3He/4He Signature of Magmatic Fluids from Telica (Nicaragua) and Baru (Panama) Volcanoes, Central American Volcanic Arc
Round 1
Reviewer 1 Report
The study provides for the first time noble gas fluid inclusion data supplemented with bulk rock and mineral chemistry for two, previously unstudied centers in the Central American Volcanic Arc. The results and the findings are robust and the authors give an insight to the nature of the noble gas systematics of the arc system.
I could not see the figures neither within the article nor as separately uploaded material (only the figures for the Supplementary file), which did not help to get the complete picture of the study.
Since you mention the possibility OIB-source, it would be interesting to see the Ne isotopic systematics as well, to see whether there is any implication towards OIB in the Ne isotope ratios (at least for those samples which are the least air contaminated).
Besides the figures are not accessible in the uploaded material, the Figure 1 of the Supplementary is just partly visible, things are missing from it (it seems as it was uploaded or saved incompletely).
There are some inconsistencies with the citations: most of the times it follows the numbering style of the journal, but at few places, a different style appears (e.g., Lines 194-195, Line 353, Line 394, Line 501, Line 512).
The English is generally good in the manuscript, it should be double checked though again before final submission.
Line 57 – 25 to 17 Ma
Lines 62-63 – 62.2° (in case you refer here to the degree of the angle), 56.9° and 58.9°
Lines 70-72 – please rephrase the beginning of the sentence
Lines 98, 99, 118, 207, 264, 325 – closing brackets are missing
Line 103-104 – one of the best studied arcs
Line 107 – mantle source signature is…
Line 307 – useful to recognize recycling…
Line 338 – Section 4.1 – could you provide further evidence/comment on that the 3He/4He signature is truly different at Telica and Baru, and these values are not just due to the different extent of atmospheric contamination of a very similar source?
Line 369 – of Baru [15].
Line 380 – data from fumarole gases…
Line 390 – we derived…
Line 407 – it would be better to use [68] instead of ‘The Authors’
Line 431 – Recent works have demonstrated…
Line 415 – We therefore attempt to evaluate
Lines 460-461 – respect to the neighboring…
Line 497 – from a higher presence
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
This manuscript is describing interesting results on helium isotope ratios in fluids included crystals from two volcanoes of the Central America Volcanic Arc and the interpretation of along-arc variation in the helium isotopes. However, the manuscript set does not contain any figures quoted in the text, probably due to some mistakes by authors. As far as reading the manuscript with supplemental figures, I can’t fully understand how important and reasonable the interpretation is. Therefore, it is unfortunate that I cannot recommend this manuscript for the publication. Should resubmit with the complete style.
The followings are my comments, based on the manuscript without the illustrations.
- This looks one of pioneer works for analyzing the helium isotope ratio using crystals. Regarding the helium isotope ratios, the merits of analyzing crystals in erupted materials rather than spring water around volcanoes should be insisted more in this manuscript.
- General meaning of fluids trapped crystals should be explained more. Cleavage or cracks in crystals can trap fluids after their crystallization and during the storage in magma chamber or their ascent with magma to the surface, and melt/fluid inclusions in crystals were trapped during the crystallization. The present analytical procedure collect all stages of fluids in the crystal history.
- Contamination and mixing by slab sediment/crustal material are mentioned even for fluids analyzed in this study, though the extents of contamination and mixing are smaller than in spring waters. However, the similar conclusion on the interpretation of the along-arc variation can be introduced even without the present fluid data from two volcanoes (adopting the maximum 3He/4He ratios of spring waters), can’t it?
- In my personal opinion, 145 references are too much for the length of this text, although the figures were constructed by referring to many published papers, as understood from captions of figures. The readers will feel hard to recognize which references are critical. It may be better to choose indispensable and important references, if possible.
- In Figure S1. Values Mg# are shown in percentage and ratio for Cpx. Please fix.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
The presented manuscript proposes the first geochemical data of noble gases (He, Ne, Ar) trapped in fluid inclusions within magmatic crystals from volcanoes located in the Nicaraguan and Panamanian segments of CAVA (Central American Volcanic Arc). The latter is a fascinating, and well-studied, subduction related volcanic arc system. In such a context, deciphering the 3He/4He signature of degassed magmatic fluids is of paramount importance for a better understanding of nature of mantle sources. In order to obtain this type of information the authors studied in detail the geochemical signature of volatiles from fluid inclusions observed in olivines and pyroxenes within volcanic rocks from two volcanic systems, Telica, in Nicaragua, and Baru, in Panama.
The main strength of this type of investigation is to highlight the factors that control the potential variations in the composition of the mantle wedge: subduction of sediments, magma differentiation, and/or crustal contamination. Consequently, the presented work will be of broad interest to the scientific community working on volcanic arcs and subduction dynamics. The premise of the study is commendable and the acquired geochemical data are of high quality.
The methods used are fully mastered by the authors and the results obtained are analysed and discussed in detail. In particular, these new data are compared with all the available geochemical data, obtained by other methods, on the studied volcanic systems.
The chosen manuscript organization proposed by the authors is coherent, the methods used are well presented and the data are distinctly separated from the interpretations. In other words, the presented work is consistent and useful and deserved to be published.
From a purely formal point of view, the introduction is lengthy, as the authors have chosen to present the scientific question addressed and the overall geological/geodynamic context. Perhaps we should separate these two aspects and present the geological setting as such for a more fluid reading of this excellent manuscript.
However, the figures cited in the text were not present in the downloaded PDF document. This is unfortunate because I would have appreciated having them in order to better follow the approach of the authors.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
- Although I tried to check their replies to my comments in the text, I could not be sure whether the comments were reflected in this version or not. Yellowed lines are just for English improvement.
- For example, they replied the figure in the supplement (cpx's Mg#) was corrected due to my comments, however, no change is found. So that I feel that this time revision was too surficial.
- Therefore, I decide that their revision is incomplete, looking as just putting all the illustrations which were not accompanied in the first version.
- References in the captions are shown in the author(s) and year, but in numbers in the text and the references. It is impossible for all readers to refer the original papers in the captions in the reference sites.
- In Fig. 2, helium los is shown in dashed pink line. The authors should explain the reason why the isotopic ration changes due to helium loss.
Author Response
"Please see the attachment"
Author Response File: Author Response.docx
