Sedimentary age determination and palaeogeographic pattern of Neoproterozoic Qingshuijiang Formation in Central Guizhou Province

This paper is the result of geological survey engineering.

Objective The Qingshuijiang Formation in Kaiyang area of Central Guizhou is a set of epimetamorphic terrigenous clastic rocks intercalated with pyroclastic rocks, which formed at the margin of the Yangtze block in Neoproterozoic. In order to accurately determining the depositional age, the provenance and the paleogeographic pattern of the Qingshuijiang Formation, the sedimentary characteristics of terrigenous clastic rocks and the chronology of pyroclastic rocks are studied in this paper.

Methods Based on the detailed geological survey, the detrital zircon U-Pb age of the tuffites at the top of this Formation was determined by LA-ICP-MS analysis, and the regional stratigraphic correlation was carried out.

Results Zircon U-Pb ages are divided into two groups, 2488-1821 Ma in Paleoproterozoic and 838-779 Ma in Neoproterozoic, respectively, with a weighted average of (802±24) Ma for the youngest age group. The statistical results of pyroclastic content shows that the magma activity in this period has obvious episodic distribution and periodicity. Regional stratigraphic correlation results show that the exposure nature of the Qingshuijiang Formation in Kaiyang area is similar to Tongren and Yinjiang area, and may be equivalent to the bottom of the Qingshuijiang Formation in southeast Guizhou area.

Conclusions The latest depositional age limit of the Qingshuijiang Formation in Central Guizhou is about 800 Ma. The provenance mainly comes from Sichuan-Yunnan-Guizhou region on the western margin of the Yangtze Landmass. and the abundant volcanics may come from the second to third episodes of tectonic magmatic activity during the breakup of the supercontinent in the middle Neoproterozoic. The sea-land conversion occurred in the subsequent Xuefeng movement, and formed an ancient land extending in the northeast with a higher distribution of altitude in the south than the north, which established the paleogeographic framework of the Nanhua period in the middle Neoproterozoic.