Tracing pollution of the mantle with isotopically anomalous Mo and U

用同位素异常 Mo 和 U 追踪地幔污染

• 批准号: NE/H023933/1
• 负责人: Timothy Elliott
• 金额: $ 39.26万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH023933%2F1
• 关键词: Tracing; pollution; mantle; isotopically; anomalous

Over the 4.5 billion year course of Earth History most of the silicate portion of the Earth (i.e. all the solid planet except the core) has likely been processed through the plate tectonic cycle at the Earth's surface. While at the Earth's surface, alteration by seawater imparts a distinctive chemical signature to the top of the plate before it is returned by subduction back to the mantle. Tracking such chemical traces of old plates is an important task. If we can identify these signatures in material erupted again at the surface it gives us a means to understand how the mantle has been stirred. Whilst there are improving models of mantle convection, it is a complex problem and needs to be calibrated with observations. A major question remains as to how well the upper and lower portions of the mantle are mixed. It used to be thought that they were isolated from one another. Recent work from seismology has made this picture untenable, but it is nevertheless unsure as to just how much communication there is between top and bottom. We are attempting to solve this problem by looking at two elements (Mo and U) that are returned to the mantle with a distinctive isotopic label. They are also 'recycled' in sufficient abundance to be able to result in a different isotopic signature in the upper and lower mantle, if they are not well mixed . We can effectively sample upper and lower mantle using melts that come from ocean ridges and oceanic island respectively. If the whole mantle is well mixed they will have identical isotopic signatures of Mo and U, if not we predict small but significant differences. This work is new in that it has only recently become possible to measure the isotopic ratios of suitable elements for this problem with high enough accuracy. Our initial work suggests that distinct differences in Mo and U between upper and lower mantle are present, but these results need to be investigated in much greater detail to have full confidence in their significance and implications. This is the work we propose.

在45亿年的地球历史进程中，地球的大部分硅酸盐部分(即除了核心之外的所有固体行星)很可能是通过地球表面的板块构造旋回来处理的。而在地球表面，在板块俯冲返回地幔之前，海水的变化会给板块顶部带来独特的化学特征。追踪这些旧车牌的化学痕迹是一项重要的任务。如果我们能在地表再次喷发的物质中识别出这些特征，就能让我们了解地幔是如何被搅动的。虽然有改进的地幔对流模型，但这是一个复杂的问题，需要通过观测进行校准。一个主要的问题仍然是，地幔的上下部分混合的程度如何。过去人们认为他们彼此隔绝。地震学最近的研究使这一图景站不住脚，但它仍然不确定顶部和底部之间到底有多少交流。我们正试图通过观察返回地幔的两种元素(钼和铀)来解决这个问题，这些元素带有独特的同位素标签。如果它们没有很好地混合，它们也会在足够丰富的情况下被“循环”，从而在上地幔和下地幔中产生不同的同位素特征。我们可以利用分别来自大洋海脊和大洋岛的熔体来有效地采集上地幔和下地幔的样本。如果整个地幔混合良好，它们将具有相同的钼和铀的同位素特征，否则，我们预测会有微小但显著的差异。这项工作是新的，因为直到最近才有可能以足够高的精度测量适合这一问题的元素的同位素比率。我们的初步工作表明，上地幔和下地幔之间存在着明显的钼和铀差异，但这些结果需要更详细地研究，才能充分相信它们的意义和含义。这就是我们提出的工作。

项目成果

A modern framework for the interpretation of 238U/235U in studies of ancient ocean redox

• DOI: 10.1016/j.epsl.2014.05.051
• 发表时间: 2014-08-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Andersen, M. B.;Romaniello, S.;Lyons, T. W.
• 通讯作者: Lyons, T. W.

Uranium isotope fractionation during slab dehydration beneath the Izu arc

• DOI: 10.1016/j.epsl.2019.07.006
• 发表时间: 2019-09-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Freymuth, Heye;Andersen, Morten B.;Elliott, Tim
• 通讯作者: Elliott, Tim

Carbon fluxes from subducted carbonates revealed by uranium excess at Mount Vesuvius, Italy

意大利维苏威火山铀过剩揭示了俯冲碳酸盐的碳通量

• DOI: 10.1130/g39766.1
• 发表时间: 2018
• 期刊: Geology
• 影响因子: 5.8
• 作者: Avanzinelli R

Rapid onset of ocean anoxia shown by high U and low Mo isotope compositions of sapropel S1

• DOI: 10.7185/geochemlet.2027
• 发表时间: 2020-09
• 作者: M. B. Andersen;A. Matthews;M. Bar-Matthews;D. Vance

Tracing subducted black shales in the Lesser Antilles arc using molybdenum isotope ratios

• DOI: 10.1130/g38344.1
• 发表时间: 2016-12
• 期刊: Geology
• 影响因子: 5.8
• 作者: H. Freymuth;T. Elliott;M. V. Soest;S. Skora