Splitting of dislocations in olivine, cross-slip-controlled creep and mantle rheology

Details Splitting of dislocations in olivine, cross-slip-controlled creep and mantle rheology Splitting of dislocations in olivine, cross-slip-controlled creep and mantle rheology

May 1978

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978pepi...16..370p&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 16, Issue 4, p. 370-378.

Physics

6

Scientific paper

The splitting of the [100] dislocations of forsterite Mg2SiO4 is investigated in a hard-sphere model. Glissile splittings exist in (001) and the most energetically favorable is the one that does not involve cutting of SiO4 tetrahedra: [100] --> [1/6, 1/9, 1/6 + [2/3, 0, 0] + [1/6, 1/9, 1/6 [100] screw dislocations are shown to be able to split simultaneously on (001) and (010) according to the reaction: [100] = [1/6, 1/36, 1/4] + [1/6, 1/9, 1/6] + [1/3, 0, θ] + [1/6, 1/36, 1/4] + [1/6, 1/6, 1/6] This sessile configuration is analogous to the one found for screw dislocations of body-centered cubic metals. It accounts forthe long rectilinear sessile screw segments commonly observed, in experimentally and naturally deformed olivine. A new creep model for the upper mantle is proposed, where recovery is controlled by cross-slip of screw dislocations instead of climb of edge dislocations. The creep law, fitted on the experimental results of the literature is: ɛ˙= 1.2 . 104 σ2 exp - [(125000 - 11.7σ + PV*/RT]> (σ in bars) the activation volume for cross-slip is estimated and viscosity-depth curves are plotted. The proposed creep mechanism is grain-size independent and less non-Newtonian than the climb-controlled one; it is found to be dominant over the latter at stresses smaller than 100 bar.

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