【摘要】 滇西莴中新生代高镁富钾火山岩富含橄榄石斑晶,其核部Fo含量变化较大（94～75%）,由大斑晶（1mm）、中等粒径斑晶（0．3～1mm）至小斑晶（＜0．3mm）,Fo含量总体变小;橄榄石斑晶CaO含量大于0．1wt%,随着Fo含量的降低,MnO含量升高,而NiO含量降低,并具有明显的岩浆结晶分异趋势,均为岩浆成因,但来源复杂;大斑晶和中等粒径斑晶的核部Fo含量明显与全岩MgO不平衡,均属于捕虏晶来源。橄榄石斑晶中的尖晶石包裹体高Cr^#（0．77～0．94）、低Mg^#（0．17～0．65）,具有较低的Al₂O₃含量（＜10wt%）;尖晶石包裹体的TiO₂含量总体上较低（＜1．0wt%）,暗示了绝大部分橄榄石属于岛弧型岩浆成因,来源于富集交代的方辉橄榄岩部分熔融岩浆;少量高TiO₂尖晶石包襄体（1．36～3．96wt%）的存在则暗示了部分橄榄石斑晶的形成可能与峨眉山大火成岩省有关。大斑晶和中等粒径斑晶橄榄石均具明显的成分梯度变化,由核部、幔部至边部,其Fo、NiO含量降低而MnO、CaO含量增大,并且边部成分特征与小斑晶橄榄石相类似,其源区至少存在两次岩浆作用过程,核部成分变化反映的是早期高Mg^#岩浆中的橄榄石结晶分离作用过程,而边部以及小斑晶橄榄石的成分变化则反映了后期喷发岩浆（Mg^#略低）体系中橄榄石的结晶分离作用过程。更多还原

【Abstract】 Cenozoic high-Mg and K-rich lavas from Wozhong,western Yunnan province contain abundant olivine phenocrysts with Fo in mineral cores varying between 94～75%.As a whole,Fo contents decrease from macrophyric olivines （＞1mm） to medium sized olivines （0.3～1mm） and to the small olivines （＜0.3mm）.All the olivine phenocrysts contain high CaO （＞0. 1wt%）,which is indicative of a magmatie origin.NiO contents decrease with decreasing Fo contents in the phenocrysts,which reflects the fractional differentiation trend in magmas.The origin of these olivine phenocrysts is complex.The disequilibrium between whole rock MgO and Fo contents of the macrophyric and medium olivine cores suggests that they are xenecrysts.The spinel inclusions in olivine phenocrysts have high Cr^#（0.77～0.94）,low Al₂O₃ contents （＜10%） and low Mg^# values （0. 17～0.65）.TiO₂ contents in most of the spinel inclusions are lower than 1.0wt%.This suggests that the majority of olivine phenocrysts were crystallized from arc-type magmas derived from partial melting of metasomatic harzburgite.However,a small number of spinel inclusions are high in TiO₂ （1.36～3.96wt%）,which could be related to the Emeishan flood volcanism.Both macrophyric and medium olivine phenocrysts are compositionally zoned with Fo and NiO contents decreasing,MnO and CaO content increasing from core via mantle to rim.The rims of these large phenocrysts are compositionally similar to small olivines.At least two stages of magmatic processes have been involved in the genesis of the Wozhong high-Mg and K-rich lavas.The compositional variation in the core of the macrophyric and medium phenocrysts may have resulted from fractional differentiation of the early highly magnesian magmas which may not be genetically related to the host magmas.In contrast,compositional trends in the rims and the small olivines were likely related to the differentiation of the more evolved host magmas.更多还原