五台山区太古宙/元古宙界线划分及其地球演化意义

太古宙/元古宙界线代表地球演化历史上的重大事件,如何准确标定和划分这一界线对认识早期演化历史具有重要意义。区域构造及同位素地质年代学研究表明,华北克拉通新太古代构造演化明显滞后于欧美澳等克拉通,成为有利于建立太古宙/元古宙界线的关键地区。山西五台山区保留了较完整的新太古代-古元古代地层记录。先前研究主要依据该区地层、区域构造、叠层石记录进行界线划分,并对界线争议较多。本文在五台山区长期野外研究的基础上,通过对磨拉石沉积、同构造花岗岩、裂解环境相关玄武岩的综合探讨,建议这一界线划分在东冶亚群与豆村亚群之间。初步的同位素年龄制约表明,这一界线的时代介于2549±22Ma到2450±10Ma之间,与早期大陆克拉通伸展裂解、隆升剥蚀相关,并涉及岩石圈、水圈、大气圈性质的重大变化。

DIVISION OF ARCHEAN/PROTEROZOIC BOUNDARY AND ITS IMPLICATION FOR GEOLOGICAL EVOLUTION IN WUTAI MOUNTAIN AREA, NORTH CHINA

It is very important to define and divide the Archean-Proterozoic (Ar-Pt) boundary as the boundary represents fundamental evolutionary changes in earth history. As indicated by widespread geological research and high-precision geochronology, the late Archean tectonic evolution of North China craton clearly lagged behind those of Superior and Yilgarn Cratons, but is synchronous with that of Southern India shield. So the late Archean tectonic evolution of North China craton becomes a good candidate and a perfect example in terms of definition of the Ar-Pt boundary. Here the complete Neoarchean-Proterozoic sequences are well preserved in the Wutai metamorphic terrain. Despite the fact that the Wutai area has been widely investigated, much argument remains as to its early Precambrian geological division, which is mainly based on its stratigraphy, regional geology, magmatism, stromatolite correlation. In this paper, the Ar-Pt boundary is divided between the Dongye and Doucun subgroups (with interval of 2549±22Ma~2450±10Ma), and is constrained by the molasses sequence, the syn-tectonic granite, and the flood-basalt. A gap of tens of millions of years is revealed at this boundary. The Ar-Pt boundary in North China marks the onset of cratonic extension, breakup and erosion, which are associated with the evolution of lithosphere, hydrosphere and atmosphere in the region.