HR: 1340h
AN: DI33A-1120    [Abstracts]
TI: Volatile (H, C, Cl, S) Concentrations in Ocean Island Basalt Glasses From Pitcairn and the Society Islands
AU: * Koleszar, A M
EM: alison.koleszar@geo.oregonstate.edu
AF: Dept of Geosciences, Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331,
AU: Kent, A J
EM: adam.kent@geo.oregonstate.edu
AF: Dept of Geosciences, Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331,
AU: Wallace, P J
EM: pwallace@uoregon.edu
AF: Dept of Geological Sciences, University of Oregon, 1272 University of Oregon, Eugene, OR 97403,
AU: Woodhead, J D
EM: jdwood@unimelb.edu.au
AF: School of Earth Sciences, University of Melbourne, Victoria, 3010, Australia
AB: Submarine lavas from Pitcairn and the Society Islands offer a unique opportunity to investigate volatile contents in melts derived from mantle OIB sources, and in particular to constrain the composition and origin of the EM-1 and EM-2 mantle endmembers. We present here the results of a study on volatile abundances in dredged glasses from Pitcairn and the Society Islands, two well-documented OIB localities with EM-1 and EM-2 isotopic compositions. Samples for this study consist of submarine glasses, dredged from 485-2829 m depth and representing a range of melt compositions (42.7-59.7 wt% SiO₂, 1.08-11.69 wt% MgO). The EM-2 lavas of the Society Islands have H₂O concentrations between 0.9-2.6 wt%, whereas Pitcairn's EM-1 lavas typically contain 0.8-1.8 wt% H₂O. Both locations have CO₂ abundances that range from low (<190 ppm for Society, <115 ppm for Pitcairn) to below detection, suggesting significant degassing of CO₂ ± H₂O. H₂O/Ce ranges from 55-170 for Pitcairn lavas, and the highest H₂O/Ce ratios are observed in samples with the highest CO₂ concentrations (least degassed). Samples with H₂O/Ce lower than typical MORB or EM sources (<100) may have volatile contents modified by magmatic degassing. Sulfur concentrations (200-1000 ppm for Society, 400-1450 ppm for Pitcairn) may be largely controlled by sulfide saturation. Concentrations of Cl in Society (650-1400 ppm) and Pitcairn (400-1100 ppm) basalts correlate inversely with ⁸⁷Sr/⁸⁶Sr, and do not show evidence of Cl assimilation. Cl/K ratios vary from 0.03 to 0.07 for both sample suites, ranging from only slightly higher than enriched MORB (0.01-0.02) to within the HIMU field (0.04-0.08). Pitcairn lavas with the lowest Cl/K have the strongest EM-1 signature (lowest ²⁰⁶Pb/²⁰⁴Pb). Similarly, Society lavas with the lowest Cl/K have the strongest EM-2 signature (highest ⁸⁷Sr/⁸⁶Sr). We suggest that these represent primary mantle signatures.
DE: 1025 Composition of the mantle
DE: 1038 Mantle processes (3621)
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 8410 Geochemical modeling (1009, 3610)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting