Origin and Evolution of the Absolute and Relative Highly Siderophile Element Abundances Present in the Early Earth

早期地球中绝对和相对高亲铁元素丰度的起源和演化

• 批准号: 0946629
• 负责人: Igor Puchtel
• 金额: $ 29.28万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-03-15 至 2014-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0946629&HistoricalAwards=false
• 关键词: Origin; Evolution; Absolute; Relative; Highly

Intellectual Merit. This project is designed to constrain the origin and temporal evolution of the absolute and relative abundances of highly siderophile elements (HSE: Re, Os, Ir, Ru, Pt, Pd) in the early Archean mantle. This task is crucial for understanding fundamental planetary processes including Earth's primary differentiation, late accretion, and subsequent chemical evolution. The study focuses on ultramafic magmas (komatiites) from the Barberton Greenstone Belt (BGB), which preserved relicts of the very early stages of the Earth's evolution at a time when its mantle was less modified by processes of melt extraction, re-fertilization via crustal recycling, and core-mantle interaction. The BGB komatiites have unique chemical compositions, including extremely high MgO contents and a variety of LREE- and HREE-depleted/enriched signatures that clearly distinguish them from younger komatiites and imply very specific conditions of their magma generation. A total of ca. 150 chemically well characterized komatiite whole rock samples and olivine and chromite separates from the 3.48 Ga Komati, 3.30 Ga Weltevreden, and 3.30 Ga Mendon Formations of the BGB will be examined for high-precision absolute HSE abundances and 186,187Os/188Os isotope systematics. Well-preserved samples, ranging from Al-depleted to Al-enriched compositions, either are already in hand, or will be provided by collaborators; additional samples will become available through the ICDP Barberton Drilling Project, of which the PI is an active participant. Absolute and relative HSE abundances will be estimated for the mantle sources of the three respective komatiite systems at UMd. Together with lithophile trace element and isotopic data, these HSE data will be compared with high precision HSE data for chondritic meteorites, primitive upper mantle, lunar impact melts, and Archean komatiite systems to evaluate secular variations in the composition of the Archean komatiite mantle sources, and to develop models regarding the origin and evolution of HSE in the mantle. Extant hypotheses include [1] additions of HSE as a result of continuous accretion of planetesimals, [2] high pressure metal-silicate equilibration under the magma ocean conditions, and [3] subsequent modifications resulting from mass transfer in subduction zone environments and recycling of oceanic lithosphere.Broader Impacts. Outreach efforts of this project will foster collaborations between scientists from four continents, including the PI and Christophe Robin, a Ph.D. student of Nick Arndt (Univ. Grenoble), and members of the ICDP Barberton Drilling Project. It also will involve a UMd undergraduate student. Support for this research will help sustain the IGL's mission to share and collaborate world-wide, especially with those lacking access to necessary analytical facilities. Due to the unique nature of the Barberton region, it is currently being nominated as a UNESCO World Heritage Site. This project will provide added scientific support for this motion to protect and preserve the natural heritage of the area.

智力优点。该项目旨在限制早期太古代地幔中高亲铁元素（HSE：Re、Os、Ir、Ru、Pt、Pd）的绝对和相对丰度的起源和时间演化。这项任务对于理解基本的行星过程至关重要，包括地球的初级分化、晚期吸积和随后的化学演化。这项研究的重点是来自巴伯顿绿岩带（BGB）的超镁铁质岩浆（科马提岩），它保存了地球演化早期阶段的遗迹，当时地幔因熔体提取、地壳循环再肥化和核幔相互作用过程而发生的改变较少。 BGB 科马提岩具有独特的化学成分，包括极高的 MgO 含量以及各种 LREE 和 HREE 贫化/富集特征，这些特征清楚地将它们与较年轻的科马提岩区分开来，并暗示其岩浆生成的非常特殊的条件。总共约。将检查来自 BGB 3.48 Ga Komati、3.30 Ga Weltevreden 和 3.30 Ga Mendon 地层的 150 个经过充分化学表征的科马提岩全岩样品以及橄榄石和铬铁矿分离物，以获取高精度绝对 HSE 丰度和 186,187Os/188Os 同位素系统学。保存完好的样品，从贫铝到富铝成分，要么已经在手，要么将由合作者提供；其他样品将通过 ICDP 巴伯顿钻探项目提供，PI 是该项目的积极参与者。将估计马里兰大学三个科马提岩系统的地幔源的绝对和相对 HSE 丰度。结合亲石微量元素和同位素数据，这些 HSE 数据将与球粒陨石、原始上地幔、月球撞击熔体和太古代科马提岩系统的高精度 HSE 数据进行比较，以评估太古代科马提岩地幔来源成分的长期变化，并开发有关地幔中 HSE 起源和演化的模型。现有的假设包括[1]由于星子的持续吸积而增加了HSE，[2]岩浆海洋条件下的高压金属硅酸盐平衡，以及[3]由于俯冲带环境中的质量传递和海洋岩石圈的循环而导致的后续修改。更广泛的影响。该项目的推广工作将促进来自四大洲的科学家之间的合作，包括 PI 和博士 Christophe Robin。 Nick Arndt（格勒诺布尔大学）的学生，ICDP Barberton 钻井项目的成员。它还将涉及一名 UMd 本科生。对这项研究的支持将有助于维持 IGL 在全球范围内共享和合作的使命，特别是与那些无法获得必要分析设施的国家。由于巴伯顿地区的独特性，它目前被提名为联合国教科文组织世界遗产。该项目将为这一动议提供更多的科学支持，以保护和保存该地区的自然遗产。