Melt inclusion constraints on petrogenesis of the 2014-2015 Holuhraun eruption, Iceland
Melt inclusion constraints on petrogenesis of the 2014-2015 Holuhraun eruption, Iceland
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DOI：
10.1007/s00410-017-1435-0
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发表时间：
2018-02-01
影响因子：
3.5
通讯作者：
Halldorsson, Saemundur A.
中科院分区：
文献类型：
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作者：
Hartley, Margaret E.;Bali, Eniko;Halldorsson, Saemundur A.
2014-2015 年发生在冰岛中部 Baroarbunga 火山系统的 Holuhraun 喷发是有史以来监测最完善的玄武岩裂隙喷发之一，并提供了将岩石学和地球化学数据与重大裂谷期间的地球物理观测联系起来的独特机会。我们对 Holuhraun 喷发过程中收集的十个样品中的熔体包裹体和基质玻璃进行了主量和微量元素分析。 Holuhraun熔体包裹体中La/Yb等微量元素比例的多样性表明，岩浆是通过中地壳中多种原生熔体的同时混合和结晶而演化的。使用橄榄石-斜长石-辉石-熔体 (OPAM) 气压计，我们计算出 Holuhraun 载体熔体平衡在 2.1 +/- 0.7 kbar (7.5 +/- 2.5 km)，这与喷发前几天 Baroarbunga 中央火山和喷发地点之间的地震深度 (6 +/- 1 km) 一致。使用相同的方法，熔体夹杂物在 0.5 至 8.0 kbar 之间的压力下达到平衡，最可能的压力为 3.2 kbar。扩散计时法揭示了 Holuhraun 载体熔体中含有熔体夹杂物的宏观晶体的最短停留时间为 1-12 天。通过将熔体包裹体扩散脱水的时间尺度与Holuhraun岩浆的-H2O饱和度的计算压力相结合，我们计算出指示性岩浆上升速率为0.12-0.29 m s(-1)。正如地震和大地测量数据集所表明的那样，我们的岩石学和地球化学数据与从巴罗阿尔本加火山到浅中地壳岩脉中的喷发地点的横向岩浆输送一致。这一结果在协调火山构造时期岩浆输送的岩石学和地球物理解释方面向前迈出了重要一步，并为解释火山活动区域的先兆地震和大地测量数据提供了关键框架。
The 2014-2015 Holuhraun eruption, on the Baroarbunga 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 Baroarbunga 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 - H2O saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12-0.29 m s(-1). Our petrological and geochemical data are consistent with lateral magma transport from Baroarbunga 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.