电子探针技术在岩石学中的应用——以沙峪口岩体为例

Electron probe X-ray in petrological analysis:a case study of Shayukou Village

以沙峪口岩体的花岗闪长岩样品单矿物地球化学数据为例,揭示了电子探针在岩石学研究方面的应用,包括矿物种类鉴定、矿物环带结构研究、厘定岩浆过程等。电子探针数据显示:磷灰石的MgO含量由核到边先减小后增加随后又减小,呈震荡变化规律;黑云母的MgO含量为9.07%-9.33%,FeO含量为21.56%-22.06%,Na_(2)O含量为0.1%-0.18%,全碱(Na_(2)O+K_(2)O)含量为7.57%-9.48%,Fe^(2+)/(Fe^(2+)+Mg)的比值为0.75,应归类为铁质黑云母;斜长石的An含量变化为13.78%-28.39%,变化范围较小,与典型岩浆混合过程中结晶的斜长石特征不一致。磷灰石的元素含量变化和矿物学特征指示其形成于岩浆演化过程早期;黑云母属于再平衡原生黑云母,且具有壳幔混合源区属性,指示其形成于岩浆混合作用过程中,与沙峪口花岗闪长岩体中暗色微粒包体和中基性同深成岩墙广泛出露的现象相符合;斜长石由核到边的An含量整体较为均一,指示岩浆演化晚期的均一化过程。

With the help of the geochemical data of single mineral from the Shayukou granodiorite samples,we revealed the us-age of the electron microprobe in geological research,including mineral identification,mineral zonal structure analysis and major element determination used in the magma processes.The electron probe data showed that the MgO content of apatite first de-creased in the core,then increased in the mantle and finally decreased in the edge,showing an oscillation variation pattern.The biotite has a MgO content of 9.07%-9.33%,FeO of 21.56%-22.06%,Na_(2)O of 0.1%-0.18%,total alkali(Na_(2)O+K_(2)O)of 7.57%-9.48%,and Fe^(2+)/(Fe^(2+)+Mg)of 0.75,belonging to the iron biotite.The An content in plagioclase is 13.78%-28.39%,which is relatively uniform overall and inconsistent with the characteristics of plagioclase formed by the typical magma mixing process.The element content and mineralogy characteristics of apatite indicate that it was formed in the early stage of magmatic evolution.Biotite belongs to the re-balanced primary biotite and has the attribute of crust-mantle mixing source area,indicating a production of magma mixing process,which is consistent with the common exposure of mafic microgranular enlaves and neutral to basic syn-plutonic dyke in Shayukou granodiorite.The An contents in the Plagioclase are relatively uniform,indicating the ho-mogenization process in the late stage of magma evolution.