Open AccessSteady-state creep in the mantle
Author(s) -
Giorgio Ranalli
Publication year - 2010
Publication title -
annals of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 60
eISSN - 2037-416X
pISSN - 1593-5213
DOI - 10.4401/ag-4831
Subject(s) - mantle (geology) , geology , creep , asthenosphere , grain size , olivine , diffusion creep , strain rate , transition zone , dislocation creep , petrology , geophysics , mineralogy , thermodynamics , materials science , seismology , lithosphere , grain boundary , composite material , physics , geomorphology , microstructure , tectonics
SUMMARY - The creep equations for steady-state flow of olivine at high
pressure and temperature are compared in an attempt to elucidate the rheological
behaviour of the mantle. Results are presented in terms of applied deformation
maps and curves of effective viscosity v depth.
In the upper mantle, the transition stress between dislocation and diffusion
creep is between 10 to 102 bar (as orders of magnitude) for grain sizes from
0.01 to 1 cm. The asthenosphere under continents is deeper, and has higher
viscosity, than under oceans. Predominance of one creep mechanism above the
others depends on grain size, strain rate, and volume fraction of melt; the
rheological response can be different for different geodynamic processes.
In the lower mantle, on the other hand, dislocation creep is predominant
at all realistic grain sizes and strain rates. If the effective viscosity has to be only
slightly higher than in the upper mantle, as some interpretations of glacioisostatic
rebound suggest, then the activation volume cannot be larger than
11 cm3 mole^1
pressure and temperature are compared in an attempt to elucidate the rheological
behaviour of the mantle. Results are presented in terms of applied deformation
maps and curves of effective viscosity v depth.
In the upper mantle, the transition stress between dislocation and diffusion
creep is between 10 to 102 bar (as orders of magnitude) for grain sizes from
0.01 to 1 cm. The asthenosphere under continents is deeper, and has higher
viscosity, than under oceans. Predominance of one creep mechanism above the
others depends on grain size, strain rate, and volume fraction of melt; the
rheological response can be different for different geodynamic processes.
In the lower mantle, on the other hand, dislocation creep is predominant
at all realistic grain sizes and strain rates. If the effective viscosity has to be only
slightly higher than in the upper mantle, as some interpretations of glacioisostatic
rebound suggest, then the activation volume cannot be larger than
11 cm3 mole^1