攀西裂谷南段鸡街碱性超基性岩矿物学与岩石化学

对攀西裂谷南段云南鸡街碱性超基性岩的岩相学、矿物化学和岩石化学进行了详细研究。单斜辉石和霞石是该岩体的主要造岩矿物,两者互为消长,在霞霓钠辉岩、霓霞岩和磷霞岩中以不同比例组合。辉石多见环带结构,辉石包裹橄榄石的包裹结构和反应边结构发育,共同指示岩浆的快速侵入结晶过程。橄榄石捕掳晶的Fo=75.43～77.42,明显高于同期结晶橄榄石的Fo值(72.02～72.95),可初步判定母岩浆经历了早期的橄榄石分异。通过对全岩主要化学成分及相关组合参数(M、CA、AR、SI、DI)的研究,判定母岩浆系钠质强碱性Si不饱和岩浆。在Harker图解上MgO与其他氧化物均呈良好的相关关系,指示岩浆演化过程中经历了橄榄石和单斜辉石控制的分离结晶作用。lgSI与主量氧化物成分间具有良好的相关关系,指示岩浆演化过程中很少或未受到大陆地壳混染作用。

A study of mineralogy and petrochemistry of Jijie alkaline-ultramafic rocks, southern part of Panxi rift

This paper reports the lithofacies, mineral-chemistry and petrochemistry of alkaline-ultramafic rock complex in Jijie, the southern part of Panxi rift, Yunnan Province. Clinopyroxene and nepheline are the main component minerals, which have negative correlations in melteigite, ijolite and urtite. The Fo value of xenocryst olivine(75.43 - 77.42) is obviously higher than that of the phenocryst olivine(72.02 - 72.95) in melteigite, which suggests that the parent magma had undergone a previous olivine crystal differentiation. The prevalent zone structure in clinopyroxene, and the package structure and reaction edge structure between clinopyroxene and olivine indicate a relatively rapid ascent and crystallization progress of the parent magma. The characteristics of the major elements and related parameters (M, CA, AR, SI, DI) suggest that the parent magma of Jijie complex was strongly Si-undersaturated, Na-rich alkaline magma. The well linear correlation between MgO and other oxides in Harker diagram indicates that olivine and clinopyroxen were the main crystalline phase during the magma fractionation. The well linear correlation between lgSI and the compositions of major oxides suggests that there was no or little crustal contamination during the magma evolution.