Analysis of gravity and magnetic fields in the Canadian Shield using standard and wavelet-based methods.

摘要

This thesis presents a geophysical study of the Canadian Shield using gravity and magnetic data. The first part is about the methodology. Standard methods and wavelet-based methods are presented. A method to characterize the causative sources of the field anomalies is described. A wavelet method to compute the elastic thickness of the lithosphere is presented. The second part concerns the applications on geophysical data from the Canadian Shield.; A study of the continuation of the Proterozoic Trans-Hudson orogen and the Archean eastern Superior province features under the sedimentary cover of the Williston basin in Central Canada is the subject of a chapter. We produce maps of gravity and magnetic fields for a visual interpretation of the geological structures. Details were enhanced by the way of horizontal derivatives of fields. We studied fields at different scales with the wavelet transform. A depth to magnetic basement map has been produced using Euler's deconvolution. We have shown that some structures of the Trans-Hudson orogen in northern Manitoba and Saskatchewan extend at least as far south as the U.S. border and that the Superior subprovinces extend westward under the sedimentary cover in Manitoba. We looked at two tectonic structures: a contact between two geological provinces and a major fault. We have determined their positions and we have characterized their vertical extensions and their dips.; The following chapter concerns elastic thickness calculation in eastern Canadian Shield. We calculated this thickness with standard methods and we have shown that the lithosphere in Quebec and Labrador is very strong. We developed a method based on wavelet transform to study the anisotropy of this parameter. This method has shown that the rigidity is highly anisotropic in the Superior province whereas it tends to be more isotropic in the Grenville province.; In the last chapter, we present a study of the gravity and magnetic fields in Ungava Bay. We have mapped potential fields from a compilation of data of different origins: land and satellite data for the gravity field and airborne and shipborne for the magnetic field. The interpretation of these maps leads to the conclusion that a small part of the Superior province was rifted away to the east of the New-Quebec orogen and that several geological structures seen in Labrador extend across the Ungava Bay to Baffin Island. This chapter has been published in a synthesis volume of the ECSOOT (Eastern Canadian Shield Onshore-Offshore Transect) project in the Canadian Journal of Earth Sciences.