New Insights Into the Heat Sources of Mantle Plumes, or: Where Does all the Heat Come From, Heat Producing Elements, Advective or Conductive Heat Flow?

HR: 16:00h
AN: V24A-01 [Abstracts]
TI: New Insights Into the Heat Sources of Mantle Plumes, or: Where Does all the Heat Come From, Heat Producing Elements, Advective or Conductive Heat Flow?
AU: * Rushmer, T
EM: trushmer@els.mq.edu.au
AF: GEMOC/Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia
AU: Beier, C
EM: cbeier@els.mq.edu.au
AF: GEMOC/Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia
AU: Turner, S
EM: sturner@els.mq.edu.qu
AF: GEMOC/Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia
AB: Melting anomalies in the Earth's upper mantle have often been attributed to the presence of mantle plumes that may originate in the lower mantle, possibly from the core-mantle boundary. Globally, mantle plumes exhibit a large range in buoyancy flux that which is proportional to their temperature and volume. Plumes with higher buoyancy fluxes should have higher temperatures and experience higher degrees of partial melting. Excess heat in mantle plumes could reflect either a) an enrichment of the heat producing elements (HPE: U, Th, K) in their mantle source leading to an increase of heat production by radioactive decay or b) advective or conductive heat transport across the core-mantle boundary. The advective transport of heat may result in a physical contribution of material from the core to the lower mantle. If core material is incorporated into the lower mantle, mantle plumes with a higher buoyancy flux should have higher core tracers, e.g. increased ¹⁸⁶Os and Fe concentrations. Geophysical and dynamic modelling indicate that at least Afar, Easter, Hawaii, Louisville and Samoa may all originate at the core-mantle boundary. These plumes encompass the whole range of known buoyancy fluxes from 1.2 Mgs ^-1(Afar) to 6.5 Mgs ^-1 (Hawaii) providing evidence that the buoyancy flux is largely independent of other geophysical parameters. In an effort to explore whether the heat producing elements are the cause of excess heat we looked for correlations between fractionation corrected concentrations of the HPE and buoyancy flux. Our results suggest that there is no correlation between HPE concentrations and buoyancy flux (with and without an additional correction for variable degrees of partial melting). As anticipated, K, Th and U are positively correlated with each other (e.g. Hawaii, Iceland and Galapagos have significantly lower concentrations than e.g. Tristan da Cunha, the Canary Islands and the Azores). We also find no correlation between currently available Fe concentration data and buoyancy flux. The apparent lack of correlation suggests that excess heat may be a result of conductive heat contribution from the core. Additional precise ¹⁸⁶Os and Fe data are needed to further assess these conclusions.
DE: 3621 Mantle processes (1038)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8130 Heat generation and transport
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting