During explosive eruptions, a suspension of gas and pyroclasts rises rapidly within a conduit. Here, we have analysed textures preserved in the walls of a pyroclastic feeder dyke of the AD 1886 Tarawera basaltic Plinian fissure eruption. The samples examined consist of basaltic ash and scoria plastered onto a conduit wall of a coherent rhyolite dome and a welded rhyolitic dome breccia. We examine the textural evidence for the response of the wall material, built of ∼75 vol.% glass and ∼25 vol.% crystals (pore-free equivalent), to mass movement in the adjacent conduit. In the rhyolitic wall material, we quantify the orientation and aspect ratio of biotite crystals as strain markers of simple shear deformation, and interpret juxtaposed regions of vesiculation and vesicle collapse as evidence of conduit wall heating. Systematic changes occur close to the margin: (1) porosity is highly variable, with areas locally vesiculated or densified, (2) biotite crystals are oriented with their long axis parallel to the margin, (3) the biotites have greater aspect ratios close to the margin and (4) the biotite crystals are fractured. We interpret the biotite phenocryst deformation to result from crystal fracture, rotation and cleavage-parallel bookcase translation. These textural observations are inferred to indicate mechanical coupling between the hot gas-ash jet and the conduit wall and reheating of wall rock rhyolite. We couple these observations with a simple 1D conductive heating model to show what minimum temperature the conduit wall needs to reach in order to achieve a temperature above the glass transition throughout the texturally-defined deformed zone. We propose that conduit wall heating and resulting deformation influences conduit margin outgassing and may enhance the intensity of such large basaltic eruptions.

中文翻译：

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公元 1886 年新西兰塔拉威拉火山玄武质普林尼阶喷发期间的管道边缘加热和变形

在爆炸性喷发期间，气体和火山碎屑的悬浮液在管道内迅速上升。在这里，我们分析了公元 1886 年塔拉威拉玄武质普林尼裂隙喷发的火山碎屑馈线堤壁中保存的纹理。所检查的样品由玄武灰和灰泥组成，它们涂在连贯的流纹岩圆顶和焊接的流纹岩圆顶角砾岩的管道壁上。我们检查了壁材料对相邻管道中质量运动的响应的纹理证据，壁材料由~75 vol.% 玻璃和~25 vol.% 晶体（无孔等效物）构成。在流纹岩壁材料中，我们将黑云母晶体的取向和纵横比量化为简单剪切变形的应变标记，并将水泡形成和水泡塌陷的并列区域解释为管道壁加热的证据。系统变化发生在边缘附近：(1) 孔隙度变化很大，区域局部成泡状或致密化，(2) 黑云母晶体的长轴平行于边缘，(3) 黑云母具有更大的纵横比，接近边缘和（4）黑云母晶体破裂。我们将黑云母斑晶变形解释为晶体断裂、旋转和解理平行书架平移造成的。推断这些结构观察表明热气-灰射流与管道壁之间的机械耦合以及围岩流纹岩的再加热。我们将这些观察结果与一个简单的 1D 传导加热模型相结合，以显示导管壁需要达到的最低温度，以便在整个纹理定义的变形区域达到高于玻璃化转变的温度。