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

原始弧岩浆作用——俯冲带热结构的实验限制和影响

基本信息

批准号：
NE/N001966/1
负责人：
Jonathan Blundy
金额：
$ 46.67万
依托单位：
University of Bristol
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FN001966%2F1
关键词：
Primitive arc magmatism experimental constraints

项目摘要

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.

火山弧是火山爆发、地震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，而且对从根本上了解我们的星球都有影响。尽管对弧火山作用进行了几十年的集中研究，但我们对岩浆活动与原生熔体起源之间联系的了解仍然非常有限。例如，关于是什么导致幔源（原始）玄武岩的化学多样性，以及是什么过程导致这些岩浆转化为主要由安山岩组成的地壳岩石，人们没有达成一致意见。同样不清楚的是，弧下的地幔在这一过程中起着什么作用，以及俯冲衍生的流体和熔体如何影响这些过程。我们的目标是解决这个不确定性，通过结合现场，岩石学和建模研究，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，包括30个活跃的成层火山和近200个单成因喷口。克柳切夫斯基火山是克柳切夫斯基火山群的一部分，在过去的5,000年里，克柳切夫斯基火山每年平均产生6300万吨岩浆。克柳切夫斯基火山每年向大气中释放40万吨硫和60万吨二氧化碳，占全球火山排放量的8%。就目前的弧火山活动而言，千岛-堪察加是一个主要的参与者。克柳切夫斯基火山群以其各种原始玄武岩浆而闻名，这些岩浆来自地幔楔，被认为是其余火成岩套的母体。原始弧岩浆活动在世界范围内是非常罕见的，但对于了解弧岩浆的形成和演化至关重要。克柳切夫斯基火山群的另一个重要特征是地幔捕虏体的出现，这些捕虏体是由岩浆带到地表的地幔碎片。这些提供了一个难得的机会，一瞥地球的更深的内部，是了解融化的起源来源。像原始岩浆一样，弧环境中的地幔捕虏体并不常见。在同一火山环境中出现不同的原始岩浆和地幔捕虏体，使堪察加成为回答三个基本问题的理想场所：是什么控制着原始弧岩浆的变异性？这些岩浆是在什么条件下产生的？地幔的不均匀性在形成原始岩浆多样性中起什么作用？本研究将：1）收集和分析天然样品（2）对克柳切夫斯基火山和托尔巴奇克火山的两个原始玄武岩进行高压高温实验，以确定岩浆生成、演化和地幔热状态的压力和温度条件; 3）将联合收割机的实验结果与对自然样品的观察相结合，为提出的问题提供答案。对克柳切夫斯基火山群的研究将增加我们对弧火山作用和俯冲带地球动力学性质的理解。