A late Triassic age for the Rochechouart impact structure, France

Abstract

Argon-40/Argon-39 laser spot fusion dating of pseudotachylyte from the ∼25 km diameter Roche-chouart impact structure of western-central France yields a matrix age of 214 ± 8 Ma (2σ). Field evidence indicates that the pseudotachylyte was generated during the modification stage of the impact process, probably during transient cavity collapse. This new age is considerably older than the previously accepted age of 186 ± 8 Ma for this structure, which was obtained from hydrothermally-altered melt sheet samples. The new age is in accordance with earlier paleomagnetic and fission track data, which indicated that Rochechouart was formed during the late Triassic. Moreover, the new determination is in agreement with the regional geological setting and field relations of the structure. The new age of 214 ± 8 Ma falls within the Norian stage of the Triassic system.