40Ar/39Ar thermochronology of Paleoproterozoic granitoids of northeast Burkina Faso, West African Craton: Implications for regional tectonics

Abstract

The greenstone belts of northeast Burkina Faso in the West African Craton (WAC) comprise Birimian meta-sedimentary and mafic–ultramafic complexes that are intruded by granitoids and late dolerite dykes. The granitoid–greenstone belt assemblages underwent at least two phases of deformation that have resulted in their principal NW and NE trends.We performed a detailed 40Ar/39Ar dating together with zircon U–Pb ages in order to unravel the thermo-chronological history of the studied granitoids.Our previous zircon U–Pb data indicated that the granitoids were emplaced between 2138±7 and 2181±7Ma. This period is well known for crustal growth in the WAC. The emplacement of granitoids was concomitant with D1 or the Tangaean event (2130–2170Ma). Amphibole and micas yield two 40Ar/39Ar age groups; the first group (2046±12–2132±13Ma) constrained the D2 deformation event, and the second group (1918±24 to 1984±12Ma), constrained the D3 or Wabo-Tempelse event.Considering closure temperatures of the isotopic systems, the U–Pb ages and the present 40Ar/39Ar dating results suggest that after emplacement, the granitoids cooled to 315̊C at ca. 2020Ma with a mean cooling rate of 6.5̊C/Ma; corresponding to a mean uplift rate of 0.65km/Ma. The additional K-feldspar 40Ar/39Ar data indicate a later slow cooling stage with a rate of 0.54̊C/Ma, corresponding to a mean uplift rate of 0.054km/Ma, subsequent to the end of the major crustal growth in the WAC at ∼2000Ma