含柯石英超高压榴辉岩的早期变形——以苏北东海碱场榴辉岩体为例  

EARLY DEFORMATION OF COESITE-BEARING ULTRA-HIGH-PRESSURE ECLOGITES:AN EXAMPLE FROM JIANCHANG,DONGHAI COUNTY,NORTHERN JIANGSU PROVINCE,CHINA

作　　者：索书田[1] 杨启军[2] 钟增球[2] 周汉文[2] 游振东[2] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质大学地球科学学院,湖北武汉430074

出　　处：《地质科技情报》2003年第4期1-8,共8页Geological Science and Technology Information

基　　金：国家重大基础发展项目(G19990755506);国家自然科学基金资助项目(49972067)

摘　　要：以超高压矿物组合的各种后成合晶及冠状体等卸载不平衡结构为参考标志,将含柯石英的超高压榴辉岩的变形序列分成两个部分。后成合晶及冠状体发育之前的变形为早期变形,是在大陆深俯冲和碰撞条件下发育的超高压变质变形组构。后成合晶及冠状体发育之后的变形为晚期变形,是在超高压岩石折返剥露过程中,主要是在角闪岩相甚至绿片岩相条件下发育的。构造上江苏省北部东海县碱场含柯石英榴辉岩体,分为块状榴辉岩和面理化榴辉岩两种类型,分别代表超高压变质岩早期变形的两个构造阶段或世代(D1、D2)。详细描述了它们的矿物组合、中小尺度及显微尺度下的组构特征,讨论了两者的几何关系和区域构造意义,强调指出,只有含柯石英榴辉岩的早期变形组构,才能记录和反映斜向大陆深俯冲及碰撞的动力学过程。The Jianchang coesite-bearing eclogite body exposed within the Dabie-Sulu ultra high-pressure (UHP) metamorphic belt experienced a polyphase metamorphic and deformation evolution. Two structural types of eclogite rocks in the Jianchang eclogite body can be distinguished,called massive eclogite and foliated eclogite respectively. Both the massive eclogite and foliated eclogite typically underwent plastic deformation under UHP eclogite-facies conditions,and formed prior to the various fine-grained symplectite and corona formation around the host mineral grains. Outcrop to microscale eclogite fabrics, representing the early deformation (D_1,D_2) of coesite-bearing eclogites, are dominantly described. The massive eclogites, generally occurring as decimetre zised lenses, are surrounded by the foliated eclogites, forming a clast-matrix rheology pattern. The structures similar to those in the Jianchang eclogite body are visible in different parts of the Dabie-Sulu UHP metamorphic belt. The absence of a larger reference frame makes the movement picture difficult at a regional scale during the early deformation stages to constrain. However, there are a few areas where abundant, rather scarse kinematic and strain indicators are probably suspected to be related to the oblique deep suduction and collision, such as asymmetric massive eclogite lenses or boudins, S-C structures and asymmetric, tight vertical folds with hinges lying subparallel to mineral stretching lineations, displaying mainly a compressional regime accompanied by a significant component of subhorizontal right-lateral shearing. Several lines of evidence indicate that only the early deformation fabrics would record and reflect the dynamic processes responsible for the deep subduction, collision and the formation of UHP metamorphic rocks. Naturally, very precise and reliable petrological and chronological data for the Dabie-Sulu UHP metamorphic belt are required.

关 键 词：超高压变质岩 含柯石英榴辉岩 块状榴辉岩 面理化榴辉岩 深俯冲 变形组构 

分 类 号：P542.2[天文地球—构造地质学]