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首页> 外文期刊>Journal of South American earth sciences >Decoupling of paired elements, crossover REE patterns, and mirrored spider diagrams: Fingerprinting liquid immiscibility in the Tapira alkaline-carbonatite complex, SE Brazil
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Decoupling of paired elements, crossover REE patterns, and mirrored spider diagrams: Fingerprinting liquid immiscibility in the Tapira alkaline-carbonatite complex, SE Brazil

机译：成对元素，交叉REE模式和镜像蜘蛛图的解耦：巴西东南部Tapira碱碳酸盐复合物中的指纹液体不溶混性

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摘要

Tapira is an alkaline silicate-carbonatite complex belonging to the kamafugite-carbonatite association in the Late-Cretaceous Alto Paranaiba Igneous Province (APIP). It is dominated by coarse-grained plutonic rocks (bebedourite - a phlogopite-, apatite-, and perovskite-rich clinopyroxenite - with subordinated dunites, wehrlites, carbonatites and phoscorites). The plutonic rocks are crosscut by fine-grained ultra-mafic alkaline rocks (phlogopite picrites, bebedouritic dikes) and fine-grained carbonatites. Both types of dike-rocks show petrographic evidence of the coexistence of immiscible silicate and carbonatite liquids, such as carbonate ocelli present in the silicate rocks and, more rarely, silicate ocelli within carbonatites. A detailed geochemical study of the rock types in the complex, with emphasis on the fine-grained varieties, showed that whilst some rocks may be related to each other through crystal fractionation (e.g. phlogopite picrites and bebedouritic dikes), others display anomalous trace-element behaviour that cannot be readily explained by the fractionation of a particular phase or combination of phases. We interpret such anomalous geochemical signatures as produced by silicate-carbonate liquid immiscibility, on the basis of available experimental data on partition coefficients between coexisting immiscible liquids. The immiscibility signatures comprise: (a) decoupling of geochemical pairs, such as Nb-Ta and Zr-Hf; (b) rotation of REE patterns, which cross over the patterns of the primitive liquids; and (c) matching and opposite enrichment-depletion trace elements relationships in spider diagrams of conjugate immiscible liquids. We suggest that, once established, such geochemical signatures are very difficult to erase during the subsequent petrogenetic evolution processes, which may result in superimposed conflicting signatures.
机译：Tapira是一种碱性硅酸盐-碳酸盐复合物，属于晚白垩世上阿拉那巴州火成岩省（APIP）中的卡马夫石-碳酸盐岩联合体。它主要由粗粒岩体（贝脱石-金云母，磷灰石和钙钛矿富含的斜辉石-带有次要的杜尼铁矿，白云母，碳酸盐岩和辉石）主导。深成岩被细粒的超镁铁质碱性岩石（金云母的苦盐岩，贝脱岩的堤防）和细粒的碳酸盐岩横切。两种类型的堤防岩都显示了不溶混的硅酸盐和碳酸盐岩液体共存的岩石学证据，例如存在于硅酸盐岩中的碳酸盐岩和很少存在于碳酸盐岩中的硅酸盐岩。对复合体中岩石类型的详细地球化学研究（重点是细粒度的物种）显示，尽管有些岩石可能通过晶体分级而彼此关联（例如金云母微晶岩和松软岩堤），但其他岩石则表现出异常的痕量元素特定相的分离或相组合无法轻易解释的行为。我们根据现有的关于共存不溶混液体之间分配系数的实验数据，解释了由硅酸盐与碳酸盐液体不溶混产生的异常地球化学特征。不混溶性特征包括：（a）地球化学对，例如Nb-Ta和Zr-Hf，解耦； （b）横穿原始液体图案的REE图案的旋转； （c）在共轭不混溶液体的蜘蛛图中，匹配和相反的富集-消耗痕量元素关系。我们建议，一旦建立，这样的地球化学特征很难在随后的岩石成因演化过程中消除，这可能导致叠加的相互矛盾的特征。

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  • 来源
    《Journal of South American earth sciences》 |2013年第1期|41-56|共16页
  • 作者

    Jose Affonso Brod; Tereza Cristina Junqueira-Brod; Jose Carlos Gaspar; Ivan Alejandro Petrinovic; Sergio de Castro Valente; Artur Corval;

  • 作者单位

    Universidade Federal de Goias, Institute de Estudos Sotio-Ambientais, Campus Samambaia, C.P. 131, 74.001-970 Goiania, GO, Brazil,Universidade de Brasilia, Institute) de Geociencias, Campus Universitario Darcy Ribeiro, Asa Norte, 70.910-900 Brasilia, DF, Brazil;

    Universidade Federal de Goias, Institute de Estudos Sotio-Ambientais, Campus Samambaia, C.P. 131, 74.001-970 Goiania, GO, Brazil;

    Universidade Federal de Goias, Institute de Estudos Sotio-Ambientais, Campus Samambaia, C.P. 131, 74.001-970 Goiania, GO, Brazil,Universidade de Brasilia, Institute) de Geociencias, Campus Universitario Darcy Ribeiro, Asa Norte, 70.910-900 Brasilia, DF, Brazil;

    Centro de Investigations en Cientias de la Tierra, CICTERRA/CONICFJ, Universidad National de Cdrdoba, Av. Velez Sarsfield 1611, X5016GCA Cordoba, Argentina;

    Universidade Federal Rural do Rio de Janeiro, Departamento de GeociSntias, BR-465, Km 7, CEP 23890-000, Seropedka, RJ, Brazil;

    Universidade Federal Rural do Rio de Janeiro, Departamento de GeociSntias, BR-465, Km 7, CEP 23890-000, Seropedka, RJ, Brazil;

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  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

    Nb-Ta decoupling; Zr-Hf decoupling; crossover REE patterns; liquid immiscibility; alto paranaiba; carbonatite; bebedourite;

    机译：Nb-Ta去耦;Zr-Hf去耦;交叉REE模式;液体不溶混;中音巴拉那巴碳酸盐岩钙矾石;

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