中国东南大陆边缘若干问题的认识

中国东南大陆边缘自元古宙以来就以沟-弧-盆形式向洋增生扩张。浙闽变质带属于震旦纪至早古生代岛弧。华南地槽区是在这一时期由扩张作用形成的弧后盆地。这一沟弧盆系统在加里东期褶皱变质,与大陆拼贴。在晚古生代,沿海地区有新的扩张带形成。周期性的扩张和挤压是中国东南大陆边缘地壳演化的特征。

AN UNDERSTANDING ON PROBLEMS ABOUT THE CONTINEN-TAL MARGIN OF SOUTHEASTERN CHINA

Different viewpoints about the tectonic framework of continental margin of Southeastern China heve existed for a long time. Disagreements have recently been focused on the tectonic significance of the metamorphic basement in Zhejiang and Fujian Provinces and Caledonian fold belt in South China.Based on study of think isotopic chronology, stratigraphy and petrology, we think that Zhejiang Fujian region was in an old island arc environment after Jinning Movement, Early-middle Proterozoic tectonic formations in this region were of some separated island uplifts rather than of integrated ancient continent. These island uplifts was a part of the Jiangnan Old Land, and have been separated from it in late Proterozoic to form an island arc during Sinian to Early Palaeozoic. Caledonian geosynclinical area in South China is an arc-back basin formed by spreading activity. In late Cambrian Period, tectonic movement in this area changed from spreading to compression, as a result, Zhejiang-Fujian region was metamorphosed, and the back-arc basin in South China began to close. In late palaeozoic Era, new spreading belt was developed in the coastal area. Island arc zone of the same age probably existed beyond the spreading belt.Crustal movement in the continental margin of Southeastern China is characterised by periodical spreading and compression. In the period of spreading fragments of crust was separated from the continent, and floated towards the ocean, and island and back-arc basin were hence formed. During the period of compression backarc basin was closed, and the island arcs were attached to the continent. As a result of the evolution, the continent accretes gradually towards the ocean