P. Schmoldt, PhD - MTNet - DIAS

5. Earth’s properties observable with magnetotellurics
1000/T (K -1 )
1.6
1.4
1.2
1
0.8
0.6
Ionic conduction
Proton conduction
Small polaron conduction
0.4
0 1 2 3 4 5 6 7
Log (ρ) (Ωm)
10
Fig. 5.12.: Conductivity of hydrogen-iron bearing mantle silicate minerals; redrawn from Yoshino [2010]
Mineral σ0H (S/m) HH (eV) σ0P (S/m) H0 P
(eV) α
Wadsleyite 399(311) 1.49(10) 7.74(4.08) 0.68(3) 0.02(2)
Ringwoodite 838(442) 1.36(5) 27.7(9.6) 1.12(3) 0.67(3)
Tab. 5.5.: Parameter values for wadsleyite and ringwoodite derived in lab studies by Yoshino et al. [2008]. Numbers in parentheses
denote the errors determined through nonlinear least squares fitting (1 σ standard deviation).
(Fig. 5.12). One of the most recent formulation for the relationship between mantle mineral
semiconduction and its controlling parameters was given by Yoshino et al. [2008].
The authors extended earlier formulations by taking into account the influence of both the
intrinsic and the extrinsic conductivity, as well as the effect of water onto the extrinsic
term:
σ = σ0H exp − ∆HH
kBT
+ σ0PCw exp
⎛
⎜⎝ −∆H0
P
− αC1/3
W
kBT
⎞
⎟⎠
(5.11)
with CW: water content in wt%, α: fitting factor, and subscripts H and P denoting small
polaron (hopping) conduction and proton conduction, respectively. Parameter values for
the olivine high-pressure polymorphs wadsleyite and ringwoodite, derived by the authors
by fitting measured laboratory data to Equation 5.11, are given in Table 5.5. Conductivity
of the individual mantle materials, their specific parameters, and relation to pressure,
temperature, and fluid content are examined in more detail in Section 5.3.
5.2.3. The Earth’s core
The Earth’s core is situated beneath the CMB at around 2890 km depth, down to the centre
of the Earth, approximately 6378 km from the Earth’s surface. The core is subdivided
into a liquid outer core and a solid inner core. The existence of a solid inner core was
first proposed by Inge Lehmann in 1936, using the observations of seismic waves caused
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