HR: 11:20h
AN: V52A-05    [Abstracts]
TI: Volatile contents of komatiite magmas and the Archaean mantle: Insights from melt inclusions in komatiites
AU: Woodhead, J
EM: jdwood@unimelb.edu.au
AF: University of Melbourne, Parkville, Melbourne, VIC 3010 Australia
AU: * Kent, A J
EM: adam.kent@geo.oregonstate.edu
AF: Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97330 United States
AU: Hergt, J
EM: jhergt@unimelb.edu.au
AF: University of Melbourne, Parkville, Melbourne, VIC 3010 Australia
AU: Bolhar, R
EM: robert.bolhar@canterbury.ac.nz
AF: University of Canterbury, Te Whare Wananga o Waitaha, Christchurch, 4800 New Zealand
AU: Rowe, M C
EM: rowem@geo.oregonstate.edu
AF: Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97330 United States
AB: Relatively little is known about the abundances of volatile elements (H, C, Cl, S) in komatiite magmas, although this information provides potentially important constraints on the volatile content, evolution and outgassing of the Archaean mantle. One means to obtain this information is via studies of melt inclusions in komatiites and other olivine-bearing Archaean lavas, although samples that contain preserved primary olivine are rare. Komatiite lavas from the Belingwe greenstone belt contain igneous olivine phenocrysts (Fo90-93) with abundant melt inclusions. Rehomogenization experiments suggest trapping temperatures of ~1300-1325°C. SIMS and EMPA provide measurements of H, C, Cl and S contents as well as major elements and future LA-ICP-MS analyses are planned for trace elements.
Water contents measured in melt inclusions range up to 1.1 wt.%, similar to those previously reported in spinel-hosted melt inclusions from Belingwe. Many inclusions have detectable CO₂ contents (up to >200 ppm), suggesting minimal degassing loss of H₂O, but the presence of lower water contents in inclusions with detectable CO₂ may record diffusive loss of H after trapping. Sulfur contents of inclusions are typically 500-750 ppm. These are below the projected S solubility of these melts and this may reflect source melting beyond the point of sulfide out. Chlorine contents are ~400-700 ppm and Cl/K₂O ratios are ~0.8 to 1.5, which is significantly enriched over uncontaminated modern MORB and OIB. This is unlikely to relate to contamination and may represent a mantle source that has not outgassed Cl, or addition of a Cl (plus H?) - rich flux prior to melting.
DE: 1025 Composition of the mantle
DE: 1038 Mantle processes (3621)
DE: 1043 Fluid and melt inclusion geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005