Palaeomagnetism is responsible for determining the directions of the various components that the remanent magnetisation of a rock may have, and which are closely related both to the geological processes to which it has been subjected since its formation and to the palaeodirection of the geomagnetic field at different times in its history. Upon formation, either by cooling from an original magma or by sedimentation and subsequent lithification, a rock may acquire a remanent magnetisation parallel to that of the geomagnetic field, as "seen" by the rock at that instant. Subsequently, the rock may undergo various tectonic displacements and deformations, which will cause the direction of its primary remanent magnetisation to no longer coincide with that of the geomagnetic field experienced by the rock. Similarly, processes of metamorphism or metasomatism, or mere lightning strikes, may cause new components to appear in the remanent magnetisation of the rock. These new components, which will be called secondary components, can make the primary component disappear totally or partially, in which case we will have the coexistence of several components of the magnetisation with different directions and with different degrees of overlapping. The result is what is called Natural Remanent Magnetization (NRM).

By means of an appropriate treatment in the laboratory, either by applying gradual increases in temperature or by subjecting the sample to alternating magnetic fields of increasing maximum intensity, the NRM of the rock is progressively destroyed and demagnetised. Since this demagnetisation takes place step by step, measuring the NRM after each step allows us to analyse which components made up the NRM of the sample and their respective directions. With the spatial orientation data taken when the rock sample was collected in the field, we can restore the directions of the different components of the magnetisation to the geographical context of the sampled rock outcrop. All this can be complemented with the application of various field tests, such as the fold test, the inversion test or the conglomerate test, which provide us with valuable information about the age of the different components of the NRM, always relative to the ages of the geological processes being considered when applying the respective test (rock folding, conglomerate formation, etc.).

All this information, properly contrasted or complemented with geological and structural data, as well as with rock magnetism experiments that allow to determine which minerals are the NRM carriers, can provide important evidence about many aspects of the geological history experienced by the rocks or about the behaviour of the geomagnetic field in past times. Thus, among the applications of palaeomagnetism are the following:

-Magnetostratigraphy. The study of changes in the polarity of the geomagnetic field. It can be used as a tool for stratigraphic correlation and relative dating.

-Palaeogeography. Comparison of the position of the virtual palaeomagnetic poles (determined from the NRM of rocks) for a given age with the geographic poles allows, given the conditions that the geomagnetic field can be described as that of an axial, geocentric dipole, to reconstruct the distribution of the continents at that time, as well as the relative movements experienced since then.


- Tectonic deformations. Comparison of the NRM directions between rocks forming a relatively stable part of a continental mass and rocks located in a deformed region allows the geometry of these deformations to be reconstructed. For example, it is possible to know the rotations of blocks around vertical axes that occur in various continental margins subject to deformation, as in the case of the Betic Chain.


Examples of Paleomagnetism works developed by the UCM Paleomagnetism Group:

Ruiz-Martínez, V.C., Torsvik, T. H., Van Hinsbergen, D. J. J., & Gaina, C. (2012), “Earth at 200 Ma: Global palaeogeography refined from CAMP palaeomagnetic data”. Earth and Planetary Science Letters, 331, 67-79; DOI: 10.1016/j.epsl.2012.03.008.

Palencia-Ortas, A., Ruiz-Martínez, V.C., Villalaín, J.J., Osete, M.L., Vegas, R., Touil, A., Hafid, A., McIntosh, G., van Hinsbergen, D.J.J., Torsvik, T.H. (2010), “A new 200 MA paleomagnetic pole for Africa, and paleo-secular variation scatter from Central Atlantic Magmatic Province (CAMP) intrusives in Morocco (Ighrem and Foum Zguid dykes)”. Geophysical Journal International, 185, 1220-1234. DOI: 10.1111/j.1365-246X.2011.05017.x

Villasante-Marcos, V., Osete, M.L., Gervilla, F., García-Dueñas, V. (2003), "Paleomagnetic study of the Ronda perioditites (Betic Cordillera, southern Spain). Tectonophysics, 377, 119-141. PDF.