Elsevier, Precambrian Research, (243), p. 88-109, 2014
DOI: 10.1016/j.precamres.2013.12.016
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The aim of this paper is to explore the link between the metamorphic record of a Palaeoproterozoic orogeny and its thermo-mechanical evolution, in order to discuss the burial and exhumation processes of moderate- to high-pressure volcano-sedimentary rocks (6–8 to >10 kbar) in the Birimian Province (2.2–2.0 Ga) of the West African Craton. Metamorphic data collected in Burkina Faso, southwest Ghana and eastern Senegal suggests a Palaeoproterozoic Birimian crust dominated by moderate apparent geothermal gradients of 20–30 °C/km (M2a), which fit a purely conductive thermal crustal regime. This produced greenschist- to amphibolite-facies metamorphic assemblages that developed during the Eburnean orogeny (∼2.1 Ga), associated with regional shortening and granitoid intrusions. The M2a gradient is superimposed on an early thermal regime (M1: <10–15 °C/km) that produced high-P greenschist- to blueschist-facies metamorphic assemblages. M1 most likely recorded an earlier thermal history in the volcano-sedimentary basins where the protolith of the metamorphic terrains formed. Whether M1 is related to distributed burial associated with sediment accumulation or early subduction-related tectonics remains an open question, not directly addressed here.