Geochronology and geological significance of the strata of the Neoproterozoic Nanhua System, SW North China Craton

Abstract

A set of low-grade clastic metamorphic and carbonate rocks, and greenschists outcropping in the southwestern (SW) margin of the North China Craton (NCC), was originally classified as the Paleoproterozoic Xiong'er Group according to stratigraphic correlation. To verify the age, this paper carried out detrital zircon U–Pb LA-ICP-MS dating of low-grade clastic metamorphic rocks exposed in the Changqing area at the SW margin of the Ordos Block in the SW part of the NCC. Results from detrital zircon dating indicate that the metamorphic and carbonate rocks can be classified into the Neoproterozoic Nanhua System, which is the only Nanhua System stratum in this block so far, and it probably could provide new clues to Rodinia break-up and Snowball Earth of the NCC. The nine peak ages of the low-grade clastic metamorphic rocks reflected its relatively complex provenance, and almost all major geological events experienced by the NCC basement since the Neoarchean, but some age peaks were difficult to correspond to that of the NCC, indicating that the southwestern part of the Ordos Block was also affected by the Qinling and Qiliang orogenic belts during Nanhua System of Neoproterozoic. Combined with provenance analysis, it was revealed that the current southwest boundary of the Ordos Block was the previous southwest boundary of the Ordos Block during the Qingbaikou-Nanhua Period of the Neoproterozoic.