Seismic imaging of the enigmatic Sudbury Structure

Abstract

The Sudbury Structure on the southern margin of the Superior craton was created by a catastrophic explosion in 1.85 Ga and hosts one of the world's largest Ni‐Cu reserves. As a unique terrestrial geological feature, its genesis has been vigorously debated for more than a century. In an effort to optimize the image from seismic reflection data acquired across the center of the Sudbury Structure, we have developed a straight‐line common midpoint binning strategy and employed cross‐dip corrections. These pseudo‐three‐dimensional seismic processing techniques, coupled with standard processing methods, have overcome limitations associated with conventional two‐dimensional seismic data processing and have substantially enhanced the seismic image, warranting a more detailed and reliable structural interpretation. The new image has revealed a major, previously unrecognized, zone of imbricated NW thrusts. Interpretation of these thrusts provides critical timing constraints relating the Sudbury tectonic deformation to deposition of the Sudbury Basin sediments. The Onwatin argillites are penetrated by blind thrust faults, whereas the overlying Chelmsford turbidites are undeformed and most likely postdate the thrusting. Thus the uniform paleocurrent trends observed in the Chelmsford reflect subsequent deformation history and may be dismissed as evidence against an impact origin. Based on our interpretation of the seismic image, the original volume of the Sudbury Igneous Complex, likely an impact melt sheet, is ∼1 × 104 km3, supporting the claim that the Sudbury Structure represents the eroded and tectonized remanent of one of the largest known impact structure (∼200 km) on Earth.

Seismic methods in mineral exploration and mine planning: A general overview of past and present case histories and a look into the future

“…Lithoprobe was instrumental in establishing acquisition, processing, and interpretation approaches suitable for the hard-rock environment that is typical to several volcanogenic massive sulfide mining camps across Canada. This includes the Bathurst , Buchans (Spencer et al, 1993;Wright et al, 1994), Manitouwadge (Roberts et al, 2003), Matagami (Milkereit et al, 1992a;Adam et al, 1996Adam et al, , 1998Adam et al, , 2003Calvert and Li, 1999), Noranda (Adam et al, 1992;Verpaelst et al, 1995;Perron and Calvert, 1998), Selbaie (Milkereit et al, 1992b;Perron et al, 1997), Sudbury (White et al, 1994;Wu et al, 1995;Adam et al, 2000;Milkereit et al, 2000), and Thompson (White et al, , 2000 mining camps. During Lithoprobe, seismic reflection methods were proposed as a deep exploration tool that could improve the knowledge of structures and stratigraphy in existing mining camps, but also to provide drilling targets at depths beyond those achieved with conventional geophysical mining methods.…”

MT and reflection seismics in northwestern Skellefte Ore District, Sweden

“…CDP sorting was carried out over a straight line because it led to stronger and more continuous reflections than a slalom line (e.g., Wu et al, 1995;Rodriguez-Tablante et al, 2007). Different means of binning were tried to optimize the stack, as will be discussed in more detail in the next section.…”

“…It is present when the survey line is not perpendicular to the strike of the reflectors (Larner et al, 1979;Wu et al, 1995;Nedimović and West, 2003; O'Dowd et al, Table 2. Processing steps of the seismic reflection survey (see Figure 2).…”

“…The estimation of the necessary cross-dip angle ϕ i , can be done by visually inspecting stacked sections cross-dip corrected with different ϕ i (e.g., Wu et al, 1995;O'Dowd et al, 2004;Rodriguez-Tablante et al, 2007;Dehghannejad et al, 2010;Lundberg and Juhlin, 2011). In our case, because the azimuth of the CDP bins is not perpendicular to the staking line (see previous section), the transverse offset, Y ij , is not the shortest distance to the stacking line, but the distance along the rotated CDP bins.…”

In situ seismic measurements in borehole LB‐08A in the Bosumtwi impact structure, Ghana: Preliminary interpretation

“…The structures as delineated by seismic means depend on many variables such as the volume and extent of melt sheets, the amount of brecciation or damage, and the size of the structure. The number of seismological studies of impact structures has grown substantially over the last few years with studies at scales ranging from hundreds of kilometers over large impact structures such as Chicxulub in Mexico (Morgan et al 2000) and Sudbury (Wu et al 1995;Boerner et al 2000) to smaller structures such as the Mjølnir structure, which is 40 km in diameter (Dypvik et al 2004) in the Barents Sea, and the buried (but not yet confirmed to be an impact) Silverpit structure, which is ~10 km in diameter, that was well resolved in 3-D seismic images (Stewart and Allen 2005). The age range for these seismically studied structures extends from the 2.02 Gyr old Vredefort-Witwatersrand structure of South Africa (cf.…”