华北陆台中段吕梁期的SW-NE向碰撞──晋蒙高级区孔兹岩系进入下地壳的构造机制  

EARLY PROTEROZOIC SW→NE COLLISION MODEL FOR THE CENTRAL PART OF THE NORTH CHINA CRATON: IMPLICATIONS FOR TECTONIC REGIME OF THE KHONDALITE DOWNWARD INTO LOWER CRUST IN JIN-MENG HIGH-GRADE REGION

作　　者：吴昌华[1] 钟长汀[1] 

机构地区：[1]中国地质科学院天津地质矿产研究所,天津300170

出　　处：《前寒武纪研究进展》1998年第3期28-50,共23页Progress in Precambrian Research

基　　金：国家自然科学基金!49472141

摘　　要：华北陆台北部近千公里的麻粒岩带并非同为太古宙的同一地体，其东不含孔兹岩系的冀东地体是太古宙古陆，其西含古元古代孔兹岩的晋蒙高级区是吕梁期的碰撞带。孔兹岩系在鄂尔多斯古陆北缘和东缘周边分布，也在冀东古陆西缘分布，分别是两陆缘的古元古代沉积岩系，其间从晋蒙到五台则是太古宙～古元古代的洋弧沟盆系。华北陆台中段在太古宙时期并非为统一大陆，而是由西向东的陆－弹－陆的板块构造格局。晋蒙、吕梁、太行孔兹岩系的构造走向和夕线石线理一致为SW－NE向，不代表原始沉积方位，而是碰撞运动方向。两陆的碰撞可能从太古宙末期就已启动，于吕梁期渐进增强直至陆一陆合拢。碰撞缝合带上部形成的NW向褶皱山带已被剥蚀殆尽，现在出露的碰撞根部带则表现为孔兹岩系、洋壳物质、基底片麻岩三者相互近水平的剪切叠置和构造增厚，因此下地壳缝合带宽而不规则难以识别。据缝合线垂直于碰撞方向推断，原缝合线洋带应为NW向，但因造山带根部剪切不均匀而变位成“之”字形的南北向。以怀安－五台一线为界古元古代孔兹岩系于东西两侧对称分布，从北往南一致发育NW向的中元古代基性岩墙群，东西两侧不变质盖层分别为中上元古界和寒武系，表明从晋蒙到吕梁、五台、太行不但存在过NW向或近南北向的古山链，?The amphibolite- to granulite-facies basemnt of North China platform has consistently been regarded by most of internal and external geologists as a unified Archean craton,consequently the granulite belt in the north part of the craton, extending for about 1000 km from Eastern Hebei west into Jin-Meng (northern Shanxi and Inner Mongolia), has been thought as a unified Archean one either, specially based on 3. 5 Ga±constrains for the amphibolite-facies rocks from Eastern Hebei Province. Taking the presence or absence of khondalite series as the mark, however, this belt can be divided into two segments, having Chicheng as the beundary.The western part (Jin-Meng high-grade region) differs from the eastern (Eastern Hebei terrain)by the developed khondalite and a series of other geological features (Table 1 ).Eastern Hebei terrain with nearly N - S structural trend can be still thought as an old continent that had widely experienced cratonization in the middle and late Archean, whereas Jin-Meng high-grade region is postulated in this paper as an orogenic belt by the collision of Archean Ordos blork on the west of the belt with Eastern Hebei continent. Because the age of khondalite is constrained to be 1. 8~1. 9 Ga (Fig. 1) the timing of collision must be Early Proterosoic that is the Luliang Movementfamous in China. Thus, it can be concluded that the North China craton was once separated during Archena rather than unified.Jin-Meng collision belt can be divided into three subbelts, named Daqingshan granulite,Liangcheng khondalite and Huai'an granulite from north to south, each of which trends NE-SW and parallels another, converging slightly towards NE (Fig. 2). It is generally thought that since the orogenic trend is perpendicular to the motional direction, the collisional orientation was believed to be NW - SE. This view, however, is open to questions because the high-grade region analogous to Mattauer's (1980) orogenic root or the lower structural level (Fig. 3). Thus, the NE trend symbolizes the motional direction

关 键 词：华北陆台中段 孔兹岩系 吕梁运动 SW-NE向碰撞 

分 类 号：P542[天文地球—构造地质学]