Modern-style plate subduction preserved in the Palaeoproterozoic West African craton

Ganne, J. and De Andrade, V. and Weinberg, R. F. and Vidal, O. and Dubacq, B. and Kagambega, N. and Naba, S. and Baratoux, L. and Jessell, M. and Allibon, J. (2011) Modern-style plate subduction preserved in the Palaeoproterozoic West African craton. Nature Geoscience, advanc. ISSN 1752-0894 EISSN:1752-0908 DOI

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The timing of onset of modern-style plate tectonics is debated. The apparent lack of blueschist metamorphism1—a key indicator of modern plate subduction2—in rocks aged more than about 1 billion years calls into question the existence of plate tectonics during the Archaean and Palaeoproterozoic eras3, 4. Instead, plate tectonics and subduction could have either not occurred at that time5, or could have proceeded differently6 owing to warmer conditions in the early Earth mantle7. Here we use thermodynamic models8, 9, 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 °C and under a geothermal gradient of 10–12 °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.

Item Type: Article
Uncontrolled Keywords: 2011AREP; IA63;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Nature Geoscience
Volume: advanc
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 21 Dec 2011 16:41
Last Modified: 23 Jul 2013 10:03

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