关键词: 紫金山碱性杂岩体, 矿物学特征, 电子探针分析, 岩体成因

Abstract:

With pyroxene, feldspar and nepheline as the study objects and by using electron microprobe technology, the authors discussed the petrogenesis for Zijinshan complex on the basis of petrography and petrogeochemistry study. The petrochemistry data shows that Zijinshan complex is a potash-rich alkaline-parlkaline rock. According to the mineral assemblages in rocks for different periods, the rocks in seven periods can be divided in two magma series: classical alkaline magma series and non-classical magma alkaline series.  Rocks belong to classical alkaline magma series contain feldspathoid (nepheline or leucite), orthoclase, and aegirine-augite (sodic pyroxene) except rocks at the third stage, and there is no plagioclase. However, rocks belonging to non-classical alkaline magma series contain diopside (calcium pyroxene), and parts of them contain plagioclase without feldspathoid.  Combined with the data of Sr-Nd isotope for whole rock in two magma series and the regional geological materials, it can be speculated that the petrogenesis of Zijinshan complex is as following: continuous asthenospheric upwelling made asthenosphere mantle，lithosphere mantle and lower crust  melt and mixed by different proportions for several times，and then each episodic of mixed magmas welled up to the shallow area of the crust. The proportions of crust-derived material in rocks from different stages are different, and they can be divided into two rock series by their mineral assemblages.

Key words: Zijinshan alkaline complex, mineral characteristic, electron microprobe analysis, petrogenesis