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Structural and Petrological Studies of Granulite Formation

麻粒岩地层的结构和岩石学研究

基本信息

批准号：
06640623
负责人：
YOSHIDA Masaru
金额：
$ 1.28万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

Tectonics of granulite mobile belts in East Gondwana were studied first, reviewing various published studies. The ca 1100 Ma events are characterized by overfolds, thrust faults, and granulite metamorphism which are regarded to be the characteristics of convergent tectonics and thus are explained to reflect the amalgamation of East Gondwana. The ca 550 Ma events which are correlated with the Pan-African events in West Gondwana include various folds, faults and metamorphisms associated with extensive granitic activities and are explained to form the rejuvenation of already formed crust. The ca 550 Ma events are associated with the incipient charnockite formation. The conjugate fracture system associated with this charnockite in Sri Lanka shows maximum extenstional stress axis normal to the major fold axs and is regarded to be supportive to the tectonic setting of the incipient charnockite occurrence demonstrated by Yoshida and Santosh (1994). During the middle to later periods of the research project, various analysis of granulite samples from the above areas were conducted and the following results were obtained. Carbon isotope studies of graphite and fluid inclusion studies clarified the influx and removal behavour of CO_2 fluid during the granulite metamorphism. It was found that there is an intimate relationship of CO_2 fluid with the rare element pegmatites which are characteristic in the Pan-African terranes. Studies of Sm-Nd isotopic systematics clarified the major granulite metamorphism of South India, SriLanka and Antarctica to have formed at ca 550 Ma. Compiling these results, the Pan-African granuilte formation in East Gondwana is considered principally to be under the extensional tectonics, most possibly related with some riftogenic crustal conditions. All these tectonic situations of the Pan-African granulite events are again supportive to the tectonic model of the incipient charnockite formation proposed by Yoshida and Santosh (1994).

本文首先对冈瓦纳大陆东部麻粒岩移动的带的构造进行了研究，并对各种已发表的研究成果进行了回顾。1100 Ma左右的事件以褶皱、逆冲断层和麻粒岩变质作用为特征，反映了东冈瓦纳板块的拼合作用。与西冈瓦纳泛非事件相关的约550 Ma事件包括与广泛的花岗岩活动有关的各种褶皱、断层和变质作用，并被解释为形成已形成地壳的再生。约550 Ma的事件与早期紫苏花岗岩形成有关。与斯里兰卡紫苏花岗岩相关的共轭断裂系统显示出最大伸展应力轴垂直于主要褶皱轴，并被认为支持Yoshida和Santosh（1994）所证明的早期紫苏花岗岩产状的构造背景。在研究项目的中后期，对上述地区的麻粒岩样品进行了各种分析，得到了以下结果。石墨碳同位素研究和流体包裹体研究阐明了麻粒岩变质过程中CO_2流体的流入和排出过程。发现CO_2流体与泛非大陆特有的稀有伟晶岩有密切的关系。Sm-Nd同位素系统学研究表明，印度南部、斯里兰卡和南极洲的麻粒岩变质作用形成于550 Ma左右。综合这些结果，认为冈瓦纳东部泛非麻粒岩建造主要是在伸展构造作用下形成的，很可能与某些裂陷地壳条件有关。泛非麻粒岩事件的构造环境再次支持了Yoshida和Santosh（1994）提出的早期紫苏花岗岩形成的构造模式。