| 从哥伦比亚超大陆裂解事件论古/中元古代的界限 |
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| 引用本文： | 耿元生,旷红伟,杜利林,柳永清,赵太平.从哥伦比亚超大陆裂解事件论古/中元古代的界限[J].岩石学报,2019,35(8):2299-2324. |
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| 作者姓名： | 耿元生 旷红伟 杜利林 柳永清 赵太平 |
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| 作者单位： | 中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037,中国地质科学院地质研究所, 北京 100037,中国科学院广州地球化学研究所矿物学与成矿学重点实验室, 广州 510640 |
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| 基金项目： | 本文受国家重点研发计划深地资源勘查开采专项（2016YFC0601001）、国家自然科学基金项目（41630211、41472082）和中国地质调查项目（12120115068901）联合资助. |
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| 摘 要： | 国际前寒武纪地层表中始终把古/中元古代的界线置于1. 6Ga,我国则一直将这一界线置于1. 8Ga。存在认识分歧的根本原因是对1. 8Ga前后时期地质事件及其性质的理解与认识的差异或偏颇。本文通过阐述1. 8～1. 6Ga期间地质事件及其性质,重点分析和讨论古/中元古代(界)界限的划分及相关地质事件的标志与意义。大量的地质资料显示,超大陆从1. 8～1. 75Ga开始裂解,形成一系列的陆内盆地,如北美(劳伦古陆)的Thelon盆地、澳大利亚北部的Leichhardt超级盆地、南美巴西圣弗兰西斯科盆地、华北南缘的熊耳裂谷盆地以及扬子地块西南缘的东川盆地等。在这些盆地形成的早期沉积了冲积扇相、河流相的碎屑岩,之后伴有较广泛的火山岩喷发,中晚期从河流相、湖相碎屑岩沉积过渡到浅海碳酸盐台地沉积,反映一个拉伸裂解的过程。在复原的哥伦比亚超大陆内,广泛分布有1. 78～1. 72Ga的非造山花岗岩,包括AMCG组合(斜长岩、纹长二长岩、紫苏花岗岩和花岗岩)、环斑花岗岩、A型花岗岩等,以及广泛分布的基性岩墙群。这些岩浆岩都反映了拉伸裂解的地球动力学背景。在1. 8～1. 6Ga,不论是沉积事件还是岩浆事件,绝大部分与超大陆的拉伸裂解有关,并未显示造山作用、大陆固结和克拉通化的特点,用固结纪来概括这一阶段地质事件的性质并不合适。哥伦比亚超大陆上的许多盆地在1. 6Ga左右经历了一次广泛的抬升,使沉积作用短时间间断,之后原有盆地继续发展,接受了更广泛的沉积,这种沉积作用可以一直延续到1. 4～1. 3Ga左右。与裂解有关的岩浆事件也以幕式方式从1. 78Ga一直断续持续到1. 4～1. 32Ga左右。从1. 8Ga(或1. 78Ga)到1. 4～1. 3Ga,不论是盆地的沉积事件还是与裂解有关的岩浆事件,基本是连续的。以1. 6Ga作为年代界线划分古/中元古代,人为地隔断了连续的沉积事件和岩浆事件,显然与"尽可能少地截断沉积作用、火成侵位或造山运动的主要序列"的前寒武纪地层划分原则相悖。连续的裂谷盆地沉积事件和非造山岩浆事件可以追溯到1. 8Ga(或1. 78Ga)。因此,我们建议将古/中元古代的界线置于1. 8Ga或1. 78Ga。考虑到裂谷作用的本质是在已有超大陆或克拉通的基础上盖层的发育过程,因此我们建议将～1. 8Ga或1. 78～1. 4Ga都归入盖层系。
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| 关 键 词： | 古/中元古代界限 超大陆裂解 裂谷盆地 非造山花岗岩 基性岩墙群 |
| 收稿时间： | 2019/2/1 0:00:00 |
| 修稿时间： | 2019/5/22 0:00:00 |
On the Paleo-Mesoproterozoic boundary from the breakup event of the Columbia supercontinent |
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| GENG YuanSheng,KUANG HongWei,DU LiLin,LIU YongQing and ZHAO TaiPing.On the Paleo-Mesoproterozoic boundary from the breakup event of the Columbia supercontinent[J].Acta Petrologica Sinica,2019,35(8):2299-2324. |
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| Authors: | GENG YuanSheng KUANG HongWei DU LiLin LIU YongQing and ZHAO TaiPing |
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| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China and Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China |
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| Abstract: | In the International Precambrian Stratigraphic Chart, the Paleo-/Mesoproterozoic boundary is always set at 1.6Ga while in Chinese literatures, this boundary is always placed at 1.8Ga. The fundamental reason for this difference is the understanding of the nature of the geological events in this period. This paper focuses on discussing the boundary between Paleoproterozoic and Mesoproterozoic from the nature of the geological events during 1.8~1.6Ga. A large amount of geological data shows that the Columbia/Nuna supercontinent began to stretch and breakup from 1.8Ga to 1.75Ga and formed a series of intracontinental rifting-sag basins, such as Thelon basin in North America (Laurentia), Leichhardt superbasin in northern Australia, São Francisco basin in South America, Xiong''er rifting basin in the southern margin of the North China Craton, Dongchuan basin in the southwestern margin of the Yangtze Block, and others. During the early stage of basin formation, the clastic rocks of alluvial fan facies and fluvial facies were deposited, followed by extensive volcanic eruptions. During the middle and late stage, the ealier fluvial facies and lacustrine facies rocks were overlied by carbonate platform sediments deposited in shallow sea, which reflects a process of stretching and breakup. Anorogenic magmatic rocks of 1.78~1.72Ga distributed widely in continents/blocks that formed the Columbia supercontinent, including bimodal igneous rocks, AMCG assemblages (anorthosite, mangerite, charnockite and granite), rapakivi granite, A-type granite, etc., as well as widely distributed mafic dyke swarms. All these igneous rocks reflect the stretching and breaking process. During 1.8~1.6Ga, both sedimentary events and magmatic events were related to the stretching and breaking of the supercontinent, but did not show the characteristics of orogeny, continental solidation and cratonization. Therefore, it is not appropriate to use the Statherian to summarize the nature of the geological events in this stage. In Columbia supercongtinent, many intracontinental basins experienced a wide uplift at around 1.6Ga, resulting in a short interval of sedimentation. After that, the original basins continued to develop and accepted a wider range of sedimentation, which sustained until about 1.4~1.3Ga. Magmatic events related to supercontinental stretching and breaking can also be intermittent from 1.78Ga to 1.4~1.32Ga. From 1.8Ga (or 1.78Ga) to 1.4~1.3Ga, both sedimentary events in the basins and magmatic events related to stretching and breaking are basically continuous. Therefore, the set of Paleo-Mesoproterozoic boundary at 1.6Ga artificially destroys the continuity of global sedimentary events and magmatic events, which were obviously contrary to the principle that the major sequences of sedimentation, igneous emplacement, or orogeny should be cut off as little as possible in the Precambrian stratigraphic division. Since the time of the successive depositional events in rifting-basins and of the anorogenic magmatic events in continents can be traced back to 1.8Ga (or 1.78Ga), we propose to place the Paleo-Mesoproterozoic boundary at 1.8Ga or 1.78Ga, rather then 1.6Ga. Considering that the rifting process leads to the development of the overlying strata on the preexisting supercontinent or craton, we suggest classifying the sediments of ca. 1.8~1.4Ga into the Calymmian. |
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| Keywords: | Paleo-Mesoproterozoic boundary Supercontinental breakup Rifting basin Anorogenic granite Mafic dyke swarms |
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