K–Ar mineral ages and thermal history of magmatic and metamorphic Paleoproterozoic units from the northern part of Kedougou Kenieba Inlier, West African Craton (Eastern Senegal)
The northern part of the Kedougou Kenieba Inlier (Eastern Senegal) is composed of Palaeoproterozoic volcano-plutonic and volcanosediment areas cross-cut by differentiated plutonic bodies of gabbroic to granitic composition. They are emplaced in an arc-type environment and accreted during the Eburnean Orogeny. We present here new K–Ar ages obtained on several plutons from different mineralogical phases, each characterized by a different closure temperature for the K–Ar system. Ages from hornblende, between 2013±29 and 2141±30Ma, constrain the cooling history of the magma bodies through the 550°C isotherm. They are slightly younger than U–Pb ages previously obtained from the same units, attesting of a rapid cooling, tectonically controlled, of about 7°C/Myr. Ages obtained on biotite minerals range from 1955±28 to 1893±27Ma, suggesting that from 550 to 325°C, cooling rate decreased to about 3°C/Myr. Signi?cantly younger ages ranging from 1704±24 to 1615±23Ma have been obtained on plagioclase and microcline. They can be interpreted in terms of either a slow cooling with a rate of only 1°C/Myr, from about 1.9 to 1.6Ga, or either re?ecting the occurrence of a rather limited thermal event younger than 1.7Ga. Since no age younger than 2.0Ga has previously been obtained for plutonic rocks from the early Birimian in the West African Craton, ages of 1.7–1.6Ga obtained here from feldspars might be the ?rst evidence for a regional re-heating event having occurred in the East–North Kedougou Kenieba inlier.
Auteur(s) : IBRAHIMA SAGNA, XAVIER QUIDELLEUR, FRANÇOIS NDIAYE, PIERRE-YVES GILLOT, JEAN-CLAUDE LEFEVRE and EDMOND DIOH
Année de publication : 2015
Revue : GEOLOGICAL JOURNAL
Type : Article
Mise en ligne par : DIOH Edmond