Observations and interpretations at Vredefort, Sudbury, and Chicxulub: Towards an empirical model of terrestrial impact basin formation

By analogy with Vredefort, this suggests that the larger estimates for the original final crater diameter of Sudbury may be overestimates.

“By analogy with Vredefort, this would suggest that the larger estimates for the original final crater diameter of Sudbury (e.g., Tuchscherer and Spray 2002;Spray et al. 2004) may be overestimates.”

• cites Tuchscherer and Spray 2002Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Spray et al. 2004 sourceSupported

At Chicxulub, drill holes C-1 and S-1 indicate impact-melt-bearing lithologies (suevitic breccia and impact-melt rock) of unknown thickness (>500 m) interior to the inner topographic ring.

“At Chicxulub, drill holes C-1 and S-1 indicate impactmelt-bearing lithologies (suevitic breccia and impact-melt rock) of unknown thickness (>500 m) interior to the inner topographic ring (e.g., Kring et al. 2004), which is consistent with the occurrence of the SIC interior to the postulated position of the inner topographic ring at Sudbury.”

• cites Kring et al. 2004 sourcePartly supported

  The Distribution and Thickness of Impact Melt and Melt-Bearing Breccias section (page unavailable) places Chicxulub-1 and Sacapuc-1 within the peak ring and reports polymict breccias overlying impact melt. It says the central melt sheet’s thickness is unknown and the boreholes indicate at least several hundred metres, but it does not establish the claimed lower bound of >500 m. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Concentric structures are evident in synoptic topographic data sets, such as from the Shuttle Radar Topography Mission (SRTM), over Vredefort.

“Concentric structures are also evident in synoptic topographic data sets, such as from the Shuttle Radar Topography Mission (SRTM), over Vredefort (Fig. 2).”

The comparison of observations/interpretations across Vredefort, Sudbury, and Chicxulub, assuming they originally had the same morphology, does not result in any major inconsistencies.

“This does not result in any major inconsistencies but requires that the observations be scaled spatially.”

The Huronian outliers west and north of the SIC lie between the 90 and 130 km diameter rings of Spray et al. (2004).

“The Huronian outliers west and north of the SIC lie between the 90 and 130 km diameter”

• cites Spray et al. (2004) sourceNot checked yet

  A check is scheduled.

The most distinct and continuous ring in the gravity data at Chicxulub is the outer edge of a gravity low at ~100 km diameter.

“The most distinct and continuous ring in the gravity data is the outer edge of a gravity low at ~100 km diameter.”

Topographic features corresponding to either the Landsat or Sudbury Breccia rings of Butler (1994) and Thompson and Spray (1994), respectively, are not obvious.

“Similarly, topographic features corresponding to either the Landsat or Sudbury Breccia”

• cites Butler (1994)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Thompson and Spray (1994)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Examination of 90 m resolution SRTM data of the Sudbury area reveals little in the form of arcuate features in the footwall of the North Range of the SIC.

“Examination of the 90 m resolution SRTM data of the Sudbury area reveals little in the form of arcuate features in the footwall of the North Range of the SIC.”

Even when illuminated from the center of the Sudbury Basin to emphasize arcuate topographic features, circumscribing impact-related residual topographic features are not evident at Sudbury beyond the outcrop pattern of the SIC itself.

“circumscribing impact-related residual topographic features are not evident at Sudbury beyond the outcrop pattern of the SIC itself.”

At the resolution of the seismic data, movements of crustal blocks on the scale of kilometers along discrete impact-induced and impact-reactivated structures do not appear to occur in the crystalline core of the Vredefort Dome.

“While there is a sense of movements of crustal blocks on the scale of kilometers along discrete impact-induced and impact-reactivated structures, at the resolution of the seismic data, this does not appear to be the case in the crystalline core of the Vredefort Dome.”

The relative position of the inward-dipping, outward-directed innermost Vredefort-derived thrusts are, in the case of Sudbury, close to the North Range-footwall contact.

“The relative position of the inward-dipping, outward-directed innermost”

The structural and lithological character of the topographic peak ring at Chicxulub is unknown.

“The structural and lithological character of the topographic peak ring is unknown.”

The inner peak ring is identified in the seismic data by a high-amplitude reflector with a rough surface that is onlapped by post-impact sedimentary fill.

“The inner peak ring is identified in the seismic data by a high-amplitude reflector with a rough surface that is onlapped by post-impact sedimentary fill (Fig. 10).”

Drill holes exterior to the Chicxulub inner topographic rim, Y-6 and Yax-1, indicate impact-melt-bearing lithologies ~100-500 m thick.

“Similarly, drill holes exterior to the inner topographic rim, Y-6 and Yax-1 (Figs. 8, 10, and 11), at Chicxulub also indicate the presence of impact-meltbearing lithologies (~100-500 m thick, e.g., Stöffler et al. 2004).”

• cites Stöffler et al. 2004 sourceNot checked — no full text of the source

The original center of the Sudbury Structure estimated here from scaling Vredefort observations lies south of the present South Range of the SIC, just west of the city of Sudbury.

“This center, so defined, lies south of the present position of the South Range of the SIC, just west of the city of Sudbury.”

Chicxulub has an observable final crater diameter in seismic data of ~180 km according to Turtle et al. (2005).

“Chicxulub has an”

• cites Turtle et al. (2005)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The location of the original center of the Sudbury Structure estimated here from scaling Vredefort observations is within a few kilometers (<5 km) of the original center estimated by Butler (1994) from lineament analysis.

“Interestingly, the location of the original center of the Sudbury Structure, as estimated here from scaling Vredefort observations, is within a few kilometers (<5 km) of the estimated location of the original center by Butler (1994), based on his lineament analysis.”

• cites Butler (1994)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

With the exception of some radial structures near Johannesburg, the concentric and tangential thrusts related to Vredefort formation lie within the estimated position of the original rim at Vredefort based on scaled Chicxulub data.

“With the exception of some radial structures in the far north, in the area of Johannesburg, the concentric and tangential thrusts related to the formation of the Vredefort structure lie within the estimated position of the original rim at Vredefort, based on the scaled Chicxulub data (Fig. 15).”

At Sudbury, the dominant lithology inward of the postulated peak-ring position is the Levack gneisses, which are granulite-facies gneisses partially retrograded to amphibolite facies.

“At Sudbury, the dominant lithology inward of the postulated position of the peak ring are the Levack gneisses (Fig. 13), which are granulite facies gneisses partially retrograded to amphibolite facies.”

Preliminary 40Ar-39Ar ages on amphibole separates from the Levack gneisses are consistent with decompression textures and retrograde amphibolite metamorphism being the result of uplift in the Sudbury impact event.

“Preliminary 40 Ar- 39 Ar ages on amphibole separates from the Levack gneisses are, however, consistent with the decompression textures and retrograde amphibolite metamorphism (James et al. 1992) being the result of uplift in the Sudbury impact event (N.Wodicka, Geological Survey of Canada, personal communication, 2003).”

• cites James et al. 1992Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites N.Wodicka, Geological Survey of Canada, personal communication, 2003Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Evidence from Vredefort indicates that transient cavity formation clearly exploited preexisting structures in the target rocks.

“the evidence from Vredefort indicates that transient cavity formation clearly exploited preexisting structures in the target rocks.”

The inner edge of the terrace zone lies directly beneath an inner peak ring on several seismic reflection profiles.

“The inner edge of the terrace zone lies directly beneath an inner peak ring on several seismic reflection profiles.”

Haughton data suggest a fault dip of around 60° closest to the surface, becoming more listric with depth.

“In agreement with this, the Haughton data suggest a fault dip of around 60° closest to the surface, becoming more listric with depth (Scott and Hajnal 1988).”

• cites Scott and Hajnal 1988 sourceNot checked — no full text of the source

The termination of the Matachewan dike magnetic signature coincides with the known termination of the radial Foy offset dike.

“The termination of the magnetic signature of the Matachewan dikes coincides with the known termination of the radial Foy offset dike (Fig. 6; Spray et al. 2004), which makes the suggestion that the termination of the magnetic signatures also marks the extent of the original impact-melt sheet an attractive working hypothesis (Pilkington and Hildebrand 2003).”

• cites Spray et al. 2004 sourceNot checked yet

Vredefort data indicate that motions in parautochthonous rocks of the true crater floor from transient cavity rim and wall collapse are along inward-dipping listric faults, at least at upper to middle crustal depths.

“Whatever the case, the Vredefort data clearly indicate that motions in the parautochthonous rocks of the true crater floor from transient cavity rim and wall area collapse are along inward-dipping, listric faults, at least at upper to middle crustal depths.”

The offset dikes at Sudbury have somewhat evolved and varying compositions.

“The offset dikes at Sudbury have somewhat evolved and varying compositions.”

Both Vredefort and Sudbury display the classic pattern of upturning of lithologies and exposure of deeper stratigraphic levels in parautochthonous crater-floor rocks as the center is approached.

“Both the Vredefort and Sudbury structures display the classic pattern of the upturning of lithologies and the exposure of deeper stratigraphic levels in the parautochthonous rocks of the crater floor, as the center of the structure is approached (Lana et al. 2003;Riller 2005;Wieland et al. 2005).”

• cites Lana et al. 2003 sourceNot checked — no full text of the source
• cites Riller 2005 sourceNot checked — no full text of the source
• cites Wieland et al. 2005 sourceNot checked — no full text of the source

The Chicxulub low-velocity zone can be traced to depths of ~7 km.

“The low velocity zone can be traced to depths of ~7 km.”

At Chicxulub, the inner topographic ring lies stratigraphically above and slightly inward of the last identifiable blocks of Cretaceous strata down-dropped cumulatively some 4-6 km during transient cavity rim collapse.

“At the higher stratigraphic levels of Chicxulub, the inner topographic ring lies stratigraphically above and slightly inward of the last identifiable blocks of Cretaceous strata down-dropped cumulatively some 4-6 km in the collapse of the transient cavity rim area.”

The inner Sudbury Basin has an erosion level similar to that of Chicxulub.

“The inner Sudbury Basin has an erosion level similar to Chicxulub.”

In the Vredefort Dome, planar mineral fabrics in the crystalline core are steep and similar to collar rocks only in the outermost part adjacent to the supracrustal collar.

“The planar mineral fabrics in the crystalline core are steep and similar to the attitude of the collar rocks only in the outermost part of the crystalline core of the Vredefort Dome, adjacent to the collar of supracrustal rocks.”

At mid-crustal levels exposed in the Vredefort crystalline core, movement appears to have been accomplished by cumulative small-scale differential rock displacements (shearing and rotation) facilitated by pervasive pseudotachylitic breccia veining and high postshock temperatures.

“At these levels, movement appears to have been accomplished by cumulative small-scale differential rock displacements (shearing and rotation) that is facilitated by pervasive pseudotachylitic breccia veining and high postshock temperatures (Lana et al. 2003;Dressler and Reimold 2004;Gibson and Reimold 2005).”

• cites Lana et al. 2003 sourceNot checked — no full text of the source
• cites Dressler and Reimold 2004 sourceNot checked — no full text of the source
• cites Gibson and Reimold 2005 sourceNot checked — no full text of the source

Exterior to the Sudbury Basin and the SIC, the erosional level at Sudbury is more comparable to that at Vredefort.

“Exterior to the Sudbury Basin and the SIC, the erosional level at Sudbury is more comparable to that at Vredefort.”

At Chicxulub, prominent reflectors with an inward dip of 30° run stratigraphically between the outer edge of the inner topographic ring and the inner edge of the last identifiable down-dropped Cretaceous block.

“There are a number of prominent reflectors (structures?) with an inward dip of 30°, which run stratigraphically between the outer edge of the inner topographic ring and the inner edge of the last identifiable down-dropped Cretaceous block at Chicxulub (Fig. 10; Brittan et al. 1999).”

• cites Brittan et al. 1999 sourceNot checked — no full text of the source

The major attributes of the model include a set of outward-directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor.

“a set of outward-directed thrusts in the parautochthonous rocks of the outermost environs of the crater floor”

Where the Vredefort structure is not covered by post-impact Karoo Supergroup cover rocks (in the north and west), remote-sensing imagery indicates radial and concentric features out to a radial distance of ~125 km.

“Where the structure is not covered by post-impact, Karoo Supergroup cover rocks, i.e., in the north and west, remotesensing imagery indicates radial and concentric features out to a radial distance of ~125 km (Phillips et al. 1999).”

• cites Phillips et al. 1999Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The rock displacements on the intermediate, inward and innermost, outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift.

“The rock displacements on the intermediate, inward and innermost, outward sets of structures are consistent with the assumption that a peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift.”

• AssumptionThe authors state this as an assumption: A peak ring will result from the convergence of the collapse of the transient cavity rim area and the collapse of the structural uplift.

Reasoned estimates of the amount of original structural uplift at Vredefort are 20-30 km.

“Reasoned estimates of the amount of original structural uplift and the apparent diameter of the Vredefort impact structure are 20-30 km and 250-300 km, respectively (Therriault et al. 1997;Gibson and Reimold 2001;Henkel and Reimold 1998).”

• cites Therriault et al. 1997Not checked — no full text of the source
• cites Gibson and Reimold 2001Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Henkel and Reimold 1998 sourceNot checked — no full text of the source

Vredefort has a small meteoritic component in impact-melt rocks as evidence for impact.

“evidence for a small meteoritic component in impact-melt rocks (Koeberl et al. 1996)”

• cites Koeberl et al. 1996Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The interpretation of offshore reflection seismic data leaves no doubt as to the existence of an inner topographic peak ring with a diameter of ~80 km at Chicxulub.

“the interpretation of offshore reflection seismic data leaves no doubt as to the existence of an inner topographic peak ring with a diameter of ~80 km at Chicxulub (Morgan andWarner 1999a and1999b;Turtle et al. 2005).”

• cites Morgan and Warner 1999a and 1999bNot matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Turtle et al. 2005Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Vredefort has coesite and stishovite as evidence for impact.

“the occurrence of coesite and stishovite (Martini 1978)”

• cites Martini 1978 sourceNot checked — no full text of the source

There has been some post-impact deformation at Vredefort, with shortening in a NW-SE direction in the outer regions.

“There has been some post-impact deformation at Vredefort, with shortening in a NW-SE direction in the outer regions.”

• cites Henkel and Reimold 1998 sourceNot checked — no full text of the source

Vredefort has shatter cones as evidence for impact.

“Evidence for impact includes shock metamorphic features such as shatter cones (e.g., Hargraves 1961)”

• cites Hargraves 1961Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

At Vredefort, McCarthy et al. (1986) noted a series of concentric anticlinal and synclinal structures that extend out to a diameter of some 300 km from the central uplifted core of basement rocks.

“At Vredefort, McCarthy et al. (1986) noted a series of concentric anticlinal and synclinal structures that extend out to a diameter of some 300 km from the central uplifted core of basement rocks.”

• cites McCarthy et al. 1986Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

More recent work has confirmed the extensive development of Vredefort-aged pseudotachylitic breccia throughout the northern and northwestern parts of the Witwatersrand Basin along bedding-parallel fault zones, such as the Ventersdorp Contact Reef (VCR).

“More recent work (e.g., Trieloff et al. 1994;Reimold and Colliston 1994) has confirmed the extensive development of Vredefort-aged pseudotachylitic breccia throughout the northern and northwestern parts of the Witwatersrand Basin along bedding-parallel fault zones, such as the Ventersdorp Contact Reef (VCR), the feature investigated by Killick et al. (1988).”

• cites Trieloff et al. 1994Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Reimold and Colliston 1994Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The model includes inward-directed motions along the same outermost structures and along a set of structures at intermediate radial distances during transient cavity collapse.

“inward-directed motions along the same outermost structures and along a set of structures, at intermediate radial distances, during transient cavity collapse”

The central area of Vredefort has only been mildly affected by post-impact deformation.

“The central area, (1986,1990).however, has only been mildly affected by post-impact deformation (Henkel and Reimold 1998).”

• cites Henkel and Reimold 1998 sourceNot checked — no full text of the source

Reasoned estimates of the apparent diameter of the Vredefort impact structure are 250-300 km.

“Reasoned estimates of the amount of original structural uplift and the apparent diameter of the Vredefort impact structure are 20-30 km and 250-300 km, respectively (Therriault et al. 1997;Gibson and Reimold 2001;Henkel and Reimold 1998).”

• cites Therriault et al. 1997Not checked — no full text of the source
• cites Gibson and Reimold 2001Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Henkel and Reimold 1998 sourceNot checked — no full text of the source

The three largest known terrestrial impact structures, Vredefort, Sudbury, and Chicxulub, all have some evidence for various expressions of ring forms.

“The three largest known terrestrial impact structures, Vredefort (South Africa), Sudbury (Canada), and Chicxulub (Mexico), all have some evidence for various expressions of ring forms.”

• cites McCarthy et al. 1986Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Spray et al. 2004 sourceNot checked yet
• cites Morgan and Warner 1999a and 1999bNot matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Vredefort has planar deformation features (PDFs) in quartz as evidence for impact.

“planar deformation features (PDFs) in quartz (e.g., Carter 1965; Leroux et al. 1994)”

• cites Carter 1965 sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

• cites Leroux et al. 1994 sourceNot checked — no full text of the source

Vredefort has shock deformation of zircon as evidence for impact.

“shock deformation of zircon (Kamo et al. 1996;Reimold et al. 2002)”

• cites Kamo et al. 1996 sourceNot checked — no full text of the source
• cites Reimold et al. 2002 sourceNot checked — no full text of the source

Some of the outward-directed thrusts are pre-existing structures that have been reactivated during transient cavity formation.

“some of which are pre-existing structures that have been reactivated during transient cavity formation”

The Rand Anticline marks the limit of the occurrence of substantial pseudotachylitic and cataclastic breccias believed, because of geochronological data and their massive occurrence, to be associated with the Vredefort structure.

“The Rand Anticline also marks the limit of the occurrence of substantial pseudotachylitic and cataclastic breccias believed, because of geochronological data and their massive occurrence, to be associated with the Vredefort structure (Reimold and Gibson 2005).”

• cites Reimold and Gibson 2005Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

At Chicxulub, there are ring structures in the potential field geophysical data that have been related to crater structure.

“At Chicxulub, there are ring structures in the potential field geophysical data that have been related to crater structure.”

• cites Pilkington et al. 1994 sourceNot checked — no full text of the source
• cites Espindola et al. 1995 sourceNot checked — no full text of the source
• cites Sharpton et al. 1996 sourceNot checked — no full text of the source

Slickenslide orientations in the thrusts in the northwest quadrant of the Basin indicate an overall radial direction of movement with respect to the center of the Vredefort Dome.

“Slickenslide orientations in the thrusts in the northwest quadrant of the Basin clearly indicated an overall radial direction of movement, with respect to the center of the Vredefort Dome.”

• cites Brink et al. 1997 sourceNot checked — no full text of the source

Similar-sized structures identified in radar imagery of Venus, which has a surface gravity close to that of the Earth, are classified as multi-ring structures.

“similar-sized structures identified in radar imagery of Venus, which has a surface gravity close to that of the Earth, are classified as multi-ring structures (e.g., Alexopolous and McKinnon 1994).”

• cites Alexopolous and McKinnon 1994Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The model includes structural uplift in the center followed by a final set of radially outward-directed thrusts at the outer edges of the structural uplift during uplift collapse.

“structural uplift in the center followed by a final set of radially outward-directed thrusts at the outer edges of the structural uplift, during uplift collapse”

The effects of the Vredefort impact structure encompass the entire Witwatersrand Basin and the associated world-class goldfields.

“At such a size, the effects of the Vredefort impact structure encompass the entire Witwatersrand Basin and the associated world-class goldfields (Grieve 2005;Reimold et al. 2005).”

• cites Grieve 2005 sourceNot checked — no full text of the source
• cites Reimold et al. 2005Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Lana et al. (2003) failed to identify fault-bounded blocks in the crystalline core at Vredefort.

“Although exposures are limited , Lana et al. (2003) failed to identify fault-bounded blocks in the crystalline core at Vredefort.”

• cites Lana et al. (2003) sourceNot checked — no full text of the source

Due to burial and relatively flat topography of the Chicxulub area (<50 m elevation difference over 150 km), SRTM data do not lend themselves to the type of processing and interpretation carried out for Vredefort and Sudbury.

“Due to burial and the relatively flat topography of the area (<50 m elevation difference over a distance of 150 km), the SRTM data do not lend themselves to the type of processing and interpretation that was carried out for Vredefort and Sudbury.”

The Foch Thrust Zone indicates at least two generations of movement, initially outward and then inward.

“These inner structures are surrounded by thrusts or thrusts with splayed and converging faults (the Foch Thrust Zone in the terminology of Brink et al. 1997) that indicate at least two generations of movement (Fletcher and Reimold 1989), initially outward and then inward (Ellis and Reimold 1999).”

• cites Fletcher and Reimold 1989Not checked — no full text of the source
• cites Ellis and Reimold 1999Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Given that the collar rocks at Vredefort display the expected steep dips observed in structural uplifts at other smaller terrestrial complex craters, the sub-horizontal mineral fabrics in the center of the crystalline core are likely a primary function of some additional aspect of the structural uplift process at Vredefort.

“Given that the collar rocks at Vredefort display the expected steep dips that are observed in structural uplifts at other smaller terrestrial complex craters, the sub-horizontal mineral fabrics in the center of the crystalline core are likely a primary function of some additional aspect of the structural uplift process at Vredefort.”

The current geological situations at Sudbury and Vredefort are not directly comparable.

“The current geological situations at Sudbury and Vredefort, however, are not directly comparable.”

The Sudbury structure has been extensively tectonized following the impact.

“The structural situation is further complicated by the fact that the Sudbury structure has been extensively tectonized following the impact (Riller 2005;Klimczak et al. 2007).”

• cites Riller 2005 sourceNot checked — no full text of the source
• cites Klimczak et al. 2007 sourceNot checked — no full text of the source

The lack of observable arcuate impact-related features at Sudbury is ascribed to the effects of post-impact tectonism and, more importantly, glacial sculpting to form the current surface.

“The lack of observable arcuate impact-related features is ascribed to the effects of post-impact tectonism and, more importantly, glacial sculpting to form the current surface.”

Although there is a large proprietary database on Sudbury held by industry, it is much more spatially limited than at Vredefort.

“Thus, although there is a large proprietary database on Sudbury held by industry, it is much more spatially limited than at Vredefort.”

The originally deepest rocks of the crystalline core of the Vredefort Dome are from mid-crustal levels.

“The originally deepest rocks of the crystalline core of the Vredefort Dome are from mid-crustal levels (Lana et al. 2003)”

• cites Lana et al. 2003 sourceNot checked — no full text of the source

The only clear expression of the onshore portion of the Chicxulub structure is a semi-circular ring of sinkholes (cenotes), with a diameter of ~160 km.

“The only clear expression of the onshore portion of the structure is a semi-circular ring of sinkholes (cenotes), with a diameter of ~160 km (Pope et al. 1993).”

• cites Pope et al. 1993 sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

The local term Sudbury Breccia encompasses a variety of breccia types, including clastic and pseudotachylitic breccias, as well as breccias that have been recrystallized due to the thermal metamorphic effects of the SIC.

“Although sometimes referred to as pseudotachylite (Thompson and Spray 1994), the local term Sudbury Breccia encompasses a variety of breccia types, including clastic and pseudotachylitic breccias, as well as breccias that have been recrystallized due to the thermal metamorphic effects of the SIC (Müller-Mohr 1992;Rousell et al. 2003).”

• cites Thompson and Spray 1994Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Müller-Mohr 1992Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Rousell et al. 2003 sourceNot checked — no full text of the source

Due to the high degree of post-impact tectonization in the South Range of the SIC, observations in the footwall outside the North Range offer the best opportunity to decipher impact-related structures.

“Due to the high degree of post-impact tectonization in the South Range of the SIC, observations in the footwall outside the North Range offer the best opportunity to decipher impact-related structures.”

Argon-argon dating of impact-melt rock from Chicxulub and tektite-like glasses from Cretaceous-Tertiary boundary sediments indicates they are coeval, with an age of ~65 Ma.

“Argon-argon dating of impact-melt rock from Chicxulub, obtained in the course of exploration drilling for hydrocarbons, and of tektite-like glasses from Cretaceous-Tertiary boundary sediments, indicates that they are coeval, with an age of ~65 Ma (Swisher et al. 1992).”

• cites Swisher et al. 1992 sourceNot checked — no full text of the source

The north and west quadrants of Vredefort have no covering by post-impact (180-250 Ma) Karoo Supergroup sedimentary rocks.

“This is also the area where there is no covering by post-impact (180-250 Ma) Karoo Supergroup sedimentary rocks.”

The SIC represents the differentiated impact-melt sheet within the impact structure.

“It is now widely accepted that the SIC represents the differentiated impact-melt sheet within the impact structure (Grieve et al. 1991;Dickin et al. 1999;Therriault et al. 2002).”

• cites Grieve et al. 1991 sourceNot checked — no full text of the source
• cites Dickin et al. 1999 sourceNot checked — no full text of the source
• cites Therriault et al. 2002 sourceNot checked — no full text of the source

The preservation and structural character of the Huronian outliers are more consistent with being originally in the final annular trough, where they would be preserved from erosion due to down-faulting during transient cavity modification.

“Their preservation and structural character are more consistent with being originally in the final annular trough (Dence et al. 1977), where they would be preserved from erosion due to down-faulting during transient cavity modification.”

• cites Dence et al. 1977Not checked — no full text of the source

Deformation and folding of the SIC has resulted in the preservation of the entire impact sequence from the parautochthonous, locally brecciated, target rocks of the crater floor, through the impact-melt sheet (SIC), to the postimpact sediments within the central Sudbury Basin.

“This deformation and folding of the SIC has resulted in the preservation of the entire impact sequence from the parautochthonous, locally brecciated, target rocks of the crater floor, through the impact-melt sheet (SIC), to the postimpact sediments within the central Sudbury Basin.”

Potential field modelling at Sudbury has been largely in the form of two-dimensional profiles along the LITHOPROBE transect.

“Although there has been some potential field modelling at Sudbury, it has been largely in the form of two-dimensional profiles along the LITHOPROBE transect.”

This is generally inconsistent with the Spray et al. (2004) interpretation, which places these Huronian outliers radially between the trace of the collapsed transient cavity rim (130 km) and the structural uplift (90 km).

“This is generally inconsistent with the Spray et al. (2004) interpretation, which places these Huronian outliers radially between the trace of the collapsed transient cavity rim (130 km) and the structural uplift (90 km).”

• cites Spray et al. (2004) sourceNot checked yet

A north-south reflection seismic traverse across the SIC and the Sudbury Basin, in the course of a LITHOPROBE transect, indicated significant northwest thrusting of the South Range of the SIC.

“The extent of this post-impact deformation was only appreciated following a north-south reflection seismic traverse across the SIC and the Sudbury Basin, in the course of a LITHOPROBE transect, which indicated significant northwest thrusting of the South Range of the SIC (e.g., Milkereit et al. 1992;Boerner et al. 2000).”

• cites Milkereit et al. 1992Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Boerner et al. 2000 sourceNot checked — no full text of the source

The general interpretation of the published literature is largely supported, with slight differences, by a detailed confidential report from the industry.

“This general interpretation of the published literature is largely supported, with slight differences, by a detailed confidential report from the industry (S. Ellis, personal communication, 2005), which is based on the interpretation of reflection seismic and potential field data, constrained by geologic and drill hole information.”

• cites S. Ellis, personal communication, 2005Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The original final crater diameter at Sudbury is estimated to have been ~130-180 km.

“Turtle et al. (2005) estimated the original final crater diameter at Sudbury to have been ~130-180 km.”

• cites Turtle et al. (2005)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Where pre-existing structures were more radial, motions induced by the Vredefort event were more strike-slip than thrusting.

“In cases where pre-existing structures were more radial, e.g., the Bank and West Rand Faults in the north (Fletcher and Reimold 1989) or the Sugarbush Fault in the east (Brink et al. 1997), motions induced by the Vredefort event were more strike-slip than thrusting.”

• cites Fletcher and Reimold 1989Not checked — no full text of the source
• cites Brink et al. 1997 sourceNot checked — no full text of the source

Extensive ductile shearing and brittle faulting corresponds at the surface to the South Range Shear Zone.

“This extensive ductile shearing and brittle faulting corresponds at the surface to the South Range Shear Zone (Fig. 5; Shanks and Schwerdtner 1991;Riller et al. 1998).”

• cites Shanks and Schwerdtner 1991 sourceNot checked — no full text of the source
• cites Riller et al. 1998Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

A shallow attitude of post-impact structures in the center of eroded and exposed structural uplifts is not a feature of smaller terrestrial complex craters, e.g., at Gosses Bluff.

“Such a shallow attitude of post-impact structures in the center of eroded and exposed structural uplifts is not a feature of smaller terrestrial complex craters, e.g., at Gosses Bluff (Milton et al. 1996).”

• cites Milton et al. 1996Not checked — no full text of the source

In general, differentiation between preimpact and impact-induced deformation is not possible in the geophysical data at Sudbury.

“Unfortunately, in general, differentiation between preimpact and impact-induced deformation is not possible in the geophysical data at Sudbury (Boerner et al. 2000).”

• cites Boerner et al. 2000 sourceNot checked — no full text of the source

The lack of evident arcuate features at Sudbury is most likely due to preferential erosional effects of glaciation, particularly with respect to linear faults and dikes.

“This is most likely due to the preferential erosional effects of glaciation, particularly with respect to linear faults and dikes (Fig. 7).”

The age of the Sudbury impact event is ~1.85 Ga.

“The age of the Sudbury impact event is ~1.85 Ga (Krogh et al. 1984).”

• cites Krogh et al. 1984Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

There is a progressive increase in recorded postimpact temperatures from ~300 °C in the outer collar rocks to >700 °C, and locally as high as 1000 °C, in the central core of the Vredefort Dome, due to the geothermal gradient prior to impact-induced uplift and shock heating.

“there is a progressive increase in recorded postimpact temperatures from ~300 °C in the outer collar rocks to >700 °C, and locally as high as 1000 °C, in the central core due to the geothermal gradient prior to impact-induced uplift and shock heating (Gibson et al. 1998;Gibson 2002;Gibson and Reimold 2005).”

• cites Gibson et al. 1998Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Gibson 2002 sourceNot checked — no full text of the source
• cites Gibson and Reimold 2005 sourceNot checked — no full text of the source

Potential field modelling at Sudbury was designed more to determine whether models of the potential field data were compatible with the seismic interpretation than as an independent set of interpretations.

“They were also designed more to determine whether or not models of the potential field data were compatible with the seismic interpretation than as an independent set of interpretations (e.g., McGrath and Broome 1994).”

• cites McGrath and Broome 1994 sourceNot checked — no full text of the source

These high temperatures may have assisted in mechanical strength degradation during structural uplift and modification at Vredefort.

“These high temperatures may have also assisted in mechanical strength degradation during structural uplift and modification.”

External to the folded SIC and the Sudbury Basin, erosion has removed essentially all allochthonous impact lithologies, except the Sudbury Breccia and several radial and concentric dikes of impact melt (offset dikes), and exposed the parautochthonous rocks of the crater floor.

“External to the folded SIC and the Sudbury Basin, however, erosion has removed essentially all allochthonous impact lithologies, except the so-called Sudbury Breccia and several radial and concentric dikes of impact melt (offset dikes), and exposed the parautochthonous rocks of the crater floor (Dressler 1984).”

• cites Dressler 1984Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

At the Potchefstroom Fault, reactivation by the Vredefort impact event resulted in strike-slip motions.

“There are some exceptions, however, such as the Potchefstroom Fault, where the orientations of pre-existing structures were such that their reactivation by the Vredefort impact event resulted in strikeslip motions.”

• cites Brink et al. 1997 sourceNot checked — no full text of the source

Outward thrusting in the inner zone (Ensels Thrust Zone) around the Vredefort Dome occurred after the uplift and local overturning of the collar rocks around the basement core.

“They also noted that outward thrusting in the inner zone (so-called Ensels Thrust Zone; Fig. 3) around the Vredefort Dome occurred after the uplift and local overturning of the collar rocks around the basement core, an observation also made by Simpson (1978).”

• cites Brink et al. 1997 sourceNot checked — no full text of the source
• cites Simpson 1978Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

There is evidence for more than one generation of Sudbury Breccia, which have been equated with both the transient cavity formation and subsequent modification stages of crater formation.

“As at Vredefort, there is evidence for more than one generation of Sudbury Breccia, which have been equated with both the transient cavity formation and subsequent modification stages of crater formation (Thompson and Spray 1994).”

• cites Thompson and Spray 1994Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Initial outward-directed thrusting exploited pre-existing structures tangential to the center of Vredefort.

“In some cases, this initial outward-directed thrusting exploited pre-existing structures tangential to the center of Vredefort.”

It is possible that the difference in pseudotachylitic breccia zones between Sudbury and Vredefort may be more apparent than real.

“Given the relatively arbitrary spacing of three out of the four”

• cites Spray et al. (2004) sourceNot checked yet

Forward modelling of the potential field data at Vredefort does not provide the level of detail on structural features afforded by the reflection seismic data.

“Although forward modelling of the potential field data at Vredefort has been used to constrain the impact event and the extent of impact-related crustal movements at the regional scale (Henkel and Reimold 1998), they do not provide the level of detail on structural features afforded by the reflection seismic data.”

• cites Henkel and Reimold 1998 sourceNot checked — no full text of the source

There are a series of circumferential thrusts around the basement core at Vredefort.

“Thus, the public domain literature can be summarized as cumulatively indicating that there are a series of circumferential thrusts around the basement core at Vredefort.”

The industry report shows more complexity than noted in the earlier public domain work of Brink et al. (1997, 2000).

“In this industry report, there is clearly more complexity than noted in the earlier public domain work of Brink et al. (1997Brink et al. ( , 2000)).”

• cites S. Ellis, personal communication, 2005Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The arrangement of a structurally uplifted central area surrounded by a synclinal feature in which there is evidence for movement towards the center is common to both Sudbury and Vredefort.

“Similarly, the arrangement of a structurally uplifted central area surrounded by a synclinal feature in which there is evidence for movement towards the center is common to both structures.”

The presence of pseudotachylitic breccia suggests that the Benny Belt and Pumphouse shear zones were (re)activated as a consequence of the impact at Sudbury.

“Although Boerner and Milkereit (1999) proposed that structures such as the Benny Belt and Pumphouse shear zones pre-date the impact, the presence of pseudotachylitic breccia suggests that these shear zones were (re)activated as a consequence of the impact at Sudbury (Fueten et al. 1992).”

• cites Fueten et al. 1992Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Boerner and Milkereit 1999 sourceNot checked — no full text of the source

The amount of erosion since the Sudbury impact event is estimated at 5-6 km for the parautochthonous basement rocks north of the SIC.

“The amount of erosion that has taken place since the impact event is estimated at 5-6 km for the parautochthonous basement rocks north of the SIC (Thompson et al. 1998), similar to the lower estimate at Vredefort.”

• cites Thompson et al. 1998Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

It is difficult to assess the true independence of the estimated Chicxulub melt-sheet thickness from the known SIC thickness.

“Although the geophysical modelling includes both potential field and seismic data, it is difficult to assess the true independence of the estimated melt sheet thickness in the interior basin at Chicxulub based on geophysics from the known thickness of the SIC.”

The short-wavelength, high-amplitude magnetic anomalies (<90 km in diameter) at Chicxulub are modeled as local magnetized zones at depths of 1-1.5 km, due to magnetic sources at the top of the impact-melt sheet and/or suevitic breccias.

“The short-wavelength, high-amplitude anomalies (<90 km in diameter) are modeled as local magnetized zones at depths of 1-1.5 km, due to magnetic sources at the top of the impact-melt sheet and/or suevitic breccias (Pilkington and Hildebrand 2000).”

• cites Pilkington and Hildebrand 2000 sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

The model by Hildebrand et al. (1998) may be too complex in detail given the relative paucity of measured densities and density contrasts at Chicxulub.

“Given the relative paucity of measured densities and density contrasts at Chicxulub, the model by Hildebrand et al. (1998) may be too complex in detail.”

• cites Hildebrand et al. 1998 sourceNot checked — no full text of the source

There is a degree of overall coherency with respect to the original spatial arrangement of target lithologies despite differential movements.

“Although there are clearly differential movements, the sense is of a degree of overall coherency with respect to the original spatial arrangement of the target lithologies.”

Unlike Vredefort and Sudbury, Chicxulub has topographic features corresponding to the original rim, annular trough, inner peak ring, and central basin.

“Unlike Vredefort and Sudbury, however, Chicxulub has topographic features corresponding to the original rim, annular trough, inner peak ring, and central basin.”

The radial termination of the Matachewan dike magnetic signatures at 130 km diameter at Sudbury is consistent with the estimated original final crater diameter of 150 km for Sudbury based on Chicxulub scaling.

“In the case of Sudbury, the radial termination of the magnetic signatures of the Matachewan dikes at 130 km diameter (Fig. 6) is consistent with the estimated original final crater diameter of 150 km for Sudbury, based on scaling of the relative location of the inner topographic ring and final crater diameter from Chicxulub.”

As this is close to the diameter of the inner topographic ring, it suggests a potential role for the structural uplift in inner ring formation.

“As this is close to the diameter of the inner topographic ring, it suggests a potential role for the structural uplift in inner ring formation.”

The hydrocode model of Collins et al. (2002) for peak-ring formation indicates that the outward collapsing structural uplift overrides the inward collapsing transient cavity rim area to form an inner topographic peak.

“The hydrocode model of Collins et al. (2002) for peakring formation indicates, specifically, that the outward collapsing structural uplift overrides the inward collapsing transient cavity rim area to form an inner topographic peak.”

• cites Collins et al. 2002 sourceNot checked — no full text of the source

The extension and scaling of the inner ring assumption for Vredefort to Sudbury would place such an inner ring immediately exterior to the North Range of the SIC.

“The extension and scaling of this assumption for Vredefort to Sudbury would place such an inner ring immediately exterior to the North Range of the SIC (Fig. 13).”

• AssumptionThe authors state this as an assumption: An inner ring exists at Vredefort and Sudbury.
• AssumptionThe authors state this as an assumption: Such an inner ring is, in principle, the result of the convergence of inward and outward displaced materials during transient cavity modification.

Observations at terrestrial complex impact structures, where parautochthonous rocks of the structural uplift are exposed at the level of the crater floor or below (including Vredefort and Sudbury), do not indicate a wide, identifiable megabreccia zone surrounding a core of more coherent uplifted basement.

“Observations at terrestrial complex impact structures, where the parautochthonous rocks of the structural uplift are exposed at the level of the crater floor or below (including Vredefort and Sudbury), do not indicate a wide, identifiable megabreccia zone surrounding a core of more coherent uplifted basement.”

Preexisting structures tangential to radial motions in transient cavity formation developed into thrusts, accomplishing outward-directed material displacements.

“In particular, preexisting structures tangential to the radial motions in transient cavity formation developed into thrusts, accomplishing outward-directed material displacements.”

The postulated inner-ring position at Sudbury is generally consistent with the current spatial distribution of deeper structural-uplift and shallower transient-cavity-rim parautochthonous lithologies in the footwall of the North Range of the SIC.

“Thus, the postulated position of the inner ring at Sudbury is generally consistent with the current spatial distribution of”

None of the drill holes Y-6, S-1, and C-1 provide constraints on the nature of the peak ring at Chicxulub.

“Therefore, none of these drill holes provide constraints on the nature of the peak ring at Chicxulub.”

The drilling information indicates that impact-melt lithologies occur both within the inner crater basin and radially beyond the peak ring.

“Although the drilling information does not constrain the nature of the topographic peak ring, they do indicate that impact-melt lithologies occur both within the inner crater basin and radially beyond the peak ring.”

Based on scaling from Chicxulub, the estimated original final crater diameter at Vredefort is ~180 km.

“Based on this approach, the estimated original final crater diameter, according to the definition of Turtle et al. (2005), at Vredefort is ~180 km.”

• cites Turtle et al. (2005)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Based on Chicxulub observations, the original impact-melt-bearing lithologies at Sudbury (now the SIC) would have extended beyond the original inner peak ring to at least a diameter of 120-130 km.

“Based on these observations, the original impact-melt bearing lithologies (now represented only by the SIC) at Sudbury would have extended beyond the original inner peak ring to, at least, a diameter of 120-130 km.”

Impact-generated and impact-reactivated structures related to outward motions during transient cavity formation and inward motions during modification should largely lie within the final crater diameter.

“This is a broadly consistent picture, as the impact-generated and impactreactivated structures related to outward motions during transient cavity formation and inward motions related to transient cavity modification should largely lie within the final crater diameter.”

The marine seismic transects of Chicxulub are not comparable in the level of detail and subsequent interpretation to the numerous land transects at Vredefort, which are tied to both surface and subsurface geological observations.

“Furthermore, the marine seismic transects of Chicxulub are not comparable in the level of detail and subsequent interpretation to the numerous land transects at Vredefort, which are tied to both surface and subsurface geological observations.”

If seismically imaged structures exterior to the Chicxulub rim are similarly scaled, the outer limit of impact-related deformation at Vredefort is ~300 km in diameter, corresponding to apparent rim diameter estimates of Therriault et al. (1997) and Henkel and Reimold (1998).

“If the seismically imaged structures exterior to the rim at Chicxulub are similarly scaled, the outer limit of impact-related deformation at Vredefort is ~300 km in diameter, which corresponds to the apparent rim diameter estimates of Therriault et al. (1997) and Henkel and Reimold (1998), using the definitions of Turtle et al. (2005).”

• cites Therriault et al. (1997)Not checked — no full text of the source
• cites Henkel and Reimold (1998) sourceNot checked — no full text of the source
• cites Turtle et al. (2005)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The major motions in transient cavity formation are perceived as discrete packages of target rocks with scales of several kilometers.

“The perception of the major motions in this process is as discrete packages of target rocks, with scales of several kilometers.”

The ~300 km apparent diameter estimate corresponds to the estimate of the outer limit of deformation related to Vredefort according to Turtle et al. (2005).

“This estimate of ~300 km in apparent diameter corresponds to the estimate of the outer limit of deformation related to Vredefort, according to Turtle et al. (2005).”

• cites Turtle et al. (2005)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Observations and interpretations at individual structures and their integration are generally consistent with the two model assumptions.

“Although there is no single proof, observations and interpretations at the individual structures, and the results when these are extended and integrated between structures, as outlined above, are generally consistent with these assumptions.”

• AssumptionThe authors state this as an assumption: All three structures (Vredefort, Sudbury, and Chicxulub) initially had the same form, including an inner topographic peak ring.
• AssumptionThe authors state this as an assumption: The topographic peak ring reflects convergence of inward-moving material from collapse of the transient cavity rim and wall area and outward-moving material from collapse of an over-heightened structural uplift during the modification stage of cratering.

The Sudbury original final crater diameter estimate is the least constrained because of extensive post-impact deformation.

“The Sudbury estimate is the least constrained, because of the extensive post-impact deformation.”

Based on Chicxulub observations and Sudbury interpretation of original impact-melt sheet diameter, scaling to Vredefort suggests the original melt sheet at Vredefort was ~145-155 km in diameter.

“Based on the observations at Chicxulub and the interpretation from Sudbury, regarding the original diameter of the impact-melt sheet, scaling to Vredefort suggests that the original melt sheet at Vredefort was ~145-155 km in diameter.”

Scaling the postulated inner-ring position from Chicxulub to Sudbury yields an estimated original final crater diameter at Sudbury of ~150 km.

“If the postulated position of the inner ring, derived from Chicxulub, is used to also scale, from Chicxulub, a position for the original final crater diameter at Sudbury, the estimated final crater diameter is ~150 km.”

Spray et al. (2004) observed that the magnetic signature of the pre-impact 2.47 Ga Matachewan dike swarm terminates at a diameter of 130 km in the North Range footwall at Sudbury.

“As noted earlier, Spray et al. (2004) observed that the magnetic signature of the pre-impact, 2.47 Ga Matachewan dike swarm terminates at a diameter of 130 km in the North Range footwall at Sudbury.”

• cites Spray et al. (2004) sourceNot checked yet

The topographic peak ring is coincident at its outer margin with an inward dipping, low-velocity-zone (LVZ) in the seismic data, where the overall P-wave velocity contrast with the surrounding rocks is 100-500 m s-1, between depths of 1 and 7 km.

“It is coincident at its outer margin with an inward dipping, low-velocity-zone (LVZ) in the seismic data (Fig. 11), where the overall P-wave velocity contrast with the surrounding rocks is 100-500 m s -1 , between the depths of 1 and 7 km (Morgan et al. 2000).”

• cites Morgan et al. 2000 sourceNot checked — no full text of the source

Similar composition of pseudotachylitic breccia veins and host rocks and relatively minor displacements (generally <0.5 m) across such veins at Sudbury and Vredefort argue against major individual motions at smaller scales.

“The similar composition of pseudotachylitic breccia veins and their host rocks and the observation of relatively minor displacements (generally less than 0.5 m) across such veins at Sudbury and Vredefort would, however, seem to argue against major individual motions at smaller scales (Dressler and Reimold 2004).”

• cites Dressler and Reimold 2004 sourceNot checked — no full text of the source

Recent numerical calculations by Ugalde et al. (2005) indicate complete destruction of magnetic signatures of synthetic vertical magnetic dikes due to thermal and shock effects out to a radial distance approaching the final rim of their model craters.

“Recent numerical calculations by Ugalde et al. (2005), with synthetic vertical magnetic dikes, indicate the complete destruction of their magnetic signature due to thermal and shock effects out to a radial distance approaching the final rim of their model craters.”

• cites Ugalde et al. (2005)Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

The structural data from Vredefort suggest that the most likely manifestation of the location of an inner ring, at the current level of erosion, is at the convergence of movements between the outward-directed, inward-dipping thrusts of the inner zone surrounding the Vredefort Dome and the inward-directed, outward-dipping reverse faults at intermediate radial distances in the industry data.

“In this context, the structural data from Vredefort would suggest that the most likely manifestation of the location of such a ring, at the current level of erosion, is at the convergence of movements between the outward-directed, inward-dipping thrusts of the inner zone surrounding the Vredefort Dome (Ensels Thrust Zone in the terminology of Brink et al. 1997Brink et al. , 2000) ) and the inward-”

• cites Brink et al. 1997 sourceNot checked — no full text of the source
• cites Brink et al. 2000 sourceNot checked — no full text of the source

• AssumptionThe authors state this as an assumption: An inner ring exists at Vredefort and Sudbury.

The ~150 km Sudbury estimate is apparently consistent with an earlier estimate of 150-200 km.

“This estimate is apparently consistent with an earlier estimate of 150-200 km (Grieve et al. 1991).”

• cites Grieve et al. 1991 sourceNot checked — no full text of the source

The ~180 km Vredefort final crater diameter estimate is closer to the Turtle and Pierazzo (1998) model crater diameter of 120-200 km.

“This estimate of the final crater diameter for Vredefort is closer to that of the model crater diameter of Turtle and Pierazzo (1998) of 120-200 km.”

• cites Turtle and Pierazzo (1998) sourceNot checked — no full text of the source

The peak of the inner topographic ring imaged in the seismic data has an average diameter of ~80 km.

“The peak of the inner topographic ring (arrow in Fig. 10) imaged in the seismic data has an average diameter of ~80 km (Morgan et al. 1997;Morgan andWarner 1999a and1999b).”

• cites Morgan et al. 1997 sourceNot checked — no full text of the source
• cites Morgan and Warner 1999a and 1999bNot matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

Radial motions from structural uplift collapse occur, at least in later stages, by discontinuous deformation along specific dislocations.

“The radial motions from structural uplift collapse occur, at least in their later stages, by discontinuous deformation along specific dislocations.”

Following structural uplift and cavity modification, transient cavity floor material will fail to be manifested as a topographic central peak because it has no mechanical strength and cannot form a positive topographic feature.

“Following structural uplift and cavity modification, this material of the transient cavity floor will fail to be ultimately manifested as a topographic central peak, as it has no mechanical strength and can not result in a positive topographic feature.”

The composite empirical model, heavily influenced by Vredefort structural interpretations, differs in one detail from hydrocode models.

“The composite empirical model, which is heavily influenced by the structural interpretations at Vredefort, does differ in one detail from the results of hydrocode models.”

A principle facet of the model is the extent to which block movements in formation and modification of the transient cavity rim area exploited preexisting structures in target rocks.

“Another principle facet of the model is the extent to which block movements in the formation and modification of the transient cavity rim area exploited preexisting structures in the target rocks.”

Under the initial assumption of original form, the Vredefort/Sudbury pattern is consistent with the model assumption that structural uplift participates in forming an inner topographic ring, as suggested by hydrocode calculations.

“Under the basic initial assumption of the original form of these structures, this is consistent with the model assumption that structural uplift is an intimate participant in the physical process(es) that result in an inner topographic ring, as suggested by recent hydrocode calculations (e.g., Collins et al. 2002;Ivanov 2005).”

• cites Collins et al. 2002 sourceNot checked — no full text of the source
• cites Ivanov 2005 sourceNot checked — no full text of the source

• AssumptionThe authors state this as an assumption: All three structures (Vredefort, Sudbury, and Chicxulub) initially had the same form, including an inner topographic peak ring.
• AssumptionThe authors state this as an assumption: The topographic peak ring reflects convergence of inward-moving material from collapse of the transient cavity rim and wall area and outward-moving material from collapse of an over-heightened structural uplift during the modification stage of cratering.

Observations and interpretations regarding peak-ring formation at Vredefort and Chicxulub are broadly compatible with the representation of the same process.

“The observations and interpretations regarding the process of peak ring formation at Vredefort and Chicxulub are broadly compatible with the representation of the same process.”

Evidence for later-stage outward motions manifest as inward-dipping thrusts in the outer structural uplift at Vredefort is generally not observed at smaller terrestrial complex impact structures.

“Similarly, the evidence for the later-stage outward motions manifest in the outer portion of the structural uplift as inward-dipping thrusts, such as those at Vredefort, is generally not observed at smaller terrestrial complex impact structures.”

The integrated empirical model of a terrestrial ring basin is generally consistent with the observations and interpretations at Vredefort, Sudbury, and Chicxulub.

“Model is generally consistent with the observations and interpretations in the text, concerning the characteristics and interpretations at Vredefort, Sudbury, and Chicxulub.”

Once transient cavity modification is complete, impact melt will pool on the crater floor both inside and outside the inner topographic ring.

“Once transient cavity modification is complete, the impact melt will pool on the crater floor both inside and outside the inner topographic ring.”

The same structures can be exploited for both transient cavity formation and subsequent modification.

“In addition, the same structures can be exploited for both transient cavity formation and subsequent modification.”

At Vredefort erosional level, interpretations of seismic data for the empirical model suggest the inner ring occurs at convergence of outwardly dipping structures in collapsed transient cavity units and inwardly dipping structures in collapsed structural uplift units.

“At the erosional level of Vredefort, however, interpretations of seismic data for the empirical model suggest that the inner ring occurs at the convergence of outwardly dipping structures in the collapsed transient cavity units and inwardly dipping structures in the collapsed structural uplift units (Fig. 16).”

This pattern is characteristic of structural uplift in transient cavity modification at complex impact structures.

“This is characteristic of the process of structural uplift in transient cavity modification at complex impact structures (Grieve and Therriault 2004).”

• cites Grieve and Therriault 2004 sourceNot checked — no full text of the source

In some cases, particularly at greater radial distances from the center, motions were along the same preexisting structures in the crater floor that were exploited previously during outward-directed transient cavity formation.

“In some cases, particularly at the greater radial distances from the center, motions were along the same preexisting structures in the crater floor that were exploited previously, during outward-directed motions in the formation of the transient cavity.”

There is a net difference in the final result of uplift at Vredefort compared to smaller complex terrestrial impact structures.

“There is, however, a net difference in the final result of uplift here, compared to smaller complex terrestrial impact structures.”

The absence of a residual or remanent central topographic peak from peak-ring formation can be attributed to materials that could constitute such a central peak (uplifted transient cavity floor) being within the original volume of impact melt at terrestrial impact events of this magnitude.

“Finally, the absence of a residual or remanent central topographic peak from the process of peak-ring formation can be attributed to those materials that could ultimately constitute such a central peak (the uplifted transient cavity floor) being within the original volume of impact melt at terrestrial impact events of this magnitude.”

Localization of strain along very narrow zones and discrete displacements is a feature of apparent smooth average strain and bulk coherent flow in model calculations.

“Localization of strain concentrated along very narrow zones and discrete displacements are, in fact, a feature of the apparent smooth average strain and bulk coherent flow of model calculations (Collins et al. 2004).”

• cites Collins et al. 2004 sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

This discontinuous deformation is not necessarily at odds with bulk coherent flow of overriding low-strength material in collapsing structural uplift in model calculations.

“This is not necessarily at odds with the sense of bulk coherent flow of overriding lowstrength material in the collapsing structural uplift in model calculations (e.g., Collins et al. 2002).”

• cites Collins et al. 2002 sourceNot checked — no full text of the source

This excess-volume model has similarities to a model explaining the transition from complex central peak craters to central peak basins on the Moon.

“This model involving”

• cites Hale and Grieve 1982 sourceNot checked — no full text of the source

The former is indicative of well-known inward and upward kinematics in parautochthonous crater-floor rocks observed in structural uplifts at centers of smaller terrestrial impact structures.

“The former is indicative of the well-known inward and upward kinematics in the parautochthonous rocks of the crater floor observed in structural uplifts at the centers of smaller terrestrial impact structures (Grieve and Therriault 2004).”

• cites Grieve and Therriault 2004 sourceNot checked — no full text of the source

This exploitation is particularly prevalent for pre-existing structures with tangential geometries to radial movement, which develop as thrusts.

“This is particularly prevalent for pre-existing structures with tangential geometries to the radial sense of movement, which develop as thrusts.”

This composition pattern is indicative of successive tapping of the overlying melt sheet for dike material as the melt sheet differentiated.

“This is indicative of successive tapping of the overlying melt sheet for dike material as the melt sheet differentiated.”

Indicators for outward motions around the Haughton structural uplift are not exactly equivalent to late-stage motions in the larger structures considered here.

“The indicators for outward motions observed by Osinski and Spray (2005) around the structural uplift at the smaller Haughton structure are not exactly equivalent to these late-stage motions in the structural uplift at the larger structures under consideration here.”

• cites Osinski and Spray 2005 sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.

The situation may be different in the core of the structural uplift, as suggested by lack of discrete structures and sub-horizontal impact-related mineral fabrics in the center of the Vredefort core.

“The situation, however, may be different in the core of the structural uplift, as suggested by the lack of discrete structures and the sub-horizontal impact-related mineral fabrics in the center of the core at Vredefort (Lana et al. 2003).”

• cites Lana et al. 2003 sourceNot checked — no full text of the source

This fault-dip pattern corresponds well with observations on the inner rim structure of smaller impact structures such as Tswaing and Bosumtwi.

“This corresponds well with observations on the inner rim structure of smaller impact structures such as Tswaing and Bosumtwi (Brandt and Reimold 1999;Reimold et al. 1998).”

• cites Brandt and Reimold 1999Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

• cites Reimold et al. 1998 sourceNot checked — no full text of the source

Unlike on the Moon, greater impact melting relative to transient cavity dimensions at similar-sized terrestrial impact structures results in impact-melt volume reaching below the transient cavity floor at the sizes considered here.

“Unlike on the Moon, the greater amount of impact melting, relative to transient cavity dimensions at similar-sized terrestrial impact structures, results in the impact-melt volume reaching below the floor of the transient cavity at structures with the sizes under consideration here (Grieve and Cintala 1992).”

• cites Grieve and Cintala 1992 sourceNot checked — no full text of the source

The outward-directed, inward-dipping thrusts at Vredefort are consistent with a model of a structural uplift collapsing back down its central axis into a modified transient cavity.

“The outward-directed, inwarddipping thrusts at Vredefort are consistent with a model of a structural uplift that collapses back down its central axis into a modified transient cavity.”

With the assumption of same morphology, scaling of various attributes of individual structures to all structures yields a generally self-consistent picture with no obvious spatial, structural, or lithological anomalies.

“With this assumption, scaling of the various attributes of individual structures to all structures yields a generally self-consistent picture with no obvious spatial, structural, or lithological anomalies.”

• AssumptionThe authors state this as an assumption: All three structures (Vredefort, Sudbury, and Chicxulub) initially had the same form, including an inner topographic peak ring.

A similar observation of the same structures being exploited in both formation and modification of the transient cavity has been made at the Haughton impact structure.

“A similar observation with the same structures being exploited in both the formation and the modification of the transient cavity has been made recently at the Haughton impact structure (Osinski and Spray 2005).”

• cites Osinski and Spray 2005 sourceNot checked yet

  Checked before — its earlier verdict is held back until a new check runs.