关键词: 滹沱群, 沉积组合, 构造样式, 角度不整合, 前陆盆地, 陆内裂谷盆地

Abstract:

The tectonic setting and geological evolution of the Paleoproterozoic Hutuo Group distributed in the Wutaishan area are crucial constraints on the formation time and evolution of the TransNorth China Orogenic Belt between the Western and Eastern Blocks of the North China Craton. Through integrated analyses of the contact relation between the Hutuo Group and underlying geological bodies, the assemblage of the sedimentary sequence, the structural patterns and recent geochronological data of the Group, the following results were obtained: (1) the Hutuo Group unconformably overlies the three geological units of varying metamorphic degrees of the Neoarchean Wutai Group (the Shizui, Taihuai and Gaofan subgroups) and TTG, suggesting that the Neoarchean subductioncollision orogenic belt recorded by the Wutai Group and TTG had completed its collision and orogenic process and then underwent longterm uplift and erosion before depositing the Hutuo Group; (2) both the assemblage of the sedimentary sequence and the tectonic feature of the volcanic rocks of the Group demonstrate the depositional setting of intracontinental rift basins rather than foreland basins; (3) the formation time of the Hutuo Group was 2.141.83 Ga and that of the Wutai Group and TTG ca.2.5 Ga, with a gap of 0.30.35 Ga from the beginning of the Hutuo sedimentation, and thus it is inappropriate to place the two groups into one structure system; (4) the Hutuo Group predominantly underwent a crustal shortening process through regional NWSE structural compression and the structural pattern was an upside down fan in shape and the deformation direction was fixed, which was quite different from that of the Wutai Group of complex deformation history and the fanshaped structural pattern of the general collision orogenic belt. So the Hutuo Group can not be interpreted as forming in foreland basins or backarc (forearc) basins, but forming in the intracontinental rift basins after the ca.2.5 Ga cratonization of the North China Craton. Therefore, the various geological evolution models of assembling the western and eastern blocks of the NCC along the 1.85 Ga TransNorth China orogenic belt through the way of integrating the geochronological, geochemical and metamorphism data need further examination. The research of the field relations between geological units in the Central Orogenic Belt should be enhanced in order that the proposed plate tectonic model of the Belt accords with the geological facts and the misinterpretation is reduced to the least.
Key words: Hutuo Group; sedimentary assemblage; structural pattern; unconformity; foreland basin; intracontinental rift basin
摘要：分布于五台山地区的古元古界滹沱群形成的大地构造环境和地质演化过程，对华北克拉通东、西部陆块之间的华北中部碰撞造山带的形成时代和演化具有关键性的地质约束。通过对滹沱群与下伏地质体之间的接触关系、滹沱群沉积岩石序列组合特征、构造变形样式和已有同位素年代学资料的综合分析，认为（1）滹沱群呈区域性角度不整合覆盖于新太古代五台群变质程度不同的3个地质单元（石咀亚群、台怀亚群和高凡亚群）和TTG之上，说明了滹沱群沉积之前，以五台群和TTG为地质记录的新太古代俯冲碰撞造山带已经完成了其碰撞造山过程，并且之后还经历了漫长的抬升剥蚀作用；（2）滹沱群的沉积岩石序列组合和火山岩构造属性指示了其具有克拉通内裂谷盆地基本特征，而不具备前陆盆地沉积序列组合的特征；（3）滹沱群形成时代为214~183 Ga，而五台群及其TTG等形成于25 Ga左右，与滹沱群开始接受沉积的时间相差03~035 Ga时间跨度，因此，把两者置于同一个构造演化系统在时间上也是不恰当；（4）滹沱群主要经历了一次区域性北西南东向构造挤压作用下的地壳缩短过程，构造样式呈倒扇形构造，并且变形方位稳定，与五台群经历了复杂的多期变形的构造样式显著不同，也与碰撞造山带一般具有的正扇形构造样式不同。因此，滹沱群不能被解释为华北克拉通中部碰撞造山带的前陆盆地或弧后（前）盆地，而是25 Ga华北克拉通化后的陆内裂谷盆地。那么，目前主要依据地质年代学、地球化学和变质地质学的资料而提出的华北克拉通东、西部陆块是通过华北中部185 Ga碰撞造山带碰撞拼合而克拉通化的各种构造演化模式值得进一步商榷，特别是应加强华北中部造山带内不同地质体构造单元之间的野外地质关系研究，使得华北中部板块构造演化模式更与地质事实相吻合，避免引起可能的误解。

Key words: 滹沱群, 沉积组合, 构造样式, 角度不整合, 前陆盆地, 陆内裂谷盆地