The East Variscan Shear Zone (EVSZ) and Its Regional Mylonitic Complex: A New Geodynamic Interpretation of the Variscan Axial Zone in Sardinia (Italy)?

Round 1

Reviewer 1 Report

Dear Federico and Franco Marco,

I read with interest your manuscript titled “The East Variscan Shear Zone (EVSZ) and its related mélange: a new geodynamic interpretation about the Variscan Axial Zone 3 in Sardinia (Italy)?”.

I find it interest and well written with a great amount of data. However, I believe it suffers of two major flaws. The term mélange in the title and in the conclusion is overused. I strongly recommend to avoid the use of this term for this case-study. In addition, I believe that the discussion section must be improved, it seems not fully linked to the presented data.

Below and in the attached pdf file you can find my detailed comments.

 Comment to the manuscript The East Variscan Shear Zone (EVSZ) and its related mélange: a new geodynamic interpretation about the Variscan Axial Zone 3 in Sardinia (Italy)?

The introduction section is a weak point for this manuscript. It presents the geological setting of the Variscan belt, and the geology of the Variscan belt in western and central Europe. However, it is completely lacking of the scope of the manuscript and the scientific problem that the Authors are trying to address with their research. It is also not clear what is the object of this study among the different tectono-metamorphic domains and untis of the Variscan Belt. It is mandatory for the Authors to introduce in this section these topics: 1) the scientific problem and controversy; 2) the scope of the paper; 3) how the new data would contribute to improve the knowledge of this problem 4) on which domain the Authors focused their research.

Lines 137-142. I suggest to revise this part of the text as some sentences are not clear (see annotate pdf). In brief, for the D2 and D3 events, you described the foliation using in the same sentence a structural feature (syn-kinematic) and a metamorphic facies (granulite or amphibolite). I think the English here it is not clear and may lead to misunderstanding, and it must be improved. I suggest to change for example “The D2 event is marked by the syn-kinematic S2 foliation developed at P-T conditions of granulite facies”  

It is not clear which are the constraints and data to merged the D2 and D3 events of Elter et al 2010, in a single D2 event as shown in Table 2. Following the proposed simplification, you merged together structural and metamorphic parageneses formed at different P-T condition as stated in this table (Granulite and Amphibolite). In addition, if crosscutting relatihonships between the two different granulite and amphibolite paragenesis exist, they should be achieved during distinct episodes (i.e., at different ages) of the tectono-metamorphic evolution of the HGMC.

Lines 289-291: the relathionship between the dextral and the sinistral shear zones are not fully clear. I am wondering if this cinematically different shear zones show the same orientation and can be seen and time-different deformative episodes, or if they show different orientations. Please add some explanations.

The section 5.3 is not sufficiently clear in my opinion. In particular, the relationship between the OGC and the NGC are not fully clear. I think this issue also affect the discussion, where this aspect is discussed for the regional evolution of the Variscan belt in Sardinia. I think you should emphasize their map-scale relationships and explain what do you mean with interaction between the OGC and the NGC (lines 302-304). Is fragments of the OGC within the NGC? Explain better

As it stands now, I think that the discussion seems not linked with the presented data. It presents a description of the regional geology of the Variscan belt rather than a proper discussion of the presented data and their implications. I suggest to deeply revised it, focusing to a discussion of the structural data presented, and then to discuss their implications for the geology of the Variscan belt in Sardinia.

The main problem in this paper is the usage of the term mélange. This term is used in the title, but it comes out in the text only in the conclusion section. It seems that you propose that the entire HGMC represent a mélange. This might be true but you do not provide any introduction to this term and its meaning, and your data do not support this conclusion. I think this term is here overused, and I suggest to remove it from the text. The definition for mélange ask for a clear introduction, adding proper references (e.g., Festa et al 2019 Gond. Res. And reference therein), a description of the mélange structures and fundamental elements (i.e., the presence of exotic blocks within a matrix), and its usage should be support by data. In this manuscript, I honestly cannot see the rational for the usage of this term.   

Fig. 1: the shear zones cited in the text are not clearly visible in this figure. I suggest to enanche the thickness of the lines representing these structures. In addition, I suggest enlarging the labels for the different shear zones. As they stand now, It is difficult to read.

Fig. 4: there are several field photos for each rock types. I think you can simplify this figure reducing the number of panel without losing significant information. 

Comments for author File: Comments.pdf

The English is generally in a good shape. Some minor corrections would help.

Author Response

Dear Reviewer n°1,

we wish to extend our deepest gratitude for the thorough examination you dedicated to our scientific article. Your critical analysis and detailed comments have been an invaluable contribution to refining and perfecting the work. We are sincerely thankful for your commitment and professionalism demonstrated in providing such a comprehensive and insightful review. The revisions made in response to your invaluable suggestions have significantly enriched the quality and solidity of the article. We are confident that the amendments reflect your expectations.

Comments in response to your suggestions and queries are visible in the text.

In any case below are the changes made and responses to your major comments point by point:

Reviewer: The main problem in this paper is the usage of the term mélange. This term is used in the title, but it comes out in the text only in the conclusion section. It seems that you propose that the entire HGMC represent a mélange. This might be true but you do not provide any introduction to this term and its meaning, and your data do not support this conclusion. I think this term is here overused, and I suggest to remove it from the text. The definition for mélange ask for a clear introduction, adding proper references (e.g., Festa et al 2019 Gond. Res. And reference therein), a description of the mélange structures and fundamental elements (i.e., the presence of exotic blocks within a matrix), and its usage should be support by data. In this manuscript, I honestly cannot see the rational for the usage of this term.

Authors:  we agree with the reviewer's observation regarding the incorrect use of the term "mélange”. While the initial idea was in line with the reviewer's intuition, the data collected did not ultimately allow for the correct utilization and definition of the term "melange" as defined in Festa et al. 2019. Therefore, we have changed the title and the term within the paper accordingly.

Reviewer: (Fig. 1) the shear zones cited in the text are not clearly visible in this figure. I suggest to enanche the thickness of the lines representing these structures. In addition, I suggest enlarging the labels for the different shear zones. As they stand now, It is difficult to read.

Authors: we enhanced the thickness of the lines representing structures cited in text; we enlarged the labels for the different shear zones.

Reviewer: The introduction section is a weak point for this manuscript. It presents the geological setting of the Variscan belt, and the geology of the Variscan belt in western and central Europe. However, it is completely lacking of the scope of the manuscript and the scientific problem that the Authors are trying to address with their research. It is also not clear what is the object of this study among the different tectono-metamorphic domains and untis of the Variscan Belt. It is mandatory for the Authors to introduce in this section these topics: 1) the scientific problem and controversy; 2) the scope of the paper; 3) how the new data would contribute to improve the knowledge of this problem 4) on which domain the Authors focused their research.

Authors: we added 1) the scientific problem and controversy; 2) the scope of the paper; 3) how the new data would contribute to improve the knowledge of this problem 4) on which domain the authors focused their research.

Reviewer: I suggest to revise this part of the text as some sentences are not clear (see annotate pdf). In brief, for the D2 and D3 events, you described the foliation using in the same sentence a structural feature (syn-kinematic) and a metamorphic facies (granulite or amphibolite). I think the English here it is not clear and may lead to misunderstanding, and it must be improved. I suggest to change for example “The D2 event is marked by the syn-kinematic S2 foliation developed at P-T conditions of granulite facies”.

Authors: we rephrased as suggested in order to be more correct and comprehensible.

Reviewer: It is not clear which are the constraints and data to merged the D2 and D3 events of Elter et al 2010, in a single D2 event as shown in Table 2. Following the proposed simplification, you merged together structural and metamorphic parageneses formed at different P-T condition as stated in this table (Granulite and Amphibolite). In addition, if crosscutting relatihonships between the two different granulite and amphibolite paragenesis exist, they should be achieved during distinct episodes (i.e., at different ages) of the tectono-metamorphic evolution of the HGMC.

Authors: we have added the constraints and biography that explain why we merged D2 and D3 event into a single one.

Reviewer: (Fig.4 c-e) there are several field photos for each rock types. I think you can simplify this figure reducing the number of panel without losing significant information.

Authors: we agree that the lithotypes are similar, but we prefer to not eliminate the panels c, d and e, because outcrop are in different locations and distant from each other.

Reviewer: (Fig.4 i-k) there are several field photos for each rock types. I think you can simplify this figure reducing the number of panel without losing significant information.

Authors: we agree that the lithotypes are similar and we eliminate panel k so former panel l become panel  k. Panel j and k are similar but in different location. We corrected also caption of figure 4.

Reviewer: the relathionship between the dextral and the sinistral shear zones are not fully clear. I am wondering if this cinematically different shear zones show the same orientation and can be seen and time-different deformative episodes, or if they show different orientations. Please add some explanations.

Authors: we rephrased the sentence answering your question.

Reviewer: The section 5.3 is not sufficiently clear in my opinion. In particular, the relationship between the OGC and the NGC are not fully clear. I think this issue also affect the discussion, where this aspect is discussed for the regional evolution of the Variscan belt in Sardinia. I think you should emphasize their map-scale relationships and explain what do you mean with interaction between the OGC and the NGC (lines 302-304). Is fragments of the OGC within the NGC? Explain better.

Authors: we have rephrased some sentences to better explain the relationships between OGC and NGC. As reviewer 1 understood, the OGC appears as fragments within the NGC. We have also modified figure 11 by adding the corresponding acronyms.

Reviewer: As it stands now, I think that the discussion seems not linked with the presented data. It presents a description of the regional geology of the Variscan belt rather than a proper discussion of the presented data and their implications. I suggest to deeply revised it, focusing to a discussion of the structural data presented, and then to discuss their implications for the geology of the Variscan belt in Sardinia.

Author: we don't fully agree with the comment on the discussion paragraph. We understand the "Discussion" paragraph as one where the data are commented on in relation to the aims of the paper, which in this case are 1) the interrelations among the various events in northeastern Sardinia (discussed in the first 6 paragraphs); 2) the potential regional-scale correlations (discussed in the subsequent paragraphs). The "Conclusions" section will then emphasize what has emerged from the discussions. In any case, we have added several sentences to highlight the existing correlations between the study area of our paper and other correlable Variscan zones in order to make the flow of thought leading to the conclusions clearer.

Once again, we wish to cordially thank you for your pivotal contribution and the attention you have bestowed upon our work.

Regards

Federico Mantovani & Franco Marco Elter

Author Response File: Author Response.pdf

Reviewer 2 Report

The data present new structural data of the entire axial zone of the Variscan Sardinian High-Grade Metamorphic Complex. The authors use only structural analysis, without additional analytical methods. It doesn't make the article any worse. The material is presented very clearly, the method is applied in a classical style. The conclusions drawn are justified, mainly to those who are engaged in the geology of the Mediterranean region.

There are no serious comments on the article, only a few typos:

line 329 – table 6 replace table 3 ?

inside table 3 – PSVZ and ESCZ replace PVSZ and EVSZ

Author Response

Dear Reviewer n°2,

we wish to extend our deepest gratitude for the thorough examination you dedicated to our scientific article. We are truly grateful and happy for your positive comments. Comments in response to your suggestions and queries are visible in the text.

In any case below are the changes made and responses to your comments:

Reviewer: line 329 – table 6 replace table 3.

Authors: we corrected.

Reviewer: inside table 3 – PSVZ and ESCZ replace PVSZ and EVSZ.

Authors: we corrected.

Once again, we wish to cordially thank you for your pivotal contribution and the attention you have bestowed upon our work.

Regards

Federico Mantovani & Franco Marco Elter

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper present an (in part) original interpretation of the High Grade Complex of the  NE Sardinia. The data presentation and some of the claims  has to be improved  in order to strengthen the proposed interpretation.

Some suggestions and comments may be find in the attached annotated pdf. Please take into account the reference suggested and consider them in the discussion.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer n°3,

we wish to extend our deepest gratitude for the thorough examination you dedicated to our scientific article. Your critical analysis and detailed comments have been an invaluable contribution to refining and perfecting the work. We are sincerely thankful for your commitment and professionalism demonstrated in providing such a comprehensive and insightful review. The revisions made in response to your invaluable suggestions have significantly enriched the quality and solidity of the article. We are confident that the amendments reflect your expectations.

Comments in response to your suggestions and queries are visible in the text.

In any case below are the changes made and responses to your major comments point by point:

Reviewer: The data presentation and some of the claims  has to be improved  in order to strengthen the proposed interpretation.

Authors: we improved data presentatios, discussion and coclusion.

Reviewer: The Middle Permian event in the Mediterranean realm is not directly linked to the extension-related NeoTethys opening… please rephrase.

Authors: we have rephrased.

Reviewer:  Grighini Shear Zone is not in the HGMC but in the internal nappe zone.

Authors: we rectify the Grighini Shear Zone location.

Reviewer: the PVSZ in its SE transect is indicated in figure 3 as NW-SE not W-E.

Authors: there was an error on our part in drawing the PSVZ on the map. We corrected modifying both Fig. 3 and Fig. 14.

Reviewer: maybe will be better to document the superimposition of fabric (PVS-related and NGC-related) with a map scale view.

Authors: the structure described outcropping at Punta Orvili is also given regional importance in the literature despite those relationships being visible only in that specific outcrop. In any case, we explain this focus point in the discussion with the existing associated bibliography. Moreover, as suggested, we added sentences to highlight the importance of the “small” P.ta Orvili outcrop and why it define relationship between OGC, NGC and PVSZ.

Reviewer: (Fig. 14) I suggest to insert a real cross-section (similar to fig 3 in Elter et al., 2010) to complete and support the ideal scheme of fig. 14.

Authors: we don't agree with the insertion of the cross-section from Elter et al., 2010; the block diagram itself in Figure 14 is a reinterpretation of the aforementioned section. Additionally, even the figure from Elter et al., 2010 is a schematic representation and not to scale.

Reviewer: I suggest to consider in the discussion and in the reference the paper of casini et al., 2015 which discussed the role and setting of magma emplacement in Late Carboniferous-Early Permian… the presence of these granitoids preclude a relevant role of shearing (documented in your manuscript) after 315 Ma.

Authors: we added citation in agree with Casini et al., 2015.

Reviewer: (Fig. 15) Please consider this figure and compare with fig. 1 in Padovano et al., 2014. The position of Corsica-Sardinia is quite different please add a more deep discussion.

Authors: we added citations in caption; figures is modified after Padovano et al., 2014 but we better agree with the position of Sardinia-Corsica block highlited by Edel et al., 2014, 2015, 2018).

Reviewer: dealing with sardinian Variscan belt maybe some quotation of the carmignani and pertusati papers and maps would be appropriate.

Authors: we added suggested quotation.

Once again, we wish to cordially thank you for your pivotal contribution and the attention you have bestowed upon our work.

Regards

Federico Mantovani & Franco Marco Elter

Author Response File: Author Response.pdf