新元古代—寒武纪高精度同位素地质年代学李献华

兰中伍

摘 要：华北地台周围前寒武纪晚期的地层对比格架和演化历史逐渐成为地质学界研究的焦点，受到了国内外地质学家广泛的关注。其中，从蓟县剖面的侵入岩或者间层火山灰中测得的锆石U-Pb年龄已经为华北地台北缘中新元古代地层高精度年代格架提供了确凿证据。这些年龄数据不仅解决了这套中新元古代地层的划分和全球对比问题，而且为前寒武纪生物的起源和演化也提供了时间锚点。相比之下，由于缺乏可靠的同位素年龄制约，华北地台南缘的汝阳群和洛峪群，苏皖北部的徐淮群、辽南地区的金县群、五行山群、细河群、永宁群的沉积时限和地层归属问题一直存在争议。同样，华南南华系（也即国际上的成冰系）的底界及年龄、长安冰期和古城冰期的年龄以及南华系的划分及对比问题也一直未得到解决。华北地台北缘和南缘这套中-新元古代地层蕴含着丰富的疑源类和宏观藻类以及可能的后生动物实体化石和遗迹化石等生命信息，而且其沉积过程伴随着哥伦比亚超大陆的裂解。华南成冰系地层的沉积伴随着罗迪尼亚超大陆的裂解演化，冰期蕴含丰富的疑源类、宏观藻类和多细胞动物化石，因此，对华北地台周边元古代地层以及华南成冰系地层进行精确的年代约束、重新厘定其地层划分对比，将为哥伦比亚超大陆和罗迪尼亚超大陆的裂解演化以及早期生命的起源演化等重大科学问题提供新的年代学证据。

关键词：华北 华南 元古代 地层 沉积年龄

Abstract：Late Precambrian stratigraphic correlation framework and evolution history around the areas bordering the North China Craton （NCC） has increasingly become the target of intense research that attracted comprehensive domestic and foreign attention. Intermittent reports of zircon U-Pb ages from intrusive rocks or interbedded volcanic tuff beds within critical stratigraphic horizons have provided solid evidence for establishing high precision chronostratigraphic framework for the Meso-Neoproterozoic strata in the Jixian Section， northern margin of NCC. These absolute ages not only have contributed to the classification of the Meso-Neoproterozoic strata in NCC and its global correlation， but also have provided key age constraints on the origination and evolution of Precambrian biota， especially on the macroscopic algae. In contrast， owing to lack of reliable radiometric age constraints， the depositional ages and stratigraphic attributions of the Ruyang and Luoyu groups in the southern margin of NCC， the Xuhuai Group in northern Jiangsu and Anhui provinces， the Jinxian， Wuhangshan， Xihe， and Yongning groups in southern Liaoning Province has long been disputed. Likewise， the age of the Nanhuan System （equivalent of Cryogenian） in South China is loosely controlled. The Proterozoic strata bordering the NCC contain abundant acritarchs， macroalgae， and possible metazoan fossils， their deposition being accompanied by the breakup of Columbian Supercontinent. Likewise， the formation of Nanhuan System was accompanied by the breakup of Rodian Supercontinent， and contains abundant acritarchs， macroalgae， and multicellular life fossils. Accordingly， precisely dating the depositional ages of the Proterozoic sedimentary successions distributed in the north and south China blocks will provide new， reliable age constraints on the breakup history of Columbian and Rodian supercontinents， and on the origin and evolution of early life.

Key Words：North China； South China； Proterozoic； Strata； Depositional age

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