The Origin and Survival of Chemical Heterogeneities in the Earth's Mantle

地幔中化学异质性的起源和存续

• 批准号: 1754186
• 负责人: Igor Puchtel
• 金额: $ 30.65万
• 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: 2018
• 资助国家: 美国
• 起止时间: 2018-06-01 至 2022-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1754186&HistoricalAwards=false
• 关键词: Origin; Survival; Chemical; Heterogeneities; Earth

Accurately determining the Earth's chemical composition has been and remains one of the most fundamental challenges in Earth sciences. It has important implications not only for the long-debated question of how terrestrial planets form and evolve, but also for our understanding of the consequences of the ongoing processes on our planet. The Earth's mantle is the largest of all terrestrial reservoirs; it constitutes 83% of the Earth's volume and extends to 2900 km below its surface. The chemically and isotopically heterogeneous nature of this vast reservoir has long been established as a result of previous pioneering studies of the terrestrial rock record. Some of the heterogeneities have been argued to be primordial, reflecting initial planetary accretion/differentiation and magma ocean crystallization processes. Others were likely created as a result of a protracted, violent terrestrial accretion history, or to have resulted from later processes associated with the dynamic regime of the planet, especially crustal recycling. Despite the long-term, concerted research effort, the nature, origin, scale, and longevity of early mantle chemical and isotope heterogeneities are still not well understood. This project is aimed at filling the existing gaps in our understanding of these fundamental issues by applying a carefully chosen, comprehensive set of state-of-the-art modern analytical tools to a collection of unique 3.5 to 2.7 billion year old komatiite samples from western Australia. These samples are especially advantageous to study processes that occurred within the first 2 billion years of Earth history, before the crust formation and recycling processes, similar to those occurring today, took over as the main driver of chemical differentiation of the Earth's interior and erased all the evidence of Earth's youthful exuberance.This research effort is aimed at constraining the origin and temporal evolution of chemical and isotopic heterogeneities in the early Earth's mantle. The primary goals are to: (1) assess the magnitude of chemical/isotopic heterogeneities recorded in the mantle sources of 3.52 to 2.69 Ga komatiites from Western Australia, (2) establish which of such fundamental early Earth processes, as late accretion, magma ocean crystallization, primordial crust extraction, and crustal recycling, were responsible for creating these heterogeneities, and (3) integrate the new short- and long-lived isotopic and trace element abundance data for these rocks with the existing data for Archean komatiite systems into models for the origin and temporal evolution of global chemical/isotope heterogeneities in the Earth's mantle. In order to achieve these goals, the team will study isotope systematics, and lithophile trace element and highly siderophile element abundances in diamond drill core samples of the 3.5 to 2.7 Ga komatiite systems using the thermal ionization mass-spectrometry and inductively-coupled plasma mass-spectrometry techniques. These komatiitic systems are from the ancient Pilbara and Yilgarn Cratons of Western Australia, and their formation spans a time interval of ca. 800 Ma of Earth history. These localities were selected in order to cover the greatest possible extent of temporal variations within spatially related Archean cratons, because the selected samples are well preserved by Archean standards and are expected to provide a window into the early terrestrial mantle, and because limited existing data indicate that these komatiite systems record very early mantle differentiation processes. The results are expected to allow us to assess the possible effects of differentiation of a primordial magma ocean, late accretion, and crustal recycling, as well as permit new constraints to be placed on the mixing times of the mantle during the first half of Earth's history.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.

准确确定地球的化学成分一直是地球科学中最基本的挑战之一。它不仅对长期争论的类地行星如何形成和演化的问题具有重要意义，而且对我们对地球上正在进行的过程的后果的理解也具有重要意义。地幔是所有陆地储层中最大的；它占地球体积的83%，延伸到地表以下2900公里处。这一巨大储层的化学和同位素非均质性早已通过前人对陆相岩石记录的开创性研究而确立。一些非均质性被认为是原始的，反映了最初的行星吸积/分异和岩浆海洋结晶过程。另一些可能是由于漫长而剧烈的陆地增生历史造成的，或者是由于与地球动态机制有关的后期过程，特别是地壳再循环造成的。尽管经过了长期、协调一致的研究，但早期地幔化学和同位素非均质性的性质、起源、规模和寿命仍未得到很好的认识。该项目旨在填补我们对这些基本问题的理解上的现有空白，通过对来自西澳大利亚的35至27亿年前的独特科马地岩样本进行精心选择，全面采用一套最先进的现代分析工具。这些样本对于研究地球历史最初20亿年间发生的过程尤其有利。在此之前，地壳形成和循环过程（类似于今天发生的过程）成为地球内部化学分化的主要驱动力，并抹去了地球年轻繁荣的所有证据。这项研究的目的是限制早期地幔化学和同位素非均质性的起源和时间演化。主要目标是：(1)评价了西澳大利亚地区3.52 ~ 2.69 Ga科马岩源幔源记录的化学/同位素非均质性的大小；(2)确定了晚增生、岩浆海洋结晶、原始地壳提取和地壳再循环等早期地球基本过程中哪些是造成这些非均质性的原因；(3)将这些岩石的短、长寿命同位素和微量元素丰度新数据与太古宙科马地岩系统的现有数据整合到地球地幔全球化学/同位素非均质性的起源和时间演化模型中。为了实现这些目标，研究小组将利用热电离质谱和电感耦合等离子质谱技术研究3.5 ~ 2.7 Ga科马地岩体系金刚石钻芯样品的同位素系统，以及亲石微量元素和高亲铁元素的丰度。这些科马提岩系来自澳大利亚西部的古皮尔巴拉和伊尔冈克拉通，它们的形成跨越了大约800 Ma的地球历史时间间隔。选择这些地点是为了尽可能覆盖空间上相关的太古宙克拉通的时间变化范围，因为所选的样品按照太古宙标准保存得很好，有望为研究早期陆地地幔提供一个窗口，并且因为有限的现有数据表明这些科马提岩系统记录了非常早期的地幔分化过程。预计这些结果将使我们能够评估原始岩浆海洋的分化、晚期增生和地壳再循环的可能影响，并允许对地球历史上半期地幔混合时间进行新的限制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Contrasting platinum-group mineral assemblages of the Kondyor massif (Russia): Implications for the sources of HSE in zoned-type ultramafic massifs

Kondyor 地块（俄罗斯）的铂族矿物组合对比：对分区型超镁铁地块中 HSE 来源的影响

• DOI: 10.1016/j.lithos.2020.105800
• 发表时间: 2020
• 期刊: Lithos
• 影响因子: 3.5
• 作者: Malitch, Kreshimir N.;Puchtel, Igor S.;Belousova, Elena A.;Badanina, Inna Y.
• 通讯作者: Badanina, Inna Y.

Ultra-depleted 2.05 Ga komatiites of Finnish Lapland: Products of grainy late accretion or core-mantle interaction?

芬兰拉普兰的超贫化 2.05 Ga 科马提岩：颗粒状晚期吸积或核幔相互作用的产物？

• DOI: 10.1016/j.chemgeo.2020.119801
• 发表时间: 2020
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Puchtel, Igor S.;Mundl-Petermeier, Andrea;Horan, Mary;Hanski, Eero J.;Blichert-Toft, Janne;Walker, Richard J.
• 通讯作者: Walker, Richard J.

The komatiite testimony to ancient mantle heterogeneity

科马提岩对古代地幔异质性的证明

• DOI: 10.1016/j.chemgeo.2022.120776
• 发表时间: 2022
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: Puchtel, Igor S.;Blichert-Toft, Janne;Horan, Mary F.;Touboul, Mathieu;Walker, Richard J.
• 通讯作者: Walker, Richard J.

Early global mantle chemical and isotope heterogeneity revealed by the komatiite-basalt record: The Western Australia connection

科马提岩-玄武岩记录揭示了早期全球地幔化学和同位素异质性：与西澳大利亚的联系

• DOI: 10.1016/j.gca.2021.11.030
• 发表时间: 2022
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: Puchtel, I.S.;Nicklas, R.W.;Slagle, J.;Horan, M.;Walker, R.J.;Nisbet, E.G.;Locmelis, M.
• 通讯作者: Locmelis, M.