ABR: Studies of Partial Melting of the Mantle and Deep Earth Volatile Cycles

ABR：地幔部分熔融和地球深部挥发循环的研究

• 批准号: 1426772
• 负责人: Marc Hirschmann
• 金额: $ 35.48万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1426772&HistoricalAwards=false
• 关键词: ABR; Studies; Partial; Melting; Mantle

In this Accomplishment Based Renewal, two projects will be executed that both relate to the chemical dynamics of melting in Earth's interior. One project aims to understand the relationship between molten sulfides and carbon in the mantle. A significant portion of Earth's carbon may be dissolved in molten sulfide in the mantle, and so it may play an important role in cycling of carbon between different Earth reservoirs. It may also play an important role in the origin of diamonds, as well as affect but geophysical properties of the mantle. The second project investigates the relationship between magma formation and the oxidation state of Fe in Earth's mantle. Subtle differences in the proportions of oxidized (Fe3+) and reduced (Fe2+) iron in Earth's mantle could have profound effects on melting behavior. For example, mantle enriched in Fe3+ may melt more readily, thereby affecting the relationship between mantle temperature and the volume of volcanic material erupted at mid-ocean ridges or oceanic islands such as Hawaii. More oxidized mantle also initiates melting at greater depth, which determines how the mantle and crust change composition through time and the masses of volatiles such as H2O, CO2, and sulfur that are liberated from the mantle during volcanic activity. This also influences geophysical properties, including the mantle's resistance to convection, and how both seismic waves and electric currents propagate through Earth's interior. Finally, inferences about the oxidation state of Earth's interior based on compositions of volcanic rocks require knowledge of the melting behavior of Fe3+ during melting. Experimental studies will be conducted to improve understanding of both of these topics. Preliminary data indicates that the melting point of sulfide is diminished significantly by the presence of carbon, and new experiments will be conducted to explore how this relationship changes with pressure and sulfide composition, as well as to determine the C solubility in sulfide melts. The experiments will take into account the changing activity of metal that occurs with increasing pressure in the mantle, and in particular how the ratio of metal to sulfide changes. Experiments will be conducted with piston cylinder and multianvil devices up to 18 GPa and will be analyzed by electron microprobe and SIMS. Investigation of the behavior of Fe3+ during partial melting of the mantle will focus on the behavior in pyroxene, as this is the chief reservoir of oxidized iron in the mantle and there are few previous measurements. Experiments and X-ray spectroscopy will determine the partitioning of Fe3+ between pyroxene and silicate melt during partial melting to quantify the relationship between melting and mantle oxidation state. Additional experiments will explore the relationship between oxidation state of peridotite and partial melting behavior.

在这种基于成就的续约中，将执行两个项目，这两者都与地球内部融化的化学动力学有关。 一个项目旨在了解地幔中熔融硫化物和碳之间的关系。 地球碳的很大一部分可能溶解在地幔中的熔融硫化物中，因此它在不同的地球储层之间的碳循环中可能起重要作用。 它在钻石的起源以及地幔的地球物理特性中也可能发挥重要作用。 第二个项目调查了地球地幔中岩浆形成与铁的氧化状态之间的关系。 在地球底层中，氧化（Fe3+）和减少（Fe2+）铁的比例的细微差异可能会对熔融行为产生深远的影响。 例如，富含Fe3+的地幔可能更容易融化，从而影响地幔温度与夏威夷等海洋山脊或海洋岛（如夏威夷）的火山物质之间的关系。 更多的氧化套也会引发更大的深度融化，这决定了地幔和地壳如何通过时间变化，以及在火山活动期间从地幔中释放的挥发物（例如H2O，CO2和硫）等挥发物的质量。 这也影响了地球物理特性，包括地幔对流的抵抗力，以及地震波和电流如何在地球内部传播。 最后，基于火山岩组成的地球内部氧化状态的推论需要了解熔化过程中Fe3+的熔融行为。 将进行实验研究，以提高对这两个主题的理解。初步数据表明，碳的存在显着减少了硫化物的熔点，并将进行新的实验，以探索这种关系如何随压力和硫化物组成的变化，并确定硫化物融化中的C溶解度。 实验将考虑到随着地幔压力增加的增加，尤其是金属与硫化物的比率变化的变化，金属的活性变化。 实验将使用活塞缸和多轴线设备进行18 GPA，并将通过电子微探针和SIMS分析。 对地幔部分融化过程中Fe3+的行为的研究将集中在辉石的行为上，因为这是地幔中氧化铁的主要储层，并且以前几乎没有测量。实验和X射线光谱将确定在部分熔融过程中Fe3+之间的Fe3+分配，以量化融化与地幔氧化态之间的关系。其他实验将探索橄榄岩的氧化状态与部分熔化行为之间的关系。