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New magnetic image of a tectonically active planet

Using 70 years of data (airborne, satellite, field...), a French team (LMV, IPGP and LPG) has just published the most accurate global map to date of the magnetic field produced by magnetized terrestrial rocks.

New magnetic image of a tectonically active planet

Publication date: 26/11/2021

Press, Research

Related teams :
Geomagnetism

The Earth’s magnetic field is dominated by a main field produced by a self-sustaining dynamo mechanism that draws its energy from the convection of the metallic core at a depth of 2900 km. It is this main field that is responsible for the presence of a North Magnetic Pole and a South Magnetic Pole at the Earth’s surface. Behind this large-scale field, however, lie other fields, produced by more discrete sources. One of the most fascinating is that produced by rocks that have been magnetized by the main field. Mapping this field provides invaluable information, both on the distribution and origin of the magnetization of the rocks responsible for it, and on the turbulent tectonic history of the Earth’s surface.

With the support of CNES and as part of the ESA’s Swarm space mission, a French team including LMV, IPGP and LPG (laboratories from CNRS and the Universities of Clermont Auvergne, Paris and Nantes), has just published the most accurate global map of this field to date.

Global planetary image of the radial component of the magnetic field produced by terrestrial rocks (red: outgoing field, blue: incoming field), down to scales of the order of 40 km.

Over 70 years of airborne surveys, sea campaigns and low-orbit satellite observations have been used to produce a model describing this field from the largest scales not dominated by the main field down to scales of the order of 40 km.

This model reveals the magnetic signatures that testify to the prodigious telluric forces that have shaped the Earth’s surface and still govern its dynamics. This magnetic signal comes mainly from igneous and metamorphic rocks cold enough to carry a magnetization, mainly present in the Earth’s crust. Their magnetic signatures will enable us to further constrain geodynamic models of the crust, define the contours of geological provinces at depth, particularly in inaccessible areas such as Antarctica, better locate and circumscribe ancient impact structures, follow the extensions of tectonic faults, and more generally, better highlight the magnetic contrasts produced by continental collisions, the extension of oceanic floors and subduction. As rock magnetization cannot be maintained above a temperature of around 580°C, this global model will also provide a valuable constraint on the thermal state of the Earth’s crust by revealing thick “cold” zones, producing stronger signals, and shallower “hot” zones, producing weaker signals.

 

Ref : Thébault, E., Hulot, G., Langlais, B., & Vigneron, P. A Spherical Harmonic model of Earth’s lithospheric magnetic field up to degree 1050. Geophysical Research Letters, https://doi.org/10.1029/2021GL095147

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