Comparison of thermal lithosphere-asthenosphere models with geophysical observations
Abstract
It is agreed that the lithosphere-asthenosphere transition comprises the base of the mantle's top thermal and mechanical boundary layer. However, there is significant debate about whether melts, fabric, composition and fluids also significantly contribute to the structure of the transition. Over the years, it has been shown by studies that combine constraints from topography/bathymetry, surface heatflow and seismic velocity and attenuation structure that many of these can be reconciled within their uncertainties and resolution with expected boundary layer thermal structures under both continents and oceans if anelasticity is sufficiently temperature dependent. Recent fully dry experimental attenuation laws are insufficiently temperature sensitive. Melts could enhance this sensitivity. However, an effect of fluids on the temperature sensitivity of attenuation, either as direct signature, influence on oxygen fugacity or pre-melting effects below a water-lowered solidus is probably the easiest way to reconcile the range of seismic velocities as a function of lithospheric age below oceans and continents as well as the generally strong attenuation and low seismic velocities in subduction mantle wedges. Dehydration and depletion by melt extraction below ridges can also explain higher shear velocities in mantle above about 60 km depth than expected from simple cooling models without such effects. Although there is evidence of expressions of melt, fabric and variable composition, thermal structure and a somewhat hydrated asthenosphere can explain most of the first order observations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T54B..04B
- Keywords:
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- 7208 Mantle;
- SEISMOLOGYDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8125 Evolution of the Earth;
- TECTONOPHYSICSDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS