Investigation of Ancient and Modern Melting Processes Preserved in Sub-oceanic Island Mantle

发生在地表的板块构造过程最终是由地幔内部的对流控制的。理解地幔对流过程需要对地幔的成分和热变化有更全面的了解。该项目旨在通过研究加那利群岛熔岩中喷发的地幔碎片，即“捕虏体”，来解决地幔成分的变化问题。这些捕虏体保存了它们起源的地幔经历了古代熔融事件（1ga）的证据，但这些事件的化学证据部分被后来在熔岩内部合并和喷发期间对捕虏体的修饰所掩盖。该项目的目标是开发方法，以确定在海洋岛屿（如加那利群岛）下的海洋地幔中保存的古代和现代融化过程，并利用这些新信息来了解地球上地幔的成分变化。对地幔非均质性何时以及如何形成以及在某些情况下如何被破坏的更精确的理解，对我们对地幔熔融过程、熔体成分和地幔物理行为的理解具有深远的影响。通过测量一系列捕体中的Nd-Hf-Os同位素、高亲铁元素以及主元素和痕量元素丰度来解决科学问题，以了解地幔中的长期演化和HSE分布，并研究非均质地幔的生成和保存过程。新数据还将用于评估样品中的熔体相互作用和交代作用。我们的方法将检验关于在海洋或大陆环境中枯竭的地幔域的形成、演化和破坏的假设。这将包括将岛屿上的现代熔融过程与保存在捕虏体中的可能的古代熔融过程进行比较，评估在俯冲带、羽流或山脊环境中产生难熔地幔的模式，或作为全球规模的熔融事件，并探索高度枯竭的难熔地幔域的模式，作为在一些板内岩浆中记录的独特同位素和元素特征的来源。

Plate tectonic processes occurring at the surface are ultimately governed by convection occurring within Earth's mantle. Understanding mantle convection processes requires a fuller understanding of both compositional and thermal variations in the mantle. This project aims to address compositional variations in the mantle, through the study of mantle fragments, known as "xenoliths", erupted in lavas from the Canary Islands. These xenoliths preserve evidence that the mantle from which they originated experienced ancient melting events (1 Ga), but that the chemical evidence for these events have been partly obscured by later modification of the xenoliths during incorporation and eruption within the lavas. Goals of the project are to develop methods to identify ancient and modern melting processes preserved in oceanic mantle beneath ocean islands, like the Canary Islands, and to use this new information to understand compositional variation in the Earth's upper mantle.A more refined understanding of when and how mantle heterogeneities are formed and, in some cases, destroyed has profound impact on our understanding of mantle melting processes, melt composition and physical behaviour of the mantle. Science questions will be addressed by measuring Nd-Hf-Os isotopes, highly siderophile elements and major- and trace-element abundances in a suite of xenoliths to understand the long-term evolution and HSE distribution in the mantle and to examine processes involved in generation and preservation of heterogeneous mantle. The new data will also be used to evaluate melt interactions and metasomatism in samples. Our methods will test hypotheses for the formation, evolution and destruction of depleted mantle domains in oceanic or continental environments. This will include comparison of modern melting processes in the islands with possible ancient melting processes preserved in the xenoliths, to assess models for the generation of refractory mantle in subduction-zone, plume or ridge settings, or as global-scale melting events, and to explore models for highly-depleted, refractory mantle domains as sources of distinct isotopic and elemental signatures recorded in some intraplate magmas.