Abstract:

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(75.4377.42) is obviously higher than that of the phenocryst olivine(72.0272.95) 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.   

Key words: Panxi rift, alkalineultramafic rock, zone structure, parent magma, crust contamination