Petrological and geochemical (trace elements and Sr–Nd isotopes) characteristics of the Paleozoic Kovdor ultramafic, alkaline and carbonatite intrusion (Kola Peninsula, NW Russia)
Petrological and geochemical (trace elements and Sr–Nd isotopes) characteristics of the Paleozoic Kovdor ultramafic, alkaline and carbonatite intrusion (Kola Peninsula, NW Russia)
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DOI：
10.1016/s0024-4937(99)00072-9
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发表时间：
2000-03
期刊：
影响因子：
3.5
通讯作者：
Anne Verhulst;E. Balaganskaya;Y. Kirnarsky;D. Demaiffe
中科院分区：
文献类型：
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作者：
Anne Verhulst;E. Balaganskaya;Y. Kirnarsky;D. Demaiffe
科夫多尔岩体属于古生代（380-360 Ma）科拉碱性和碳酸盐岩省（俄罗斯西北部）。它显示了一个完整的岩石序列，包括按侵入顺序，超镁铁岩，黄长石，碱性硅酸盐岩的熔融岩-伊乔岩系列，磷云母和碳酸岩，和晚霞石正长岩脉（后者没有研究）。超镁铁岩序列（纯橄榄岩-橄榄岩-单斜辉石岩）由橄榄石-单斜辉石堆晶岩（Mg#=86-70）和堆晶间金云母、磁铁矿和晚期方解石组成。蜜胺，最多35重量% CaO（黄长石堆晶）是岩浆而不是交代成因。熔长岩-蛇绿岩系列的岩石是非常不均匀的（粒度、矿物学和模态比例的变化），并显示不平衡的纹理（核吸收和单斜辉石的复杂分区），这表明岩浆混合或污染。在多元素蛛网图上，所有岩石都有强烈的不相容元素富集。稀土元素配分模式陡峭，（La/Yb）N>20，近平行，无Eu异常。Nb/Ta比值的变化和稀土元素的分布表明，碳酸岩和辉长岩-蛇绿岩系列岩石不是共轭不混溶液体。大多数岩石（超镁铁质岩、黄长石岩、碳酸岩和磷云母）在Nd-Sr图解中处于亏损地幔象限，（87 Sr/86 Sr）比值较低（0.70332 ~ 0.70377），εNd（t）值为正（+5.2 ~+0.6）。相当大的范围内的同位素组成是不赞成一个简单的，封闭的系统岩浆演化，它表明一个复杂的演化意味着几个岩浆批次来自同位素异质性地幔源或从不同的混合比例的两个地幔水库。熔融岩的同位素组成，Ijelite需要一个稍微富集的成分，可能是类似的Kandalaksha超镁铁质Lamerites和捷尔斯基海岸和阿尔汉格尔斯克金伯利岩。
The Kovdor intrusion belongs to the Paleozoic (380–360 Ma) Kola alkaline and carbonatite province (NW Russia). It displays a complete sequence of rocks that include in order of intrusion, ultramafic rocks, melilitolites, alkaline silicate rocks of the melteigite–ijolite series, phoscorites and carbonatites, and late nepheline syenite dykes (the latter were not studied). The ultramafic sequence (dunite–peridotite–clinopyroxenite) consists of olivine–clinopyroxene cumulates (Mg#=86–70) with intercumulus phlogopite and magnetite and late calcite. Melilitolites, with up to 35 wt.% CaO (melilite cumulates), have a magmatic rather than metasomatic origin. Rocks of the melteigite–ijolite series are very heterogeneous (variations of grain size, mineralogy and modal proportions) and show disequilibrium textures (core resorption and complex zoning of the clinopyroxenes) suggesting either magma mixing or contamination. All the rocks have strong incompatible element enrichments in multi-element spidergrams. The rare earth element (REE) patterns are steep with (La/Yb)N>20; they are subparallel and do not show any Eu anomaly. The variations of Nb/Ta ratios and the REE distributions suggest that the carbonatites and the rocks of the melteigite–ijolite series are not conjugate immiscible liquids. Most rocks (ultramafics, melilitolites, carbonatites and phoscorites) plot in the depleted mantle quadrant of the Nd–Sr diagram with low (87Sr /86Sr )iratios (0.70332 to 0.70377) and positive εNd(t) values (+5.2 to +0.6). The fairly large range of isotopic compositions is not in favour of a simple, closed system magmatic evolution; it suggests a complex evolution implying several magma batches derived either from an isotopically heterogeneous mantle source or from various mixing proportions of two mantle reservoirs. The isotopic composition of the melteigites–ijolites requires a slightly enriched component that could be similar to that of the Kandalaksha ultramafic lamprophyres and of the Tersky Coast and Arkhangelsk kimberlites.