云南中甸峨眉山玄武岩中超基性—基性岩包体的地幔流体微观踪迹及其熔离成矿意义

通过对中甸峨眉山玄武岩中超基性—基性岩包体的岩相学、电子探针、扫描电镜和能谱分析,发现在光学显微镜下呈黑色不透明的物质,在电子显微镜下表现为硅酸盐和尖晶石族氧化物为主的超显微隐晶—非晶质集合体。结合超微晶矿物晶体化学和元素地球化学分析认为,该物质是一种具熔浆和超临界性质及地幔流体属性的富铁(微晶)玻璃,是深部地质过程中,包含于幔源岩浆并与其同步运移但互不混熔的地幔流体作用遗留的微观踪迹物质。该地幔流体在伴随幔源岩浆的结晶成岩过程中,表现出由硅酸盐→尖晶石→磁铁矿→铬铁矿→钛铁矿的熔离作用,并相应触发主岩和包体岩石的交代蚀变和金属矿化,是推动和引发地壳中成岩成矿的重要动力源和物质源。由此进一步认识到,滇西地区上地幔发育峨眉地幔柱活动,为该区二叠纪之后的不同部位和不同矿种的内生多金属成矿提供了有利的深部地质背景条件。

The Microcosmic Traces of Mantle Fluid and the Implications for Liquation Metallogenesis from Ultrabasic-basic Xenoliths in Emeishan Basalt, Zhongdian, Yunnan

Based on the research of mineralogy and petrology using EMPA,SEM and Energy Spectra,we found a kind of Black Opaque Material(BOM) which is composed of microcrystalline silicate and spinel group mine-rals from ultrabasic-basic xenoliths in Emeishan Basalt.From the crystal chemistry and element geochemistry of these microcrystalline minerals,we draw that they are the products and relics of mantle fluid which is not immixed with the host magma(e.g.basalt magma).During the evolution of the mantle fluid,differentiation by liquation is expressed as silicate→spinel→magnetite→chromite→ilmenite.The mantle fluid can also lead to the alternation and mineralization for host rocks and xenoliths,composing to be an important dynamic and substance source,while the mantle plume in western Yunnan is favorable to the endogenous metal mineralization after Permian.