Chalcophile Element Geochemistry

亲铜元素地球化学

• 批准号: 1757313
• 负责人: Roberta Rudnick
• 金额: $ 13.87万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-02-01 至 2021-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1757313&HistoricalAwards=false
• 关键词: Chalcophile; Element; Geochemistry

The geochemical behavior of the economically important chalcophile (sulfur-loving) elements is relatively poorly understood due to historical difficulties in analyzing these elements at the low concentrations in which they occur in common rocks. Recent advances in analytical methods now provides the ability to analyze these elements at relatively high precision at very low (e.g., nanogram per gram) concentration levels. This team aims to use the concentrations of nominally chalcophile elements (specifically Cu, Ga, Ge, As, Mo, Ag, Cd, In, Sn, Sb, W, Tl, Pb, and Bi) to address three fundamental questions in Earth science: a) how has the continental crust formed and evolved over time?, b) how much oxygen was in the atmosphere following the "Great Oxidation Event" (GOE) that occurred at 2.3-2.4 billion years ago?, and c) what is Earth's volatile element inventory?Researchers will investigate these questions through three complementary projects. The first seeks to understand why molybdenum is systematically depleted in granites relative to rare earth elements by analyzing its concentrations in rocks (eclogites) that represent the residues of ancient subducted oceanic crust, and by determining the behavior of Mo during magmatic differentiation that produces granites. Through these studies, they will evaluate whether the upper crustal Mo depletion is due to its retention in subducted slabs, its retention in lower continental crustal cumulates, or its partitioning into a magmatic vapor phase and precipitation in molybdenum sulfide (molybdenite) in hydrothermal veins. The results will shed light on the main processes responsible for generation of the upper continental crust (UCC) and will place constraints on total amount of molybdenite in the UCC, allowing for more robust calculation of pO2 in the ancient atmosphere. The second project seeks to determine the cause of the change in the molybdenum isotope composition of the upper continental crust over geologic history, as observed in glacial deposits (diamictites). The team will analyze Mo isotopes in several modern weathering profiles to determine whether the onset of weathering in the presence of oxygen can explain the diamictite data. If they find that Mo isotopes fractionate during weathering in today's oxygenated atmosphere, it may allow them to use the diamictite data to place constraints on the amount of atmospheric oxygen that was present in the past. Finally, they will determine the distribution of the full suite of chalcophile elements within rocks of the upper mantle that are now exposed in the Pyrenees Mountains. Unlike similar rocks that are rapidly transported to Earth's surface in magmas, these mantle outcrops have retained sulfides, and thus will allow researchers to determine how these elements behave during mantle melting, and also allow for an independent estimate of Earth's abundance of moderately to highly volatile chalcophile elements such as As, Cd, Ga, In, Sn and Tl. Determining the volatile element abundances of Earth provides insights into how our planet formed.

由于历史上的困难在分析这些元素时，在共同岩石中分析这些元素时，人们对经济上重要的豆科植物（热爱硫）元素的地球化学行为相对较少了解。现在，分析方法的最新进展提供了能够以非常低的（例如，每克）浓度水平相对较高的精度分析这些元素。该团队的目标是利用名义上的核花元素（特别是Cu，Ga，ge，aS，Mo，Mo，ag，cd，in，sn，sb，s，W，Tl，pb和bi）来解决地球科学中的三个基本问题：a）大陆壳形成和进化的氧化如何？ 2.3-24亿年前？和c）什么是地球的易变元素清单？研究人员将通过三个补充项目调查这些问题。第一个试图通过分析其在岩石（eclogites）中的浓度来理解为什么在花岗岩中有系统地耗尽花岗岩的原因，这些岩石浓度代表了古代俯冲的海洋壳的残基，并通过确定产生花岗岩的岩浆差异过程中MO的行为来确定MO的行为。通过这些研究，他们将评估上层甲壳的耗竭是由于其保留在俯冲板中，其保留在下层大陆堆积累积中，还是将其分配到岩浆蒸气相中，以及在水热静脉中的钼（钼酸钼）中的降水量。结果将阐明负责产生上层大陆壳（UCC）的主要过程，并将对UCC中的钼酸盐总数施加限制，从而可以在古代气氛中对PO2进行更强大的计算。第二个项目旨在确定在地质历史上上大陆壳的钼同位素组成变化的原因，如在冰川沉积物（散虫）中所观察到的那样。该团队将分析几个现代风化概况中的MO同位素，以确定在氧气存在下风化的发作是否可以解释二氧化碳数据。如果他们发现在当今的含氧大气中，在风化过程中，MO同位素分馏，则可以使他们可以使用二氧化碳数据来对过去存在的大气氧气量放置约束。最后，他们将确定现在在比利牛斯山脉中暴露的上地幔岩石中的整个豆科植物元素的分布。与在岩浆中迅速运输到地球表面的类似岩石不同，这些地幔露头保留了硫化物，因此将使研究人员能够确定这些元素在地幔熔化过程中的行为方式，还可以独立地估计地球中等程度的高度挥发性的杂质元素，例如，cd，cd，cd，ga，in，sn，sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and sn and tl。确定地球的挥发性元素丰度为我们的行星形成方式提供了见解。

项目成果

Geochemistry of molybdenum in the continental crust

• DOI: 10.1016/j.gca.2018.06.039
• 发表时间: 2018-10-01
• 期刊: GEOCHIMICA ET COSMOCHIMICA ACTA
• 影响因子: 5
• 作者: Greaney, Allison T.;Rudnick, Roberta L.;Clemens, John D.
• 通讯作者: Clemens, John D.

Assessing molybdenum isotope fractionation during continental weathering as recorded by weathering profiles in saprolites and bauxites

• DOI: 10.1016/j.chemgeo.2021.120103
• 发表时间: 2021-04
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: A. Greaney;R. Rudnick;S. Romaniello;Aleisha C. Johnson;A. Anbar;M. Cummings

Molybdenum isotope fractionation in glacial diamictites tracks the onset of oxidative weathering of the continental crust

• DOI: 10.1016/j.epsl.2020.116083
• 发表时间: 2020-03-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Greaney, Allison T.;Rudnick, Roberta L.;Anbar, Ariel D.
• 通讯作者: Anbar, Ariel D.