Publication Date:
2003-01-01
Description:
Single-grain 40Ar/39Ar dating of detrital white mica from Oligocene to Miocene (31-13 Ma) sediments of the North Alpine Foreland Basin in Switzerland reveals three prominent age clusters indicating cooling of the source rocks below 350-420{degrees}C in Carboniferous, Early Permian, and Tertiary times. Precise calibration of sedimentation age throughout the study area enables the thermal evolution of the hinterland in space and time to be precisely traced. Palaeozoic mica ages are documented in all samples and are used as additional provenance indicators. Tertiary mica ages are restricted to sediments younger than 21 Ma, and are only found in central and western drainage systems. Tertiary micas document progressively increasing average cooling rates up to 34-41{degrees}C/Ma in the source area (Lepontine Dome), between 21 Ma and 14 Ma. The observed cooling rates and the time-span for rapid cooling in the source area (between 19 and 14 Ma) agree with thermal models derived from currently exposed rocks of the Lepontine metamorphic dome. This study proves that detrital mica geochronology is a robust tool for deciphering the thermal histories of ancient orogens which are no longer exposed today.
