Radiogenic Isotope Constraints on Relationships between Carbonatites and Associated Silicate Rocks—a Brief Review
Radiogenic Isotope Constraints on Relationships between Carbonatites and Associated Silicate Rocks—a Brief Review
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DOI：
10.1093/petroj/39.11-12.1987
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发表时间：
1998-11
影响因子：
3.9
通讯作者：
K. Bell
中科院分区：
文献类型：
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作者：
K. Bell
碱性碳酸岩复合体中硅酸盐岩石的多样性与海岛玄武岩（OIB）的同位素相似，不能归因于母岩浆的分化，大多数碳酸岩的母熔体是在封闭的化学条件下产生的。来自同位素贫乏地幔的 Nd、Pb 施加的约束。然而，争论和锶同位素数据需要耦合离散的部分熔融事件，继续关于碳酸岩的起源及其在某些情况下的开放系统行为，涉及与相关硅酸盐岩石的混合关系。对于碳酸岩的起源，提出的其他地幔熔体或来源、或下大陆的模型包括：（1）地壳熔融。由碳酸盐岩碳酸盐地幔的同位素比图显示的模式显示出生成原生岩和来自东非的一些霞岩，表明混合主导的碳酸岩熔体（例如 von Eckermann，1948；Sweeney，通过两个地幔端元（与 HIMU 和 EMI 大致相似），1994），（2）首先在大洋中认识到的碳酸盐的分步结晶 玄武岩。在一定范围内混合足够的碱性硅酸盐液体（例如King＆Sutherland，1960年；以产生：（1）一致但可变比率的碳酸岩，来自Lee＆Wyllie，1994），以及（3）与东非大部分地区的不混溶分离，以及（2）一些碳化硅酸盐熔体（例如Koster van Groos＆来自非洲的硅酸盐岩石）之间的可变同位素比率 同一喷发中心（例如 Oldoinyo Wyllie，1963 年；Kjarsgaard & Hamilton，1989 年）。虽然Lengai，Shombole）。碳酸岩熔化实验之间的重叠同位素比率现在表明，来自东非和其他地方的熔体的碳酸岩和一些霞石岩可以通过不同的方式产生，所缺乏的是与岩浆分异（晶体分馏，是可用于分离初级液体不混溶性的强有力的标准）一致的，或者是与由来自东非和其他地方的熔体产生的相同或同位素碳酸岩熔体的熔化相一致的。 区分相似来源。母体硅酸盐熔体的伊若长石显示出广泛的同位素变化。响岩、正长岩甚至一些霞岩需要碳酸岩的出现以及其他地幔成分和/或大陆地壳的相关硅酸盐参与。岩石如流、塞、堤、锥片和基台，为两组岩石的岩浆起源提供了整体支持。尽管大多数杂岩中碳酸岩的体积相对较小，通常<10%，但大多数
The diversity of silicate rocks in alkaline–carbonatite complexes isotopic similarities to ocean island basalts (OIBs), and cannot be attributed to differentiation of parent magmas operating that parental melts to most carbonatites are generated under closed chemical conditions. Constraints imposed by Nd, Pb from an isotopically depleted mantle. However, debate and Sr isotope data require discrete partial melting events coupled, continues about the origin of carbonatites and their in some cases, with open-system behaviour that involves mixing relationship to associated silicate rocks. Models proposed either with other mantle melts or sources, or with lower continental for the origin of carbonatites include: (1) melting of crust. Patterns shown by isotope ratio diagrams for carbonatites carbonate-bearing mantle to generate a primary carand some nephelinites from East Africa indicate mixing dominated bonatitic melt (e.g. von Eckermann, 1948; Sweeney, by two mantle end-members (broadly similar to HIMU and EMI), 1994), (2) fractional crystallization of a carbonated first recognized in oceanic basalts. Mixing is on a scale sufficient alkaline silicate liquid (e.g. King & Sutherland, 1960; to generate: (1) coherent but variable ratios in carbonatites from Lee & Wyllie, 1994), and (3) immiscible separation from much of East Africa, and (2) variable isotope ratios among some a carbonated silicate melt (e.g. Koster van Groos & of the silicate rocks from the same eruptive centre (e.g. Oldoinyo Wyllie, 1963; Kjarsgaard & Hamilton, 1989). Although Lengai, Shombole). Overlapping isotope ratios between carbonatites melting experiments have now shown that carbonatitic and some nephelinites from complexes from East Africa and elsewhere melts can be produced in different ways, what are lacking are consistent with magmatic differentiation (crystal fractionation, are robust criteria that can be used to separate primary liquid immiscibility), or the melting of the same or isotopically carbonatitic melts from those produced by differentiation similar sources. The wide isotopic variation shown by the ijolites, of a parent silicate melt. phonolites, syenites and even some of the nephelinites requires the The occurrence of carbonatites and associated silicate involvement of other mantle components and/or continental crust. rocks as flows, plugs, dykes, cone sheets, and sills, lends overall support to a magmatic origin for both groups of rocks. Although the volume of carbonatite in most complexes is relatively small, normally <10%, most of