Spatio-temporal evolution of crystal-mush horizons in the Icelandic crust - A case study of the northern segment of the Bárdarbunga volcanic system

在过去的三十年中，岩石学和地球物理研究日益挑战了以熔体为主的单一岩浆库的经典观点。垂直扩展的“岩浆柱”概念由一个错综复杂的相互连接的网络组成，嵌入在部分凝固的晶体糊状带中的多层次岩浆储存层（基）现在被认为是更现实的。晶体浆糊区是动态体，由流变学上“更硬”的晶体浆糊框架组成，具有不同形状和大小的分散熔融透镜；在晶体糊区，晶体与熔体的比例随时间和空间的变化而变化。尽管许多证据都支持冰岛轴向裂谷下地壳中存在晶体糊状带，但我们的理解仍然有限。尽管如此，它的存在对岩浆的快速生成和动员意义重大。为了解决水晶泥带在冰岛火山活动中的作用，我们着重于以下关键问题。(1)岩浆储存的性质是什么？(2)存储网络的垂直范围是什么？(3)浆糊带是由什么构成的？浆糊带是如何处理岩浆的？(4)岩浆储存、加工和动员的时间尺度是什么？我们将使用一种将纹理数据与最先进的定量岩石地球化学方法和高精度扩散建模相结合的综合方法来研究这些问题。我们的方法将应用于一套独特的时间和地球化学约束良好的拉斑玄武岩，这些玄武岩来自高度活跃的Bárðarbunga裂缝群的北段，这是冰岛最具生产力和最大的火山系统之一。这个为期3年的项目提供了一种新的、定量的评估岩浆储存、聚集、再动员和通过Bárðarbunga裂缝群规模的晶体-糊状带转移的时空演化。该研究将对中、下洋地壳的厚度、结构、组成和物理状态提供重要的认识，并将巩固我们对活动扩张边缘地壳增生和形成的认识。

Classical views of magma storage in melt-dominated single chambers have been increasingly challenged by petrological and geophysical studies over the past three decades. The concept of vertically extensive ‘magma columns’ consisting of an intricate network of interconnected, multi-level magma storage horizons (sills) embedded in partially solidified crystal-mush zones is now considered more realistic. Crystal-mush zones are dynamic bodies comprising a rheologically ‘stiffer’ framework of crystal-mush with interspersed melt lenses of variable shape and size; the proportion of crystal to melt fractions within crystal-mush zones varies in both space and time. Although the existence of crystal-mush zones in the crust beneath the Icelandic Axial Rift is supported by many lines of evidence, our understanding remains limited. Nevertheless, the implications of its existence for the rapid generation and mobilisation of magma are highly significant. In order to address the role of crystal-mush zones in volcanism in Iceland we focus on the following key questions. (1) What is the nature of magma storage? (2) What is the vertical extent of the storage network? (3) What is the mush zone made of and how does it process magma? (4) What are the timescales of magma storage, processing, and mobilization? We will investigate these questions using an integrated approach linking textural data with state-of-the-art quantitative petrological-geochemical methods and high-precision diffusion modelling. Our approach will be applied to a unique suite of temporally and geochemically well-constrained tholeiitic basalts from the northern segment of the highly-active Bárðarbunga fissure swarm, one of Iceland’s most productive and largest volcanic systems. This 3-year project offers a novel, quantitative assessment of the spatial and temporal evolution of magma storage, accumulation, remobilisation and transfer through crystal-mush zones one the scale of Bárðarbunga fissure swarm. The proposed study will provide key insights into to the thickness, structure, composition and physical state of the mid- to lower oceanic crust and will consolidate our understanding of crustal accretion and formation in an active spreading margin.