滇桂交界处古特提斯的洋岛和岛弧火山岩

基于详细的野外调查和系统的岩石化学工作 ,探讨了滇桂交界处二叠纪—中三叠世火山岩的大地构造背景。洋岛玄武岩以弄槐枕状熔岩为代表性火山岩 ,原为古特提斯洋盆中的夏威夷型洋岛 ,现保存在印支期前陆褶皱冲断带的一个外来岩席中。采自鱼塘—那塘、羊加山和甫听河的安山岩—玄武岩指示洋盆从二叠纪至中三叠世一直处于消减中 ,反映了与滇西南古特提斯演化不同的地球动力学背景。以上认识为中、越交界地区构造上属古特提斯造山带提供了新证据 ,为重塑该地的古特提斯演化提供了重要资料。

VOLCANIC ROCKS OF PALEOTETHYAN OCEANIC ISLAND AND ISLAND-ARC BORDERING YUNNAN AND GUANGXI, CHINA

Based on systematic petrochemistry and detailed field survey this paper explores the tectonic settings of volcanic rocks bordering Yunnan and Guangxi during Permian Middle Triassic. The oceanic island basalt is represented by the Nonghuai pillow lava, which is, originally Hawaii type one in the Paleotethyan ocean, an allochthon in the Indosinian foreland fold and thrust belt. In the Tongchang Copper Mine, it can be observed that the thick pillow lava overlies the basalt of oceanic crust, which provides a succession of oceanic island volcanic rocks. The andesitic basaltic rocks from Yutang Natang,the Yangjia Mts. and the Futing River indicate the oceanic basin subducted, overall, from Permian right up to Middle Triassic, only sometimes the plate convergence may be relatively slower so that the compressive stress field relaxed temporarily, which reflects distinct geodynamic background of the Paleotethyan evolution from that in southwest Yunnan. The knowledge provides new testimonies for the area bordering China and Vietnam being, tectonically, Paleotethysides and key data for reconstructing Paleotethyan evolution there.