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.

在这个基于成就的更新中，将执行两个项目，它们都与地球内部融化的化学动力学有关。其中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的熔融硫化物中，因此它可能在不同地球储集层之间的碳循环中起重要作用。它也可能在钻石的起源中发挥重要作用，并影响地幔的地球物理性质。第二个项目研究岩浆形成与地幔中铁的氧化态之间的关系。地幔中氧化铁（Fe3+）和还原铁（Fe2+）比例的细微差异可能对熔融行为产生深远影响。例如，富含Fe3+的地幔可能更容易熔化，从而影响地幔温度与中洋脊或大洋岛屿（如夏威夷）喷发的火山物质体积之间的关系。更多氧化的地幔也会在更深的地方开始融化，这决定了地幔和地壳如何随着时间的推移而改变组成，以及火山活动期间从地幔中释放出的大量挥发物，如H2O、CO2和硫。这也会影响地球物理特性，包括地幔对对流的阻力，以及地震波和电流如何在地球内部传播。最后，根据火山岩成分推断地球内部的氧化状态需要了解Fe3+在熔融过程中的熔化行为。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，碳的存在显著降低了硫化物的熔点，新的实验将进行，以探索这种关系如何随着压力和硫化物组成的变化，以及确定C在硫化物熔体中的溶解度。这些实验将考虑到随着地幔压力的增加而发生的金属活性的变化，特别是金属与硫化物的比例如何变化。实验将使用活塞缸和多砧装置进行，最高可达18 GPa，并将通过电子探针和SIMS进行分析。由于辉石岩是地幔中氧化铁的主要储集层，因此对部分熔融过程中Fe3+行为的研究将集中在辉石岩中的行为上，而之前的测量很少。实验和x射线光谱将确定部分熔融过程中辉石和硅酸盐熔体之间的Fe3+分配，以量化熔融与地幔氧化态之间的关系。进一步的实验将探讨橄榄岩的氧化态与部分熔融行为之间的关系。