太平寨古老变质岩的变质结构

区域变质作用过程中,矿物受到热力与动力作用,相应地发生结晶、重结晶与变形两个方面的变化,产生出多种型式的变质结构。依据变质结构的特点,矿物本身的变化和共生矿物之间的相互关系,可以分析多期变质作用的期次、顺序,也可以鉴别结晶作用与变形作用的先后关系,因此能够通过这种研究来复原变质地体的变质变形历史。本文研究河北省迁西县太平寨地区及附近各地的古老变质地体的变质结构特点,并研讨其地质意义。

METAMORPHIC STRUCTURAL ANALYSIS OF THE ANCEINT METAMORPHIC ROCKS IN TAIPINGZHAI, QIANXI COUNTY,HEBEI PROVINCE

In this paper,the met amorphic texture of early Archaean metamorphic rocks from Taipingzhai,Qianxi County,Hebei,is analysed.According to the characteristics of the metamorphic textures formed during pre-,syn-and post-tectonic crystallization and in the sequence of metamorphism of minerals,there may be divided four metamorphic phases (M₁ to M₄) with four corresponding deformation episodes (D₁ to D₄).The metamorphism in first phase was granulitic grade and yields a Kb-Sr date 3670?230 m.y..Thereafter,the metamorphism retrograded ordinally to upper amphibo-lite facies (M₂,2736 m.y.ago),lower amphibolite facies (M₃,2448 m-y.ago) and greenschist facies (M₄? 1950 m.y.ago?).Each metamorphic phase appeared somewhat earlier than its corresponding deformation period.The metamorphic grades were decreased with time and the deformation intensities had the same trend too.These results obtained are compatible with the studies of metamorphic structures and P-T conditions of the metamorphism.