Studies of mantle flow and evolution

Harvard University, Cambridge MA

Investigators

Abstract

The proposed research addresses one of the central problems in understanding the evolution and current state of the solid Earth: Whether the Earth?s mantle convects as a whole, or whether it is composed of separately convecting layers. This determines the extent of communication of material from the Earth?s deepest interior to the surface. Evidence from geochemistry, seismology and geodynamics has so far produced contradictory conclusions, and an important consideration involves the high viscosity of the deeper mantle. This proposal is to develop and investigate models of convection and the thermal evolution of the Earth and its dependence on viscosity layering in the mantle, as well as on some aspects of plate tectonics. The results will include estimates of the heat and mass transport from the lower mantle over Earth history, as well as its dependence of various parameters of the model. This will be compared with estimates from geochemical models based on noble gas isotopic measurements that constrain the lower mantle mass flux. The models will be based on parameterized treatments of mass and energy conservation, and will be verified against numerical calculations. They will allow the results of more detailed numerical calculations to be understood in the context of uncertainties in the governing parameters and features such as variable plate geometry. The model will also address some effects that arise from the three dimensional nature of convection and plate tectonics on the Earth. The expected results of the models will contribute to the understanding of the evolution of the Earth and its internal state, and questions such as whether or not there is a need for undiscovered or hidden layers deep in the mantle. It will also help to understand the temporal variability of convection and plate tectonics on the Earth, and estimate how representative the present state is of the longer term evolution of the Earth.