高度爆炸性的玄武岩喷发:由快速结晶引起的岩浆碎裂

F. Arzilli, G. La Spina, M. Burton, M. Polacci, N. Le Gall, M. Hartley, D. Di Genova, B. Cai, N. Vo, Emily C. Bamber, S. Nonni, R. Atwood, E. Llewellin, R. Brooker, H. Mader, P. Lee
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引用次数: 1

摘要

玄武岩喷发是地球和行星上最常见的火山活动形式。玄武岩岩浆的低粘度通常有利于喷发性和轻度爆炸性火山活动。高爆炸性玄武岩喷发发生的频率较低,其喷发机制仍有争议,这对爆炸性玄武岩火山活动的重大危害有影响。特别是,高度爆炸性的喷发需要岩浆破碎,但目前尚不清楚玄武岩岩浆如何达到破碎阈值。在火山导管中,上升岩浆的结晶动力学是由脱气和冷却驱动的。迄今为止,通过离地结晶实验对岩浆的结晶动力学进行了估计。然而,这种实验方法导致了对硅酸盐熔体结晶动力学的低估。这个# 160;& # 160;本研究中报道的结晶实验是在英国Harwell的Diamond Light Source(实验EE12392在I12光束线上)原位进行的,使用2001年埃特纳火山喷发的玄武岩作为起始材料。我们将定制的高温环境电池与快速同步加速器x射线微断层扫描相结合,实时成像结晶的演变过程。在亚液相状态(1170 °C和1150 °C)下4小时后,系统通过快速冷却(0.4 °C/s)受到扰动,导致过冷度突然增加。我们的研究报告了首次在粗玄武质岩浆中异常快速的斜长石和斜辉石结晶的原位观察。我们将结晶动力学和粘度演化的这些限制与数值管道模型结合起来,表明异常快速的同喷发结晶是在高应变速率下触发玄武岩岩浆破碎所需的基本过程。我们的现场实验和自然观测结合数值管道模型使我们得出结论,火山爆发前的温度
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Highly explosive basaltic eruptions: magma fragmentation induced by rapid crystallisation

Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas generally favours effusive and mildly explosive volcanic activity. Highly explosive basaltic eruptions occur less frequently and their eruption mechanism still remains subject to debate, with implications for the significant hazard associated with explosive basaltic volcanism. Particularly, highly explosive eruptions require magma fragmentation, yet it is unclear how basaltic magmas can reach the fragmentation threshold.

In volcanic conduits, the crystallisation kinetics of an ascending magma are driven by degassing and cooling. So far, the crystallisation kinetics of magmas have been estimated through ex situ crystallization experiments. However, this experimental approach induces underestimation of crystallization kinetics in silicate melts. The   crystallization experiments reported in this study were performed in situ at Diamond Light Source (experiment EE12392 at the I12 beamline), Harwell, UK, using basalt from the 2001 Etna eruption as the starting material. We combined a bespoke high-temperature environmental cell with fast synchrotron X-ray microtomography to image the evolution of crystallization in real time. After 4 hours at sub-liquidus conditions (1170 °C and 1150 °C) the system was perturbed through a rapid cooling (0.4 °C/s), inducing a sudden increase of undercooling. Our study reports the first in situ observation of exceptionally rapid plagioclase and clinopyroxene crystallisation in trachybasaltic magmas. We combine these constraints on crystallisation kinetics and viscosity evolution with a numerical conduit model to show that exceptionally rapid syn-eruptive crystallisation is the fundamental process required to trigger basaltic magma fragmentation under high strain rates. Our in situ experimental and natural observations combined with a numerical conduit model allow us to conclude that pre-eruptive temperatures <1,100°C can promote highly explosive basaltic eruptions, such as Plinian volcanism, in which fragmentation is induced by fast syn-eruptive crystal growth under high undercooling and high decompression rates. This implies that all basaltic systems on Earth have the potential to produce powerful explosive eruptions.

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