Regional-Scale Paleoproterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and ⁴⁰Ar/³⁹Ar Chronology

Round 1

Reviewer 1 Report

The article presented by Sato and co-authors contains new, interesting material that makes it possible to trace the tectonic-thermal evolution of the region and reconstruct the sequence and dynamics of collisional and post-collisional tectonic processes based on the transverse transect of the Acasta gneiss area and part of the Wopmay orogen.

The reviewer has almost no significant editorial comments on the text of the article. There is a wish to provide tables of analytical Ar/Ar dating data. This is important so that readers have the opportunity to analyze the data for age plateaus and isochronous regressions. It is advisable in the article to provide isochronous diagrams in addition to the available Ar/Ar diagrams. This is especially important in cases where it is impossible to calculate a conventional plateau in the age spectrum, in addition, it suggests itself, since the authors are discussing the problem of excess argon in the lattice of the studied minerals.

The main question is the interpretation of the data obtained. The authors believe that the reason for the rejuvenation of the K/Ar isotope system of amphibole and biotite of the studied ortho- and paragneiss samples was the thermal effect associated with the introduction of magmatic rocks of the Hepburn plutons.

Several observable facts contradict this assumption: 1) the Hepburn plutons were intruded in the rocks of Allochthon, which during the Wopmay orogeny was pulled over the rocks of the Slave craton and, accordingly, could not have direct contact with the gneisses of the craton; 2) After their introduction, the Hepburn plutons cool down, as a rule, within several Ma, well, at most – within 10 Ma, while the observed the spread of amphibole dating reaches 100 Ma and even more; 3) the maximum values of amphibole dating are observed at a distance of 6-8 km from the boundary with Allochthon rocks; 4) at the same time, biotite K/Ar dating, unlike amphibole, does not form a “wave”, but a linear trend with values gradually decreasing to the east; 5) the assumption of a “wave” of excessive radiogenic argon in this situation seems too artificial – there are no signs of high-pressure metamorphism superimposed on gneiss, with which the authors draw an analogy.

It seems that there is a noticeably less contradictory explanation of the observed pattern. Apparently, before the collision, or in the process of collision, the rocks of the modern erosive section of the Acasta gneiss were submerged to a depth of more than 15-20 km. When exposed at this depth, the crystal lattice loses both biotite and amphibole of all radiogenic ⁴⁰Ar* formed as a result of spontaneous decay. During the Wopmay collision, basement-involved folding of regional scale, capturing the strata of the basement floor of the Slave craton (Hoffman et al., 1988, Geol. Society of America Special Paper V218). During the formation of these folds with an amplitude of tens of km and an N-S orientation of the axes, an anticlinal rise of a part of the rocks of the lower levels of craton occurred above the level corresponding in terms of the Fission Track analysis to the "zone of partial rejuvenation" of the K/Ar isotope system of the amphibole. This led to the closure of amphiboles in the corresponding part of the region studied (samples Numbers 10-14). After the culmination stage, the erosion of the formed orogenic structure occurred. The dynamics of this erosion can be reconstructed, based on the closure of the K/Ar isotope system of biotites. Whereas in the western part of the studied transect, the closure of the biotite isotope system occurred on average about 1.84 billion years, in the eastern part – around 1.8 billion years, 50 Ma later. This means that rocks corresponding to the modern erosion level were exhumed to depths of less than 6-10 km (the "zone of partial rejuvenation" of the K/Ar isotope system of biotite) first in the eastern part and then gradually this process reached the western part of the studied area.

Author Response

Reply to the comments and suggestions by Reviewer 1

The article presented by Sato and co-authors contains new, interesting material that makes it possible to trace the tectonic-thermal evolution of the region and reconstruct the sequence and dynamics of collisional and post-collisional tectonic processes based on the transverse transect of the Acasta gneiss area and part of the Wopmay orogen.

The reviewer has almost no significant editorial comments on the text of the article. There is a wish to provide tables of analytical Ar/Ar dating data. This is important so that readers have the opportunity to analyze the data for age plateaus and isochronous regressions. It is advisable in the article to provide isochronous diagrams in addition to the available Ar/Ar diagrams. This is especially important in cases where it is impossible to calculate a conventional plateau in the age spectrum, in addition, it suggests itself, since the authors are discussing the problem of excess argon in the lattice of the studied minerals.

Response: We provided the analytical data as Supplementary Table 1 (ST1). We once tried to create a conventional isochron diagram but could not get any reasonable diagram. We hope some readers will try to create any specific diagram to solute the excess argon problem.

The main question is the interpretation of the data obtained. The authors believe that the reason for the rejuvenation of the K/Ar isotope system of amphibole and biotite of the studied ortho- and paragneiss samples was the thermal effect associated with the introduction of magmatic rocks of the Hepburn plutons.

Response: We do not say that the reason for the rejuvenation of biotite and amphibole was the thermal effect associated with the introduction of magmatic rocks of the Hepburn plutons. We noted that the heat source that rejuvenated the K-Ar system ages could be the asthenospheric intrusion in the subduction system that took place due to the subduction rollback. In discussion, we argued this problem carefully. Finally, we noted it in summary (see Lines 387-389).

Several observable facts contradict this assumption: 1) the Hepburn plutons were intruded in the rocks of Allochthon, which during the Wopmay orogeny was pulled over the rocks of the Slave craton and, accordingly, could not have direct contact with the gneisses of the craton; 2) After their introduction, the Hepburn plutons cool down, as a rule, within several Ma, well, at most – within 10 Ma, while the observed the spread of amphibole dating reaches 100 Ma and even more; 3) the maximum values of amphibole dating are observed at a distance of 6-8 km from the boundary with Allochthon rocks; 4) at the same time, biotite K/Ar dating, unlike amphibole, does not form a “wave”, but a linear trend with values gradually decreasing to the east; 5) the assumption of a “wave” of excessive radiogenic argon in this situation seems too artificial – there are no signs of high-pressure metamorphism superimposed on gneiss, with which the authors draw an analogy.

Response: The reviewer 1 gives us the comments from 1) to 5) on the basis of that the reason for the rejuvenation of biotite and amphibole was the thermal effect associated with the introduction of magmatic rocks of the Hepburn plutons. As described above, we noted that the heat source that rejuvenated the K-Ar system ages could be the asthenospheric intrusion in the subduction system that took place due to the subduction rollback. Then, the comments from 1) to 5) by reviewer 1 do not apply.

It seems that there is a noticeably less contradictory explanation of the observed pattern. Apparently, before the collision, or in the process of collision, the rocks of the modern erosive section of the Acasta gneiss were submerged to a depth of more than 15-20 km. When exposed at this depth, the crystal lattice loses both biotite and amphibole of all radiogenic 40Ar* formed as a result of spontaneous decay. During the Wopmay collision, basement-involved folding of regional scale, capturing the strata of the basement floor of the Slave craton (Hoffman et al., 1988, Geol. Society of America Special Paper V218). During the formation of these folds with an amplitude of tens of km and an N-S orientation of the axes, an anticlinal rise of a part of the rocks of the lower levels of craton occurred above the level corresponding in terms of the Fission Track analysis to the "zone of partial rejuvenation" of the K/Ar isotope system of the amphibole. This led to the closure of amphiboles in the corresponding part of the region studied (samples Numbers 10-14). After the culmination stage, the erosion of the formed orogenic structure occurred. The dynamics of this erosion can be reconstructed, based on the closure of the K/Ar isotope system of biotites. Whereas in the western part of the studied transect, the closure of the biotite isotope system occurred on average about 1.84 billion years, in the eastern part – around 1.8 billion years, 50 Ma later.

This means that rocks corresponding to the modern erosion level were exhumed to depths of less than 6-10 km (the "zone of partial rejuvenation" of the K/Ar isotope system of biotite) first in the eastern part and then gradually this process reached the western part of the studied area.

Response: The idea that the age rejuvenation is due to intrusive rocks is wrong, so the reviewer 1 states his/her own reasoning. As described above, we noted that the heat source that rejuvenated the K-Ar system ages could be the asthenospheric intrusion in the subduction system that took place due to the subduction rollback. We cannot accept at all his logic. He doesn't seem to understand anything about the closure temperatures of K-Ar system, the argon release during deformation and the excess argon waves. We discussed the apparent age relations observed here using these phenomena.

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript Title: Regional-Scale Paleo-Proterozoic heating event on Archean Acasta gneisses in Slave Province, Canada: Insights from K-Ar and 40Ar/39Ar chronology

 Manuscript ID: minerals-2813283

This manuscript presents new K-Ar and Ar-Ar dating results for biotite and amphibolite from a variety of samples from the Acasta gneiss and the adjacent Wopmay orogen. Although the new thermochronology dating results are promising and attractive to me, there are several issues that should be considered and addressed before publication. The main issue is that the Ar-Ar results are poorly presented and even not convincible to me, making the subsequent discussion and conclusion vulnerable. The detailed comments are listed below.  

1.     Abstract: The main part of the abstract needs to be rewritten. The authors addressed too much about the K-Ar and Ar-Ar results (see line 19-30) and even further compared the Ar-Ar plateau age vs. total gas age, which is not necessary here. The main results can be shortened to 2-3 sentences by summarizing your preferred ages. The comparison among K-Ar age, Ar-Ar plateau age and Ar-Ar total gas age can be removed as this is not your research objective.

2.     Introduction: introduction needs to be revised based on more recent zircon results, as some of the description/statements do not reflect the most recent progress on the Acasta Gneiss Complex (AGC) studies. Also the introduction is oversimplified and provides nearly no useful information.

Line 45-54. The authors are suggested to add more recent publications to address the latest findings in the AGC (please refer to the Reimink et al. (2016, 2018, 2019, 2020)). Also, based on these results, the authors should conclude the crystallization/emplacement ages of the AGC and Wopmay orogen as they are the basis for your comparison with the K-Ar and Ar-Ar results. Please use the exact age or age range.

The details are needed for the readers to evaluate your statement/descriptions. For example, in Line 56-57, you should give the age results for the readers to evaluate why and how “similar” they are. Same issue for the other part (e.g., Line 207). Please revise the whole manuscript accordingly.

A brief summary of the main tectonic events that occurred after the formation of AGC is needed. Now there is nearly no useful information (see your Line 54) for any of the events. Ar-Ar thermochronology can only record the last tectonic event that heated the system above the closure temperature.

3.     The whole results need to be completely revised as now, they are very vague.

a)     As shown here, you provided K-Ar age, Ar-Ar total gas age and Ar-Ar plateau age, and some of them are even not comparable with each other (e.g., Hwp2). So please provide a table to summarize all your preferred age results for each of the sample. Also I didn’t find the raw data for Ar-Ar dating results, please provide them in the appendix and address it in the main text as well.

Fig. 5 is not acceptable for chronology study as all the data presented lack uncertainty. Please provide error bar for each of the datapoints. Also provide the zircon crystallization age range for the AGC and/or Wopmay orogen for comparison.

b)    What are your criteria to define a “plateau age”? Plateau age is traditionally defined as the weighted mean age of continuous incremental heating steps (comprising >50% of the total 39Ar released during the experiment) with dates consistently within error of each other, or more recently, the weighted mean of the longest succession of steps that pass the generalized Chauvenet Criterion for outliers (Vermeesch, 2018). The main point is, however, the steps grouped for plateau age calculation should be “comparable” with each other. See your results of Hwp 1, 2, 4, 14 and many others. None of them fits the criteria I mentioned. The authors are suggested to revise all the plateau ages based on either of the criteria (IsoplotR from Vermeesch 2018 is helpful for calculating the plateau ages).

c)     Total gas age: the total gas age presented here is a mess and none of the results look reliable to me. You even cannot find a plateau age, so how could you determine a total gas age? Such variable results for each sample may either reflect technique issue, or variable extents of undiscernible Ar contamination, either Ar gain or loss, in your analyses. In either case, the age results are not reliable. See your results of Hwp11, 15 and many others. My suggestion is to completely remove all these results and put them in the Appendix. Only present the reliable results.

d)    Line 247-276: this whole part regarding comparison among K-Ar age, Ar-Ar plateau age and Ar-Ar total gas age makes no sense to me. My suggestion is to simply summarize your preferred results only and do not go into details of the comparison (some general justification is enough). Currently, the justification of this whole part is based on the assumption that your Ar-Ar ages are more reliable than the K-Ar ages, or Ar/Ar plateau age is more precise than total gas age, which, although are true , will invalid all your K-Ar dating results (and vice versa). You also provide no explanation on why one is more precise than the other. For example, in Line 250-251, you stated that K-Ar age is younger than Ar/Ar age and then concluded that (younger K-Ar age?) is caused by Ar loss. In this statement, you assume Ar/Ar age is more precise than the K-Ar age without any explanation. If this the case, I will suspect all your K-Ar ages are caused by the Ar loss effect. Also the same issue for the Ar/Ar plateau vs. total gas age, although your total gas age is a mess (see above). The age spectrum you presented is much more complex than your justification. It is not only about Ar loss, but could also be Ar gain perhaps caused by unknown mineral inclusions, crack and/or alteration. Based on the data you provided, it is impossible to distinguish these contaminations.

4.     Discussion.

a)     As mentioned, it is the same issue here that there is not enough information provided here and the whole discussion is vague (e.g., Line 291-295).

b)    Line 302: where did you get the closure temperature > 600 C for white mica. This is incorrect to me. See Harrison et al. (2009).

c)     The further evaluation of the thermal history cannot be done by me due to the issues of the K-Ar and Ar-Ar dating results as mentioned. The authors are suggested to revise this section accordingly based on the updates of their thermochronology results.

The English Language is overall good, but some improvements are need for the scientific part.

Author Response

Reply to the comments and suggestions by Reviewer 2

Comments and Suggestions for Authors

Manuscript Title: Regional-Scale Paleo-Proterozoic heating event on Archean Acasta gneisses in Slave Province, Canada: Insights from K-Ar and 40Ar/39Ar chronology

 Manuscript ID: minerals-2813283

This manuscript presents new K-Ar and Ar-Ar dating results for biotite and amphibolite from a variety of samples from the Acasta gneiss and the adjacent Wopmay orogen. Although the new thermochronology dating results are promising and attractive to me, there are several issues that should be considered and addressed before publication. The main issue is that the Ar-Ar results are poorly presented and even not convincible to me, making the subsequent discussion and conclusion vulnerable. The detailed comments are listed below.

Abstract: The main part of the abstract needs to be rewritten. The authors addressed too much about the K-Ar and Ar-Ar results (see line 19-30) and even further compared the Ar-Ar plateau age vs. total gas age, which is not necessary here. The main results can be shortened to 2-3 sentences by summarizing your preferred ages. The comparison among K-Ar age, Ar-Ar plateau age and Ar-Ar total gas age can be removed as this is not your research objective.

Response: We significantly revised Abstract to the following:

Abstract: Slave Province in Canada is an Archean granite-supracrustal terrane at the northwestern corner of the Canadian Shield. It is bordered by the Thelon–Taltson orogen (2.0 to 1.9 Ga) to the southeast and the Wopmay orogen (1.9 to 1.8 Ga) to the west. Acasta gneisses exposed in the westernmost Slave province and the Wopmay rocks close to the gneisses were collected systematically for K-Ar and laser step-heating 40Ar /39Ar single crystal analyses of the biotite and amphibole. The K-Ar biotite ages of the four Wopmay samples range from 1816 ± 18 Ma to 1854 ± 26 Ma. The 40Ar/39Ar biotite analyses of the three Wopmay samples give the plateau ages of 1826 ± 21 Ma, 1886 ± 13 Ma, and 1870 ± 18 Ma. These ages are within the reported U-Pb zircon age range of the Wopmay orogen. The K-Ar biotite ages of the fifteen Acasta gneisses range from 1779 ± 25 Ma to 1877 ± 26 Ma, except for a younger sample (1711 ± 25 Ma). The 40Ar/39Ar analyses of the biotite crystals from three samples give the plateau ages of 1877 ± 8 Ma, 1935 ± 14 Ma, and 1951 ± 11 Ma. The 40Ar/39Ar analyses of the amphibole crystals show the varied age relations. The two samples give the plateau ages of 1814 ± 22 Ma and 1964 ± 12 Ma. Some samples have the apparent old age of 2000 Ma in the middle temperature fractions. These old fractions are due to that the originally existed amphibole crystals formed in Archean were affected by the thermal events during the Wopmay orogeny, but did not fully reset. These results suggest that the K-Ar system ages of the biotite and amphibole of the Archean Acasta gneiss were rejuvenated in the Paleo–Proterozoic ages. It is discussed that the heat source that rejuvenated the K-Ar system ages may have arisen due to the asthenospheric intrusion into the wedge mantle, which took place because of the subduction rollback.

2. Introduction: introduction needs to be revised based on more recent zircon results, as some of the description/statements do not reflect the most recent progress on the Acasta Gneiss Complex (AGC) studies. Also the introduction is oversimplified and provides nearly no useful information.

Response: We revised Introduction according to the comments below.

Line 45-54. The authors are suggested to add more recent publications to address the latest findings in the AGC (please refer to the Reimink et al. (2016, 2018, 2019, 2020)). Also, based on these results, the authors should conclude the crystallization/emplacement ages of the AGC and Wopmay orogen as they are the basis for your comparison with the K-Ar and Ar-Ar results. Please use the exact age or age range.

Response: We referred the papers by Reimink and others and added the following sentence in the part.

“Reimink and others have carried out the analyses of various isotopes (O, U-Pb, Nd-Sm, W, Hf), extinct nuclide and trace elements of zircon in the Acasta and the related gneiss and discussed about the hadean continental crust, the petrogenesis and tectonics of the Acasta gneiss and the progressive crustal growth in the Slave craton [5,6,7,8]. (Reimink et al., 2016; 2018; 2019; 2020).”

The details are needed for the readers to evaluate your statement/descriptions. For example, in Line 56-57, you should give the age results for the readers to evaluate why and how “similar” they are. Same issue for the other part (e.g., Line 207). Please revise the whole manuscript accordingly.

Response: We changed this part to “because the ⁴⁰Ar /³⁹Ar ages were within the zircon U-Pb ages of the Wopmay orogen.”

A brief summary of the main tectonic events that occurred after the formation of AGC is needed. Now there is nearly no useful information (see your Line 54) for any of the events. Ar-Ar thermochronology can only record the last tectonic event that heated the system above the closure temperature.

Response: We added the geological events such as the crystallization of zircon core (4.2 Ga), the formation of the oldest diorites and tonalities, the tonalite formation, the granodiorite formation and the associated anatexis, the regional metamorphism with granitoid formation and the granite intrusion (2.6 Ga).

3. The whole results need to be completely revised as now, they are very vague.
4. a)     As shown here, you provided K-Ar age, Ar-Ar total gas age and Ar-Ar plateau age, and some of them are even not comparable with each other (e.g., Hwp2). So please provide a table to summarize all your preferred age results for each of the sample. Also I didn’t find the raw data for Ar-Ar dating results, please provide them in the appendix and address it in the main text as well.

Response: We provided the ⁴⁰Ar /³⁹Ar analytical data as Supplementary Table 1 (ST1). The biotites in Hwp 1 and Hwp 4 show that K-Ar age, ⁴⁰Ar /³⁹Ar total gas age and ⁴⁰Ar /³⁹Ar plateau age are completely the same within their analytical error, giving the most reliable ages. This means that the biotites has experienced no argon loss after the formation in the Wopmay orogeny. As described in text, the biotite and amphibole in the AGC have some complicated age relations due to several events such as the argon loss in the later stage, the incomplete resetting and the excess argon trapping.

Fig. 5 is not acceptable for chronology study as all the data presented lack uncertainty. Please provide error bar for each of the datapoints. Also provide the zircon crystallization age range for the AGC and/or Wopmay orogen for comparison.

Response: Since multiple materials were collected from the same location, it would be difficult to understand if errors were included in all data points. Each error is about 1.5%, so the error bar was placed near the center of the figures. Please consider the error of each age as the range of the error bar and look at the whole. We revised the figure caption to the following:

Figure 5. Ages plotted along a traverse 18 km east–west stretch of the boundary between the Wopmay orogen and the Acasta gneiss. The error of each age is within the range of the error bar shown in the figure. Duplicate argon analyses were carried out for the biotite of Hwp1, Hwp9, and Hwp14, and for the amphibole of Hwp11, Hwp14, and Hwp15. The weighted average for these samples is shown in red. The error is halved from the age error bar.

1. b)    What are your criteria to define a “plateau age”? Plateau age is traditionally defined as the weighted mean age of continuous incremental heating steps (comprising >50% of the total 39Ar released during the experiment) with dates consistently within error of each other, or more recently, the weighted mean of the longest succession of steps that pass the generalized Chauvenet Criterion for outliers (Vermeesch, 2018). The main point is, however, the steps grouped for plateau age calculation should be “comparable” with each other. See your results of Hwp 1, 2, 4, 14 and many others. None of them fits the criteria I mentioned. The authors are suggested to revise all the plateau ages based on either of the criteria (IsoplotR from Vermeesch 2018 is helpful for calculating the plateau ages).

Response: A plateau is defined as one where successive ³⁹Ar fractions coincide within a margin of error and occupy more than 80% of the total release. It is also important to show the age spectrum without the plateau to see an accurate view of the behavior of argon. As described in text (Lines 268-276), the two amphibole crystals from Hwp12 were analyzed. Crystal (a) shows consistent age relations between the plateau ages (1847 ± 15 Ma) and the total gas ages (1827 ± 14 Ma). Crystal (b) shows no plateau age spectra and has the apparent old age of 2000 Ma in the middle temperature fractions. These old fractions have very important information that the originally existed amphibole crystals formed in Archean were affected by the thermal events during the Wopmay orogeny., but did not fully reset.

1. c)     Total gas age: the total gas age presented here is a mess and none of the results look reliable to me. You even cannot find a plateau age, so how could you determine a total gas age? Such variable results for each sample may either reflect technique issue, or variable extents of undiscernible Ar contamination, either Ar gain or loss, in your analyses. In either case, the age results are not reliable. See your results of Hwp11, 15 and many others. My suggestion is to completely remove all these results and put them in the Appendix. Only present the reliable results.

Response: K-Ar age corresponds to the ⁴⁰Ar/³⁹Ar total age. The total gas age is calculated even if the plateau age is not available. When a system is disturbed by external events, K-Ar age (i.e. total age) is affected significantly, and shows no longer a meaningful age. If the plateau age and total gas age match, the result is considered to be highly reliable (Hwp 1 and Hwp 4). This means no secondary argon losses or excess argon traps. Therefore, it is important to carefully compare plateau ages, total gas ages, and K-Ar ages. It is important to show the entire age spectrum. Showing only spectra with plateau ages does not provide an accurate view of the behavior of argon.

The errors are slightly larger than in normal bulk analyses because step heating is carried out for an "individual" single crystal grains of 0.5 mm or less.

1. d)    Line 247-276: this whole part regarding comparison among K-Ar age, Ar-Ar plateau age and Ar-Ar total gas age makes no sense to me. My suggestion is to simply summarize your preferred results only and do not go into details of the comparison (some general justification is enough). Currently, the justification of this whole part is based on the assumption that your Ar-Ar ages are more reliable than the K-Ar ages, or Ar/Ar plateau age is more precise than total gas age, which, although are true , will invalid all your K-Ar dating results (and vice versa). You also provide no explanation on why one is more precise than the other. For example, in Line 250-251, you stated that K-Ar age is younger than Ar/Ar age and then concluded that (younger K-Ar age?) is caused by Ar loss. In this statement, you assume Ar/Ar age is more precise than the K-Ar age without any explanation. If this the case, I will suspect all your K-Ar ages are caused by the Ar loss effect. Also the same issue for the Ar/Ar plateau vs. total gas age, although your total gas age is a mess (see above). The age spectrum you presented is much more complex than your justification. It is not only about Ar loss, but could also be Ar gain perhaps caused by unknown mineral inclusions, crack and/or alteration. Based on the data you provided, it is impossible to distinguish these contaminations.

Response: As described above, it is important to carefully compare plateau ages, total gas ages, and K-Ar ages. It is important to show the entire age spectrum. Showing only spectra with plateau ages does not provide an accurate view of the behavior of argon. As described in text (Lines 268-276), the two amphibole crystals from Hwp12 were analyzed. Crystal (a) shows consistent age relations between the plateau ages (1847 ± 15 Ma) and the total gas ages (1827 ± 14 Ma). Crystal (b) shows no plateau age spectra and has the apparent old age of 2000 Ma in the middle temperature fractions. These old fractions have very important information that the originally existed amphibole crystals formed in Archean were affected by the thermal events during the Wopmay orogeny., but did not fully reset. This fact also suggests that the amphibole grains in a rock sample were affected by heterogeneous heat.

4. Discussion.
5. a)     As mentioned, it is the same issue here that there is not enough information provided here and the whole discussion is vague (e.g., Line 291-295).

Response: We added the geological events such as the crystallization of zircon core (4.2 Ga), the formation of the oldest diorites and tonalities, the tonalite formation, the granodiorite formation and the associated anatexis, the regional metamorphism with granitoid formation and the granite intrusion (2.6 Ga).

1. b)    Line 302: where did you get the closure temperature > 600 C for white mica. This is incorrect to me. See Harrison et al. (2009).

Response: See Itaya, T. (2020) K-Ar phengite geochronology of HP-UHP metamorphic rocks-An in-depth review. J. Mineral. Petrol. Sci., 115(1), 44-58. This review paper shows the examples that UHP rocks and eclogites in the collisional orogenic belts have muscovite (phengite) with unusually old ages. In the Western Alps, the rocks of Variscan age (ca. 250 Ma) have undergone Alpine metamorphism, but the muscovite (phengite) in UHP rocks gives an age of 150 Ma, and the muscovite (phengite) in eclogites is older than 200 Ma. These facts indicate that the K-Ar system age was not reset under the metamorphic temperatures (600 C and higher) of UHP rocks and eclogites.

1. c)     The further evaluation of the thermal history cannot be done by me due to the issues of the K-Ar and Ar-Ar dating results as mentioned. The authors are suggested to revise this section accordingly based on the updates of their thermochronology results.

Response: We believe the sections (6-2 and 6-3) of Discussion are well described on the basis of our K-Ar system age data and the available geological data.

Comments on the Quality of English Language

The English Language is overall good, but some improvements are need for the scientific part.

Submission Date

22 December 2023

Date of this review

09 Jan 2024 16:07:09

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Minor corrections are needed for Ar/Ar raw data report format. Please follow the minimum report criteria  (see Renne, P.R., Deino, A.L., Hames, W.E., Heizler, M.T., Hemming, S.R., Hodges, K.V., Koppers, A.A., Mark, D.F., Morgan, L.E., Phillips, D. and Singer, B.S., 2009. Data reporting norms for 40Ar/39Ar geochronology. Quaternary Geochronology, 4(5), pp.346-352.).

Also double check the grammar and format.  

N/A

Author Response

Reply to Reviewer 2-2

Comments and Suggestions for Authors

Minor corrections are needed for Ar/Ar raw data report format. Please follow the minimum report criteria (see Renne, P.R., Deino, A.L., Hames, W.E., Heizler, M.T., Hemming, S.R., Hodges, K.V., Koppers, A.A., Mark, D.F., Morgan, L.E., Phillips, D. and Singer, B.S., 2009. Data reporting norms for ⁴⁰Ar/³⁹Ar geochronology. Quaternary Geochronology, 4(5), pp.346-352.).

Response: Our ⁴⁰Ar/³⁹Ar analysis was performed before 2009. At that time, it was based on York's laboratory method at the University of Toronto. Although Renne and others method is a necessary method for Quaternary chronology, it seems unnecessary for our samples of Proterozoic age. I don't think it will make any difference in age. In the first place, it is impossible to change the table because it is not measured using their method. Please understand.

Also double check the grammar and format.

Response: Yes, we checked the grammar and format. I realized there are miss types in Abstract. Revised ones with line number are in blue as seen in the following.

yield (line 21) from “yield”, observations (line 30) from “observation”, discussion (line 31) from “discussions” and process (line 33) from “processes”.

Comments on the Quality of English Language

N/A

Submission Date

22 December 2023

Date of this review

26 Jan 2024 14:22:55

Author Response File: Author Response.pdf