区域变质杂岩的构造序列规律探讨

根据实地观测和有关资料的研究表明,不论前寒武纪地质区或是显生宙的造山带,其变质杂岩普遍存在着构造变形的某些共同规律,表现于面、褶皱和线构造的发生、发展和转化,遵循着大致类同的顺序,形成构造序列,集中反映了区域变质造山带的变形与演化过程。如果将面、褶皱和线构造各序列中同期的构造形迹相组合,就形成构造组合,代表变形幕。相继生成的构造组合表明一个构造旋迴的变形序列。过去对造山带变质杂岩的构造研究很少注意构造演化中的序列规律。

A PRELIMINARY DISCUSSION ON THE REGULARITY OF STRUCTURAL SUCCESSIONS OF THE REGIONAL METAMORPHIC COMPLEXES

Structural elements occurred in rocks suffered deformation and metamorphism always have their own definite positions in time scale of tectonic cycle development and commonly exhibit forms of succession.Three main kinds of tectonic succession,i.e.,the planar,folding and linear,have been classified.Synchronous elements for respective ones constitute the tectonic assemblages which are indicator of alternating episodes ol deformation throughout a tectonic cycle.Study of many representative examples shows that only the earliest cycle to which a rock group subjected possesses relatively complete successive constitution in this group,and all later cycles,superimpose on them in incomplete forms.All of the successions reveal a general trend of prevailing in ductile decteasing throughout process of rock deformation,and are governed by change of ’ strength of thermal flow field within regional metamorphic orogenic belt.Establishment and correlation of structural successions in individual rock group provide important clues for stratigraphic dividing of metamorphic complexes and for the distinguishing of the contact relations between them.Although alternating episodes of deformation may display various superposing relationships,the most complicated one generally exists between D1 and D2.To analyze superimposition,both the basic configuration of deformational episodes and superposing conditions must be considered simultaneously.Tectonic transposition is another form of deformational superimposition,which shows different manners and results for different deformational and metamorphic stages.In addition to planar type,there are also folding and linear transposition.Rock groups of Presinian basement distributed in Anshan area,Liaoning Province,and Songshan area,Henan Provice on the North China platform are chosen as typical examples for illustration.