Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.t32c..10j&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #T32C-10
Other
5480 Volcanism (8450), 8120 Dynamics Of Lithosphere And Mantle: General, 8121 Dynamics, Convection Currents And Mantle Plumes, 8130 Heat Generation And Transport, 8149 Planetary Tectonics (5475)
Scientific paper
The coexistence of mantle plumes with plate-scale flow is problematic in geodynamics. Significant problems include the fixity of hotspots with respect to plate motions, the spatial distribution and duration of hotspots, the geophysical and geochemical signatures of plume-ridge interactions, and the relation between mantle plumes and heat flux across the core-mantle boundary. We present results from laboratory experiments aimed at understanding the effects of an imposed large-scale circulation on thermal convection at high Rayleigh number (up to 109) in a fluid with a strongly temperature-dependent viscosity. In a large tank, a layer of corn syrup is heated from below while being stirred by large-scale flow due to the opposing motions of a pair of conveyor belts immersed in the syrup at the top of the tank. Three regimes are observed, depending on the velocity ratio V of the imposed horizontal flow velocity to the rise velocity of plumes ascending from the hot boundary. When V<<1, large scale circulation has a negligible effect and convective upwelling occurs as randomly-spaced axisymmetric plumes that interact with one another. When V>10, plume instabilities are suppressed entirely and the heat flux from the hot lower boundary is carried by a central sheet-like upwelling. At intermediate V, ascending plumes are advected along the bottom boundary layer, and the heat flux from the boundary is found to scale (according to a simple boundary layer theory) with V and the ratio of the viscosity of cold fluid above the thermal boundary layer to the viscosity of the hottest fluid in contact with the bottom boundary. For large viscosity ratios (10-100), only about 1/5th or less of the total heat flux from the hot boundary layer is carried by plume instabilities, even for modest imposed horizontal flow velocities (V of order 1). When applied to Earth, our results suggest that plate-scale flow focuses ascending mantle plumes toward mid-ocean ridges, and that plumes may be entirely captured by sufficiently rapid upwelling flow beneath ridges. This behavior may explain why hotspots are more abundant near slow-spreading ridges than near fast ridges. Such a model also predictes, in apparent accord with geochemical observations, that while slow ridges exhibit more variable isotopic and trace element signatures than fast ridges, their average signatures should be about the same. The laboratory experiments further suggest that plumes originating at the core-mantle boundary (CMB) may carry only a small fraction of the total CMB heat flux, the remainder being swept away by large-scale mantle flow associated with plate-scale convection.
Jellinek Mark A.
Richards Anita M.
No associations
LandOfFree
Plume Capture by Divergent Plate Motions: Implications for the Distribution of Hotspots, Geochemistry of Mid-Ocean Ridge Basalts, and Heat Flux from the Core-Mantle Boundary does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Plume Capture by Divergent Plate Motions: Implications for the Distribution of Hotspots, Geochemistry of Mid-Ocean Ridge Basalts, and Heat Flux from the Core-Mantle Boundary, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plume Capture by Divergent Plate Motions: Implications for the Distribution of Hotspots, Geochemistry of Mid-Ocean Ridge Basalts, and Heat Flux from the Core-Mantle Boundary will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1239955