Étude gravimétrique des astroblèmes du Lac à l'Eau Claire, Nouveau-Québec

Abstract

Two- and three-dimensional gravimetric models of two meteoritic craters from Clearwater Lake are presented. The gravimetric data were obtained from the Geophysics Division of the Geological Survey of Canada and a survey carried out during this investigation. A regional gravity map was extracted from the Bouguer anomaly corrected for topography. The negative residual anomalies are circular and concentric with respect to the morphologies of the two basins of the lake. The anomaly of the western basin has an intensity of − 100 μm s⁻² and is composed of two superimposed anomalies (∼-26 km and ∼-8 km in diameter respectively). The anomaly of the eastern basin has an intensity of about −95 μm s⁻²and a diameter of ∼ 16 km. The models obtained through direct modelling are characterized by a bowl-shaped geometry. The western basin is characterized by two concentric zones; the central zone has the highest density contract (−210 kg m⁻³) with respect to the bedrock outside the crater rim. The intermediate zone has a contrast of −250 kg m⁻³ with respect to the surrounding bedrock. The bodies of the model are dipping towards the centre and a thickening of the structure takes place in its centre. The eastern basin is more difficult to model because of the occurrence of layers of overburden and sedimentary rocks deposited in the crater after the meteoritic impact.