40Ar/39Ar thermochronology of Paleoproterozoic granitoids of northeast Burkina Faso, West African Craton: Implications for regional tectonics
Journal
Precambrian Research
Journal Volume
235
Pages
208-229
Date Issued
2013
Author(s)
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. © 2013 Elsevier B.V.
Type
journal article