A Mixed Up Mantle Beneath Ocean Islands?

大洋岛屿下的混合地幔？

• 批准号: 1918322
• 负责人: James Day
• 金额: $ 24.41万
• 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: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1918322&HistoricalAwards=false
• 关键词: Mixed; Up; Mantle; Beneath; Ocean

Basaltic volcanic islands, which occur in all major ocean basins, do not fit particularly well in plate tectonic theory. The lavas from these islands have distinct compositions from basaltic rocks erupted at mid-ocean ridges, indicating the presence of subducted oceanic crust in some of their mantle sources. Current models for the generation of ocean island basalts favor either partial melting of mantle sources with two different rock-types, pyroxenite and peridotite, or sources with only "fertile" peridotite that can readily partially melt. The models are driven by the observation that direct partial melting of recycled oceanic crust cannot generate basaltic compositions. Both source types are therefore thought to form by melting and melding of subducted crust with peridotite in Earth's mantle. How these sources form and melt, in detail, are quite different, with pyroxenite indicating large-scale mantle heterogeneity. An accepted means for detecting pyroxenite is through precise measurement of olivine compositions in basalts. Precious metals such as osmium can also be used to examine between peridotite versus pyroxenite-dominated melting, and the most sensitive method for detecting recycled crustal contributions is from long-lived radiogenic isotopes, like strontium. This work will combine these methods to test whether pyroxenite exists in oceanic island sources through study of two locations where significant recycled crust components are known to exist; Mangaia in the Cook Islands, and the Canary Islands archipelago. New results, which will be partially generated by undergraduate students engaged in research and in the Scripps Undergraduate Research Fellowships (SURF) program, and who will also help publicly communicate the work, will enhance understanding of the fundamental process of basaltic melt generation, and enhance understanding of how ocean islands fit in plate tectonic theory.This project will examine the role of pyroxenite-peridotite or fertile peridotite melting in the generation of ocean island basalts (OIB) through examination of two key OIB localities. The first locality is Mangaia (Cook Islands), where long-lived radiogenic isotope (Sr-Nd-Os-Pb) variations will be coupled with olivine compositions to examine a location without a strong pyroxenite melting signature but that does have a strong recycled crustal signature (HIMU). The goal of this task is to quantify mantle source composition for an extreme recycled endmember composition in OIB petrogenesis. The second task is to evaluate pyroxenite-peridotite contributions to Canary Islands that also have a HIMU signature. Studies have argued for pyroxenite contributions, but with different endmember compositions. Here, new high-precision electron microprobe data will be collected for olivine grains in lavas from the islands to combine with Sr-Nd-Os-Pb isotope variations and highly siderophile element abundances. With these data, it will be possible to discriminate between depleted or enriched pyroxenite sources and to investigate if high pressure-temperature melting of fertile peridotite might offer an alternative. Research will include integration of undergraduates and underrepresented minorities who will also be engaged, along with the PI and graduate student, in outreach events that will take place in the San Diego region and in the Canary Islands, and through participation in organized STEM events.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

玄武岩火山岛，出现在所有主要的海洋盆地，并不特别适合板块构造理论。来自这些岛屿的熔岩具有与大洋中脊喷发的玄武质岩石不同的成分，表明在它们的一些地幔来源中存在俯冲洋壳。目前的洋岛玄武岩的生成模型有利于两种不同的岩石类型，辉石岩和橄榄岩，或只有“肥沃”的橄榄岩，可以很容易地部分熔融的地幔源部分熔融。这些模型是由观察到的，直接部分熔融回收的海洋地壳不能产生玄武岩成分。因此，这两种源类型都被认为是通过俯冲地壳与地幔中的橄榄岩熔融和融合而形成的。这些物质源的形成和熔融的详细方式是完全不同的，辉石岩指示大规模的地幔不均匀性。一种公认的检测辉石岩的方法是通过精确测量玄武岩中的橄榄石成分。锇等贵金属也可以用来检查橄榄岩与辉石为主的熔融之间的关系，而检测再循环地壳贡献的最敏感方法是来自长寿命放射性同位素，如锶。这项工作将联合收割机结合这些方法，通过研究两个已知存在重要再生地壳成分的地点，即库克群岛的曼加亚和加那利群岛，来测试辉石岩是否存在于大洋岛屿来源中。新的结果，这将部分由从事研究和斯克里普斯大学本科研究奖学金（SURF）计划的本科生产生，谁也将有助于公开交流工作，将加强对玄武岩熔体生成的基本过程的理解，并加强对海洋岛屿如何适应板块构造理论的理解。本项目将研究辉石岩的作用-橄榄岩或肥沃的橄榄岩熔融在洋岛玄武岩（OIB）的产生，通过检查两个关键的OIB地点。第一个地点是Mangaia（库克群岛），其中长寿命的放射性同位素（Sr-Nd-Os-Pb）的变化将与橄榄石成分相结合，以检查一个没有强烈的辉石岩熔融签名，但确实有很强的再循环地壳签名（HIMU）的位置。这项任务的目标是量化地幔源组成的极端回收OIB岩石成因的端元组合物。第二个任务是评估辉石岩橄榄岩的贡献，加那利群岛也有一个HIMU签名。研究认为辉石岩的贡献，但不同的端元组成。在这里，将收集新的高精度电子探针数据的火山岩中的橄榄石颗粒从岛屿联合收割机与Sr-Nd-Os-Pb同位素的变化和高度亲铁元素丰度。有了这些数据，将有可能区分贫化或富集的辉石岩来源，并调查是否高压-高温熔融肥沃的橄榄岩可能提供一种替代方法。研究将包括本科生和代表性不足的少数民族的整合，他们也将与PI和研究生一起沿着参与将在圣地亚哥地区和加那利群岛举行的外联活动，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

项目成果

High-precision Pb and Hf isotope and highly siderophile element abundance systematics of high-MgO Icelandic lavas

• DOI: 10.1016/j.chemgeo.2021.120436
• 发表时间: 2021-11
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: R. Nicklas;A. Brandon;T. Waight;I. Puchtel;J. Day

Mantle sources of ocean islands basalts revealed from noble gas isotope systematics

稀有气体同位素系统学揭示海岛玄武岩的地幔来源

• DOI: 10.1016/j.chemgeo.2021.120626
• 发表时间: 2022
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Day, James M.D.;Jones, Tim D.;Nicklas, Robert W.
• 通讯作者: Nicklas, Robert W.

Temporally variable crustal contributions to primitive mantle-derived Columbia River Basalt Group magmas

地壳的时间变化对原始地幔来源的哥伦比亚河玄武岩群岩浆的贡献

• DOI: 10.1016/j.chemgeo.2021.120197
• 发表时间: 2021
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Day, James M.D.;Nutt, Kimberley L.R.;Mendenhall, Brendon;Peters, Bradley J.
• 通讯作者: Peters, Bradley J.

Oxidation of La Réunion lavas with MORB-like fO2 by assimilation

通过同化作用用 MORB 样 fO2 氧化留尼旺熔岩

• DOI: 10.7185/geochemlet.2205
• 发表时间: 2022
• 期刊: Geochemical Perspectives Letters
• 影响因子: 4.9
• 作者: Nicklas, R.W.;Hahn, R.K.M.;Day, J.M.D.
• 通讯作者: Day, J.M.D.

Forearc origin for Coast Range Ophiolites inferred from osmium isotopes and highly siderophile elements

• DOI: 10.1016/j.chemgeo.2020.119723
• 发表时间: 2020-09
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Eric Snortum;J. Day