HR: 0800h
AN: T11C-0738    [Abstracts]
TI: Supercontinent Formation in 3-D Spherical Mantle Convection Models With Multiple Continental Blocks
AU: * Zhang, N
EM: nan.zhang@colorado.edu
AF: Department of Physics, University of Colorado at Boulder, Boulder,Colorado,80309, Boulder, CO 80309, United States
AU: Zhong, S
EM: Shijie.Zhong@colorado.edu
AF: Department of Physics, University of Colorado at Boulder, Boulder,Colorado,80309, Boulder, CO 80309, United States
AU: McNamara, A
EM: allen.mcnamara@asu.edu
AF: School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, Tempe, AZ 85287, United States
AB: Much of the large-scale tectonics on the Earth in the last Ga is predominated by the assembly and breakup of supercontinents Rodinia and Pangea. However, the mechanism that is responsible for supercontinent formation remains poorly understood. Zhong et al [2007] recently showed that mantle convection with moderately strong lithosphere and lower mantle is characterized by a largely degree-1 planform in which one hemisphere is predominated by upwellings while the other by downwellings. They further suggested that the downwellings should attract all the continental blocks to merge in the downwelling hemisphere, thus leading to supercontinent formation there. However, Zhong et al. [2007] did not consider drifting and collision processes of continents. In this study, we explore the supercontinent formation mechanisms by including drifting and collision processes of multiple continental blocks in 3-D spherical mantle convection models. We use thermochemical CitcomS code to model 3-D spherical mantle convection with continental blocks. In our models, particles are used to represent continents and to track their motions. We found that for models with mantle viscosity (i.e., moderately strong lithosphere and lower mantle) that leads to degree-1 convection as reported in Zhong et al. [2007], initially evenly- distributed continental blocks always merge to form a supercontinent on a time-scale of about 6 transit times (i.e., corresponding to about 300 Ma). The hemisphere where a supercontinent is formed is predominated by downwellings as continents merge towards there, while the other hemisphere by upwellings. However, after the supercontinent formation, upwellings are generated beneath the supercontinent. This scenario is qualitatively consistent with what Zhong et al. [2007] proposed. We also found that while some convection models with intrinsically small-scale planforms may also lead to formation of a supercontinent, some other models may fail to produce a supercontinent. For these models with intrinsically small-scale planforms, the merged continental blocks promote long-wavelength mantle structure near the continents. However, in non-continental regions, convective wavelengths remain relatively small. We suggest that time-scales for supercontinent formation and convective wavelengths in non-continental area are important parameters that help constrain mechanisms for supercontinent formation.
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8125 Evolution of the Earth (0325)
DE: 8149 Planetary tectonics (5475)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting