Ice-confined construction of a large basaltic volcano—Austurfjöll massif, Askja, Iceland
Ice-confined construction of a large basaltic volcano—Austurfjöll massif, Askja, Iceland
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一座大型玄武岩火山的冰封建筑——Austurfjöll 地块，Askja，冰岛
作者：
A. Graettinger;D. McGarvie;I. Skilling;Á. Höskuldsson;K. Strand
Austurfjöll是冰岛中部Askja火山最大的玄武岩冰川火山地块，通过对其火山学和地球化学特征的详细研究，我们详细介绍了冰岛一座大型玄武岩火山的冰盖构造序列和结构。特别是，Austurfjöll代表了喷口的几何形状，以及由此产生的冰川火山形态，这在以前的冰盖玄武岩火山中是没有记载的。Austurfjöll是在玄武岩火山活动的两个主要阶段建造的，通过以分散裂隙为主的喷发经历了七次喷发。最早的一次事件涉及一次罕见且曝光较少的空中活动，随后发生了六次事件，涉及冰封枕状熔岩的喷发和许多重叠的裂缝喷发的云雾状火山灰。当地地下熔岩和冰盖岩层的证据表明，当地火山喷发中心在湖面上方生长，随后发生洪水，但没有长期的地面活动。局部的冰接触相、古水位和直径表明，在Austurfjöll建造过程中，冰的位置和厚度是不同的，在最后一次冰川时期，可能发生了多个不同级别的融水湖的喷发活动。岩相证据，包括从溢流沉积到爆炸沉积的分级转变，一致相以上碎屑相的叠加，以及排泄通道，表明喷发方式的变化主要是由排泄和地块海拔上升等外部因素驱动的。这项研究强调了奥斯图夫约尔火山的独特特征，它由大的枕状熔岩席、大量(>； 40)重叠的冰火山丁达尔组成，作为其漫长冰盖喷发历史的产物，只有局部的新生沉积，这与以前对风亚和丁达尔的描述形成了鲜明对比。
Austurfjöll is the largest basaltic glaciovolcanic massif at Askja volcano (Central Iceland), and through detailed studies of its volcanological and geochemical characteristics, we provide a detailed account of the sequence and structure of the ice-confined construction of a large Icelandic basaltic volcano. In particular, Austurfjöll represents a geometry of vents, and resulting glaciovolcanic morphology, not previously documented in ice-confined basaltic volcanoes. Austurfjöll was constructed during two major phases of basaltic volcanism, via seven eruptive episodes through disperse fissure-dominated eruptions. The earliest episode involved a rare and poorly exposed example of subaerial activity, and this was succeeded by six episodes involving the eruption of ice-confined pillow lavas and numerous overlapping fissure eruptions of phreatomagmatic tephra. Evidence of local subaerial lavas and tephras indicates the local growth of eruptive centers above englacial lake levels, and subsequent flooding, but no prolonged subaerial activity. Localized ice-contact facies, paleowater levels, and diamictons indicate the position and thickness of the ice was variable during the construction of Austurfjöll, and eruptive activity likely occurred in multiple and variable level meltwater lakes during the last glacial period. Lithofacies evidence including gradational transitions from effusive to explosive deposits, superposition of fragmental facies above coherent facies, and drainage channels suggest that changes in eruptive style were driven largely by external factors such as drainage and the increasing elevation of the massif. This study emphasizes the unique character of Austurfjöll, being composed of large pillow lava sheets, numerous (> 40) overlapping glaciovolcanic tindars, and only localized emergent deposits, as a product of its prolonged ice-confined eruptive history, contrasts with previous descriptions of tuyas and tindars.