The dynamics of magma storage and ascent beneath an active arc volcano (Villarrica, Chile)

火山弧，形成沿着会聚板块边缘，产生地球的陆上火山活动，并负责最大和最具破坏性的历史喷发。在弧，在俯冲板块上方的地幔中产生的岩浆上升通过岩石圈，在那里它被储存和化学处理，然后在地表喷发，通常来自大型成层火山。了解控制这些储存的岩浆最终何时以及如何离开其地壳水库喷发的因素，以及喷发可能的规模，仍然是火山学的中心目标，并应有助于更准确地预测未来的喷发。该项目将采用地球化学和岩石学方法来限制从智利南部（比利亚里卡）一座弧火山喷发的岩浆的喷发前过程、储存条件和（或）来源，该火山曾在冰川期后造成多次规模不等的喷发。比利亚里卡是智利最活跃的火山之一，是南部火山区（SVZ）火山群的一部分。火山活动沿着SVZ受到构造的强烈影响，比利亚里卡沿着与区域走滑断层系统（Liquine Ofqui断层带）相关的断裂系统。该火山还经历了广泛的晚更新世冰川作用，其山顶地区仍然永久被冰雪覆盖。冰后期活动在比利亚里卡已经从小体积的喷发事件，大熔结凝灰岩形成火山碎屑喷发。尽管在喷发规模的范围，值得注意的是，大多数这些事件涉及相对镁铁质岩浆，典型的玄武质到玄武安山岩的成分。因此，比利亚里卡的大爆发并不涉及与那些供给较小的低强度爆发相比经历了显著程度的储存和/或分馏的岩浆。同样值得注意的是，虽然较小的喷发通常在成分上彼此不同，但大体积的喷发往往在成分上相对均匀，这意味着构成岩浆系统的离散熔融批次的有效混合，为更常见的较小喷发提供原料。此外，大地测量研究表明，比利亚里卡周围地面变形的最大程度被推断与岩浆运动有关，偏离火山中心数公里，这意味着至少有一些注入火山的岩浆横向穿过地壳。这项研究将涉及一个比较研究的条件下，岩浆生成和存储与喷发的比利亚里卡，不同的大小之间的小锥形成事件，大火山碎屑喷发。您将在智利进行实地考察，从几次火山爆发中采集沉积物样本，以覆盖尽可能广泛的火山爆发规模。在对这些样品进行岩相学表征后，您将开始一项旨在限制这些熔体的起源以及喷发前储存条件的分析计划。

Volcanic arcs, formed along convergent plate margins, produce most of Earth's subaerial volcanic activity and are responsible for the largest and most devastating historical eruptions. At arcs, magma generated in the mantle above the subducting slab ascends through the lithosphere, where it is stored and chemically processed before feeding eruptions at the surface, typically from large stratovolcanoes. Understanding the factors that govern when and how this stored magma ultimately leaves its crustal reservoir(s) to be erupted, and what size that eruption is likely to be, remains a central goal of volcanology and should facilitate more accurate forecasts of future eruptions. This project will employ geochemical and petrological methods to constrain pre-eruptive processes, storage conditions and/or origins of magmas erupted from an arc volcano in southern Chile (Villarrica) that has produced numerous post-glacial eruptions of varying magnitude. Villarrica is one of Chile's most active volcanoes and forms part of the southern Volcanic Zone (SVZ) group of volcanoes. Volcanism along the SVZ has been strongly influenced by tectonics and Villarrica lies along a fracture system associated with a regional strike-slip fault system, the Liquine Ofqui fault zone. The volcano has also experienced extensive late-Pleistocene glaciation and its summit region remains permanently ice-covered. Postglacial activity at Villarrica has varied from small-volume eruptive events to large ignimbrite forming pyroclastic eruptions. Despite this range in eruption magnitude, it is notable that the majority of these events involve relatively mafic magmas, typically basaltic to basaltic-andesitic in composition. Large explosive eruptions of Villarrica do not therefore involve magmas that have undergone significant extents of storage and/or fractionation compared to those feeding smaller lower-intensity eruptions. It is also notable that while smaller eruptions typically vary in composition from each other, large volume eruptions tend to be relatively compositionally homogenous, implying efficient mixing of the discrete melt batches that constitute the magma system feeding the more common smaller eruptions. In addition, geodetic studies show that maximum extents of ground deformation around Villarrica, inferred to be linked to magma movement, are offset from the centre of the volcano by several kms, implying that at least some of the magmas feeding the volcano move laterally through the crust. This research will involve a comparative study of the conditions of magma generation and storage associated with eruptions of Villarrica that vary in size between small cone forming events to large pyroclastic eruptions. You will undertake fieldwork in Chile to sample deposits from several eruptions, selected to cover as wide a range of eruption magnitudes as possible. After petrographic characterization of these samples, you will embark on an analytical programme designed to constrain the origin of these melts as well as the condition of pre-eruptive storage.