湖北省凤凰关地区前寒武纪大别杂岩内构造要素及相互关系

STRUCTURAL FEATURES AND RELATIONSHIPS IN THE PRE-CAMBRIAN DABIE COMPLEX, FENG HUANG GUAN AREA, HUBEI PROVINCE, CHINA

凤凰关地区出露的大别杂岩的混合岩中,至少有30种构造和侵入活动事件,使其构造面貌显得特别复杂。褶皱形式从等斜的片内褶皱、与韧性剪切带紧密伴生的构造到脆性剪切带、尖棱褶皱、开阔褶皱和平缓的弯曲,且大多褶皱都伴有矿物生长以及平行或近平行其轴面或一个翼的淡色脉体的贯入。有些褶皱发育很好的平行枢纽的粗线理,有些褶皱伴生劈理构造。很多长英质新成脉体是谐和的或大体上谐和的,而在韧性剪切带内的淡色脉体则与某些褶皱的轴面平行。根据构造叠加基本原理,可以利用构造间的相互关系来确定变形序列。文中依次描述了各种构造要素,阐述了用于揭示前寒武纪结晶杂岩地质历史的基本野外方法。此外,推测大别杂岩内相继形成的构造是所研究的该部份地壳在一个右行剪切带内遭受连续剪切应变形成的,这个剪切带似乎代表了一个与地体或板块边界平行的带。

More than 30 tectonic and intrusive structures contribute to the complexity of the migmatites of the Dabie complex exposed near the reservoir at Feng Huang Guan. Folds range from isoclinal, intrafolial, through structures closely associated with ductile shear zones to brittle shears,angular folds,open folds and broad warps. Most are associated with mineral growths and,or,leucocratic veins parallel or subparallel with their axial traces or to one or other fold limb. Parallel to some fold hinges there is a well-developed coarse lineation while cleavages are associated with some fold sets. Many of the quartzofeldspathic neosome veins are concor-dant or subcpncordant but leucocratic veins within ductile shear zones are para-llel to some axial planes. Structural relationships permit the determination of a deformational sequence on the basic principle of overprinting. The various structural features are described sequentially and the field - based methods used to unravel the geological history of Precambrian crystalline complexes are illustrated. In addittion, the successively formed structures in the Dabie complex are interpreted as having been formed in a crustal segment subjected continually to shear within a zone which maintained a dextral sense, such as would be the case in a zone parallel to a terrane or plate boundary.