Abstract
Fission track dating of apatites from the Auriat granite (Massif Central, France) has revealed a complex thermal history incorporating three major events. Initial emplacement of the granite at 324 Ma was followed by pervasive chloritization associated with localized intrusion of lamprophyres. Uplift and erosion continued into the Stephanian at 270 Ma. A mild hydrothermal alteration event which attained temperatures of greater than 130°C at all depths within the granite has been dated at 170 Ma. This activity may be associated with an extensional orogenic event during the Permian. A second phase of more severe hydrothermal activity, which may be related to the development of the Pyrénées, has been dated as Upper Cretaceous between 71 and 118 Ma. This alteration event attained temperatures of greater than 130°C at depth within the granite, but only reached between 60 and 130°C in the top portion of the granite, indicating emplacement of this activity from depth. Finally, fluid circulation associated with the Alpine orogenic event has not reached temperatures above 60°C. Fission track dating can thus contribute to the understanding of the function of a fossil hydrothermal system such as at Auriat, and provide an insight into the potential behaviour (such as alteration temperature, mineralogical changes and fluid circulation) of a granite under high-level radioactive waste (HLW) repository conditions.
Published Version
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