Evidence of the contrasted fission-track clock behavior of the apatites from In Ouzzal carbonatites (northwest Hoggar): The low-temperature thermal history of an Archean basement
This fission-track study is performed on the apatites from the In Ouzzal (northwest Hoggar, Algeria) carbonatite complex and permits us to present a complete thermal history of this Archean core. Two types of apatites, the pink ones (early carbonatites) and the green ones (late carbonatites), have been dated. The temperature during the Pan-African orogeny would have reached 100-120 °C in the In Ouzzal core, as both types of apatites from the carbonatites have recorded this event (500-630 m.y.). A mild Permian thermal event reset only the fission-track clock of the green, late apatites. This Permian thermal event is of quite a large extent in the Hoggar shield; it has also been detected in the Pharusian belt and in central Hoggar. This event is related to the opening of the Atlantic Ocean. The very high U-Th content of some of these apatites, and consequently, the amount of radiation damage in the mineral lattice, has been shown to possibly influence the fission-track clock behavior of these minerals. The F-Cl content of the apatites does not show any correlation with the degree of age reductions.