Late-stage volatile saturation as a potential trigger for explosive volcanic eruptions
Late-stage volatile saturation as a potential trigger for explosive volcanic eruptions
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DOI：
10.1038/ngeo2639
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发表时间：
2016-03
影响因子：
18.3
通讯作者：
M. Stock;M. Humphreys;V. Smith;R. Isaia;D. Pyle
中科院分区：
文献类型：
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作者：
M. Stock;M. Humphreys;V. Smith;R. Isaia;D. Pyle
岩浆库被认为生长相对缓慢，在挥发物饱和的条件下逐渐聚集。喷发可能是由于注入富含挥发物的熔体或由于长时间结晶而产生的过压而引发的。在这里，我们分析了在岩浆演化的不同阶段捕获的磷灰石晶体中的氟、氯和水，以及大约 4,000 年前意大利 Campi Flegrei 火山口爆发时喷出的单斜辉石和黑云母晶体的熔体包裹体中的氟、氯和水。我们将地球化学分析与热力学模型相结合，重建导致爆炸性喷发的岩浆挥发物含量的演化。我们发现岩浆库在其生命周期的大部分时间里一直处于水不饱和状态。即使是在喷发前不久与熔体接触的晶体也表明岩浆是挥发性的——不饱和的。我们的模型表明，在喷发之前，熔体在低温下达到了挥发饱和度。我们认为，后期挥发性饱和可能引发了喷发，并得出结论，岩浆系统喷发的“启动”可能发生在比岩浆储库聚集典型的十年到百年时间尺度短得多的时间尺度上。因此，记录 Campi Flegrei 和其他类似岩浆系统下方深处岩浆聚集的地表变形脉冲可能不会立即发生喷发；爆炸性喷发可能会在没有任何警告的情况下开始。
Magma reservoirs are thought to grow relatively slowly, assembling incrementally under volatile-saturated conditions. Eruptions may be triggered by injections of volatile-rich melt, or generation of over-pressure due to protracted crystallization. Here, we analyse fluorine, chlorine and water in apatite crystals trapped at different stages of magma evolution, and in melt inclusions from clinopyroxene and biotite crystals expelled during an explosive eruption of the Campi Flegrei caldera, Italy, about 4,000 years ago. We combine our geochemical analyses with thermodynamic modelling to reconstruct the evolution of magmatic volatile contents leading up to the explosive eruption. We find that the magma reservoir remained persistently water-undersaturated throughout most of its lifetime. Even crystals in contact with the melt shortly before eruption show that the magma was volatile-undersaturated. Our models suggest that the melt reached volatile saturation at low temperatures, just before eruption. We suggest that late-stage volatile saturation probably triggered the eruption, and conclude that ‘priming’ of the magma system for eruption may occur on timescales much shorter than the decadal to centennial timescales thought typical for magma reservoir assembly. Thus, surface deformation pulses that record magma assembly at depth beneath Campi Flegrei and other similar magmatic systems may not be immediately followed by an eruption; and explosive eruptions may begin with little warning.