Other
Scientific paper
Mar 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000e%26psl.176..171m&link_type=abstract
Earth and Planetary Science Letters, Volume 176, Issue 2, p. 171-183.
Other
9
Scientific paper
Back-arc basin glasses from the Mariana Trough and Manus Basin display contrasting oxygen isotope characteristics that require differences in their mantle sources. In both basins, the lavas that are most depleted in high field strength elements possess δ18O values of around 6.0‰, that are elevated with respect to mid-ocean ridge basalt (MORB). This characteristic is consistent with a mantle source that has been infiltrated by fluids released from subducted oceanic lithosphere. The nature of the more fertile mantle component differs between the two basins. The lowest δ18O values in the Mariana Trough are similar to MORB and suggest that the ambient upper mantle interacts with a subduction-modified mantle to produce Mariana Trough back-arc basin basalts. Oxygen isotope ratios of basaltic glasses from the Manus Basin display a negative correlation with helium isotope ratios. The subduction-modified component is associated with 3He/4He ratios typical of the upper mantle. Glasses with 3He/4He ratios greater than average MORB, characteristic of a deep mantle plume, have δ18O values that are lower than expected for upper mantle melts. This suggests that the Manus Basin plume taps a reservoir that is 18O-depleted relative to the source of MORB. Two mechanisms are identified that might generate this reservoir. Deep recycling of oceanic crust that has been hydrothermally altered at high temperature may provide large 18O-depleted domains in the deep mantle. Alternatively, we propose that interactions between silicate and iron alloy during the segregation of the Earth's core may have the potential to generate such reservoirs. Resolution between these mechanisms requires further experimental investigation of oxygen partitioning between silicates and iron alloy. Each of these mechanisms has distinct implications for the origins and dynamics of the Manus Basin plume.
Hilton David R.
Macpherson Colin. G.
Mattey David P.
Sinton John M.
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