Building Ice-Age Dyngjufjöll: Processes, Products and Environments

大体积、多成因、冰封的火山的过程、产物和古环境非常鲜为人知。位于冰岛的Dengjufjoll(“Askja”)是地球上最大、暴露最好的玄武岩火山之一，以前被冰封住了，但以前的工作主要集中在它最近的全新世(即无冰)的演化上。该项目将重点关注其更古老的更新世历史，目标是保存数百米厚冰川火山岩的一个大地块(Austurfjoll)。最近，人们对火山成因、冰下融化和排放作为冰盖快速移动的润滑剂的作用及其对冰盖不稳定的可能性产生了相当大的兴趣。此外，大量火山成因融水洪水的源头过程和产品(即jokulhlaps)对冰岛南部的基础设施(道路、桥梁)和当地经济是一个重大危险。这项研究的结果将有助于填补有关火山-冰相互作用过程的地质和环境影响方面的一些知识空白。像Dengjufjoll这样的火山也是与限制大型长寿玄武岩屏蔽火山和火星冰相互作用模型最相关的陆地类似物。这项研究将作为与英国和冰岛科学家国际合作的一部分进行。该项目将提供对融水源区两个相关方面的见解，即上覆冰厚度的时间变化以及水排水和积水的性质，包括可能的约库拉普(即大量火山成因融水的释放)事件。目前还没有关于火山建筑物源头的约库拉普记录的研究。对Austurfjoll的枕皮玻璃的挥发性分析将有助于限制对冰岛中部古冰层厚度的估计，以及将该地区冰川消融与火山活动速度增加联系起来的模型。Dygjufjoll冰川-火山地块的年龄目前尚不清楚，但自2.5 Ma以来，冰岛已发现多达16次陆地冰川事件，因此这些岩石有可能记录下冰川最大厚度之前的证据。建议将详细的定量玻璃结构和成分分析、地球化学分析、40Ar-39Ar测年、详细的构造和相填图以及测井应用于地层学。这一对比项目和方法对于解释冰岛许多(1000)裂缝喷发、冰川火山、碎屑为主的层序(即“丁达尔”)特别相关，这些层序代表了冰岛冰川历史的一个巨大数据库。该项目的成果将有助于完善确认冰川-火山(特别是碎屑)序列中存在以前冰的标准，从而有助于越来越多地使用这种岩石作为过去气候的指示。

The processes, products and paleoenvironments of large volume, polygenetic, ice-confined volcanoes are very poorly known. Dyngjufjoll ("Askja"), in Iceland, is one of the largest and best exposed, formerly ice-confined,basaltic volcanoes on Earth, but previous work has concentrated on its more recent Holocene (i.e. ice-free) evolution. This project will focus on its older Pleistocene history by targeting one large massif (Austurfjoll) that preserves several hundred meters of glaciovolcanic rocks. There has been considerable interest recently in the role of volcanogenic, subglacial ice melting and drainage as a lubricant for rapid ice sheet movement, and its potential for sheet destabilization. Also, source area processes and products of large-volume volcanogenic meltwater floods (i.e.jokulhlaups)are a significant hazard to infrastructure (roads, bridges) and the local economy in south Iceland. The results of this study will help close some gaps in knowledge regarding the geologic and environmental impacts of volcano-ice interaction processes. Volcanoes like Dyngjufjoll are also the most relevant terrestrial analogs to constraining models of the interaction of large long-lived basaltic shield volcanoes and ice on Mars. The study will be conducted as part of an international collaboration with scientists from the UK and Iceland.This project will offer insights into two relevant aspects of the meltwater source region, namely temporal variations in the overlying ice thickness and the nature of water drainage and ponding, including possible jokulhlaup (i.e. release of large-volume volcanogenic meltwater) events. There are no studies of the record of jokulhlaups at a volcanic edifice source. Volatile analysis of pillow rind glass at Austurfjoll will help constrain estimates of paleo-ice thicknesses in central Iceland, and models that link deglaciation with increased rates of volcanism in this area. The age of the Dyngjufjoll glaciovolcanic massifs are currently unknown, but up to 16 terrestrial glacial events have been recognized in Iceland since 2.5Ma, so there is potential for these rocks to record evidence of pre-late glacial maximum ice thicknesses. It is proposed to apply an integrated approach to stratigraphy using detailed quantitative glass texture and component analysis, geochemical analysis, 40Ar-39Ar dating, detailed structural and facies mapping and logging. This project and approach to correlation is particularly relevant to interpreting the very many (1000) fissure-erupted, glaciovolcanic, clastic-dominated sequences (i.e. 'tindars') in Iceland, which represent an enormous database on the glacial history of Iceland. The results of this project will help refine the criteria by which the presence of former ice in glaciovolcanic (particularly clastic) sequences is recognized, and hence contribute to the growing use of such rocks as indicators of past climate.