Conduit margin heating and deformation during the AD 1886 basaltic Plinian eruption at Tarawera volcano, New Zealand.
Conduit margin heating and deformation during the AD 1886 basaltic Plinian eruption at Tarawera volcano, New Zealand.
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DOI：
10.1007/s00445-016-1006-7
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发表时间：
2016
影响因子：
3.5
通讯作者：
Dingwell DB
中科院分区：
文献类型：
--
作者：
Schauroth J;Wadsworth FB;Kennedy B;von Aulock FW;Lavallée Y;Damby DE;Vasseur J;Scheu B;Dingwell DB
在爆炸性喷发过程中，气体和火山碎屑的悬浮物在管道中迅速上升。在这里，我们分析了保存在公元1886年塔拉韦拉玄武岩普林尼裂缝喷发的火山碎屑馈线堤坝的墙壁纹理。所检查的样品包括玄武岩灰和火山渣涂在一个连贯的流纹岩圆顶和一个焊接流纹岩圆顶角砾岩的导管壁。我们研究了墙壁材料的响应的纹理证据，由10075 vol. %玻璃和25 vol. %晶体（无孔等效物），在相邻管道中的质量运动。在流纹岩壁材料，我们量化的方向和长宽比的黑云母晶体的应变标记的简单剪切变形，并解释并列地区的囊泡和囊泡崩溃的证据管道壁加热。系统的变化发生在靠近边缘的地方：（1）孔隙度变化很大，局部区域出现泡状或致密化，（2）黑云母晶体的长轴与边缘平行，（3）靠近边缘的黑云母具有较大的纵横比，（4）黑云母晶体断裂。我们解释了黑云母斑晶变形是由于晶体断裂、旋转和解理平行书柜平移。这些纹理观察推断，以表明热气体-灰射流和管道壁和围岩流纹岩的再加热之间的机械耦合。我们将这些观察结果与一个简单的一维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中实现高于玻璃化转变的温度。我们建议，导管壁加热和由此产生的变形影响导管边缘放气，并可能提高这种大型玄武岩喷发的强度。本文的在线版本（doi：10.1007/s 00445 -016-1006-7）包含补充材料，可供授权用户使用。
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. The online version of this article (doi:10.1007/s00445-016-1006-7) contains supplementary material, which is available to authorized users.