Ganne Jérôme auteur aut IRD De Andrade V. auteur aut IRD Weinberg R.F. auteur aut IRD Vidal O. auteur aut IRD Dubacq B. auteur aut IRD Kagambega N. auteur aut IRD Naba S. auteur aut IRD Baratoux Lenka auteur aut IRD Jessell Mark auteur aut IRD Allibon J. auteur aut IRD text journalArticle eng text/pdf born digital access The timing of onset of modern-style plate tectonics is debated. The apparent lack of blueschist metamorphism(1)-a key indicator of modern plate subduction(2)-in rocks aged more than about 1 billion years calls into question the existence of plate tectonics during the Archaean and Palaeoproterozoic eras(3,4). Instead, plate tectonics and subduction could have either not occurred at that time(5), or could have proceeded differently(6) owing to warmer conditions in the early Earth mantle(7). Here we use thermodynamic models(8-10) to investigate the formation conditions of metamorphic minerals in the 2.2-2.0 Gyr old West African metamorphic province. We find a record of blueschist metamorphism in these rocks. We show that minerals such as chlorite and phengite formed at high pressures of 10-12 kbar, low temperatures of 400-450 degrees C and under a geothermal gradient of 10-12 degrees C km(-1). These conditions are typical of modern subduction zones. We therefore suggest that modern-style plate tectonics existed during the Palaeoproterozoic era. We conclude that ancient blueschist metamorphism may exist in other parts of the world, but the identification of these rocks has so far been hampered by methodological problems associated with deciphering their pressure and temperature evolution. specialized AFRIQUE DE L'OUEST BURKINA FASO 064 5 1 60-65 2012 1752-0894 https://www.documentation.ird.fr/hor/fdi:010054292 10.1038/ngeo1321 1752-0894 [F B010054292] https://www.documentation.ird.fr/hor/fdi:010054292 https://www.documentation.ird.fr/intranet/publi/2012/01/010054292.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2012-02-01 2017-08-23 fdi:010054292 fre