Acquisition of Equipment to Establish a High-Pressure Single-Crystal X-Ray Laboratory

点击翻译按钮获取中文摘要

0131979LagerA high-pressure, single-crystal X-ray diffraction laboratory will be established at the University of Louisville. An existing, fully operational CAD4 diffractometer will be adapted for high-pressure use with a diamond-anvil cell. The laboratory will also house an electrostatic drilling machine and stereomicroscope for loading the cell and a laser spectrometer for pressure calibration. A second X-ray unit will also be upgraded with a solid-state generator. A precession camera mounted on this unit will be used as a check on crystal quality and to determine the orientation of single crystals in the pressure cell. The new laboratory will be dedicated to studies of hydrous minerals at high pressure. This group of earth materials plays an important role in mantle processes related to earthquake activity. For example, volume changes associated with phase transitions in hydrous minerals have been linked to the localization of stress and the occurrence of earthquakes along subduction zones. Experiments in this project will focus on hydrous magnesium silicate (OH-clinohumite) and hydrogarnet. Phase-equilbria studies indicate that clinohumite is a stable water-bearing phase in subduction zones to depths of ~400 km (transition zone). Its high-pressure infrared spectrum shows several anomalies at ~13 GPa. The possibility that these anomalies are related to a phase transition will be investigated using the converted CAD4 diffractometer system. Synthetic Si-free hydrogarnet (katoite) has been used as a model to understand how OH is incorporated in silicate garnets that occur in the crust and mantle. The katoite structure undergoes a phase transition at 5 GPa. X-ray data will be collected with the CAD4 at high pressures to determine if a similar transition is observed in naturally occurring hydrogarnets. ***