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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Explosive destruction of a Pliocene hot lava dome underwater: Dogashima (Japan)
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Explosive destruction of a Pliocene hot lava dome underwater: Dogashima (Japan)

机译：水下上新世热熔岩圆顶的爆炸性破坏：多嘉岛（日本）

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Transition from effusive to explosive volcanism is common during subaerial eruptions, and here we demonstrate that this behavior is also possible underwater. The pyroclastic facies produced underwater are distinctive and can be used to distinguish subaqueous from subaerial eruptions and depositional settings. The Pliocene Dogashima Formation (Izu Peninsula, Japan) is a pumice-rich succession originally deposited in an open-marine, below wave-base setting (Jutzeler et al., 2014a). A thick, clast-supported, gray andesite breccia composed of very coarse, dense andesite clasts with quenched margins was sourced from disintegration of an active lava dome. Overall, the gray andesite breccia is gradationally to sharply overlain by thick, graded, clast-supported white pumice breccia chiefly composed of angular pumice clasts and free broken crystals. Regional setting and distinctive facies show that this succession was produced by a fully underwater, magmatic volatile-driven, pumice-forming explosive eruption. The gradational contact between the two breccias, compositional similarities, rare mingled clasts, and fluidal textures in the gray andesite clasts suggest that the explosive eruption destroyed a hot lava dome and generated an eruption-fed, high-concentration density current. In most places, the coarsest hot lava dome fragments were deposited first, followed by the lower density white pumice clasts. The low amount of fine (<2 mm) components, well-developed hydraulically controlled grading and sorting, clast angularity, and very coarse dome-derived clasts, some including well-defined quenched margins and common fluidal textures, distinguish the products of subaqueous effusive-to-explosive eruptions from their subaerial counterparts. (C) 2015 Elsevier B.V. All rights reserved.
机译：从喷发性火山向爆炸性火山的转变在地下喷发期间很常见，在这里我们证明了这种行为在水下也是可能的。水下产生的火山碎屑相具有独特性，可用于区分水下和地下喷发以及沉积环境。上新世八a岛组（日本伊豆半岛）是富含浮石的岩层，最初沉积在波基以下的一艘开放海洋中（Jutzeler等人，2014a）。由活跃的熔岩穹顶崩解而产生的厚的，由碎屑支撑的灰色安山岩角砾岩由非常粗糙，致密的安山岩碎屑组成，边缘具有淬火的边缘。总体而言，灰色安山岩角砾岩逐渐地被厚的，渐变的，由碎屑支撑的白色浮石角砾层覆盖，主要由角状浮石碎屑和游离的碎晶体组成。区域背景和独特的相表明，这种演替是由完全水下的岩浆挥发物驱动的浮石形成的爆发性喷发产生的。两种角砾岩之间的梯度接触，成分相似性，稀有的混合碎屑和灰色安山岩碎屑中的流体质地表明，爆发性喷发破坏了热熔岩穹顶并产生了由喷发喂养的高浓度密度电流。在大多数地方，首先沉积最粗的热熔岩圆顶碎片，然后沉积较低密度的白色浮石碎屑。少量（<2毫米）的细小成分，完善的液压控制分级和分选，碎屑角度和非常粗糙的穹顶碎屑（其中包括定义明确的淬火边距和常见的流体质地），可以区分水下喷出的产品从空中同伴爆发到爆发性喷发。 （C）2015 Elsevier B.V.保留所有权利。

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