Chemical heterogeneities in the early Earth and planetary analogues: their formation, preservation and destruction

早期地球和类似行星的化学异质性：它们的形成、保存和破坏

• 批准号: RGPIN-2015-03982
• 负责人: RizoGarza, Hanika
• 金额: $ 1.97万
• 依托单位: Université du Québec à Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=612696
• 关键词: Chemical; heterogeneities; early; Earth; planetary

A fundamental question in Earth and planetary sciences is how the planets formed and how they evolved through time. Geochemical and numerical models, as well as planetary analogs suggest that Earth accreted from complex processed materials and then evolved rapidly after its formation. Early events such as core segregation, mantle differentiation and crust formation seem to have occurred shortly after the Earth’s accretion. Furthermore, the composition of the Earth’s mantle was modified by the continued accretion of materials during the final stages of formation. In the past few years, the development of short-lived isotopic chronometers has allowed chronological studies of the events that followed shortly the Earth’s accretion. Mixing through mantle convection and crustal recycling associated with plate tectonics has attenuated the magnitude of primordial mantle heterogeneities. However, recent documentation of early-formed isotope variations in Archean rocks requires the persistence of primordial chemical reservoirs for > 1 billion years. Over the next five years my research program will focus on three key problems involving Earth and planetary sciences: 1) What are the nature and timing of the major events affecting the chemical composition of the early Earth’s mantle? 2) How long did early-formed chemical heterogeneities survive in the convective mantle, and what was the style of convection of the early Earth? 3) Is the early evolution of the Earth comparable to other planetary analogues like the asteroid Vesta? This research program is strongly focused on the development, improvement and acquisition of data from extinct and long-lived radioactive isotope systematics, as well as obtaining siderophile element abundances for different planetary materials. These geochemical tools are ideal to constrain core and mantle early evolution, and investigate the timing and chemical consequences of late accretionary additions. The findings of this project will help to improve models of the internal dynamics of the Earth during its early stages of development, and provide geological knowledge about the oldest terrains in northern Canada. This research program is designed to involve several undergraduate and four graduate students who will acquire a unique set of skills that are relevant to both academia and industry.

地球和行星科学中的一个基本问题是行星是如何形成的，它们是如何随时间演变的。地球化学和数值模型以及行星类比表明，地球是从复杂的加工材料中吸积而来的，然后在形成后迅速演化。早期的事件，如核分离、地幔分异和地壳形成，似乎发生在地球吸积后不久。此外，地幔的组成在形成的最后阶段由于物质的持续积累而改变。在过去的几年里，短寿命同位素计时器的发展使得对地球吸积后不久发生的事件进行了年代学研究。与板块构造有关的地幔对流和地壳再循环的混合减弱了原始地幔不均质性的程度。然而，最近关于太古宙岩石早期形成的同位素变化的记录要求原始化学储集层持续存在10亿年。 在接下来的五年里，我的研究计划将重点研究涉及地球和行星科学的三个关键问题： 1)影响早期地幔化学成分的重大事件的性质和时间是什么？ 2)早期形成的化学不均质在对流地幔中存在了多久，早期地球的对流类型是什么？ 3)地球的早期演化可以与其他类似行星如灶神星相媲美吗？ 这一研究方案的重点是发展、改进和获取已灭绝和寿命长的放射性同位素系统学数据，以及获取不同行星材料的亲铁元素丰度。这些地球化学工具是约束核和地幔早期演化的理想工具，也是研究晚期增生作用的时间和化学后果的理想工具。该项目的发现将有助于改进地球在早期发展阶段的内部动力学模型，并提供有关加拿大北部最古老的地形的地质知识。这项研究计划包括几名本科生和四名研究生，他们将获得一套独特的与学术界和行业相关的技能。