Late Archaean granites: a typology based on the Dharwar Craton (India)
Late Archaean granites: a typology based on the Dharwar Craton (India)
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DOI：
10.1016/s0301-9268(03)00183-9
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发表时间：
2003-11
影响因子：
3.8
通讯作者：
J. Moyen;H. Martin;M. Jayananda;B. Auvray
中科院分区：
文献类型：
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作者：
J. Moyen;H. Martin;M. Jayananda;B. Auvray
在东达瓦尔克拉通进行了广泛的野外工作，结合岩石学和地球化学（主要元素和微量元素）调查，可以区分出晚太古代花岗岩类的四种主要类型。(1)富钠花岗质花岗岩（TTG），具有强分选REE模式和低REE含量特征，一般解释为变质水合玄武岩部分熔融形成的“板熔体”，极有可能是在俯冲环境中形成的。(2) Sanukitoids，为富钾、镁二长岩和花岗闪长岩，具有TTG-like REE模式，并伴有明显的lle富集，被认为是俯冲环境下生成的板熔体与地幔楔橄榄岩的相互作用和同化的结果。(3)罕见的高hfse、Mg、K花岗岩，REE和lile富集较强，可能是由富集地幔源部分熔融形成的；与类sanukitae成因不同，在这种情况下，平板熔体被认为完全被与地幔矿物反应消耗，导致地幔富集。这一富集地幔随后的熔融作用（可能是在俯冲后的环境中）产生了高hfse、镁和钾岩浆。在达瓦尔克拉通的Closepet花岗岩中，热幔源岩浆可以诱发大陆地壳的熔融，并与无水成岩产物混合。(4)富钾、贫镁的浓殖质黑云母花岗岩，REE分选少，Eu负异常。这些花岗岩是由旧基底或新近增生的岩体重熔形成的，两者都含有TTG成分。这种深熔既可以发生在俯冲中，也可以发生在俯冲后的环境中。该类型以暴露良好的达瓦尔克拉通为基础，可扩展到世界各地的晚太古代花岗岩类。编制了大约500个分析，并提出了一些基于主量元素和微量元素的判别图。观察到的岩石类型最可能的构造背景是一个大陆块体在俯冲系统上增生的增生造山带，随后是新增生的大陆物质的热改造。然而，研究发现太古宙“俯冲相关”花岗岩类与现代花岗岩类明显不同，这意味着从太古宙到现在，汇聚边缘岩浆生成方式发生了递进式变化。
Extensive field work in the Eastern Dharwar Craton, associated with petrographic and geochemical (major and trace elements) investigations, allows four main types of Late Archaean granitoids to be distinguished. (1) Na-rich granitoids of trondhjemitic, tonalitic and granodioritic composition (TTG) that are characterised by strongly fractionated REE patterns and low HREE contents and generally interpreted as “slab melts” generated by partial melting of metamorphosed hydrated basalt, most likely in a subduction environment. (2) Sanukitoids, which are K- and Mg-rich monzonites and granodiorites with TTG-like REE patterns associated with marked LILE-enrichment, and considered to result from the reaction of slab melts generated in a subduction environment with, and assimilation of, mantle wedge peridotite. (3) Uncommon high-HFSE, Mg and K granites with strongly REE and LILE-enrichment that, probably formed by partial melting of an enriched mantle source; unlike in the genesis of sanukitoids, in this case the slab melt is considered to be wholly consumed by reaction with mantle minerals, resulting in mantle-enrichment. Subsequent melting of this enriched mantle (probably in a post-subduction setting) gives rise to high-HFSE, Mg and K magmas. As demonstrated for the Closepet Granite (Dharwar Craton), the hot mantle-derived magma can induce melting of continental crust and then mix with the anatectic products. (4) K-rich, Mg-poor anatectic biotite-granites with REE patterns that are less fractionated and show negative Eu anomalies. These granites result from the remelting of old basement or recently accreted plutons, both with TTG compositions. Such anatexis can occur either in a subduction or in a post-subduction environment. This typology, based on the well-exposed Dharwar Craton, can be extended to Late Archaean granitoids from all over the world. About such 500 analysis were compiled, and a number of discriminant diagrams, based on both major and trace elements, are proposed. The most likely tectonic setting for the observed rock types is an accretionary orogen with accretion of continental blocks above a subduction system, followed by thermal reworking of the newly accreted continental material. However, it has been found that Archaean “subduction-related” granitoids are significantly different from their modern counterparts, implying progressive changes in the modes of magma generation at convergent margins from the Archaean to the present.