Hartley Margaret E, Bali Enikö, Maclennan John, Neave David A, Halldórsson Sæmundur A
1School of Earth and Environmental Sciences, University of Manchester, Manchester, UK.
2Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland.
Contrib Mineral Petrol. 2018;173(2):10. doi: 10.1007/s00410-017-1435-0. Epub 2018 Jan 12.
The 2014-2015 Holuhraun eruption, on the Bárðarbunga volcanic system in central Iceland, was one of the best-monitored basaltic fissure eruptions that has ever occurred, and presents a unique opportunity to link petrological and geochemical data with geophysical observations during a major rifting episode. We present major and trace element analyses of melt inclusions and matrix glasses from a suite of ten samples collected over the course of the Holuhraun eruption. The diversity of trace element ratios such as La/Yb in Holuhraun melt inclusions reveals that the magma evolved via concurrent mixing and crystallization of diverse primary melts in the mid-crust. Using olivine-plagioclase-augite-melt (OPAM) barometry, we calculate that the Holuhraun carrier melt equilibrated at 2.1 ± 0.7 kbar (7.5 ± 2.5 km), which is in agreement with the depths of earthquakes (6 ± 1 km) between Bárðarbunga central volcano and the eruption site in the days preceding eruption onset. Using the same approach, melt inclusions equilibrated at pressures between 0.5 and 8.0 kbar, with the most probable pressure being 3.2 kbar. Diffusion chronometry reveals minimum residence timescales of 1-12 days for melt inclusion-bearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of HO saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12-0.29 m s. Our petrological and geochemical data are consistent with lateral magma transport from Bárðarbunga volcano to the eruption site in a shallow- to mid-crustal dyke, as has been suggested on the basis of seismic and geodetic datasets. This result is a significant step forward in reconciling petrological and geophysical interpretations of magma transport during volcano-tectonic episodes, and provides a critical framework for the interpretation of premonitory seismic and geodetic data in volcanically active regions.
2014 - 2015年发生在冰岛中部巴尔达本加火山系统的霍鲁赫拉恩火山喷发，是有史以来监测最为全面的玄武岩裂隙式喷发之一，为在一次重大裂谷活动期间将岩石学和地球化学数据与地球物理观测联系起来提供了独特契机。我们展示了在霍鲁赫拉恩火山喷发过程中采集的一组十个样本的熔体包裹体和基质玻璃的主量和微量元素分析结果。霍鲁赫拉恩熔体包裹体中诸如镧/镱等微量元素比值的多样性表明，岩浆是通过中地壳中多种原始熔体的同时混合和结晶而演化的。利用橄榄石 - 斜长石 - 辉石 - 熔体（OPAM）压力计，我们计算出霍鲁赫拉恩携带熔体在2.1±0.7千巴（7.5±2.5千米）的压力下达到平衡，这与喷发开始前几天巴尔达本加中央火山和喷发地点之间地震的深度（6±1千米）一致。使用相同方法，熔体包裹体在0.5至8.0千巴的压力下达到平衡，最可能的压力为3.2千巴。扩散计时法揭示了霍鲁赫拉恩携带熔体中含熔体包裹体的大晶体的最小停留时间尺度为1 - 12天。通过将熔体包裹体的扩散脱水时间尺度与计算出的霍鲁赫拉恩岩浆的水饱和压力相结合，我们计算出指示性岩浆上升速率为0.12 - 0.29米/秒。我们的岩石学和地球化学数据与岩浆从巴尔达本加火山沿浅至中地壳岩脉横向运移至喷发地点的情况一致，正如基于地震和大地测量数据集所推测的那样。这一结果在协调火山构造活动期间岩浆运移的岩石学和地球物理学解释方面向前迈出了重要一步，并为解释火山活跃地区的前兆地震和大地测量数据提供了关键框架。
