Preferential dissolution of SiO2 from enstatite to H2 fluid under high pressure and temperature.
Preferential dissolution of SiO2 from enstatite to H2 fluid under high pressure and temperature.
复制标题
在高压和高温下，SiO2 从顽辉石中优先溶解到 H2 流体中。
DOI：
10.1007/s00269-015-0792-3
复制
发表时间：
2015
影响因子：
1.4
通讯作者：
Nakano S. and Yagi T.
中科院分区：
文献类型：
--
作者：
Shinozaki A.;Kagi H.;Hirai H.;Ohfuji H.;Okada T.;Nakano S. and Yagi T.
在3.1-13.9 GPa和1500-2000 KK的压力和温度范围内，用激光加热的金刚石砧座研究了顽火辉石和H_2流体共存时的稳定性和相关系。X射线衍射仪测量表明，顽火辉石受热分解，形成镁橄榄石、方镁石和柯石英/辉钛矿。在回收的样品中，在加热热点的边缘发现了SiO_2颗粒，表明SiO_2组分在加热过程中溶解在H_2O_2流体中，当其溶解度随着温度的降低而降低时，SiO_2组分会析出。共存流体相的拉曼光谱和红外光谱表明，SiH4和H2O分子是通过溶解的二氧化硅和氢气反应形成的。相反，在热点内发现了镁橄榄石和方镁石晶体，推测它们取代了最初的斜方辉石晶体而没有溶解。辉石的SiO_2组分在H_2流体中的优先溶解以及在镁橄榄岩H_2体系和石英H_2体系中观察到的结果表明，富H_2流体促进了地幔矿物流体与固相之间的Mg/Si分馏。
Stability and phase relations of coexisting enstatite and H2fluid were investigated in the pressure and temperature regions of 3.1–13.9 GPa and 1500–2000 K using laser-heated diamond-anvil cells. XRD measurements showed decomposition of enstatite upon heating to form forsterite, periclase, and coesite/stishovite. In the recovered samples, SiO2grains were found at the margin of the heating hot spot, suggesting that the SiO2component dissolved in the H2fluid during heating, then precipitated when its solubility decreased with decreasing temperature. Raman and infrared spectra of the coexisting fluid phase revealed that SiH4and H2O molecules formed through the reaction between dissolved SiO2and H2. In contrast, forsterite and periclase crystals were found within the hot spot, which were assumed to have replaced the initial orthoenstatite crystals without dissolution. Preferential dissolution of SiO2components of enstatite in H2fluid, as well as that observed in the forsterite H2system and the quartz H2system, implies that H2-rich fluid enhances Mg/Si fractionation between the fluid and solid phases of mantle minerals.