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Peer-Review Record

Geochemistry, Geochronology, and Hf-S-Pb Isotopes of the Akechukesai IV Mafic-Ultramafic Complex, Western China

Reviewer 1: Anonymous
Reviewer 2: Anonymous
Minerals 2019, 9(5), 275; https://doi.org/10.3390/min9050275
Received: 13 March 2019 / Revised: 29 April 2019 / Accepted: 1 May 2019 / Published: 2 May 2019
(This article belongs to the Section Mineral Deposits)

Round 1

Reviewer 1 Report

General and specific comments are provided in the attached file

Comments for author File: Comments.pdf

Author Response

Prof. Fengyue Sun

                      College of Earth Sciences

                      Jilin University

                      No. 2199 Jianshe Street

                      Changchun, 130061, China

April 15, 2019

Mr Jax Jiang

Assistant Editor,Minerals

 

Re: minerals-469475

 

Dear Mr Jax Jiang,

 

Thank you very much for returning the comments on our manuscript (minerals-469475) entitled Geochemistry,  Geochronology and Hf-S-Pb isotopes of the Akechukesai Ⅳ mafic-ultramafic complex, Western China”. All suggestions are valuable and helpful for improving the quality of the paper. We have considered the editor’s comments and thoroughly revised the paper. We appreciate your great efforts in improving our paper.

 

In the following, we explain where and how the reviewers’ comments have been incorporated.

 

Responses to the comments by Reviewer#1:

General comments:

The manuscript by Yan and co-authors is a resubmission after a first submission of a manuscript which had several points that needed to be addressed. The new manuscript, although improved from the point of view of English, still contains a number of problems that need to be carefully addressed by the authors. Generally speaking, the problems concern the interpretation of some geochemical data and the hypotheses made, that result strongly inconsistent at this stage.

 

1. From the geological description it turns out that the four complexes are so small and close to one other, that they are probably part of a unique intrusive body. This implies that there should be no significant geochemical differences among them. So why should Hf only be so different? See also other general comments below concerning Hf content and isotopic composition.

Response: We thank the reviewer for his positive comments on our paper. We have fully considered all comments raised by you and the reviewers and thoroughly revised the paper [see Changes marked with red color and Revision note].First of all, I agree with the reviewer. The four complexes are probably part of a unique intrusive body, but from our research, we are not sure yet. So there may be differences in geochemical characteristics.

2. Line 98 – “the magma that formed pyroxenites”; line 177 – “pyroxenite magma”.

Which magma can generate a pyroxenite? As far as I know, there is no mantle source able to

generate a pyroxenite magma by partial melting. Pyroxenites have a completely different

genesis. The authors should be very careful about this point.

Response: Thanks for suggestions. We will revised these words and be very careful about this point.

3. Section 5.2. Zircon U–Pb ages and Hf isotopic data. TDM1 ages of 1535–1092 Ma associated to eHf(t = 424 Ma) values of –1.2 to –11.3. These TDM1 ages are neither used nor discussed in the following sections, why? Why did you calculate them? Also, at lines 166-167, it is said “These extremely negative Hf values contrast with the positive Hf values previously determined for the Xiarihamu and Akechukesai I mafic–ultramafic complexes (Figure 7).” This oddity is coupled with the anomalously high Hf content, it cannot be a coincidence.

Response: Thanks for suggestions. I have added some discussion in section 5.2 and 6.2.

4. Section 6.1 Crustal contamination. This is one of the most problematic part of the

manuscript. First of all, from the photos of Figure 3 it is impossible to see any evidence of

crustal contamination and metasomatism, as the authors claim. But, let trust the authors.

Then, at lines 177-179 the authors claim: “The geochemistry of the units in the study area

also provide evidence of assimilation and contamination [these are synonymous] of crustal

material…”. Therefore, it seems that talking about crustal contamination, the authors are

talking about some process that modified the original geochemical features of the magma

when it was intruding the crust. And/or some process that occurred after the cooling of the

magma, as one could guess from the presence of marble at the contact with the igneous unit.

The following discussion, however, makes me think that the authors give a completely different meaning to the word contamination. Indeed, as claimed at lines 179-180, “the variations in the ratios of elements with similar distribution coefficients present in the gabbros cannot be controlled by partial melting and fractional crystallization alone”. So, the authors use trace element ratios to demonstrate “crustal contamination”. By the way, previously in the manuscript the authors said that the Hf anomaly is due to crustal contamination (lines 151-152: “The samples also have positive Hf anomalies that are suggestive of crustal contamination of the primitive magma that formed these gabbros”). Then, why they do not use any trace element ratio involving Hf? Successively, at lines 152-155, the authors say: “The shaded area in Figure 5b also shows the compositions of samples from the Akechukesai I mafic–ultramafic complex, with the similarity of compositions of samples from these two complexes suggesting they are cogenetic.” My question is: if they are cogenetic, and I agree with this hypothesis, then why complex IV has a Hf spike, and complex I does not? The explanation that the Hf anomaly is due to crustal contamination does not convince me. If that was true, many other elements, such as Rb, Sr, Ba, K would be anomalously enriched too. Also, why should Hf be so highly concentrated in a crustal rock? And, what kind of crust are the authors thinking of? I strongly suspect that this high Hf content is due to some either analytical or procedural problem. But, certainly, it is not due to any process, either deep or shallow, that involves fluids, since Hf is fluid-immobile. The following sentence, at lines 190-192, needs a sharp clarification: “This suggests that the magmas that formed the complex assimilated both upper and lower crustal material, with the upper crustal material contributing some 40%–50% of the overall contamination”. If I understand, you are saying: A N-MORB source (or melt? not clear) is contaminated by 40-50% of upper crust and by 50-60% of lower crust. But, what is the total amount of contamination? If I look at the mixing curves of Fig. 10, I see more than 40% of

contamination, which is difficult to believe. Anyway, you should be much clearer in the

meaning of the term “contamination”. In other words: i) if the term contamination is referred

to crustal material assimilated by a melt (hence, after partial melting occurred, and happening during magma rising through the crust), then 40% or more of contamination is way too much, thermodynamically impossible to achieve; ii) if the term contamination is referred to crustal material added to a mantle source, and in that case, you MUST name it source contamination”, not crustal contamination nor assimilation, then even 40% of contamination could be possible, but some quantitative estimate (a mass balance calculation with major and trace elements) should be presented to be convincing. And, please, include Hf in the mathematical modeling, if you really believe that its anomaly is related to this process. The authors must carefully evaluate this critical point. The final aspect of the problem with contamination concerns Sulphur. Even in this case, the authors must specify if the isotopic features of Sulphur of their samples are related to crustal contamination or source contamination. For example, at line 206 the authors say: Assimilation of crustal S…”. Here I got confused: In the previous sentences the authors were talking about S addition to the mantle by fluid metasomatism, and here the authors talk about assimilation of crustal S. This because the terms contamination and assimilation are used with ambiguous meaning.

Response: Thanks for suggestions. First of all, the occurrence of contaminated rock is the product of the interaction between mantle-derived magma and marble, and is the direct evidence of crustal contamination, especially in deposits associated with mafic-ultramafic intrusions. Contaminated rock is a special type of rock, which composition is between marble and pyroxenite. However, pyroxenite and marble still retain the original geochemical features. As for the Hf spike, there are many explanations, such as the distribution coefficients between the garnet and the melt and mantle source heterogeneity can result in the different Hf components (Pertermann M et al., 2004, Experimental determination of trace element partitioning between garnet and silica-rich liquid during anhydrous partial melting of MORB-like eclogite. Geochemistry Geophysics Geosystems) Certainly, Hf is fluid-immobile. (Weyer S, Earth and Planetary Science Letters2003205: 309-324. Nb /TaZr/Hf and REE in the depleted mantle: Implications for the differentiation history of the crustmantle system have demonstrated that the variation of Zr/Hf ratios may reflect the partial melting of mantle).Through the objective reviews of reviewer, I find that there are still some deficiencies in this modeling. Although we consider that the sulfur of source contamination comes from the oceanic crust. Ok! We will specify the term.

 

5. Section 6.2 – Mantle source characteristics. The authors have discussed the source in the previous section too; anyway, I suggest reordering them: discuss mantle source

characteristics first, including primary features and source contamination, if any, and then

crustal contamination, i.e., processes that magmas suffered when rising through the crust, if any. In this section there are several inconsistencies. One concerns Nb and Ta anomalies. At lines 222-223, the authors say: Sample of the Akechukesai maficultramafic complex have positive Nb and Ta anomalies relative to both OIB and ORB…”. In the spiderdiagram of Fig. 7b I see a strong negative anomaly of Nb relative to PM. Perhaps, the authors should put an OIB and a MORB patterns for reference. With reference to the use of trace element ratios, I suggest the following article, where there is a rigorous analysis of the mantle source characteristics deduced from geochemical data of primitive basalts in a post-collisional setting: Mazzeo and co-authors, 2014. ubduction-related enrichment of the Neapolitan volcanoes (Southern Italy) mantle source: new constraints on the characteristics of the slabderived components. Chemical eology 386, 165–183. By the way, in this article the Zr/Hf ratio is used… The second inconsistency concerns Pb isotopes. At lines 228-230, the authors say: However, these samples plot in the MORB area of 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams (Figure 9c, d), suggesting they have a MORB affinity.” This is substantially not true; the samples plot outside the MORB field. The third inconsistency concerns the amounts of mantle components. At lines 232-233, the

authors say: “This indicates that the magma source was most likely dominated by MORB

components.”. In the previous section, the authors claim that there are more than 40% of

upper and lower crustal components in the mantle source. Please, reconcile the two.

The fourth inconsistency regards the Hf content and isotopic composition anomaly again. At lines 242-245, the authors say: “This would suggest that the low Hf(t) values of the gabbros in the study area reflect subduction-related metasomatism in a similar fashion to the Xiarihamu mafic–ultramafic complexes (Hf(t) = 4–10) and the Weibao volcanic rocks (Hf(t) = –2.6 to +7.5).”. Firstly, Hf is immobile in fluids, so the authors should specify that low Hf(t) values could reflect subduction-related metasomatism by MELTS, not by fluids. But then, what about all the evidence of just fluids (see Ba/La ratio, Sulphur) that have contaminated (=metasomatized) the mantle source? Secondly, in the comparison of Hf(t) values between the studied complex, and Xiarihamu and Weibao, the latter have Hf(t) from slightly negative to strongly positive; the Akechukesai data are all strongly negative, so where is the similar fashion??

 

Response: Thanks for suggestions. We will changed the subtitle.1.Sorry, it is really negative Nb-Ta anomaly. We will revised the problem. In addition, we have carefully read the article recommended by the reviewer. Through this article, we have learnt some useful knowledge. 2. As for Pb isotopes, our data mainly plot near the MORB area of 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams. We also consider that source contamination can affect their isotope ratios. Hence we believe they have a MORB affinity. 3. We have considered that 40% is a little bit high. And we revised this problem. 4. First of all, I agree with low eHf(t) values could reflect subduction-related metasomatism by MELTS, not by fluids. Zhang et al., 2014, Early Paleozoic high-Mg diorite-granodiorite in the eastern Kunlun Orogen,western China:Response to continental collision and slab break-off. Lithos, 210-211, 129-146. have reported that High-Mg porphyritic diorites derived from mantle metasomatized slab melts. Hence we have reasons to believe that slab melts can contribute to the formation of intrusions. Besides, low Hf(t) values could also reflect the involvement of ancient continental crust materials and so on. In my paper, Ba/Th, Ba/La and S isotopes are indicative of the existence of fluid-related metasomatism, but not only. Subduction-related metasomatism by fluids is intended to demonstrate the migration of S. Based on the fact that they all deviate from the depleted mantle, we consider that they have similar fashion. However, our data are all strongly negative, different levels of enrichment (addition of ancient crustal materials) may be one reason. In the EKOB, this is a universal phenomenon. Furthermore, Couzinié et al. 2016 also determined that post-collisional mafic magmatism in the Variscan French Massif Central and proposed a hybrid source containing subducted components and depleted-mantle material.

 

6. Section 6.3 - Geodynamic implications. At the end, the authors say (lines 300-302): “This

would allow hot asthenospheric mantle material to ascend through the resulting slab

window, causing shallower decompression melting. This slab break-off model is consistent

with the linear distribution of mafic–ultramafic complexes along the middle Kunlun fault.”

Is this shallow melting consistent with the melting model in both garnet- and spinel-bearing

mantle? Then, I am not sure that slab break-off can occur in cases when the lithosphere is

thicker than normal. Please check the literature.

Response: Thanks for suggestions. Based on the above facts, we consider that the magma source should be asthenosphere mantle. Hence the Akechukesai IV mafic–ultramafic complex is formed by the asthenosphere mantle in both garnet- and spinel-bearing stability domain. Here we address slab break-off of oceanic lithosphere. Slab break-off can occur [7].

 

SPECIFIC COMMENTS

In the Abstract there is no mention to the Hf positive anomaly of gabbros and its interpretation as due to crustal contamination. Instead, TDM ages are mentioned, but they are not used/discussed in the text. Anyway, the text of the abstract needs to be modified according to the general comments given above. The same holds for the Conclusions.

Response: Thanks for suggestions. We will revise the problem.

Line 37 – delete the word “research”

Response: Thanks for suggestions. We will revise the problem.

Line 41 – change the word “understood” with “investigated”

Response: Thanks for suggestions. We will revise the problem.

Lines 45-46 – change the sentence “The Xiarihamu deposit is one…” with “The Xiarihamu deposit, one…”

Response: Thanks for suggestions. We will revise the problem.

 

Line 47 – change the sentence “between the late Silurian and the Early Devonian…” with “between late Silurian and Early Devonian”

Response: Thanks for suggestions. We will revise the problem.

Line 94 – delete the second word “alteration”

Response: Thanks for suggestions. We will revise the problem.

Line 102 – delete the word “present”

Response: Thanks for suggestions. We will revise the problem.

Line 103 – delete the word “present”

Response: Thanks for suggestions. We will revise the problem.

Line 105 – change the word “must be” with “were”

Response: Thanks for suggestions. We will revise the problem.

Line 105 – change the sentence “to a ~200 mesh” with “to ~200 mesh”

Response: Thanks for suggestions. We will revise the problem.

Line 106 – The XRF spectrometer is not equipped with fused glass disks; the samples are analyzed as fused glass disks. Please, specify.

Response: Thanks for suggestions. We will revise the problem.

Line 107 – TFe2O3: use either Fe2O3tot or Fe2O3T, and put numbers as subscript

Response: Thanks for suggestions. We will revise the problem.

Lines 107-108 – change the sentence “after the acid digestion” with “after acid digestion”

Response: Thanks for suggestions. We will revise the problem.

Line 114 – “which conforms to standard procedure” is too generic: what procedure are you referring to? Please, specify.

Response: Thanks for suggestions. We will revise the problem.

Line 116 – change the word “from” with “on”

Response: Thanks for suggestions. We will revise the problem.

Lines 117-118 – change the sentence “Aurora M90 ICP-MS and New Wave UP213, as the laser ablation system” with “Aurora M90 ICP-MS interfaced with a New Wave UP213 laser ablation system”

Response: Thanks for suggestions. We will revise the problem.

Line 121 – change the sentence “procedure in Liu et al.” with “procedure described in Liu et al.”

Response: Thanks for suggestions. We will revise the problem.

Line 124 – change the word “microprobe” with “system”

Response: Thanks for suggestions. We will revise the problem.

Line 130 – “δ34S”: put number as superscript

Response: Thanks for suggestions. We will revise the problem.

Lines 132-133 – check homogeneity of the font in these sentences

Response: Thanks for suggestions. We will revise the problem.

Line 132 – change the word “basic” with “elution through”

Response: Thanks for suggestions. We will revise the problem.

Line 134 – “the 204Pb/206Pb and 208Pb/206Pb ratios”: put number as superscript

Response: Thanks for suggestions. We will revise the problem.

Line 145 – “but depleted in the heavy REE (HREE).”: Not much, I'd say slightly enriched with respect to chondrites

Response: Thanks for suggestions. We will revise the problem.

Line 159 – change the word “during” with “under”

Response: Thanks for suggestions. We will revise the problem.

Line 168 – delete “and Pb” (Pb is not mentioned in this sentence)

Response: Thanks for suggestions. We will revise the problem.

Line 170 – change “A further nine” with “Nine”

Response: Thanks for suggestions. We will revise the problem.

Line 178 – delete “and contamination” (contamination and assimilation are synonymous)

Response: Thanks for suggestions. We will revise the problem.

Line 184 – change “Lower Ce/Pb” with “Low Ce/Pb”

Response: Thanks for suggestions. We will revise the problem.

Line 186 – delete “the” (twice)

Response: Thanks for suggestions. We will revise the problem.

Line 187 – change “transferal of this Pb the mantle” with “transfer of this Pb to the mantle”

Response: Thanks for suggestions. We will revise the problem.

Lines 192-193 – “Some samples have upper-crust-type ratios that cannot be explained by crustal contamination alone,…”. Which ones? All samples seem homogeneous in terms of Ta/Th, Th/Yb and Nb/Th ratios. Please, specify.

Response: Thanks for suggestions. We will revise the problem.

Line 198 – “…relatively low Th/Yb and Ba/La values”. The Ba/La values are not so low, actually.

Response: Thanks for suggestions. We will revise the problem.

Line 208 – delete “in question”

Response: Thanks for suggestions. We will revise the problem.

Lines 215-219 – Very confusing sentences, maybe there are repetitions. Please check carefully.

Response: Thanks for suggestions. We will revise the problem.

Line 222 – “provide evidence of magma sourcing”: What do you mean? maybe source

characteristics? 

Response: Thanks for suggestions. We will revise the problem.

Line 223 – “…positive Nb and Ta anomalies relative to both OIB and MORB…”: Where is this evidence?? In the spiderdiagram I see a strong negative anomaly of Nb relative to PM.

Response: Thanks for suggestions. We will revise the problem.

Line 225 – change “different to those” with “different from those”

Response: Thanks for suggestions. We will revise the problem.

Lines 239-240 – Weibao volcanic rocks: Where is this? What relation is there between this place and the complex under investigation? The authors didn’t talk about it in the geological setting section.

Response: Thanks for suggestions. We will revise the problem. We have added the within the EKOB.

Line 262 – delete “research by”

Response: Thanks for suggestions. We will revise the problem.

Line 267 – change “formed by” with “derived from”

Response: Thanks for suggestions. We will revise the problem.

Line 290 – change “These complexes include the” with “Among these, the”

Response: Thanks for suggestions. We will revise the problem.

Lines 291-292 – change “are the best studied complexes in this area” with “are primarily studied in this area”

Response: Thanks for suggestions. We will revise the problem.

Line 312 – change “The assimilation of higher crustal S may be more conducive to S saturation” with “The assimilation [define the meaning] of high amounts of crustal S may have had a significant role in driving S saturation”

Response: Thanks for suggestions. We will revise the problem.

Line 320 – change “for analyzing” with “for the analyses”

Response: Thanks for suggestions. We will revise the problem.

Line 411 – change “pircites” with “picrites”

Response: Thanks for suggestions. We will revise the problem.

Figure 1 – change “Sketch tectonic map” with “Tectonic sketch map”. However, I cannot see any tectonic features in this map, only black curves without indication of their meaning. 

Response: Thanks for suggestions. We will revise the problem. We have written ❶-North Kunlun fault; ❷-Middle Kunlun fault; ❸-South Kunlun fault; ❹-Altyn Tagh fault.

Figure 3 – In d, pyroxene is perhaps pyroxenite. In the legend, c and f are not field photos, they are cores.

Response: Thanks for suggestions. We will revise the problem.

Figure 4 – Left: crossed polars; right: parallel polars. Specify this in the caption.

Response: Thanks for suggestions. We will revise the problem.

Figure 7 – change maifc with mafic. What does the vertical black box represent? Data from AKCKS IV complex too? In the caption, delete “and professor Sun’s scientific research team”, it’s useless.

Response: Thanks for suggestions. We will revise the problem.

Tables 2 and 3 still need to be improved, there are too many numbers not aligned. They are unreadable.

Response: Thanks for suggestions. In our paper, tables 2 and 3 are in the standard forms.I don't know the reason. 

 

 

 

 

 

Again, we really appreciate the editor’ comments that are helpful in improving the quality of our paper.

 

 

Sincerely yours

 

Fengyue Sun 

Jilin University


Reviewer 2 Report

Please see my detailed comments in the annotated pdf in the attachment. I summarize my major concerns below:

The authors should provide more descriptions about analytical equipment and procedures to justify the quality of data, especially for zircon Lu-Hf isotopes.

Interpretations about mixing between NMORB and lower crust, and between NMORB and upper crust seem contradictory (Fig. 10a, b). The authors should reconsider that part.

The gabbro assimilated 40-50% crust, this could have induced dramatic variations in many other major and trace elements besides those used in the paper. For instance, the authors can model if SiO2 can be reproduced with such assimilation degrees. These results may provide further verification of the conclusions.

S isotopes in sulfides seem interesting but only weakly discussed. The authors proposed S from slab fluids can induce the large deviation from mantle value, but they didn't demonstrate what form the sulfur took, as sulfide or sulfate? and how this S affect the residue mantle souce.

S isootpic difference with the two ore types seem, again, weakly discussed. The authors proposed the vein sulfide represents more contribution from crustal S but in the meantime suggesting the two types come from a common source. How could this be possible? Is there a second crustal contaminant aside from slab fluids?

The gabbros have subchondritic Nb/Ta ratio (about 5 versus 17.5 for mantle), and this deviation could be significant. The authors should consider this and add some discussions.

Last but not the least, the English style (although clear enough for basic understanding) needs some work. Unnecessary repetition of some expressions (such as the name of the complex) makes it a bit difficult to read.

Comments for author File: Comments.pdf

Author Response

Prof. Fengyue Sun

                      College of Earth Sciences

                      Jilin University

                      No. 2199 Jianshe Street

                      Changchun, 130061, China

April 15, 2019

Mr Jax Jiang

Assistant Editor,Minerals

 

Re: minerals-469475

 

Dear Mr Jax Jiang,

 

Thank you very much for returning the comments on our manuscript (minerals-469475) entitled Geochemistry,  Geochronology and Hf-S-Pb isotopes of the Akechukesai Ⅳ mafic-ultramafic complex, Western China”. All suggestions are valuable and helpful for improving the quality of the paper. We have considered the editor’s comments and thoroughly revised the paper. We appreciate your great efforts in improving our paper.

 

In the following, we explain where and how the reviewers’ comments have been incorporated.

 

 

Responses to the comments by Reviewer#2:

1. Please specify sample lithology, pyroxenite? gabbro? or both?

Response: Thanks for suggestions. We will revise the problem.

2. not Ta?

Response: Thanks for suggestions. We will revise the problem. Ta is weakly depleted- not depleted.

3. sulfides (please specify the minerals).

Response: Thanks for suggestions. We will revise the problem.

4. please specify how many sources and what they are.

Response: Thanks for suggestions. We will revise the problem.

5. it's important with repect to what? geology? geomorphology? natural resources?

Response: Thanks for suggestions. We will revise the problem.

6. Jinshuikou Group and the Ordovician–Silurian Tanjianshan Group.please generally describe rock types in these two groups.

Response: Thanks for suggestions. We will revise the problem.

7. you can specify the distance, if it's important.

Response: Thanks for suggestions. Adjacent to is OK here.

8. The Ni mineralization identified to date is primarily hosted by pyroxenite units although marginal Cu grades were also identified within several drillholes. Confusing. Please rephrase.

Response: Thanks for suggestions. We will revise the problem.

9. good?

Response: Thanks for suggestions. We will revise the problem.

10. This in turn means that the complex is the focus of increased amounts of exploration, and more drilling is expected.

Response: Thanks for suggestions. We will revise the problem.

11. crustal contamination-related and metasomatic evidence of interaction between the magmas that formed the pyroxenites and the surrounding marble. Seems very important. please specify what the evidence is.

Response: Thanks for suggestions. We will revise the problem.

12. Better to describe XRF and ICPMS separately.

Response: Thanks for suggestions. Here we have described the XRF (pw1401/10) and ICP-MS (Agilent 7500a).

13. 1.Zircons were from gabbros? Please add some descriptions about zircon morphology and size. I guess the grains should be elongated and small, since gabbros are silica unsaturated. 2. have you observed zircon in thin sections? If yes, this would provide strong evidence that zircons are from gabbros. their internal characteristics. please specify CL textures.

Response: Thanks for suggestions. We have specified CL texture in Section 5.2.

14. What standard did you use for calibration? What were the accuracy and precision of the instrument?

Response: Thanks for suggestions. We will revise the problem.

15. Wu et al. [18] and Guo et al. [19] have previously discussed the laboratory apparatus, testing process and data capturing process. Even though, you should provide a description about the instrument and analytical parameters.

Response: Thanks for suggestions. We will revise the problem.

16. please specify sulfide types, pure pentlandite or mixtures with pyrrhotite and chalcopyrite?

Response: Thanks for suggestions. We will revise the problem.

17. Please provide descriptions about S and Pb analyses. It's essential to assess the quality of data.move the next paragraph here.

Response: Thanks for suggestions. We will revise the problem.

18. 34S/32S ratio?

Response: Thanks for suggestions. It is δ34SV-CDT.

19. why bolded and unerlined?

Response: Thanks for suggestions. We strongly suspect that the formats have changed.

20. What are the values and errors?

Response: Thanks for suggestions. We will revise the problem.

21. 204Pb/206Pb and 208Pb/206Pb ratios. Superscript.

Response: Thanks for suggestions. We will revise the problem.

21. No Eu anomaly (Eu/Eu*=give formular, 0.96-1.0) was observed.

Response: Thanks for suggestions. We will revise the problem.

22.1. provide values 2. depleted in Nb, P, Ti? comparing to primitive mantle? It is obvious that these elements are about 10, 5, 3 times higher. 3. There is Nb negative anamoly, but not for Ta. The Nb/Ta ratios are around 5, significantly lower than chondrite value of 17.5 (Dostal and Chatterjee, 2000, Chem Geol. 163: 207-218). This looks quite abnormal to me.

Response: Thanks for suggestions. Values have been provided in Table 1. In this section, comparable to HFSEs, LILEs are enrichment. However, comparable to LILEs, HFSEs are enrichment. After reading Dostal and Chatterjee, 2000, we have found that low Nb/Ta is due to a significant increase of the concentrations of Ta, implying that the addition of mineralizing fluids and fluid fractionation played a key role in its variation.

23. Why positive Hf anomaly suggests crustal contamination?

Response: Thanks for suggestions. As for the Hf spike, there are many explanations, such as the distribution coefficients between the garnet and the melt and mantle source heterogeneity can result in the different Hf components (Pertermann M et al., 2004, Experimental determination of trace element partitioning between garnet and silica-rich liquid during anhydrous partial melting of MORB-like eclogite. Geochemistry Geophysics Geosystems) Certainly, Hf is fluid-immobile. (Weyer S, Earth and Planetary Science Letters2003205: 309-324. Nb /TaZr/Hf and REE in the depleted mantle: Implications for the differentiation history of the crustmantle system have demonstrated that the variation of Zr/Hf ratios may reflect the partial melting of mantle).

24. Although I agree with the conclusion, REE pattern alone is not convincing in demonstrating petrogenesis.

Response: Thanks for suggestions. REE patterns of the Akechukesai I mafic–ultramafic complex were used as a contrast. We will revise the problem.

25. 1. OK. Ignore my previous comment about zircon morphology. 2. But the length: width ratio of 1-3 looks like zircon from mafic rocks? I'm not an expert on this but interested to know. Did the authors observed zircon in thin sections?

Response: Thanks for suggestions. We will revise the problem. The length: width ratios should be 1:1–1.5:1.

26. Since fractionation factor between pyrite and pyrrhotite is different, it's better to indicate the proportion of these two minerals.

Response: Thanks for suggestions. Sulfide minerals have been shown in Table 4. Samples are selected for analyses, respectively. Maybe we will specify better.

27.the units. pyroxenite or gabbro?

Response: Thanks for suggestions. We will revise the problem.

28. As such, these elemental ratios are likely to reflect crustal contamination. This is not convincing. There might be other factors. Is this interpretation from the ref [25]?

Response: Thanks for suggestions. It is not just the ref [25]. Deng et al., 2015.Lithos 227 have stated similar facts.

29. On Nb/Th-Th/Yb (fig. 10b), the samples plot along the NMORB-UC mixing line, but on Ta/Th-Th/Yb, the samples plot on neither mixing lines. So, to me, these two diagrams give somehow discrepant results, with one suggesting mixing between NMORB and UC (fig. 10b) and the other suggesting neither mixing with UC nor LC (fig. 10a).

Response: Thanks for suggestions. We will revise the problem. Through the objective reviews of reviewer, I find that there are still some deficiencies in this modeling.

 

30. Not convincing, especially for lower crust contamination. see my previous comment.

Response: Thanks for suggestions. We will revise the problem. Through the objective reviews of reviewer, I find that there are still some deficiencies in this modeling.

 

31. 1. How did the authors derive these values? some descriptions should be provided.

2. With such high level of crustal contamination, other major and trace elements should show.

Response: Thanks for suggestions. We will revise the problem. Through the objective reviews of reviewer, I find that there are still some deficiencies in this modeling.

32. which samples?

Response: Thanks for suggestions. We will revise the problem.

33. sulfur was the most likely element. The single most? Really? what about Cl, C, Na, Fe...

Response: Thanks for suggestions. We will revise the problem.

34. research? Please provide more description about this research.

Response: Thanks for suggestions. We will revise the problem.

35. confusing expression. Please rephrase; during mantle melting? in the resultant melt? in residue mantle?

Response: Thanks for suggestions. We will revise these problems.

36. 34S composition of the metasomatized mantle source. What's the oxidation state of the sulfur? What's the mineral phases hosting these sulfur?

Response: Thanks for suggestions. We know sulfur has more than one valence state (-2, 0, +4, +6 and so on). The study of oxidation state and mineral phases hosting these sulfur is the next step.

37. crustal sulfur in what form? S2-, H2S, SO2, SO42-...?

Response: Thanks for suggestions. The study of oxidation state and mineral phases hosting these sulfur is the next step.

38. suggesting the complex contains crustal S. Not necessarily. It could also be produced by sulfur isotopic fractionation.

Response: Thanks for suggestions. First of all, from the point of view of mineralization, the features of sulfur isotopic is the direct evidence. According to Ripley and Li, 2007, Earth Science Frontiers, 14, 124-131. d34S values (5.0‰–13.4‰) that are higher than the expected value for the mantle (0‰ ± 2‰) indicate that external S were incorporated into.

39. subducted oceanic crustal material. what are values for these materials?

Response: Thanks for suggestions. In the previous paragraph, we have cited that the researches of Métrich et al and Mclnnes et al. Our magma source have undergone metasomatism in the previous subduction event. So we deduce that the possible source of sulfur.

40. sounds unlikely. They are from different S sources? if the same source, how could they assimilate different concentrations of crustal materials?

Response: Thanks for suggestions. We know that S can be incorporated into the magma in the magma source or during ascent, which belong to crustal S (oceanic crustal S and continental crust S). Here we address the source contamination. However, we cant ignore the continental crust contamination during ascent. Different d34S values may be associated with the continental crust contamination during ascent.

41. OK then Pb isotope argues against your previous statement that vein-like ore contain more crustal sulfur.

Response: Thanks for suggestions. Here Pb isotopic data reflected the influence of orogeny. However, they are mainly derived from mantle source.

42. The subchondritic Nb/Ta value of around 5 looks interesting, and their origin should be considered as well.

Response: Thanks for suggestions. We have found that low Nb/Ta is due to a significant increase of the concentrations of Ta, implying that the addition of mineralizing fluids and fluid fractionation played a key role in its variation.

43.Where are the diagrams?

Response: Thanks for suggestions. We will revise the problem.

44. Have the authors proved this?

Response: Thanks for suggestions. We will prove it in Section 6.3 and we will revise the problem.

45. But samples from Akechukesai IV intrusions have much lower Hf isotopes. Why?

Response: Thanks for suggestions. The addition of ancient crustal materials may be one reason. We will revise the problem.

46. confusing. with Hf isotopes alone, you can assess the level of contribution of NMORB and Crust, since composition of NMORB is known, and the only value needed is the crust.

Response: Thanks for suggestions. We will revise the problem. In previous reviews, reviewers have recommended using the Sr-Nd isotope. This is a reply.

47.What are the SiO2 contents for the resultant melts? Just interested to know if by assiminating 40-50% upper crus (containing 60-70% SiO2) can produce 50% SiO2 for the gabbro samples.

Response: Thanks for suggestions. We will revise the problem.

48. Such ambitious conclusion can be derived only from presence of biotite and amphibole?

Response: Thanks for suggestions. We will revise the problem.

49. If the authors add someages about the orogenic process, it'd be easier to identify if the gabbros formed in post-orogenic process.

Response: Thanks for suggestions. We will revise the problem.

50. based on what evidence?

Response: Thanks for suggestions. We will revise the problem.

51. due to slab subduction?

Response: Thanks for suggestions. Slab subduction is one reason. But we cant rule out the continental crust contamination.

 

 

 

Again, we really appreciate the editor’ comments that are helpful in improving the quality of our paper.

 

 

Sincerely yours

 

Fengyue Sun 

Jilin University


Round 2

Reviewer 1 Report

See attached file

Comments for author File: Comments.pdf

Author Response

Prof. Fengyue Sun

                      College of Earth Sciences

                      Jilin University

                      No. 2199 Jianshe Street

                      Changchun, 130061, China

April 27, 2019

Mr Jax Jiang

Assistant Editor,Minerals

 

Re: minerals-469475

 

Dear Mr Jax Jiang,

 

Thank you very much for returning the comments on our manuscript (minerals-469475) entitled Geochemistry,  Geochronology and Hf-S-Pb isotopes of the Akechukesai Ⅳ mafic-ultramafic complex, Western China”. All suggestions are valuable and helpful for improving the quality of the paper. We have considered the editor’s comments and thoroughly revised the paper. We appreciate your great efforts in improving our paper.

 

In the following, we explain where and how the reviewers’ comments have been incorporated.

 

Responses to the comments by Reviewer#1:

General comments:

The third version of the manuscript by Yan and co-authors presents improvements with respect to the previous version, although some points concerning data interpretation still need to be addressed. Moreover, several minor corrections are needed.

In my previous review I asked for a more rigorous treatment of geochemical data to model the hypothesized contamination processes, but the authors did not present any. I realize this is a hard task, so I will not insist on asking that, although I believe its an important point. 

 

1. Lines 181-184 The paper by Dostal and Chatterjee (2000) deals with extremely fractionated granites, in which fractionation of fluids, formed in the granitic magma itself, is supposed to change the Nb/Ta ratios. This is not the case, as you are dealing with a completely different magma (gabbro)! Its better to attribute the unusual values of both Nb/Ta and Zr/Hf ratios to either mantle metasomatic processes, or fractionation of accessory mineral phases, or both.

Response: We thank the reviewer for his positive comments on our paper. We have fully considered all comments raised by you and the reviewers and thoroughly revised the paper [see Changes marked with red color and Revision note].

 

2. Line 228 – “…reactions between calcium-rich marble and mantle-derived magma”. If you are convinced that the interaction occurred involving a melt, then there is the alternative possibility that the pyroxenite may be a reaction product of mafic magma-limestone interaction occurred at shallow depth in the crust. In other words, a mafic magma may have induced thermo-metamorphism on limestone, changing limestone to marble, and turning the mafic magma into a pyroxenite upon calcium assimilation. Please, evaluate this possibility on the basis of field observations and

literature data.

Response: Thanks for suggestions. First of all, there is no evident that marble was metamorphosed from limestone. Because we found that marble is ubiquitous with or without basic magma in the Akechukesai area.

 

3.Lines 229-232 – Again, you are using the terms assimilation and contamination in an ambiguous way. Here you are talking about assimilation of crustal material, which is a process that occurs WITHIN the, usually continental, crust. Right below, instead, you are talking about SOURCE CONTAMINATION. Indeed, you conclude the paragraph by saying that the primitive magma of these intrusions was originated from a metasomatized mantle source. This is OK, but please don’t confuse the reader! 

Response: Thanks for suggestions. We will clarify the terms.

4.Lines 264-265 – Please, don’t use the word assimilation here, given that you believe that S is introduced in the mantle source by fluid metasomatism.

Response: Thanks for suggestions. We will clarify the terms.

5.Line 277 – “…with the crustal Pb present added as a result of orogenic processes that occurred…” Just for clarity: are these orogenic processes THE SAME that introduced S in the source and determined high Ba/La and Ba/Th ratios? Please, clarify.

Response: Thanks for suggestions.First of all, orogenic processes contain subduction, syn-collision and post-collision stage.We know that they happen continuously.Generally, high Ba/La and Ba/Th ratios were caused by subduction-related metasomatism. Due to Pb and S are fluid-mobile, they can also be added in subduction-related metasomatism. Moreover, Pb and S from continental crust can be added during ascent.

6.Lines 295-297 Be careful: you are comparing Pb-isotope data on S-bearing ores with those on basalts (MORB and OIB)! This must be specified. Also, you say that Sulphur has derived from the subducted crust.  

Response: Thanks for suggestions. We understand what you mean. Here we mainly compared with the source region characteristics of MORB and OIB.

 

 

SPECIFIC COMMENTS

Line 13 – change the sentence “gabbro samples” with “gabbros”

Response: Thanks for suggestions. Revised as suggested.

Line 14 – change the word “but” with “with”

Response: Thanks for suggestions. Revised as suggested.

Lines 15-17 – This sentence bears some wrong concepts. You cannot invoke any processes involving fluids when immobile elements are concerned! This must be changed. See my comments below, when you cite Dostal and Chatterjee 2000

Response: Thanks for suggestions. Revised as suggested.

Line 24 – change the sentence “mantle source and crustal source” with “mantle and crustal sources”

Response: Thanks for suggestions. Revised as suggested.

Line 26 – change the word “garnet-stable” with “garnet-bearing” Response: Thanks for suggestions. Revised as suggested.

Line 38 – change the word “comprised by” with “including”

Response: Thanks for suggestions. Revised as suggested.

Line 50 – change the sentence “with respect to petrology features” with “in terms of petrological features”

Response: Thanks for suggestions. Revised as suggested.

Line 56 – change the sentence “analysis with respect to the experimental results” with “analysis of experimental results”

Response: Thanks for suggestions. Revised as suggested.

Line 64 – change the sentence “with respect to” with “testifying to an”

Response: Thanks for suggestions. Revised as suggested.

Line 71 – change the word “dramatically” with “extensively”

Response: Thanks for suggestions. Revised as suggested.

Line 73 – “This belt also contains well-exposed units.” Please, specify the kind of units

(sedimentary, magmatic, …)

Response: Thanks for suggestions. Revised as suggested.

Line 94 – change the sentence “drillholes), which intercepted…” with “drillholes) intercepted”

Response: Thanks for suggestions. Revised as suggested.

Line 123 – change the word “method” with “methods”

Response: Thanks for suggestions. Revised as suggested.

Line 137 – change the sentence “was a Aurora” with “was an Aurora” Response: Thanks for suggestions. Revised as suggested.

Line 139 – change the sentence “entering into the ICP” with “entering the ICP”

Response: Thanks for suggestions. Revised as suggested.

Line 140 – change the word “optimize” with “standardize”

Response: Thanks for suggestions. Revised as suggested.

Line 141 – change the sentence “correction are shown in Yuan et al.” with “correction are from Yuan et al.”

Response: Thanks for suggestions. Revised as suggested.

Line 142 – change the word “ICPMS” with “ICP-MS”

Response: Thanks for suggestions. Revised as suggested.

Lines 156-158 – check font size

Response: Thanks for suggestions. Revised as suggested.

Line 177 – change the sentence “are from professor Fengyue Sun ’s scientific research team”. Withare from a compilation of literature data”

Response: Thanks for suggestions. Revised as suggested.

Line 184 – change the sentence “area in Figure 5b also shows the compositions of samples” witharea in Figure 5b includes samples”

Response: Thanks for suggestions. Revised as suggested.

Line 185 – change the word “with” with “showing”

Response: Thanks for suggestions. Revised as suggested.

Lines 203-204 – change the sentence “crustal composition may have been incorporated into.” Withcrustal material may have been incorporated into the source.”

Response: Thanks for suggestions. Revised as suggested.

Line 216 – see comment to line 177

Response: Thanks for suggestions. Revised as suggested.

Line 241 – change the word “whereas” with “but”

Response: Thanks for suggestions. Revised as suggested.

Line 242 – change the word “are” with “were”

Response: Thanks for suggestions. Revised as suggested.

Line 245 – change the word “metasomatic” with “metasomatized”

Response: Thanks for suggestions. Revised as suggested.

Line 260 – change the sentence “references there in” with “and references therein”

Response: Thanks for suggestions. Revised as suggested.

Line 262 – change the sentence “references there in” with “and references therein”

Response: Thanks for suggestions. Revised as suggested.

Line 275 – delete the word “that”

Response: Thanks for suggestions. Revised as suggested.

Line 283 – change the sentence “(Positive Nb and Ta)” with “(positive Nb and Ta anomalies)”

Response: Thanks for suggestions. Revised as suggested.

Lines 318-320 – There are many other examples of Variscan post-collisional mafic magmatism derived from crust-mantle hybrid sources. One very recent is reported in

Franciosi, L., D’Antonio, M., Fedele, L. et al. Int J Earth Sci (Geol Rundsch) (2019).

https://doi.org/10.1007/s00531-019-01689-8

Response: Thanks for suggestions. We have cited this reference.

Line 354 – change the sentence “in the post-collisional” with “in a post-collisional”

Response: Thanks for suggestions. Revised as suggested.

 

Line 394 – change the sentence “primitive magma” with “the original source”

Response: Thanks for suggestions. Revised as suggested.

Line 395 – change the sentence “sources are” with “source is”

Response: Thanks for suggestions. Revised as suggested.

Lines 397-399 – change the sentence “Addition of sulfur is crucial to S saturation and leads to the precipitation of sulfide minerals. The assimilation of high amounts of S may have had a significant role in driving S saturation.” with “Addition of high amounts of sulfur may have had a significant role in driving S saturation, leading to the precipitation of sulfide minerals.” (to avoid the repetition)

Response: Thanks for suggestions. Revised as suggested.

Lines 481-483 – Number 24 is a wrong reference. The right reference is:

Jochum, K.P., Seufert, H.M., Spettel, B., Palme, H., 1986. The solar-system abundances of Nb, Ta and Y, and the relative abundances of refractory lithophile elements in differentiated planetary bodies. Geochim. Cosmochim. Acta 50, 1173–1183.

Response: Thanks for suggestions. Revised as suggested.

 

 

 

 

 

Again, we really appreciate the editor’ comments that are helpful in improving the quality of our paper.

 

 

Sincerely yours

 

Fengyue Sun 

Jilin University


Reviewer 2 Report

I am happy to see the obvious improvement of the manuscript, especially with repect to language. Now my main concerns are with the Discussion part besides some minor suggestions about figure improvement (see the attached pdf). I outline my main concerns below:

About the bivariate diagrams using trace element concentrations and ratios (Fig. 10 and 11), the authors should describe how the diagram works in order to interpret what the meanings are of plotting in a specific region or trend.

It is unclear to me (haven't been clearly explained in the manscript either) that how crustal signatures (both elemental and isotopic) can be attained by remelting of a previously subduction modified mantle wedge. For instance, how can subduction process modify the S isotopic composition of mantle? This is linked to my next question.

The authors have to explain the big Hf isotope difference between AKS IV and Xirihamu? and also the S isotope difference between vein and disseminations. The current explanation for S isotopes is not convincing.

I'd like the authors to consider if the contamination is due to existing arc rocks that are not exposed, instead of source contamination?

At the end, the authors should discuss if it can explain all data at hand. And I didn't see any implications for Cu-Ni deposits as indicated in the Introduction.

Comments for author File: Comments.pdf

Author Response

Prof. Fengyue Sun

                      College of Earth Sciences

                      Jilin University

                      No. 2199 Jianshe Street

                      Changchun, 130061, China

April 27, 2019

Mr Jax Jiang

Assistant Editor,Minerals

 

Re: minerals-469475

 

Dear Mr Jax Jiang,

 

Thank you very much for returning the comments on our manuscript (minerals-469475) entitled Geochemistry,  Geochronology and Hf-S-Pb isotopes of the Akechukesai Ⅳ mafic-ultramafic complex, Western China”. All suggestions are valuable and helpful for improving the quality of the paper. We have considered the editor’s comments and thoroughly revised the paper. We appreciate your great efforts in improving our paper.

 

In the following, we explain where and how the reviewers’ comments have been incorporated.

 

Responses to the comments by Reviewer#2:

General comments:

I am happy to see the obvious improvement of the manuscript, especially with repect to language. Now my main concerns are with the Discussion part besides some minor suggestions about figure improvement (see the attached pdf). I outline my main concerns below:

About the bivariate diagrams using trace element concentrations and ratios (Fig. 10 and 11), the authors should describe how the diagram works in order to interpret what the meanings are of plotting in a specific region or trend.

It is unclear to me (haven't been clearly explained in the manscript either) that how crustal signatures (both elemental and isotopic) can be attained by remelting of a previously subduction modified mantle wedge. For instance, how can subduction process modify the S isotopic composition of mantle? This is linked to my next question.

The authors have to explain the big Hf isotope difference between AKS IV and Xiarihamu? and also the S isotope difference between vein and disseminations. The current explanation for S isotopes is not convincing.

I'd like the authors to consider if the contamination is due to existing arc rocks that are not exposed, instead of source contamination?

At the end, the authors should discuss if it can explain all data at hand. And I didn't see any implications for Cu-Ni deposits as indicated in the Introduction.

Response: We thank the reviewer for his positive comments on our paper. We have fully considered all comments raised by you and the reviewers and thoroughly revised the paper [see Changes marked with red color and Revision note].

 

 

SPECIFIC COMMENTS

1. (ref needed).

Response: Thanks for suggestions. Revised as suggested.

2. (ref needed).

Response: Thanks for suggestions. Revised as suggested.

3. where is this on map?(Xiarihamu)

Response: Thanks for suggestions. Revised as suggested.We have added in Fig.1b.

4. (ref needed).

Response: Thanks for suggestions. Revised as suggested.

5. expecting to see relavent discussion in Discussion

Response: Thanks for suggestions. Revised as suggested. In this paper, in terms of tectonic background, magma source and S addition,etc,we discuss the newly-discovered Akechukesai complex. Moreover, we compared it with Xiarihamu complex, Shitoukengde complex and Akechukesai complex.We believe that it is helpful for regional prospecting.

6. where is this on map?(Shitoukengde)

Response: Thanks for suggestions. Revised as suggested.We have added in Fig.1b.

7. in gabrro?

Response: Thanks for suggestions. Revised as suggested.However, in pyroxenites.

8. Again, you should give general description about analytical process.

Response: Thanks for suggestions. Revised as suggested.We have added.

9. 0.005 instead of 0.005%?

Response: Thanks for suggestions. Revised as suggested.

 

10. move this to Discussion, and explain more about why!

Response: Thanks for suggestions. Revised as suggested.

11. Also move to discussion. Combine it with Nb/Ta interpretation

Response: Thanks for suggestions. Revised as suggested.

12. S-Pb isotopic data are also included under this title?

Response: Thanks for suggestions. Revised as suggested.

13. should be LA-ICP-MS

Response: Thanks for suggestions. Revised as suggested.

14. Please be consistent with the name

Response: Thanks for suggestions. Revised as suggested.

15. move this to Discussion, and elaborate more!

Response: Thanks for suggestions. Revised as suggested.

16. You haven't corrected this. It is a legend. It's very confusing.

Response: I am so sorry. Thanks for suggestions. Revised as suggested.

17. 1. The figure is quite massy. Try to make it less busy by moving some of the words into a legend. 2. what are the data sources for 1.8Ga, 2.5 Ga and 3.0Ga lines?

Response: Thanks for suggestions. Revised as suggested.

18. I don't think this is appropriate. Better to say (Sun et al. unpublished data) and give a full reference in the list.

Response: Thanks for suggestions. Revised as suggested.

19. Explain the abbreviations in the caption and give citations for the data.

Response: Thanks for suggestions. Revised as suggested.

20. in Akechukesai IV? But no contact is seen from surface (Fig. 2)

Response: Thanks for suggestions. We have described the Tanjianshan group marble in Geological setting.

21. What are the specific mineralogy? Based on what observation the authors state it is a reaction product between mafic magma and marble?

Response: Thanks for suggestions.Contaminated rock is a rock, which chemical composition is between marble and pyroxenite. Based on the field observation (Fig.3).

22. For instance which element pair? how the element pair can indicate partial melting and fractional crystallization?

Response: Thanks for suggestions. Here the ratios of elements with similar distribution coefficients in the gabbros cannot be explained by partial melting and fractional crystallization alone.

23. What are the partition coefficients for Ce and Pb between gabbro magma and mantle?

Response: Thanks for suggestions. Here we address the variation of ratio of Ce/Pb.

24. If there is no crustal contamination, the ratio should be 25? Suspicious because Ce and Pb are different in both charge and radius, so they won't behave completely the same. In other words, there will be fractionation.

Response: Thanks for suggestions. We say the ratio is 25 ± 5. It is a range, not a specific ratio.

25. Not quite. Crust is <15, but the samples are around 2.

Response: Thanks for suggestions. It is just a range. Our samples plot in this range. It is ok.

26. this Pb will stay in mantle after subduction? or it will completely enter the magma and leave the mantle unchanged with respect to Pb content?

Response: Thanks for suggestions.We consider that Pb will partially go into the magma.

27. Again, what are the partition coefficients for these two elements? How do they behave during mantle melting? How can they be used as a tracer?

Response: Thanks for suggestions. Here we address the ratio of Nb/U. During mantle melting,the Nb/U ratio barely changed.

28. But what if there are materials in this region have low Nb/U ratios? Such as arc-derived materials formed during previous subduction?

Response: Thanks for suggestions.We have discussed the variation of Nb/U ratios.

29. What are the Nb/U ratios of the metasomatic mantle?

Response: Thanks for suggestions. It is similar to the arc volcanic rocks.

30. Generally explain how this diagram works please.

Response: Thanks for suggestions.Revised as suggested.

31. Again, explain how this diagram works! It's important to judge how reliable the interpreations are.

Response: Thanks for suggestions.Revised as suggested.

32. What association?

Response: Thanks for suggestions.Revised as suggested. We have emphasized the ability to transport S.

33. from mantle? or from subducted slab?

Response: Thanks for suggestions.Revised as suggested.

34. Why?

Response: Thanks for suggestions.Revised as suggested. It is likely to be related to the arc setting, fO2 and fS2.

35. But subduction has ceased when the complex form, hasn't it?

Response: Thanks for suggestions.Magma source may predate the formation of complex.

36. How could this happen? They have different magma source? or the source is heterogeneous like you suggested previously? But how could the hetergeneity happen? and even if this is true, the magmas for vein and disseminate sulfides emplace in crust separately?

Response: Thanks for suggestions. According to Métrich et al.1999, spatial and temporal variations of fO2 , fS2,P,T and etc can lead to this heterogeneity. Based on the observation, we found that vein and disseminate sulfides emplace in different place.

37. with respect to 176Hf/177Hf?

Response: Thanks for suggestions. With respect to TDM1 ages.

38. How do you evaluate the relative contribution?

Response: Thanks for suggestions. Combined with the Zr/Nb and Sm/Nd ratios and Pb isotopes.

39. Fields; Specify!

Response: Thanks for suggestions. Revised as suggested.

40. what about S, P, Lu-Hf isotopes?

Response: Thanks for suggestions. We know that arc magmas are Nb, P, and Ti depletions and enrichment in the LILE (Rb, U, and K). Thats just one of the features.  

41. this is pyroxenite, right? It is more basic than gabbro, so maybe less crustal contamination. that the contamination is from previous arc-derieved rocks where are still in the deep crust?

Response: Thanks for suggestions. This is pyroxenite. It is one possibility.

42. But the subduction has ceased, so the subducted endmember has disappeared. It's now only question of level of enrichment of the mantle according to your model.

Response: Thanks for suggestions. Magma source (mantle) can be enriched in previous process. Moreover, magma can also be enriched during ascent. We consider that level of enrichment are related to the geochemical characteristics and metallogenetic potentially.

43.Could spinel and garnet coexist in mantle rocks? At what P and T?

Response: Thanks for suggestions. Generally, we believe that they could be coexist under certain conditions.

44.50%Grt and 50% Sp? Please indicate clearly on the mixing curves.

Response: Thanks for suggestions. Ok. We believe that it is not difficult to understand. The closer you are to the bottom, the higher the garnet proportion.

45. the black square is your sample?

Response: Thanks for suggestions. We have added a legend.

46. Is this consistent with garnet-spinel stable mantle?

Response: Thanks for suggestions. It is consistent with fluid metasomatism.

47. what do you mean? How could sedimentation related to ridge subduction?

Response: Thanks for suggestions. I have been aware of some issues that are being addressed and I have revised.

48. of the metasomatized mantle? How could this process explain:

1. the Hf isotopic difference between AKC IV and Xiarihamu

2. S isotope difference between vein and disseminates

3. the discussed element pairs

Response: Thanks for suggestions. Except for metasomatized mantle, if they ever existed ancient crustal materials can lead to the Hf isotopic difference between AKC IV and Xiarihamu; According to Métrich et al., 1999, the partitioning of sulfur between different S-bearing phases during mantle melting generates a strongly heterogeneous distribution of bulk sulfur concentrations in the resultant melt as well as variations in the 34S composition of the metasomatized mantle source; There are specific conditions for the discussed element pairs. We have discussed.

 

 

 

 

 

 

 

 

 

 

 

 

 

Again, we really appreciate the editor’ comments that are helpful in improving the quality of our paper.

 

 

Sincerely yours

 

Fengyue Sun 

Jilin University


This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.


Round 1

Reviewer 1 Report

This is a rather inconsequential manuscript.  Certainly, the field area will be of interest and the data appear to meet international standards.  However, the discussion and conclusions are non-persuasive, derivative and inconsequential.  There is little new insight into process, even locally.  See annotated manuscript for further comments

You need to put significant effort into improving the English - I started out trying to have an input to this but it would have take too long to explain every mistake - though many are generic and are the same mistakes made multilel times.

I know it is difficult for Chinese people but before you will able to write good English, you need to figure out how to use the definite article - a, an, the.  Even European languages like French and Italian differ in this respect and it is complicated because it is largely done on instinct not a clear set of rules - not rules I could explain anyway.  One eminent French colleague spends a lot of money on translation services for his group because, while he speaks enough English to hold a conversation,he knows he can't write papers in acceptable English.

Comments for author File: Comments.pdf

Reviewer 2 Report

Dear Editor,

I finished to review the paper  “Geochemistry, Geochronology and Hf-S-Pb isotopes of the Akechukesai IV Mafic-Ultramafic Complex, Western China” by Yan et al. The paper deals with zircon U-Pb datings of the complex, zircon Lu-Hf isotope and sulfides Pb and S isotope, as well as wr major and trace element,  analyses used as constraints for the geochemical and petrological genesis and evolution of the complex. On the whole, the manuscript organization is fairly correct and the presented data are of good quality. Tables 1 and 2 have to be reformatted, whereas some Figure1  and 2 are of bad quality and have to be simplified in order to become readable.

I have two major concerns regarding this paper, one regarding the petrological interpretation and another one on use of the Hf model age:

1) The authors have to clarify, all along the discussion (and conclusions), that the geochemical fingerprint of the mafic-ultramafic complex reflects a magma generation from mantle sources in suprasubduction setting. The “crustal contamination” inferred by the authors is never supported by the presented data, neither properly discussed and quantified by the authors. They recall this process mainly to explain the sulfur concentration and isotopic data, but even in this case the sulfur recycling in subduction setting is a well-studied phenomenon that can provide abundances and isotopic ratios similar to those reported in the paper. In this light, the authors didn’t take into consideration some important papers that I suggest to consider and quote such as, for example:

McInnes B. I. A., Gre´goire J., Binns R. A., Herzig P. M. and Hannington M. D. (2001). Hydrous metasomatism of oceanic sub-arc mantle, Lihir, Papua New Guinea: petrology and geochemistry of fluid-metasomatized mantle wedge xenoliths. Earth Planet. Sci. Lett. 188, 169–183.

Métrich N., Schiano P., Clocchiatti R. and Maury R. C. (1999). Transfer of sulfur in subduction zone settings: an example from Batan Island (Luzon volcanic arc, Philippines). Earth Planet. Sci. Lett. 167, 1–14.

In order to assess and estimate crustal contamination processes, Sr (and/or Nd) isotopic data are needed. The available Pb isotopic compositions are compatible with mantle values.

2) Zircon U-Pb  datings are useful and consistent with previous data from the neighboring similar complexes. On the other hand Hf model ages, never discussed in the text, are meaningless since the DM composition is not appropriate. Thus I suggest to eliminate Hf model ages.    

Minor comments:

The authors have to check the text for grammar and typesetting errors before to resubmit it.


Reviewer 3 Report

Please, see comments in the attached document

Comments for author File: Comments.pdf

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