罗迪尼亚超大陆与晋宁运动和震旦系

云南晋宁地区即晋宁运动命名地的区域地质表明,晋宁运动指的是发生在中元古代晚期的一次区域性造山运动,其大地构造性质和时代完全可以与国际上格林威尔造山运动进行对比,因此以下震旦统底界作为晋宁(运动)不整合面的认识有悖于命名地的地质事实,也违反了不整合面地质意义的判定原则。扬子、塔里木等陆块的晋宁期造山作用记录表明,在罗迪尼亚超大陆聚合过程中它们作为小型陆块被包裹在格林威尔造山带之中;而华北陆块可能属于西伯利亚大陆的一部分参与了超大陆的聚合过程。新元古代早期,扬子陆块周缘地段发育的火山—沉积岩系是大陆裂解作用的产物,标志着罗迪尼亚超大陆解体的开始。其中,大部分的裂谷在莲沱期泛海侵沉积之前就已夭折,仅有边缘区的一些裂谷发展成裂陷槽或洋盆。因此,在扬子陆块莲沱期泛海侵沉积在区域上高角度不整合沉积在晋宁期夷平面之上,在局部地段平行或小角度不整合沉积在夭折的裂谷沉积之上,而在裂陷槽和大陆边缘区则为连续沉积。考虑到国际晚前寒武纪研究的趋势,本文建议将传统的震旦系予以解体:提出震旦系(纪)应只含灯影组(期)和陡山沱组(期),对应国际地层指南中的新元古Ⅲ纪代;建立独立的南华冰纪和扬子纪。

JINNING MOVEMENT AND SINIAN SYSTEM IN CHINA:THEIR RELATIONSHIP WITH RODINIA SUPERCONTINENT

Based on the study of regional geology in Jinning area, Yunnan province, we suggested that the Jinning movement was an orogenic movement during late period of Middle Proterozoic, and it could be compared with the Grenville orogeny. The study of Jinning movement in the Yangtze and Tarim blocks suggested that the both blocks were some kinds of small massifs lie in the Grenville orogenic belt which developed between the Australian and Siberian continents within the matching of Rodinia supercontinent. However, the records of Jinning movement in strata along the southern margin and the Proterozoic sedimentary cover of North China block, did not undergo the deformation and metamorphism. This evidence indicated that the North China should be a part of Siberian continent when the Rodinia matched and the orogenic belt lies in the south. During the early of Late Proterozoic (900 Ma ago), the rifting of Yangtze block might imply the splitting of Rodinia. The most of the continental rifts were abortive, but a few of the rifts continued to develop into aulacogen and ocean, such as the Danzhou aulacogen and the Qinling-Dabie ocean. The Lower Sinian was a series of continental littoral facies, and covered the planation surface in the Yangtze block and deposits of the abortive rifts. So, it was easy to find the high angle unconformity between the Lower Sinian and planation surface territorially, and we could also observe the low angle unconformity or disconformity between the Lower Sinian and the deposits of abortive rifts on some locations. And at the same time, there was no unconformity between them in the aulacogen or passive margin. Based on the above discussion, the authors suggested the following opnions. The Jinning movement was an orogenic movement, occurred during late period of the Middle Proterozioc; and the Sinian should be shortened to include the Dengying and Doushantuo Formations only.