Mathematics – Logic
Scientific paper
Aug 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995e%26psl.134..155r&link_type=abstract
Earth and Planetary Science Letters, vol. 134, Issue 1-2, pp.155-168
Mathematics
Logic
57
Scientific paper
We investigate the dynamics of mantle plumes rising beneath mid-ocean ridges. To clarify the physics of this process, we examine first a simple `lubrication theory' model in which a point source (analogous to a plume `stem') of volume flux Q located directly beneath the ridge releases buoyant fluid into a viscous corner flow driven by a velocity boundary condition u ( x ) = U tanh( x / d ), where U is the half-spreading rate and the `gap width' between the diverging plates is ~ 5 d . Numerical solutions of the differential equation governing the plume head thickness S ( x , y ) show how the width W of the plume head along the ridge depends on Q , U , d , and frsol | g /48 , where is the density deficit of the plume and is the viscosity. In the geophysically relevant `narrow gap' limit ( Q / ) 1/4 >> d , W ~ ( Q / U ) 1/2 II b 0.053 , where II b = Q / U 2 is the `buoyancy number'. Numerical solutions of a more realistic 3D convection model with strongly temperature and pressure-dependent viscosity obey a nearly identical scaling law, and show no evidence that W is increased by `upslope' flow of plume material toward the ridge along the sloping base of the rheological lithosphere. To apply our model to Iceland, we incorporate into it a melting parameterization that allows prediction of the excess crustal thickness produced by melting in the plume head. This extended model shows that the observed depth anomalies along the Mid-Atlantic Ridge near Iceland cannot be explained by a hot (temperature contrast T ~ 250°C) and narrow (radius ~ 60 km) ridge-centered plume. Instead, the anomalies are consistent with a much cooler and broader upwelling.
Christensen Ulrich R.
Ribe Neil M.
Theißing J.
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