滇西思茅大平掌矿区火山岩特征及其构造环境

滇西大平掌铜多金属矿床的含矿建造(龙洞河组)主要由细碧岩-角斑岩-石英角斑岩和流纹岩-硅质岩组成,伴有部分火山角砾岩、凝灰岩,属双峰式火山岩组合。火山岩具明显的Na2O>K2O和Nb、Ta、Zr、Hf、Ti亏损。岩石化学和微量元素判别标志指示含矿建造形成于岛弧裂陷环境。结合区域构造古地理资料分析,它是滇西南古特提斯洋壳在晚石炭世-早二叠世由西向东俯冲过程中岩浆作用的结果。

CHARACTERISTICS OF THE VOLCANIC ROCKS IN DAPINGZHANG, WESTERN YUNNAN AND THEIR TECTONIC SETTINGS

The ore bearing formation (Longdonghe Formation), located in the Dapingzhang Cu polymetal deposit in western Yunnan, is mainly composed of spilite, keratophre, quartz keratophyre, rhyolite and siliceous rock with some intermediate acid pyroclastics and tuffites, and belong to the biomodal volcanic association. All rocks exhibit the typical geochemical features of N2O>K2O and remarkable depletion of Nb, Ta, Zr, Hf, Ti. Especially, various petrochemical and trace element discrimination signs of the volcanic rocks indicate that the ore bearing formation in the studied area was developed in a special tectonic setting belonging to a rift basin within island arc. Combined with the data analyses of the regional tectonic palaeogeography, it is pointed out that the ore bearing formation is the result of magmatism due to eastward subduction of the palaeo. Tethys oceanic crust in southwestern Yunnan during late Carboniferous to early Permian.