Physical Properties and Water Content of Volcanic Glasses and Olivines Included in Submarine Volcaniclastic Rocks from North Lau Eruption Sites

M.H. Manghnani¹*, B. Houghton¹, & A. Hushur¹

Corresponding author: murli@soest.hawaii.edu
¹University of Hawaii, School of Ocean and Earth Science & Technology Honolulu, HI 96822

Abstract:
Water dissolved as hydroxyl groups or molecular water in eruptive melts plays important role in the viscosity and hence in eruptive style of the ascending magma. Investigation of the water content in refined hyperquenched (basaltic) glasses can provide useful constrains of water contents of the ascending magmas and information on the interaction of magma with seawater. The capability of confocal micro-Raman spectroscopy to determine the total amount of water dissolved in natural and synthetic glasses and minerals has been recently demonstrated [1, 2]. High- T Raman experiments enable us to understand the behavior of water after entrapment and the interface processes between melt inclusion and its host mineral [3]. Proposed Work, Methods and Anticipated Results:

1. Measure the physical properties (density, elastic-wave velocity Vp, Vs and moduli, and glass transition temperature, Tg) of selected basaltic glasses by Brillouin scattering at ambient and high temperatures.
2. Determine water content in basaltic glasses by confocal micro-Raman spectroscopy. High temperature (1300 oC) Raman measurements will also be carried out to determine the water lost. Results from (1) and (2) above will be compared in light of composition, water content and structure of the basaltic glasses..
3. Physical properties and water contents of olivine crystals in basaltic glasses and volcaniclastic rocks will provide information regarding the nature of OH bonding and interaction of ascending magma with sea water.

Recently, we have synthesized pure forsterite (Fo) and Fo97Fa3 olivine with water contents up to 0.9 wt% water, and have studied the structure, vibrational properties and protonation characteristics by XRD and Raman spectroscopy [4, 5, 6] at high pressures.

Contributions to Integration and Synthesis:
Several studies of natural and experimentally synthesized/hydrated of olivine show that it can incorporate substantial amounts of OH, which has important implications for rheology, melting behavior and transport properties of mantle.

References:
Mercier et al., Influence of glass polymerisation and oxidation on micro-Raman water analysis in alumino-silicate glasses, Geochim. Cosmochim. Acta, 73, 197, 2009.
Thomas et al., American Mineralogist, Laser Raman spectroscopic measurements of water in unexposed glass inclusions, 91, 467, 2006
Mercier et al., Water content and behavior in mafic glasses and melt inclusions: An approach using micro Raman spectroscopy, abstract, Fall AGU meeting, 2008.
Smyth et al., Olivine hydration in the deep upper mantle: Effects of temperature and silica activity, Geophysical Research Letters, 33, L15301, 2006.
Hushur et al., Crystal chemistry of hydrous forsterite and its vibrational properties up to 41 GPa, American Mineralogist, 94, 751–760, 2009.
Manghnani et al., Compressibility and structural stability of hydrous olivine Fo97Fa3 up to 34 GPa by XRD and Raman spectroscopy (manuscript in preparation).