华北克拉通东部胶北地体早前寒武纪表壳岩系：研究进展与综述

胶北地体是华北克拉通早前寒武纪基底岩系的代表性出露区，变质表壳岩系在该地体的分布较为普遍。由于这些表壳岩系对探究华北克拉通早前寒武纪地质演化历史、资源和表生环境演化等的重要作用，国内外学者从岩石单元划分、时代框架、变质演化、含矿性及对表生环境演化的启示等多个方面开展了研究工作，并取得很多重要的研究进展。但是由于研究者对这些表壳岩系的岩石单元划分提出了多个不同方案，造成了岩石单元定义不清、使用混乱的情况。对表壳岩的岩石类型、空间分布和时间格架的研究，也存在多种不同意见，其中对古元古代变质沉积岩形成时代的争议最大。本文对不同的岩石单元划分方案进行梳理，总结研究进展，并对研究中存在的问题和争议进行讨论，明确未来研究方向。传统观点认为，胶北地体早前寒武纪表壳岩系包括中太古界唐家庄岩群、新太古界胶东岩群以及古元古界荆山群和粉子山群。本文在综述相关研究进展的基础上，结合地质年代学研究结果和野外地质关系发现：(1)唐家庄岩群和胶东岩群的一部分岩石记录太古宙晚期和古元古代两期变质作用，表明这部分岩石的形成时代应该在新太古代之前，但是目前对两个岩石单元的原岩形成时代尚无明确约束；(2)唐家庄岩群变质级别普遍为麻粒岩相，而胶东岩群岩石大多显示角闪岩相矿物组合；(3)分布于昌邑-莱州一带的含铁岩系原来被划归古元古界粉子山群小宋组，一些学者依据新的定年结果提出小宋组的形成时代应该为新太古代(约2.7~2.5Ga)，属于新太古界胶东岩群；(4)古元古代(约2.2~2.1Ga)的花岗岩和辉长岩在胶北地体较为常见，呈现双峰式岩浆特征，在一些地区识别出古元古代岩浆岩与小宋组含铁岩系、荆山群野头组变质沉积岩呈侵入接触关系，暗示两个岩石单元的形成时代应该早于~2.1Ga；(5)从野外产状特征来看，胶北地体唐家庄岩群和胶东岩群的很多变质基性-超基性岩的原岩可能并不是火山岩，而是侵入岩。基于胶北地体古元古代岩浆活动、表壳岩系与其底部岩系的接触关系，并综合考虑其沉积、变质和岩浆活动的时代框架，本文认为胶北地体古元古代表壳岩系形成的构造背景为克拉通伸展盆地，代表华北古元古代活动带在胶北地体的早期响应。虽然关于胶北地体早前寒武纪表壳岩系的研究取得很多进展，但由于多期变质变形的叠加改造，表壳岩原始结构和构造已经被后期变形样式置换，对其岩石单元划分、每个岩石单元的岩石组成、区域对比关系、年代学框架和构造含义等多个方面，仍然存在很多问题和争议有待于深入研究。

A review on the research progress of the Early Precambrian supracrustal rocks in the Jiaobei Massif

The Jiaobei Massif is a typical and representative Early Precambrian terrane of the North China Craton (NCC) and metamorphosed supracrustal rocks are widespread in this area. These supracrustal units are of great importance for the understanding of the tectonic evolution history of the NCC, as well as the mineralization and responses of the environment. Therefore, various studies, concerning the definition of lithological units, the geochronological framework, metamorphism, mineralization and the implications for environmental evolution, have been carried out. However, several different definitions of the supracrustal units of this region exist which are sometimes confusing for detailed studies. This paper first summarizes the different definitions of the lithological units in order to unravel the distinctions and connections between the different models of definition. We then introduce the research progresses, and discuss the questions and controversies, with a purpose of pointing out future research areas. The Early Precambrian supracrustal rocks of the Jiaobei Massif have been traditionally classified into the Mesoarchean Tangjiazhuang Group, the Neoarchean Jiaodong Group, the Paleoproterozoic Jingshan and Fenzishan groups. Based on the summarization of the research progress as well as the new observation results in the field, the following proposals can be made. (1) Part of the lithologies from both the Tangjiazhuang and the Jiaodong Groups show two episodes of metamorphism, during Neoarchean and Paleoproterozoic, indicating that these rocks were formed before the Neoarchean metamorphism. But their protolith ages have not been well constrained. (2) The metamorphic grade of the Tangjiazhuang Group rocks is normally at granulite facies while that of the Jiaodong Group rocks is usually at amphibolite facies. (3) The BIF-bearing lithologies occurring near Changyi was previously classified as the Xiaosong Formation of the Paleoproterozoic Fenzishan Group. Some geologists suggested that this lithological unit was formed during Neoarchean and should be re-allocated to the Neoarchean Jiaodong Group. (4) Although the scales for most outcrops are small, the Paleoproterozoic (ca. 2.2-2.1Ga) bimodal magmatism can usually be seen in this region and they can be seen showing intrusive relations with the lithologies of the Xiaosong Formation as well as the Paleoproterozoic meta-sedimentary rocks of the Yetou Formation, Jingshan Group, implying that rocks of both lithological units are older than the Paleoproterozoic magmatic rocks. (5) Field occurrences of the metamorphosed mafic-ultramafic rocks of both the Jiaodong and Tangjiazhuang Groups tend to imply that they were previously intrusive rocks, rather than volcanic rocks. Based on the occurrences of the Paleoproterozoic bimodal magmatism, the contacting relations between the Paleoproterozoic sedimentary rocks with Archean basement, and in combination with the geochronological framework of magmatism, sedimentation and metamorphism, we propose that the Jingshan and Fenzishan Groups were formed in an extensional basin. This basin is the early response of the Paleoproterozoic mobile belt in this area. The research achievements notwithstanding, questions and controversies still exist because of the multiple episodes of high-grade metamorphism and deformation of this region. Future studies should pay special attention on the definition of the lithological units and their rock assemblages, regional comparison, detailed geochronological framework and tectonics implications and so on.