Regional gravity setting of the Sudbury Structure

Abstract

In the vicinity of Sudbury, Ontario, Canada, the boundary between the Southern and Superior tectonic provinces is overlain by the elliptical Sudbury Structure. On the basis of gravity modeling, genesis of the Sudbury Structure has been attributed to either a magmatic origin (having a dense hidden differentiate zone) or a meteorite impact origin (there being no dense hidden mass). The difference between the two gravity models centers on the problem of regional‐residual separation. As shown by numerous previous studies, any such separation of components is nonunique. This becomes especially problematic when, as in Sudbury, a portion of the near‐surface geology has a similar orientation and dimension to more deep‐seated source. In this paper, several numerical methods (upward continuation, downward continuation, wavelength filtering, trend‐surface analysis) for determining the regional component of the gravity field associated with the Sudbury Structure have been applied and evaluated. Of the numerical methods used, the upward and downward continuation operators provided the most insight into the deep structural controls of the Sudbury Basin. Our preferred interpretation of the regional gravity field invokes a two‐component structure. Underlying the southern half of the Sudbury Structure is a laterally continuous gravity anomaly that is probably associated with a zone of uplifted Huronian volcanics. The gravity anomaly under the northern portion of the Sudbury Structure has a more restricted spatial extent. The close association between the northern limit of the gravity anomaly and the surface outcrop of the Levack Gneiss suggests the source of this anomaly is probably a slab of dense Levack Gneiss. This interpretation favors a meteorite impact origin for the Sudbury Structure.

Lake-based magnetic mapping of contaminated sediment distribution, Hamilton Harbour, Lake Ontario, Canada

“…For this study, an observation height of 15 m was chosen as a suitable level to maintain sufficient high frequency content, while minimising the use of the downward continuation operator on the grid to avoid potential aliasing and noise enhancement (Reid, 1980). The near-surface magnetic signal was then enhanced by performing a regional-residual separation (Cowan and Cowan, 1993;Hearst and Morris, 2001). This involves subtraction of an upward continued grid (50 m) from the total field to obtain a residual magnetic field map that is enhanced in short spatial wavelengths.…”

The Sudbury Structure: A circular impact crater?

“…To achieve a satisfactory fit between proposed potential field models and observed gravity and magnetic data requires the existence of a magnetic and density enhanced phase at depth beneath the SIC. The northernmost limit of the gravity and magnetic anomalies is coincident with the northern boundary of the Levack Gneiss Complex [ Hearst and Morris , 2001]. The optimum model fit is achieved with the Levack Gneiss unit having a limited depth extent.…”

Delineation of sub-basalt sedimentary basins in hydrocarbon exploration in North Ethiopia

“…The various numerical methods used in separating the deeper features from the shallower (Gupta and Ramani, 1980;Hearst and Morris, 2001;Nettleton, 1976) have been evaluated and two approaches have given better results and provided roughly similar gravity anomaly features. In the first approach the gravity field is upward continued to various heights to extract gravity signatures at the corresponding depths following the theory of Jacobsen (1987) which stated that upward continuation to a height of 2Z is used to extract the field associated to sources at and below depth Z.…”