A Paleoarchaean impact crater in the Pilbara Craton, Western Australia

Domain: earth_science
Published: 2025-03-06
Editorial outcome: accept

Abstract
The role of meteorite impacts in the origin, modification, and destruction of crust during the first two billion years of Earth history (4.5–2.5 billion years ago; Ga) is disputed. Whereas some argue for a relatively minor contribution overall, others have proposed that individual giant impactors (>10–50 km diameter) can initiate subduction zones and deep mantle plumes, arguably triggering a chain of events that formed cratons, the ancient nuclei of the continents. The uncertainty is compounded by the seeming absence of impact structures older than 2.23 Ga, such that the evidence for the terrestrial impact flux in the Hadean and Archaean eons is circumstantial. Here, we report the discovery of shatter cones in a complex, dominantly metasedimentary layer, the Antarctic Creek Member (ACM), in the centre of the East Pilbara Terrane, Western Australia, which provide unequivocal evidence for a hypervelocity meteorite impact. The shocked rocks of the crater floor are overlain by (unshocked) carbonate breccias and pillow lavas, stratigraphically constraining the age of the impact to 3.47 Ga and confirming discovery of the only Archaean crater known thus far.

Introduction
With more than a million craters exceeding 1 km in diameter, and around forty more than 100 km across1,2, the Moon preserves an exquisite record of the intense bombardment endured by bodies in the inner solar system during the first billion years or so of its history (Fig. 1a)3. On Earth, this early impact record has seemingly been lost, reflecting the destructive efficiency of erosion and subduction in recycling primary (basaltic, oceanic) crust back into the convecting mantle. Nevertheless, the oldest parts of many cratons, the ancient Archaean (4.0–2.5 billion years ago; Ga) nuclei of the continents, formed at or before 3.5 Ga4, and should preserve some evidence for an impact flux that would have exceeded that of a similar area of the Moon of comparable age5–7 (Fig. 1a). However, the oldest recognized terrestrial impact structure, at Yarrabubba, Western Australia, is dated at 2.23 Ga8. Where are all the Archaean craters?

Finding direct evidence for Archaean impacts (i.e., craters or impact structures8), and thereby better constraining the Archaean impact flux, is important. Large impactors (here bodies > or >> 10 km in diameter) travelling in excess of 10 km s–1 deliver enormous quantities of kinetic energy, most of which will decay to heat, warming the crust and upper mantle9, with potential consequences for plausible tectonic modes on the early Earth10,11. Further, numerical models have shown that individual bolide impacts can instigate subduction, mantle upwellings (plumes), and voluminous production of primary (basaltic) crust12–14. Moreover, impacts provide a ready mechanism to fracture (brecciate) the crust and, in the presence of a hydrosphere15, drive intense hydrothermal alteration of this regolith, concentrating key mineral deposits16. Notably, impact craters may have provided the physical and chemical environments required for life to emerge on Earth and elsewhere17,18.

The East Pilbara Terrane (EPT), part of the Pilbara Craton of Western Australia, is a near-pristine, approximately 200 km diameter fragment of (mostly) Paleoarchaean (3.53–3.23 Ga) cratonic crust comprising domes of sodic granite (TTG) separated by steeply-inclined greenstone belts dominated by ultrabasic to basic volcanic rocks19 (Fig. 1b). Many interpret the EPT as a long-lived volcanic plateau formed by polyphase plume-driven magmatism, probably involving short-lived episodes of (proto)subduction19–21. More recently, it has been argued that the EPT ultimately formed at the site of a large bolide impact22, and that such an origin for the initiation of cratons may be generally applicable22,23.

Here, we report the discovery of an impact crater at the North Pole Dome, near the centre of the EPT (Fig. 1b, c). Exceptionally preserved shatter cones within a dominantly siliciclastic horizon (Fig. 2a, b), the Antarctic Creek Member (ACM), which has previously been shown to contain spherules (quenched and devitrified impact-melt droplets)24,25, provide unequivocal evidence for a hypervelocity meteorite impact 3.47 billion years ago. Both spherules and shatter cones are found within the same siliciclastic unit within the ACM, requiring at least two (one proximal, one distal) Paleoarchaean or earlier impact events7,26.

Results
The North Pole Dome and Antarctic Creek Member (ACM)

At the base of the Pilbara Supergroup, the 10–15 km thick Warrawoona Group is dominated by weakly metamorphosed ultramafic to mafic volcanic rocks with subordinate felsic volcanic/volcaniclastic rocks and chert19 (Fig. 1b, c). Pillow lavas near its base are pervasively hydrothermally altered and cut by chert–barite veins and overlain by chemical sediments (mostly chert) containing the oldest known (stromatolite) fossils27. At higher stratigraphic levels, within the core of a structural dome (the North Pole Dome; Fig. 1c), a 2–3 km thick sequence of ultramafic–mafic volcanic rocks (the Mount Ada Basalt) contains a thin (up to 20 m) sedimentary unit, the Antarctic Creek Member, which consists of (silicified and carbonate-altered) felsic to mafic volcaniclastic rocks, chert, argillite, arenite and jaspilite intruded by dolerite19,28.

The ACM preserves evidence for the oldest known meteorite impact in the form of one or more layers containing spherules19,24, interpreted by most as globally-distributed airfall impact ejecta19,24,25,29,30, but whose petrogenesis is debated31,32. It contains detrital zircon grains with 207Pb/206Pb ages of 3470±2 Ma24, providing a maximum depositional age, but has not been dated directly. However, underlying felsic rocks near the base of the Mount Ada Basalt (3469±3 Ma), and at the base of the overlying sequence of felsic volcanic rocks (the Duffer Formation; 3468±2 Ma) constrain deposition of the ACM to around 3470 Ma (3469.2+1.8/–1.2 Ma; ref. 19).

Fieldwork in 2021 in a small area of the North Pole Dome identified shatter cones throughout most of the thickness of the ACM (Fig. 2a; Supplementary Fig. 1). The shatter cones crop out more-or-less continuously for at least several hundred metres extending broadly northeast from where the ACM crosses the track at 21° 02’ 54” S, 119° 23’ 35” E (Fig. 1c). At outcrop, the variably curved surfaces of the shatter cones are smooth, with divergent and branching ribs and a mean apical angle of around 90° (Fig. 2a; Supplementary Information Fig. 1a–d; see also a 3D model at: https://sketchfab.com/3d-models/shatter-cone-2-cd89206c6d6b4765be766659a6e377da), similar to the average of literature values33. Although the orientation of individual cone axes varies, almost all are steeply inclined and splay (the ribs diverge) downwards (Fig. 2a; Supplementary Fig. 1a–d)33, consistent with a right-way-up stratigraphy19. On a larger scale, the cones are clearly visible as hut-like structures, some several metres tall, which extend across the hillside (Supplementary Fig. 1e).

Immediately overlying the shocked (shatter cone-bearing) ACM is a 5–10 m thick stratabound sequence of polymictic carbonate breccias (occupying the more strongly eroded gully in Supplementary Information Fig. 1e) containing angular fragments of underlying rocks, conspicuously chert (Supplementary Information Fig. 2). The stratabound layer of carbonate breccias is clearly distinct from the (very recent) calcrete deposits that cover the surface of many exposures, and includes distinctive orange dykes up to a metre thick (Supplementary Fig. 2b) that extend for many tens of metres into the footwall. Directly overlying the carbonate breccias are hydrothermally altered basalts (the upper part of the Mount Ada Basalt), which are pillowed near their base (Supplementary Fig. 1e, f) and contain layers of chert at higher stratigraphic levels. We have found no shatter cones in either the pillow basalts or carbonate breccias/dykes.

Methods
We combine field observations and deductive reasoning with published geochronological data from the Geological Survey of Western Australia GSWA, as summarized in ref. 19.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "A review of “A Paleoarchean impact in the Pilbara Craton, Western Australia” by G. R. Osinski.\nIt was a pleasure to read this revised version of a previous manuscript submitted to [REDACTED]. The authors have done a\ngood job of addressing the comments of all three reviewers, which strengthens their case for shatter cones in ~3.47 Ga\nrocks, which I agree provides the first evidence of a preserved meteorite impact crater in the Archaean. I will restate that this\nis an important and exciting discovery.\nBelow I provide a series minor comments on the manuscript, which I hope the authors will find useful.\nMy one major comment is about the location of the shatter cones and their abundance. This was also raised by me and other\nreviewers in the original manuscript and needs to be addressed. Science requires that observations are reproducible, which\nfor field geology, means that somebody else needs to be able to view these same rocks. The authors need to provide UTM\ncoordinates (on lines 101-102) and label (e.g., with a star) the location of the shatter cones on Figure 1. In addition, they\nneed to state how many outcrops they have documented shatter cones in.\nWhile the authors may wish to keep these outcrops secret, this location data needs to be published to support their\narguments. I would also like to add, to the authors and editor, that I was approached by another high-ranking journal last\nweek to review a manuscript on what appear to be these very same shatter cones based on the abstract that was provided. I\nwanted to complete this review first before accepting this potentially competing review.\nL37: It would be good to add to this sentence that these spherule layers represent distal ejecta as some readers may not be\nfamiliar with what these deposits are.\nL41-44: I might suggest some slight rewording here – although I am uncertain if the numbers exist – but a large amount\n(perhaps most) of the kinetic energy transferred to the crust ends up melting large volumes of rock (producing impact melt).\nL57-59: It would be easier to follow and more consistent if the legend labelled the dashed black line as the Antarctic Creek\nMember rather than “spherule-bearing chert”.\nL71: Similar to the previous comment, to avoid confusion, mention the ACM here first, rather than on line 74. You should also\ndefine this acronym again upon first mention in the main body of the text.\nL94: I think you need a ) after “2 Ma”.\nL97-99> I’m not sure of the journal’s requirements, but it’s usually best to state what the scale is for each sub-image, even if\nobvious. So a finger for a, an x-com long rock hammer for b. What about c?\nL101: The placement of the refs 39-41 reads like these papers discovered the shatter cones in question. I would split this\nsentence. First state you identified the shatter cones, and then make it more explicit for the uninformed reader: state that\nshatter cones are the only macroscopic shock metamorphic indicator, and then use those 39-41 refs. See also my comment\nabove about providing UTM coordinates and identifying the location of the shatter cones on Figure 1.\nL103: I read their response to my previous comment about the potentially glassy shatter cone surface, but I would remove\nthis here. Not only do they not provide evidence, why/how could this surface still be glassy after 3.5 billion years. The\nspherules certainly are not.\nL143: This is difficult to assess as the authors have not provided information on the location of these shatter cones and their\nabundance (i.e., number of outcrops).\nL149: These breccias look far to coarse-grained to be airfall deposits. You could just shorten this and remove some\nspeculation by shortening to just say “impact-related products”.\nL157-159: Given the authors have documented evidence for two large impacts within 10 Ma of each other at a single\nlocation, (b) and (c) seem much more likely. I’ll let the authors decide if they want to make a bolder statement to this effect.", "reviewer_2": "Dear Authors,\nI think your finding of Archean shatter cones is very interesting and an important discovery. However, I find the manuscript\nlacking some important information, i.e., more detailed investigations are needed in order to support many of the claims in\nthe manuscript.\nThe major issues that I see are:\n1) the lack of a detailed description of the shatter cone distribution and relation to geological units. The authors claim that the\ncrater has a diameter of at least 100 km, based on the width of the North Pole Dome, but are shatter cones found on the\nwhole of the dome? It is from the current text highly unclear what the spatial distribution is (the area is not even marked on\nthe map)?\n2) The authors claim that the shatter cone area to be situated on the flank of a central uplift? This needs to be supported by\nbetter field evidence.\n3) The authors speculate that the carbonate breccia represents crater fill, but this is not supported by any hard evidence, one\nwould expect highly shocked material and injected veins of melt rock in this, but this is not presented.\n4) I do not understand the purpose of including the overlying spherule bed in the manuscript, how is this relevant to this\nstudy?\n5) Geologic and petrographic descriptions throughout the manuscript are sparse and insufficient.\nUnless the authors cannot present better evidence supporting their claims of a very large and old impact structure, then I\nthink this should not be published in Nature Communications.\nBest regards,\nCarl Alwmark"}, "author_response": "Response to reviewer comments (NGS-2024-10-02678-T)\nWe are grateful to the expert reviewers for their comments, and provide our responses\n(in red) below.\nReviewer #1 (Remarks to the Author):\nA review of “A Paleoarchean impact in the Pilbara Craton, Western Australia” by G. R.\nOsinski.\nIt was a pleasure to read this revised version of a previous manuscript submitted to\n[REDACTED]. The authors have done a good job of addressing the comments of all thre\ne reviewers, which strengthens their case for shatter cones in ~3.47 Ga rocks,\nwhich I agree provides the first evidence of a preserved meteorite impact crater in the\nArchaean. I will restate that this is an important and exciting discovery.\nWe are pleased that the reviewer sees the importance of our observations and\nconsiders that we have done a good job in responding to the former comments.\nBelow I provide a series minor comments on the manuscript, which I hope the authors\nwill find useful.\nMy one major comment is about the location of the shatter cones and their abundance.\nThis was also raised by me and other reviewers in the original manuscript and needs to\nbe addressed. Science requires that observations are reproducible, which for field\ngeology, means that somebody else needs to be able to view these same rocks. The\nauthors need to provide UTM coordinates (on lines 101-102) and label (e.g., with a star)\nthe location of the shatter cones on Figure 1. In addition, they need to state how many\noutcrops they have documented shatter cones in.\nWe have mapped the shatter cones over a distance of a few hundred metres from\nwhere they cross the track at 21 02’ 54” S, 119 23’ 35” E to the northeast. The shatter\ncones crop out almost continuously over that distance, and continue into the hills. We\nhave added a sentence (beginning line 102 of the revised version) to clarify this:\n“The shatter cones crop out more-or-less continuously for at least several hundred\nmetres extending broadly northeast from where the ACM crosses the track at 21 02’\n54” S, 119 23’ 35” E”.\nWe have now added the location of the studied outcrops on Fig. 1c.\nWhile the authors may wish to keep these outcrops secret, this location data needs to\nbe published to support their arguments. I would also like to add, to the authors and\neditor, that I was approached by another high-ranking journal last week to review a\nmanuscript on what appear to be these very same shatter cones based on the abstract\nthat was provided. I wanted to complete this review first before accepting this potentially\ncompeting review.\nAs detailed in our former correspondence including the letter from the Department of\nMines, we only wanted to protect the location until the site can be protected by state\nlegislation. Much of the key exposures of the Jack Hills conglomerate and Ediacaran\n1\nfossils were removed by overseas parties and we do not want to same to happen here.\nHowever, we now provide those location details.\nBeing beaten to the discovery has obviously been our concern throughout, as\nexpressed several times to the editors of Nature family journals that have seen the\nmanuscript. We are extremely grateful that the reviewer has given us this renewed\nopportunity to get this published.\nL37: It would be good to add to this sentence that these spherule layers represent distal\nejecta as some readers may not be familiar with what these deposits are.\nDone.\nL41-44: I might suggest some slight rewording here – although I am uncertain if the\nnumbers exist – but a large amount (perhaps most) of the kinetic energy transferred to\nthe crust ends up melting large volumes of rock (producing impact melt).\nWe disagree. We have a paper in review at Nature (2024-09-19860) that models the\nenergetic effects of large impacts (individually and cumulatively) using a Lattice–\nBolzmann approach. I’m happy to share it with the editor and reviewer if it is treated in\nthe strictest confidence. In essence, most of the impact energy is transferred to the\nmantle, then back to the crust when the mantle melts. It is clear that impact-induced\nmantle melting is a contentious point, so we have mostly removed it on the request of\nthe reviewers of the earlier version. We have changed “most” to “much” in the hope this\nsentence will be more acceptable.\nL57-59: It would be easier to follow and more consistent if the legend labelled the\ndashed black line as the Antarctic Creek Member rather than “spherule-bearing chert”.\nHere we are simply showing the mapped location of spherule-bearing chert layers within\nthe ACM as we think these are important. However, we take the point that the ACM is\nnot labelled, so have modified Fig. 1c to make it clearer (between the lower and upper\nMount Ada Basalt). We add the information relating to spherules in the revised caption.\nL71: Similar to the previous comment, to avoid confusion, mention the ACM here first,\nrather than on line 74. You should also define this acronym again upon first mention in\nthe main body of the text.\nDone.\nL94: I think you need a ) after “2 Ma”.\nWe do indeed. Done.\nL97-99> I’m not sure of the journal’s requirements, but it’s usually best to state what the\nscale is for each sub-image, even if obvious. So a finger for a, an x-com long rock\nhammer for b. What about c?\nIndeed. It is a hand lens which is 31 mm long at its widest. We have added this to the\ncaption.\nL101: The placement of the refs 39-41 reads like these papers discovered the shatter\n2\ncones in question. I would split this sentence. First state you identified the shatter\ncones, and then make it more explicit for the uninformed reader: state that shatter\ncones are the only macroscopic shock metamorphic indicator, and then use those 39-41\nrefs. See also my comment above about providing UTM coordinates and identifying the\nlocation of the shatter cones on Figure 1.\nWe agree. Now changed as suggested.\nL103: I read their response to my previous comment about the potentially glassy shatter\ncone surface, but I would remove this here. Not only do they not provide evidence,\nwhy/how could this surface still be glassy after 3.5 billion years. The spherules certainly\nare not.\nWe have now removed “potentially glassy” or any other mention that they have been\nglass.\nL143: This is difficult to assess as the authors have not provided information on the\nlocation of these shatter cones and their abundance (i.e., number of outcrops).\nWe now provide the location of the section of near continuous outcrops of the shatter-\ncone-bearing ACM as they extend for at least several hundred metres across the\nhillside (there are hundreds or thousands of individual outcrops). We do couch this\nsentence as an interpretation, but it is one that is entirely consistent with the map scale\nstructure (a large dome in which the shatter-cone-bearing ACM forms an outward-\ndipping component).\nL149: These breccias look far to coarse-grained to be airfall deposits. You could just\nshorten this and remove some speculation by shortening to just say “impact-related\nproducts”.\nFair point and done.\nL157-159: Given the authors have documented evidence for two large impacts within 10\nMa of each other at a single location, (b) and (c) seem much more likely. I’ll let the\nauthors decide if they want to make a bolder statement to this effect.\nWe agree 100%. However, we have made other bold statements that reviewers have\nobjected strongly to, so we would prefer to leave this open for the reader to ponder.\nReviewer #2 (Remarks to the Author):\nDear Authors,\nI think your finding of Archean shatter cones is very interesting and an important\ndiscovery. However, I find the manuscript lacking some important information, i.e., more\ndetailed investigations are needed in order to support many of the claims in the\nmanuscript.\nWe are pleased that the reviewer also recognises the importance of our discovery. As\nwe have stated several times, including in our detailed responses to previous reviews,\nwe have outcrop observations from a section exposed across the hillside for a few\nhundred metres. However, the (published) mapped extent of the ACM, the regional\n3\nstratigraphy and the large-scale structure of which it forms a part (a dome) leads us to\nour stated interpretations.\nThe major issues that I see are:\n1) the lack of a detailed description of the shatter cone distribution and relation to\ngeological units. The authors claim that the crater has a diameter of at least 100 km,\nbased on the width of the North Pole Dome, but are shatter cones found on the whole of\nthe dome? It is from the current text highly unclear what the spatial distribution is (the\narea is not even marked on the map)?\nIn the discussion we state (below) our preferred interpretation is based on the mapped\nextent of the ACM. We have now marked the locality of that section on Fig. 1c. We think\nthe North Pole Dome is a central uplift based on our discovery of shatter cones. Others\nhave interpreted it to be a huge volcanic edifice, and this forms part of the published\nliterature as cited in the manuscript.\n“Importantly, the 3.47 Ga ACM dips away from the core of the (aptly named) North Pole\nDome (Fig. 1c), such that we interpret the exposed rocks to represent a section through\nthe flanks of the central uplift of a large impact crater and its fill (Fig. 3), consistent with\nthe spatial distribution of shatter cones in younger terrestrial complex craters41,44 (Fig.\n3). If so, the maximum width of the North Pole Dome (around 45 km; Fig. 1b,c) implies a\ncrater with a diameter of 100 km or more41.”\n2) The authors claim that the shatter cone area to be situated on the flank of a central\nuplift? This needs to be supported by better field evidence.\nSee comments above. The shatter cones are located on the flank of the North Pole\nDome, as defined in the literature. It is our interpretation that this reflects a central uplift\nas opposed to a megavolcano or something else. Based on the current field evidence\nour interpretation is valid.\n3) The authors speculate that the carbonate breccia represents crater fill, but this is not\nsupported by any hard evidence, one would expect highly shocked material and injected\nveins of melt rock in this, but this is not presented.\nYes, that is the nature of speculation. We would prefer to be able to interpret our\nobservations based on the outcrop and map evidence we have. Notwithstanding, and in\naccord with the comments of reviewer 1, we have toned this down somewhat.\n4) I do not understand the purpose of including the overlying spherule bed in the\nmanuscript, how is this relevant to this study?\nIt is not overlying, but part of the ACM, as detailed in the sentence copied below\n(starting line 69). Spherules are the products of distal giant impacts, which seem to us\nhighly relevant to this study and emphasise that large impacts were common, consistent\nwith the lunar record.\n“Exceptionally preserved shatter cones within a dominantly siliciclastic horizon (Fig.\n2a,b), the Antarctic Creek Member (ACM), which has previously shown to contain\nspherules (quenched and devitrified impact-melt droplets)34,35, provide unequivocal\nevidence for a hypervelocity meteorite impact 3.47 billion years ago.”\n4\n5) Geologic and petrographic descriptions throughout the manuscript are sparse and\ninsufficient.\nIt's not clear to us what more the reviewer needs here. We provide detailed geological\nand petrological descriptions in the text as recognised throughout the review process,\nand additional information in the extended data. We believe what we present provides\nunequivocal evidence for a Paleoarchaean impact, as does reviewer 1. Our\ninterpretations are based on the discovery of shatter cones in a stratigraphic layer of\nknown age and mapped extent. However, in the extended data we now provide an\nadditional image (Extended Data Fig. 3) of a spectacular shatter cone surface that\nillustrates its petrological features.\nBest regards,\nCarl Alwmark\n5"}]

Decision letter