福建明溪锆石巨晶中的斜锆石、锆石矿物包裹体及其成因启示

Baddeleyite and Zircon Mineral Inclusions:Evidence for the Genesis of Zircon Megacrysts Related to Cenozoic Volcanic Rocks in Mingxi,Fujian

福建明溪是我国和火山岩有关的锆石巨晶的典型产地。通过对该地的锆石巨晶晶体形态及其包裹体的研究发现,福建明溪锆石巨晶四方柱明显较双锥发育,表面有熔蚀结构,内部结构均匀;锆石巨晶中发现的斜锆石包裹体和其它产地斜锆石相比具有贫大离子半径元素U,Th,Y,Zr Hf高的特点。巨晶中的锆石包裹体的拉曼光谱有两种不同类型,其中一类锆石包裹体的拉曼谱和变质及热处理锆石相似,说明锆石巨晶形成时曾经历过变质作用过程。锆石巨晶及其包裹体特征暗示锆石巨晶不是玄武岩结晶产物,和伴生的刚玉巨晶相比其来源可能更深,是壳一幔物质相互作用产物。

Mingxi,Fujian,is a typical location of zircon megacrysts related to volcanic rocks in China. The studies on the crystal forms and inner inclusions of zircon megacrysts show that zircon megacrysts have more developed prism than pyramid,have surface melting, uniform internal structure. In comparison to baddeleyite inclusions from other localities,the baddeleyite inclusions of Mingxi are depleted in large incompatible elements U,Th and Y,and have higher ratio Zr/Hf. Zircon inclusions in megacryst zircon have two types of raman spectra among which the raman spectra of pseudosecondary zircons are analogous to those of metamorphosed or heat_treated zircons,reflecting the metamorphosed experience of zircon megacrysts. The mineral inclusion studies infer that megacryst zircons are not directly crystallized from the magma of hosted volcanic rocks,may be the product of the interaction between crust and mantle.