Densités et anomalies gravimétriques de l'intrusif du mont mégantic

An accurate estimate of the Bouguer density is needed to make corrections of the gravity data and to interpret the results. Many methods have been used for this purpose. Amongst these, the following can be mentioned: field sampling and laboratory measurements, geophysical logs, data relative to seismic velocities and gravity data. Surface sampling and the relation density-seismic velocity are affected by surficial alteration of the rock units. This is why an indirect determination with the help of gravimetry is often more representative. However, the relation Bouguer anomaly versus altitude for estimate of density is lacking precision. A more rigorous method related to the free air anomaly is proposed. This density determination method is applied to the Mount Megantic area, an intrusive of Cretaceous age belonging to the Monteregian Group. The mean density for the whole of the area investigated is 2647 kg m⁻³. The density of each geological formation was estimated individually. The results obtained show that the calibration: free air anomaly versus altitude is the most reliable.