H2O solubilities in Al-free and Al-bearing high-pressure silica polymorphs as a function of pressure and temperature: H2O storage in the lower mantle

无铝和含铝高压二氧化硅多晶型物中的水溶解度与压力和温度的函数关系：下地幔中的水储存

• 批准号: 518398967
• 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
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/518398967?language=en
• 关键词: H2O; solubilities; Al; free; bearing

To understand the deep H2O cycle, it is necessary to know the H2O solubility in the mantle min-erals. Some upper-mantle minerals have high H2O storage capacity, but the H2O solubility in lower-mantle peridotite minerals is negligible. Hence, we speculate that silica minerals in basaltic fragments of subducted slabs host H2O in the lower mantle. Laser-heated diamond-anvil-cell (LH-DAC) experiments reported large H2O solubility in high-pressure silica minerals, namely, stishovite and CaCl2-structured SiO2, under conditions of the upper part of the lower mantle, which is referred to as the mid-mantle. However, the results of the LH-DAC studies were contra-dictory. Therefore, we will investigate the H2O solubility in stishovite and CaCl2-structured SiO2 under mid-mantle conditions using our advanced multianvil technology. Since Al is known to increase H2O solubility of stishovite and is considered a major secondary cation for stishovite, both Al-bearing and Al-free systems will be investigated in this project. This project consists of two sub-projects. Sub-project I is an in situ X-ray diffraction study using the multi-anvil press on beamline P61B of PETRA-III at DESY. First, we will investigate whether H2O loss occurs from high-pressure silica during and after decompression. Next, we will cali-brate the relationship between volume and H2O-content at ambient temperature and high pres-sure. We will then measure the volumes of high-pressure silica at pressures of 10, 20, 30, 40 and 50 GPa and increasing temperatures to 2000 K in 100 K steps. At each temperature step, the sample will be once quenched to ambient temperature, and the H2O content is determined from the volume – H2O-content relationship determined above. At the same time, splits of (120)-(210), (211)-(121), and (130)-(310), and (031)-(301) peaks will carefully be observed to determine the phase transition between stishovite and CaCl2-structured SiO2. In the Sub-project II, single crystals of Al-free and Al-bearing high-pressure silica will be synthe-sized at pressures of 14 - 35 GPa and temperatures of 1300 - 2300 K. The synthesized single crystals will be used to determine the H2O content using Fourier transform infrared spectrosco-py and secondary ion mass spectrometry. Prior to the single-crystal growth, the maximum Al2O3 solubility will be determined as a function of the pressure and temperature in the Al-bearing system.

为了了解深H2O循环，有必要了解地幔Min-erals中的H2O溶液。一些上层矿物质具有高H2O储存能力，但是下层橄榄岩矿物质中的H2O溶液可以忽略不计。因此，我们推测俯冲板的玄武岩片段中的硅胶矿物质在下地幔中寄主H2O。激光加热的钻石 - 墨水细胞（LH-DAC）实验报告了高压硅胶矿物质中的大H2O溶液，即在下层上部的上部的条件下，即stishovite和stishovite和cacl2结构化的SiO2，这被称为中间甲板。但是，LH-DAC研究的结果是矛盾的。因此，我们将使用我们先进的Multianvil技术在中型条件下研究Stishovite和CaCl2结构的SIO2中的H2O解决方案。由于已知Al会增加雌雄同体的H2O溶液，并被认为是替代岩的主要次要阳离子，因此将在该项目中研究Al-Barewer和无AL-FREARGENS系统。该项目由两个子项目组成。亚项目I是一项在DESY的Petra-III的梁线p61b上使用多动力压力机的原位X射线衍射研究。首先，我们将研究H2O损失是否来自减压期间的高压二氧化硅。接下来，我们将在环境温度和高压下的体积与H2O容量之间的关系。然后，我们将在10、20、30、40和50 GPA的压力下测量高压二氧化硅的体积，并以100 K步长到2000 K的温度升高。在每个温度步骤中，样品将一旦淬灭至环境温度，而H2O含量是根据上面确定的体积 - H2O-content关系确定的。同时，（120） - （210），（211） - （121）和（130） - （310）和（031） - （301）将仔细观察到峰，以确定Stishovite和CACL2结构的SIO2之间的相变。在亚项目II中，无Al-Free和Al-Bearth高压二氧化硅的单晶体将以14-35 GPA的压力进行合成大小，温度为1300-2300K。合成的单晶将用于使用H2O含量，用于使用傅立叶变换谱谱谱系和二世离子质量谱图确定H2O含量。在单晶生长之前，将确定最大AL2O3溶液，这是Al-Barearing系统中压力和温度的函数。