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首页> 外文期刊>The Journal of Geology: a semi-quarterly magazine of geology and related sciences >The Upper Visean Magdalen Islands Basalts of Eastern Quebec, Canada: A Complex Assemblage of Contrasting Mafic Rock Types Erupted in Peak Stages of Transtensional Basin Development above a Mantle Plume
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The Upper Visean Magdalen Islands Basalts of Eastern Quebec, Canada: A Complex Assemblage of Contrasting Mafic Rock Types Erupted in Peak Stages of Transtensional Basin Development above a Mantle Plume

机译：加拿大魁北克东部的上扶扶马群岛荒野：一种复杂的荆棘盆地高峰阶段爆发的对比毛岩类型的复杂组合，在地幔羽流上

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A thick succession of mafic upper Asbian volcanic rocks is exposed as cap rocks in the Magdalen Islands of eastern Quebec. This succession records peak stages of a Late Devonian to Early Carboniferous magmatic system that regionally developed from transtensional tectonics above a mantle plume. In the upper part of the succession, tholeiitic basalts with enriched mid-oceanic ridge basalt (E-MORB) affinities are tightly interbedded with highly alkaline basalts with ocean island affinities, whereas the lower part is composed of moderately alkaline basalts and pyroclastic deposits that are interpreted as the products of mixing between these two compositionally distinct melts. Based on trace-element contents and geological constraints, the tholeiitic basalts were produced by decompressional melting in depleted uppermost asthenospheric mantle material enriched over the average (E-MORB-type source) at the top of the plume, whereas the highly alkaline basalts were produced subsequently when decompressional melting reached down into the enriched mantle (ocean island basalt-type source). These two primary melts may have been thermally stratified below the lithosphere before being tapped by transtensional structures to feed a thick magmatic underplating that regionally developed at the base of the crust, where magma mixing may have occurred. Interbedding of the two contrasting melts in the upper part of the succession implies that, although the two primary mantle sources were still being tapped into, magma mixing was by then no longer occurring. Above a small gap, the uppermost flow is a fluorine-rich tholeiitic basalt with arc affinities that suggest partial melting of the regional subcontinental lithospheric mantle source, which was previously enriched by nearly continuous subduction below eastern Canada in early to middle Paleozoic times. The latter setting seemingly corresponds to the local waning of the magmatic system in uppermost Asbian times, possibly because of the we
机译：在魁北克东部的Magdalen岛上暴露为帽岩，厚厚的镁铁岩石岩。这一继承记录了晚德农岛到早期石炭系岩石系统的高峰阶段，这些系统从地幔羽流上的静音构造区域开发。在继承的上半部分，富含富含海洋脊髓玄武岩（E-MORB）亲密性的烟草玄武岩与海岛亲和力的高度碱性玄武岩紧密互相堵塞，而下部由中等碱性玄武岩和发酵淤积组成解释为在这两个合成的不同熔体之间混合的产品。基于微量元素内容和地质约束，通过在羽流顶部富含富含血液（E-MORB型源）的耗尽最高的哮喘的哮喘的肉体材料中的减压熔化产生了烟草基础，而产生高度碱性基础随后，当减压熔化到达富含富含碎屑（海岛玄武岩型源）时。在通过横静结构中挖掘之前，这两个初级熔体可能在岩石圈下方被热分裂以馈送厚的岩石底漆，该厚的岩土地在地壳的底部地区开发的岩石底部，可能已经发生了岩浆混合。连续的两个对比熔体的互补意味着，尽管仍然被敲入了两个主要的披风源，但是岩浆混合通过然后不再发生。最高的差距，最上面的流动是富含氟的烟玄核，具有弧感，表明区域亚平坦岩石型裂缝源的部分熔化，以前在加拿大东部的几乎连续的俯卧次以早期古生代的级数富集。后一种情况似乎对应于岩浆系统在最上层的时代的局部衰弱，可能是因为我们

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