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Project Progress

We have been working on two major problems. First, two-dimensional numerical simulations of mantle convection with ductile/brittle rheology have been performed to map the boundary separating plate tectonics from stagnant lid convection regime. We use large aspect ratio numerical domains to minimize wall effects and allow a more realistic development of plate tectonics. The results obtained so far point to a very small critical yield stress required for initiation of plate tectonics. A 16-node Beowulf cluster will be built in the summer 2002 to accelerate the calculations. Second, a number of arguments point out that the difference between the strength of a wet lithosphere and that of a dry lithosphere can be big enough to control the very existence of plate tectonics and that the presence of liquid water can be essential for sustaining plate tectonics. We constructed a simple box model to understand the feedback between mantle convection, rheology and water and carbon cycles. By considering such competitive processes as partial melting induced dehydration of the mantle and recycling of water through percolation of water into the lithosphere from the surface, we find that under certain conditions the system tends to ?avoid? temperatures below the freezing point or above the boiling point of water. Outside this temperature range percolation of water into the lithosphere is inefficient and plate tectonics ceases.