TY - JOUR

T1 - Analytical Parameterization of Self-Consistent Polycrystal Mechanics

T2 - Fast Calculation of Upper Mantle Anisotropy

AU - Goulding, Neil

AU - Ribe, N. M.

AU - Olivier, Castelnau

AU - Walker, Andrew

AU - Wookey, James

PY - 2015/10

Y1 - 2015/10

N2 - Progressive deformation of upper mantle rocks via dislocation creep causes their con-
stituent crystals to take on a non-random orientation distribution (crystallographic pre-
ferred orientation or CPO) whose observable signatures include shear-wave splitting and
azimuthal dependence of surface wave speeds. Comparison of these signatures with man-
tle flow models thus allows mantle dynamics to be unraveled on global and regional
scales. However, existing self-consistent models of CPO evolution are computationally
expensive when used in 3-D and/or time-dependent convection models. Here we propose
a new method, called ANPAR, which is based on an analytical parameterisation of the
crystallographic spin predicted by the second-order (SO) self-consistent theory. Our pa-
rameterisation runs ≈2-6
x 104
times faster than the SO model and fits its predictions for
CPO and crystallographic spin with a variance reduction
>
99%. We illustrate the AN-
PAR model predictions for the deformation of olivine with three dominant slip systems,
(010)[100], (001)[100] and (010)[001], for three uniform deformations (uniaxial com-
2
Neil J. Goulding et al.
pression, pure shear, simple shear) and for a corner-flow model of a spreading mid-ocean
ridge.

AB - Progressive deformation of upper mantle rocks via dislocation creep causes their con-
stituent crystals to take on a non-random orientation distribution (crystallographic pre-
ferred orientation or CPO) whose observable signatures include shear-wave splitting and
azimuthal dependence of surface wave speeds. Comparison of these signatures with man-
tle flow models thus allows mantle dynamics to be unraveled on global and regional
scales. However, existing self-consistent models of CPO evolution are computationally
expensive when used in 3-D and/or time-dependent convection models. Here we propose
a new method, called ANPAR, which is based on an analytical parameterisation of the
crystallographic spin predicted by the second-order (SO) self-consistent theory. Our pa-
rameterisation runs ≈2-6
x 104
times faster than the SO model and fits its predictions for
CPO and crystallographic spin with a variance reduction
>
99%. We illustrate the AN-
PAR model predictions for the deformation of olivine with three dominant slip systems,
(010)[100], (001)[100] and (010)[001], for three uniform deformations (uniaxial com-
2
Neil J. Goulding et al.
pression, pure shear, simple shear) and for a corner-flow model of a spreading mid-ocean
ridge.

KW - crystal preferred orientation

KW - crystallographic spin

KW - mantle convection

KW - seismic anisotropy

KW - olivine

M3 - Article (Academic Journal)

JO - Geophysical Journal International

JF - Geophysical Journal International

SN - 0956-540X

ER -