摘要
本文对大别山地区的柯石英榴辉岩进行了详细全面的岩相学和矿物化学研究,确定了柯石英榴辉岩的变质条件,识别出了榴辉岩化前的矿物包体及其角闪岩化、绿帘角闪岩化和绿片岩化3期退变质作用,进而再塑了一个呈顺时针方向旋转的复杂P-T-t轨迹。由此讨论了柯石英榴辉岩的形成机制和地球动力学意义。
On the studies of the geological setting,field relationships,petrography and mineral chemistry of coesite eclogites from the Dabieshan,the metamorphic P-T conditions of coesite eclogites are determined, and three retrograded metamorphic stages(amphibolitic,epidote-amphibolitic and green-schist stages) and the metamorphic amphiboles before the coesite eclogite facies metamorphism are understood. The coesite eclogites follow a clockwise P-T-t path,the main feature are the following-(l)The prograde transition from the epidote-amphibolitic facies to the coesite-eclogite facies along a very steep positive P/T- gradient towards very high pressure (P≥ 2. 6GPa) and moderate temperature (T= 600℃ ) > (2)The pressure climax does not match the thermal climax,the maximum temperature conditions are in fact achieved during the early stage of uplift; (3)A decrease in temperature, suggested by the appearance of Na-amphibole after the amphibolitic symplektitej (4)Successive uplift accompanied by a decrease in temperature and pressure. The complexity of the P-T-t path drawn for the coesite eclogites can be explained with two mechanisms; (l)Eclogite climax,characterized by the maximum pressure an by an increase in temperature due to the successive subduction of the o-ceanic crust between the North China and Yangtze plates; (2)successive cooling,interpreted as due to the underthrusting of the cooler tectonic unit. The Dabieshan blueschist belt is probably the tectonic unit responsible for the cooling process reflected by the strong inflection of the P-T-t path of the coesite eclogites.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
1992年第2期141-149,T001,共10页
Earth Science-Journal of China University of Geosciences
关键词
柯石英
榴耀岩
变质作用
P-T-T轨迹
coesite ecloglte,petrography,mineral chemistry,P-T-t path,metamorphic mecha- nism, Dabieshan.
