Primitive arc magmatism - experimental constraints and implications for subduction zone thermal structure

火山弧是火山爆发、地震活动和新大陆地壳形成的场所。了解导致这些现象的相互关联的过程不仅对自然灾害评估有影响，而且对对我们这个星球的基本理解也有影响。尽管几十年来对弧火山作用进行了集中研究，但我们对岩浆活动和原始熔体起源之间的联系的了解仍然非常有限。例如，关于是什么导致地幔(原始)玄武岩的化学多样性，以及什么过程导致这些岩浆转化为以安山岩为主的地壳岩石，目前还没有达成一致意见。目前还不清楚，弧下的地幔在这一过程中扮演了什么角色，以及俯冲衍生的流体和熔体如何影响这些过程。我们的目标是通过现场、岩石学和模型相结合的研究来解决这种不确定性，使用千岛-堪察加火山弧作为我们的天然实验室。千岛-堪察加火山弧是世界上最活跃的弧之一，由30个活跃的层状火山和近200个单生喷口组成。Klyuchevskoy火山是Klyuchevskoy火山群的一部分，在过去的5000年里，它本身每年平均产生6300万吨岩浆。Klyuchevskoy每年向大气中排放40万吨硫和60万吨二氧化碳，占全球火山排放量的8%。Klyuchevskoy火山群以其各种原始玄武岩岩浆而闻名，这些原始玄武岩岩浆源自地幔楔体，被认为是火成岩系列其余部分的母体。原始弧岩浆作用在世界范围内非常罕见，但对于理解弧岩浆的形成和演化是至关重要的。Klyuchevskoy火山群的另一个重要特征是地幔包体的存在，地幔包体是被岩浆带到地表的地幔碎片。这些资料提供了一次难得的机会来窥探地球更深的内部，也是了解熔融起源的来源。与原始岩浆一样，弧形环境中的地幔包体并不常见。在同一火山背景下，不同的原始岩浆和地幔包体的出现使堪察加成为回答三个基本问题的理想地点；是什么控制了原始弧形岩浆的变异性？这些岩浆是在什么条件下产生的？地幔的不均一性在形成原始岩浆多样性中起到了什么作用？本研究将：1)收集和分析Klyuchevskoy和Tolbachk火山的自然样品(岩浆和地幔包体)；2)对Klyuchevskoy和Tolbachk火山的两个原始玄武岩进行高压和高温实验，以约束这些火山下的岩浆生成、岩浆演化和地幔的热状态的压力和温度条件；3)将实验结果与对自然样品的观察相结合，为所提出的问题提供答案。这次对Klyuchevskoy火山群的调查将增加我们对弧火山活动和俯冲带地球动力学性质的理解。

Volcanic arcs are sites of explosive volcanism, seismicity, and the formation of new continental crust. Understanding the linked processes that lead to these phenomena has implications not only for natural hazard assessment but also for the fundamental understanding of our planet. Despite several decades of focussed research on arc volcanism, our knowledge of the links between magmatism and the origin of primary melts remains remarkably limited. There is, for instance, no agreement on what causes the chemical diversity of mantle-derived (primitive) basalts and what processes lead to the conversion of these magmas to crustal rocks with a predominantly andesitic composition. It is also unclear, what role the mantle beneath an arc plays in this process and how subduction-derived fluids and melts influence these processes. We aim to address this uncertainty through a combined field, petrological and modelling study, using the Kuril-Kamchatka volcanic arc as our natural laboratory.Kuril-Kamchatka arc is one of the most active arcs in the world, comprising 30 active stratovolcanoes and nearly 200 monogenetic vents. The Klyuchevskoy volcano, part of the Klyuchevskoy volcanic group, on it own has produced an average of 63,000,000 tons of magma per year over the last 5,000 years. Klyuchevskoy releases 400,000 tons of sulfur and 600,000 tons of CO2 per year into the atmosphere, accounting for up to 8% of the global volcanic discharge. In terms of current arc volcanism Kuril-Kamchatka is a major player.The Klyuchevskoy volcanic group is known for its variety of primitive basaltic magmas, which are derived from the mantle wedge and believed to be parental to the rest of the igneous suite. Primitive arc magmatism is very uncommon worldwide but vital for understanding the formation and evolution of arc magmas. Another important feature of the Klyuchevskoy volcanic group is the occurrence of mantle xenoliths, which are fragments of the mantle carried up to the surface by the magmas. These offer a rare opportunity to glance into the Earth's deeper interior and are a source for understanding the origin of melts. Like primitive magmas, mantle xenoliths in arc settings are not very commonly found.The appearance of diverse primitive magmas and mantle xenoliths in the same volcanic setting makes Kamchatka an ideal place to answer three fundamental questions; what controls the variability of primitive arc magmas? at what conditions are these magmas generated? what role does heterogeneity of the mantle play in generating the diversity of primitive magmas?This study will:1) Collect and analyse natural samples (magmas and mantle xenoliths) from the Klyuchevskoy and Tolbachik volcanoes;2) Conduct high-pressure and high-temperature experiments on two primitive basalts from the Klyuchevskoy and Tolbachik volcanoes to constrain the pressure and temperature conditions of magma generation, magma evolution and thermal state of the mantle beneath these volcanoes;3) Combine experimental results with observations on natural samples to provide the answers to posed questions. This investigation of the Klyuchevskoy volcanic group will increase our understanding of the nature of arc volcanism and subduction zone geodynamics.