Internal triggering of volcanic eruptions: tracking overpressure regimes for giant magma bodies
Internal triggering of volcanic eruptions: tracking overpressure regimes for giant magma bodies
复制标题
火山喷发的内部触发：跟踪巨型岩浆体的超压状态
DOI：
10.1016/j.epsl.2017.05.014
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发表时间：
2017
影响因子：
5.3
通讯作者：
M. Ghiorso
中科院分区：
文献类型：
--
作者：
S. Tramontano;G. Gualda;M. Ghiorso
了解硅质喷发的触发因素对于破译火山爆发及其潜在的社会危害至关重要。在这里，我们使用相平衡模型来确定内部触发的潜在作用-其中岩浆自然演化到不可避免的喷发状态-在流纹岩岩浆体中。从五个大型到超大型流纹岩矿床的全岩成分是用流纹岩熔体模拟的。通过运行不同水分含量的模拟，我们可以跟踪岩浆凝固过程中的结晶和气泡出溶。对于这五个组分，我们使用变热焓和固定压力的模拟。气泡出溶和结晶之间的相互作用可导致体系体积的增加，从而导致岩浆超压。我们发现，在低于300兆帕(地壳深度11公里)的压力下结晶的高硅流纹岩岩浆可以进行内部触发，揭示了上地壳内高硅质喷发的喷发窗口。在较高的压力下，只有当结晶度较高时，才会达到喷发的临界超压阈值，这使得岩浆无法移动--从这样的深度喷发高硅质流纹岩需要外部触发，但例子很少或完全没有。对于许多系统，达到临界超压阈值时计算的结晶度与自然样品中观察到的晶体含量相比较有利，这表明内部演化在触发喷发中起着关键作用。相对于结晶而言，流体饱和发生较晚的系统或脱气有效的系统可以延迟或避免内部触发。我们认为，结晶引发和气泡出溶是岩浆喷发的关键，而外部触发只是爆发性流纹岩喷发的最后一击，而不是驱动力。
Understanding silicic eruption triggers is paramount for deciphering explosive volcanism and its potential societal hazards. Here, we use phase equilibria modeling to determine the potential role of internal triggering – wherein magmas naturally evolve to a state in which eruption is inevitable – in rhyolitic magma bodies. Whole-rock compositions from five large to super-sized rhyolitic deposits are modeled using rhyolite-MELTS. By running simulations with varying water contents, we can track crystallization and bubble exsolution during magma solidification. We use simulations with variable enthalpy and fixed pressure for the five compositions. The interplay between bubble exsolution and crystallization can lead to an increase in the system volume, which can lead to magma overpressurization. We find that internal triggering is possible for high-silica rhyolite magmas crystallizing at pressures below 300 MPa (<11 km depth in the crust), revealing a window of eruptibility within the upper crust from which high-silica eruptions emanate. At higher pressures, the critical overpressure threshold for eruption is only reached once crystallinities are high, >50 wt.%, which makes magma immobile – high-silica rhyolite eruptions from such depths would require external triggering, but examples are scarce or entirely absent. Calculated crystallinities at which the critical overpressure threshold is reached compare favorably with observed crystal contents in natural samples for many systems, suggesting that internal evolution plays a critical role in triggering eruptions. Systems in which fluid saturation happens late relative to crystallization or in which degassing is effective can delay or avoid internal triggering. We argue that priming by crystallization and bubble exsolution is critical for magma eruption, and external triggering serves simply as the final blow – rather than being the driving force – of explosive rhyolitic eruptions.
影响因子：
18.3
作者：
M. Stock;M. Humphreys;V. Smith;R. Isaia;D. Pyle
通讯作者：
M. Stock;M. Humphreys;V. Smith;R. Isaia;D. Pyle
影响因子：
5.3
作者：
S. Watt;D. Pyle;T. Mather
通讯作者：
S. Watt;D. Pyle;T. Mather
影响因子：
18.3
作者：
Caricchi, Luca;Annen, Catherine;Pinel, Virginie
通讯作者：
Pinel, Virginie