Constraining the thermal evolution of the oceanic lithosphere
Abstract
The existence of a secondary scale of convection associated with convective instabilities in the lithosphere (called sublithospheric or small scale convection), separate from the large scale circulation of plate tectonics, has long been considered in geophysics. This secondary scale of convection has been proposed to explain the deviations of bathymetry and heat flow in the old ocean basins, as well as having a role in the thermal evolution of Earth due to it's effect on plate thickness. Recently, theoretical work on the onset and structure of sublithospheric scale convection suggests that this convective mode likely exists on Earth. In order to provide further constraints on the existence of small scale convection in Earth's mantle we consider a combined effort employing geodynamic modeling and seismic observations from Earth's ocean basins. Our hypothesis is that temperature variations and deformation associated with small scale convection can be detected seismically and that the scale of variability in the observations can constrain the range of viable flow models. To that end we have developed geodynamic models to predict the resultant thermal and deformation structure associated with sublithospheric convection. We consider a two-dimensional, open box model of convection in which we specify the velocity of the top boundary of a shear flow and the flow-through boundary conditions at the side boundaries. We simultaneously track the deformational history of a series of particles in our domain, and calculate the texturing and elastic anisotropy for aggregates of mantle minerals within the flow field. Initial results indicate that temperature variations associated with sublithospheric convection produce a signal that should be seismically observable in the surface wave data. Also, the secondary flow associated with small scale convection disrupts the previously developed plate-motion-parallel LPO, thus potentially reducing the anisotropic signature that is detected with long-period seismic data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.U23D0075L
- Keywords:
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- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general;
- 8130 TECTONOPHYSICS / Heat generation and transport