Distinguishing Sediment, Serpentinite, and Altered Oceanic Crust in the Source of Aleutian Volcanic Rocks Using Boron & Molybdenum Isotopes

使用硼区分阿留申火山岩源头中的沉积物、蛇纹岩和蚀变洋壳

• 批准号: 2050271
• 负责人: Gene Yogodzinski
• 金额: $ 37.08万
• 依托单位: University of South Carolina at Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-05-15 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2050271&HistoricalAwards=false
• 关键词: Distinguishing; Sediment; Serpentinite; Altered; Oceanic

Subduction is the fundamental geologic process where one tectonic plate sinks beneath another into the hot interior of the Earth. Subduction has many important human impacts, especially hazards from seismic and volcanic activity that are a constant threat to population centers and commerce worldwide. Subduction also plays a key role in shaping the earth's surface and is important in the formation of continents and the mineral resources they contain. As a result, subduction-related processes are the subject of broad public and scientific interest. The key goal of this work is to understand how fluids (superheated water at high pressures) drive subduction magmatism, which is manifest in volcanoes at the earth’s surface. Under this project, chemical data will be collected on volcanic rocks of the Aleutian Island Arc. Data collection will focus on the elements boron (B) and molybdenum (Mo), which are relatively water-soluble in earth-surface systems, and as a result, are abundant in seawater and are easily transferred to rocks that underlie the ocean basins. When subduction pushes the hydrated oceanic crust back into the Earth’s interior, the water is driven out of the rocks by chemical reactions that produce fluids rich in B and Mo. Under the extreme pressures and temperatures of the Earth’s interior, fluids lower the melting point of the rocks that they encounter and trigger the melting processes that lead to volcanic eruptions at the Earth’s surface. In turn, the concentrations of B and Mo in these volcanic rocks reveal key information about the paths that the fluids follow and the rocks that are melted along the way. Immediate societal benefit of this work will be research training of the graduate students who will be supported under the project. The project also initiates an after-school intern program for students from Dreher High School, in Columbia, South Carolina. The student interns will assist with sample preparation, data reduction, and data management. The interns will also produce a small data set of their own as a final project. The goals of the program are to expose high-school students to areas of applied chemistry and to NSF-funded research in the earth sciences.The key technical goal of the project is to take advantage of the fluid-mobile behavior of boron and molybdenum in order to distinguish the competing roles of subduction inputs (sediments, serpentinite and altered basaltic crust) in the generation of the Aleutian Arc magmas. We will collect B and Mo isotope data for subduction inputs (sediment, altered oceanic crust, abyssal peridotite) and outputs (volcanic rocks) along the Aleutian arc and link the chemical results to physical parameters such as subduction rate, sediment flux, and thermal parameter, which change systematically along the arc. Boron isotopes are used as tracers of fluid pathways, which also respond to changes in the thermal state of the subducting plate. The importance of Mo isotopes stems from their value as a tracer of both fluids and sediment type. The combined B and Mo isotope tracers and Aleutian natural laboratory create opportunities to distinguish sources in subducted sediment, serpentinite, and altered oceanic crust, especially at the point along the arc where the Amlia Fracture Zone enters the trench, and in the western-most Aleutians, where hot-slab effects are uniquely well expressed.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.

俯冲是一种基本的地质过程，其中一个构造板块沉入另一个构造板块之下，进入地球炎热的内部。俯冲对人类有许多重要的影响，特别是地震和火山活动的危害，对世界各地的人口中心和商业构成持续的威胁。俯冲作用在塑造地球表面方面也起着关键作用，对大陆及其所含矿产资源的形成也很重要。因此，与俯冲有关的过程成为公众和科学界广泛关注的主题。这项工作的主要目标是了解流体（高压过热水）如何驱动俯冲岩浆作用，这在地球表面的火山中表现出来。在这个项目下，将收集阿留申岛弧火山岩的化学数据。数据收集将侧重于硼（B）和钼（Mo）元素，这两种元素在地球表面系统中相对来说是水溶性的，因此在海水中含量丰富，很容易转移到海洋盆地下面的岩石中。当俯冲作用将含水的海洋地壳推回地球内部时，水通过化学反应从岩石中排出，产生富含B和Mo的流体。在地球内部的极端压力和温度下，流体降低了它们遇到的岩石的熔点，并引发了导致地球表面火山爆发的熔化过程。反过来，这些火山岩中的B和Mo的浓度揭示了有关流体所遵循的路径以及沿着路径熔化的岩石的关键信息。这项工作的直接社会效益将是研究生的研究培训，他们将在项目下得到支持。该项目还为南卡罗来纳州哥伦比亚德雷尔高中的学生启动了一个课后实习计划。学生实习生将协助样品制备，数据简化和数据管理。实习生还将制作一个自己的小数据集作为最终项目。该计划的目标是让高中生接触应用化学领域和NSF资助的地球科学研究。该项目的关键技术目标是利用硼和钼的流体流动行为，以区分俯冲输入（沉积物，蛇纹岩和蚀变玄武质地壳）在阿留申弧岩浆生成中的竞争作用。我们将收集沿着阿留申岛弧俯冲输入（沉积物、蚀变洋壳、深海橄榄岩）和输出（火山岩）的B和Mo同位素数据，并将化学结果与物理参数联系起来，如俯冲速率、沉积物通量和热参数，这些参数沿岛弧沿着系统地变化。硼同位素被用作流体路径的示踪剂，这也对俯冲板块的热状态的变化作出反应。钼同位素的重要性源于其作为流体和沉积物类型示踪剂的价值。结合B和Mo同位素示踪剂和阿留申群岛天然实验室，为区分俯冲沉积物、蛇纹岩和蚀变洋壳中的来源创造了机会，特别是在沿着阿姆利亚断裂带进入海沟的弧上，以及在最西部的阿留申群岛，热-平板效应得到了很好的表达。该奖项反映了NSF的法定使命，并通过使用基金会的学术价值和更广泛的影响审查标准。

项目成果

Serpentinite fluids and slab-melting in the Aleutian arc: Evidence from molybdenum isotopes and boron systematics

• DOI: 10.1016/j.epsl.2022.117970
• 发表时间: 2023-02
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Ekaterina Rojas-Kolomiets;O. Jensen;M. Bizimis;G. Yogodzinski;L. Ackerman