Reconstructing Slab and Mantle Fluxes During th Eocene-Oligocene Evolution of the Izu-Bonin Volcanic Arc

重建伊豆-小笠宁火山弧始新世-渐新世演化过程中的板片和地幔通量

• 批准号: 0453515
• 负责人: Susanne Straub
• 金额: --
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-06-01 至 2009-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0453515&HistoricalAwards=false
• 关键词: Reconstructing; Slab; Mantle; Fluxes; During

ABSTRACT - Goldstein (0453515)Intellectual Merit: This research investigates geologic factors, such as tectonics, subduction, and changes in the compositional evolution of the upper mantle, that affect volcanism through time, an objective being to determine how these factors relate to changes in volcanic chemical signals. To accomplish this task, samples of fragmental volcanic rocks (tephra) from Eocene to Oligocene deep sea sediment cores from the Izu Bonin-Mariana arc in the western Pacific were targeted for a host of geochemical and isotopic analyses. Justification of this work comes from the fact that volcanic arc lavas and tephra contain geochemical components that reflect melts, volatiles, and melt processes that occur as the ocean floor subducts and the subducting slab reassimilates into the mantle. Such processes are responsible for many of the chemical characteristics of present day seawater and the atmosphere and are related to the genesis of major earthquake events. One of the most completely characterized records of arc volcanism comes from the Izu Bonin-Mariana arc which has been active for ~ 50 million years. At that location, however, there is a gap in the oldest part of the magmatic record (Eocene-Oligocene) because lavas erupted in the early stages of arc construction are buried and generally inaccessible to study. Nevertheless, tephra from eruptions that took place during this time gap, are easily accessible from deep sea sediment cores because they are airfall deposits that are deposited over large geographical areas. A complete record of such tephra has been collected during coring expeditions of the NSF-funded Ocean Drilling Program (ODP). This research program uses tephra samples from ODP cores that occur in the Eocene-Oligocene time gap to identify secular changes in Izu Bonin-Mariana arc during this time interval using major element and trace element analyses. In addition, Sr-Nd-Pb-Hf isotopic ratios will be determined for the same samples to infer changing slab and mantle magma sources. The use of tephra to unravel volcanic arc evolution is a new approach in this area and geochemical analyses will focus on elements and ratios that are sensitive to both the composition of slab fluids and melt components. In addition to the tephra, similar geochemical analyses will be performed on select Oligocene lavas to tie the tephra results to the lavas erupted in the region. The tephra samples used in this study have been carefully selected for freshness to prevent analysis of altered materials for which the original chemical signature has changed. Broader Impacts: This research is an essential element of the NSF-funded MARGINS subduction factory initiative. It supports two female researchers, one of which is hearing disabled and has performed pioneering work in establishing the chemical evolution of the Izu-Bonin arc through tephra studies, and the other who is returning to the full-time workforce. The work also supports analytical infrastructure at Columbia University and engages an undergraduate student in research.

摘要- Goldstein（0453515）学术成就：这项研究调查了地质因素，如构造、俯冲和上地幔成分演化的变化，这些因素随着时间的推移影响火山活动，目的是确定这些因素如何与火山化学信号的变化相关。 为了完成这项任务，对西太平洋伊豆小笠原-马里亚纳岛弧始新世至渐新世深海沉积物岩心的碎屑火山岩（火山碎屑岩）样品进行了大量的地球化学和同位素分析。 这项工作的理由来自于这样一个事实，即火山弧熔岩和火山灰含有反映熔融物，挥发物和熔融过程发生的洋底俯冲和俯冲板片再同化到地幔的地球化学成分。 这些过程是造成当今海水和大气的许多化学特性的原因，并与大地震事件的成因有关。 最完整的弧火山活动记录来自伊豆小笠原-马里亚纳弧，该弧已经活跃了约5000万年。 然而，在那个位置，在岩浆记录的最古老部分（始新世-渐新世）有一个空白，因为在弧构造的早期阶段喷发的熔岩被掩埋，通常无法进行研究。 然而，在这段时间间隔内发生的火山喷发的火山灰很容易从深海沉积物岩心中获得，因为它们是沉积在大片地理区域的大气沉降物。 在美国国家科学基金会资助的大洋钻探计划（ODP）的取芯考察期间，已经收集了这种火山灰的完整记录。 本研究计划使用火山碎屑岩样品ODP核心发生在始新世渐新世时间间隔，以确定长期的变化，在此期间，伊豆小笠原马里亚纳弧的主要元素和微量元素分析。 此外，Sr-Nd-Pb-Hf同位素比值将确定相同的样品，以推断不断变化的板幔岩浆来源。 利用火山灰来揭示火山弧演化是该领域的一种新方法，地球化学分析将重点关注对板片流体和熔体成分的组成敏感的元素和比例。 除火山灰外，还将对选定的渐新世熔岩进行类似的地球化学分析，以将火山灰结果与该地区喷发的熔岩联系起来。 本研究中使用的火山灰样品经过精心挑选，以保持新鲜，防止分析原始化学特征发生变化的改变材料。更广泛的影响：这项研究是NSF资助的MARGINS俯冲工厂计划的重要组成部分。 它支持两名女性研究人员，其中一名是听力残疾者，通过火山灰研究在建立伊豆-小笠原弧的化学演变方面进行了开创性工作，另一名正在返回全职工作队伍。 这项工作还支持哥伦比亚大学的分析基础设施，并使一名本科生参与研究。