Abstract The process of meteorological lightning-induced modification of coherent volcanic rocks is examined by geochemical, textural, and experimental analysis of fulgurites from South Sister volcano, Oregon Cascades, USA. Lightning's effects on volcanic target rocks was simulated with an arc-welding device in order to reproduce the geochemical and textural features of natural fulgurites and to constrain temperatures of melting and devolatilization behavior during lightning strikes. Melting of volcanic target rocks produces melts of exceptional compositional diversity, ranging from those with pure mineral compositions (e.g., diopside and plagioclase), resulting from congruent melting reactions, to those that are highly mixed and compositionally identical to the target rock. Geochemical and textural observations on fulgurites suggest that melting proceeds rapidly, by an in situ modal batch process whereby individual crystals melt and contribute small aliquots to a larger batch that is then mixed by viscous flow. Hydrous species remaining in the glasses are trace (OH≪0.1 wt.%), and consistent with partial equilibration to high temperature (>2000 °C) supra-liquidus, 1-atm conditions. Lightning also induces physical weathering, in that the target rocks may be vapourized to form channels through the rock, representing injection of elemental components to the atmosphere. Finally, lightning acts as a multi-faceted producer of dry, chemically equivalent volcanic glass, which may be subject to long-term hydration by environmental waters at surface conditions. These re-hydration signatures contrast those of volcanic glasses, which have both magmatic and meteoric components, and are used herein to examine the post-lightning environmental history of these glasses, including age dating lightning events by diffusion chronometry. Our study of volcanic fulgurites illustrates the potential to use their hydration signatures to date paleoweather events at decadal to centuries scale. Because the lightning strike is in and of itself so effective at devolatilizing melts in an instant, the resultant fulgurites are a unique earth material that record individual weather events (i.e., a thunderstorm), and also longer-term paleoweather intervals.

中文翻译：

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卡斯卡迪亚火山峰的闪电风化

摘要 通过对来自美国俄勒冈州喀斯喀特的南姐妹火山的电灼岩的地球化学、结构和实验分析，研究了气象闪电引起的连贯火山岩的改性过程。闪电对火山目标岩石的影响用弧焊设备模拟，以再现天然电灼石的地球化学和结构特征，并限制雷击期间熔化和脱挥发分行为的温度。火山目标岩石的熔化产生具有异常组成多样性的熔体，从具有纯矿物成分（例如透辉石和斜长石）的熔体，由一致的熔化反应产生，到高度混合且成分与目标岩石相同的熔体。对电闪石的地球化学和结构观察表明，通过原位模式批处理过程，熔化进行得很快，其中单个晶体熔化并将小等分试样加入更大的批次，然后通过粘性流动进行混合。玻璃中残留的含水物质是痕量的 (OH≪0.1 wt.%)，并且与高温 (>2000 °C) 超液相线、1-atm 条件的部分平衡一致。闪电还会引起物理风化，因为目标岩石可能会蒸发形成穿过岩石的通道，代表元素成分向大气中注入。最后，闪电作为干燥的、化学等效的火山玻璃的多方面生产者，可能会在地表条件下受到环境水的长期水合作用。这些再水化特征与火山玻璃的特征形成对比，火山玻璃具有岩浆和陨石成分，在本文中用于检查这些玻璃的闪电后环境历史，包括通过扩散计时法测定闪电事件的年龄。我们对火山熔岩的研究说明了利用它们的水合特征来确定年代际到数百年规模的古天气事件的潜力。由于雷击本身在瞬间使熔体脱挥发分非常有效，因此产生的电灼石是一种独特的地球材料，可以记录个别天气事件（即雷暴），以及更长期的古天气间隔。包括通过扩散计时法测定闪电事件的年龄。我们对火山熔岩的研究说明了利用它们的水合特征来确定年代际到数百年规模的古天气事件的潜力。由于雷击本身在瞬间使熔体脱挥发分非常有效，因此产生的电灼石是一种独特的地球材料，可以记录个别天气事件（即雷暴），以及更长期的古天气间隔。包括通过扩散计时法测定闪电事件的年龄。我们对火山熔岩的研究说明了利用它们的水合特征来确定年代际到数百年规模的古天气事件的潜力。由于雷击本身在瞬间使熔体脱挥发分非常有效，因此产生的电灼石是一种独特的地球材料，可以记录个别天气事件（即雷暴），以及更长期的古天气间隔。