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

海底岛幔中保存的古代和现代融化过程的调查

• 批准号: 1447130
• 负责人: James Day
• 金额: $ 25万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-01 至 2018-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1447130&HistoricalAwards=false
• 关键词: Investigation; Ancient; Modern; Melting; Processes

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.

地表发生的板块构造过程最终受地幔内发生的对流控制。了解地幔对流过程需要更全面地了解地幔的成分和热变化。 该项目旨在通过研究加那利群岛熔岩中喷发的地幔碎片（称为“捕虏体”）来解决地幔的成分变化。这些捕虏体保存了证据，表明它们起源的地幔经历了古代熔化事件（1 Ga），但这些事件的化学证据已部分被熔岩内合并和喷发过程中捕虏体后来的改变所掩盖。 该项目的目标是开发方法来识别加那利群岛等海洋岛屿下方的海洋地幔中保存的古代和现代熔化过程，并利用这些新信息来了解地球上地幔的成分变化。更深入地了解地幔异质性何时以及如何形成以及在某些情况下被破坏，对我们对地幔熔化过程、熔体成分和地幔物理行为的理解产生深远影响。通过测量一组捕虏体中的 Nd-Hf-Os 同位素、高亲铁元素以及主量和微量元素丰度来解决科学问题，以了解地幔的长期演化和 HSE 分布，并研究异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。我们的方法将测试海洋或大陆环境中贫乏地幔域的形成、演化和破坏的假设。这将包括将岛屿上的现代熔融过程与捕虏体中保存的可能的古代熔融过程进行比较，以评估在俯冲带、地幔柱或山脊环境中形成耐火地幔的模型，或作为全球范围的熔融事件，并探索高度贫化的耐火地幔域的模型，作为一些板内记录的不同同位素和元素特征的来源 岩浆。