秦岭地幔柱源岩浆活动及其动力学意义

通过秦岭不同时代玄武岩地幔源区类型的地球化学鉴别 ,揭示出北秦岭地幔柱源岩浆活动开始于古元古代 ,并至少断续延续到新元古代中晚期 ;而南秦岭地幔柱源岩浆活动则开始于中元古代晚期 ,并至少延续到新元古代之末。根据地幔柱活动中心显示出的随时间自北向南迁移的规律 ,结合该区北面的商丹洋盆打开在前 (新元古代—早古生代 ) ,南面勉略洋盆打开在后 (晚古生代 ) ,两洋盆均属于扬子陆块内部裂解类型 ,以及北秦岭于新元古代前属于扬子板块等情况 ,提出秦岭造山带发展动力学特征表现为扬子的裂解和华北的增生 ,并处于全球冈瓦纳大陆裂解和亚洲大陆增生的总动力学体系之中。

MAGMATIC ACTIVITIES FROM PLUME-SOURCEIN THE QINLING OROGENIC BELT AND ITS DYNAMIC SIGNIFICANCE

Mantle sources of the basalts of different geological periods from Qinling Orogenic Belt are geochemically identified. The results indicate that the magmatic activity of plume-type in North Qinling began at the Paleoproterozoic and lasted episodically till at least the Late Neoproterozoic, whereas that in South Qinling began at the Late Mesoproterozoic and lasted episodically till at least the end of Neoproterozoic. Therefore, the center of the plume magmatic activity migrated with time from the north to the south in the whole Qinling region. In the orogenic belt the northern Shang-Dan ocean was opened earlier at the Neoproterozoic ,whereas the southern Mian-Lue ocean at the Late Paleozoic. The two ancient oceanic basins have proved to be formed by continental break-up within the Yangtze plate, and the North Qinling has been identified to belong to the Yangtze plate prior to the Neoproterozoic. Based on synthesis of the above information, it is suggested that the orogenic development in Qinling should be expressed dynamically as the form of the Yangtze plate dispersion and the North China plate accretion.