Metasomatic Evolution of Coesite-Bearing Diamondiferous Eclogite from the Udachnaya Kimberlite

Round 1

Reviewer 1 Report

Review of the manuscript entitled “Metasomatic Evolution of Coesite-Bearing Diamondiferous Eclogite  from the Udachnaya Kimberlite” by Mikhailenko, D. S., et al.

 

This study deals with the characterization of the main chemical features of the phase constituents of an eclogite xenolith brought to the surface by the Udachnaya kimberlitic pipe (Siberia). Major/trace element composition of clinopyroxene and garnet, ⁸⁷Sr/⁸⁶Sr isotopic concentration of clinopyroxene and major element chemistry of secondary-formed phases (e.g., ol, opx, phlog, sodalite, and djerfisherite) were used to model the interaction between the eclogitic matrix, metasomatic agents and the host kimberlite. According to the authors, a first enrichment process took place at depth and caused both modal and cryptic metasomatism. Later on, the infiltration of the host kimberlitic melt into the eclogite xenolith induced the precipitation, at shallower depth, of a second-generation mineral assemblage.

 

As a general comment, the manuscript deals with an interesting topic, since depletion and enrichment processes in sub-cratonic mantle in general, and in Siberian one in particular, are hotly debated, and a huge compilation of works can be found in literature. In my opinion, the manuscript structure requires some re-shaping, since some sections are missing, and others can be extended. For example, I would appreciate a section dealing with geological setting and state of art about metasomatic processes invoked by other authors for the lithospheric mantle beneath Udachnaya. The various models proposed in literature should also be discussed more in detail in section 4, where the authors should better highlight how their findings confirm (or differ from) what has been already proposed. In this respect, authors should also more exhaustively constrain which are the geochemical features of the metasomatic melt (or fluid), since it is not clear to me whether the modelled agent has kimberlitic or carbonatitic nature (see detailed comments below). English language can be improved as well.

 

At the present stage, I think that the manuscript requires significant changes; therefore, I recommend publication after major revision (see detailed comments below).

 

Federico Casetta

 

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Major comments:

The manuscript is lacking a geological setting section at all. I understand that Udachnaya kimberlitic pipe is quite well-known, but I would appreciate a brief introduction to the geological context and the still debated topics. This can be useful to the reader, especially in some sections where the main goal of this study should be framed into a more comprehensive picture I think that some problems occurred during references (or reference list) formatting. In the reference list, I can find 81 references, but up to 120 are cited in the text. As a consequence, it is quite difficult to verify if all related literature studies were properly cited. Line 216: if Eu* = 1, by definition it cannot be considered as an anomaly. Lines 242-244: explain which kind of calculations were performed, as well as which phases and elements were taken into account for the application of the cited thermobarometric models. I also suggest to include the results in the supplementary files, together with the related errors. Line 249: how did you remove “a priori” the effect of the kimberlitic melt? This is a hotly debated point in studies dealing with xenoliths from kimberlites, so I think that it would be appropriate to spend more time on this point. Moreover, this “removal” should be addressed only after having demonstrated that minor constituents have a secondary origin. Section 4: this section is the hearth of the manuscript. It is suggested that interaction between eclogite and a kimberlitic-like melt induces precipitation of a secondary assemblage of minerals, including, among the others, olivine, orthopyroxene, phlogopite and sodalite. In my opinion, the scenario in which these reaction/s took place is not very clear, and some points need to be addressed. 1) Orthopyroxene crystallization is not excepted in a reaction with a kimberlitic agent. If it was related to garnet destabilization, I would expect to see some chemical evidences. 2) Olivine Fo content is low when compared to those of phenocrysts reported in kimberlites, and olivine zoning means that the entraining kimberlite melt differs from the previous kimberlitic-like agent, is it true? 3) Does the trace element signature of clinopyroxene bear witness of the inferred metasomatic process? Are there any differences between cpx cores and rims in terms of trace elements? The metasomatic process should have been particularly efficient on cpx if it led to the precipitation of new phases and to the development of garnet zoning. Sr isotopes on clinopyroxene separates are poorly used to constrain the model proposed in the manuscript. Therefore, I suggest to insert a more exhaustive discussion on this point, especially in comparison with the huge amount of data on Udachnaya xenoliths and host kimberlite available in literature. Throughout the manuscript, it is not very clear to me whether the first metasomatic event occurring at depth was kimberlitic or carbonatitic. This point is crucial, since the nature of the metasomatic agent strongly affect the possible reactions in terms of major/trace element distribution in garnet and cpx, as well as the newly forming mineral assemblage (see comment/s above). For example, in the caption of Fig. 8 there is the first clear statement about the alkali-carbonatitic nature of this agent, whereas in the text the term kimberlitic-like is used; similar misleading statements are also present in the conclusion section.

 

Minor comments:

Lines 54-57: A forsterite component range of 90 to 95 cannot be considered as narrow. Furthermore, the link between the two sentences may require some clarification: how can the composition of diamond-hosted olivine inclusions be compared to the various olivine types identified by Kamenetsky et al. (2008)? Lines 60-62: This sentence needs to be clarified. Lines 75-82: This section is the core of the introduction, so I would suggest to clearly state what you did and why. What is Griba? How is it related to Udachnaya? Is it a coheval kimberlitic pipe? When subduction/metasomatism are thought to have taken place, and how are these processes related to your case study? Which isotopic concentrations were determined? On which phase/s? Lines 96 and 103: state in which laboratory did you perform in situ trace element and isotopic analyses Figure 1: I would suggest to re-organize the layout of this figure, since both thin section scan and BSE images are poorly readable. Figure 2: in the caption, please explain what A, B, C and dashed lines are referred to Figure 3: explain what the arrow indicates Line 155-156: what is the Mg# of orthopyroxene? Lines 173-174: if Fo content ranges from 76 to 69 they are not homogeneous Lines 175-178 and figure 6: some of the discussed trace elements concentrations could be below EPMA detection limits Line 207: insert reference for chondrite normalization values Lines 467-468: remove mineral formulas Lines 469-471: I think that the presence of mica means that the melt was hydrous Figure 8: in the caption, replace “geological history” with a more appropriate title (e.g. “Sketch”, “model” or “reconstruction” of the metasomatic processes..etc…) Supplementary figures: provide captions Supplementary tables: provide APFU calculations for all the detected mineral phases.

Author Response

Reviewer №1

As a general comment, the manuscript deals with an interesting topic, since depletion and enrichment processes in sub-cratonic mantle in general, and in Siberian one in particular, are hotly debated, and a huge compilation of works can be found in literature. In my opinion, the manuscript structure requires some re-shaping, since some sections are missing, and others can be extended. For example, I would appreciate a section dealing with geological setting and state of art about metasomatic processes invoked by other authors for the lithospheric mantle beneath Udachnaya. The various models proposed in literature should also be discussed more in detail in section 4, where the authors should better highlight how their findings confirm (or differ from) what has been already proposed. In this respect, authors should also more exhaustively constrain which are the geochemical features of the metasomatic melt (or fluid), since it is not clear to me whether the modelled agent has kimberlitic or carbonatitic nature (see detailed comments below). English language can be improved as well.

Major comments:

The manuscript is lacking a geological setting section at all. I understand that Udachnaya kimberlitic pipe is quite well-known, but I would appreciate a brief introduction to the geological context and the still debated topics. Added

 

This can be useful to the reader, especially in some sections where the main goal of this study should be framed into a more comprehensive picture I think that some problems occurred during references (or reference list) formatting. In the reference list, I can find 81 references, but up to 120 are cited in the text. As a consequence, it is quite difficult to verify if all related literature studies were properly cited. The used literature (see ‘Reference’ section) fully complies with the numbering. All the cited works can be found in Reference section.

 

Line 216: if Eu* = 1, by definition it cannot be considered as an anomaly. Corrected

 

Lines 242-244: explain which kind of calculations were performed, as well as which phases and elements were taken into account for the application of the cited thermobarometric models. I also suggest to include the results in the supplementary files, together with the related errors. Methods used to estimate the temperature and pressure are routine for mantle petrology and references to corresponding works are provided. Estimates employed compositions from the central parts of garnet and omphacite. Calculation error is indicated next to the resulting value in the corresponding section (Line 245).

 

Line 249: how did you remove “a priori” the effect of the kimberlitic melt? This is a hotly debated point in studies dealing with xenoliths from kimberlites, so I think that it would be appropriate to spend more time on this point. Moreover, this “removal” should be addressed only after having demonstrated that minor constituents have a secondary origin. Kimberlite is a very mobile component that does not only infiltrate grain boundaries but also occurs along optically invisible cracks during laser ablation. Only those analyses of the minerals were used in the article that fit the selection criteria described in the work of Aulbach et al., 2016 (Appendix B). Following this, we used a conservative value of >0.1 ppm Ba in garnet and >0.5 ppm in cpx as a first indication of kimberlite contamination. This is predicated on mineral-carbonated melt distribution coefficients and calculated mixes of pristine eclogite minerals and kimberlite melt.

 

Section 4: this section is the hearth of the manuscript. It is suggested that interaction between eclogite and a kimberlitic-like melt induces precipitation of a secondary assemblage of minerals, including, among the others, olivine, orthopyroxene, phlogopite and sodalite. In my opinion, the scenario in which these reaction/s took place is not very clear, and some points need to be addressed. 1) Orthopyroxene crystallization is not excepted in a reaction with a kimberlitic agent. If it was related to garnet destabilization, I would expect to see some chemical evidences. Formation of kelyphitic rim and orthopyroxene is linked to reaction of kimberlite melt and transportation of eclogite onto the surface. Formation of Mg-rich cores in olivine, orthopyroxene, K-feldspar and phlogopite results from hybridization of a kimberlite‐related melt with eclogite bodies residing in the mantle lithosphere beneath Udachnaya, with high activity of alkaline components (K, Na) and Cl in metasomatic reaction. Fe-rich olivine rims, sodalite and djerfisherite were produced by the latest metasomatic reactions, possibly during eclogite transport by the kimberlite melt. To clarify this for the reader, we have added the above information as a summary statement at the end of section 5.2.4, with reference to Figure 9.

 

2) Olivine Fo content is low when compared to those of phenocrysts reported in kimberlites, and olivine zoning means that the entraining kimberlite melt differs from the previous kimberlitic-like agent, is it true? We find that olivine core formation is linked to kimberlite-related melt, whereas olivine zoning is linked to the final stage of evolution of this melt within near-surface conditions and formation of Olivine Fo is most probably was happening within surface conditions, in the area of stability of djerfisherite and sodalite.

 

3) Does the trace element signature of clinopyroxene bear witness of the inferred metasomatic process? Are there any differences between cpx cores and rims in terms of trace elements? The metasomatic process should have been particularly efficient on cpx if it led to the precipitation of new phases and to the development of garnet zoning. Sr isotopes on clinopyroxene separates are poorly used to constrain the model proposed in the manuscript. This is why we used in situ data, obtained from both cores and rims of primary clinopyroxene. This shows no differences between core and rim. Reports in the literature where Sr/Sr ratio is suspected to have changed are Aulbach et al., 2019; Shu et al., 2016, 2018.

 

Therefore, I suggest to insert a more exhaustive discussion on this point, especially in comparison with the huge amount of data on Udachnaya xenoliths and host kimberlite available in literature. Although we agree that eclogites archive a wealth of information, the subject of this study is metasomatic history of the specific eclogite with extremely “atypical” mineral association. We prefer to not dilute this aspect by opening new discussions on the origin  of eclogites in Udachnaya or elsewhere.  For the particular and peculiar assemblage of the eclogite investigated here, comparison to literature data from Udachnaya or elsewhere will not add any value.

 

Throughout the manuscript, it is not very clear to me whether the first metasomatic event occurring at depth was kimberlitic or carbonatitic. This point is crucial, since the nature of the metasomatic agent strongly affect the possible reactions in terms of major/trace element distribution in garnet and cpx, as well as the newly forming mineral assemblage (see comment/s above). For example, in the caption of Fig. 8 there is the first clear statement about the alkali-carbonatitic nature of this agent, whereas in the text the term kimberlitic-like is used; similar misleading statements are also present in the conclusion section. The question is indeed interesting in view of the fact that the kimberlite melt is a result of evolution of carbonatitic melts! This is, in fact, the topic of the work of Golovin A V, Sharygin I S, Kamenetsky V S, et al more detailed. Alkali-carbonate melts from the base of cratonic lithospheric mantle: links to kimberlites[J]. Chemical Geology, 2018, 483: 261-274 .

 

Minor comments:

Lines 54-57: A forsterite component range of 90 to 95 cannot be considered as narrow. If we compare all worldwide dataset for ultramaphic olivine it is narrow range. In case of Udachnaya dataset, 90% analyses locate in range 91-95. We have clarified our statement in the introduction.

 

Furthermore, the link between the two sentences may require some clarification: how can the composition of diamond-hosted olivine inclusions be compared to the various olivine types identified by Kamenetsky et al. (2008)?. There is no difference in the chemical composition between olivine from diamond crystals and various olivines analysed in the work of Kamenetsky et al. (2008) were not found.

 

Lines 60-62: This sentence needs to be clarified. Done – we now explain that pyroxenes and garnet are liquidus minerals at high pressure.

 

Lines 75-82: This section is the core of the introduction, so I would suggest to clearly state what you did and why. The introduction states that “The aim of this study is to reconstruct the metasomatic history of an extraordinary eclogite xenolith sample containing both coesite (eclogitic mineral) and olivine and orthopyroxene (peridotitic mineral), from mineralogy, element compositions, and isotope data.”

 

What is Griba? How is it related to Udachnaya? Is it a coheval kimberlitic pipe? Corrected.

 

When subduction/metasomatism are thought to have taken place, and how are these processes related to your case study? Eclogite is a result of subduction of Archean ocean crust, which is therefore its protolith. During residence in the subcontinental lithosphere, it may multiply interact with fluids and/or melts. Both are important steps that allow us to place unique assemblage in the studied eclogite into context.

 

Which isotopic concentrations were determined? On which phase/s? ⁸⁷Sr/⁸⁶Sr isotope concentration in primary omphacite were determined - added.

 

Lines 96 and 103: state in which laboratory did you perform in situ trace element and isotopic analyses. Information added: Institute of Geosciences, Frankfurt University.

 

Figure 1: I would suggest to re-organize the layout of this figure, since both thin section scan and BSE images are poorly readable. We suspect that this was a low-resolution version for the review purpose.

 

Figure 2: in the caption, please explain what A, B, C and dashed lines are referred to. The reference in the description is indicated.

 

Line 155-156: what is the Mg# of orthopyroxene? #Mg_84-86

 

Lines 173-174: if Fo content ranges from 76 to 69 they are not homogeneous. These ranges are for olivine rims. Olivine has homogeneous compositions within the grain.

 

Lines 175-178 and figure 6: some of the discussed trace elements concentrations could be below EPMA detection limits. Yes - more information added, in particular detection limits - see also reply to Editor comments.

 

Line 207: insert reference for chondrite normalization values. Added

 

Lines 467-468: remove mineral formulas. Mineral formulas are given to highlight that all these minerals contain chlorine

 

Lines 469-471: I think that the presence of mica means that the melt was hydrous. Please see lines 471-475 with detailed description of this question.

 

Figure 8: in the caption, replace “geological history” with a more appropriate title (e.g. “Sketch”, “model” or “reconstruction” of the metasomatic processes..etc…) Yes, we added “cartoon” in the capture.

 

Supplementary figures: provide captions Supplementary tables: provide APFU calculations for all the detected mineral phases. There are captures to the supplementary figures/tables. We feel that APFU calculations are derivative data the provision of which is not essential.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript describes a rather interesting system. However substantial improvement is required before it is considered again for publication.

The writing style is inadequate, and the results are not clearly discussed as most of the manuscript.

Furthermore, the reference list is incomplete (81 vs. 129 in the main text) and it must be improved.

The authors must do an important effort in order to present their results in a better way and to simplify the manuscript. Graphics and tables in the actual version are not a help; on the contrary, contribute to make the manuscript even more difficult. Photomicrograph and BSE images must be improved in order to support the main interpretations.

A significant rewriting of the results section (number 3) and the improvement of sections 4 is recommended for a more efficient and clear presentation of results. Some suggestion to be considered, are:

Textural descriptions should be simplified and shortened; supplementary figures and tables can help to lighten up the text. Tables of geochemical results are more desirable than long texts with the same information. Please consider the inclusion of supplementary tables in the corresponding subsections of the main text. Previously, double check the coherency between text and tables, particularly check carefully the subsections 3.2.1 and 3.2.2.

Figures improving – Figures 2 and 3 have to be redraw in a fascinating and useful way, as well as figures 6 and 7, where the authors have to clarify all the symbols, labels and axis.

Please re-read carefully the final text and correct some mistakes.When these issues are resolved, the manuscript will have the potential to be an important contribution.

Author Response

The writing style is inadequate, and the results are not clearly discussed as most of the manuscript. More specific comments, rather than this sweeping comment would have been helpful.

Furthermore, the reference list is incomplete (81 vs. 129 in the main text) and it must be improved. Reference list is complete and the main text contains all the references

The authors must do an important effort in order to present their results in a better way and to simplify the manuscript. Graphics and tables in the actual version are not a help; on the contrary, contribute to make the manuscript even more difficult. Photomicrograph and BSE images must be improved in order to support the main interpretations. We made important changes in response to this and other reviewers’ comments and checked references to figures and tables. All the descriptions and interpretation are adequately supported with images and tables.

A significant rewriting of the results section (number 3) and the improvement of sections 4 is recommended for a more efficient and clear presentation of results. Some suggestion to be considered, are:

Textural descriptions should be simplified and shortened; supplementary figures and tables can help to lighten up the text. Tables of geochemical results are more desirable than long texts with the same information. Please consider the inclusion of supplementary tables in the corresponding subsections of the main text. added

Previously, double check the coherency between text and tables, particularly check carefully the subsections 3.2.1 and 3.2.2. Checked.

Figures improving – Figures 2 and 3 have to be redraw in a fascinating and useful way, as well as figures 6 and 7, where the authors have to clarify all the symbols, labels and axis. Corrected.

Please re-read carefully the final text and correct some mistakes. When these issues are resolved, the manuscript will have the potential to be an important contribution. Text was re-read and corrected.

Author Response File: Author Response.pdf

Reviewer 3 Report

Review of manuscript Minerals-673193, submitted to Minerals: Metasomatic Evolution of Coesite-bearing Diamondiferous Eclogite from the Udachnaya Kimberlite by Mikhailenko et al.

The authors studied eclogitic xenolith in a kimberlite from Udachnaya with detailed major element and trace element chemistry. The major and trace element chemistry was used to demonstrate that the eclogite derived subducted oceanic crust. Empirical thermobarometry was used to calculate P-T conditions. The author argued that the zoning in the xenoliths derived from metasomatism in the kimberlite diatreme. The research strategy used in the manuscript seem to be sounding; however, numerous details of the manuscript need improvements. Additionally, the language and writing of the manuscript need to be improved in order to make it a strong contribution.  

Major comments:

I. The Introduction section of the manuscript needs to be rewritten. The current writing of the Introductions contains numerous inaccurate information, and does not create a niche to demonstrate the necessity of this research.

II. The Petrography section needs significant improvement. The current petrographic description just demonstrates an overview of the rock textures, with many details described along with mineral chemistry, which is difficult to read. What about the specific petrographic texture? For example, what are the inclusions and inclusion texutres in garnet? Your omphacite seems to be the primary clinopyroxene, so it is better to name it as a Cpx I, following your current format of Cpx II. Various other textures such as olivine-, phlogopite- and diamond-bearing assemblages could be demonstrated.

III. The mineral chemistry sections needs to be more accurately described. The current mineral chemistry is reported in terms of endmembers (which is fine) and weight percentages from instrument analysis. However, mineral chemistry is typically reported in terms of per formula unit after normalization. Reporting weight percentages in text and in tables do not give readers direct information on how reliable your mineral chemistry is, which will undermine any further discussion. All figures (Figs. 2, 3 & 6) could be merged into one figure for mineral chemistry.

IV. Empirical thermobarometry, trace element chemistry and recalculated bulk rock composition of the eclogite need to be improved. These sections are lack of details to further evaluate the accuracy of the manuscript.

Minor comments:
Line 35–36: This is an incorrect statement. Origin of eclogite could be oceanic crust or continental crust (e.g. Grenville eclogite in eastern Canada and eclogite in North-East Greenland). Eclogite did not originated from Archean crust; in fact, the majority of documented eclogite is derived from post-Archean time. There are plenty of Phanerozoic high-pressure and ultrahigh-pressure eclogite (e.g. western Alps). See major comment I.

Line 36: What do you mean by mantle-derived? Are you referring to as eclogite formed at mantle depth?

Line 44–45: What exactly do you mean by ‘grossular-rich’ and ‘jadeite-rich’?

Line 45: The minerals, coesite, kyanite, rutile and pyrrhotite are not necessarily eclogitic. They could also be present in ultrahigh-pressure metapelite.

Line 45–46: The minerals ‘orthopyroxene, pyrope garnet, chromite and Ni-rich sulfide’ are not necessarily peridotitic phases.

Line 65: Are you sure that these inclusions are mainly found in ‘fibrous diamonds’?

Line 82: What results did you find in this research?

Line 87: Did your mineral chemistry come from the TESCAN SEM? As you are probably aware, that SEM, although arguably to be ‘quantitative’, do you give accurate quantitative results of mineral chemistry.

Line 90–91: What are the natural and synthetic standards you used for mineral chemistry? This information is critical because it tells the readers how accurate your mineral chemistry is.

Line 91: You need to tell the readers that EMP is electron microprobe.

Line 93: How many spectrometers is the EMP equipped with?

Line 93–95: Were the X-ray maps mapped with EMP? If so, what are the step sizes for your maps?

Line 118: How are the modal percentages estimated? The minerals, Cpx II, Ol, Pl and Kfsp seem to take more than 1 vol%. You could use an electron microprobe to map the whole thin section and get a more accurate estimate of mineral modes.

Line 130-131: The mineral chemistry needs to be reported in terms of per formula unit, rather than wt%.  You need to illustrate to the readers what kind of composition the garnet has.  See major comment III.

Line 134–135: Any BSE images to illustrate that kelyphite exists in the specimen? The current photomicrograph does not clearly show this mineral textural relation. See also major comment II.

Line 142–143: See major comment III. 

Line 144: What do you mean by ‘rock-forming omphacite’?

Line 145-146: Any images for the detailed textures?

Line 148: How come the Jd content in secondary clinopyroxene could be higher than the primary clinopyroxene? How did it form?

Line 155: What does the Enstatite [79] mean?

Line 158: See major comment III.

Line 162–163: Here you started using Grt I and Grt II, but this is not described in the text. To show the consistency of the text and images, you need to rewrite the petrography and mineral chemistry section.  See major comments II.

Line 166: What exactly does the cathodoluminescence topogram show, and why is this used here?

Line 167: These compositions are not all albite.  Does plagioclase show any compositional zoning?

Line 182-183: What is the point showing the X-ray maps of this large area? This needs to be clearly explained in the text. Is this mapped with electron microprobe or scanning electron microscope?

Line 185: Why is the core composition of olivine showing such large CaO & MnO distribution?

Line 189–196: What are the detailed mineral chemistry of these minerals? For example, what exactly is the meaning of ‘a significant percentage of…’ in Line 193?

Line 198: What do you mean by ‘rock-forming garnet’?

Line 223–228: What about the A, C and D in this figure? 

Line 237–245: It is unclear how P-T conditions estimated here, because of 1) the lack of details of thermobarometry used for the calculation, and 2) no references of the 91–97 in the list.  Additionally, in Line 239, the presence of diamond does not predict temperature.  So how did you come to this temperature estimates? See major element IV.

Line 251–253: How did the mineral modes estimated? You would need to get an accurate estimate (e.g. by whole thin section mapping) to retrieve detailed bulk composition, using software such as XMapTools. See major element IV.

Line 253–255: So what exactly is the density used in this calculation? See major element IV.

Without accurate determination of the mineral chemistry and bulk rock composition, the Discussion section 4.2 cannot be evaluated for exact details. Additionally, this section contains many reiterations of previous information (e.g. core-rim composition of garnet). Instead of simply reiterating analytical results, a more in-depth discussion of the forming mechanism, forming conditions, and metasomatic agents need to be presented.

Line 474: Did the volumes of garnet, omphacite olivine, and coesite change? The cartoon seems to show constant volume with change conditions.  Would the rim from another growth event on top of the original minerals?

Figure S1: What is the point of showing the map of this area? The textural relationship could be demonstrated with one backscattered electron image of this area. Additionally, the resolution of the scalebar is too low.

Figure S2: Again, what is the point showing the X-ray maps of this area? What does MKM stand for? If you intend to show the zoning in minerals (e.g. olivine), you need to enhance the zoning in the maps.

Table S1: Why did you report all the minerals just in wt%, instead of a normalized composition? What is the Orthopyroxene’s abbreviation?  There are two phlogophite analyses, one reported BaO and the other not. Di you change the analytical procedure for phlogopite analyses? Same for P2O5 for K-feldspar and phlogopite.

Table S2: All the analyzed isotopes could be marked with the standard format.  For example, ⁷Li instead of Li7.  Although most people read the manuscript could understand, you still need to write it in the standard format; otherwise, you will have to define what they mean. There are also other abbreviations which you need to define (e.g. rsde, dl).  What is the mineral that the last two analyses were on?  Why did some garnet reported core and rim composition, and others reported just core or rim?

Table S3: See comments on Table S2 for the name of isotope.  What is the density used for the calculation? 

Author Response

The authors studied eclogitic xenolith in a kimberlite from Udachnaya with detailed major element and trace element chemistry. The major and trace element chemistry was used to demonstrate that the eclogite derived subducted oceanic crust. Empirical thermobarometry was used to calculate P-T conditions. The author argued that the zoning in the xenoliths derived from metasomatism in the kimberlite diatreme. The research strategy used in the manuscript seem to be sounding; however, numerous details of the manuscript need improvements. Additionally, the language and writing of the manuscript need to be improved in order to make it a strong contribution.  

Major comments:

The Introduction section of the manuscript needs to be rewritten. The current writing of the Introductions contains numerous inaccurate information, and does not create a niche to demonstrate the necessity of this research. What do you mean? All details in introduction were support by references. Introduction has been amplified, also in response to editorial and other reviewers’ comments. It states clearly at the end the uniqueness of the sample, the problem and the data which will be employed towards solving the problem. The Petrography section needs significant improvement. The current petrographic description just demonstrates an overview of the rock textures, with many details described along with mineral chemistry, which is difficult to read. What about the specific petrographic texture? For example, what are the inclusions and inclusion texutres in garnet? The studied sample contains diamonds, which makes it unfortunately difficult to produce thin sections. Moreover a lot of valuable information will be lost in that case. As a result, the studied polished section is not a classical petrographic thin section. Because of the link between petrography and composition, we feel that the combined characteristics are better described together. This also avoids some repetition.

Your omphacite seems to be the primary clinopyroxene, so it is better to name it as a Cpx I, following your current format of Cpx II. Various other textures such as olivine-, phlogopite- and diamond-bearing assemblages could be demonstrated. Yes, we now clarify in captions to Fig. 1 and 4 that omphacite = CpxI (see also response to editorial comment).

III. The mineral chemistry sections needs to be more accurately described. The current mineral chemistry is reported in terms of endmembers (which is fine) and weight percentages from instrument analysis. However, mineral chemistry is typically reported in terms of per formula unit after normalization. Reporting weight percentages in text and in tables do not give readers direct information on how reliable your mineral chemistry is, which will undermine any further discussion. The mineral chemical compositions are the primary data we acquired, whereas cations per formula unit (cpfu) are only derivative data that are only sometimes reported. However, appreciating the reviewer’s concern (see also reviewer 2), we added a statement to the text that the stoichiometry was checked based on cpfu, which serves as a check on the quality of the analyses.

All figures (Figs. 2, 3 & 6) could be merged into one figure for mineral chemistry. I don’t quite understand why there is a need to include/cite per formula unit after normalization. In our area of study they usually include only minerals and specific oxides for source minerals.

Empirical thermobarometry, trace element chemistry and recalculated bulk rock composition of the eclogite need to be improved. These sections are lack of details to further evaluate the accuracy of the manuscript. The rationale and methods for the thermobarometry and bulk rock reconstruction, which are routine procedures in studies of eclogite xenoliths, are clearly laid out, with appropriate references in the sections where the data are described.

Minor comments:

Line 35–36: This is an incorrect statement. Origin of eclogite could be oceanic crust or continental crust (e.g. Grenville eclogite in eastern Canada and eclogite in North-East Greenland). Eclogite did not originated from Archean crust; in fact, the majority of documented eclogite is derived from post-Archean time. There are plenty of Phanerozoic high-pressure and ultrahigh-pressure eclogite (e.g. western Alps). See major comment I. This is of course a provocative statement that ignores modern models of mantle eclogite formation (Jacob 2004; Aulbach and Jacob 2016, and references therein), which are based combined compositional, isotopic, thermodynamic and experimental evidence for a low-pressure protolith formed by partial melting at comparatively low pressures, as applies to modern spreading ridges. There is a need to distinguish typical HP-HT eclogites from metamorphic complex and xenoliths of mantle eclogites from kimberlites, which mainly have Archean and Palaeoproterozoic ages. In fact, several independent age estimates for Siberian eclogites using different geochronometers clearly document an Archean protolith.

Line 36: What do you mean by mantle-derived? Are you referring to as eclogite formed at mantle depth? We clarified this – we here imply ultramafic rocks, such as peridotites or pyroxenites.

Line 44–45: What exactly do you mean by ‘grossular-rich’ and ‘jadeite-rich’? It means that It means that garnets of the eclogite paragenesis contain a more substantial grossular component than garnets of the peridotitic paragenesis. These characteristics of chemical composition indicate the mineral paragenesis.

Line 45: The minerals, coesite, kyanite, rutile and pyrrhotite are not necessarily eclogitic. They could also be present in ultrahigh-pressure metapelite. Firstly, an ultra-high pressure metapelite is an eclogite. Secondly, in mantle eclogites, the low-pressure protoliths of which have been identified based on multiple constraints (see response above), these minerals formed by prograde metamorphism of a broadly basaltic protolith.

Line 45–46: The minerals ‘orthopyroxene, pyrope garnet, chromite and Ni-rich sulfide’ are not necessarily peridotitic phases. Review articles show that “orthopyroxene, pyrope garnet, chromite and Ni-rich sulfide” the main peridotitic phases in diamond (Sobolev 1977; Meyer 1987; Stachel 2008; )

Line 65: Are you sure that these inclusions are mainly found in ‘fibrous diamonds’? According to the previous studies these mineral inclusions prevail in fibrous diamonds (see references: Izraeli, E.S.; Harris, J.W.; Navon, O. Brine inclusions in diamonds: a new upper mantle fluid. Earth and Planetary Science Letters 2001, 187, 323-332; Klein-BenDavid, O.; Izraeli, E.S.; Hauri, E.; Navon, O. Mantle fluid evolution—a tale of one diamond. Lithos 2004, 77, 243-253; Klein-BenDavid, O.; Izraeli, E.S.; Hauri, E.; Navon, O. Fluid inclusions in diamonds from the Diavik mine, Canada and the evolution of diamond-forming fluids. Geochimica et Cosmochimica Acta 2007, 71, 723-744; Klein-BenDavid, O.; Logvinova, A.M.; Schrauder, M.; Spetius, Z.V.; Weiss, Y.; Hauri, E.H.; Kaminsky, F.V.; Sobolev, N.V.; Navon, O. High-Mg carbonatitic microinclusions in some Yakutian diamonds—a new type of diamond-forming fluid. Lithos 2009, 112, 648-659; Weiss, Y.; Kessel, R.; Griffin, W.; Kiflawi, I.; Klein-BenDavid, O.; Bell, D.; Harris, J.; Navon, O. A new model for the evolution of diamond-forming fluids: Evidence from microinclusion-bearing diamonds from Kankan, Guinea. Lithos 2009, 112, 660-674; Zedgenizov, D.; Rege, S.; Griffin, W.; Kagi, H.; Shatsky, V. Composition of trapped fluids in cuboid fibrous diamonds from the Udachnaya kimberlite: LA-ICP-MS analysis. Chemical Geology 2007, 240, 151-162; Zedgenizov, D.; Ragozin, A.; Shatsky, V.; Araujo, D.; Griffin, W.L.; Kagi, H. Mg and Fe-rich carbonate–silicate high-density fluids in cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia). Lithos 2009, 112, 638-647; Zedgenizov, D.; Ragozin, A.; Shatsky, V.; Griffin, W. Diamond formation during metasomatism of mantle eclogite by chloride-carbonate melt. Contributions to Mineralogy and Petrology 2018, 173, 84.

Line 87: Did your mineral chemistry come from the TESCAN SEM? As you are probably aware, that SEM, although arguably to be ‘quantitative’, do you give accurate quantitative results of mineral chemistry. We appreciate the concern. Trace elements in olivine were acquired quantitatively, please see response to editor and addition to the text.

Line 90–91: What are the natural and synthetic standards you used for mineral chemistry? This information is critical because it tells the readers how accurate your mineral chemistry is. We used natural standards for measuring trace elements in olivine. The detailed description of standards can be found in work of Lavrent’ev, Y.G. [Ref.72]

Line 91: You need to tell the readers that EMP is electron microprobe. Corrected

Line 93: How many spectrometers is the EMP equipped with? WDS equipped by 5 spectrometers.

Line 93–95: Were the X-ray maps mapped with EMP? If so, what are the step sizes for your maps? All the given maps are mapped with EPMA equipment WDS. Step size is 1 micron, as detailed in the methods section.

Line 118: How are the modal percentages estimated? The minerals, Cpx II, Ol, Pl and Kfsp seem to take more than 1 vol%. You could use an electron microprobe to map the whole thin section and get a more accurate estimate of mineral modes. The calculation of percentage content of each mineral was made in program CorelDraw with a special plug-in “SanM Curve”. Each mineral was circled, after it we made a calculation of its area with help of plug-in. Indeed, using electron microprobe maps for calculation of accurate percentage content is an alternative though not intrinsically more accurate way. In fact, inaccuracies in the calculated modes are small relative to the uncertainty related to the limited area combined with a coarse-grained sample. The metasomatic history of this particular eclogite sample is here illuminated using petrographic observation combined with detailed mineral compositional data for both primary and secondary minerals. While the calculation of the percentage content of secondary minerals may add some information on the volumes involved in the metasomatic reaction, they add no information on the processes involved, and therefore are inconsequential for the aims of this study.

Line 130-131: The mineral chemistry needs to be reported in terms of per formula unit, rather than wt%.  You need to illustrate to the readers what kind of composition the garnet has.  See major comment III. Please see our response above.

Line 134–135: Any BSE images to illustrate that kelyphite exists in the specimen? The current photomicrograph does not clearly show this mineral textural relation. See also major comment II. Kelyphitization is not main object of this study and detailed characterization of this phenomenon has been reported in numerous previous studies of mantle xenoliths. Moreover, see other images in the manuscript which characterize kelyphite rims (Fig 4-D; Fig S2)

Line 142–143: See major comment III. Please see our response above

Line 144: What do you mean by ‘rock-forming omphacite’? We mean that is primary clinopyroxene – omphacite. We now clarify in the introduction what we imply by rock-forming minerals in the context of eclogites.

Line 145-146: Any images for the detailed textures? These textures were described earlier in many articles (also see Misra et al., 2004 and Mikhailenko et al., 2016)

Line 148: How come the Jd content in secondary clinopyroxene could be higher than the primary clinopyroxene? How did it form? Figure 4 illustrates that secondary and primary Cpx have non-overlapping compositions. Secondary clinopyroxene is result of decompression and partial melting during transformation by kimberlite melt.

Line 155: What does the Enstatite [79] mean? According to the common approved classification by Morimoto 1989, secondary orthopyroxene is enstatite. 

Line 158: See major comment III.

Line 162–163: Here you started using Grt I and Grt II, but this is not described in the text. To show the consistency of the text and images, you need to rewrite the petrography and mineral chemistry section.  See major comments II. Description added.

Line 166: What exactly does the cathodoluminescence topogram show, and why is this used here? Cathodoluminescence topogram shows the internal structure and growth zones of diamond, which were described in the lines 197-203

Line 167: Does plagioclase show any compositional zoning? Yes, this is now clarified in the text: Commonly plagioclase stands out for its homogeneity within the grain and large variations of content between grains within the sample.

Line 182-183: What is the point showing the X-ray maps of this large area? This needs to be clearly explained in the text. Is this mapped with electron microprobe or scanning electron microscope? All the presented maps are mapped with help of EPMA equipment WDS. The map demonstrates the state of main source minerals in relation to secondary. In addition, it illustrates the zoning on distribution MnO and MgOin olivine.

Line 185: Why is the core composition of olivine showing such large CaO & MnO distribution? Most likely the reason of such considerable variability is the result of differential ratio of reactive fluid/melt with garnet- omphacite, but the results section is not the appropriate place to discuss this.

Line 189–196: What are the detailed mineral chemistry of these minerals? For example, what exactly is the meaning of ‘a significant percentage of…’ in Line 193? The proportion of the hercynite component is now given. Previous work devoted to the study of secondary minerals in eclogites from kimberlites have elaborated at length on this issue (Misra et al., 2004; Mikhailenko et al., 2016). We feel that a more detailed description does not add to the discussion developed in this manuscript.

Line 198: What do you mean by ‘rock-forming garnet’? Corrected

Line 223–228: What about the A, C and D in this figure? Added

Line 237–245: It is unclear how P-T conditions estimated here, because of 1) the lack of details of thermobarometry used for the calculation, Additionally, in Line 239, the presence of diamond does not predict temperature.  So how did you come to this temperature estimates? See major element IV. Yes, we now give more information in the section: Estimation of eclogite formation P-T condition has been carried out by help of combination of garnet- clinopyroxene thermometer EllisGreen1979 and barometer of Beyer et al., 2015. The results were checked against the known regional conductive geotherm (Boyd et al 1997).

2) no references of the 91–97 in the list. All the indicated references are in the section References.

Line 251–253: How did the mineral modes estimated? You would need to get an accurate estimate (e.g. by whole thin section mapping) to retrieve detailed bulk composition, using software such as XMapTools. See major element IV. Please see reply to Line 118.

Line 253–255: So what exactly is the density used in this calculation? See major element IV. Without accurate determination of the mineral chemistry and bulk rock composition, the Discussion section 4.2 cannot be evaluated for exact details. Additionally, this section contains many reiterations of previous information (e.g. core-rim composition of garnet). Instead of simply reiterating analytical results, a more in-depth discussion of the forming mechanism, forming conditions, and metasomatic agents need to be presented. We used density for main minerals in the garnet (almandine 4,32; andradite 3,85; grossular 3,59; pyrope 3,58) and primary clinopyroxene (jadeite 3,25; diopside 3,25, hedenbergite 3,56). The general discussion has been amplified in response to all reviewers’ comments.

Line 474: Did the volumes of garnet, omphacite olivine, and coesite change? The cartoon seems to show constant volume with change conditions.  Would the rim from another growth event on top of the original minerals? This scheme is designed to demonstrate only the process-oriented metasomatic history for the studied eclogite, not the fluxes involved. We now clarify this in the caption to Figure 8. Based on the P-T parameters the rate of diffusion is very high and, at mantle conditions, all the traces of zoning, if initially present, would completely have disappeared.

Figure S1: What is the point of showing the map of this area? The textural relationship could be demonstrated with one backscattered electron image of this area. Additionally, the resolution of the scalebar is too low. This map demonstrates location of all secondary mineral assemblages and their relationships (location on depend each other, intergrowth and etc). Backscattered electron image can’t provide full information on the location secondary mineral assemblages or zoning or lack thereof if not accompanied by significant changes in BSE response.

Figure S2: Again, what is the point showing the X-ray maps of this area? What does MKM stand for? If you intend to show the zoning in minerals (e.g. olivine), you need to enhance the zoning in the maps. Corrected

Table S1: Why did you report all the minerals just in wt%, instead of a normalized composition? Because it is a generally accepted style of presenting analytic data when studying mantle rocks.

What is the Orthopyroxene’s abbreviation?  Corrected

There are two phlogophite analyses, one reported BaO and the other not. Di you change the analytical procedure for phlogopite analyses? Same for P2O5 for K-feldspar and phlogopite. When measuring the chemical composition of the minerals there were used the same measuring parameters.

Table S2: All the analyzed isotopes could be marked with the standard format.  For example, ⁷Li instead of Li7.  Although most people read the manuscript could understand, you still need to write it in the standard format; otherwise, you will have to define what they mean. Corrected

There are also other abbreviations which you need to define (e.g. rsde, dl).  Added

What is the mineral that the last two analyses were on? Added description

 Why did some garnet reported core and rim composition, and others reported just core or rim? Only those analyses of the minerals are used in this work that fit the selection criteria described in the work of Aulbach et al., 2016 (Appendix B). Following this, we used a conservative value of >0.1 ppm Ba in garnet and >0.5 ppm in cpx as a first indication of kimberlite contamination.

Table S3: See comments on Table S2 for the name of isotope.  What is the density used for the calculation? Corrected.

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Review of the manuscript entitled “Metasomatic Evolution of Coesite-Bearing Diamondiferous Eclogite from the Udachnaya Kimberlite” by Mikhailenko, D. S., et al.

I found the reviewed manuscript significantly improved with respect to the earlier version. Authors addressed almost all the points raised during the previous round of revision, and modified the text accordingly. In my opinion, the manuscript requires few further modifications (see below), thus I recommend publication after minor revision.

---------

Minor comments:

Line 146: Substitute “crystalized” with “crystallized” Lines 148-149: References to be reported as numbers according to journal’s formatting style Line 204: delete “and” Fig. 2: explain in the caption what do the dashed arrow and letters A, B, C indicate Lines 429-430: report in the text the opx Mg# as done in the revision notes Line 807: delete “kimberlite” Supplementary table S1B: authors stated in the revision notes that APFU calculations are derivative and not essential. In my opinion, APFU calculations are fundamental to understand the quality of each mineral phase analysis. I feel that providing APFU for the secondary peculiar mineral assemblage detected in the eclogite (as done for garnet, cpx and olivine in table S1A) could be extremely important in the light of the main findings of this study.

Author Response

Line 146: Substitute “crystalized” with “crystallized” Corrected

Lines 148-149: References to be reported as numbers according to journal’s formatting style Corrected

Line 204: delete “and” Deleted

Fig. 2: explain in the caption what do the dashed arrow and letters A, B, C indicate  Added

Lines 429-430: report in the text the opx Mg# as done in the revision notes Added

Line 807: delete “kimberlite” Corrected

Supplementary table S1B: authors stated in the revision notes that APFU calculations are derivative and not essential. In my opinion, APFU calculations are fundamental to understand the quality of each mineral phase analysis. I feel that providing APFU for the secondary peculiar mineral assemblage detected in the eclogite (as done for garnet, cpx and olivine in table S1A) could be extremely important in the light of the main findings of this study. Added

Author Response File: Author Response.docx

Reviewer 2 Report

The authors did a good reorganization of the manuscript. In its present form, the manuscript is much more readable, and now results and conclusions are clearly presented.

Just a few corrections are necessary:

line 177: ,from Udachnaya kimberlite pipe,

line 188: However -> unfortunately

line 273: …7.5 cm in maximum length, -> with a 7.5 cm….

line 424: (Table S1;) -> (Table S1)

line 426: typical Raman peaks in olivine -> typical olivine Raman peaks

line 473-474: together with the secondary mineral assemblage of CpxII, plagioclase, and sodalite -> together with secondary CpxII-plagioclase-sodalite assemblage

line 514: Rare earth elements in… -> Rare earth elements (REE) omphacite patterns show a humped shape with…decrease toward HREE (….

line 807: in the Udachnaya-East kimberlite -> from the Udachnaya-East body

Author Response

line 177: ,from Udachnaya kimberlite pipe, Added

line 188: However -> unfortunately Corrected

line 273: …7.5 cm in maximum length, -> with a 7.5 cm…. Corrected

line 424: (Table S1;) -> (Table S1) Corrected

line 426: typical Raman peaks in olivine -> typical olivine Raman peaks Corrected

line 473-474: together with the secondary mineral assemblage of CpxII, plagioclase, and sodalite -> together with secondary CpxII-plagioclase-sodalite assemblage Corrected

line 514: Rare earth elements in… -> Rare earth elements (REE) omphacite patterns show a humped shape with…decrease toward HREE (….Corrected

line 807: in the Udachnaya-East kimberlite -> from the Udachnaya-East body Corrected

 

Author Response File: Author Response.docx