From tropical bauxites to orogenic exhumation in Provence (France) constrained by hematite and goethite (U-Th)/He thermochronology

Reconstructing post-depositional thermal histories in carbonate basins is challenging because conventional thermochronometers are scarce and lack the required temperature sensitivity. We established karst-hosted bauxites as an alternative archive, using coexisting hematite (Hm) and goethite (Gt) formed during tropical weathering. We report Hm (U-Th)/He (HHe) and Gt (U-Th)/He (GHe) dates to and thermal inversions of karst bauxites from Provence (France). These deposits formed during mid-Cretaceous uplift (ca. 120−105 Ma) and were subsequently buried beneath Upper Cretaceous−Cenozoic sediments. Analyses of 133 Hm-Gt grains yielded reproducible ages from 85 ± 6 Ma to 12 ± 1 Ma, younger than the overlying sediments, indicating post-depositional resetting. HHe systematically yields older ages (85−22 Ma) than coexisting GHe (32−12 Ma), reflecting higher He retentivity. Hm (U-Th)/He thermal modeling, consistent with regional geology, reveals two thermal events: (1) heating to 90−120 °C until 60−45 Ma during Pyrenean compression, followed by cooling; and (2) reheating to 50−60 °C between 35 Ma and 15 Ma during the onset of the West European Rift, which partially reset HHe. This second event matches the GHe reset and points to a temperature sensitivity of <60 °C for the GHe system. Our results establish karst bauxites as a robust archive for investigating shallow thermal histories.