A 100 km-long paleomagnetic traverse radial to the Sudbury Structure, Canada and its bearing on Proterozoic deformation and metamorphism of the surrounding basement

Abstract

The 1850 Ma Sudbury Igneous Complex (SIC), considered to be a composite melt sheet of a major meteorite impact, has been deformed into an oval-shaped basin known as the Sudbury Structure. This paper explores to what extent this deformation has been communicated to the surrounding Archean basement around the northern margin of the SIC. Paleomagnetism of 2450 Ma Matachewan dykes and 1850 Ma impact breccia along a traverse, about 100 km-long and normal to strike of the contact between the SIC and the basement, suggests that the basement beneath the NW corner of the Sudbury Structure has been tilted to the SE within about 10 km of the contact. At this distance a possible fault separates the tilted region from one that shows no evidence of tilting. Petrographically the dykes out to a distance of about 50 km distant from the SIC are altered to upper greenschist facies of metamorphism with a fibrous amphibole replacing pyroxene and with loss of primary texture that characterizes less altered Matachewan dykes at distances greater than 50 km. The direction of magnetization found in the altered Matachewan dykes is an overprint which is probably associated with regional metamorphism related to orogenesis, or possibly with thermo-chemical alteration associated with SIC emplacement. The direction of the component is compatible with an age of about 1.8 to 1.9 Ga suggesting that the Penokean orogen is the most likely cause, if not the impact event. The paleomagnetism of the breccias, together with shatter cone orientation data, suggests that within 10 km of the SIC/basement contact, basement tilting to the southeast increases towards the SIC.