Consequences of plate tectonics in a compressible mantle

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Continents slowly drift across the Earth's surface due to the forces of plate tectonics. Oceanic crust is generated at mid-oceanic ridges and is returned after some one hundred million years back into the Earth's interior at subduction zones. Seismological investigations give us a blurry few of the subducting slabs that appear to sink towards the base of the mantle. Geochemical sampling at mid-oceanic ridge volcanoes and at hotspots such as Hawaii tell us the long term story about how the ancient slabs are absorbed by the mantle and brought back up by the slow churning of mantle convection. The formation and recycling of oceanic crust has a clear strong influence on the chemical and the thermal evolution of the Earth, but we remain in the dark as how changes in physical properties, that occur deeper in the Earth, affect the behavior of the crust and its mixing back into the mantle. This research project will add a third way of looking at the dynamic Earth by use mathematical models that predict how plate tectonics affects the composition and thermal state of the Earth. The mathematical models are suited to predict the dynamical evolution of the Earth over its entire age. The predictions can then be compared to the observations of the present day Earth (as provided by seismology) and the longer term perspective that geochemistry provides.The new aspects of the modeling approach include the consistent treatment of compressibility and the associated phase changes that occur primarily between 440 and 670 km depth in the Earth's mantle. The compressible effects will allow the PI to consider thermodynamically consistent modeling where the results can be compared directly to seismological observations of the present day state of the Earth's mantle. The investigators will use high resolution finite element models of mantle convection that include a energetically consistent approach to simulated plates.