Temporal/spatial scales of mantle wedge composition and processes investigated with young boninites and basalts from the unusually active NE Lau Basin

这个项目是对俯冲带火山岩的研究，以了解它们是如何形成的。俯冲带是地球表面的物质（沉积物、火山岩和其他岩石物质）返回地幔的地方。在这个过程中，流体从俯冲物质的“板块”中下降，导致上覆的地幔融化，产生岩浆，推动了地球上很大一部分的火山活动。尽管对岩浆活动发生的方式和地点、火山样式和产物的范围以及它们对人类社会的贡献（危害、矿石形成、景观演变等）进行了50年的研究，但关于地幔融化的条件和时间尺度、可能融化的不同类型的岩石以及这些不同地下岩石区域的大小和形状，仍然存在许多问题。此外，对于所有这些因素是如何影响最终喷发的岩浆类型以及喷发的方式（例如，多大、多频繁、多爆炸性），科学家们仍然知之甚少。这个研究项目利用最近爆发的稀有火山岩来解决这些问题。这些岩石是在高温条件下将水加入到浅层地幔中形成的。地球化学、同位素地球化学和这些岩石中自然发生的放射性元素分布的工具将用于分析已经存在的、独特的一组样品。项目目标是确定：(1)俯冲带下地幔成分的多样性和空间尺度，(2)它们融化的时间尺度，(3)岩浆如何形成并迁移到地表，以及(4)这对火山活动的影响。这些问题的答案对社会和国家利益具有更广泛的影响，因为它们提供了在俯冲带导致岩浆活动和火山活动（以及相关的危害和利益）的过程的信息，这些俯冲带既发生在美国西海岸以外，也发生在美国的许多美洲、加勒比和环太平洋地区的伙伴国家（如日本、台湾和新西兰）的海岸。此外，该项目将资助EPSCoR州（夏威夷）的一所机构，支持一名早期职业研究人员，并通过NOAA外联引擎和夏威夷大学网站开展公众外联。本项目将研究洋间俯冲带的火山作用，使用一组独特的年轻博宁岩和相关的基性/超基性样品，这些样品来自9座马塔火山和邻近的弧后火山（东北劳和福瓦莱扩张中心）。u系列不平衡、Sr-Nd-Pb-Hf同位素分析以及已收集的火山玻璃、矿物和整块岩石中的主要/微量元素丰度将用于研究活动洋间弧/弧后高分辨率（km尺度）地幔楔体非均质性、俯冲流体输入的次千年变化以及宝钢岩和其他岩浆成岩条件。假设将被测试，以解决俯冲板块的流体如何引起上覆地幔的融化，不同成分的地幔如何融化，不同的岩浆如何以在小空间尺度上保持岩浆成分大变化的方式被输送到地表，以及这些不同过程的时间尺度，初步数据表明，在某些情况下，这些过程可能比迄今为止认识到的要快得多。

This project is a study of subduction zone volcanic rocks to understand how they form. Subduction zones are places where materials from Earth's surface (sediments, volcanic rocks, and other rocky materials) are returned to the mantle. During this process fluids are drawn from the "slab" of subducting material while it descends, causing the overlying mantle to melt, producing magmas that drive a significant portion of Earth's volcanism. Despite 50 years of research about how and where this magmatic activity occurs, the range of volcanic styles and products, and their contributions to human society (hazards, ore formation, landscape evolution, etc.), numerous questions remain about the conditions and timescales of melting in the mantle, the different types of rocks that might melt, and the sizes and shapes of these different subterranean rock regions. In addition scientists still have a very incomplete picture of how all of these things contribute to what type of magma is ultimately erupted and what style the eruptions take (for example, how big, how frequent, how explosive). This research project addresses these questions using recently erupted, rare, volcanic rocks called boninites. These rocks form when H2O is added to the shallow mantle under very high temperature conditions. The tools of geochemistry, isotope geochemistry, and naturally-occurring radioactive element distributions in these rocks will be used to analyze an already existing, unique, set of samples. Project goals are to determine: (1) the variety and spatial scale of mantle compositions beneath this subduction zone, (2) the timescales over which they melt, (3) how magma forms and migrates to the surface, and (4) how this contributes to volcanic activity. Answers to these questions have broader impacts to society and the national interest because they provide information on processes leading to magmatism and volcanism (and associated hazards and benefits) at subduction zones, which occur both off the western coast of the United States and along the coasts of many of our partner nations in the Americas, Caribbean and Pacific Rim, like Japan, Taiwan and New Zealand. In addition, the project will fund an institution in an EPSCoR state (Hawaii), support an early career researcher, and carry out public outreach through the NOAA outreach engine and U Hawaii websites. This project will study interoceanic subduction zone volcanism, using a unique set of young boninite and related mafic/ultramafic samples from the nine Mata Volcanoes and neighboring rear arc and back arc volcanoes (Northeast Lau and Fonualei Spreading Centers). U-series disequilibria and analyses of Sr-Nd-Pb-Hf isotopes, and major/trace element abundances in already-collected volcanic glasses, minerals and whole rocks will be used to investigate high resolution (km-scale) mantle wedge heterogeneity at an active inter-oceanic arc/backarc, sub-millennial variations in subduction fluid inputs, and conditions of boninite and other magma petrogenesis. Hypotheses will be tested to address how fluids from the subducting slab induce melting in the overlying mantle, how different compositions of mantle melt, how different magmas are delivered to the surface in a way that preserves large variations in magma composition over small spatial scales, and the timescales of these various processes, which prelimimary data indicates is likely to be much faster in some cases than heretofore realized.