摘要
碧口群由一套中晚元古代的变质双峰式火山岩及复理石型沉积岩组成,其变质作用分为蓝片岩相和绿片岩相。据其野外分布及白云母b_0值的变化可分成A、B、C三个变质带。蓝片岩相以钠质问石+绿帘石共生为特征,在A带的大面积绿片岩中呈条带或残片状分布。对区内的角门石、绿泥石、绿帘石及白云母等矿物及其间的交代关系研究表明蓝片岩和绿片岩并非同一物理化学条件下的产物。蓝片岩相的温度为300—400℃,压力为0.5—0.6GPa;A、B带中绿片岩相的温度与之相似,但压力为0.4GPa左右,从蓝片岩相到绿片岩相代表了一个近等温的抬升过程。碧口群的岩石组合及矿物组合等特征表明其蓝片岩变质作用与陆内小洋盆闭合时所伴随的陆壳加厚或A型俯冲有关。
The Bikou Group is composed of Mid-Late Proterozoic meta-bimodal volcanic rocks and flysch sediments. Its metamorphism can be divided into blueschist and greenschist facies. Three metamorphic belts, i.e. A,B and C belts, are determined according to the field distribution of metamorphic rocks and muscovite bo values. The blueschist is characterized by the coexistence of sodic amphibole and epidote and occurs as bands or remnants in the extensive greenschist of belt A. Studies on minerals such as amphibole, chlorite, epidote and muscovite and on the textural relations between them indicate that the blueschist and greenschist are not formed under the same metamorphic condition as proposed by some geologists. The p-t condition of the blueschist facies is 300-400℃, and 0.5-0.6GPa; the temperature of the greenschist facies in belts A and B is similar to that of the blueschist facies but the pressure is lower, about 0.4 GPa. The transformation from the blueschist to greenschist facies is a nearly isothermal decompressional process. The rock and mineral assemblages of the group indicate that the blueschist metamorphism may be ralated to the crustal thickening or A-type subduction accompanying the closure of an intracontinental small ocean basin.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1994年第3期241-254,共14页
Acta Geologica Sinica
基金
国家自然科学基金(编号 49070098)
关键词
蓝片岩
绿片岩
变质作用
碧口群
metamorphic mineral, greenschist, blueschist, metamorphism, Bikou Group
