DS10 - Défi de tous les savoirs

Secular Variation and Paleointensity in Mexico during the Plio-Quaternary – SVPIntMex

Secular Variation and Paleointensity in Mexico during the Plio-Quaternary

This project aims to acquire new experimental data of the Earth's magnetic field (in direction and intensity), with archaeological and volcanic material from Mexico to<br />• improve the secular variation curve and better define the temporal evolution of the Earth's magnetic field,<br />• develop archeomagnetism, a powerful tool for dating archaeological sites when the curve of secular variation is well defined,<br />• magnetically trace obsidian artefacts.


Mexico is a very rich archaeological area, with also abundance of recent volcanic material. However Mexican secular variation curve remains patchy and not in agreement with predictions of global models. Are the models too smoothed to fit nicely the Mexican data or is there a bias with the Mexican paleointensity?<br /><br />The main objective of this project is to acquire new and reliable experimental data of the geomagnetic field behaviour (direction and intensity) during the archaeological and the recent geological past, from Pliocene to Present, to refine the secular variation curve of the Earth magnetic field, essential for a good understanding of one of the critical geophysical parameter for mankind.<br /><br />Archaeologists want to understand how and why things happen during the pre-history. To understand the different periods, it is necessary to know when the events took place. In some cases, knowledge of the chronology of the events can already answer these questions. However for older periods, especially before Christ, the means for dating the archaeological sites are getting less and less numerous, and archaeomagnetism is the only option left for periods older than the early Holocene. Thus, the construction of complete secular variation curve (direction and intensity) of the geomagnetic field for pre-historical periods is essential for the Mesoamerican region.<br /><br />We also propose to develop an original method, using rock magnetism and paleointensity, to discriminate different geographic sources for obsidian artefacts.<br /><br />New, high quality Pliocene paleointensity of lava flows will help to better describe the recent transition between the weak Mesozoic magnetic field and the strong present field.<br /><br />Finally, a regional platform, gathering all archaeological, paleomagnetic and rock magnetic data available for Mexico, will be constructed for the benefit of the whole community. A critical analysis of the available data will also be made, following the most recent quality criteria.

As lava cools and solidifies, it preserves the direction of the ambiant field so looking at rocks that has formed over time gives us an idea of the evolution of the Earth’s magnetic field through time. The same phenomenon occurs during the cooling of an archeological artefact (ovens, potteries, ceramics), even though the magnetic mineralogy can be slightly different. Therefore, the methodology to be applied is the same in both cases, just changing the temporality of the material.

The techniques that will be used for the project are mainly :

•. Rock magnetism, optical microscopy (transmitted and reflected lights) and electron microscopy (SEM) to define the magnetic carriers,

•. Thermal and alternating field demagnetizations to isolate the direction(s) of magnetisation carried by the rocks,

•. Paleointensity analysis with the Thellier-Thellier to compare the thermoremanent magnetisation acquired in a known laboratory field with the natural magnetisation of the rocks and define the intensity of the filed during cooling,

•. Radiometric ages to precisely date the cooling of the rocks and therefore the age of the magnetisation..

in progress



For the last two decades, experimental and numerical models of the Earth magnetic field have advanced significantly, approaching more and more a realistic geodynamo model. For example, many of the models designed now to reproduce the movement in the Earth core are able to simulate reversals. However, to further constrain these models, the evolution of the Earth magnetic field through time has to be known with much more details, from historical time down to geologic time. This will improve our understanding of the functioning of the core through time, the core-mantle interactions, and provide realistic input parameters for even more precise geodynamo models. New, reliable data are therefore badly needed, especially from central and south America, which represent for the moment only a few per cent of the paleointensity dataset.
On the other hand, when the secular variation curve is well known for a given region, it can be a very powerful tool to date archaeological materials. As Mexico is a very rich archaeological area but with a secular variation curve, and especially its intensity, still poorly defined, here again new data are essential.
Finally, we propose to use paleointensity and rock magnetism as a new method to look for the provenance of obsidian artefacts.
The overall purpose of this project is therefore to acquire new and reliable experimental data of the geomagnetic field behaviour (direction and intensity), using archaeological and volcanic materials from Central America. The methodology to be applied is the same for both archaeomagnetism and paleomagnetism, just changing the temporality of the material, historical to geological, respectively. We will focus more precisely the investigation of this proposal on Mexican material. Mexico is an extremely pertinent area for this type of study, firstly because of the abundance of archaeological and volcanic material, but also because of the small number of studies focused on that matter up to now. In this context, our project is timely and strongly justified.
Up to now, we have contact with many archaeologists that will provide us archaeological artefacts and access to ovens for sampling, and we will also sample well-dated, oriented volcanic flows and obsidians covering a period from Pliocene to Present. Therefore, we are confident that, during the course of our project, we will get significant knowledge about the behaviour of the magnetic field during the past five million years and will also greatly improve the rock magnetic and paleomagnetic tools for archaeology.

Project coordination

Mireille Perrin (Centre National de la Recherche Scientifique délégation Provence et Corse [Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement])

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


UNAM Laboratorio de Paleomagnetismo, Instituto de Geofisica
CNRS DR12 [CEREGE] Centre National de la Recherche Scientifique délégation Provence et Corse [Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement]

Help of the ANR 211,778 euros
Beginning and duration of the scientific project: November 2015 - 36 Months

Useful links

Explorez notre base de projets financés



ANR makes available its datasets on funded projects, click here to find more.

Sign up for the latest news:
Subscribe to our newsletter