Tungsten and Ruthenium Isotopic Study of the Chemical Evolution of Earth

地球化学演化的钨和钌同位素研究

• 批准号: 1624587
• 负责人: Richard Walker
• 金额: $ 46万
• 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: 2016
• 资助国家: 美国
• 起止时间: 2016-07-15 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624587&HistoricalAwards=false
• 关键词: Tungsten; Ruthenium; Isotopic; Study; Chemical

The Earth was likely built as a result of a series of a series of collisions of increasingly larger planetesimals, during the first 50 million years of Solar System history. Growth of the planet largely terminated after a final, giant impact that led to melting of much of the Earth and the creation of the Moon. Surprisingly, there is strong evidence present in the isotopic compositions of some elements in both ancient and young rocks that domains were created within the Earth?s mantle during the primary construction period of the Earth before the giant impact, and these domains have been somehow preserved to the present. This study will examine the tungsten and ruthenium isotopic compositions of rocks derived from these domains to provide new insights to processes occurring within the Earth as it grew, as well as help to constrain the genetic origins of the building blocks of our planet. Small variations in the abundance of 182-tungsten in terrestrial rocks likely reflects the decay of 182-hafnium, coupled with very early chemical fractionations of the two elements within the silicate portion of the Earth. Prior studies have suggested that modest variations in 182-tungsten among some primitive rocks may reflect processes occurring in early-formed magma oceans. This study will seek to more fully establish the causes of the isotopic heterogeneities, and assess why convective stirring of the mantle has not mixed away the heterogeneities in more than 4.5 billion years. The isotopic composition of Ru varies among planetary bodies in our Solar System as a result of the incorporation of diverse mixtures of nucleosynthetic components. Hence, if the Earth was built from genetically diverse materials, early-formed mantle domains identified by tungsten isotopic variations, may contain ruthenium that is isotopically distinguishable from the dominant composition of the mantle today. If so, the particular building block identified may be tied to a specific type of cosmochemical precursor.

在太阳系历史的前 5000 万年里，地球很可能是由越来越大的星子发生一系列碰撞而形成的。在一次最终的巨大撞击导致地球大部分融化并形成月球后，地球的增长基本上终止了。令人惊讶的是，在古代和年轻岩石中一些元素的同位素组成中存在强有力的证据，表明在巨大撞击之前的地球初级建造时期，地幔内产生了区域，并且这些区域以某种方式保存至今。这项研究将检查来自这些领域的岩石的钨和钌同位素组成，为地球生长过程中发生的过程提供新的见解，并帮助限制我们星球的组成部分的遗传起源。陆地岩石中 182-钨丰度的微小变化可能反映了 182-铪的衰变，以及地球硅酸盐部分中这两种元素非常早期的化学分馏。先前的研究表明，一些原始岩石中 182 钨的适度变化可能反映了早期形成的岩浆海洋中发生的过程。这项研究将寻求更全面地确定同位素异质性的原因，并评估为什么地幔的对流搅拌在超过 45 亿年的时间里没有消除异质性。由于核合成成分的不同混合物的结合，钌的同位素组成在我们太阳系的行星体之间有所不同。因此，如果地球是由遗传多样性材料构成的，通过钨同位素变化识别出的早期形成的地幔区域可能含有钌，其同位素与当今地幔的主要成分不同。如果是这样，那么所识别的特定结构单元可能与特定类型的宇宙化学前体有关。

项目成果

182W and 187Os constraints on the origin of siderophile isotopic heterogeneity in the mantle

• DOI: 10.1016/j.gca.2023.11.003
• 发表时间: 2023-11-15
• 期刊: GEOCHIMICA ET COSMOCHIMICA ACTA
• 影响因子: 5
• 作者: Walker，Richard J.;Mundl-Petermeier，Andrea;Chauvel，Catherine
• 通讯作者: Chauvel，Catherine