大兴安岭五岔沟地区中生代粗安岩中斜长石环带特征及其地质意义

Zoning characteristics of the plagioclase from the Mesozoic trachyandesite in Wuchagou area of the Da Hinggan Mountains and its geological implications

大兴安岭五岔沟地区中生代粗安岩中的斜长石晶体具有多次熔蚀现象并发育环带结构。长石分类图表明斜长石主要是拉长石,其次为更长石和中长石。通过探讨斜长石环带的成因,认为微量元素含量的变化(Fe、Sr、Ba等)可用来判断斜长石反环带的形成机制。最后根据斜长石环带特征和电子探针成分分析,做出斜长石环带间微量元素Fe和Sr随An的变化曲线,得出该区斜长石在其结晶过程中经历了3次岩浆混合作用的结论。

The plagioclase crystals in trachyandesite from the Late Jurassic Manitu Formation in Wuchagou of the Da Hinggan Mountains have obvious corrosion phenomenon and well-developed zoning texture. The feldspar nomenclature diagram shows that the plagioclases consist mainly of labrador and surbodinately oligoclase and an- desine. The variations of the minor elements （Fe, Sr, Ba, etc. ） composition can determine the formation mech- anisms of reverse zoning on the basis of investigating the causes of plagioclase zoning. According to the evidence from the electron microprobe analyses and textures of the plagioclase, the authors also analyzed the variation curves of trace elements Fe and Sr with An and, on such a basis, reached the conclusion that the zoning resulted from three magma mixing events in the process of plagioclase crystallization.