Geochemical Characterization of Zircon in Fyfe Hills of the Napier Complex, East Antarctica

Round 1

Reviewer 1 Report

The comments and suggestions - attached (pdf)

Comments for author File: Comments.pdf

Author Response

Reply to Reviewer 1

Thank you very much for soliciting helpful reviews of our work. All reviewers provided constructive comments, which we have closely followed while revising our work. We provide a detailed response to all reviewers’ comments, demonstrating how we have fully addressed all the issues raised in the review.

We largely revised the section of the result and discussion, especially the zircon domains’ description and interpretation, following the comments.

The text including abstract was rewritten according to the editor’s and reviewers’ suggestion.

 

Reply to questions

1. The history of the complex includes several (at least two high-temperature episodes, including the UHT) after the protolith formation and it is difficult to understand why the authors select the “largest” 2501 Ma peak among the wide total spread of ages as representing the UHT event? I could see no prove either from REE-patterns (they are simply different within the different ages), neither from oxygen isotopes (they are more or less similar and, as the authors state, could be affected by superimposed processes), nor from CL-images (metamorphic zones, but why UHT metamorphic?).

 

Reply:

We justified the largest age peak (2501Ma) means the UHT metamorphism in the Napier Complex, based on the mineral assemblage in the Fyfe Hills sample and the U-Pb age obtained in this study is consistent with the timing of the UHT metamorphism proposed by the several previous studies. Petrological description (2.2. Sample) and a photomicrograph (Figure 2) of this sample were added in the manuscript.

 

2. What could be the interpretation of the “multiple age peaks” (p.5). Do they correspond to a single durable event, or reflect several (how many) separate processes?

Reply:

The authors consider that the largest age peak (2501Ma) means a single event which can be divided from the other peaks. Also, the older peaks (2533~2810Ma) mean igneous event(s), and the younger peaks (2423~1978Ma) mean local fluid infiltration or local deformation event(s). The authors cannot determine the number of the igneous and local event(s), respectively, because we have no evidence to determine this issue in this study.

 

3. Am not a native English speaker but would strongly suggest improving the language and style considerably.

Reply:

The language in the manuscript was checked by a native writer.

Reviewer 2 Report

This paper presents new REE, age, and isotopic data of zircon separated from one sample, which is collected from the Napier Complex in Antarctica. The presented data mostly confirm the information reported in previous studies and contributes to our understanding of the Archaean crustal processes. The authors also distinguish between three zircon domains, based on the CL signal, REE pattern, and the isotopic age. This is a concise contribution with robust data, however, authors would need to provide a significantly revised version for it to be accepted. I have some concerns regarding the novelty and significance of the study as well as the clarity of the presentation of material.

 

Major comments:

1. The English need significant improvement, there are many typos, unclear sentences, and wrong grammatical constructions throughout the text. Some checkup by a native speaker or an editing service is critical.
2. In many paragraphs, sentences are not connected logically. One paragraph should express one thought and one thought should logically follow the next one. I will give specifics below.
3. Internal textures in zircon are not explained or shown in images, it makes it very confusing to understand the domain classification.
4. The classification of domains is unclear and inconsistent. There is a “metamorphic domain”, “inherited domain” and “young age domain”. “Metamorphic” and “inherited” are terms that suggest interpretation – but the justification for such interpretation is not presented in the paper. Young-age domain, in contrast, is a factual term, based on data, and interpretation is given. You need to explain this terminology and justify your interpretation.
5. Another thing about the domain classification. The order of events suggests that (1) “inherited” domains formed first, these are the CL- dark cores; then (2) “metamorphic” domains form, these are CL-bright metamorphic rims; then the “young-age” domains formed, which is, according to your interpretation, a product of disturbance of U-Pb system. But why are they listed not in this order? Why metamorphic domain is listed as (a) and inherited as (b)? Justify.
6. Provide a petrographic image of the rock sample, and expand the petrographic description. This will help in understanding the zircons in context.
7. In the introduction, you mention two scenarios for UHT metamorphism that exist in the current literature: (i) and (ii). You promise to clarify, which one is confirmed by your study. But I did not see this discussion. Obviously, this is a scenario (ii), but you need to say it in the discussion.
8. Young-age domains are explained as a product of U-Pb system disturbance. What was the cause of such disturbance? Did you observe these analyses on the Discordia line? Are the data points discordant? If not, then there was no disturbance.
9. The paper is lacking a bigger context; it is not explained how this contribution will advance our knowledge and what does it mean for our understanding of geological processes, etc. This should be provided in the abstract, discussion, and conclusion.

For minor comments see the attached file. 

I hope this helps. 

Comments for author File: Comments.pdf

Author Response

Reply to Reviewer 2

Thank you very much for soliciting helpful reviews of our work. All reviewers provided constructive comments, which we have closely followed while revising our work. We provide a detailed response to all reviewers’ comments, demonstrating how we have fully addressed all the issues raised in the review. We largely revised the section of the result and discussion, especially the zircon domains’ description and interpretation, following the comments. The text including abstract was rewritten according to the editor’s and reviewers’ suggestion.

Reply to minor comments are described in the attached PDF.

 

Reply to major questions and comments

1. The English need significant improvement, there are many typos, unclear sentences, and wrong grammatical constructions throughout the text. Some checkup by a native speaker or an editing service is critical.

Reply:

The language in the manuscript was checked by a native writer.

 

2. In many paragraphs, sentences are not connected logically. One paragraph should express one thought and one thought should logically follow the next one. I will give specifics below.

Reply:

The sentences in the section of Introduction and Discussion were mainly corrected basically according to the comments by the reviewer 2.

 

3. Internal textures in zircon are not explained or shown in images, it makes it very confusing to understand the domain classification.

Reply:

The authors modified the description about internal textures of zircons in the figure and the figure caption (Figure 3).

 

4. The classification of domains is unclear and inconsistent. There is a “metamorphic domain”, “inherited domain” and “young age domain”. “Metamorphic” and “inherited” are terms that suggest interpretation – but the justification for such interpretation is not presented in the paper. Young-age domain, in contrast, is a factual term, based on data, and interpretation is given. You need to explain this terminology and justify your interpretation.

Reply:

The authors modified the description about the classification of zircon domains in the manuscript according to the comments by the reviewer 2. The expressions of “metamorphic”, “inherited” and “young age” were changed because these are open to misunderstanding. The description of the classification, in particular how to divide the three groups, were explained in the manuscript.

 

5. Another thing about the domain classification. The order of events suggests that (1) “inherited” domains formed first, these are the CL- dark cores; then (2) “metamorphic” domains form, these are CL-bright metamorphic rims; then the “young-age” domains formed, which is, according to your interpretation, a product of disturbance of U-Pb system. But why are they listed not in this order? Why metamorphic domain is listed as (a) and inherited as (b)? Justify.

Reply:

The order of the three domains (“metamorphic”, “inherited”, and “young age”) were derived from the priority in the study. The authors think that the timing of the metamorphic event(s) is one of the most important topics in the study of the Napier Complex. However, the authors understand the suggestion by the reviewer 2 because the order suggested by the reviewer 2 are easier for the readers to understand the timing which the domains were formed. So, the order of the domain classification was modified according to the suggestion by the reviewer 2.

 

6. Provide a petrographic image of the rock sample, and expand the petrographic description. This will help in understanding the zircons in context.

Reply:

The authors added a petrographic image (Figure 2) and description (“2.2. Sample”) about petrography of the sample in the manuscript.

 

7. In the introduction, you mention two scenarios for UHT metamorphism that exist in the current literature: (i) and (ii). You promise to clarify, which one is confirmed by your study. But I did not see this discussion. Obviously, this is a scenario (ii), but you need to say it in the discussion.

Reply:

The authors added the description about the scenario for the UHT metamorphism in the discussion of the manuscript.

 

8. Young-age domains are explained as a product of U-Pb system disturbance. What was the cause of such disturbance? Did you observe these analyses on the Discordia line? Are the data points discordant? If not, then there was no disturbance.

Reply:

In general, Concordia curve means a series of plots on which both two ratios (i.e. 207/206 and 238/206) indicate the same value of each age (i.e. 207Pb/206Pb age and 238U/206Pb age). So, even if all data are plotted on or around Concordia curve, all data cannot be said to be undisturbed. As shown in the Concordia plot (Figure 4), a single Discordia line can be drawn from ~2.5Ga to ~1.9Ga.

Moreover, when the U-Pb data were interpreted together with these REE patterns and CL images of the “young age domains” (Group III in the manuscript), the data means younger ages. The more detail discussion is described in the section of 4.3. Interpretation of post metamorphic ages.

 

9. The paper is lacking a bigger context; it is not explained how this contribution will advance our knowledge and what does it mean for our understanding of geological processes, etc. This should be provided in the abstract, discussion, and conclusion.

Reply:

The authors summarized new insights for understanding of geological processes from this study in the section of conclusion as follows.

• The UHT metamorphism occurred after 2532 Ma which is the newfound igneous components, and the metamorphic overgrowth or recrystallization of zircon occurred at 2501 Ma under high temperature conditions.
• REE abundance is a useful indicator of metamorphic zircon in garnet-bearing gneiss, whereas the Th/U ratio is not always useful.
• Oxygen isotope composition in zircon re-equilibrated after metamorphism under dry UHT conditions.

Author Response File: Author Response.pdf

Reviewer 3 Report

Row 90: "Rocks" stands for samples, probably?

Row 156: A reference stands in the text (Song et al. 1996) which is not included in the reference list.

Row 168: The term "inherited core" is mentioned here (and "inheritance" stands on Fig. 2), but "inherited domains" are introduced in the first paragraph of the discussion, row 218 only. It would be better to write simply about cores before the discussion.

Figure 4: The reference on the figure also should be indicated with the [1] number of the list.

Row 188 and Table S2: Why do you calculate Eu* and Ce* values as arithmetic means? There are several solutions (e.g. Zhong, S., Seltmann, R., Qu, H. et al. Characterization of the zircon Ce anomaly for estimation of oxidation state of magmas: a revised Ce/Ce* method. Miner Petrol 113, 755–763 (2019)), but the most common approach is to use geometric means.

Row 228: In the Analytical Method chapter you write that zircons were randomly selected. Here you write that zircons were selected with regard of transparency. Please remove the contradiction!

Row 236: Why do you think that the REE patterns reflect HT growth or modification? Please indicate also the reasons (the indicative properties of the REE pattern) for this!

Paragraphs in rows 230-253: You use the Th/U ratio similarly to the HREE/MREE ratio in your reasoning. It would be useful to construct a class scatter plot similar to Figure 6 also from the Th/U - calculated age relationship data, maybe as a Fig 6b.

Conclusion (iv): It is not clear from the discussion, that oxygen isotope distribution was necessarily changed, and cannot be homogeneous originally. Even if so, the mechanism "thermal diffusion without fluid" is based on the conclusion of a referred article (UHT metamorphism under dry condition) and is not discussed here.

There are minor spelling errors (e.g. row 163: systemtic - systematic, row 225: consisistent - consistent, row 236: temperatrue - temperature, and there should be a grammar check done mainly on the Discussion chapter.

Author Response

Reply to Reviewer 3

Thank you very much for soliciting helpful reviews of our work. All reviewers provided constructive comments, which we have closely followed while revising our work. We provide a detailed response to all reviewers’ comments, demonstrating how we have fully addressed all the issues raised in the review. We largely revised the section of the result and discussion, especially the zircon domains’ description and interpretation, following the comments. The text including abstract was rewritten according to the editor’s and reviewers’ suggestion.

 

Reply to questions

Row 90: "Rocks" stands for samples, probably?

Reply:

Yes. The description was modified to avoid misleading.

 

Row 156: A reference stands in the text (Song et al. 1996) which is not included in the reference list.

Reply:

The authors added the reference (Song et al., 1996) into the reference list.

 

Row 168: The term "inherited core" is mentioned here (and "inheritance" stands on Fig. 2), but "inherited domains" are introduced in the first paragraph of the discussion, row 218 only. It would be better to write simply about cores before the discussion.

Reply:

The authors modified the expressions into more simple ones in the manuscript.

 

Figure 4: The reference on the figure also should be indicated with the [1] number of the list.

Reply:

Yes. The authors modified the figure including the expression into more simple one in order to avoid misleading.

 

Row 188 and Table S2: Why do you calculate Eu* and Ce*values as arithmetic means? There are several solutions (e.g. Zhong, S., Seltmann, R., Qu, H. et al. Characterization of the zircon Ce anomaly for estimation of oxidation state of magmas: are vised Ce/Ce* method. Miner Petrol 113, 755–763 (2019)), but the most common approach is to use geometric means.

Reply:

The authors use the arithmetic means to make consistent with the ratio calculation of the same sample in the previous works (Horie et al., 2012).

 

Row 228: In the Analytical Method chapter you write that zircons were randomly selected. Here you write that zircons were selected with regard of transparency. Please remove the contradiction!

Reply:

The authors picked up about 500 grains randomly in the process of hand-picking, and then selected about 70 grains with regard of transparency in the 500 grains hand-picked. This description is open to misunderstanding and unnecessary. So, this description “randomly” was deleted in the manuscript.

 

Row 236: Why do you think that the REE patterns reflect HT growth or modification? Please indicate also the reasons (the indicative properties of the REE pattern) for this!

Reply:

The authors consider the REE in zircon reflect the HT growth or modification because

 

Paragraphs in rows 230-253: You use the Th/U ratio similarly to the HREE/MREE ratio in your reasoning. It would be useful to construct a class scatter plot similar to Figure 6 also from the Th/U - calculated age relationship data, maybe as a Fig 6b.

Reply:

The authors think that it is difficult to use the Th/U ratios similarly to the H/MREE ratios of the sample. As shown in the plot of calculated age vs Th/U ratio attached, the Th/U ratios show no correlation with the ages. The authors consider the difference between Th/U and H/MREE are derived from the valance in zircon crystal: Th and U are tetravalent, whereas REE are basically trivalent. 

 

Conclusion (iv): It is not clear from the discussion, that oxygen isotope distribution was necessarily changed, and cannot be homogeneous originally. Even if so, the mechanism "thermal diffusion without fluid" is based on the conclusion of a referred article (UHT metamorphism under dry condition) and is not discussed here.

Reply:

The authors modified the discussion about the oxygen isotope in the zircons in the section of “4.4. Oxygen Isotope in High-Grade Metamorphic Zircons” and deleted a referred article to avoid misleading according to the comments by the reviewer 3.

 

There are minor spelling errors (e.g. row 163: systemtic -systematic, row 225: consisistent - consistent, row 236: temperatrue - temperature, and there should be a grammarcheck done mainly on the Discussion chapter.

Reply:

The language in the manuscript was checked by a native writer. Those spelling errors have been corrected.

Round 2

Reviewer 1 Report

Two small comments

1. "to verify and obtain new insights about the timing of the UHT metamorphism. Multiple U–Pb ages in the sample have already been reported..." (raws 46-47 in the ms)

Authors reply: We justified the largest age peak (2501Ma) means the UHT metamorphism in the Napier Complex, based on the mineral assemblage in the Fyfe Hills sample and the U-Pb age obtained in this study is consistent with the timing of the UHT metamorphism proposed by the several previous studies.

So, the authors aim to verify the timing of the UHT metamorphism, based on the timing of the UHT metamorphism proposed by previous studies. For me it looks a bit controversial. Would be worth to clarify.

2. The native English speakers very often do not know e.g., when "Fyfe Hills" and when "the Fyfe Hills" etc. But these points I would rather leave to the editors

Author Response

1st Reviewer

The text was rewritten on the basis of the reviewers’ suggestion.

 

Reply to comments:

1. "to verify and obtain new insights about the timing of the UHT metamorphism. Multiple U–Pb ages in the sample have already been reported..." (raws 46-47 in the ms)

Authors reply: We justified the largest age peak (2501Ma) means the UHT metamorphism in the Napier Complex, based on the mineral assemblage in the Fyfe Hills sample and the U-Pb age obtained in this study is consistent with the timing of the UHT metamorphism proposed by the several previous studies.

So, the authors aim to verify the timing of the UHT metamorphism, based on the timing of the UHT metamorphism proposed by previous studies. For me it looks a bit controversial. Would be worth to clarify.

 

Reply: 

The authors agree with the reviewer 1. In this study, the authors focused on and discuss the geochronology of Fyfe Hills. The authors added the description “(v) The UHT metamorphism in Fyfe Hills occurred after 2533 Ma, which is the newfound igneous components, and the metamorphic overgrowth or recrystallization of zircon occurred at 2501 Ma under high temperature conditions “ in the conclusion.

 

2. The native English speakers very often do not know e.g., when "Fyfe Hills" and when "the Fyfe Hills" etc. But these points I would rather leave to the editors

 

Reply: 

The language in the manuscript was checked by native speaker and finally checked by the public proofreading service.

Reviewer 2 Report

Thank you for addressing the comments from the previous round of revision. The manuscript improved but still needs some work.

 

Main problems remain:

• No introductory sentence and problem statement in the abstract.
• Confusing description of the CL zones, which is not supported by figures.
• Lack of discussion of the significance of your results.
• English remains poor. I strongly recommend doing something about it. I give a few suggestions/corrections below, but it’s definitely not all issues

See the line comments in the attached file.

Comments for author File: Comments.pdf

Author Response

2nd Reviewer

The text was rewritten on the basis of the reviewers’ suggestion.

 

 

Reply to main problems:

• No introductory sentence and problem statement in the abstract.

Reply:

The following sentences were added to the abstract.

Line 10–12 “Ultra-high temperature (UHT) metamorphism plays an essential role in the development and stabilization of continents through accretionary and collisional orogenesis. The Napier Complex, East Antarctica, preserves UHT metamorphism, and the timing are still debated.”

 

• Confusing description of the CL zones, which is not supported by figures.

Reply:

CL images were added to Figure 3. Also, the CL images were referred in the text. Please check from Line 146.

 

• Lack of discussion of the significance of your results.

Reply:

The authors insist that this text already contains the important discussion.

The timing of the UHT metamorphism in the Napier Complex is critical issue for unraveling the Earth’s crustal evolution from Hadean to Paleoproterozoic. In the present study, only one sample collected from Fyfe Hills was analyzed, but the data are important to discuss about the crustal evolution in the Napier Complex. In the Napier Complex, the UHT metamorphism affected nearly 100,000 km² of crust. Most UHT region is covered by ice and outcrops are limited to coast, islands, and inland mountains. Moreover, the newfound igneous components of 2533 Ma will be very important information for the thermal history in the Napier Complex.

In addition, re-equilibration of the oxygen isotope data in the UHT zircons has never been reported before. The information is also important information for behavior of oxygen under metamorphic conditions.

 

• English remains poor. I strongly recommend doing something about it. I give a few suggestions/corrections below, but it’s not all issues

Reply:

The language in the manuscript was checked by native speaker and finally checked by the public proofreading service.

 

Reply to line comments:

Lines 10-13: no problem statement

Reply:

The following sentences were added to the abstract.

Line 10–12 “Ultra-high temperature (UHT) metamorphism plays an essential role in the development and stabilization of continents through accretionary and collisional orogenesis. The Napier Complex, East Antarctica, preserves UHT metamorphism, and the timing are still debated.”

 

Lines 18-19: two parts of the sentence are disconnected. I do not understand what you are trying to say. Do you want to say: “The 207Pb/206Pb ages of Group II have an age peak centered at 2501 Ma, therefore, the quartzo-feldspathic gneiss experienced high-temperature metamorphism at 2501 Ma.” ?

Reply:

The sentence was modified to “The ²⁰⁷Pb/²⁰⁶Pb ages of Group II have an age peak at 2501 Ma, therefore, the gneiss experienced high temperature metamorphism at 2501 Ma.”.

 

Line 26: remove “one”

Reply:

Removed.

 

Line 28: should read: “and is the famous UHT terrane” famous for what?!!

Reply:

The sentence was changed to “Ultra-high temperature (UHT) metamorphism is critical to understanding the large scale tectonic processes affecting the deep crust and lithosphere throughout Earth history. The UHT metamorphism is recognized at over 60 areas or localities [1]. The Napier Complex in East Antarctica is the location where the regional UHT metamorphism was first recognized”.

 

Line 34: “(ii) it occurred from ~2500 to 2450 Ma” – this age range can also be described as not earlier than 2840 Ma, which you attribute to (i) only

Reply:

The sentence was changed to “(i) the UHT metamorphism occurred no earlier than 2840 Ma and possibly from 2590 to 2550 Ma, (ii) it occurred from around 2500 to 2450 Ma”.

 

Lines 37-38: “provides an opportunity for integration between age and crystallization condition such as temperature and melt composition.” I do not understand this sentence. What is the integration between age and crystallization condition? Sould it be “conditions”?

Reply:

The sentence was changed to “provides an opportunity for integration between age and melt composition.”.

 

Line 41: “provide useful information for insights into” – select one, either “provide useful information about” or “provide insights into” – not both

Reply:

The sentence was changed to “provide useful information about”.

 

”exchange during” – exchange between what and what? Unclear

Reply:

The sentence was changed to “isotope exchange between zircon and surrounding minerals”.

 

Line 45: “we focus on the garnet-bearing”

Reply:

Modified.

 

Line 50: remove “observation of the”

Reply:

Removed.

 

Line 60: “Archean crustal records have been collected at several localities of the Napier Complex ([8] and references therein).” This sentence is out of place here. Move it either after lines 54-55 or after 58

Reply:

Move it after lines 54-55.

 

Line 62: “the age of most of the rocks”

Reply:

Modified.

 

Line 64: “mid- to late-Archean”

Reply:

Modified.

 

Figure 1: still did not explain what the black dots on the map are. Outcrops? Sampling locations? Unclear.

Reply:

Black dots indicate outcrops. Explanation was added to the figure caption.

 

Line 72: “broken line shows the position of the boundary”

Reply:

the position of the boundary. Explanation was added to the figure caption.

 

Line 76: “sampling location” (not “sampling point”)

Reply:

Modified.

 

Line 84: you previously had these peaks in the figure, which was convenient. I would prefer you to bring them back to the figure

Reply:

The data of probability density diagram using in previous version were cited from Horie et al. (2012). Same data were cited in Figure 4, and so, the authors removed the figure from here.

 

Line 99: do you mean, “the most transparent”? More transparent than what?

Reply:

Modified to “the most transparent”.

 

Line 100: “zircon grains” – how many?

Reply:

67 grains. One grain removed from the resin disc during polishing. Number was added to the text.

 

Line 101: information on the polishing method is still missing.

Reply:

The polishing method was added to the text. It is very conventional method.

 

Line 134: should read: “were collected using Faraday cups with a width of 300 μm.”

Reply:

Modified.

 

Section 3.1. - confusing description, not supported by figures. All descriptions should be supported by citing figures AND figure panels

Reply:

CL images were added to Figure 3. Also, the CL images were referred in the text. Please check from Line 146.

 

Line 142: “round in shape” OR “have rounded shapes” (not “have rounded in shape”)

Reply:

Modified to “have rounded shapes”.

 

Line 143-144: “approximately half of the zircon grains in the sample show core-rim structures with…” – which ones are these in your figure?!

Reply:

CL images were added to Figure 3c–g.

 

Line 146: “characterized by broad zoning with a dark CL response” – in figure 3a I see a zircon with a bright core, dark mantle, and bright rim. Which one is that in your classification?

Reply:

The grain has core-rim structure, namely oscillatory zoning core and rim with a bright CL response.

 

Lines 150-152: “other half of the zircon grains with no apparent core-rim structure can be divided into broad zoning with dark CL response, oscillatory zoning, sector zoning, broad zoning with bright CL response, and nebulous to fir-tree zoning as well as core and rim” which ones are these in your figure? At the beginning of the sentence you said that these grains do not have core-rim structure, and then you talk about “as well as core and rim”. This is very confusing.

Reply:

CL images of non-core-rim grain were added to Figure 3c–g.

 

Figure 3. cut off the edges of each panel, leaving only described grains in the images. The figures are not cited in your text and do not correspond to your descriptions in text.

Reply:

CL images of non-core-rim grain were added to Figure 3c–g. Also, the CL images were referred in the text. About “cut off the edges”, these are based on original images by SEM observation. If modified them, there are risk of falsification and then we use original ones.

 

Line 168: “The broad zoned cores with dark a CL response” -> “with a dark CL response”

Reply:

Modified.

 

Line 170: “grains with nebulous to fir-tree zoned textures” – which are these? With core-rim? Without core-rim texture? Where are these in figures? Do you mean core or rims with nebulous texture?

Reply:

Non-core-rim structure. The sentence was modified to “The Th/U ratios of the non-core-rim structured grains with nebulous to fir-tree zoned textures” and the CL images were referred.

 

Line 179: “were absent in this study” – in which study? In [1] or in yours?

Reply:

The present study. The sentence was modified.

 

Previously you had all these peaks shown in the figure, which added much more clarity to your discussion

Reply:

The data of probability density diagram of Horie et al. (2012) includes Figure 4 (gray color plots and line).

 

Section 3.3. Give references to the figure AND to the figure panels

Reply:

The references were added to the text and the figure caption.

 

Line 188: remove this sentence.

Reply:

Removed.

 

Line 192: “from the rims”

Reply:

Modified.

 

Line 193: “fractionation”?

Reply:

Modified.

 

Line 194: “of the cores”

Reply:

Modified.

 

Lines 198-199: “The REE patterns of the grains with no evident core-rim structure depend on internal zoning (Figure 5).” – depend how?

Reply:

The sentence was modified to “The REE patterns of the non-core-rim structured grains with oscillatory or sector zoning (HREE/MREE=0.49~7.29, HREE/LREE=34~1505, and Eu/Eu*=0.014~0.617) are similar to those of cores (Figure 5; Table S2). Those of the non-core-rim structured grains with nebulous to fir-tree zoned textures (HREE/MREE=0.23~1.98, HREE/LREE=9~159, and Eu/Eu*=0.014~0.078) are similar to those of rims (HREE/MREE=0.41~1.53, HREE/LREE=11~133, and Eu/Eu*=0.014~0.234).”.

 

Figure 5: what does “grain” means?

Cores and rims (not just “core” and “rim” – I assume, you analyzed several?)

Reply:

Modified.

 

Line 226: these peaks are not shown in the figures

Lines 230-231: these peaks are not shown in the figures

Reply:

The ages are not peak ages, but spot ages listed in Table S1. Citation of Table S1 was added.

The Figure 6 is probability density diagram and each peaks include some age components (spot ages) and errors. The following figure (left, the figure cannot be pasted in this form, so please check an attached PDF.) indicates age components of each age peaks. The age components are not equal to the peak age. Therefore, to avoid causing confusion, the left-side figure does not use.

 

Line 235: are you talking about cores or rims?

Line 236: are you talking about cores or rims? “with a” (not “witha”)

Reply:

All grains, namely cores, rims, and non-core-rim structured grains. The text was modified.

 

Line 247: “in this study” – in which study? [1] or yours? Unclear. Replace “there are” with “we report”

Reply:

The present study. The sentence was modified.

 

Lines 262-263: should read: “Previous works suggest that domains with Th/U ratios lower than 0.1 can be interpreted as forming during high-grade metamorphism”

Reply:

Modified.

 

Line 273: in your figure, the peak is at 2533 Ma (not 2532 Ma). Change the text or the figure. Give a reference to a figure.

Reply:

Modified.

 

Lines 273-300: Give references to the figure AND to the figure panels

Reply:

The references were added to the text and the figure caption.

 

Line 277: Figure 7a

Line 292: Figure 7c

Line 303: “inherited coreS”

Reply:

Modified.

 

Line 305: “δ18O in the overgrowth and recrystallization” - overgrowth and recrystallization are processes, they can not have oxygen composition

Reply:

The sentence was modified to “the overgrowth and recrystallization domains”.

 

Lines 312-314: grammar is messed up, re-phrase.

Reply:

The sentence was modified to “It is uncommon that multiple components in the protolith have similar δ¹⁸O. In addition, δ¹⁸O of the rim is equal to that of the core because, δ¹⁸O of the rim results from oxygen isotope exchange with the host rock.”.

 

318: “precious”?!! in geology, precious can be metals and some gemstones, not opportunity

Reply:

The word was modified to “valuable”.

 

Discussion abruptly ends with no consideration of the implications of your works for Napier Complex or anything like that.

Reply:

The authors insist that this text already contains the important discussion.

 

Figure 9: should be placed in results section

Reply:

4.3. Interpretation of Post Metamorphic Ages was modified. The geological event(s) after the UHT metamorphism was not reported by previous field-based studies, but similar ages have occasionally been reported. Previous studies suggested that the younger age distribution represents a disturbance of the U–Pb system in zircon grains by local fluid infiltration or local deformation event(s). One of the evidence is that the younger zircons (spots 7.1, 43.1, 46.2, and 64.1) show the REE patterns with lower HREE/MREE ratios which are features of metamorphic zircons (overgrowth and recrystallization) under high temperature conditions. The high temperature metamorphism never occurred after 2501 Ma. Another evidence is that the core (spot 10.1: 2478 ± 7 Ma) of grain No. YH1606A-10 is younger than the rim (spot 10.2: 2502 ± 7 Ma) (Figure 3b), which indicates the radiogenic Pb loss from the core.

 

Line 335: “disturbance of the U–Pb system” – you did not demonstrate or discussed this disturbance. Why did it happen? What is the evidence? Explain it in detail or remove the claim.

Reply:

Figure 9 includes interpretation and is not result only. Therefore, Figure 9 was not moved.

 

 

Line 336: comma before “which”

Reply:

Modified.

 

Please provide concluding remarks on:

- What have you learned about NC?

- About the UHT metamorphism?

Reply:

The timing of the UHT metamorphism in the Napier Complex is critical issue for unraveling the Earth’s crustal evolution from Hadean to Paleoproterozoic. In the present study, only one sample collected from Fyfe Hills was analyzed, but the data are important to discuss about the crustal evolution in the Napier Complex. In the Napier Complex, the UHT metamorphism affected nearly 100,000 km² of crust. Most UHT region is covered by ice and outcrops are limited to coast, islands, and inland mountains. Moreover, the newfound igneous components of 2533 Ma will be very important information for the thermal history in the Napier Complex.

In addition, re-equilibration of the oxygen isotope data in the UHT zircons has never been reported before. The information is also important information for behavior of oxygen under metamorphic conditions.

Author Response File: Author Response.pdf