佳木斯中间地块前寒武纪地质研究

本文对前人确定的黑龙江群与麻山群的界限、接触关系及两群变质地体的性质提出疑义。笔者认为,两群变质地体的界限不在湖南营组(原黑龙江群顶部)与西麻山组(原麻山群底部)之间,而在湖南营组与下伏的原山嘴子组之间;它们不呈整合过渡接触,而是呈构造接触。本文重新认识和研究了黑龙江群变质地体的性质,认为不是区域变质地层单元,而且存在大型韧性剪切带,并论述了大型韧性剪切带的糜棱岩、微构造、变质作用等性质。

PRECAMBRIAN GEOLOGY OF THE JIAMUSI MASSIF

This paper throws doubt upon the boundaries defining the Heilongjiang Group and Mashan Group and the behavior of their contact. Based on researches both in the field and laboratory, the auther of the present paper suggests that the boundary of the two Groups does not follow the boundary dividing the Hunanying Forma tion(e.g.the top part of the Heilcngjiang Croup)from the Ximashan Forma-tion(e.g.the basal part of the Mashan Group) as previously supposed but occurs oetween the Hunanying Formation and the underlying Shanzhuizhi Formation. Besides, the two Groups are not in conformable contact,but in fault contact.The paper concludes, based on a great deal of evidence, that the original Hei-longjiang Group (except the Hunanying Formation)is not a metamorphosed stratig-raphic unit, but a large ductile shear zone made up of varied mylonites, in which microstructuras, plastic flowage and rotational strain of minerals are apparent. The greenschist facies metamorphism of the ductile shear zone was a product in an important tectonic event in which a dynamic retrograde metamorphism was imposed on an original amphibolits facies of rocks. Thus the papar gives a more logical interpretation of the previously noted"retrograde metamorphism".