Fundamental to the theory of plate tectonics is the notion of a rigid lithosphere that translates over a weak asthenosphere. However, the physical and chemical properties of the lithosphere and asthenosphere that give rise to this rheological contrast are poorly understood. Variations in temperature, in volatile content, or in partial melt are the most likely explanations; furthermore, the dominant mechanism may depend on tectonic setting. While seismic velocity is widely used to estimate these factors, it is affected by temperature, composition, melt, and water content and thus provides incomplete information. I will describe two approaches I use to overcome this short-coming. I will show that seismic-wave attenuation can be used to distinguish between temperature and composition in the continental lithosphere and that jointly analyzing seismic velocity with basalt chemistry and ridge depth can distinguish between temperature and composition beneath mid-ocean ridges.
By: Colleen Dalton, Assistant Professor, Brown University
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