by: Charles O’Dale

Abstract Updates – a compilation of the many papers published on the Sudbury Igneous Structure (SIC) and quoted in this article (updated 10/2017).
  • Type: Multi ring?
  • Age (ma): 1849.53 ± 0.21 and 1849.11 ± 0.19
  • Diameter: 250 km (estimated)
  • Location: Ontario, Canada. N 46° 36′ W 81° 11′
  • Shock Metamorphism:
    • shatter cones (up to 3 m in length);
    • PDF in quartz, feldspar and zircon grains;
    • overturned collar rocks of South Range structure, and;
    • brecciation of country rocks occurring up to 80 km from the Sudbury Igneous Complex.

    a Test application, zircon from a noritic boundary phase of the Sudbury impact melt gives 1849.53 ± 0.21 Ma, while a phase from several hundred meters higher in the noritic layer is resolvably younger at 1849.11 ± 0.19 Ma (95% confidence errors). (Davis D, 2008)

    When the crater is viewed from the altitude of the International Space Station, only the SIC within the Sudbury Structure (highlighted by the oval in the landsat image) is identifiable as being related to an impact event. The structure is located in central Ontario, north of Georgian Bay and north-west of Lake Nipissing. The city of Sudbury is located to the south-east of the SIC.
    The Sudbury Igneous Complex (SIC) adjacent to the Wanapetei Impact Crater.
    The Sudbury Igneous Complex (SIC) geomorphology.
    Geological map of the study region, simplified from Geological Map 2543 of the Ontario Geological Survey (1991) From Halls 2009. “Sudbury Igneous Complex (SIC) and Whitewater Group (WG). Archean granite and gneiss (AG), Archean greenstone (AV), Levack Gneiss (LG), Agnico Lake intrusion (AL), Huronian Supergroup (HS), Nipissing diabase (N), Grenville Province (GP), Murray fault (MF),Grenville Front (GF), Benny Deformation Zone (BDZ) and Flack Lake fault (FL). The dykes of three swarms, the 2450 Ma Matachewan, 2170 Ma Biscotasing and 1230 Ma Sudbury, are shown respectively as blue green and red lines. Faults are shown as black dashed line” (Halls, 2009).

    The Sudbury Structure (Canada) offers the only example of a basin-sized (250 km diameter) impact structure on Earth that can be examined at a range of stratigraphic levels from the shocked basement rocks of the original crater floor up through the impact melt sheet and on through the fallback material and the crater-filling sedimentary sequence. It hosts one of the world’s largest concentrations of magmatic Ni-Cu-Pt-Pd-Au mineralization and has produced more than $100 billion worth of metal in over a century of production. Sudbury is the premier locality on Earth to study processes related to impact and planetary accretion, as well as a wide range of magmatic processes including the generation of large magmatic sulfide deposits through scientific drilling. After impact, the entire 1.85-Ga Sudbury structure was affected by north-west directed thrust faulting, folding and associated lower amphibolite facies metamorphism. The Sudbury Structure is characterized by prominent potential field anomalies.

    The Sudbury Igneous Complex (SIC), the preserved portion of a silicate melt body several kilometers deep and more than 60 kilometers across, was produced virtually instantaneously by shock heating and cooled without further inputs of melt. The boundary conditions on this cooling and igneous differentiation process are simpler and can potentially be better understood than at any other large igneous body on Earth.

    Because the Sudbury Structure has been deformed since its formation, its large-scale subsurface geometry remains a matter of conjecture. Several seismic reflection and refraction transects and potential field studies were conducted across the Sudbury structure and provide a unique framework, when integrated with existing knowledge from mineral exploration, for 3D subsurface models. However, some of the deep crustal reflection images can be interpreted in a number of different ways that each honor the existing borehole, gravity and magnetic field data, as well as geological and structural constraints. Some data interpretations place potential hosts for important ore deposits close enough to surface to permit future exploitation, with obvious economic ramifications. Future deep drilling at Sudbury will test competing 3-D subsurface models derived from the existing shallow borehole, geological, structural and geophysical data. In addition, any deep drilling project will make use of wire-line diamond drills with core diameters considerably smaller than drills used in the petroleum industry. The relatively light weight, low cost and the versatility of this slim-hole technology makes it the method of choice for the mineral exploration industry worldwide. In South Africa, this method was successfully employed to drill and core to 6 km depth.

    Furthermore, the Sudbury Structure is also a unique example of a very large differentiated igneous body with remarkably simple boundary conditions. As such, it is the premier locality on Earth to study processes related to impact and planetary accretion, as well as a wide range of magmatic processes including the generation of large magmatic sulfide deposits. In terms of sustainable development, future (robotic) mining at depths considerably greater than are attained today requires reliable estimates of key geotechnical parameters (such as in situ stress and temperature), something that can only be achieved through deep scientific drilling.

    The Sudbury impact crater/structure from GOZooM over the centre of the structure looking north-east. Lake Wanapetei is top left in the image and Kelly Lake right centre. The flatness of the internal crater structure is obvious. 

    Large Meteorite Impacts and Planetary Evolution II, a major portion of the data quoted in this documentation of the Sudbury impact structure, was gleaned from this particular volume that contains many articles on the Sudbury Igneous Complex.Introduction

    The controversy over the origin of the Sudbury Structure and the Sudbury Igneous Complex was ongoing before the beginning of mining in the area. My father was involved in the mining industry before the onset of WWII and he always thought that the structure was somehow involved with volcanic activity. I remember being in high school when my science teacher mentioned that he had recently read a paper hypothesizing that the Sudbury Structure may be the result of a meteorite impact. Also that it had happened long before any life had evolved to survive on land (evolution was not allowed to be taught in Ontario schools at that time!). I found this idea fascinating and I think that this was probably where my interest in meteorite craters originated.

    The magnitude of scientific information describing the Sudbury Structure over the years has amplified my desire to fully explore this crater and others. This project was one of my lifelong dreams realized and I am still amazed at the magnitude of the “event” that created this structure.

    General Area: Sudbury lies close to the junction of three major structural provinces of the Canadian Shield. The area has been glaciated and is generally timbered, with agriculture occurring within the Sudbury structure. The target rocks are crystalline.

    Specific Features: The Sudbury structure is the oldest and largest impact structure in North America. It is almost completely eroded and is most visible only as the elliptical outline of the Sudbury Igneous Complex, the interior of which is filled by post-impact sediments and appears smooth with few lakes. The original structure extended beyond the Igneous Complex but has no remaining morphologic expression. The elliptical appearance is due to post-impact tectonism, with shortening to the northwest. A weak fracture halo is developed to the north, exterior to the Igneous Complex. The Sudbury Igneous Complex has associated major nickel and copper ore-bodies, which are currently mined.

    The Sudbury Structure comprises a 200-250 km multi ring impact basin formed at 1.85 Ga.

    While documenting the Sudbury Meteorite Impact Structure from my airplane and from the ground, I realized that for a non-professional geologist the geographic features that state that “this area is a meteorite crater” are not obvious. For this reason the initial content of my article will be a geologic description of the remnants of the present day Sudbury Meteorite Crater (highlighted by the circle in this topographic image). I will also document the evidence stating that the anatomy of the Sudbury complex was formed as the result of a cosmic collision. In this way I hope to better explain my aerial and ground images of the crater.

    The Sudbury Structure comprises a 200-250 km multi ring impact basin formed at 1.85 Ga. The core of the structure is elliptical, 60 x 30 km, containing a layered 2.5 km thick impact melt sheet, referred to as the Sudbury Igneous Complex (SIC). The SIC was formed by differentiation of the impact melt pool at the probable main contact point of the impactor.

    The Sudbury Structure superimposed on the 320 km diameter Schrödinger lunar impact basin.

    The Sudbury Basin is the deeply eroded remains of the original impact structure. After impact, the entire Sudbury structure was affected by north-west directed thrust faulting, folding and associated lower amphibolite facies metamorphism.

    I want to thank Frank Brunton and James E. Mungall for their assistance and allowing me to quote from their published papers (listed at the end of this article).

    Frank Brunton: THE FACTS-SIGNIFICANCE OF SUDBURY GEOLOGY MINING HISTORY. This is Frank Brunton beside my chariot, C-GOZM (GOZooM) immediately after our aerial exploration of the crater. Note the F18 in the right background. The Sudbury airport is on the east rim of the SIC and directly over the South Range Shear Zone.

    Formation of the original crater

    The Sudbury Structure sandwiched between the Superior Geologic or Structural Province and the Southern Geologic or Structural Province Huronian Supergroup, deformed by the Penokean orogeny.

    The Sudbury Structure is situated within a unique Geotectonic setting in northeastern Ontario, being sandwiched between:

    • the Archean-age (>2.5 billion-year-old) Superior Geologic or Structural Province, situated to west and north of the structure, and;
    • the Proterozoic-age (>1.9 billion-year-old) Southern Geologic or Structural Province Huronian Supergroup, deformed by the (1.9 billion –year-old) Penokean orogeny , and situated to west, south and east of the Sudbury Structure.
    • The boundary of the Proterozoic-age (~1 billion-year-old) Grenville Geologic Province presently lies approximately 10 km to southeast of the SIC. The Grenville orogeny occurred 800 million years after the Sudbury Crater was formed. The SW-NE trend of the Grenville Front Structural Zone, which delineates the northernmost margin of the Grenville Structural Province, is roughly parallel to the long-axis of the SIC.
    Illustrated in this sketch (courtesy of James E. Mungall) is a view of the sequence of events that may have produced the current structural relations between the SIC and the Huronian outliers (Huronian sediments were deposited between 2450 and 2219 Ma on the subsiding margin of the Superior craton).

    The transgressive nature of the passive margin produced a sequence which onlapped and thinned progressively toward the northwest. The Blezardian orogeny caused the formation of basement-cored tight folds in the metasediments, which were peneplained and submerged by 1850 Ma. At 1850 Ma a large impactor created a transient crater at least 100 km in diameter and 30 km deep somewhere in the vicinity of the current SIC. Within about ten minutes of the impact, the crater had rebounded and collapsed into its final form. Inward collapse of the transient crater walls was accomplished along detachment surfaces, now preserved as anastomosing networks of pseudotachylite-filled faults (Sudbury Breccia) tens of km in length. Lateral collapse and structural uplift in the center worked together to form a crater approximately 200 km in diameter. The South Range Shear Zone (SRSZ) line on the sketch is the transition from pristine North Range to deformed South Range of the SIC and occurs over a distance of less than 20 km.

    Segments of the Crater

    The Sudbury Structure is interpreted to represent the tectonized and deeply eroded remnant of a multi-ring or peak-ring impact basin (Stoffler et al). Approximately 4 km of erosion over the eons has obliterated the crater rim. Tectonism has possibly deformed the original crater into an ellipse. The subsequent metamorphism in the structure is tied to tectonic activity such as collision of continents and folding and thrusting up of crustal rocks. A zone of deformation (shatter cones and rock metamorphism) has been documented to 74 km from the SIC.

    Geological map of the study area created by Ames et. al, (2005). This map highlights the
    Foy offset dyke and some of the large faults in the area.

    This geologic schematic of the Sudbury structure illustrates the present day remnant of the Sudbury Meteorite Crater comprising of:

    • the surrounding brecciated footwall rocks of both the Superior and southern Structural Geologic Provinces extending up to 100 km away from the present-day position of the Sudbury Igneous Complex (SIC);
    • the Sudbury Igneous Complex (that formed as a result of impact-triggered magmatism, or deep crustal melting); and
    • the Sudbury Basin within the SIC, comprising rocks of the Whitewater Group (found only in the interior of the SIC). The Whitewater Group consists of the Onaping, Onwatin and Chelmsford Formations (J.E. Mungall).

    The Sudbury Igneous Complex (SIC)

    Thick sheets of melted rocks line the bottom of many large meteor craters. Some of these impact melts are derived from the release of kinetic energy at impactor contact that is converted to heat. Also, rocks lying kilometers deep within Earth are often on the verge of melting but are prevented from doing so by the immense pressure from the weight of the material lying above them. A large impactor would blast away this weight, releasing the pressure on the buried rocks and causing the underlying minerals to melt.

    The impact melts may not fully cool for hundreds of thousands of years. In the meantime, water from the environment and the heat from the newly exposed rocks can combine to form hydrothermal systems in the heavily fractured rocks in and around the crater. Scientists believe such warm mineral-rich venues could have played a role in the early development of life on Earth. (Science News: 3/9/02, p. 147) Evidence of the hydrothermal systems is documented in my ground tour.

    The SIC is this type of large melt sheet produced from crustal melting resulting from a cosmic impact. The target rocks, which remained within the crater after the impact, ponded to form a sub horizontal sheet of magma and differentiated as it cooled. It is currently exposed as an elliptical 60 x 30 km, 2.5 km thick remnant of the original impact melt sheet and consists, from bottom to top, of inclusion-rich, in places ore-bearing, quartz diorite sub layer, norite, quartz gabbro, and granophyre layers, and, within the target rocks surrounding the SIC, the quartz dioritic offset dikes.

    RADARSAT radar image of the Sudbury (left) and Lake Wanapitei (right). The close proximity of these two impact structures is strictly coincidence. The Wanapitei crater occurred over 1.8 billion years after the Sudbury impact.

    The Whitewater Group

    The SIC is overlain by the 1.8 km thick Onaping Formation. It consists of impact melt breccia, suevite and reworked suevite from:

    Fall-back (collapse of the original crater) and Fall-out (impact debris) forming a 2 km post impact sediment over the SIC melt rock; and,

    Wash-in – post impact sediment (the impact happened in a shallow sea).

    The rock fragments in the breccias of the Onaping Formation are from the impact target Archean and Proterozoic rocks of the Superior and Huronian Provinces of the Canadian Shield (Brunton).

    The Onaping Formation is covered by 600 metres of argillites and minor exhalative carbonates and cherts of the Onwatin formation. This formation occurred during a period of quiescence after the impact basin formation.

    The end of this quiet period was signaled by the abrupt appearance of the 850 metre-thick siliciclastic turbidites (sedimentary deposits settled out of muddy water carrying particles of widely varying grade size caused by turbidity currents) of the Chelmsford Formation (Rousell, 1972, 1984), which have been interpreted as a flysch apron deposited in the foredeep ahead of an advancing late Penokean mountain front (Young et al. 2001).

    Aerial Exploration

    The next series of images will document my aerial exploration the crater. Most of my images were from approximately 2000 feet above the ground.

    This image was taken from the north of the structure while flying over the Superior province country rock. In the immediate foreground is the area containing the Matachewan dykes and the Sudbury Breccia followed by the north rim of the SIC comprising of the different minerals of the lower and upper zones. .

    This image was taken from the north of the structure while flying over the Superior province country rock. In the immediate foreground is the area containing the Matachewan dykes and the Sudbury Breccia followed by the north rim of the SIC comprising of the different minerals of the lower and upper zones. Here at the time of impact, a 1 km cross section of country rock surrounding the crater was instantaneously melted, forming about 31,000 cubic kilometers of impact melt! This represents approximately six times the volume of lakes Huron and Ontario combined, and nearly 70 percent more than the melt at Chicxulub (Pope, Geo Eco Arc Research). In the background is the internal bowl shaped portion of the SIC containing the Whitewater group.

    I took this image above the SIC north rim. The internal edge of the SIC is illustrated here by the Vermillion River which is immediately adjacent to the internal north rim of the SIC and meanders through the relatively flat area of the Whitewater Group.

    All geology enclosed by the SIC is a result of fall-back, fall-out and wash-back

    This image of the floor of the Sudbury Structure was taken from about 3000’ over the center of the structure looking east over the Proterozoic rocks of the Whitewater group.

    The deepest mine shaft in the Sudbury complex, the Creighton Deep Project, is more than twice as deep as the altitude where this image was taken from! The northern rim of the SIC is visible in the left of the image with Lake Wanapitei in the left background. The town of Val Therese is in the foreground with the town of Hanmer just behind and to the east.  Garson Lake visible to the extreme right of the image is situated in the center of the southern rim of the SIC. The long axis of Garson Lake points at the Sudbury airport which is at the south east SIC origin of the South Range Shear Zone (SRSZ). It is barely visible in the haze in the background. The meandering river visible to the north (left) of Garson Lake is approximately over and running parallel to the SRS.

    This lower altitude image is looking north east from directly over the north-east corner of the Whitewater Group. The relatively flat geology of the Whitewater Group is terminated by the sharp north east rim of the SIC. In the background beyond the SIC is Lake Wanapitei.

    Under the Sudbury Basin are thousands of kilometres of drifts (lateral tunnels) and shafts (vertical to inclined tunnels) cut into the SIC to extract nickel. If these tunnels were placed end-to-end across Canada, it would almost be possible for someone to drive, bike or walk from coast to coast underground!

    The south rim of the SIC illustrated in this image is not as well defined as the relatively intact northern rim. The infamous Sudbury “stack”, visible in the foreground, rests on the Huronian supergroup south of the SIC. The SIC south rim is visible as the “mound” behind the stack and the “bowl” of the internal Sudbury Structure is visible in the background. To give an excellent perspective of the size of the structure, the north rim of the SIC is barely discernable just below the horizon in the far background!

    The SIC has the single largest magmatic nickel source in the world. The Creighton Deep Project is currently mining and actively exploring well below the 7500-ft. level, maintaining its status as the deepest working mine in the western hemisphere. The size of the underground workings at Creighton dwarfs all man-made structures on the surface of the Earth. The No. 9 vertical shaft is between 4-5 times higher than the CN Tower!
    The Sudbury Neutrino Observatory is housed in a cavern as large as a 10-story building, in the deepest section of the Creighton Mine.

    The 200-m-thick impact melts found within the Sudbury Crater are a treasure trove of minerals. More than $1 billion of metal ores including those bearing nickel, platinum, and copper are mined from the melts each year. Isotopic analyses show that the metals come from Earth’s crust, not from the meteorite that fell from space. Before the impact melt solidified, the deep, thick blend of light silicates and dense metal ores—which didn’t mix well with each other—separated into two layers, according to density, just like oil and vinegar do. This ancient segregation makes mining today much easier (Brunton).

    The hydrothermal system created by the Sudbury impact also dissolved minerals containing copper and other metals from a broad area and then concentrated them in rich veins. (Richard Grieve, Natural Resources Canada in Ottawa).

    Ground Exploration

    The next series of images will document my ground tour of the Sudbury Meteorite Crater that was guided by geologist Frank Brunton. We started north-west of Windy Lake outside of the SIC in the country rock and worked our way south-east along highway 144 to the center of the crater. This route gives a most fascinating display of the changing geology throughout the SIC feature caused by the impactor.

    Surrounding Brecciated Footwall Rocks

    Midcrustal 2.4 to 3 billion year old migmatites (a rock that incorporates both metamorphic and igneous materials) of the Levack Gneiss Complex are found immediately outside of the north rim of the Sudbury Igneous Complex (map right).


    This 18 cm shattercone was found just outside of the Sudbury Igneous Complex (SIC). The discovery of shatter cones confirmed that a large meteorite impact caused the formation of the Sudbury Igneous Complex (Gibson, Spray 1998).
    After 1.85 Billion years the striations on the shatter cone illustrated above are still recognizable.
    Sudbury shattercone (courtesy Martin Schmieder)
    Shatter cones have been reported up to 15 kms away from the periphery of the SIC. The cones commonly point toward the centre of the Sudbury basin, indicating that the Sudbury crater structure has undergone considerable erosion since the impact occurred 1.85 billion years ago (Brunton). This 18cm shattercone was found outside the SIC basin in the Sudbury Structure country rock and was given to me by Frank Brunton. Shatter cones are shock-deformation features that form from impact pressures of typically 2-10 GPa up to ~30 GPa (the GPa, or gigapascal, is a unit of pressure that corresponds to 9900 times atmospheric pressure). They represent the only distinctive and unique shock-deformation feature that develops on a megascopic scale (e.g., hand sample to outcrop scale). They appear in outcrops as distinctively curved striated fractures that typically form partial or complete conical structures (image). They are commonly found beneath impact crater floors, usually in the central uplifts of complex impact structures, but they may also be observed in isolated rock fragments within brecciated units.


    This image of the shattered (brecciated) bedrock is taken just north-west of Windy Lake on highway 144. When driving into the SIC from the north this is the first indicator of an impact event. The pulverization of these footwall rocks illustrates the deformation of the local bedrock that immediately followed impact.


    SB pseudotachylite dikes range from veins less than 1 mm thick to massive zones measuring up to 1 km thick and extending for approximately 45 km. Formations of SB are found up to 100 km north of the SIC . Most of the SB dikes dip vertically or steeply and apparently have no obvious preferred orientation with respect to the present shape of the Sudbury Structure.

    The Sudbury impact structure – black pseudotachylite.
    The Sudbury impact structure – black pseudotachylite.

    Black pseudotachylite Matachewan Dykes (LEFT) are found throughout this area in the rock cuts along the highway. These dykes predate the formation Sudbury Meteorite Crater and possibly offered a weakness in the Levack Gneiss. Pseudotachylite Sudbury Breccia (SB), a breccia having the aspect and the black color of a volcanic rock (a tachylite), was formed within these dykes when the high pressure from the meteorite impact was applied to these rocks and then abruptly released. This caused the rock along and within these dykes to partly melt. The dykes containing the pseudotachylite were welded shut as soon as the motion created by the impact stopped. Subsequent stress was supported by the fault as though it had never been active. The entire period of activity of a fault filled with pseudotachylite may be measured in minutes. (e.g., Pseudotachylite is a rock type formed by friction-induced melting, during very rapid deformation) (Philpotts 1964; Maddock 1983).

    The pulverized and melted country rock injected into the pink gneisses has similar chemistry to the derived gneisses. The greenish rock is secondary alteration of clays and micas from existing minerals within the rock. The brecciated zones fall along structures inferred as super faults or fault-controlled structures. The crustal rocks underlying the crater would have experienced substantial fracturing from the impact and the shear concentration of the billions of tonnes of the metal-rich rock that subsequently formed could have easily have created more fracturing while sinking down deep into the crust. (F. Brunton – private correspondence with the author).

    Sudbury pseudotachylite dikes range from veins less than 1 mm thick to massive zones measuring up to 1 km thick and extending for approximately 45 km. Formations of SB are found up to 100 km north of the SIC . The pseudotachylite here is injected into the pink gneiss country rock (the toe of my boot is for scale).

    Pseudotachylyte samples from the North Range of the 1850 Ma Sudbury impact structure have been analyzed by the 40Ar/39Ar laser spot fusion method. Field and petrological evidence indicate that the pseudotachylytes were formed at 1850 Ma by comminution and frictional melting due to impact-induced faulting. The cryptocrystalline to microcrystalline grain size (<30 μm) of the pseudotachylyte matrices and the predominance of orthoclase as the main K-bearing phase, have rendered the rocks particularly susceptible to Ar loss. The age determinations range from ∼1850 to ∼1000 Ma, with some samples yielding multiple ages that cannot be correlated with known geological events in the area. However, if the finite-difference algorithm of Wheeler (1996) is used to calculate combined Ar loss and the accumulation of radiogenic Ar for the K-bearing phases, it is possible to reproduce the range of observed ages. The model infers that the long-term volume diffusion of Ar has occurred and that, as a result, the Ar system cannot be treated with a conventional closure temperature approach. The algorithm requires burial of the impact structure to 5–6 km depth and 160–180 °C at 1850 Ma, followed by exhumation at ∼1000 Ma. These ages may be equated with two events: Penokean thin-skinned overthrusting in the North Range, immediately following impact, and exhumation ∼850 Ma later, coincident with the Grenville orogeny to the southeast. The results suggest that, contrary to previously accepted paradigms, the North Range has been affected by a protracted period of postimpact, low-grade thermal metamorphism. If these events also involved tectonic shortening within the North Range (as has been documented for the South Range), then the original size of the Sudbury impact structure has been underestimated. (Spray et al, Feb 2010)

    Pseudotachylyte petrogenesis: Constraints from the Sudbury impact structure


    Pseudotachylytes and their host rocks from the North Range of the 1.85 Ga Sudbury impact structure have been investigated using analytical scanning electron microscopy, electron microprobe analysis and XRF spectrometry. The results show that the pseudotachylytes were produced in high-speed slip zones by the frictional comminution and selective melting of wall rock lithologies. The preferential assimilation of hydrous ferromagnesian phases during frictional melting produced relatively basic melts, leaving the more mechanically resistant quartz and, to a lesser extent, plagioclase as included mineral clasts. Three distinct assemblages are identified within the pseudotachylytes: (a) pre-impact (>1.85 Ga) rock and mineral clasts derived from host lithologies; (b) a syn- to immediately post-impact (1.85 Ga), rapidly cooled, quartz + sanidine + labradorite + phlogopitic biotite matrix assemblage, formed due to crystallization from a melt at 800–900°C and (c) a post-impact (<1.85 Ga) retrograde assemblage which overprints both clasts and matrices. Field evidence indicates that most pseudotachylyte formed in large-displacement fault systems during gravitational collapse of the impact-generated transient cavity. The Sudbury pseudotachylytes, like endogenic pseudotachylytes, were generated by frictional melting on fault surfaces. The difference is primarily one of scale. Large (km) displacements occurring on impact-induced ring faults can generate immense volumes of friction melt resulting in spectacular pseudotachylyte bodies up to 0.5 km thick and more than 10 km long. (Spray, Thompson 1996)


    Characteristics of the Sudbury Breccia:

    • concentrated within 5 km of the SIC;
    • formed by dynamic means during very rapid deformation. (e.g., post impact friction-induced melting during the extensive and very rapid deformation and brecciation of the footwall rocks);
    • a two component rock consisting of a fine-grained to aphanitic matrix surrounding inclusions of host-rocks and minerals;
    • comprised of mineral and rock fragments derived predominantly from wall rocks, set within a typically dark, microcrystalline to fine grained matrix, generated by grinding and frictional melting; and
    • mostly associated with the 2.5 billion year old Matachewan dykes. In the immediate area of the shattered bedrock are samples of the Matachewan dykes.
    The Sudbury impact structure – Matachewan Breccia Dykes.
    The Sudbury impact structure – felsic norite breccia rocks.

    Approximately 1 km south from Windy Lake is a hill containing the North Range lower zone of the SIC. This area experienced an instantaneous melt at impact 1.8 billion years ago. These salt and pepper coloured felsic norite rocks consist of medium course crystalline, igneous textured plagioclase containing white feldspar and dark pyroxenes & mica. The lower zone of the SIC is 500 metres thick.

    The pinkish tinged rocks of the SIC North Range upper zone of the SIC North Range upper zone.
    These “breccia” rocks experienced an instantaneous melt at impact. They are three parts granophyric intergrowth (interlocked wedge shaped quartz and feldspar crystals) to one part plagioclase feldspar plus biotite, amphibole, chlorite and opaque minerals. The upper zone is 900 metres thick. The colour and texture differences between the upper and lower zone of the SIC is caused by the different rates of cooling after the impact.

    Whitewater Group

    Onaping Formation

    Further into the structure is the Whitewater Group, a 1400 m thick section consisting of fall-back of the original country rocks that has been hydrothermally altered. Ground water had seeped into faults caused by the impact, the water boiled creating hot springs through the Whitewater Group.

    Immediately interfacing the upper SIC is the grey Whitewater breccia that contains many large angular rock fragments floating in a glass like amorphous rock. These fragments are the fallback particles from the surrounding Huronion supergroup country rock that were deposited immediately after the impact.

    Basically these rock fragments went up hundreds of km and then hours later “plopped” into this still molten rock. Note the large fragment in the lower right of the image that is hydrothermally altered and surrounded by a “chilled margin” (a mineralized area around the fragment caused by a hydrothermal vent).

    The Sudbury impact structure – darker Whitewater breccia. Further into the structure is the darker Whitewater breccia containing smaller rock fall-back fragments originating from the igneous quarts granite north range footwall. Here the breccia indicates the introduction of carbon.

    A biogenic origin of the carbonaceous material (soot) found in the black Whitewater Group is theoretically caused by the evaporation/condensation from the hot impact fireball and/or from a later global cloud. The colour of the rock is not uniform indicating that the carbon is not uniformly distributed. The impact probably occurred in a shallow sea as there is evidence of water flow-back in the top layers of the Whitewater Group. The quantity of “breccia fall-back” specifies that the fall-back segment of the impact lasted a substantial amount of time (perhaps hours) before the appearance of the returning tsunami.

    The size of the Sudbury structure implies that the hydrothermal venting continued for thousands of years after the impact. The rocks of the Whitewater Group comprise (oldest-to-youngest): initially glass-rich breccias of the Onaping Formation, carbonates and argillites of the Vermilion and Onwatin formations, and arkosic sandstones and wackes of the Chelmsford Formation (Brunton).

    Bucky balls (soccer-ball-shaped molecules of 60 carbon atoms) possibly of extraterrestrial origin and with traces of helium and argon gas trapped inside were found in this breccia.

    2017 May – Volcanism evidence

    Protracted volcanism after large impacts: Evidence from the Sudbury impact basin

    Guyett, et al

    Photomicrograph of a vesicular green shard from the Onaping Formation of the Sudbury impact basin. Image credit: Paul Guyett, Trinity College Dublin

    Morphological studies of large impact structures on Mercury, Venus, Mars, and the Moon suggest that volcanism within impact craters may not be confined to the shock melting of target rocks. This possibility prompted reinvestigation of the 1.85 Ga subaqueous Sudbury impact structure, specifically its 1.5 km thick immediate basin fill (Onaping Formation). Historically, breccias of this formation were debated in the context of an endogenic versus an impact-fallback origin. New field, petrographic, and in situ geochemical data document an array of igneous features, including vitric shards, bombs, sheet-like intrusions, and peperites, preserved in exquisite textural detail. The geochemistry of vitric materials is affected by alteration, as expected for subaqueous magmatic products. Earlier studies proposed an overall andesitic chemistry for all magmatic products, sourced from the underlying impact melt sheet. The new data, however, suggest progressive involvement of an additional, more magnesian, and volatile-rich magma source with time. We propose a new working model in which only the lower part of the Onaping Formation was derived by explosive “melt-fuel-coolant interaction” when seawater flooded onto the impact melt sheet in the basin floor. By contrast, we suggest that the upper 1000 m were deposited during protracted submarine volcanism and sedimentary reworking. Magma was initially sourced from the impact melt sheet and up stratigraphy, from reservoirs at greater depth. It follows that volcanic deposits in large impact basins may be related to magmatism caused by the impact but not directly associated with the impact-generated melt sheet.

    Plain Language Summary
    Meteorite impacts are a key process in shaping the surface of the Earth and other planetary bodies. Recent studies on Mercury, Venus, Mars, and the Moon suggest that large impact structures are related to volcanism. We have studied the geological materials filling one of the largest and best preserved impact structures on Earth: the Sudbury impact structure in Ontario, Canada. Detailed investigation of the petrology and composition of the rocks has revealed that protracted, submarine, explosive volcanic activity took place after the impact. We propose that the volcanic activity was initially fed by crustal melts directly produced by the impact, but that with time, volcanic activity was progressively fed by magmas originating at deeper levels within the Earth.


    • The deep bowl was formed 1.85 billion years ago when a large meteorite exploded as it hit the Earth’s atmosphere.
    • The basin is not only filled with remnants of melted rock from the surface, but also contains a mixture of volcanic rock fragments.
    • Those fragments had altered with time.
    • Published in the Journal of Geophysical Research: Planets, the changes were not only caused by volcanic activity right after the meteorite impact, but also by volcanism caused by magma coming from deeper levels within the Earth later.
    • The finding suggests large impacts, such as those that took place during a short period after the Earth was formed, can be followed by intense, long-lived, and explosive volcanic eruptions.

      Chelmsford Formation

      The Sudbury impact structure – Chelmsford Formation. The Chelmsford Formation comprises about 850 metres of mostly wacke and siltstone, essentially sedimentary rocks deposited over the Whitewater Group after the impact. In the image note the ripples encased in the rock caused by water flowing back and forth. Paleocurrent studies indicate that the predominant flow direction was to the southwest, parallel to the long axis of the Sudbury Basin.
      The Sudbury impact structure – top surface of the Chelmsford Formation. This image of the top surface of the Chelmsford Formation illustrates striations on the sedimentary rocks caused by the glaciers. Note the circular carbonate concretions that are caused by ground fluids passing through the carbon rich mud rocks that would have been full of organics.

      The anaerobic waters caused chemical precipitation exchanges forming these things around a nucleus of organic material. A combination of the ground water and the chemical nature of the organic material in the particular layers, determines the size. (Frank Brunton – private discussion)

      The Sudbury impact structure – SIC north wall. The rim of the SIC north wall is visible in the background. I  took this image while facing north a couple of km west of Hanmer and situated in the center of the Sudbury Structure.

      The controversy over the origin of the Sudbury Structure and the Sudbury Igneous Complex was ongoing before the beginning of mining in the area. My father was involved in the mining industry before the onset of WWII and he always thought that the structure was somehow involved with volcanic activity. I remember being in high school when my science teacher mentioned that he had recently read a paper hypothesizing that the Sudbury Structure may be the result of a meteorite impact. Also that it had happened long before any life had evolved to survive on land (evolution was not allowed to be taught in Ontario schools at that time!). I found this idea fascinating and I think that this was probably where my interest in meteorite craters originated.

      The magnitude of scientific information describing the Sudbury Structure over the years has amplified my desire to fully explore this crater and others. This project was one of my lifelong dreams realized and I am still amazed at the magnitude of the “event” that created this structure.

      Discovery of distal ejecta from the 1850 Ma Sudbury impact event

      Sudbury Impact Distal Ejecta at Hillcrest Park, Thunder Bay Ontario – 2013.

      ABSTRACT A 25–70-cm-thick, laterally correlative layer near the contact between the Paleoproterozoic sedimentary Gunflint Iron Formation and overlying Rove Formation and between the Biwabik Iron Formation and overlying Virginia Formation, western Lake Superior region, contains shocked quartz and feldspar grains found within accretionary lapilli, accreted grain clusters, and spherule masses, demonstrating that the layer contains hypervelocity impact ejecta. Zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca. 1878 Ma and 1836 Ma. The Sudbury impact event, which occurred 650–875 km to the east at 1850 ± 1 Ma, is therefore the likely ejecta source, making these the oldest ejecta linked to a specific impact. Shock features, particularly planar deformation features, are remarkably well preserved in localized zones within the ejecta, whereas in other zones, mineral replacement, primarily carbonate, has significantly altered or destroyed ejecta features. (Addison 2005).


      These images of the Sudbury Impact Distal Ejecta were taken by the author at Hillcrest Park, Thunder Bay Ontario – 2013.

      Comment by Roland Dechesne, geologist and fellow RASC member about the Hillcrest deposits: “The lapilli were poorly preserved and could have, potentially, been any number of things. However, features were present, and given the regional context, it’s probable that what (we) saw was them (Sudbury Distal Ejecta). Interestingly, they were in a coarse sandstone that had discontinuous thin blebs of cherty quartz that gave me the impression of being fiamme. If Earth impacts can create frothy pumice-like clasts, then all would be very consistent”.

      Lapilli: a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts.

      Fiamme: lens-shapes, usually millimetres to centimetres in size, seen on surfaces of some volcanic rocks.



      -from Naldrett 2009:

      There is widespread acceptance that:

      1. The Sudbury structure is the consequence of extraterrestrial impact.
      2. The crater had an original diameter, after the collapse of the initial transient crater, of in excess of 200 km.
      3. The SIC is predominantly an impact melt. The granophyre probably separated from a more mafic magma at an early stage and was augmented by incorporation of the products of melting of the overlying Onaping Formation.
      4. The Onaping Formation represents a combination of a basal surge deposit, fall-back breccia (suevite) and suevite that has been reworked in an aqueous environment.
      5. The offsets are the result of the early emplacement of impact melt along fractures resulting from impact and subsequent crater readjustment.
      6. Sulphide immiscibility occurred during cooling of the SIC, probably before much of the SIC had reached its liquidus temperature.
      7. The sulphides settled into embayments in the impact crater wall and were injected into earlyemplaced melt occupying the offset fractures.
      8. Continuous segregation of sulphide led to a depletion of chalcophile metals within the remaining impact melt.
      9. The ores fractionated as they cooled, giving rise to a Cu-, Pt-, Pd- and Au-enriched residual liquid which moved into the footwall, exploiting impact breccia and zones of pseudotachylite-like “Sudbury Breccia”.Some significant questions remain unanswered. These include:
        1. The Sudbury structure lacks the central uplift that characterises all known impact craters of equivalent size. It is possible that the documented north-northwest thrusting of the South Range over the North Range has resulted in a central uplift being covered by the allocthonous rocks, but there is no evidence to support this.
        2. The fractional crystallisation exhibited by the felsic norites and quartz gabbro of the SIC has not been documented in melt sheets of other impact craters that are apparently of equivalent size to the Sudbury structure.
        3. The concentrations of Ni and Cu that appear to have been present in the initial impact melt exceed those to be expected in a melt of average Archean-Proterozoic crust. The Ni and Cu may have come from a mafic/ultramafic Paleoproterozoic intrusion that existed in the target area, but definitive evidence of this is lacking.

        Side Notes

        RADARSAT radar image of the Sudbury (left) and Lake Wanapetei (right), double impact structures. Their close proximity is strictly coincidence. The Wanapitei impact happened over 1.8 billion years after Sudbury.
        The Clearwater West (left) and East impact craters in northern Quebec’s Canadian Shield. Their close proximity is strictly coincidence. The Clearwater impacts, shown in this image, are related only by their geological position, recent dating puts the Clearwater East at ~460–470 Ma and Clearwater West impact at 286.2 ± 2.2 (2.6) Ma.

        Pseudotachylite at the Vredfort Impact Crater

        The Sudbury and Vredfort Impact Craters both share pseudotachylite in their respective geology.
        The Vredefort Crater, southwest of Johannesburg, South Africa


        Addison, W.D., Brumpton, G.R., Davis, D.W., Fralick, Philip W., and Kissin, S.A., 2010, Debrisites from the Sudbury impact event in Ontario, north of Lake Superior, and a new age constraint: Are they base-surge deposits or tsunami deposits? Geol. Soc. Am., special Paper 465.

        Addison, W.D., Brumpton, G.R., Vallini, D.A., McNaughton, N. J., Davis, D.W., Kissin, S.A., Fralick, P.W., and Hammond, A.L., 2005, Discovery of distal ejecta from the 1850 Ma Sudbury impact event: Geology: 33:193-196.

        Ames, D.E., Buckle, J., Davidson, A., and Card, K., 2005. Sudbury bedrock compilation; Geology: Geological Survey of Canada, Open File 4570, scale 1:50 000.

        Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education

        Halls, H.C., 2009. A 100 km-long paleomagnetic traverse radial to the Sudbury Structure, Canada and its bearing on Proterozoic deformation and metamorphism of the surrounding basement. Tectonophysics, 474: 493-506.

        Jones, A.P., 2005. Meteorite Impacts as Triggers to Large Igneous Provinces, Elements, Vol 1, PP. 277-281.

        Maddock, R.H., 1983. Melt origin offault-generated pseudotachylytes demonstrated by textures, Geology, Vol 11, no 2.

        J.E. Mungall and J.J. Hanley: ORIGINS OF OUTLIERS OF THE HURONIAN SUPERGROUP WITHIN THE SUDBURY STRUCTURE. Department of Geology, University of Toronto.

        Naldrett, A.J.; Evolution of Ideas About the Origin of the Sudbury Igneous Complex and its Associated Ni-Cu-PGE Mineralization.; 2009 A Field Guide to the Geology of Sudbury Ontario

        Ostermann, M., Scharer, U., Deutsch, A., 1996. Impact melt dikes in the sudbury multi-ring basin: Implications from uranium-lead geochronology on the Foy Offset Dike.

        Philpotts, A.R. Origin of Pseudotachylites, American Journal of Science, Vol 262 1964.

        Price, G.D., Price, N.J., Decarli, P.S., and Clegg, R.A., Fracturing, thermal evolution and geophysical signature of the crater floor of a large impact structure: The case of the Sudbury Structure, Canada. Geological Society of America Special Papers, 2010, 465, p. 115-131, 2001.

        Sharpton, V.L., Dressler, B.O. (editors), Large Meteorite Impacts and Planetary Evolution II,

        Spray, J.G., Thompson, L.M., Kelley, S.P., 4 FEB 2010 – Laser probe argon-40/argon-39 dating of pseudotachylyte from the Sudbury Structure: Evidence for postimpact thermal overprinting in the North Range – Article first published online: 4 FEB 2010

        Stöffler, D., Deutsch, A., Avermann, M., Bischoff, L., Brockmeyer, P., Buhl, D., Lakomy, R. and Müller-Mohr,B., The formation of the Sudbury Structure, Canada: Towards a unified impact model. Geological Society of America Special Paper 293, pp. 303-318. 1994.

        Paul Weiblen, Sudbury impact breccia – Forest Fire on the Gunflint Trail leads to discovery of further evidence for an ancient, giant meteorite impact at Sudbury, Ontario, Canada. May 16, 2007

        Young, G.M., Long, D.G.F., Fedo, C.M., Nesbitt, H.W.,Paleoproterozoic Hunonian basin: product of a Wilson cycle punctuated by glaciations and a meteorite impact. Department of Earth Sciences, University of Western Ontario, 2001.

        Earth Impact Database

        Sudbury Geology

        A Field Guide to the Geology of Sudbury, Ontario – 2009

        The Geology and ore deposits of the Sudbury Structure – 1984

        Bedrock Geology of the Regional Municipality of Sudbury. Map Series no P3187 – 1998