HR: 0800h
AN: T11C-0719    [Abstracts]
TI: The Beginning of the Wilson Cycle, a Result of an Inherent Instability in Supercontinents Caused by the Lithosphere-Mantle System?
AU: * Beutel, E K
EM: beutele@cofc.edu
AF: College of Charleston, Dept. of Geology 66 George St., Charleston, SC 29412, United States
AB: The Wilson Cycle, the repeated creation and destruction of supercontinents, may be the result of mantle flow and volume changes driven by slab movement and slab contributions to the upper mantle. While it is clear based on the images of a few slabs penetrating the 660 km boundary that the lower mantle must contribute to the upper mantle system, it seems likely that much of the tectonics we see at the surface is mostly interacting with the upper mantle system with occasional input from the lower mantle. Based on this we have derived a series of calculations to determine the volume of mantle change under Pangea caused by slab input and determined that between 300 and 200 Ma the material input greatly exceeds the possible output by the small ridge present in the Tethys during this time. Because Pangea was generally surrounded by slabs during this time we can assume that most of the material input from the slabs was retained under Pangea. Further, because many slabs, especially if they are rolling back as many of the Pangean slabs were, appear to lie on the 660 km boundary (rather than penetrate it) we assume that the volume of material contributed by the slabs was contributed in the upper rather than lower mantle. Because the input of material under Pangea is greater than the output at the Tethys ridge we propose that the excess mantle almost immediately began to push the slabs back and to push out against the root of the continents, effectively "breaking up" the supercontinent. Thus, the lithosphere is driven apart by the change in mantle volume beneath the supercontinent, however, the volume change and confinement of that mantle is driven by the lithosphere.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting