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Evolution géodynamique des cratons des Guyanes et d'Afrique de l'Ouest. Apport des données paléomagnétiques, géochronologiques (40Ar/39Ar) et géochimiques en Guyane et Côte-d'Ivoire.

Abstract : In order to better constraint the Paleoproterozoic and Mesozoic geodynamic of the French Guyane and Ivory Coast, a multidisciplinary study (paleomagnetism, geochronology Ar/Ar and geochemistry) were done in dolerites, granitoïdes and sesimentary rocks.
The combined paleomagnetic and geochronological studies in paleoproterozoic rocks frim the French Guyana indicate that the Jurassic magmatic activity have not perturbed the magnetic remanence and the Argon geochronometer. The calculate cooling rates were low (3,5+2/-1,6°C/Ma et 4,8+2,6/-2,1°C/Ma) and homogeneous from the North to the South. We have highlighted the later cooling of the high anisotropic (P') southern Oyapok zone. Three paleoproterozïc poles were computed ‘OYA, A et B). The magnetic remanence ages varies from 2050 to 1990 Ma. The poles from French Guyana were compared with the C1, C2, C3 (2100 to 2000 Ma) from Ivory Coast, permitted to build two paleoproterozoïc apparent polar wander paths for the Guyana shield and West African craton. The two APWP were coherent after 2020 Ma confirming that the two blocks constituted one block at around 2000 Ma. The older poles were not compatible. Two hypothesis were proposed : I) The two contiental blocks were separate before 2020 Ma ; II) The two blocks were together but the missing data betwween 2080 et 2040 Ma do not allow to prove it.
Our new data from the central Atlantic magmatic province indicates that the French Guyana dolerites have particular geochemical and geochronological features as in Amapa Liberia and Ivory Coast. This restricted zone corresponds to high Ti tholeiites, wich have asthenospheric origin and were horizontally fed during multiples pulses. Moreover they are younger (197 to 192 Ma, 40Ar/39 ages) than those of rest of the central Atlantic magmatic province.
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https://tel.archives-ouvertes.fr/tel-00002336
Contributor : Nathalie Pothier <>
Submitted on : Thursday, January 30, 2003 - 10:58:32 AM
Last modification on : Thursday, March 5, 2020 - 6:49:20 PM
Long-term archiving on: : Friday, April 2, 2010 - 6:30:32 PM

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  • HAL Id : tel-00002336, version 1

Citation

Sébastien Nomade. Evolution géodynamique des cratons des Guyanes et d'Afrique de l'Ouest. Apport des données paléomagnétiques, géochronologiques (40Ar/39Ar) et géochimiques en Guyane et Côte-d'Ivoire.. Géologie appliquée. Université d'Orléans, 2001. Français. ⟨tel-00002336⟩

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