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首页> 外文期刊>Contributions to Mineralogy and Petrology >The association of potassic trachytes and carbonatites at the Dicker Willem Complex, southwest Namibia: coexisting, immiscible, but not cogenetic magmas
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The association of potassic trachytes and carbonatites at the Dicker Willem Complex, southwest Namibia: coexisting, immiscible, but not cogenetic magmas

机译：纳米比亚西南部的迪克·威廉综合体中的钾质长粒滑石和碳酸盐岩的组合：共存，不混溶但非共生岩浆

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摘要

The only significant silicate intrusive rock type in the Dicker Willem carbonatite complex is trachyte, forming, in places, an anastomosing array of minor intrusions cutting basement gneiss close to the carbonatite contact. Bodies are predominantly composite breccias, composed of trachyte clasts, commonly in the form of ellipsoidal pellets, enclosed within, and sharply delineated from, a matrix of carbonatite. Despite close temporal and spatial relationships to carbonatite magmatism, the ultrapotassic, quartz-normative composition and isotope systematics of the trachytes preclude any genetic derivation from the carbonatitic and ijolitic rocks of the central complex. Sr, Nd and Pb isotope ratios of trachytes strongly resemble those of the highest grade, potassic fenites, whose metasomatic trend converges from the unaltered basement gneiss towards the homogeneous signature of the nepheline sovite-sovite-ijolite suite. Trachytes are interpreted as forming by melting of a cupola of high-grade fenite in response to the advective heat flux from rising carbonatite magma or fluid. Mixed carbonatite and trachyte were emplaced in a fluidised system as contemporaneous, but genetically unrelated, immiscible magmas.
机译：Dicker Willem碳酸盐岩复合物中唯一重要的硅酸盐侵入岩类型是长曲形岩，在某些地方形成了一个吻合排列的细微侵入物，切割了靠近碳酸盐岩接触的基底片麻岩。物体主要是复合角砾岩，由角砾岩碎屑组成，通常呈椭圆形颗粒状，包裹在碳酸盐岩基质中并从中清晰地描绘出来。尽管与碳酸盐岩的岩浆作用在时间和空间上有着密切的关系，但长粒岩的超钾，石英规范成分和同位素系统却不能排除来自中央复合体的碳酸盐岩和硬质岩的任何遗传来源。菱形铁矿的Sr，Nd和Pb同位素比值与最高级的钾长石类似，其交代趋势从未变的基底片麻岩向着霞石，白云母-皂石-白云母组的均质特征收敛。菱形矿被解释为响应于来自上升的碳酸盐岩浆或流体的对流热通量而熔化的高级石冲天炉的形成。混合的碳酸盐和松散体被放置在流化系统中，是同时代的，但在遗传上不相关，互不相溶的岩浆。

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