Physics – Fluid Dynamics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.129..171f&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 129, no. 1-4, p. 171-182
Physics
Fluid Dynamics
23
Fluid Dynamics, Geochemistry, Mid-Ocean Ridges, Plates (Tectonics), Plumes, Buoyancy, Iceland, Thermal Diffusion, Viscosity, Volcanoes
Scientific paper
Here we explore the dynamics of plume-ridge and plume-plate interaction using laboratory experiments. We model chemically buoyant plumes, as opposed to thermally buoyant plumes, so we ignore the effects of thermal diffusion while concentrating on the strictly fluid dynamical aspects of the interaction. We find that the spreading of a continuosly fed plume beneath a fixed plate is described by a simple expression derived from a balance between plume buoyancy and viscous resistance to spreading. For plumes spreading beneath ridges we find two remarkably distinct phases of flow: At first the plume spreads approximately as it would beneath a fixed plate, then a rapid transition occurs to a steady-state condition in which the plume width along the ridge ('waist') is constant. This width is found to be proportional to a natural length scale that increases with the square root of the plume volumetric flux and the ratio of the mantle/plume viscosities, and decreases with the square root of the plate spreading velocity. Our model suggests that sufficient time has elapsed (approx. 60 Myr) for the Iceland plume to reach steady state in its interaction with the Mid-Atlantic Ridge. Using independent estimates for the plume volumetric flux at the Iceland hotspot, and assuming a viscosity ratio of one, the model predicts a minimum waist width of about 850 km, in close agreement with the observed value of about 920 km. Using estimated plume fluxes with a simple conservation of mass equation yields reasonable estimates of plume thickness ranging from 70 to 180 km for these hotspots. Thus, the experimental model appears to be reasonably consistent with observation, given that thermal diffusion has been disregarded.
Feighner Mark A.
Richards Mark A.
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