Borehole navigation surveys performed using a triaxial fluxgate magnetometer record the change in orientation of the magnetic vector versus depth. Variations in the orientation of the magnetic vector arise from either on- or off-hole magnetic sources. On-hole magnetic sources associated with magnetic property fluctuations in the immediate wall of the borehole (i.e., susceptibility) and (or) remanence polarity changes produce sharp-edged anomalies. Off-hole magnetic sources, caused by a magnetic body near, but not penetrated by, the borehole, produce broad smooth anomalies. Prior to the interpretation of borehole magnetic anomaly logs, data corrections must be applied. Data from each of the magnetic and tiltmeter sensors must be corrected for differential gain, base value offset, and nonorthogonality. By using a probe with two sets of triaxial fluxgates, it is possible to detect along hole magnetic field rotations, which compromise the borehole navigation calculations. After rotation into geographic coordinate space, borehole vector magnetic data from the Chicxulub impact crater in Mexico showed no evidence for any systematic change of magnetic property versus depth. What was originally interpreted as reversal stratigraphy has proved to be minor changes in borehole geometry. Borehole magnetic data from a borehole through the Stratmat deposit, located in the Bathurst mining camp, New Brunswick, show strong off-hole and on-hole anomalies associated with the pyrrhotite-rich ore bodies.
The basal contact of the Sudbury Igneous Complex (SIC) on the North Range is interpreted as the outer edge of a meteorite impact crater. Yet, the base of the SIC, and contacts within the SIC, and the overlying Onaping are not circular. Their outline is elliptical. This and other details of the geology of the North Range which have not been fully explained include: variations in the width of the metamorphic contact aureole, lateral discontinuous variations in the thickness of the norite and granophyre units, paleomagnetic evidence that the North Range contact of the SIC originally had a dip of around 20o, and differing magnetic fabrics in the norite / gabbro versus the granophyre. Several metrics are used to determine how much of the current outline of the North Range is the result of post-impact deformation and how much is a primary feature related to a meteorite impact. Uplift, rotation, and translation experienced by different segments of the North Range of the SIC is established using, dyke azimuth and petrographic analysis of Matachewan diabase dykes, and paleomagnetic and magnetic fabric data analysis. These analyses show: a) the elliptical form of the North Range is a primary feature associated with a near circular impact crater, b) some of the original crater wall must have been preserved, and c) deformation of the North Range is limited to regional scale block rotation producing a SW dip modified by minor block rotation tilting and vertical displacement associated with north-northwest trending faults.
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