Porosity-driven convection and asymmetry beneath mid-ocean ridges
Article first published online: 10 NOV 2010
Copyright 2010 by the American Geophysical Union.
Geochemistry, Geophysics, Geosystems
Volume 11, Issue 11, November 2010
How to Cite
2010), Porosity-driven convection and asymmetry beneath mid-ocean ridges, Geochem. Geophys. Geosyst., 11, Q0AC07, doi:10.1029/2010GC003282.(
- Issue published online: 10 NOV 2010
- Article first published online: 10 NOV 2010
- Manuscript Accepted: 23 SEP 2010
- Manuscript Revised: 21 SEP 2010
- Manuscript Received: 1 JUL 2010
- mid-ocean ridge;
- plate tectonics;
- active flow;
Seismic tomography of the asthenosphere beneath mid-ocean ridges has produced images of wave speed and anisotropy that are asymmetric across the ridge axis. These features have been interpreted as resulting from an asymmetric distribution of upwelling and melting. Using computational models of coupled magma/mantle dynamics beneath mid-ocean ridges, I show that such asymmetry should be expected if buoyancy forces contribute to mantle upwelling beneath ridges. The sole source of buoyancy considered here is the dynamic retention of less dense magma within the pores of the mantle matrix. Through a scaling analysis and comparison with a suite of simulations, I derive a quantitative prediction of the contribution of such buoyancy to upwelling; this prediction of convective vigor is based on parameters that, for the Earth, can be constrained through natural observations and experiments. I show how the width of the melting region and the crustal thickness, as well as the susceptibility to asymmetric upwelling, are related to convective vigor. I consider three causes of symmetry breaking: gradients in mantle potential temperature and composition and ridge migration. I also report that in numerical experiments performed for this study, the fluid dynamical instability associated with porosity/shear band formation is not observed to occur.