HR: 10:30h
AN: GP22A-01    [Abstracts]
TI: The (Unusual?) Longevity and Spatial Stability of Hotspots and Deep Mantle Plumes in the Earth
AU: * Jellinek, M
EM: mjellinek@eos.ubc.ca
AF: University of British Columbia, 6339 Stores Rd., Vancouver, BC V6T 1Z4 Canada
AU: Manga, M
EM: manga@seismo.berkeley.edu
AF: University of California, Department of Earth and Planetary Science, Berkeley, CA 94720-4767 United States
AB: A physical link has been proposed between hotspots, regions with particularly persistent, localized, and high rates of volcanism, and underlying low viscosity deep mantle plumes constructed of large spherical heads and long-lived narrow trailing conduits. This plume model has provided a way to interpret observable phenomena including the volcanological, petrological and geochemical evolution of large igneous provinces, ocean island volcanoes, the relative motion of plates, continental breakup, global heat flow and the Earth's magnetic field within the broader framework of the thermal history of our planet. Despite the plume model's utility, the underlying dynamics giving rise to hotspots as long-lived stable features have remained elusive. An essential test of the mantle plume hypothesis is, thus, to understand the longevity of hotspot volcanism and spatial stability of hotspots themselves in terms of the mechanics governing the formation of mantle plumes at the core-mantle boundary. Using a combination of laboratory experiments, numerical simulations and scaling analyses we show that: 1) The high temperatures (and low viscosities) inferred for mantle plumes are likely a result of strong cooling of the mantle by large-scale stirring driven by plate tectonics; 2) The head-tail structure of such plumes is a necessary but insufficient condition for their longevity; 3) The longevity and spatial stability of mantle plumes are a consequence of interactions between plate tectonics, core cooling and a dense, low viscosity layer within D", which is plausibly composed of a mixture of silicate partial melt and outer core material. Under certain conditions, analysis of entrainment from this dense layer leads to a further prediction that the variation in 3He/4He (or any tracer of the silicate component of the lower mantle plume source) will be proportional to plume buoyancy flux, which is broadly consistent with observations.
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2005 Joint Assembly