峨眉山玄武岩是弧后扩张的产物吗?

本文对峨眉山玄武岩产于弧后扩张环境的论点提出了质疑。主要论据是:(1)近年来的调查表明,与此相关的金沙江—哀牢山俯冲带(及甘孜—理塘俯冲带)在海西—印支期是向西而非向东消减的;(2)从峨眉山玄武岩的主要和微量元素成分中未探查出可靠的来自消减带的组分;(3)古地磁的观测结果说明,晚二叠世扬子地块位于南半球很靠近赤道的低纬地区,此后扬子地块即迅速向北漂移;(4)世界上绝大多数大陆溢流玄武岩的形成与消减过程无关。因此,作者认为,峨眉山玄武岩的成因与消减作用无明显关系,它的喷发很可能是由于古生代末扬子地块西缘及邻区的地幔区域性上涌,从而导致了有关陆块的破裂和分离。

WERE THE EMEISHAN BASALTS ERUPTED AS A CONSEQUENCE OF BACK-ARC SPREADING?

In this paper the suthor is challenging the claim that the Emeishan basalts were erupted as a consequence of back-arc spreading, with the following arguments: (1) the investigation in recent years indicates that the subduction polarity of the Jinshajing-Ailaoshan suture zone (as \\ell as the Ganzi-Litang suture zone) might well point to the west rather than the east during the Hercynian-Indosinian; (2) no component related to the subduction has been detected from the major and trace element data of the Emeishan basalts; (3) the paleomagnctic study indicates that the Yangtze Block was in the southern hemisphere but very close to the equator in the Late Permian and afterwards drifted fast northward; (4) the eruption of most continenlal flood basalts in the world has little to do with subduction process. It appears that the eruption of the Emeishan basalts was due to the regional upwelling of the mantle in the western margin of the Yangtze Block and neighboring area during the Late Paleozoic, eventually resulting in the splitting and separation of the relavant continental blocks.