| 中国前寒武系的划分 |
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| 引用本文：孙大中,陆松年.1985.中国前寒武系的划分[J].地球学报,7(1):17-36. |
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| 中文摘要:前寒武系在中国广泛分布。前寒武纪可划分为太古宙和元古宙两个时间单元,时间界线置于2500百万年。 据地质和同位素年龄资料,太古宙可两分,以2800百万年作为早—中太古代和晚太古代的时间界线。元古宙分为早、中和晚三代。以1900百万年和1000百万年分别作为元古宙内部划分的时间界线。寒武纪和前寒武纪的界线年龄推测为610百万年。 |
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| A SUBDIVISION OF THE PRECAMBRIAN OF CHINA |
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| Abstract:Precambrian rocks are widely distributed in China. It is pertinent to subdivide the Precambrian into two time units, i.e., Archaean and Proterozoic. Both of them with the status of Eons are separated into three chronological intervals with the status of Eras, with prefix of Early, Middle or Late.The time boundary between the Archaean and Proterozoic Eon in principle is 2500 Ma.According to the present isotopic data, the proposed subdivision for the Archaean of China is two-fold. The age of the Fuping Group is younger than 2800-2900 Ma, and that of the Qianxi Group and the corresponding strati-graphic units of eastern Liaoning are older than 2800 Ma, so that 2800 Ma is selected as the boundary between the Early-Middle and Late Archaean.Based on the representative stratigraphic units, the Wutai and Huto Groups, and an intervening major unconformity formed by Wutaiian Orogeny at 2200-2300 Ma, the Early Proterozoic is further divided into two periods, with a time demarcation of 2200 Ma. A major episode of orogeny known as the "Luliangian Movement" occurred at the end of the Early Proterozoic about 1900 Ma age, and this disturbance was so extensive and in a way responsible for the difference in geological conditions between the Lower and Middle-Upper Proterozoic in China. The boundary (1900Ma) relative to the Luliangian Movement is more important than that corresponding to the time boundary of 1600 Ma which is recommended as the time boundary between the Proterozoic Ⅰ and Ⅱ, so we propose to use 1900 Ma as the boundary between the Early and Middle Proterozoic in China.The time boundary between the Middle Proterozoic, including the Cha-ngcheng System and the Jixian System, and the Late Proterozoic which is composed of the Qingbaikou and Sinian System is about 1000 Ma. The age for the boundary between Cambrian and Precambrian, based upon the recent isochron data, is inferred to be 610 Ma. |
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