Measurement of Si self-diffusion coefficients of wadsleyite as a function of water content

硅锰矿硅自扩散系数随含水量变化的测量

• 批准号: 251472533
• 负责人: Professor Dr. Tomoo Katsura
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/251472533?language=en
• 关键词: Measurement; Si; self; diffusion; coefficients

Dynamic motion in the mantle accounts for a wide variety of geological and geophysical phenomena. Understanding dynamic mantle flow is therefore essential for solid-state geophysics. Rock deformation experiments have shown a large decrease in the creep strength of mantle minerals by hydration (hydrolytic weakening). However, deformation experiments are technically difficult, and the inherent lack of control on key parameters makes interpretation of experimental results problematic. Measurements of Si self-diffusion coefficients have the potential to provide an essential and independent source of information about the high-temperature rheology of minerals, because the slow high-temperature creep of silicate minerals should be controlled by Si self-diffusion. We have studied the effect of water on the Si self-diffusion of forsterite (Fei et al., 2013). This study suggests that the effect of water on mantle rheology is much smaller than previously considered; although the water content exponent on the olivine rheology was considered to be 1.2, it is actually only 0.3. This striking conclusion should be extended by examining other important mantle minerals. Wadsleyite is a dominant constituent mineral in the mantle transition zone. In this study, we will measure Si self-diffusion coefficient of both Fe-free and Fe-bearing wadsleyite with water contents from <1 to 1000 ppm at temperatures of 1400 and 1600 K, determining them as a function of temperature and water content. In this kind of study, use of single crystal samples is essential for reliable measurement. We will synthesize wadsleyite single crystals based on the techniques developed in our previous study. The measurement of Si self-diffusion coefficients of wadsleyite will be conducted by following those in our previous study for forsterite. For the iron-bearing samples, pre-annealing and diffusion annealing will be conducted under constant oxygen fugacity buffered by Mo + MoO2. Based on the results of this project, we will examine and improve our understanding of the effects of water on mantle rheology. This work will provide important insights required to properly understand the dynamic behavior of the mantle.

地幔中的动态运动是多种地质和地球物理现象。因此，了解动态地幔流对于固态地球物理学至关重要。岩石变形实验表明，通过水合（水解性弱），地幔矿物的蠕变强度大大降低。但是，变形实验在技术上很困难，并且对关键参数的固有缺乏使实验结果的解释有问题。 SI自扩散系数的测量可能有可能提供有关矿物质高温流变学的必不可少的信息来源，因为硅酸盐矿物质的缓慢高温蠕变应通过SI自扩散来控制。我们已经研究了水对脱石石的Si自扩散的影响（Fei等，2013）。这项研究表明，水对地幔流变学的影响比以前考虑的要小得多。尽管橄榄石流变学上的水含量指数被认为是1.2，但实际上仅为0.3。应通过检查其他重要地幔矿物来扩展这一明显的结论。瓦德斯利石（Wadsleyite）是地幔过渡区的主要组成矿物。在这项研究中，我们将在1400和1600 K的温度下测量无铁和含水的wadsleyite的Si自扩散系数，水含量从<1到1000 ppm，确定它们是温度和水含量的函数。在此类研究中，使用单晶样品对于可靠的测量至关重要。我们将根据我们先前研究中开发的技术合成Wadsleyite单晶。 Wadsleyite的SI自扩散系数的测量将通过在我们先前的脱叶岩研究中进行的研究来进行。对于含铁样品，将在MO + MOO2缓冲的恒定氧气散热下进行预停机和扩散退火。根据该项目的结果，我们将研究并改善我们对水对地幔风湿病的影响的理解。这项工作将提供重要的见解，以正确理解地幔的动态行为。