Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.u62a..01k&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #U62A-01
Physics
8120 Dynamics Of Lithosphere And Mantle: General, 8121 Dynamics, Convection Currents And Mantle Plumes
Scientific paper
More than three decades ago, Turcotte and Oxburgh published their landmark paper showing how mantle convection drives motion of the continents, with the cold thermal boundary layers representing the surface plates. Since that time, models of mantle convection have made remarkable advancements and have been applied to the interiors of the terrestrial planets and moons, with many fundamental contributions by Don Turcotte and inspired by his work. Here, I will address some of the recent advances and innovations in mantle convection, with special emphasis on ideas emerging from the application of nonlinear dynamics and chemical geodynamics. Numerical models of convection, combined with observations from heat flow, cosmochemistry, and mantle geochemistry, provide constraints on models of the composition and structure of the mantle. Geochemical and heat flow observations appear to require long-lived heterogeneity in the mantle, while numerical models of convection generally exhibit rapid mixing, creating a distinctive ``marble-cake'' texture of recycled lithosphere. A variety of models have been suggested to reconcile these diverse inferences about mantle dynamics and structure from seemingly contradictory geochemical and geophysical observations. One straightforward explanation of combined geochemical and geophysical observations is a compositionally heterogeneous lowermost mantle. A difference between the composition of the MORB source and the composition of the deep mantle is also consistent with estimates of the properties of perovskite at high pressures and temperatures. Heterogeneity in the lower mantle may take the form of a hot abyssal layer of variable thickness starting at the mid-mantle or in the lowermost mantle, or may consist of "blobs" in the lower mantle. The hot abyssal layer model has an advantage over the blob model, because hot, neutrally buoyant blobs are unlikely to persist for the long times required by chemical geodynamics. Chemical geodynamics provides bounds on the volumes of different mantle reservoirs.
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