Dr Dear Muñoz-López,
Thank you for submitting a revised version of your manuscript that addresses reviewer comments. I feel that significant progress has been made when compared to the original submission. A bit more work, however, will be required in order for the submission to be an acceptable state for publication in Solid Earth. I would like to reconsider this manuscript following minor revisions. Please see below for details.

The majority of my current concerns for this manuscript are related to presentation. There are a few sections of text that are still a bit rough around the edges, sometimes in areas where clarity is particularly paramount to understanding the presented work. I have made many specific comments below, but will reiterate some of the main issues with the presentation / writing quality here.

1) The writing has a tendency to confuse fact and interpretation, mainly in the discussion. As an example, consider the text: “As veins V1a and V2 developed during the Alpine reactivation of the Estamariu thrust, the geochemistry of their related calcite cements Cc1a and Cc2 record the fluid system during this tectonic event.” It is only your interpretation that the veins formed during Alpine reactivation. The structural data support it, but without actual geochronology this cannot be known independently. The language should reflect that.

2) The age descriptions of various events need to be revised. Right now there is a tendency mix global (i.e. Neogene) and local (i.e. Variscan) terms. The readership for this journal is international, and those outside of Europe may not immediately know the age range of the latter.

3) The overall text is, in my opinion, considerably longer than it needs to be. Significant shortening could be accomplished in most sections. Methods that produced no data (i.e. U-Pb) need not be mentioned. This is also true of aspects of the geological setting description that do not directly impact the overall interpretations presented here (whether or not this is the case I will leave to you).

4) The overall quality of the writing tends to decrease toward the end of the manuscript. Please revise the manuscript for brevity and clarity. In the discussion, for example, the last 4 sections tend to either reiterate the same points continuously, or call upon complicated theoretical considerations to underpin interpretations that you have actual data to support (see comments related to section 5.5). These sections would quite easily be condensed into a single section just a few paragraphs in length.

From a scientific perspective I think things are largely in good shape, but please do address the issue of negative clumped isotope temperatures and their impact on d18O-fluid interpretations.

Best,
Randy Williams

19: I am skeptical that clumped isotope analysis allows us to know temperature this precisely even from an analytic perspective, let alone a natural one. Suggest “50 - 100 C”, here and throughout.

21: Suggest “...hydrothermal fluids that had interacted with crystalline basement rocks and been expelled…”

23: “Cc5 cements”

A general comment I have on the abstract is that it is stating interpretations as a matter of fact. Please rephrase to make clear that these are your interpretations, citing the relevant observations / data where necessary to support your case.

46-47: Those unfamiliar with the tectonics of the area are unlikely to know the age of the events you are referring to here.

49-50: It is not clear to me why a lack of knowledge of the age of a fault precludes examination of fluid-fault interaction?

53: Suggest, “In contrast, few studies have examined the relationship between deformation and fluid flow in the Paleozoic basement…”, or similar.

66: Please do not mix local age/orogen terms with established geological periods, which are global. The latter are preferred.

81-82: Same comment as above.

105: “Basically”?

General comments on geologic setting: I would encourage you to consider shortening this section. It is not clear to be that all of this information is required given the specific focus on the Estamariu thrust.

114: Please restructure this sentence. Too many “ands” and not enough commas.

115: “The structural data includes the orientation of bedding, folations, and fractures in addition to cross-cutting relationships and kinematics”.

124: As it relates to isotope analysis, “isotopy” is not actually a word. Suggest “...selected for stable isotope analysis”.

General Comments on Methods: These can and should be shortened substantially. The “dirty details” of the analyses should be moved to a supplemental document, leaving the main text to focus on what was done at a higher level.

197-199: I thought it was strange that the U-Pb work was not mentioned until the methods. If this didn’t produce anything useful for the present study then it would be best to remove it all together. I would note, however, that if the problem was low U and high Pb then you now have Pb isotope data, which previous work has shown to be very effective in tracing fluid origin / pathway information in faults (see Williams et al., 2019, Journal of Structural Geology - Radiogenic isotopes record a ‘drop in a bucket’–A fingerprint of multi-kilometer-scale fluid pathways inferred to drive fault-valve behavior).

202: “Subordinate”

216: “Points to…”

210-245: The orientation information here is very hard to follow. Figure 3 helps but more could be done. Suggest adding a stereonet figure that shows the average orientation of each of the named structural elements, such that their relationship to each other is easily visualized.

288-293: The D47 value will not be interpretable to most. You could simplify this text by just stating that D47 values were converted to temperature using Kluge and then simply report the temperature range for each generation.

304-307: Similar to U-Pb comments, it is difficult to believe that Nd/Nd values for just two samples shed any real light on the story. This system is highly atypical in studies of fluid-rock interaction, and would likely be difficult to interpret confidently even if a lot of data were available. Seems like two data points provide little more than speculation.

318: Consistent age terminologies please.

340: I do not see how fibrous crystals orthogonal to fracture walls indicate extensional deformation? I have seen identical structures in a variety of thrust environments. Are you implying that syntaxial veins cannot form during thrust/reverse faulting, or is the “extension” in this case referring to the fracture only?

353-354: This is an interpretation that has the effect of being stated as a fact here. Please be careful with phrasing related to this here and throughout the manuscript.

370-375: Please rephrase these lines for clarity. A big part of your argument rests here, but the text related to it is a bit cumbersome.

390-393: Interesting. Fluids at ~200 C at a depth of only a few hundred meters should have experienced boiling. Any evidence that would suggest that happened?

405-406: I do not see how any of your observations can reasonably support this assertion. I would argue we have no idea how long that event was, nor even how long or short it would have to be to result in the resetting of clumped isotope data. The line below is specific to temperatures in excess of 120 C, but the process of reordering is almost certainly kinetically controlled and may therefore scale exponentially with temperature. The only observation that can reasonably support the integrity of the other earlier cement generations is the lack of apparent recrystallization structures.

408: “Crumpled” isotopes. Obviously a typo, but quite funny nevertheless.

411-412: This is a bit of a sticking point for me. The stable isotope composition of calcite cannot indicate any type of fluid origin on its own. Only the calculated d18O-fluid can provide that information.

416: How can the abundance or size of the veins be indicative of meteoric fluids? I have seen fault systems with a significant abundance of very large veins that formed almost exclusively from meteoric fluids.

418: I`m sorry, but -5 C? That is ice for fresh water (which you seem to be inferring), even at high altitude. This suggests that perhaps your D47 data for this generation (at least) are skewing a bit lower than reality, which has implications for the d18O-fluid values you calculate. This certainly warrants some discussion.

440-458: I do not quite understand the point of this section given the last paragraph of the previous. Is it just to say that fluids circulating through mesozoic and cenozoic cover sediments have a different Sr isotope composition then those circulating through basement rocks? This is more or less what would be expected. I would also point out that, since you are referencing other studies that employed a 0.710, “limit value” for inferring interaction with older crystalline materials, that Williams et al. (2015, Geology) employed the same value for fluids in the Rio Grande rift, USA.

497: Was all of the above discussion in this section meant to argue that the fluids precipitating the calcites examined in this study interacted with basement rocks? Surely your actual data (mainly Sr/Sr) demonstrated that fairly conclusively already? I am struggling to understand the utility of this section.

515-516: These types of sentences / ideas would be much better constructed as “Stable oxygen and clumped isotope analyses indicate that meteoric fluids were circulating through the fault during these periods, at temperatures of XX-YY”.

516-517: What does “increased the fluid-rock interaction” mean, and what is the evidence for it?

523-525: This is a strange central conclusion to fall back on. It is exactly what would be predicted, and moreover it has been shown by several previous studies looking at Sr/Sr systematics in both fault cements and modern hot spring fluids. The conclusion feels a bit like it was put together as an afterthought, when I would argue it is one of the most important sections in the paper.

Hello Dr Muñoz-López,
Thank you for again diligently revising your manuscript in response to my comments. I feel that all major issues with the presentation and science have now been resolved. As such, I am happy to inform you that the manuscript is very nearly ready for publication. There are, however, just a few remaining minor issues that I identified while reading the current draft. As such, I am rendering a decision of "Publish subject to technical corrections". Please address these issues such that your manuscript may proceed with typesetting, etc.

Looking forward to seeing this in print.

Cheers,
Randy Williams
Topical Editor


NOTE: The line numbers referenced here are with respect to the tracked changes version in your author response letter.

General comment: Thank you for updating/rounding the temperatures derived from clumped isotopes. This appears to have been done inconsistently, however, some areas still retain the original formatting, see “Results” section. Please update for consistency throughout.

95: Please clarify the meaning of “most important”.

431: Might be better to say there is “little evidence” for resetting, as the chance is really unknown.

423: “...derived FROM and/or…”

440: Please delete “its” from this line. Not clear what the possessive is indicating.

455: Suggest “more” radiogenic signature. Please update here and throughout

537: Regardless OF.

Dear authors,
please take the technical issues mentioned by the Topical Editor Randy Williams into consideration. After their implementation, the manuscript is ready being published.
With best regards, Lotte Krawczyk.