SHAPE OF THE SIDOBRE GRANITE MASSIF (MONT AGNE NOIRE, FRANCE) - SENSITIVITY OF GRAVIMETRIC DATA INVERSION TO DENSITY CONTRAST

A detailed gravimetric study has been performed in the Sidobre granite pluton (southern Massif Central, France). The Bouguer anomaly has a v ery low magnitude (2-3 mgal). The residual anomaly satisfactorily fits the granite contour, except to the east of Les Ferrieres and north of Lacrouzette where the granite is interpreted as dipping at a low angl e under its cover-rocks. Density values and sensitivity to density con trasts of the calculated depths of the granite floor have been particu larly studied because of the small magnitude of the anomaly. It is pro posed that the massif is a sill, rooted at the southwest (< 3 km), and separated into three domains by normal faults N120-degrees-E in strik es, could have emplaced during the NE-SW regional extensional event re cently described by authors for the southern Massif Central.