Influence of Titanium on Water Incorporation, Rheology and Seismic Properties of Olivine

钛对橄榄石吸水性、流变性和抗震性能的影响

• 批准号: 1321889
• 负责人: Ulrich Faul
• 金额: $ 31万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1321889&HistoricalAwards=false
• 关键词: Influence; Titanium; Water; Incorporation; Rheology

The Earth's interior may contain as much water as in the oceans, but it occurs in trace amounts in silicate minerals which make up the Earth's mantle. In the upper mantle, olivine is the major phase, occupying at least 60% of its volume. It dominates the physical properties such as the viscosity involved in convection and plate tectonics. Deformation experiments show that water has a large effect on the viscosity of olivine, lowering it by an order of magnitude or more. How much water is contained in olivine depends on the capacity of the crystal structure to incorporate it as a trace element, but also on the availability of water. Except above subducting plates, the capacity of olivine to incorporate water substantially exceeds the water available in the mantle, so that the olivine is far from water saturation. By contrast, published deformation experiments have only been carried out either dry or under water-saturated conditions. The proposed experiments will be conducted under water-undersaturated conditions representative of those in the Earth. The bonding environment of hydrogen in the crystal lattice of olivine can be investigated with infrared spectroscopy. Comparison of spectra from water-undersaturated xenoliths with those from water saturated experiments show significant differences. The xenolith spectra can be reproduced when trace amounts of titanium are added to synthetic olivine encapsulated in noble metals like platinum. The spectra confirm that the amount and bonding environment of hydrogen in these synthetic samples matches the natural samples. Exploratory deformation experiments show that these samples are weaker than dry samples, suggesting that water saturation is not necessary for water-weakening. If confirmed these findings imply that in the presence of titanium hydrogen is comparatively stable in the olivine structure, and that even small amounts of water will induce weakening. This has implications not only for the rheology of the Earth, but potentially also for drier planetary bodies such as the Moon or Mars.

地球内部可能含有与海洋一样多的水，但它存在于构成地幔的硅酸盐矿物中。在上地幔中，橄榄石是主要的相态，至少占其体积的60%。它支配着物理性质，如对流和板块构造中涉及的粘度。变形实验表明，水对橄榄石的粘度有很大的影响，使其降低一个数量级或更多。橄榄石中含有多少水取决于晶体结构将其作为微量元素的能力，但也取决于水的可用性。除俯冲板块外，橄榄石的含水量大大超过地幔中的含水量，因此橄榄石远未达到含水饱和。相比之下，已发表的变形实验仅在干燥或水饱和条件下进行。拟议的实验将在代表地球的水不饱和条件下进行。氢在橄榄石晶格中的成键环境可以用红外光谱进行研究。水饱和捕虏体的光谱与水饱和捕虏体的光谱相比，有明显的差异。捕虏体光谱可以重现时，微量的钛被添加到合成橄榄石封装在贵金属如铂。光谱证实，这些合成样品中的氢的量和成键环境与天然样品相匹配。探索性变形实验表明，这些样品比干燥样品更弱，这表明水饱和度不是水弱化的必要条件。如果得到证实，这些发现意味着在钛的存在下，氢在橄榄石结构中相对稳定，即使是少量的水也会引起弱化。这不仅对地球的流变学有影响，而且可能对月球或火星等更干燥的行星体也有影响。