Modeling The Thermochemical Evolution of Planets with Plate Tectonics or Rigid Lids

Tuesday, March 19, 2002 - 10:30am - 11:30am
Keller 3-180
Paul Tackley (University of California, Los Angeles)
It is well-established that the strong temperature-dependence of mantle viscosity leads by itself to a rigid lid style of convection, which is probably representative of Mars or Venus but not Earth. Recent numerical studies in both 2-D and 3-D have shown that accounting for the finite strength of the lithosphere by introducing a simple pseudo-plastic yield stress can lead to a plate-tectonic-like style of convection, with self-consistently generated passive spreading centers and subduction zones. While promising, it is important to note that this physical description is clearly not complete because (i) the plate regime occurs with a yield stress of order 100 MPa, which is several times lower than the strength of rocks measured in laboratory experiments, (ii) subduction is double-sided, and (iii) new plate boundaries can spring up anywhere, rather than in previously weakened areas as observed on Earth. Nevertheless, such models provide a useful tool for studying other aspects of terrestrial planetary dynamics such as their thermochemical evolution. Models that incorporate melting and major- and trace-element differentiation for rigid lid, plate tectonic, or episodic plate tectonic planets have been developed and will be presented and compared to observational constraints (e.g., geochemical reservoir signatures, crustal thicknesses, outgassing histories) for Earth, Venus and Mars.