Interpretation of the “Northeastern Japan Anomaly” in Electrical Conductivity of the Upper Mantle

We have developed and tested a new frequency-domain, spherical harmonic-finite element approach to the inverse problem of global electromagnetic (EM) induction. It is based on the quasi-Newton minimization of data misfit and regularization, and uses the adjoint approach for fast calculation of misfit gradients in the model space. Thus, it allows for an effective inversion of satellite-observed magnetic field induced by tidally driven flows in the Earth's oceans in terms of 3-D structure of the electrical conductivity in the upper mantle. Before proceeding to the inversion of Swarm-derived models of tidal magnetic signatures, we have performed a series of parametric studies, using a 3-D conductivity model WINTERC-e as a testbed.The WINTERC-e model has been derived using state-of-the-art laboratory conductivity measurements of mantle minerals, and thermal and compositional model of the lithosphere and upper mantle WINTERC-grav. The latter model is based on the inversion of global surface waveforms, satellite gravity and gradiometry measurements, surface elevation, and heat flow data in a thermodynamically self-consistent framework. Therefore, the WINTERC-e model, independent of any EM data, represents an ideal target for synthetic tests of the 3-D EM inversion. We tested the impact of the satellite altitude, the truncation degree of the spherical-harmonic expansion of the tidal signals, the random noise in data, and of the sub-continental conductivity on the ability to recover the sub-oceanic upper-mantle conductivity structure. We demonstrate that with suitable regularization we can successfully reconstruct the 3D upper-mantle conductivity below world oceans.

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Distribution of Electrical Conductivity in Crust and Upper Mantle in the Area of the Geothermal Anomaly of Tuscany/Italy

Advances in European Geothermal Research ◽

10.1007/978-94-009-9059-3_75 ◽

1980 ◽

pp. 843-853 ◽

Cited By ~ 2

Author(s):

V. Haak ◽

G. Schwarz

Keyword(s):

Electrical Conductivity ◽

Upper Mantle ◽

Crust And Upper Mantle

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An Overview of the Experimental Studies on the Electrical Conductivity of Major Minerals in the Upper Mantle and Transition Zone

Materials ◽

10.3390/ma13020408 ◽

2020 ◽

Vol 13 (2) ◽

pp. 408 ◽

Cited By ~ 1

Author(s):

Lidong Dai ◽

Haiying Hu ◽

Jianjun Jiang ◽

Wenqing Sun ◽

Heping Li ◽

...

Keyword(s):

Electrical Conductivity ◽

Transition Zone ◽

Oxygen Fugacity ◽

Upper Mantle ◽

Activation Enthalpy ◽

Small Polaron ◽

Experimental Studies ◽

Transport Processes ◽

Structural Water ◽

Nominally Anhydrous Minerals

In this paper, we present the recent progress in the experimental studies of the electrical conductivity of dominant nominally anhydrous minerals in the upper mantle and mantle transition zone of Earth, namely, olivine, pyroxene, garnet, wadsleyite and ringwoodite. The main influence factors, such as temperature, pressure, water content, oxygen fugacity, and anisotropy are discussed in detail. The dominant conduction mechanisms of Fe-bearing silicate minerals involve the iron-related small polaron with a relatively large activation enthalpy and the hydrogen-related defect with lower activation enthalpy. Specifically, we mainly focus on the variation of oxygen fugacity on the electrical conductivity of anhydrous and hydrous mantle minerals, which exhibit clearly different charge transport processes. In representative temperature and pressure environments, the hydrogen of nominally anhydrous minerals can tremendously enhance the electrical conductivity of the upper mantle and transition zone, and the influence of trace structural water (or hydrogen) is substantial. In combination with the geophysical data of magnetotelluric surveys, the laboratory-based electrical conductivity measurements can provide significant constraints to the water distribution in Earth’s interior.

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