Modelling of gravity anomalies associated with granitic plutons and mafic volcanic flows in Northern New Brunswick using MAGRAV2

Abstract

This thesis examines the construction and interpretation of possible subsurface bodies obtained through modelling of Bouguer anomalies located in North Central New Brunswick. These gravity anomalies are associated with granitic plutons and mafic volcanic flows and were modelled using the MAGRAV2 software package. The models obtained were based on a four dimensional hyperspace that is, there were four model parameters: depth, width, strike length and density contrast. Modelled subsurface bodies were constrained through the investigation of outcrop data, to known geological formations and thus particular densities. Since many rock formations were present, over outcrop distances smaller than the station intervals used in the modelling an average density had to be estimated. Bodies therefore were made as a composite of several formations. After several optimization steps were applied to the initial models the difference between the observed and calculated anomalies became minimal and thus correlations seem to become apparent between the structure of the modelled bodies and the known surface geology in the area of modelling. For example several bodies resembling upright prisms and inverted prisms were constructed and were found to be in accordance with the known pas it ions of synclines and anticlines respectively. The modelling done using the MAGRAV2 also indicated that complex geometrical body shapes are the only way to explain a few observed gravity anomalies. Finally, implementation of the MAGRAV2 software package has been proved to be a very powerful tool in the interpretation subsurface features.