Fluids and Mineral Interactions in Extreme Conditions of the Earth Interior: In-Situ Observation of the Deep Earth Fluids by Using Diamond Anvil Cell

Recent ultra-high pressure and high temperature experiments provide a new opportunity to gain an insight into the fluids, fluid and matter interactions in the extreme conditions of the deep Earth interior. In-situ observations of the matter in the Earth interior under ultra-high pressure and high temperature conditions by using diamond anvil cell connected to spectrometer and microscope, combined with synchrotron radiation technique, can obtain new data and message of their molecular structures, and natures in atomic scale and in kinetics. The nature of Earth fluids would be changed by the variations of the temperatures and pressures of their locations. It is well known that the properties of water in the critical region might show anomalies in many of its physical properties. For example, the density or dielectric constant of water might drop with increasing temperature. The molecular structures of aqueous solutions (NaCl-H2O) at high temperatures and pressures (800°C, 3 GPa) have been examined using diamond anvil cell in situ observation connected to FT-IR spectrometer combined with synchrotron radiation technique. The sharp and strong O–H stretching vibration at 330°C near the critical point of water proves the breakdown of the hydrogen bonding net work. Within and near the critical region, the rapid decrease in the dielectric constant and density of water results in the destruction of the hydrogen bond net work of the water molecules. O–H vibration frequency increases with temperature. Experiments demonstrated that nature and structure of the Earth fluids will change with depth. As passing through the critical state, the anomaly properties of fluids will be affected by the variations of water molecule vibrations and hydrogen bond network broken at the critical state.