HR: 17:30h
AN: T14A-07    [Abstracts]
TI: A Modeled Confirmation That Cratons are Strong, Cold, and Long-Lived
AU: * Rupke, L H
EM: lars.rupke@fys.uio.no
AF: PGP, University of Oslo, PO Box 1048-Blindern, Oslo, 0316 Norway
AU: Simon, N S
EM: nina.simon@geo.uio.no
AF: PGP, University of Oslo, PO Box 1048-Blindern, Oslo, 0316 Norway
AU: Podladchikov, Y Y
EM: y.y.podladchikov@fys.uio.no
AF: PGP, University of Oslo, PO Box 1048-Blindern, Oslo, 0316 Norway
AB: Archean cratons and their thick keels belong to the oldest features of the Earth. Their apparent stability for billions of years has been confirmed by dating of mantle xenoliths and diamond inclusions in kimberlites show that cratonic keels have already been cold at Archean times. These first order features of cratons are quite remarkable since they require cratons to have resisted mantle convection and avoided erosion all throughout Earth's history. In fact, the stability of cratons has puzzled geodynamicists with viscous convection models failing to reproduce it. Here we present a plausible scenario for continent formation and subsequent survival throughout Earth history. The model assumes that continents formed by two segregation events from normal but hot Archean mantle. In a primary event, thick crust is produced by high degree melting of mantle material. The produced crust is hot, relatively dense and gravitationally unstable during crystallization. Gravitational layering triggers a second segregation event. The newly formed continental crust is underlain by depleted mantle. This depleted mantle has a higher melting temperature which has a two-fold effect on its rheology. First, it feeds exponentially into the viscosity making depleted mantle stronger. Secondly, any material colder than roughly half its melting temperature will deform elastically and stop creeping. This effect results in a growing elastic top boundary layer that helps to stabilize the entire continental keel. We explore these mechanisms with a new elasto-visco-plastic geodynamic model that solves for mantle flow and continental lithosphere deformation throughout Earth's history. Key to this model is the use of a realistic rheology: we account for elastic deformation and use the thermodynamic tool-box PERPLEX to accurately determine the change in melting temperature during early continental mantle depletion. Our first results indicate that this new geodynamic model can reproduce stable continents that are consistent in their evolution with their presently observed chemistry and age.
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: Fall Meeting 2005