PONE-D-21-39227Global kimberlite prospectivity from reconstructions of mantle flow over the past billion yearsPLOS ONE

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[NF and OFB were supported by Australian Research Council grant LP170100863. This research was undertaken with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government. This research was supported by the Australian Government's National Collaborative Research Infrastructure Strategy (NCRIS), with access to computational resources provided by the National Computational Infrastructure (NCI) through the National Computational Merit Allocation Scheme. Access to NCI was partly supported by resources and services from the University of Wollongong (UOW). Key model results and scripts are available at https://doi.org/10.5281/zenodo.5760115.]

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Additional Editor Comments:

Dear Dr. Nicolas Flament,

Thank you very much for submitting your interesting work to PLOS One. I have received a very detail review on your manuscript. Both reviewer and I found that the topic is interesting and novel and are worthy of publication in PLOS One after a moderate revision. The reviewer has given a numerous comments and suggestions on your manuscript (including those in the attached PDF files), which I believe are very useful for improvement of quality of the manuscript. Please consider all these comments and suggestions carefully during revision.

I am looking forward to receiving your revision manuscript soon.

Yours sincerely,

Shuan-Hong Zhang

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

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Reviewer #1: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This work builds up on the hypothesis of Torsvik et al. (2010 Nature) that kimberlites are mostly derived from plumes stemming from the margins of LLSVPs (i.e. seismically defined thermochemical piles above the core-mantle boundary), and assesses the likelihood that the position of mobile thermochemical piles better match the location of Phanerozoic kimberlites compared to fixed thermochemical piles. This is a good idea to test because it is increasingly recognised that LLVSPs are probably not fixed but must be swept around by tectonic processes and mantle convection. To achieve this goal the Authors employ a fluid dynamic model to simulate modification of the thermochemical piles position over the last 640 Myr and identify as zones of kimberlite generation those where the thermochemical piles overlay with the position of cratons (the latter monitored using state-of-the-art plate reconstruction models). They find a good match between kimberlite location and these possible zones of kimberlite generation, and conclude that using mobile rather than fixed thermochemical piles marginally improve the previously proposed hypothesis that most kimberlites are linked to upwellings from these deep mantle structures. They further conclude that this approach could be exploited to identify prospective regions for diamond exploration.

The manuscript is well written and easy to follow. The conclusions are justified by the modelling results. However, I must stress I am not a geodynamic modeller so I could not evaluate the numerical model and some of the boundary conditions. As my expertise is in kimberlite and mantle geochemistry, I have focused my review on the overall approach taken by the Authors while also assessing the soundness of the background information they provide.

I believe the manuscript has one major problem: It relies on craton outlines (those of Merdith et al., 2021) which, to me, have little geological meaning because they extend way beyond known cratonic mantle occurrences and, locally, even into oceanic domains. While the Authors also employ the craton outlines of Artemieva (2006), but hardly discuss this alternative except for one statement, there are more recent and robust definitions of craton (and especially their mantle roots) such as Pearson et al. (2021 Nature), which provide a much better fit for the theme under discussion here.

The problem with employing the craton outlines of Merdith et al becomes clear in figure 9. There is no thick lithosphere (say cratons) in most of Europe (except parts of Ukraine and NW Russia) or in most of US, including all eastern US (e.g., Pearson et al., 2021), which is the opposite of what figure 9 implies (as well as figure 1). A better definition of thick lithosphere will considerably improve the outcome of this work. This issue might seem trivial, but it is not because changing the definition of craton completely modifies the model results. As an example, at L475-476 the Authors state that using the craton outlines of Artemieva (2006) the average distance between predicted and actual position of kimberlites increases significantly, again consistent with the gross overestimation of craton sizes in Merdith et al.

In addition, or perhaps in alternative, if the ultimate aim is to assess diamond prospectivity, it might be better to run the model using as diamond prospective regions only those where the lithosphere is thicker than ~180 km (or ~150 km if the aim is to match the formation of kimberlites) for example based on global tomographic models. This definition of diamond prospective areas is not necessarily confined to cratons but also include thick pericratonic regions (e.g., Limpopo Belt between South Africa and Zimbabwe) where important diamond mines occur (e.g., Venetia). This empirical approach would also circumvent potential problems with craton definition taken from other publications such as that of Merdith and coworkers.

My second major comment will probably sound naïve and reflects my ignorance with fluid dynamic modelling. The Authors start their model at 1 Ga and the conditions are not well specified – i.e. what is the structure of deep-mantle thermochemical piles at this time? Could you please clarify it? They make sure that the model matches the present-day extension and configuration of LLSVPs above the core-mantle boundary to assess model validity, which seems to be logical. However, would not be more insightful to start with the present-day configuration of LLSVPs, which is well established (and not hypothetical) and reconstruct how the position and shape of LLSVP changed backward in time using existing geological constraints (e.g., position of paleo-subduction zones) and mantle flow models? Again, this might sound a naïve comment, but it would be nice to hear the Authors thoughts. It might perhaps be an interesting follow-up work.

Finally, referencing to the literature specific to the origin of kimberlites is often inappropriate and so are some statements – however, I do acknowledge that none of the Authors has a background in kimberlite petrology-geochemistry, so this is not a major issue from my perspective. I have suggested several amendments in the attached pdf and some notable examples follow.

L45. This statement does not make any sense (“the average depth of kimberlite eruptions is 200 km”) and no surprise it comes from obscure Russian literature. Kimberlites originate from depths in excess of 120 km and generally 150 km, this is all we know - e.g., Giuliani and Pearson (2019 Elements) for a concise review (cited later on).

L46. RE superdeep diamonds: also Pearson et al (2014 Nature) and Tschauner et al (2021 Science). However, it should be noted that the evidence supporting a deep kimberlite origin from superdeep diamonds is controversial because these diamonds could have been transported to the base of the lithosphere before being entrained by kimberlite magmas (e.g., Harte and Cayzer, 2007 Phys Chem Min).

L47. The record of kimberlite magmatism is actually episodic not continuous, e.g., Heaman et al., 2019 Elements

L74. I think the only option to link LLSVPs and kimberlites is provided by plumes, either their peripheries or weak ones (see Enrst, 2014 for an assessment of the relationship between LIPs and kimberlites)

L108-110. Unfortunately, the database of kimberlite geochronology by Tappe et al. (2018) has two biases, the first one being geographic areas of more intense exploration for diamonds and the second one being several ages for multiple kimberlite bodies from the same cluster or field (say area). In addition, there might be an inherent preservation bias, which cannot be addressed. I would just remove this statement.

L118-120. Not all kimberlites are located on craton so using Merdith et al. (2021) to obtain craton extensions is not a good idea. Many kimberlites are located in Proterozoic mobile belts and are commonly not diamondiferous. Also, cratons are confined to continental interiors unlike the assessment by Meredith et al. shown in figure 1a.

L364-365. I am not aware of any kimberlite emplaced in Western Australia at this time (~240 Ma). Not the Authors' fault, just one of the several problems with the database of Tappe et al 2018.

L541-544. Additional factors to consider when modelling potential kimberlite formation include lithospheric stress, pre-existing translithospheric structures, plume buoyancy and composition just to name a few.

Finally, it should be kept in mind that not all kimberlites (or related magmas such as those from North China; see Tompkins et al., 1999 Proc 7th Inter Kimb Conf) are necessarily linked to the deep mantle; some might be related to shallower sources including the mantle transition zone (e.g., Kjarsgaard et al., 2017 G-cubed; Chen et al., 2020 Geology) or also the lithospheric mantle (e.g., Giuliani et al., 2015 Nature Comms). This should be noted in the manuscript in my opinion.

Figures 7 and 8 would be easier to follow if the whole continental blocks were shown rather than cratons only. Similarly, the statement at L393-394 is not easy to picture because continental blocks are not shown but only craton outlines.

Additional minor edits and suggested references are included in the attached pdf.

I hope my comments will be helpful and my apologise for the late review (6-Feb-2022)

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Reviewer #1: No

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Attachments

Attachment

Submitted filename: PONE-D-21-39227_reviewer_mod.pdf

Mapping global kimberlite potential from reconstructions of mantle flow over the past billion years

PONE-D-21-39227R1

Dear Dr. Flament,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Shuan-Hong Zhang, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Dear Dr. Flament,

Thank you very much for revising the manuscript and addressed all the comments and suggestions clearly. After evaluating from the previous reviewers and my reading through of your manuscript, I am pleased to confirm that your paper has been accepted for publication in PLOS ONE.

Thank you for choosing PLOS ONE to plublish your interesting work.

Best wishes,

Shuan-Hong Zhang

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: (No Response)

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

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Reviewer #1: Yes: Andrea Giuliani