扬子陆块西缘晚古生代玄武岩浆的性质和演化——玄武岩-辉绿玢岩稀土元素-微量元素地球化学研究

以四川和云南晚二叠世-早三叠世形成的峨嵋山玄武岩和同期形成的龙门山、墨江辉绿玢岩为主要研究对象,结合与勉略、三江蛇绿岩套内的玄武岩的对比,从岩石的化学成分、稀土元素和微量元素的含量和特征比值分析,提出晚古生代扬子陆块西缘的基性岩浆活动经历了由特提斯洋壳俯冲诱发陆块内玄武岩浆的发生、洋壳消减和陆块内大规模玄武岩浆喷发及局部小规模岩浆活动的萎缩消亡3个发展演化阶段.扬子陆块内玄武岩浆主要来源于正常或富集型地幔,在发生和萎缩阶段部分岩浆源自亏损型地幔.扬子陆块西缘晚古生代时期的基性岩浆活动是全球岩石圈构造活动的局域表现,与特提斯洋的俯冲-封闭有直接联系.

NATURE AND EVOLUTION OF LATE PALEOZOIC BASALTIC MAGMAS ALONG WESTERN MARGIN OF YANGTZE CRATON: GEOCHEMICAL STUDY OF REE AND TRACE ELEMENTS

Emeishan basalt, Longmenshandiabase-prophyrite, and Mojiang diabase-prophyrite in the Late Permian-Early Triassic areimportant objects of the present paper. A correlation between the basalt in the Mianle ophiolitesuite and that in the Sanjiang ophiolite suite can be used to suggest, on the bases of thechemical compositions of the rocks, the contents of the REE and trace elements, and theratio of special elements in these rocks, that the Late Paleozoic basic magmatic activityin the western margin of Yangtze craton can be divided into three evolutionary stages (1)basaltic magma in Yangtze continent was induced by the subduction of Tethyan oceaniccrust; (2) the basaltic magma erupted on a large scale within the Yangtze craton with thesubduction of Tethyan oceanic crust, and (3) the magmatic activity turned weaker andweaker until it was extinct within a limited region. The basaltic magma within the Yangtzecraton mainly originated from the normal or concentrated mantle. During the initial andfinal evolutionary stages, part of magma originated from the depleted mantle. The LatePaleozoic basic magma activity in the western margin of the Yangtze craton must have beenpart of the tectonic changes of the global lithosphere and, therefore, must have beendirectly correlated with the subduction of Tethyan oceanic plate.