Luoyu and Ruyang Group at the South Margin of the North China Craton （NCC） Should Belong in the Mesoproterozoic Changchengian System： Direct Constraints from the LA-MC-ICPMS U-Pb Age of the Tuffite in the Luoyukou Formation, Ruzhou, Henan, China
详细信息
- 责任者：Su Wenbo (School of Earth-sciences and Resources ; China University of Geosciences （Beijing） ; Beijing 100083 ; China) ; Li Huaikun
- 刊名：Geological Survey and Research
- 出版年：2012
- 卷期：35(2)
- 页码：p.96-108
- 图表：illus., 3 tables, 89 refs.
- issnNo：ISSN1672-4135
- isbnNo：CN12-1353/P
摘要
By means of the LA-MC-ICPMS zircon U-Pb dating, the high-precise dates of the volcanic eruption, 1 611 ±8 Ma, of an interbedded tuffite layer in the middle part of the Luoykou Formation at the Yangpo Section, Ruzhou City, Henan Province, has been obtained. With this dates, the depositional age of the Luoyukou Formation can be calibrated accurately as the first time, which indicates that the top age of this formation should be most likely about 1 600 Ma. Moreover, being at the uppermost of the Luoyu Group of the conventional Chinese Neo-proterozoic Qingbaikouan System （1 000～800 Ma）, which overlies on the Ruyang Group of the Mesoproterozo-ic Jixian System （1 600 ～ 1 000 Ma）, at the south margin of the North China Craton （NCC）, the new dating achievement of the Luoyukou Formation will result in a major revision in chronostratigraphy that both of the two groups should be lowered down to the older Mesoproterozoic Changchengian System （1 800～1 600 Ma）. In addition, it also indicates that the top surface of the Luoyukou Formation might be the operable physical boundary between the Changchengian and Jixian System in this area. On the other hand, combined with the regional data, especially the recent chronostratigraphical dating of the volcanic rocks-dominated Xiong’er Group, which shows that they were erupted mainly from 1 750 Ma to 1 780 Ma in age and superimposed by the Ruyang Group, the depositional time span of both the Luoyu Group and the Ruyang Group can be limited roughly into the period from 1 750 Ma to 1600 Ma. It can correlate with the middle-late portion of the Mesoproterozoic Statherian Period （1 800～1 600 Ma） internationally, and that of the Changchengian Period in China. The direct constraints of the 1611±8 Ma zircon U-Pb age of the tuffite bed in the Luoyukou Formation and the major revision of the chronostratigraphical subdivision at the south margin of the NCC provide a up-to-date and critical timescale for some major ongoing research issues of the NCC during the Mesoproterozoic Era, such as the correlation between the northern and southern margin of NCC, the relationship between the development of the NCC and the break-up of the Columbia Supercontinent, the evolution of the early life on the Earth in the deep-time, and so on.