Magnetometrical dike hunt: a Grenvillian expedition

A dike is an intrusion into pre-existing rock by an igneous body. Since the magnetism of the pre-existing rock is usually significantly different from that of the intrusion magnetometers can be used to detect the presence of a dike. The aim of this project was to detect the presence of dikes at two locations in Ontario near the French River. The first location was along Highway 11 near Trout Creek where a dike is visible in the recent rock-cut. This location was chosen to act as a control for the second location on Highway 69 near Nobel. Identifying a dike here would allow for the westward extension of a known dike system. A Proton Precession Magnetometer (PPM) was used. It measures the total strength of the Earth’s magnetic field at a single point. The Earth’s magnetic field is affected by magnetic bodies in the subsurface. Therefore, a disturbance of the magnetic field strength allows us to infer the presence of a magnetic body at various depths. Size and other properties of the magnetic body can be obtained by fitting the measurements to computational models. The Trout Creek dike appeared to be a clear magnetic anomaly, 90m wide with an amplitude of 1.7x103nT. This fits a model of a thin dike 75m wide extending 85m deep. At Nobel we did not confirm the existence of a dike, only finding small anomalies of less than 1.3x103nT, likely caused by artifacts such as water pipes. This research was conducted to better understand mountain formation and plate movement.