Structural and Petrological Studies of Granulite Formation

首先对冈瓦纳东部麻粒岩活动带的构造进行了研究，回顾了已有的研究成果。约1100 Ma的事件以覆褶、逆冲断裂和麻粒岩变质为特征，被认为是收敛构造的特征，反映了东冈瓦纳的合并。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相关的各种褶皱、断裂和变质作用，并被解释为形成已形成地壳的复兴。大约550 Ma的事件与绿粒岩的早期形成有关。与斯里兰卡的沙诺克岩相关的共轭断裂系统显示出与主要褶皱轴正相关的最大伸展应力轴，并被认为支持Yoshida和Santosh（1994）所证明的早期沙诺克岩产状的构造环境。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流体的流入和去除行为。研究发现，CO_2流体与泛非地体中稀有元素伟晶岩有着密切的关系。Sm-Nd同位素系统研究表明，南印度、斯里兰卡和南极洲的主要麻粒岩变质作用形成于约550 Ma。综合这些结果，认为东冈瓦纳泛非麻粒岩形成主要处于伸展构造作用下，极有可能与某些裂陷性地壳条件有关。这些泛非麻粒岩事件的构造情况再次支持Yoshida和Santosh（1994）提出的砂粒岩早期形成的构造模式。

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).