The map of the Earth’s magnetic field has been enriched with a new model making it possible to better understand the thermal state of the Earth’s crust, to perceive the magnetic signatures, still in action, which have shaped the latter, to better locate the past impacts of continental collisions and follow the extensions of tectonic faults.
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[EN VIDÉO] A reversal of Earth’s magnetic field may have changed our history According to The Hitchhiker’s Guide to the Galaxy written by Douglas Adams, the answer to everything is to be found in the number 42. And researchers from the University of New South Wales (Australia) wink at him by revealing that a reversal of the magnetic field of our Earth that occurred 42,000 years ago had important consequences on the environment of our ancestors. She may even have brought Neanderthals to its demise. © University of New South Wales
the magnetic field of the Earth is dominated by a main field produced by a mechanism of dynamo self-sustaining that draws its energy in the convection of the metal core at a depth of 2,900 km. It is this main field that is responsible for the presence of a North magnetic pole and a magnetic pole South to the surface of the Earth.
Behind this large-scale field, however, also hides other fields, produced by more discreet sources. One of the most fascinating is that produced by rocks that have been magnetized by the main field. Mapping this field makes it possible to find valuable information, both on the distribution and the origin of themagnetization of the rocks that are responsible, that on tectonic history of the earth’s surface. The most precise global map ever produced to date for this field has just been published.
With the support of CNES and as part of the operation of the Swarm space mission of theESA, a French team associating the Laboratory Magmas and Volcanoes (LMV) at the University of Clermont Auvergne, the institute of physical of the globe of Paris (IPGP) at the University of Paris, and the Laboratory of Planetology and Geodynamics (LPG) at the University of Nantes have just published this map which brings together more than 70 years of airborne surveys, sea campaigns, and satellite observations in orbit low, which were thus used to produce a model describing this field from the largest scales not dominated by the main field up to scales of the order of 40 km.
The dynamics of telluric forces
This model reveals the magnetic signatures testifying to the prodigious telluric forces which have shaped the earth’s surface and still govern its dynamics. This magnetic signal in fact mainly comes from igneous rocks and metamorphic cold enough to carry a magnetization, mainly present in Earth’s crust. Their magnetic signatures will make it possible to further constrain the geodynamic models of the crust, to specify the contours of the geological provinces. in depth, in particular in inaccessible areas such as theAntarctic, to better locate and circumscribe the old impact structures, to follow the extensions of tectonic faults, and more generally, to better highlight the contrasts magnetic products produced by continental collisions, the extension of ocean floors and the subduction.
As the magnetization of the rocks 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 the thick “cold” zones. , producing more intense signals, and “hot” areas more superficial, producing weaker signals.
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