Possible Storage of H2O in Mantle Ca(Ti,Si)O3 Perovskite

水是地球宜居性的关键因素之一。虽然地球表面的70%被水覆盖，但更多的水可能存在于地球内部的岩石中。这种“深水”被认为在地质时间尺度上促进了大气和水圈的演变。然而，由于技术限制，很难获得深度大于~10 km的样品。因此，在地球内部高压-高温条件下对主要矿物进行实验室实验是很重要的。过去二十年的实验室实验表明，660公里深度以上的地幔中的一些矿物质可能含有大量的水，大约有一个海洋的水储存在地幔的这一部分。然而，实验室测量也表明，在660公里至2900公里深度的地幔中稳定的一些主要矿物的储水能力可能非常低，导致该层基本上是干燥的假设。然而，地幔下部第三丰富相Ca(Ti,Si)O3钙钛矿的储水能力尚未得到很好的研究。在本研究项目中，研究人员将在下地幔高压-高温条件下合成Ca(Ti,Si)O3钙钛矿并测量其储水能力。这些测量将提高我们对下地幔中可以储存多少水的认识，下地幔占地球体积的50%以上。研究人员还将测量水溶性对Ca(Ti,Si)O3钙钛矿物理性质的影响，为通过地震成像方法研究下地幔可能存在的富水区提供关键数据。博士生和本科生将接受高压设备和小体积产品表征方面的综合技能培训。通过一年一度的“地球与太空探索日”开放日和校园范围内的“开门之夜”活动，向公众宣传氢在地球（和其他行星）内部的重要作用。数据分析将写在Jupyter笔记本文件中，然后转换为亚利桑那州立大学矿物学和地球化学课程的教学材料。通过这笔资金，沈PI的研究小组将测量Ca(Ti,Si)O3钙钛矿的储水能力。他们将在压力-温度条件下合成高质量的钙钛矿样品，以保证Ca(Ti,Si)O3钙钛矿在大体积压机中的稳定性。合成的样品将使用一系列技术（红外和拉曼光谱、热重分析、二次离子质谱、x射线衍射和电子显微镜）仔细分析，以确定可能的H2O存储。合成的样品还将在金刚石砧池中进行研究，以测量水和钛对地幔相关压力下热弹性性能的影响。十多年来，地球科学一直在努力了解地球内部在地球大气和水圈演变中的作用。然而，下地幔的储水量仍然不确定。通过研究下地幔中第三丰富的矿物相，该研究项目将推进我们对深部水储存的认识，这对包括挥发物循环、地球形成和分化以及深部地幔地震结构在内的一系列地球科学问题具有重要意义。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Water is one of the key ingredients for the habitability of the Earth. While 70% of the Earth’s surface is covered with water, far more water may exist in the rocks of the interior. This “deep water” is believed to have been contributing to the evolution of the atmosphere and hydrosphere over geologic time scales. However, it is difficult to obtain samples from depths greater than ~10 km because of technological limitations. Therefore, it is important to conduct laboratory experiments on the main minerals at the high pressure-temperature conditions of the Earth’s interior. Laboratory experiments for the past two decades have shown that some minerals in the mantle above 660-km depth can contain large amounts of water, contributing to approximately one ocean mass of water stored in this part of the mantle. However, laboratory measurements have also shown that water storage capacities of some main minerals stable at the mantle from 660 km to 2900 km depths could be very low, leading to a hypothesis that the layer is essentially dry. However, the water storage capacity of the third most abundant phase in the lower part of the mantle, Ca(Ti,Si)O3 perovskite, has not been well studied. In this research project, researchers will synthesize Ca(Ti,Si)O3 perovskite at the high pressure-temperature conditions of the lower mantle and measure its water storage capacity. The measurements will advance our knowledge on how much water can be stored in the lower mantle, which represents more than 50% of the Earth’s volume. The researchers will also measure the impact of water solubility on the physical properties of Ca(Ti,Si)O3 perovskite, providing key data for investigating possible existence of water-rich regions in the lower mantle through seismic imaging methods. A Ph.D. student and undergraduate students will be trained for a comprehensive skill-set in high-pressure apparatus and in the characterization of very small run products. Informing the public about the important role of hydrogen in the interior of Earth (and other planets) will be achieved using the annual “Earth and Space Exploration Day” open house and the campus-wide “Night of the Open Door” event. The data analysis will be written in Jupyter notebook files and then converted to education materials for mineralogy and geochemistry courses at ASU.Through this grant, PI Shim’s research group will measure the water storage capacity of Ca(Ti,Si)O3 perovskite. They will synthesize high-quality samples at the pressure–temperature conditions for the stability of Ca(Ti,Si)O3 perovskite in the large-volume press. The synthesized samples will be carefully analyzed using a range of techniques (infrared and Raman spectroscopy, thermogravimetric analysis, secondary ion mass spectrometry, X-ray diffraction, and electron microscopy) for possible H2O storage. The synthesized samples will also be studied in the diamond-anvil cell to measure the effects of H2O and Ti on the thermoelastic properties at mantle-related pressures. Intense effort has been made in Earth science over a decade to understand the role of the interior for the evolution of Earth’s atmosphere and hydrosphere. Yet, water storage in the lower mantle still remains uncertain. By studying the third most abundant mineral phase in the lower mantle, the research project will advance our knowledge on the deep H2O storage which is important for a range of issues in Earth science, including volatiles recycling, Earth formation and differentiation, and seismic structures in the deep mantle.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.