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)智力成果：这项研究调查了地质因素，例如构造、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活动的变化相关。火山化学信号。 为了完成这项任务，对西太平洋伊豆小博宁-马里亚纳弧的始新世至渐新世深海沉积物岩心样本进行了一系列地球化学和同位素分析。 这项工作的合理性来自于这样一个事实：火山弧熔岩和火山灰含有地球化学成分，这些成分反映了海底俯冲和俯冲板片重新同化到地幔中时发生的熔化、挥发物和熔化过程。 这些过程造成了当今海水和大气的许多化学特征，并且与重大地震事件的发生有关。 最完整的岛弧火山活动记录之一来自伊豆小博宁-马里亚纳岛弧，该岛弧已活跃约 5000 万年。 然而，在那个位置，岩浆记录的最古老部分（始新世-渐新世）存在一个空白，因为在弧构造的早期阶段喷发的熔岩被埋藏起来，通常无法进行研究。 然而，在这段时间内发生的火山喷发所产生的火山灰很容易从深海沉积物核心中获取，因为它们是沉积在大片地理区域的空降沉积物。 在美国国家科学基金会 (NSF) 资助的海洋钻探计划 (ODP) 的取芯探险中收集了此类火山灰的完整记录。 该研究计划使用来自始新世-渐新世时间间隔内的 ODP 岩心的火山灰样本，通过主量元素和微量元素分析来识别伊豆博宁-马里亚纳岛弧在此时间间隔内的长期变化。 此外，还将确定相同样品的 Sr-Nd-Pb-Hf 同位素比，以推断板块和地幔岩浆来源的变化。 使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敏感的元素和比例。 除了火山灰之外，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本均经过精心挑选，确保其新鲜度，以防止分析原始化学特征已发生变化的材料。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。 它为两名女性研究人员提供支持，其中一名患有听力障碍，通过火山灰研究在建立伊豆-小笠笠弧的化学演化方面做出了开创性的工作，另一名正在重返全职工作岗位。 这项工作还支持哥伦比亚大学的分析基础设施，并让一名本科生参与研究。