论华北与扬子陆块的碰撞时代——同位素年代学方法的原理及应用

On the Time of Collision between the North China and Yangtze Continental Segments-the Principle and Application of lsotope Chronology

同位素年代学可以通过测定造山带高压变质岩形成年龄及被动大陆边缘变质、变形年龄来确定陆块碰撞时代。已有研究表明秦岭-大别山带的榴辉岩、兰片岩和高压片麻岩形成於245-209Ma,它们都是扬子陆壳及其下的岩石圈地幔在俯冲时变质形成的。该造山带的扬子被动大陆边缘普遍发育印支期动力变质作用和岩浆活动,缺乏海西期变质和岩浆事件的记录。这些都证明这两大陆块碰撞发生在二叠纪末和三叠纪初,并随后向华北陆块下俯冲。此外,本文对与陆块碰撞有关的一些地质问题也作了必要的讨论。

Isotope chronolgy can be used to determine the time of collision between continontal seg- ments by measuring the formation age of high pressure metamorphic rocks in the orogen and the age of metamorphism and deformation of the passive continental margin. Study has shown that eclogite, blue schist and high pressure gneiss of 245-209Ma in the Qingling-Dabieshan Qrogen were resulted from metamorphism of the subducted Yangtze crust and its lower lithospheric mantle. The Indosinian dy- namic metamorphism and magmatism were widely developed along the passive Yangtze continental margin. There was a lack of the record of Hercynian metamorphism and magmatism. All these suggest that the Yangtze continental segment collided with the North China during late Permian to early Trias- sic, then subducted I. A discussion is also made on the geology related to continental collision.