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Submitted to Chinese Science Bulletin 6/11/04 Simple scaling relations in geodynamics; the role of
 

Summary: 1
Submitted to Chinese Science Bulletin 6/11/04
Simple scaling relations in geodynamics; the role of
pressure in mantle convection and plume formation
Don L. Anderson
Caltech, Pasadena, U.S.A.
Pressure decreases interatomic distances in solids and this has a strong non-
linear effect on such properties as thermal expansion, thermal conductivity, and
viscosity, all in the direction of making it difficult for small-scale thermal
instabilities to form in deep planetary interiors. As a result, convection is sluggish
and is large scale at high-pressure; it does not in any way resemble widely-perceived
narrow mantle plumes of cylindrical form. The Boussinesq approximation assumes
that density, or volume (V), is a function of temperature (T) but that all other
properties are independent of T, V and pressure (P), even those properties that are
functions of V. This approximation, although thermodynamically (and
algebraically) inconsistent, appears to be useful at low pressures; it is widely used to
analyze laboratory convection and is also used in geodynamics, including whole
mantle convection simulations. Sometimes this approximation is supplemented with
a depth dependent viscosity or with T dependence of parameters other than density.
It is preferable to use a thermodynamically self-consistent approach. To first order,

  

Source: Anderson, Don L. - Division of Geological and Planetary Sciences, California Institute of Technology

 

Collections: Geosciences