Publication 137
Calibrating laboratory-determined models of electrical conductivity of mantle minerals using
geophysical and petrological observations
Alan G. Jones, Javier Fullea, Rob L. Evans, and Mark R. Muller
Abstract
Measurements of electrical conductivity of “slightly damp” mantle minerals from different laboratories
are inconsistent, requiring geophysicists to make choices between them when interpreting their
electrical observations.
These choices lead to dramatically different conclusions about the amount of water in the mantle,
resulting in conflicting conclusions regarding rheological conditions;
this impacts on our understanding of mantle convection, amongst other processes.
To attempt to reconcile these differences, we test the laboratory-derived proton conduction models
by choosing the simplest petrological scenario possible – cratonic lithosphere – from two locations
in southern Africa where we have the most complete knowledge.
We compare and contrast the models with field observations of electrical conductivity and of
the amount of water in olivine and show that none of the models for proton conduction in
olivine proposed by the three laboratories are consistent with the field observations.
We derive statistically model parameters of the general proton conduction equation that satisfy
the observations.
The pre-exponent dry proton conduction term (sigma0) and the activation enthalpy (deltaHwet) are
derived with tight bounds, and are both within the broader 2sigma errors of the different laboratory
measurements.
The two other terms used by the experimentalists, one to describe proton hopping
(exponent r on pre-exponent water content Cw) and the other to describe H2O
concentration-dependent activation enthalpy (term alphaCw^1/3 added to the activation energy),
are less well defined and further field geophysical and petrological observations are required,
especially in regions of higher temperature and higher water content.
Source
Geochemistry, Geophysics, Geosystems, 13, Q06010, doi:10.1029/2012GC004055. [PDF]
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Alan G Jones / 01 May 2012 /
alan-at-cp.dias.ie