the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Jun 2026
Advancing meteorite impact chronology with in situ mica Rb-Sr dating
Abstract. Meteorite impacts are highly energetic processes that drives deformation on Earth under extreme pressure and temperature conditions, far exceeding those of typical crustal processes. Consequently, it may promote environmental perturbations, blossoming/extinction of life and even produce suitable conditions for the formation of mineral resources. Thus, constraining the timing of impacts is pivotal to shedding light on its role in Earth’s biogeodynamics, yet less than ~20 % of the impacts worldwide are precisely dated. Here, we present novel in situ mica Rb–Sr isotopes from the Australian Acraman and Gosses Bluff impact sites collected via LA-ICP-MS/MS, including single- and multi-collector instruments to expand the chronological toolbox for dating meteorite impacts. Whilst monazite (980 ± 28 Ma) and apatite (1448 ± 79 Ma) yield older ages compared to the expected Acraman impact age of 588 ± 35 Ma, in situ Rb–Sr from muscovite-bearing domains from the Acraman ejecta layer (580 ± 8 Ma; multi-collector age) and associated fine-grained zircon (598 ± 16 Ma) are consistent with the expected impact age. Similarly, apatite (132 ± 14 Ma) and mica-bearing domains (137 ± 9 Ma; multi-collector age) are comparable to the proposed impact age of 133 ± 3 Ma, whilst zircon yields mostly discordant data. The Rb–Sr results comparison between single- and multi-collector ICP-MS/MS has shown that the latter yielded significantly more precise Sr measurements, likely due to measurement of St isotopes with high resistor Faraday cups (1013 Ω) resulting in improved signal-to-noise ratio, consequently yielding more precise isotopic ratios and isochron ages. Our findings show that in situ Rb–Sr dating of micas formed during impact metamorphism offers the means for determining the timing of meteorite impact events. This approach effectively addresses the textural complexities commonly present in impact-related rocks, which are often overlooked by bulk isotope-dilution techniques, and delivers accuracy sufficient to establish the age of impacts. The effectiveness of in situ Rb–Sr dating of impact-related micas may be attributed to their higher resistance to hydrothermal alteration compared to Ar isotopes, which often yield complex degassing spectra and younger apparent ages such as for the Acraman impact. This study shows that in situ Rb–Sr isotopes of newly grown micas in impact-related rocks refines the chronology of impacts, with potential to increase the number of dated impacts globally with a low-cost, speedy technique with minimum sample preparation. Such task is crucial for understanding the role of meteorite impacts, including their potential influence on environmental crises, mass extinctions, and the emergence of life.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-3441', Thomas Belgrano, 10 Aug 2026
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RC2: 'Comment on egusphere-2026-3441', Alicia Cruz-Uribe, 26 Aug 2026
Ribiero et al. present Rb-Sr dates determined by single and multicollector tandem mass spectrometry of impact rocks from the Acraman and Gosses bluff impact sites. I agree with the comments made by Thomas Belgrano, though in some cases I think there are a few more fundamental aspects of this work that need to be addressed in a major revision in order for it to be suitable for publication.
First and foremost, it is worth reiterating the lack of proofreading of the manuscript. Careful attention should be paid to the entire text, including subject headers (example: 3.1 automate mineralogy mapping). This is not grammatically sound in its present state; please address carefully in review. Thanks!
This also does not just apply to the basics of the grammar, but to some of the things that are said (or not). For example, lines 13-15 in the abstract are lacking the words “from the Gosses Bluff impact site”, or at least I think that’s what that sentence is referring to. Another example from line 251: “We collected 46 Rb–Sr data at the Adelaide University”. This is fairly nonsensical, and these mistakes are prevalent throughout the manuscript. Line 255: “At 1’Curtin University, we collected 53 Rb–Sr data”. Eek.
In situ should be italicized throughout.
Some notes about the methodologies presented: There is insufficient detail regarding the experimental setups of any of these labs. At a minimum, the ICP-MS parameters for every machine need to be included as supplemental tables. It is extremely difficult to assess the validity of the data, most particularly the multicollector data, without knowing the analytical setup. Additionally, in the text, the multicollector workflow needs to be detailed, including how the instrument was tuned. I feel this is a basic requirement for an untested system from this lab. Additionally, the analysis of only a single secondary mineral for Rb-Sr (LaPosta) is not sufficient, particularly given that the isochron from one session is 87 +- 4 Ma. This is not terribly convincing. Also, why were there no white mica reference materials run on the Neoma? The Acraman impact sample is dominated by white mica; reference to biotite is thus moot.
As the authors point out, matrix correction of Rb/Sr ratios is critical to account for the differences in fractionation between matrices (ala Giuliani et al. 2024). However, I do not believe there is sufficient evidence given to justify the use of the age correction on these materials in the way that I have to assume they have been done (as this is not well detailed in the text). It seems as though both samples are highly heterogeneous within each laser spot. The need for matrix correction arises from multiple processes, the sum total of which constitute the overall matrix effects in a sample. The problem with ablating domains that contain both muscovite and/or glass and/or feldspar and/or quartz is that each of these phases has 1) a distinct ablation threshold and behavior, and 2) distinct Rb-Sr fractionation behavior, leading to multiple differences in the ablation response and Rb-Sr fractionation compared to the two types of reference materials used (glass for baseline subtraction, biotite for age correction). The problems that can arise from this approach are massive differences in matrix, none of which can be characterized, and which are not directly comparable to any of the reference materials. So, how can we trust an age from a mixed sample that has been matrix corrected to a mica (and possibly the wrong mica, for instance, by using biotite to correct muscovite). The fundamental question is, do the materials analyzed behave like glass, or like mica? Or potentially, like neither?
Now, my understanding of the magnitude of fractionation on an ASI laser system is that it is less so than on an ESI or Teledyne machine due to primarily the difference in the objective lens, which effectively dictates how the focus of the laser changes downhole. However, there is no mention of the scale of the correction factors applied to any of the data. Again, please include this information in the supplementary material. Regardless of the magnitude, we know that there is still a correction that has to be done, and the authors need to demonstrate that the corrections they have done are valid for the materials in question. This is not insignificant, as the entire study hinges upon this.
Some comments on the single versus multicollector data: what are the internal precision numbers based on? Given the precision of the Sr isotope data, it appears that the precision on the Neoma is at least an order of magnitude too low for that instrument. However, it is difficult to assess the tuning protocol without the details given, so I think this can only be assessed after the manuscript has been revised. The point raised by Thomas about YO and ZrO interferences is valid, though again, impossible to assess with what is given in the methods. Please expand.
One small comment about the use of the word triple quadrupole: this was a terrible misnomer at the introduction of the 8800. None of these machines is a triple quadrupole. It really is more correct to just say quadrupole-based tandem mass spectrometer, or just ICP-MS/MS. Ok, soapbox rant over.
My final comment (since I realize that all of these comments are criticisms): I think this is really cool, and has potential. I really like the impact structure story, and the idea of using Rb-Sr to look at these systems. It will be a nice contribution once the details are cleaned up a bit.
Citation: https://doi.org/10.5194/egusphere-2026-3441-RC2
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- 1
Review of Ribeiro et al. “Advancing meteorite impact chronology with in situ mica Rb-Sr dating” for Geochronology, August 2026
The paper presents the application of a suite of modern, robustly applied geochronological methods to two Australian impact crater case studies. The writing/presentation, especially the abstract, need some editing and a thorough proof read is needed throughout. Some more details are needed for completeness in the methods section, but these are minor revisions easily implemented, as the methods as employed seem rigorous. My only significant content request is to consider how accurate Rb/Sr corrections applied to the volcanic glass pellets are – whether matrix-matched glass or compositionally similar mica is more appropriate, and whether your data allow you to assess this. I would also like to see a more detailed explanation of what was propagated into the uncertainties, and to bring this into line with convetional external uncertainty reporting (if this is not the case already).
With these minor revisions and touch ups throughout, this will be a useful contribution and no doubt will be made use of by further studies looking to reapply and develop impact-dating.
Dr. Thomas Belgrano, University College Dublin
Section/Line by Line Comments.
Abstract: The abstract is long at >400 words. Can this be refined into a more user friendly length (i.e. <250–300 words)? It is also peppered with grammatical/style errors that need a go-over before resubmission. Examples are listed below:
In the first sentence: ‘processes that drives’.
In the second sentence, reference to the previous sentence's subject as ‘it’, but there are several nouns in the previous sentence this could ambiguously refer to, and the one the authors mean is plural in any case, so ‘it’ is not appropriate.
L8. According to the journal rules, LA-ICP-MS/MS should be spelled out in the abstract and again at first use in the text.
L10. The complete geochronometers need to be stated: mineral host and isotopic system.
L13/14. Which impact is the second sentence referring to?
L17. Misspelling of the symbol Sr? Enhanced precision is unlikely to be solely due to the amplification, as Faradays are generally similarly or even less sensitive than ion-counting QQQ detectors. The major precision jump derives from simultaneous, correlated detection of isotopes and higher ion yields.
L30. It’s difficult to foresee how Rb-Sr could inform research into the emergence of life. How many unmetamorphosed impact related rocks are there from the Eoarchean? The paper is justified well-enough without this claim, or perhaps ‘extinction and diversification of life’ is a better fit?
Section 2.
Readers of this section would benefit from splitting into sub-sections labelled by each impact.
L76. *The age of the Acraman structure
L93. It would be good to introduce the relatively uncommon term suevite (e.g. on L89 at mention of impact melt breccia).
Section 3.
L130. More details are needed on the uncertainty propagation method. If only one uncertainty is reported, this should be the fully propagated external uncertainty including errors on the calibration materials, decay constants, inter-session variance, etc. following e.g. Rosel & Zack, 2022, Gilbert and Zack 2024.
L148 + L169. State the reference values and how they were measured. The ages are missing units on L148.
L174. *Thermo Scientific. The acronym ICP-MS has already been introduced? Take the opportunity to introduce MC-ICP-MS/MS.
L216-217. Need to state the results and reference values for the key secondaries here, as in the other method sections. Again, specify the uncertainty treatment (should follow the recommendations of Horstwood et al. 2016; https://doi.org/10.1111/j.1751-908X.2016.00379.x).
Treatment of common Pb, even if uncorrected for, should be explained explicitly given the mix of minerals dated.
Some Neoma labs experience ZrO-YO related interferences when analysing with NIST and biotite. This seems to have been overcome here, judging by the secondary ages, but its worthing mentioning why you are confident they are not an issue, as if present they would affect the standards but not the unknowns.
Some discussion of is needed as to matrix correction and validation of the glass pellet ages. Surely NIST would be a better calibration material than a mica? Can the authors show some downhole patterns (e.g. in the supplement at least) to support this one way or the other?
Section 4
Fig. 4./QQQ data: Why not combined the two labs data into a third isochron? If uncertainties are propagated conservatively using the higher for each parameter from each session, this should be defensible and looks like it would yield better-constrained ages. The one outlying btu included analysis from Gosses bluff (Fig. 4c) could be justifiably rejected and would likely improve the age correspondence between the two samples? It looks like a postulated secondary isochron could even be fit to all those outlying analysis, probably recording a younger devitrification/alteration event.
The mineral ‘aliettite’ is uncommon enough it needs introduction at first use.
Section 5.
L.331-335. See comment on additional sources of increased precision for the abstract.
L342. We have experienced the same, it’s worth setting out why explicitly – superior low abundance sensitivity of the QQQ compared to multi-collection but higher LOD by Neoma (or whatever the analysts attribute this to).
L404. What is meant by the lower mass resolution issues referred to here? I struggle to see how this would have an effect. Lower sensitivity and sequentially detected isotopic ratios are more likely culprits.
Sect. 5.3 is good, really useful stuff.
Sect 5.4. Worth pointing out the lack of mineral reference materials for some of the envisioned work.