Geoscience Reference
In-Depth Information
5
Electrical Conductivity of Minerals
and Rocks
SHUN-ICHIRO KARATO
1
AND DUOJUN WANG
1,2
1
Department of Geology and Geophysics, Yale University, New Haven, CT, USA
2
Key Laboratory of Computational Geodynamics, Graduate University of Chinese Academy of Sciences,
College of Earth Sciences, Beijing, China
Summary
zone,
1 wt% in the East Asian transition zone).
The majority of observations including those on
the lower crust and the asthenosphere can be
interpreted without partial melting or any fluids.
However, experimental studies on electrical
conductivity of lower mantle minerals are incom-
plete and it is not known if hydrogen enhances
the conductivity of lower mantle minerals or
not. Some discussions are also presented on the
electrical conductivity in other planetary bodies
including the Moon and Mars.
∼
Electrical conductivity of most minerals is
sensitive to hydrogen (water) content, temper-
ature, major element chemistry and oxygen
fugacity. The influence of these parameters on
electrical conductivity of major minerals has
been characterized for most of the lower crust,
upper mantle and transition zone minerals. When
the results of properly executed experimental
studies are selected, the main features of electri-
cal conductivity in minerals can be interpreted by
the physical models of impurity-assisted conduc-
tion involving ferric iron and hydrogen-related
defects. Systematic trends in hydrogen-related
conductivity are found among different types
of hydrogen-bearing minerals that are likely
caused by the difference in the mobility of
hydrogen. A comparison of experimental results
with geophysically inferred conductivity shows:
(1) Electrical conductivity of the continental
lower crust can be explained by a combination
of high temperature, high (ferric) iron content
presumably associated with dehydration. (2)
Electrical conductivity of the asthenosphere can
be explained by a modest amount of water (
5.1 Introduction
Seismic wave velocities and electrical conductiv-
ity are among the physical properties that can be
estimated fromgeophysical remote sensing. How-
ever, inferring electrical conductivity is more
challenging and subject to larger uncertainties
than for seismic wave velocities. Consequently,
although the basic framework of the inference
of electrical conductivity from electromagnetic
induction has long been known (see e.g., Banks,
1969; Rikitake, 1966), progress in the study of
electrical conductivity and its applications to the
Earth's interior have been slow until recently.
It might seem that because the resolution
of electrical conductivity is much lower than
that of seismic wave velocities, studies of elec-
trical conductivity have secondary importance
10
−
2
wt% in most regions, less than 10
−
3
wt% in
the central/western Pacific). (3) Electrical con-
ductivity of the transition zone requires a higher
water content (
∼
10
−
1
wt% in most regions,
∼
10
−
3
wt% in the southern European transition
∼
