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Redox melting processes in the mantle under reducing conditions

还原条件下地幔中的氧化还原熔化过程

基本信息

批准号：
320586258
负责人：
Professor Dr. Alan Butler Woodland
金额：
--
依托单位：
Research School of Earth Sciences
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/320586258?language=en
关键词：
Redox melting processes mantle under

项目摘要

Partial melting of the mantle is fundamental to the differentiation and chemical evolution of the Earths interior. In addition to an increase in temperature or a lowering of pressure, melting can also develop through redox reactions via processes referred to as redox melting. In this case, reduced fluids containing CH4 interact with relatively oxidized peridotite, causing carbon precipitation (e.g. as diamond). The fluid becomes richer in H2O, which lowers the peridotite solidus and induces melting without any change in temperature. There is a variety of evidence that points to this process being a viable mechanism for melt generation throughout Earth history: 1) the juxtaposition of domains with contrasting oxidation states, 2) the presence of reduced conditions in the deeper upper mantle and 3) isotopic compositions of some diamonds indicating formation from CH4-bearing fluids. However, next to nothing is known about the composition and trace element characteristics of such redox melts. The goals of this project are: i) to determine the solidus temperature of peridotite coexisting with CH4-bearing fluids at pressures corresponding to ca.120-200 km depth, ii) to determine the melt composition, including the behavior of selected trace elements, iii) to monitor the composition of coexisting minerals and fluids and iv) investigate the link between redox melting and diamond formation. Experiments will be performed using the double capsule technique, allowing the control of oxygen fugacity, which will be monitored independently using Ir-Fe redox sensors. Microprobe and LA-ICP-MS will be employed to measure major and trace element compositions, respectively. Fluids will be analysed in selected samples using capsule piercing/mass spectrometry at the ANU, Canberra.

地幔的部分熔融是地球内部分异和化学演化的基础。除了温度升高或压力降低之外，熔融还可以通过氧化还原反应经由被称为氧化还原熔融的过程来发展。在这种情况下，含有CH4的还原流体与相对氧化的橄榄岩相互作用，导致碳沉淀（例如金刚石）。流体中的H2O变得更丰富，这降低了橄榄岩的固相线，并在温度没有任何变化的情况下诱导熔融。有各种证据表明，这一过程是一个可行的机制，在整个地球历史上的熔体生成：1）并列域与对比氧化状态，2）在更深的上地幔还原条件的存在和3）同位素组成的一些金刚石表明形成从CH4轴承流体。然而，几乎没有什么是已知的组成和微量元素的特点，这样的氧化还原熔体。该项目的目标是：i）确定的固相线温度的橄榄岩共存的CH4-轴承流体在压力对应于约。120 - 200公里的深度，ii）确定熔体的组成，包括选定的微量元素的行为，iii）监测共存的矿物和流体的组成和iv）调查氧化还原熔融和金刚石形成之间的联系。实验将使用双胶囊技术进行，允许控制氧逸度，这将使用Ir-Fe氧化还原传感器独立监测。微探针和LA-ICP-MS将分别用于测量主量和微量元素组成。将在澳大利亚国立大学（堪培拉）使用胶囊穿刺/质谱法对选定样本中的液体进行分析。