东海榴辉岩的早期退变质——后成合晶的形成、特点及地质意义  

Early Retrometamorphism of the Donghai Eclogite:The Formation and Characteristics of Symplectite and Its Geological Implications

作　　者：杨天南[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2001年第1期91-96,共6页Acta Geologica Sinica

基　　金：地质矿产部重大项目"大别造山带动力学及成矿"(编号9501102);"中国大陆科学钻探"项目的部分成果。

摘　　要：在苏北东海地区出露一种由富石榴子石基质与绿辉石脉组成的榴辉岩。这种榴辉岩有些经历过很强的后榴辉岩阶段变形作用,有些则没有。不论变形与否,其早期退变质均表现为绿辉石脉中沿绿辉石边界发育的细脉状透辉石+钠长石后成合晶。后成合晶的形态及矿物成分变化特点显示:弱变形榴辉岩的退变质作用是在榴辉岩折返到一定深度后,绿辉石颗粒间产生微裂隙,富SiO_2流体进入并与绿辉石反应,形成后成合晶;而在强变形榴辉岩中,伸展性构造变形使绿辉石颗粒间形成微裂隙,富SiO_2流体沿此进入,与绿辉石反应形成后成合晶。不同原因引起的变形为流体进入榴辉岩内部提供通道。榴辉岩的早期退变质发生在绿辉石脆-塑性变形发生转换的温压条件下,反映了榴辉岩折返过程中榴辉岩体与花岗质围岩间的物质交换。Eclogites, consisting of garnet-rich matrix and omphacite veins, occur in the Donghai area, northern Jianasu. Some of them have undergone very intense deformation in the post-eclogite stage, while others not. No matter whether they are deformed or not, their early-stage retrometamorphism is displayed by the development of symplectitic intergrowths of diopside + albite in micro-cracks along grain boundaries within the omphacite veins. The geometry of the symplectite and the compositional variation of relevant minerals demonstrate that the symplectite resulted from the reaction between omphacite and a silica-rich liquid derived from the country rocks of the eclogites through micro-cracks, indicating material exchange between the eclogites and their country rocks-granitic gneissduring the exhumation of the eclogites. It is also demonstrated that deformation plays a significant role in the retrometamorphism of the eclogite.

关 键 词：榴辉岩 后成合晶 微裂隙 变形作用 退变质作用 

分 类 号：P588.12[天文地球—岩石学]