Proterozoic magmatic events recorded in 40Ar/39Ar data from the northern part of the Kedougou Kenieba Inlier (eastern Senegal)

Abstract

We present a thermal history of the Kedougou Kenieba Inlier (eastern Senegal), the western-central outcropping part of the West African Craton, based on 40Ar/39Ar analyses performed on hornblende, biotite, and K-feldspar minerals from Paleoproterozoic plutonic rocks. 40Ar/39Ar age spectra obtained for hornblendes and biotites range between 2055 ± 26 and 2028 ± 28 Ma, in very good consistency. They suggest that magmatism in the Kedougou Kenieba Inlier happened at the end of the Eburnean Orogeny (2.25–2.00 Ga). Taking into account previous zircon U–Pb ages, these new results imply that initial cooling from magmatic temperature to about 300 °C (biotite closure temperature) occurred rapidly, and that these rocks did not experience any subsequent re-heating event above 300 °C. On the other hand, 40Ar/39Ar age spectra obtained on K-feldspars display strongly disturbed patterns revealing that these minerals experienced argon loss due to re-heating events. Altogether, these data constrain a thermal history for the studied area involving two thermal events with temperatures around 275 and 225 °C, at about 1750 and 1500 Ma, respectively. These thermal events, previously inferred from U–Pb ages of intruding mafic dykes, can be related to aborted attempts of continental breakup, as the West African Craton remained attached to Baltica and Amazonia cratons during the 1.8–1.3 Ga interval.