Award funds will be used to upgrade the excitation laser used for microRaman spectroscopy, which plays a central role in experimental characterization of minerals, melts, and fluids at high temperature and pressure. These data are central to our understanding of the formation and evolution of the solid Earth, its oceans, and atmosphere. The most important research areas are:
1. Structure of silicate-C-O-H-N components in and partitioning between melt and fluid to advance modeling of transport properties and processes that involve fluids and melts in the Earth and terrestrial planets. 2. Equation-of-state and structure of COH fluids at high temperature and pressure. 3. Characterization of stable isotope partitioning between minerals, melts, and fluids at high temperature and pressure. 4. COH fluid structural speciation and isotopologues in hydrothermal environments
These objectives are reached by using externally-heated hydrothermal diamond anvil cells (HDAC) and probing the samples with vibrational (Raman and infrared) spectroscopic methods. The HDAC is employed for sample containment wherein in-situ spectroscopic measurements with samples at desired temperature, pressure, and redox conditions are carried out; optical observations can be made at the same time through the diamond windows.
Characterization of mass and energy transport processes is central to our understanding of the physics and chemistry of the formation and evolution of the Earth, volcanic, geothermal, and ore-forming, and geophysical processes (seismic activity, mass redistribution, thermal and electrical conduction). The main transport agents in the Earth’s interior are molten silicates (magma) and volatile components in the chemical system C-O-H-N-S. Water and carbon-bearing species (CO2 and CH4) are the dominant volatile species. In order to characterize materials transport, chemical and physical properties of silicate melts and fluid are determined in the laboratory. These properties can be modeled via structural information from the fluids and melts and the phenomenological links between structure and properties. The structure determination is accomplished in the laboratory where conditions in the Earth corresponding to depth exceeding several hundred km can be duplicated. Among the most important techniques employed for this purpose is use of diamond cells heated with external heaters and where vibrational (Raman and infrared) spectroscopy is employed to probe the structural environment while the samples are at the temperatures and pressures of interest. Such instrumentation is available for routine use in our laboratory. However, the technical quality at the temperature and pressure conditions under which Raman spectroscopic measurements can be made are critically dependent on the wavelength and power of the laser used for sample excitation because of signal interference from the high-temperature-heater and because high-quality spectra vary as a linear function of time and laser power and time is a critical experimental variable. This quality, in turn, is a major contributor to uncertainty in the experimental data and has been an important obstacle to the use of Raman spectroscopic data to determine melt and fluid structure at high temperature and pressure. To improve the data quality, our Raman system needed, therefore, a shorter wavelength and more powerful laser. To this end, the NSF grant EAR-1251931 was used to purchase a 500 mW Genesis MX-500 488 nm diode laser (manufacturer: Coherent™), which was then implemented by JASCO™factory engineers (the manufacturer of the Raman system) in September and October 2013. As a result of this upgrade, we have decreased the black body background by > 50% and improved signal intensity by more than one order of magnitude. Even though it is only 6 months since the laser was installed, the upgraded Raman system has been used successfully to complete several projects. Three have manuscripts currently under review [Mysen, B. O. (2014). Melt-fluid structure and property relationships in silicate-C-O-H as a function of redox conditions: An experimental study, in-situ to 1.7 GPa and 900?C. Amer. Mineral. Submitted; Foustoukos, D. F. and Mysen, B. O. (2014). The structure of water-saturated carbonate melt. Amer. Mineral. Submitted; Dalou, C., Mysen, B. O. and Foustoukos, D. (2014). In-situ measurements of fluorine and chlorine speciation and fractionation between aluminosilicate melts and aqueous fluid. Amer. Mineral. Submitted]. These involve post-doctoral fellow Celia Dalou (now at Univ. Texas, Austin), and research scientist, Dionysis Foustoukos (Co-Pi on the proposal). Aspects of this research are also integrated in to an Encyclopedia of Glass under production with Wiley Publications and aimed at a broader community of materials and glass science in addition to earth and planetary applications. There is an additional 3 projects currently well under way where structural interaction, elemental, and isotopic interactions between C-O-H-N volatile components and silicate melts are examined. These projects involve an additional post-doctoral fellow, Charles LeLosq and fellow senior staff scientist, George Cody. This personnel will be augmented by at least one college summer intern student this summer. Finally, the upgraded Raman system is available for use by our colleagues at the Geophysical Laboratory. These include fellow staff members Ying-wei Fei (Co-Pi on the proposal) and Dave Mao and their visiting scientists, post-doctoral fellows, and visitors. Their research ranges from experimental determination of thermodynamic stability relations of minerals in the Earth interior to the behavior of methane and hydrogen at high temperature and pressure. The latter research illustrates how the experimental activities aimed to characterize earth science problems have direct application to research aimed at advancing our understanding ways and means for storage of alternative energy sources. The former projects focus on chemistry and physics of the deep silicate Earth and its core.
