Timing constraints on deformation history of the Sudbury Impact Structure

Abstract

Herein, we present new high-resolution seismic images of the Sudbury Impact Structure, acquired across the Sudbury Igneous Complex and its environs, which provide evidence for the relative timing of the deformation events that reshaped the initial Sudbury Structure. The seismic images show that the lower unit of the Sudbury basinal fill sediments, the Onwatin argillite, is penetrated by a set of blind, imbricated thrusts, whereas the overlying Chelmsford turbidites are unaffected by faulting. We interpret this observation to mean that the deposition of the Chelmsford sediments postdates the latest major deformation of the Sudbury Structure, suggesting that the uniform paleocurrent trends observed in the Chelmsford turbidites are not related to the initial shape of the Sudbury Structure.Nous prksentons ici de nouvelles images sismiques de haute rCsolution de la structure d'impact de Sudbury, prClevCes en travers du Complexe ignC de Sudbury et ses environs; ces images fournissent des enseignements sur la pCriode relative des Cvknements de dCformation qui ont modifik la structure initiale de Sudbury. Les images sismiques rkvklent que I'unitC inferieure composCe des sCdiments de remplissage du bassin de Sudbury, l'argilite d'onwatin, est pCnCtrCe par un ensemble masquC de failles imbriquCes, tandis que les turbidites de Chelmsford sus-jacentes ne sont pas affectkes par les failles. Nous croyons que cette observation signifie que le dCpBt des skdiments de Chelmsford postdate la dernikre dCformation majeure de la structure de Sudbury, ce qui suggkre que les directions uniformes des palCocourants observkes dans les turbidites de Chelmsford ne sont pas likes i la morphologie initiale de la structure de Sudbury.[Traduit par la r6dactionlCan.

Crustal velocity structure of the Superior and Grenville provinces of the southeastern Canadian Shield

“…The observed times were checked to ensure that a proper distance range was used in calculating the values of Vo. This interpretation is in general agreement with the interpretation based on seismic reflection study of Wu et al (1994). However, in contrat to their mode1 which showed that the SIC is well elongated to the south, we interpret that the SIC, more or less, mimics the basinal structure shown in Fig In fact, the observed similarities in the high frequency fluctuations pattern between the free-air and the Bouguer gravity further indicates that this high frequency component is mainly caused by the near surface disturbances and not due to the effect of terrane's topography.…”

Structural evolution of the Sudbury impact structure in the light of seismic reflection data

“…A melt pond implies gravitational leveling, and is consistent with the observation that the composition (Naldrett, 1984) and isotopic signature of the SIC requires only contributions from crustal rocks (Grieve et al, 1991). Under this assumption, large-scale, non cylindrical folding may be the only means of obtaining a doubly plunging syncline exposing oblique sections through the thickness of the SIC (e.g., Cowan and Schwerdtner, 1994;Wu et al, 1994). This requirement for folding is not obviated by the structural mapping data that suggest some portion of the SIC might be intrusive (Cowan and Schwerdtner, 1997;Riller and Schwerdtner, 1997).…”

“…Perhaps 40% of the Onaping compression occurred as layer parallel shortening prior to buckling and the formation of the SRSZ (Hirt et al, 1993). While the layer parallel shortening is not visible in the seismic data, Wu et al (1994) showed strong evidence that brittle thrust faulting offsets the contact between the Onwatin and Onaping Formations (Fig. 6).…”

Comment on “Geophysical evidence for a large impact structure on the Falkland (Malvinas) Plateau”

“…() used a single profile of the sparse local seismic reflection data to support the crater hypothesis. While seismic reflection data can identify large impact structures (Morgan et al., ; Osinski & Spray, ; Poag, , ; Poag, Hutchinson, Colman, & Lee, ; Scott & Hajnal, ; Stewart & Allen, ; Wu, Milkereit, & Boerner, ), we argue that the seismic data they presented do not corroborate the crater hypothesis. Typically, impact craters identified on seismic data have the following features (French, ; French & Koeberl, ), none of which are convincingly seen in the seismic data: modest downward and inward displacements of the rocks at the crater margin; a complex ring fault system; structural disruption in a central zone, with incoherent seismic reflectors and evidence of preserved and continuous reflectors at depth. …”

“…Rocca et al (2017) used a single profile of the sparse local seismic reflection data to support the crater hypothesis. While seismic reflection data can identify large impact structures (Morgan et al, 1997;Osinski & Spray, 2005;Poag, 1996Poag, , 1997Poag, Hutchinson, Colman, & Lee, 1999;Scott & Hajnal, 1988;Stewart & Allen, 2005;Wu, Milkereit, & Boerner, 1994), we argue that the seismic data they presented do not corroborate the crater hypothesis. Typically, impact craters identified on seismic data have the following features (French, 1998;French & Koeberl, 2010), none of which are convincingly seen in the seismic data:…”