Electrical Conductivity of Minerals and Rocks - Physics and Chemistry of the Deep Earth - page 175

The main conclusions from their studies such as
''hydrous olivine unable to account for conduc-
tivity anomaly at the top of the asthenosphere''
(Yoshino et al ., 2006) and ''dry mantle transition
zone inferred from the conductivity of wadsleyite
and ringwoodite'' (Yoshino et al ., 2008a) are the
results of these inappropriate methods used in
their studies and are not supported by the well-
executed experimental studies. 10
Also there is a major difference in the in-
ferred water content from electrical conductiv-
ity by Khan and Shankland (2012) and Karato
(2011). Khan and Shankland (2012) calculated
much higher conductivity of ''dry'' mantle than
Karato (2011) (and than Yoshino et al . (2006) in
the case of the upper mantle), that leads to the
inferred lower hydrogen contents. The water con-
tent of the upper mantle inferred by Khan and
Shankland (2012) is far less than the value inferred
by the geochemical method (the water content of
the upper mantle inferred by Karato (2011) and
Dai and Karato (2009a) agrees with the geochemi-
cal estimate). The exact cause of this discrepancy
is unclear, but Khan and Shankland (2012) did not
take into account the influence of oxygen fugac-
ity and did not consider the influence of hydrogen
partitioning properly that can lead to a systematic
difference in the inferred water content.
The major remaining issue is the influence
of hydrogen on electrical conductivity of the
lower mantle minerals. The lower mantle oc-
cupies the largest portion of the Earth's mantle,
but currently we have no constraints on the water
content in this region from electrical conductiv-
ity. Because the dominant point defects in the
lower mantle minerals are ferric iron and related
defects (McCammon, 1997), and because oxygen
diffusion is fast in perovskite (Dobson, 2003), it is
not clear if hydrogen enhances electrical conduc-
tivity in the lower mantle minerals. Experimental
and theoretical studies on the influence of hydro-
gen on the electrical conductivity in lower mantle
minerals are critical to understanding the water
distribution throughout the Earth.

Acknowledgment

This work is partly supported by grants by NSF.
Most of the experimental data on electrical con-
ductivity were obtained by the post-docs and
visiting scientists (Yousheng Xu, Xiaoge Huang,
Duojun Wang, Mainak Mookhejee and Lidong
Dai) who spent some time at Yale mineral and
rock physics lab. Xiaozhi Yang, Wyatt Du Frane,
Alan Jones and Amir Khan sent us the preprints
of their papers. Xiaozhi Yang, Hans Keppler and
Taku Tsuchiya provided helpful reviews. Thank
you all.

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10 Yoshino and Katsura (2012)'s new results do not sup-
port their earlier claim of ''dry'' transition zone.