist between the late Ediacaran Zhoujieshan Formation and the overlying early Cambrian Xiaogaolu Group. The occurrences of these multiple unconformities in OLT are comparable to those in NCC, indicating that the Great Unconformity is represented by a series of lengthy denudations during the Proterozoic-early Cambrian in both the OLT and NCC, which may result from multiple tectonic activities in these two blocks.