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Calderas and magma reservoirs

机译：火山口和岩浆储层

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Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; petrolo-gists have used the eruptive products to probe conditions of magma storage (and thus processes that drive magma evolution), while volcanologists have used them to study the conditions under which large volumes of magma are transported to, and emplaced on, the Earth's surface. Traditionally, both groups have worked on the assumption that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. Here we explore the implications of complex magma reservoir configurations for eruption dynamics and caldera formation. We first examine mafic systems, where stacked-sill models have long been invoked but which rarely produce explosive eruptions. An exception is the 2010 eruption of Eyjafjallajoekull volcano, Iceland, where seismic and petrologic data show that multiple sills at different depths fed a multi-phase (explosive and effusive) eruption. Extension of this concept to larger mafic caldera-forming systems suggests a mechanism to explain many of their unusual features, including their protracted explosivity, spatially variable compositions and pronounced intra-eruptive pauses. We then review studies of more common intermediate and silicic caldera-forming systems to examine inferred conditions of magma storage, time scales of melt accumulation, eruption triggers, eruption dynamics and caldera collapse. By compiling data from large and small, and crystal-rich and crystal-poor, events, we compare eruptions that are well explained by simple evacuation of a zoned magma chamber (termed the Standard Model by Gualda and Ghiorso, 2013) to eruptions that are better explained by tapping multiple, rather than single, melt lenses stored within a largely crystalline mush (which we term complex magma reservoirs). We then discuss the implications of magma storage within complex, rather than simple, reservoirs for identifying magmatic systems with the potential to produce large eruptions, and for monitoring eruption progress under conditions where successive melt lenses may be tapped. We conclude that emerging views of complex magma reservoir configurations provide exciting opportunities for re-examining volcanological concepts of caldera-forming systems.
机译：长期以来，大型火山口喷发一直是岩石学和火山学研究的重点。石油学家使用火山喷发物探测岩浆的储藏条件（以及由此驱动岩浆演化的过程），而火山学家则用它们研究大量岩浆被运输到地球表面并在其上安放的条件。 。传统上，两个小组都基于这样的假设，即可爆发的岩浆被储存在一个长寿命的熔体中。然而，在过去的十年中，分析技术的进步为岩浆储存区域提供了新的视角，其中许多证据证明多个熔体透镜可以一次喷发，和/或大量喷出的熔体快速喷发前组装。岩浆系统的观点尚未完全融合到火山口形成火山喷发的观点中。在这里，我们探讨了复杂的岩浆储层构造对喷发动力学和破火山口形成的影响。我们首先研究铁磁系统，在该系统中长期以来一直使用堆积基石模型，但很少产生爆炸性喷发。唯一的例外是2010年冰岛Eyjafjallajoekull火山喷发，那里的地震和岩石学数据表明，不同深度的多个基岩为多相（爆炸性和喷发性）喷发。将该概念扩展到较大的镁铁质火山口形成系统，提出了一种机制来解释其许多不寻常的特征，包括其持久的爆炸性，空间可变的成分和明显的喷发内停顿。然后，我们回顾对更常见的中间和硅质破火山口形成系统的研究，以检查推断的岩浆储藏条件，熔体聚集的时间尺度，喷发触发，喷发动力学和破火山口塌陷。通过汇总大小事件，晶体丰富和晶体贫乏的事件的数据，我们比较了通过简单地疏散分区岩浆室（由Gualda和Ghiorso，2013年称为“标准模型”）与通过通过轻拍存储在很大程度上为晶体的糊状物（我们称为复杂岩浆储层）中的多个而不是单个熔融透镜，可以更好地解释。然后，我们讨论了在复杂而不是简单的储层中进行岩浆储藏的意义，这些储层对于识别有可能产生大喷发的岩浆系统，以及在连续的熔融透镜可能被抽出的情况下监测喷发的进展。我们得出的结论是，复杂岩浆储层构造的新观点为重新研究火山口形成系统的火山学概念提供了令人兴奋的机会。

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