Redox and Structural Controls on Iron Isotopic Variations in Igneous Rocks

火成岩中铁同位素变化的氧化还原和结构控制

• 批准号: 1144429
• 负责人: Nicolas Dauphas
• 金额: $ 24.97万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1144429&HistoricalAwards=false
• 关键词: Redox; Structural; Controls; Iron; Isotopic

The elevated degree of oxidation present in the Earth is a major condition of its habitability, allowing the existence of free oxygen and other oxidized species used during respiration to sustain activity in human beings and simpler life forms. Earth is more oxidized than other planetary bodies such as Mars and the reason for this is not well understood. For example, Titan's atmosphere (Titan is the largest moon of Saturn) is composed primarily of nitrogen, methane and ethane. In addition, Titan's surface is covered with lakes of hydrocarbons. It is not known whether Earth was born like it is today or whether it started with a Titan-like atmosphere and the oxidized conditions were established during Earth's history through geological processes. In this study, a new tool will be developed to measure the oxidation conditions of Earth through time. The measurements will use and develop cutting edge analytical methods at a national facility; the intense X-ray source located at the Advanced Photon Source (Argonne National Laboratory). This study will provide critical constraints on why our planet is unique and it will help us understand the nature of volcanic emissions in the distant past. On long timescales, the nature of volcanic emissions has played a key role in climate regulation and prevented the Earth from going into a permanent snowball state. The iron oxidation state of magmas (i.e., Fe3+/Fe2+ ratio) is a key parameter to trace the redox evolution of the Earth. Unfortunately, geological processes such as assimilation, degassing, crystallization, and alteration can blur this record. Iron isotopes provide insight into the conditions of mantle melting that are less susceptible to these secondary processes. A team of investigators with expertise in experimental petrology, iron isotope geochemistry, and nuclear resonance vibrational spectroscopy will calibrate the effects of redox and structural conditions on equilibrium isotopic fractionation between ferrous (Fe2+) and ferric (Fe3+) iron in magmas and minerals. This will provide a solid framework for interpreting iron isotopic variations and redox conditions in igneous rocks of all ages. Silicate glass, olivine, and spinel will be studied by the Nuclear Resonant Inelastic X-ray Scattering (NRIXS) technique to get a holistic view of iron isotopic fractionation during mantle and crustal melting, as well as mafic and felsic magma differentiation. Measurements of basalts through rhyolites produced under a range of oxygen fugacities, will allow the parameterization of iron equilibrium fractionation factors of magmas taking into account parameters such as Fe3+/Fetot ratio and NBO/T (nonbridging oxygen per tetrahedrally coordinated cation, a measure of polymerization of a silicate melt) to predict equilibrium Fe isotopic fractionation between minerals and melts.

地球上存在的氧化程度升高是其可居住性的主要条件，允许在呼吸过程中使用游离氧气和其他氧化物种，以维持人类的活动和更简单的生命形式。地球比其他行星物体（例如火星）更被氧化，而造成这种地球的原因尚不清楚。例如，泰坦的大气（泰坦是土星最大的月亮）主要由氮，甲烷和乙烷组成。此外，泰坦的表面被烃湖覆盖。尚不清楚地球是像今天一样诞生的，还是始于泰坦风格的气氛，氧化条件是通过地质过程在地球历史上建立的。在这项研究中，将开发一种新工具，以测量地球的氧化条件。测量结果将在国家设施中使用和开发最前沿的分析方法；位于高级光子源（Argonne National Laboratory）的强烈X射线源。这项研究将对我们的星球为何独特而提供关键限制，这将有助于我们了解遥远过去的火山排放的本质。在长时间的尺度上，火山排放的性质在气候调节中发挥了关键作用，并阻止了地球进入永久的雪球状态。岩浆的铁氧化态（即Fe3+/Fe2+比率）是追踪地球氧化还原演化的关键参数。不幸的是，诸如同化，脱气，结晶和改变之类的地质过程可能会模糊此记录。铁同位素提供了对地幔熔化条件的洞察力，而地幔熔化的条件不太容易受到这些次要过程的影响。一组研究人员在实验性质学，铁同位素地球化学和核共振振动光谱方面具有专业知识的团队，将校准氧化还原和结构条件对在岩浆和矿物质中铁（FE2+）和铁（FE2+）铁（FE2+）与铁（FE2+）之间平衡同位素分离的影响。这将为所有年龄段的火成岩岩石中的铁同位素变化和氧化还原条件提供一个坚实的框架。硅酸盐玻璃，橄榄石和尖晶石将通过核共振非弹性X射线散射（NRIXS）技术研究，以在地幔和地壳融化期间以及镁铁质和毛菲岩浆差异化期间对铁同位素分馏的整体视图。 Measurements of basalts through rhyolites produced under a range of oxygen fugacities, will allow the parameterization of iron equilibrium fractionation factors of magmas taking into account parameters such as Fe3+/Fetot ratio and NBO/T (nonbridging oxygen per tetrahedrally coordinated cation, a measure of polymerization of a silicate melt) to predict equilibrium Fe isotopic fractionation between矿物质和融化。