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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Mafic volcaniclastic deposits in flood basalt provinces: A review
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Mafic volcaniclastic deposits in flood basalt provinces: A review

机译：玄武岩洪水省的镁铁质火山碎屑沉积

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摘要

Flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks (mostly sills), with any pyroclastic rocks limited to silicic compositions. However, mafic volcaniclastic deposits (MVDs) exist in many provinces, and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions. The province where MVDs are the most voluminous—the Siberian Traps—is also the one temporally associated with the greatest Phanerozoic mass extinction. A lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established, but as a first step, this contribution reviews in some detail the current knowledge on MVDs for the provinces in which they are better known, i.e. the North Atlantic Igneous Province (including Greenland, the Faeroe Islands, the British Isles, and tephra layers in the North Sea basin and vicinity), the Ontong Java plateau, the Ferrar, and the Karoo. We also provide a brief overview of what is known about MVDs in other provinces such as the Columbia River Basalts, the Afro-Arabian province, the Deccan Traps, the Siberian Traps, the Emeishan, and an Archean example from Australia. The thickest accumulations of MVDs occur in flood basalt provinces where they underlie the lava pile (Faeroes: > 1 km, Ferrar province: ≥ 400 m, Siberian Traps: 700 m). In the Faeroes case, the great thickness of MVDs can be attributed to accumulation in a local sedimentary basin, but in the Ferrar and Siberian provinces the deposits are widespread ( > 3 x 10~5 km~2 for the latter). On the Ontong Java plateau over 300 m of MVDs occur in one drill hole without any overlying lavas. Where the volcaniclastic deposits are sandwiched between lavas, their thickness is much less. In most of the cases reviewed, primary MVDs are predominantly of phreatomagmatic origin, as indicated by the clast assemblage generally consisting of basaltic clasts of variable vesicularity (dominantly non- to poorly-vesicular) mixed with abundant country rock debris. The accidental lithic components often include loose quartz particles derived from poorly consolidated sandstones in underlying sedimentary basins (East Greenland, Ferrar, Karoo). These underlying sediments or sedimentary rocks were not only a source for debris but also aquifers that supplied water to fuel phreatomagmatic activity. In the Parana-Etendeka, by contrast, the climate was apparently very dry when the lavas were emplaced (aeolian sand dunes) and no MVDs are reported. Volcanic vents filled with mafic volcaniclastic material, a few tens of metres to about 5 km across, are documented in several provinces (Deccan, North Atlantic, Ferrar, Karoo); they are thought to have been excavated in relatively soft country rocks (rarely in flood lavas) by phreatomagmatic activity in a manner analogous to diatreme formation.
机译：一般认为，洪水火山的省份仅由厚熔岩和浅侵入性岩石（主要是基岩）组成，任何火山碎屑岩均限于硅质成分。但是，许多省份都存在镁铁质火山碎屑沉积物（MVDs），而形成此类沉积物的火山爆发对潜在的大气影响和与物种灭绝的联系具有潜在的意义。 MVD数量最多的省份-西伯利亚陷阱-也是与生代大规模灭绝最大的时间相关的地区。在可以建立令人信服的遗传联系之前，关于这些沉积物和火山爆发的知识尚有很多，但第一步，这项贡献详细回顾了MVD已知的省份（即北部）的当前知识。大西洋火成岩省（包括格陵兰岛，法罗群岛，不列颠群岛和北海盆地及附近的特菲拉层），安东爪哇高原，费拉尔河和卡鲁河。我们还简要概述了其他省份的MVD，例如哥伦比亚河玄武岩，非裔阿拉伯省，德干陷阱，西伯利亚陷阱，峨眉山以及澳大利亚的太古代例子。 MVD最厚的堆积发生在熔岩桩下面的玄武岩洪水省（Faeroes：> 1 km，Ferrar省：≥400 m，西伯利亚陷阱：700 m）。在Faeroes的情况下，MVD的厚薄可以归因于当地沉积盆地的堆积，但是在Ferrar和Siberian省，沉积物分布较广（后者大于3 x 10〜5 km〜2）。在Ontong Java高原上，一个钻孔中发生了300 m的MVD，没有任何覆岩。当火山碎屑沉积物夹在熔岩之间时，其厚度要小得多。在所审查的大多数情况下，主要的MVD主要是发岩岩浆来源的，如通常由变泡状玄武岩碎屑（主要为非泡状或弱泡状）和大量乡村岩石碎屑混合而成的碎屑组合所表明的那样。偶然的岩性成分通常包括来自底层沉积盆地（东格陵兰，费拉尔，卡鲁）中固结差的砂岩的石英颗粒。这些下伏的沉积物或沉积岩不仅是碎片的来源，而且还是为水化岩浆活动提供水的含水层。相比之下，在帕拉纳-埃滕德卡（Parana-Etendeka），放置熔岩（风沙丘）时，气候显然非常干燥，没有MVD的报道。几个省份（Deccan，北大西洋，Ferrar，Karoo）记录了充满镁铁质火山弹材料的火山喷口，跨度达几十米至约5公里。人们认为它们是通过岩浆活动在类似软岩的乡村岩石中（很少在洪水熔岩中）开挖的，其方式类似于异常形成。

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