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.
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