Microstructure of Vein Quartz Aggregates as an Indicator of Their Deformation History: An Example of Vein Systems from Western Transbaikalia (Russia)

Round 1

Reviewer 1 Report

The Authors studied the microstructural and crystallographic characteristics of quartz in complex environments, using back scatter electron diffraction (EBSD) and optical microscopy, to obtain information on the microstructure of quartz in very peculiar conditions, such as those found at the transition of the behavior from da to brittle to ductile. The Authors established that the most frequent deformation mechanisms detected in quartz in the studied area are dislocation, shear and creep at average strain rates and temperatures of 300-400 ° C, with subsequent heating and dynamic recrystallization.
Up to this point, the Authors explain their work flawlessly. The only observation I can make concerns the deepening of the mineralogical and microstructural aspects, which appear extremely important in the studied context. For example, it could be extremely interesting to verify if the heating caused by the shear has determined transitions between alpha and beta quartz (573 ° C), by observing any relict structures or distortions compatible with the beta form. I would also add some more observations on the different forms of silica that will be present, perhaps also as relics, for example amorphous silica, tridymite or cristobalite alpha. 

Author Response

We thank the reviewer for his careful reading of the article. We will try to consider useful comments in further research. These research are planned.

Author Response File: Author Response.pdf

Reviewer 2 Report

The submitted article give us a detailed interpretation of the different kind of quartz which occurs in that region; the most important result is the definition of the 3 generations of quartz based on the micro-structural study.

The article submitted is available for publication after minor revisions, mainly by grammar/ text editing:

Line 40: "...(T below 300ºC)..."

Line 61: "...(more than 500ºC)..."

Line 62: please delete the words: "of tension"

Line 78: "...can be characterized..."

Line 82: "...and those fragments into blocks in order to form..."

Line 89: "...have been identified..."

Line 111: please delete the word: "increases" (the first in the phrase)

Line 112/113: please delete the sentence you have between " ( )"

Line 116: "...around the C-axis..."

Line 117: "...and the crystal's..."

Line 173: "...parts of the thrust system..."

Line 186 "...from each section, and 30 of the samples were studied."

Line 187: "...veins that outcrop..."

Line 337: "In Tullis [33, 34] opinion..." (change the order of the words)

 

 

Author Response

We thank the reviewer for his careful reading of the article. Unfortunately, despite holding an English editing service checking grammar MDPI we need to correct the text. We express our special thanks to the reviewer for this help. We have made recommended text corrections.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors studied the crystallographic orientation and optical properties of quartz of different types of veins, with optical microscopy and electron back scatter diffraction (EBSD).

The manuscript presents a highly interesting topic, but it requires intermediate to major changes to be accepted for publication. Among other aspects, the syntax can be improved since in some sentences the wording makes it difficult for the reader to properly understand the ideas that the authors want to convey. The objectives and possible application of the results are not clear enough. Despite the fact that the observations and analytical results seem to be correct, as they are not contextualized (for example: description and location of each selected sample in the outcrops), the reader cannot understand the geological contribution of the results obtained. These results (typology of the veins and their relationship with the tectonic structures) are traditionally obtained in the geological field work phase. Microscale work should provide new information or corroborate that which should be observed during the field work. 

Some aspects that I think that can help to improve the manuscript are:

Title: The deformation structures (megascopic or mesoscopic scale) of the quartz veins are not described, only the deformation of the quartz mineral (within the veins) is studied on a microscopic or submicroscopic scale. In addition, the title does not report the type of analytical techniques used, nor the country where the study was carried out.

Abstract: It is necessary to contextualize the geological importance of the mineralogical results obtained on a regional scale. The practical application of the results obtained cannot be understood due to lack of this information.

Lines 23-24: multi-stage development of the territory with the formation of post- deformational quartz veins: In a geological sense, this phrase is inadequate. How the authors know that the veins are post-deformational? The connection between the study carried out and its geological meaning is not defined in the manuscript.

Line 75: In the future: What does this expression mean in this sentence?

Line 78: can characterized: replace by can be characterized

Line 90 and 118:  researchers?? Enter corresponding citations

Line 131: subsequent connection with the mechanisms and conditions of formation in the Earth's crust: This connection is never made concrete in the present manuscript because the reader does not know the nature of each sample. The relationship between the five types of vein quartz microstructures and the geological studied units is missing.

Line 134: the work area: if there is no real field work this expression is incorrect (sampling area??).

Lines 136-145: The area seems geologically and structurally very complex. The geological question to be solved is never indicated. The metamorphic degree of each zone is probably already known from previous field studies.

Line 149: rocks of these complexes: the lithology from the box rocks of the different sampled units must be detailed since it is a fundamental factor to consider in any study about deformation. Strain is intimately related with the lithology of rock in which the vein was developed.

Lines 159.162: Correlate tectonic structures described in the text with those in figure 1. The structural field data (lithology of the boxing rocks, as well as dimensions, orientation, and dip of the veins) is incomplete, and it is essential to incorporate this information into the work.

Line 167-172: we distinguished the main and echelon quartz veins……. it is necessary to show photographs or schemes and to place these types of veins in a zoom of the figure 1.

Lines 173-179: All this information seems to derive from previous geological work by other authors. Reference correctly

Line 182. Improve wording of the first sentence of the paragraph.

Lines 185-187: Include the details of the sampling in a zoom of Figure 1 and a table with the basic structural and petrographic description of each sample or group of samples.

Line 195: Crystal structure?? I do not agree. Crystal structure of minerals is defined by cell parameters.

Lines 196-197: It is not clear whether they prepared conventional petrographic thin sections (30 microns thickness) for petrographic observation. Please, specify this information.

Line 202: The scanning area was 1 mm², how was it selected? How many crystals of each textural type were studied? It is very important to specify basic statistical data of the measurements made to understand its representativeness on a larger scale. 

Line 229: Grains with a closed sinuous boundary (green) were located in the matrix of the parent grain (purple): meaning???

The second image of figure 3a does not present the characteristic colors of quartz seen under cross polarized light. Why?

Lines 329-331: This is generally deduced in field work; it is not a new contribution from the authors.

Line 400 (Table n?): The characteristics and schemes of typical structure: correlate the information with the letters (A, B, C, D, E) used to define for the five types of quartz microstructures.

Lines 401-418: the distribution of the microstructures and their relationship with the regional structures should be shown using schemes and/or images.

Lines 430-431: The number and stages of vein formation should be defined in the field, based on structural observations of the veins for deformation. The microscale study should then be used to establish the characteristics of each type of vein previously defined in the field, and not the other way around. Microscale work cannot replace the work of the geologist in the field.

 

 

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for his careful reading of the article and useful comments, which we have tried to consider.

We agree with you regarding the small saturation of geological information at different scale levels of this article. The presentation of the results of such a plan requires a significant increase in the volume of the article and the use of additional data for objective geological conclusions. In this regard, we decided to single out the study of the microstructure of quartz in a separate article in order to use them in writing the next publication.

Some conclusions are preliminary, but there is a corresponding remark. This includes the last phrase in the goal statement. She indicates what you plan to use these results for.

Line 131: …subsequent connection with the mechanisms and conditions of formation in the Earth's crust.

This statement of the problem of the article is due to the absence of such data in the abstract and in the text.

 

The basis of this work is the result of field work. (Line 134: the work area). The work area is located in the Bambukoy river basin within the Muya administrative region of the Northern Buryatia at a distance of 11 kilometers from the village of Taksimo (Western Transbaikalia, Russia) (Lines 23-24). As a result of the work, a diagram of the occurrence of quartz veins was drawn up and the geological conditions of the area of their occurrence were determined. their macrostructure was described and samples were taken for further research. A fragment of the geological map of the Republic of Buryatia has been added as a larger-scale map (Figure 1). We marked in the figure the coordinate values (latitude / longitude). The sampling sites are marked in Figure 1 with white rectangles. We provide data on the regional geological setting (133–144) and give a brief overview of the stages of deformation (158–162) of the studied area. There are no data on the dating of the rock and the age of metamorphism.

Title: The deformation structures (megascopic or mesoscopic scale) of the quartz veins are not described, only the deformation of the quartz mineral (within the veins) is studied on a microscopic or submicroscopic scale. In addition, the title does not report the type of analytical techniques used, nor the country where the study was carried out.

New article title: Microstructure research of vein quartz in the South-Muisky block of Western Transbaikalia, Russia

Revised as requested

Study of the microstructure were carried out on petrographic thin sections and by the electron backscatter diffraction method using the scanning electron microscope Tescan Mira 3 LMU. So, the inclusion of methods in the title of the article is considered inappropriate.

Lines 23-24: multi-stage development of the territory with the formation of post- deformational quartz veins: In a geological sense, this phrase is inadequate. How the authors know that the veins are post-deformational? The connection between the study carried out and its geological meaning is not defined in the manuscript.

Studies of the microstructure of these veins showed that they do not have structural defects that are formed during deformation. In this regard, we called these veins “post-deformational”, that is, formed after deformation processes in this place.

Line 75: In the future: What does this expression mean in this sentence?

Deleted

Line 78: can characterized: replace by can be characterized

Revised as requested

Line 90 and 118:  researchers?? Enter corresponding citations

This applies to links in front of this sentence.

 

Line 149: rocks of these complexes: the lithology from the box rocks of the different sampled units must be detailed since it is a fundamental factor to consider in any study about deformation. Strain is intimately related with the lithology of rock in which the vein was developed.

Thank. We will pay attention to this in the subsequent analysis.

 

Lines 159.162: Correlate tectonic structures described in the text with those in figure 1. The structural field data (lithology of the boxing rocks, as well as dimensions, orientation, and dip of the veins) is incomplete, and it is essential to incorporate this information into the work.

Line 167-172: we distinguished the main and echelon quartz veins……. it is necessary to show photographs or schemes and to place these types of veins in a zoom of the figure 1.

It is planned to include this in the next publication.

Lines 173-179: All this information seems to derive from previous geological work by other authors. Reference correctly

This presents our analysis of the literature and our field data.

Lines 185-187: Include the details of the sampling in a zoom of Figure 1 and a table with the basic structural and petrographic description of each sample or group of samples.

After the classification of the structures of the veins, it will be convenient to associate the structure with a specific type of veins and discuss the conditions for their formation using the results of additional methods. This is planned to be done in a separate publication.

Line 195: Crystal structure?? I do not agree. Crystal structure of minerals is defined by cell parameters.

Revised as requested

Lines 196-197: It is not clear whether they prepared conventional petrographic thin sections (30 microns thickness) for petrographic observation. Please, specify this information.

Line 187: we changed the expression “optical method” on “structural and petrographic description of each sample”

Line 202: The scanning area was 1 mm², how was it selected? How many crystals of each textural type were studied? It is very important to specify basic statistical data of the measurements made to understand its representativeness on a larger scale. 

The representativeness of sampling is described in the “Materials and Methods”, Line 185-190.

We have selected typical sites to characterize the boundaries of the EDSD method. The number of boundaries in the analyzed area of analysis is representative.

Line 229: Grains with a closed sinuous boundary (green) were located in the matrix of the parent grain (purple): meaning???

Figure 2. “… The symbols shown here are color-coded for the boundaries to indicate the angle of boundaries misorientation for use in the next figures…”

The grains on the figures have an inverse pole figure colors

The second image of figure 3a does not present the characteristic colors of quartz seen under cross polarized light. Why?

This is also a place. We turned the table, not the analyzer

Lines 329-331: This is generally deduced in field work; it is not a new contribution from the authors.

We used fieldwork data

Line 400 (Table n?): The characteristics and schemes of typical structure: correlate the information with the letters (A, B, C, D, E) used to define for the five types of quartz microstructures.

This is a table “…of typical structure elements” and not “types of microstructures A…E”.

Revised as requested in the table column name

Lines 401-418: the distribution of the microstructures and their relationship with the regional structures should be shown using schemes and/or images.

Lines 430-431: The number and stages of vein formation should be defined in the field, based on structural observations of the veins for deformation. The microscale study should then be used to establish the characteristics of each type of vein previously defined in the field, and not the other way around. Microscale work cannot replace the work of the geologist in the field.

We agree, but the position of the authors on the content of the article was expressed above.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have modified very few of the points which were requested in the first review, and they insist that their study is only microstructural.

The study is interesting, but as mentioned in the previous review I reaffirm the need to introduce a minimum of graphic information (photographs, diagrams, tables) of the samples and veins studied. Otherwise, it is impossible for the reader to know what kind of sample (of the 30 that the authors have collected but not placed on the map, nor summarized them in any table or graphic scheme) is being described at any point in the manuscript. The orientation of the samples with respect to the tectonic structures observed in the field is fundamental information that cannot be found anywhere in the manuscript. That is why I once again insist on saying that fieldwork does NOT exist. Collecting samples without providing concrete information is NOT fieldwork.

Finally, it should be mentioned that it is essential there is coherence between the cited references and the article that the authors are submitting. The authors cite mainly two types of articles: 1) studies (at different scales) of mineral structures, obtained in geological outcrops of tectonically deformed areas [1, 2, 4, 5, 6, 7, 17, 18, 19, 20, 21, 27, 35 the latter in the mineral magazine itself], and 2) experimental works describing results obtained by experimentally deforming minerals using laboratory instrumentation [9,10, 15, 24, 25, 32, 33, 34, 40]. The present manuscript would be a work of the first kind. In all articles of the first type (published mainly in journals of tectonics or structural geology) the contextualization of the samples presented through diagrams, photographs, or diagrams is ALWAYS there. None of these authors would ever conceive of such a work without including the details of the sampling.

Among other less important things to consider is that a) the title could still be improved to make it more informative, and b) references 5 and 23 are the same.

I want to once more encourage the authors to include the requested information (the results section does not require much modification) to make their article have the right impact and be cited by the scientific community.

 

 

Comments for author File: Comments.pdf

Author Response

We are grateful to the reviewer for carefully reading the article, serious attitude to the case and useful comments aimed to improving our work. The main part of the comments concerned a more precise formulation of the geological problem and an introduction of additional information. In accordance with this, the necessary edits were made.

1. The publication title was changed «Structure of vein quartz aggregates as an indicator of its deformation history by the example of vein quartz of South-Muisky block, Western Transbaikalia (Russia)»
2. The annotation were corrected
3. The Geological position and samples chapter were expanded significantly. The authors hope that the presented data will be sufficient to display the primary information.
4. The Discussion chapter has been adapted for better understanding the essence of the research results.
5. Information about microstructure types distribution among the veins studied has been added to the Discussion
6. Typo in the list of references were corrected.
7. In general, in the course of fieldwork, the authors discovered and studied three complex systems of quartz veins. In each system, based on geological features, the types of veins are distinguished: main and feathering. With the help of kinematic analysis, the nature of these veins was clarified. It has been established that the formation of veins is associated with filling of tectonic cracks by fluid associated with regional deformations. In the course of microstructural analysis, the conditions of their formation (temperature and force conditions for the transformation of quartz) were studied. After that, the relationship between the formation conditions of the studied microstructures and the structural confinement of veins was described. Conclusion about the development of the hydrothermal-magmatic system during the processes of regional deformations was drawn.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

In this third review, the authors made a great effort to improve the document. The inclusion of the geological sections (figures, 2, 3, 4), stereographic projections (figure 5), and Table 1 are relevant and definitely encourage the understanding and interest of the reader. That is why I consider that the manuscript can be published after attending to the minor changes mentioned below:

1. The new title includes repeated words. It is too redundant. A proposal would be:

Microstructure of vein quartz aggregates as an indicator of its deformation history: An example from South-Muisky block, Western Transbaikalia (Russia)*.

*If the proposed title does not reflect the idea that the authors want to express, they should look for another title avoiding repetitions.              

 

2. Line 16. The Word systems is repeated

 

3. Line 26: The distribution of the selected types; add: of microstructures. Otherwise the phrase is not understood.

 

4. IMPORTANT: Some paragraphs (for example lines 26 to 29, lines 149-150, lines 561-563 etc.) seem translated into English from a text in another language and are not well understood. The grammar and syntax of the entire document should be revised to facilitate understanding.

 

5. Figures 2, 3 and 4 should be shown in section only; the repeated display of these figures is redundant.

 

6. Geological references of the studied area are missing. The source of the geological map must be indicated.

 

7. The anomalous colors observed for quartz in figure 7 have not been explained.

 

 

 

 

 

Author Response

We are grateful to the reviewer for carefully reading the article, a serious attitude to the case, and useful comments.

1. In accordance with the recommendation of the reviewer, the title has been reformulated.
2. Corrected.
3. Corrected.
4. The text was sent to two geologists for reviewing, one of whom is a native speaker. Changes applied.
5. Corrected. Re-designation of figures 2, 3, 4 in figure 1 is removed.
6. Corrected. In Figure 1, an indication of the main geological structure positions of the work region has been added, which can be used as geological landmarks.
7. The geological map source is indicated in the references list at number 39.
8. These colors, which are not typical for quartz, in this figure are caused by the imaging conditions of the sample, a slightly higher thickness of the section, or the settings of the microscope camera.

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

The work is interesting, sophisticated and precise. in the experimental part it could be enriched by other integrative analytical methods, such as a high resolution TEM, but I understand that it is often this analytical technique is not available. Furthermore, the authors have used a very rigorous reading key, which leaves no room for doubt. My opinion is that the work is done very well and that it is worthy of being published without revisions. I would like to see in the future this methodological approach also applied to the quartz-rich rock specimens obtained from friction tests.

Reviewer 2 Report

The manuscript by Lychagin and others presents microstructural observations and quartz crystallographic orientation data from vein material. The authors document a range of features and distinguish five distinct types of vein microstructures. A comparative investigation into the microstructural features of deformed vein material could form the basis of an interesting study.  However, for the reasons described below, I find the current manuscript to be lacking in several key respects.

First, the English in the text needs improvement; there are grammatical errors throughout the manuscript. This is mostly not a significant problem, but there are places where the authors’ meaning is unclear. The text would benefit greatly from a careful edit by a native English speaker.

Deficiencies with the writing go beyond grammatical issues. The paper has a long introduction that summarizes much of the literature about common deformation mechanisms and microstructures in quartz. This could be fine, but the relevance of much of it is unclear. I think this is because the introduction never clearly motivates the problem – what is the purpose of this study, and why is it important? The introduction should be shortened, or more directly linked to clearly stated research objectives.

The manuscript does not provide sufficient detail and context about the geologic setting. A small geologic map is presented, but a larger map and latitude/longitude values would help the reader locate the study area. Further, there is essentially no geologic context provided. How old are the rocks? When were they deformed? What was the tectonic setting and history? I appreciate that this is a microstructural study rather than one focused on the regional geology, but nevertheless at least some context is important for the reader. This is all the more important given that the Discussion section (lines 369-374) interprets the results in terms of the regional tectonics.

Similarly, there is a lack of relevant detail provided about the sampling and analytical procedures. The text indicates that samples were taken from one of three areas. But how many samples were collected and studied? What were their specific locations (latitude, longitude)? The paper later classifies the vein material into one of five types – how common were each of these?

There are also important technical details left out about the EBSD analyses. Where were they collected? What were the analytical conditions (probe current, accelerating voltage, etc.)? What was the data acquisition strategy? What was the step-size? What was the scan area? The EBSD maps are colored with an ipf key, but the spatial direction the map is related to is not indicated. Are the areas scanned by EBSD within the area shown on the photomicrographs, or are they from a different part of the sample? It would be helpful to outline the scanned area on the photomicrographs. The figures present histograms of “disorientation angles” but what precisely is being plotted is not described (I think maybe these are the angular misorientations across the grain boundaries?). The reader cannot evaluate the work without these details.

The figures are difficult to read and interpret. The photomicrographs are all dark and hard to interpret – is it possible to lighten the images somehow? The text on all the figures is too small to read. In particular, the scale bars for both the optical images and the EBSD maps are unreadable. Are the presented figures the totality of the analyzed samples? If so, how do the authors know the analyzed areas are representative?

The interpretations in the Discussion section are, in my view, largely unjustified. The authors interpret the described microstructures in terms of changes in temperature (e.g., lines 306, 337), fluids (e.g., line 323), stress (line 345), and strain-rate (line 334). However, there are no data presented or cited that provide insight into these parameters. For example, how can the microstructures be related to changes in deformation temperature if independent information about that parameter is presented? Similarly, the quartz veins are interpreted to form during three distinct generations (line 388), but no detailed information on absolute or relative timing (e.g., cross cutting relationships) is presented. I have other more specific questions about some of the interpretations, but these are second-order compared to the issues noted above.