HR: 14:55h
AN: T32C-06    [PDF]
TI: Length and Time Scales in Continental Drift
AU: * Phillips, B R
EM: benp@princeton.edu
AF: Princeton University, Department of Geosciences, Princeton, NJ 08544 United States
AU: Bunge, H
EM: bunge@lmu.de
AF: Ludwig Maximilians University, Department of Geo and Environmental Sciences, Geophysics Section, Munich, D-80333 Germany
AB: Nonlinear feedback between continents and the mantle through thermal blanketing has long been surmised as a mechanism for continental drift and Wilson cycles. Paleomagnetism provides ample evidence for large scale (10,000 km) continental motion on time scales of several hundred million years, indicative of large scale mantle circulation. While much has been learned about the interactions between continents and mantle flow from analog and numerical modeling studies in two and three dimensions, a rigorous sensitivity study on the effects of continents in high resolution 3D spherical mantle convection models has yet to be pursued. As a result, a quantitative understanding of the scales of continental motion as they relate to relevant fluid dynamic processes is lacking. Here we focus on the effect of continental size. Continents covering 30% of the surface are representative of a supercontinent such as Pangea, smaller continents (10% of Earth's surface) are representative of present day Asia, and still smaller continents (3% of Earth's surface) are similar to present day Antarctica. These continents are introduced into simple end-member mantle flow regimes characterized by combinations of bottom or internal heating and uniform or layered mantle viscosity. We find that large scale mantle structure, and correspondingly the large scale displacement of continents, depends not only on mantle heating mode and radial viscosity structure, but also on continental size. Supercontinents promote heterogeneity on the largest scales (spherical harmonic degree one), especially when combined with strong bottom heating and a high viscosity lower mantle. Degree one heterogeneities in turn drive cyclical continental motion, with continents moving from the hot to the cold hemisphere on time scales of several hundred million years. Smaller continents are unable to initiate degree one convection. As a result, their motion is governed by shorter length and time scales. We apply these insights toward understanding the motion of several continents to study the aggregation and dispersal of continental groups.
DE: 3210 Modeling
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8155 Plate motions--general
SC: Tectonophysics [T]
MN: 2003 Fall Meeting