Inversion of Magnetic and Gravity Fields Applied to the Sub-Basalt Imaging Problem

This study investigates the feasibility to use gravity and magnetic inversion to image basalts and sub-basalt structures in sedimentary basins affected by volcanism. A regional 3D model was constructed for the Møre margin, mid-Norway, based on a wealth of seismic and petrophysical information. Resolution of the regional 3D model prevents however detailed imaging of the basalts and sub-basaltic structures. While it is difficult to identify the lateral extend of the volcanic features (at depth of 6 km) in the gravity and magnetic data, as well as in Full Tensor Gravity (FTG) data, the sub-basaltic basement architecture can be identified. The gravity gradients provide valuable information on the vertical and lateral extent below the basalts, despite the small density contrast to the surrounding. Inversion of the gravity and magnetic residuals, after correction for the regional anomalies provided by the 3D model, gives a better insight into the extent and thickness of the basaltic and sub-basaltic layers. Especially, coupled inversion increases the depth resolution, but magnetic and gravity inversion must be weighted differently. Such inversion requires detailed pre-knowledge on the regional structures and shallow sedimentary layers, and can assist other sub-basalt imaging techniques.