Effect of Hydrogen Bonding on the Compressibility of Chondrodite and Clinohumite

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LagerEAR-0073734A significant portion of our planet's water may be held within the atomic structures of minerals in the mantle. The presence of structurally-bound water in the form of hydroxyl ion (OH-) or molecular water (H2O) can lower the melting temperatures of rocks, affect the character of volcanic activity and may even generate the forces that cause earthquakes. Therefore, it is important to understand how water (hydrogen) affects the properties of hydrous minerals at pressure-temperature conditions representative of the mantle. With the recent development of high-pressure, neutron facilities, atomic-level information on the behavior of hydrogen at mantle pressures can be obtained from small-volume (90 mm3), powdered samples. The majority of minerals that have been studied using this technique have relatively simple atomic structures. In this project, high-pressure data will be obtained for the first time on structurally-complex minerals (humites) using both neutron and X-ray data collected for the same sample. X-rays will give the precision required for the heavier atoms (metals and oxygen) in these structures. Neutrons can then be used to determine the hydrogen-atom positions. Using these complementary measurements, it should be possible to improve both the accuracy and precision of the experiments and learn more about how changes in the hydrogen-atom environment at high pressure affect the compression of these minerals. In a related experiment, infrared spectra will be collected for humite minerals and correlated to neutron data on the hydrogen-atom environment. The objective is use the atomic structure of humite as a model to understand the mode of incorporation of trace amounts of hydrogen in olivine, the predominant mineral in the mantle.