Oligocene Slab Break‐Off and Pleistocene Glacial Erosion Shaped the Tectonic Evolution of the Dent Blanche Tectonic System, Western Alps

Integrating new zircon and apatite (U-Th-Sm)/He (ZHe, AHe) and muscovite 40Ar/39Ar (MAr) thermochronometric data with published data sets, we reconstruct the tectonic and thermal evolution of the Dent Blanche Tectonic System (DBTS), an Austroalpine nappe overlain by Ligure-Piemontese oceanic units in the Western Alps. We report new Late Eocene-Early Oligocene (∼35–30 Ma) ZHe ages and Miocene (∼20–12 Ma) AHe ages. An incised channel in the Valpelline Valley yields Plio-Pleistocene AHe ages (∼2.5 Ma). Scattered MAr ages (∼250–29 Ma) reveal excess radiogenic 40Ar *. Inverse thermal modeling of the cooling ages, constrained by the younger MAr ages from the same samples, identifies two distinct cooling phases: (a) rapid, widespread Eocene-Oligocene cooling linked to Alpine nappe stacking amplified by compressed isotherms following European slab break-off (∼34–32 Ma); and (b) post-Oligocene slower cooling, later followed by spatially focused Pleistocene cooling, interpreted as the localized resetting of shallow thermochronometers due to intensified glacial incision in tributary valleys. In the DBTS, the glacial imprint is evidenced by high normalized channels steepness (Ksn) values in valleys adjacent to the glacial trough. These high Ksn values are due to the steepening of the fluvial network during focused glacial erosion. The spatial and temporal resetting of shallow thermochronometers in these tributaries aligns with Pliocene-Pleistocene denudation pulses documented in the Rhone Valley and Mont Blanc massif. This correlation indicates that climate-driven glacial erosion locally overprinted earlier Oligocene tectonic signals, highlighting the dominant role of Pleistocene glacial dynamics in reshaping Alpine topography despite prolonged tectonic quiescence. Our data support a slab break-off event in the Oligocene and rule-out a younger Pliocene break-off. This demonstrates how post-orogenic landscapes preserve both geodynamic processes and climatic cyclicity, with implications for the interpretation of thermochronometric signals in exhumed terranes.