Lithium diffusion in olivine records magmatic priming of explosive basaltic eruptions
Lithium diffusion in olivine records magmatic priming of explosive basaltic eruptions
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DOI：
10.1016/j.epsl.2018.08.002
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发表时间：
2018-10
影响因子：
5.3
通讯作者：
K. Lynn;T. Shea;Michael O. Garcia;F. Costa;M. Norman
中科院分区：
文献类型：
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作者：
K. Lynn;T. Shea;Michael O. Garcia;F. Costa;M. Norman
短的持续时间（例如，几个小时到几天）的岩浆过程导致火山爆发，这是具有挑战性的特点，使用传统的岩石学和地球物理方法。对于在实施地震和大地测量监测之前（世纪中期）发生的火山爆发来说，情况尤其如此。我们提出了一个新的应用扩散测时法，利用锂分带橄榄石斑晶调查的后期，喷发前的岩浆混合在夏威夷的Kallauea火山的时间。亚ppm的锂浓度变化的扩散再平衡建模在快速淬火，定向良好的橄榄石从六个爆发期间占主导地位的爆炸期间（1500-1820 CE）。锂时标揭示了原始成分岩浆反复侵入到Keslauea的浅（约2-6公里）水库系统，通常只有几天前，每次喷发。这些时间尺度短于从同一橄榄石晶体中的铁镁和镍分带建模中检索到的数周至数年，这记录了更早的岩浆混合事件。短的锂时间尺度表明，一个入侵启动浅岩浆库可能只有几个小时到几天前爆发。因此，应在其他玄武质火山研究晚期侵入和混合事件，以更好地了解喷发前的过程，从而更好地限制喷发情景。
The short duration (e.g., hours to days) of magmatic processes leading up to volcanic eruptions are challenging to characterize using conventional petrologic and geophysical methods. This is especially true for eruptions that occurred prior to the implementation of seismic and geodetic monitoring (mid-20th century). We present a new application of diffusion chronometry that utilizes lithium zoning in olivine phenocrysts to investigate the timing of late-stage, pre-eruptive magma mixing at Kīlauea Volcano (Hawai‘i). The diffusive re-equilibration of sub-ppm changes in lithium concentration are modeled in rapidly quenched, well-oriented olivine from six eruptions during a dominantly explosive period (1500–1820 CE). Lithium timescales reveal repeated intrusion of primitive composition magma into Kīlauea's shallow (∼2–6 km) reservoir system typically only a few days prior to each eruption. These timescales are shorter than the weeks to years retrieved from modeling Fe–Mg and Ni zoning in the same olivine crystals, which record earlier magma mixing events. The short Li timescales indicate that an intrusion primed the shallow magma reservoir potentially only hours to a few days before an eruption. Late-stage intrusions and mixing events should thus be investigated at other basaltic volcanoes to better understand pre-eruptive processes, so that eruption scenarios can be better constrained.