A gravity model for the Sudbury Structure along the Lithoprobe seismic line

Abstract

Previous gravity models of the Sudbury Structure (1850 Ma) were constrained by surface geology, and by density measurements of surface and borehole rock samples. Recent high‐resolution seismic reflection data provide additional constraints for modeling new gravity observations made along the Sudbury Lithoprobe transect. Results indicate, 1) density distributions constrained by the seismic data yield calculated gravity values matching the Bouguer gravity data, 2) the main sources of gravitational disturbance are external to the Sudbury Structure, 3) the positive gravity anomaly trend south of the Sudbury Structure is associated with mafic rocks of Proterozoic age, and 4) the large, ramplike, gravity anomaly paralleling the northwest margin of the Sudbury Structure is an expression of a northward dipping boundary within the Archean basement. The presence of a hidden mafic layer beneath the Sudbury Structure is not required to model the Bouguer gravity data. An enigma is an 8 mGal, positive, gravity anomaly over the south central Sudbury Structure.

Impact melt dikes in the Sudbury multi‐ring basin (Canada): Implications from uranium‐lead geochronology on the Foy Offset Dike

“…Neodymium isotope data (Faggart et ai., 1985) indicated for the first time that the SIC consists of remelted Archean crustal material and is compatible with an impact melt origin. Detailed mineralogical-geochemical studies and field work (e.g., Avennann, 1994;Avermann and Brockmeyer, 1992;Brockmeyer, 1990;MUller-Mohr, 1992; as well as new structural and geophysical data (e.g., Butler, 1994;Cowan and Schwerdtner, 1994;McGrath and Broome, 1994;Milkereit et ai., 1992;Roest and Pilkington, 1994;Shanks and Schwerdtner, 1991) have resulted in a consistent model, in which the Sudbury Structure is plausibly interpreted as the teetonised and deeply eroded remnant of an -250 km large multi-ring impact basin, with the SIC as a coherent but complex impact melt sheet within the inner ring (e.g., Brockmeyer, 1990;Grieve et ai., 1991;Masaitis, 1993;Deutsch and Grieve, 1994;Stoffler et al, 1994;Deutsch et ai., 1995). The geochemical complexity observed for the various lithologies, which were generated by impact melting,…”

Thermal evolution and interaction between impact melt sheet and footwall: A genetic model for the contact sublayer of the Sudbury Igneous Complex, Canada

“…The target rocks, which underlie the SIC and the Huronian volcano-sedimentary sequence, consist largely of Late Archaean upper amphibolite to granulite grade felsic gneiss, known as the Levack Gneiss Complex [e.g., Dressler, 1984b]. These are exposed in the north and east ranges of the SIC but are suspected to underlie most of the SIC on the basis of geophysical modeling [e.g., McGrath and Broome, 1994]. This material represents potential lower crust which has been uplifted as much as 5 km into its post-impact position [e.g., Dressler, 1984a].…”

Variation in plagioclase clouding intensity in Matachewan dykes: evidence for the exhumation history of the northern margin of the Sudbury Igneous Complex

“…1). These rocks form the basement to the SIC (Milkereit et al 1992;Hearst et al 1994;McGrath and Broome 1994) and the Huronian supracrustal cover rocks (Fig. 1).…”