Hydration of Dense Polymorphs of Silica in Subducting Slabs

俯冲板片中二氧化硅致密多晶型物的水合作用

• 批准号: 1321976
• 负责人: Kurt Leinenweber
• 金额: $ 31.28万
• 依托单位: Arizona State University
• 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: 2013-08-01 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1321976&HistoricalAwards=false
• 关键词: Hydration; Dense; Polymorphs; Silica; Subducting

Silica, or SiO2, is one of the primary chemical components of the Earth's crust and mantle, and forms the common minerals quartz, tridymite and coesite on the Earth's surface. At higher pressures characteristic of the mantle, these minerals transform into denser minerals, ultimately transforming into the mineral stishovite (also found in impact sites such as Meteor Crater). Stishovite is of great interest because if its high density and high (6-fold) coordination of the silicon atom, as well as its expected presence in rocks initially formed at the surface, but brought deep into the Earth by subduction. Recent findings by the team, using a multi-anvil high pressure apparatus, demonstrate that under high pressure and modest temperature, ordinary water, H2O, is absorbed by stishovite in relatively significant amounts (up to several weight percent), and the hydrogen becomes part of the crystal structure of the mineral in the form of an OH- ionic molecule. The structural volume of the mineral expands as a result of the addition of H2O. No additional components are needed to achieve this behavior ? only pure H2O and SiO2. This surprising discovery raises new questions about the structural chemistry of stishovite, and the behavior of stishovite and other minerals in the Earth. In the proposed research, the investigators will pursue a more detailed study of the rates and quantities of water absorbed in stishovite at different pressures and temperatures, including those relevant to the Earth's interior. Furthermore, they will study the effect of water contents on the physical properties of the stishovite such as compressibility and sound velocity. This research is expected to contribute to fundamental understanding of the behavior of H2O in contact with silicates at high pressures, which is important for delineating processes involved in the Earth's overall hydrologic cycle. Results will clarify the crystal chemical implications of stishovite hydration. Also this research is of significant mineralogical interest in the understanding of hydrogen in minerals, and may be important in understanding the mineralogical make-up of gas giant planets.

二氧化硅，或称二氧化硅，是地壳和地幔的主要化学成分之一，在地球表面形成了常见的矿物石英、鳞石英和柯石英。在地幔特有的较高压力下，这些矿物会转化为更致密的矿物，最终转化为矿物辉钛矿(也可以在陨石坑等撞击地点发现)。辉钛矿之所以引起人们的极大兴趣，是因为如果它的高密度和硅原子的高(6倍)配位，以及它在岩石中的预期存在，最初是在地表形成的，但通过俯冲带到地球深处。该研究小组使用多砧板高压设备最近的发现表明，在高压和中等温度下，普通水H2O被辉石以相对较大的量(高达几个重量百分比)吸收，氢以OH-离子分子的形式成为矿物晶体结构的一部分。由于添加了H2O，矿物的结构体积扩大了。是否不需要其他组件即可实现此行为？只有纯净的水和二氧化硅。这一令人惊讶的发现提出了关于辉石的结构化学以及辉石和地球上其他矿物的行为的新问题。在这项拟议的研究中，研究人员将对辉石在不同压力和温度下的吸水率和吸水量进行更详细的研究，包括与地球内部相关的压力和温度。此外，他们还将研究水含量对辉石的物理性质的影响，如可压缩性和声速。这项研究预计将有助于从根本上理解水在高压下与硅酸盐接触的行为，这对于描述地球整个水文循环所涉及的过程非常重要。结果将阐明辉石水合作用的晶体化学含义。此外，这项研究对理解矿物中的氢具有重要的矿物学意义，并可能对理解气态巨行星的矿物学组成具有重要意义。