华北克拉通古元古代地层划分与对比

华北克拉通古元古代地层分布广泛,主要集中于胶辽吉带、中部带和西部孔兹岩带三个带状区域。近年来华北克拉通古元古代地层研究取得了很大的进展,根据作者的研究和前人的大量工作,本文对华北克拉通主要的古元古代地层的组成、时代、形成的构造背景等进行了总结。发现华北克拉通古元古代底部2.47～2.35Ga间的地层普遍缺失,反映了华北克拉通地质演化历史上的一个静寂时期。～2.3Ga在华北克拉通中条山及鲁山等地发育了少量的冷口变质火山岩以及上太华岩群变质地层。大量的年代学资料表明华北克拉通以往认为时代大致始于2.5Ga的滹沱群、甘陶河群、辽河岩群、绛县群、中条群等众多地层实际年龄多集中在2.2～1.9Ga之间,而且大多数地区所划分的不同的古元古代地层在时间上是并置或叠合的,没有新老或上下关系,仅在中条山地区和五台地区的古元古代地层具有从老到新连续演化的特征。目前,古元古代早期2.4～2.3Ga的地层研究程度还不高,形成的构造背景存在岛弧和裂谷两种不同的认识,我们倾向于活动大陆边缘环境,推测在鲁山-华山-中条山-吕梁山一带存在古元古代早期的岛弧与活动大陆边缘的相互作用。2.2～1.9Ga这一阶段的地层除孔兹岩系外,通常为变质火山-沉积岩系,且火山岩基本都具有双峰式火山岩特征,表明它们应该形成于伸展环境,但对伸展的机制还存在裂谷与弧后盆地的争议,根据作者等的工作本文倾向于它们形成于陆内裂谷环境,反映了华北克拉通可能从2.2Ga开始经历了强烈的伸展活动,最终导致了原有基底的裂解。

Stratigraphic division and correlation of the Pleoproterozoic strata in the North China Craton: A review

Paleoproterozoic strata are widely distributed in the North China Craton and mainly concentrated in three belts of the Jiao-liao-Ji Belt, Central Belt (Trans-North China Orogen) and western Khondalite Belt. In recent years, great progresses have been made on the Paleoproterozoic stratigraphic research of the North China Craton. Based on previous work and new data, this paper summarizes the main Paleoproterozoic strata in the North China Craton, including the composition, formation age and tectonic setting. There is a general lack of strata of ca. 2.47~2.35Ga, reflecting a Paleoproterozoic quiescence with a shutdown in magmatic activity in the North China Craton. A few stratums of~2.3Ga, including the Lengkou meta-volcanic rocks and metamorphic strata of the Upper Taihua Complex Group, were found in the Zhongtiao Mountains and Lushan area. Geochronological data indicate that the formation ages of Paleoproterozoic strata of the North China Craton, such as the Hutuo Group, Gantaohe Group, Liaohe Group, Jiangxian Group and Zhongtiao Group, are mostly concentrated in the age range of 2.2~1.9Ga. Moreover, different Paleoproterozoic strata in most areas are juxtaposed or overlapped in formation age; there is no relationship between old and new or up and down. Only the Paleoproterozoic strata in the Zhongtiao Mountains area and Wutai area show continuous evolution from old to young. At present, the strata of 2.4~2.3Ga in the Early Paleoproterozoic have not been identified. There are two different opinions on the tectonic setting of island arc and rift; we consider that an active continental margin environment was more believable. It is presumed that the interaction between the Early Paleoproterozoic arcs and active continental margin occurred in the Lushan-Huashan Moutain-Zhongtiao Moutain-Lüliang Mountain area. The strata of 2.2~1.9Ga are usually metamorphic volcano-sedimentary rocks rather than khondalite series, and the volcanic rocks are basically characterized by bimodal volcanic rocks, indicating that they should be formed in the extension environment, but the mechanism of extension (rift or back-arc basin) is still debatable. We tend to an intracontinental rift environment. This means that the North China Craton might undergo a strong extensional activity from 2.2Ga, eventually leading to dissociation of the original basement.