Crystallographic and Seismic Anisotropies of Calcite at Different Depths: A Study Using Quantitative Texture Analysis by Neutron Diffraction

Round 1

Reviewer 1 Report

Review of Crystallographic and Seismic Anisotropies of calcite at different depths: a study using Quantitative Texture Analysis by neutron diffraction from Zucali and co-authors

The manuscript aims to investigate the occurrence crystallographic preferred orientations (CPOs) in calcite bearing rocks (i.e. limestone and marbles), measured by means of neutron diffraction analysis, and compare it with seismic anisotropy at different depths in the Earth’s crust. Although the stated objective of this work is of potential interest, I strongly suggest not to recommend the manuscript for publication Minerals due to numerous critical points and flaws found, some of which I will point out here below. Overall the manuscript fails in multiple points to follow a rigorous scientific method and it is unclear how many of the results showed were obtained.

The presentation of the methods and results is not rigorous and it is not very clear how some of them where obtained. Some examples (but not the only ones) of this are:

Very vague sample characterisation throughout the text and in Table 1. What does “shallow”, “upper” or “lower” mean? Constraints in the depth, with numbers, are needed. Why are “intermediate depth samples” intermediate in depth if they were only involved in relatively shallow level deformation (Lines 54-56)? Similarly, for the temperatures presented in Table 1, numbers (or at least estimates based on some indicators) are needed. In general, a better characterisation of the samples too is needed with hand sample and/or microstructure pictures, to help the reader understating where the data presented come from. In the Methods it is stated that the neutron diffraction measurements take “approximately […] one to few hours”. Again, this is vague and unclear. Moreover, in Table 2 there is no way to know what the unit measure for “acq. time” is. What chemical compositions were used as an input for the thermodynamic calculations in PerpleX? If such analysis were performed, it would be good to have them available as supplementary material. Moreover, it is very unclear which dataset was used and the workflow behind Figure 6. At times, sample reference throughout the text is inaccurate or wrong and needs to be fixed.

 

The figures are often very difficult, if not impossible, to read. Examples of this are Figures 3, 5 and 7, where in the pole figures for the seismic velocities is impossible to see the numbers on the colourbar or the text above and below the pole figure. In Figure 8 axis labels are too small and there are no unit measures on the axes (same goes for Figure 9 too). In Figure 6 there are no numbers on the y-axis for the depth. This goes back also to the previous comment regarding the vague characterisation of the sample depth origin.

In the Discussion section, it is unclear how the results can be applied to natural scenarios. Moreover, the section fails to put the results into context and compare with other published research.

Finally, in case of a future resubmission, I would strongly encourage the authors to have the manuscript proofed for English writing. At the present state, many sentences are incomplete or too long/articulated, making very difficult for the reader to understand the authors’ message. Moreover, at times excessive or incorrect use of abbreviations (e.g. use of abbreviations not previously defined) and wrong use of punctuation hinders the reading of the manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of manuscript 646400 by Zucali et al.

General comments

The authors present CPO measurements and calculated seismic properties from a set of eight carbonate rocks selected to represent fabrics formed at various crustal depths. They analyse seismic anisotropy resulting from the CPO in terms of crustal position and fabric orientation to attempt to begin to develop a reference system for interpreting seismic velocities and their anisotropy in carbonate-dominated terranes. To my knowledge, this is the first such study that has focussed exclusively on carbonate rocks and this is certainly an area that requires a lot of work due to the complexity of potential CPO types and controls on their formation. Whilst the present manuscript is a step in the right direction, it has at least a couple of major limitations that need to be addressed if it is to have the impact that the authors intend. Specifically, my concerns can be grouped into two broad categories focussing on the generality of the results and their presentation in the manuscript, upon which I elaborate below. I suggest that the authors submit a revised manuscript once they have had an opportunity to address the points raised.

Generality of the results

Although the aim is not stated explicitly in the Introduction, the manuscript itself and the Conclusions give the impression that the aim is to provide reference material/models that can be used to interpret measured seismic anisotropy. To this end, the authors have gathered samples deformed at different crustal levels from across northern Italy and surrounding regions. However, for the data and resulting models to have broader applicability, much more information on the samples is required than is presented in the current manuscript. Key information that is missing are quantitative constraints on the conditions of fabric development, constraints to the relative contributions of different deformation mechanisms that operated in the samples, and constraints on the strain geometries recorded by the samples. All of these factors can influence the CPO (and hence seismic properties that develop) and therefore without detailed information on the samples presented in the manuscript the reader cannot assess their potential relevance to other settings (e.g., where a seismic survey may be conducted). The manuscript presents only eight out of a very large number of possible combinations of deformation conditions, mechanisms, and geometries, which in itself is understandable, but even those are not well constrained.

On a related note, no detailed comparison is made to the results of similar analyses performed previously on other crustal rock types by, for example, Geoffrey Lloyd, David Mainprice, and others including the neutron-diffraction studies referenced in the Section 3. Such comparisons are important in identifying whether/how information can be gleaned from seismic data without knowing the rock type (and its fabric) at depth a priori. Clearly, there is much overlap between different rock types (even among these carbonates) in any one parameter (e.g., P-wave velocity) and so unambiguous determination of geological information from seismic data must necessarily employ a variety of such parameters. As just one example, if we measured a P-wave velocity of ~6.5 km/s and P-wave anisotropy of ~7%, how can we tell whether the rock at depth is a marble (e.g., Figures 5–9 of this study) or an amphibolite (e.g., Figure 10 of Lloyd et al., 2011, Geol. Soc. Lond. Spec. Pubs.)? I’m not saying that there is necessarily an answer but that the non-uniqueness should be discussed.

Presentation of the manuscript

The presentation of the manuscript could be significantly improved. There are numerous instances of typographical errors and language inaccuracies that could by tidied up. The clarity of most of the figures could also be greatly improved, as follows.

Figure 1: The geological information on this figure is of no use as no legend is provided. There’s no reason why the reader should instead have to look up the references indicated in the caption. If the geology is too complex to summarise, then the authors could at least divide the units into upper, middle, and lower crustal or similar that would be relevant to the manuscript. Having the scale bar in the middle of the figure is also distracting.

Figures 3 and 4: The text associated with the pole figures is clearly too small. Probability is not an appropriate label for the legend as ‘multiples of random distribution’ is simply not a probability (as demonstrated by taking values > 1). Similarly, ‘multiples of uniform distribution’ would be more appropriate than ‘multiples of random distribution’ as a random distribution is only uniform (which is what the measured densities are normalised to) if the sample size is infinitely large. The bold red outline is distracting. The symmetry diagram on the right of Figure 3 needs some text indicating what it is. In Figure 4, why use both ‘texture’ and ‘CPO’?

Figure 5: The text associated with the plots is too small. The bold red outline is distracting.

Figure 6: This plot really needs more explanation. I infer that a composition of pure calcite was used but, if so, this should be stated. What pressures were used in the calculations (this would make a more appropriate Y-axis)? Why are there three drops in temperature with depth? How about producing one P-T plot contoured by P-wave velocity and another contoured by S-wave velocity to cover the full range of P-T space?

Figure 7: The text associated with the plots is too small.

Figure 8: The text associated with the axes and legends is too small and the axes have no labels.

Figure 9: The axes labels are oddly positioned/arranged, which makes the plot unintuitive. Simply state the label and the units (including °) in the usual position next to the axes.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In this manuscript, the authors measured crystallographic preferred orientations (CPOs) in calcite-bearing rocks deformed at different depth and temperature conditions and calculated the associated seismic properties with the objective to provide an initial framework to interpret seismic velocities and anisotropies in carbonate-rich terrains. Many critical points from the previous version of this manuscript have been addressed by the authors, and a few minor points could still be improved to better the clarity and message of the paper, which I describe here.

 

Regarding the different CPOs described, I would suggest to call TypeA a “random distribution”, and rename TypeB1 and TypeB2 CPOs as Type A and TypeB. This would help the reader throughout the manuscript remembering which CPO is which.

 

I suggest to change the name of the first Section of the Discussion into a title more explanatory of what is discussed, rather than only Textures. Moreover, I would suggest, if possible, to link the measured textures to the deformation mechanisms active in the samples as this would make the comparison with the literature more robust.

 

Finally, the writing could be improved a bit more to make the reading easier and flowing better. For example, locally sentences seem to repeat themselves (e.g. Lines 251-253).

 

Some more detailed comments:

 

Lines 103-104 “15-20 km” is not a pressure condition. Either change “pressure” with “depth” or include also pressure estimates, along with depth.

Line 112 Use “pressure” instead of “P”

Line 118 What is “Auct.”?

Line 129 I suggest to add “domain” after “Austroalpine”. Same at Lines 133 and 134.

Line 133-134 What is a large and medium grain-size? Please include grain sizes representative for the samples. Same goes for other parts in the manuscript where only qualitative description of grainsizes is used.

Line 148 Since you are referring, rightly, to multiples of a uniform distribution, “(mud)” has to be used instead of “(mrd)”. Please change this also in the rest of the manuscript.

Line 149 I don’t see the need to use bold characters throughout the manuscript when referring to the techniques used (e.g. Quantitative Texture Analysis (QTA) by neutron diffraction, Seismic Properties, thermodynamic approach), or else. I suggest to use a normal format and avoid it.

Line 161-163 Which beam lines? What is the difference between the beam lines?

Line 222 I would simply reference to the development of textures in the samples as CPOs, and not as “fiber distribution”. This is also valid for other instances in the manuscript.

Line 243 In Figure 6 (and the others) the sample shown is 04STE, not 07STE. Check carefully throughout the manuscript for the right labelling and referencing of the samples.

 

I would delete the outline in Figures 2 and 3.

 

Table 2 I suggest to use the Greek symbols for omega, phi, chi (and also theta). Moreover, I suppose those angles are in degrees, please use the measure unit. Finally, avoid abbreviations (i.e. “acq. time”) in the Table.

Author Response

Dear reviewer, 

thank you again for your help. Here your requests.

We made all the corrections requested.

2.- Report 2 by Reviewer #1:
In this manuscript, the authors measured crystallographic preferred orientations (CPOs) in calcite-bearing rocks deformed at different depth and temperature conditions and calculated the associated seismic properties with the objective to provide an initial framework to interpret seismic velocities and anisotropies in carbonate-rich terrains. Many critical points from the previous version of this manuscript have been addressed by the authors, and a few minor points could still be improved to better the clarity and message of the paper, which I describe here.

Regarding the different CPOs described, I would suggest to call TypeA a “random distribution”, and rename TypeB1 and TypeB2 CPOs as Type A and TypeB. This would help the reader throughout the manuscript remembering which CPO is which.

DONE

I suggest to change the name of the first Section of the Discussion into a title more explanatory of what is discussed, rather than only Textures.

DONE

 

Moreover, I would suggest, if possible, to link the measured textures to the deformation mechanisms active in the samples as this would make the comparison with the literature more robust.

DONE

Finally, the writing could be improved a bit more to make the reading easier and flowing better. For example, locally sentences seem to repeat themselves (e.g. Lines 251-253).
DONE

Some more detailed comments:

Lines 103-104 “15-20 km” is not a pressure condition. Either change “pressure” with “depth” or include also pressure estimates, along with depth.

DONE

Line 112 Use “pressure” instead of “P”

DONE

Line 118 What is “Auct.”?

In the old/historical Italian geological literature, it was used as a generic reference (Authors –> Auct.) that is still used mainly in geological maps where rock names refer to the original ones, here ‘Authocton’.

BUT I removed this leaving just the ‘Authocton’.

Line 129 I suggest to add “domain” after “Austroalpine”. Same at Lines 133 and 134.
DONE

 

Line 133-134 What is a large and medium grain-size? Please include grain sizes representative for the samples. Same goes for other parts in the manuscript where only qualitative description of grainsizes is used.

DONE

Line 148 Since you are referring, rightly, to multiples of a uniform distribution, “(mud)” has to be used instead of “(mrd)”. Please change this also in the rest of the manuscript.
DONE

 

 

Line 149 I don’t see the need to use bold characters throughout the manuscript when referring to the techniques used (e.g. Quantitative Texture Analysis (QTA) by neutron diffraction, Seismic Properties, thermodynamic approach), or else. I suggest to use a normal format and avoid it.
DONE

 

Line 161-163 Which beam lines? What is the difference between the beam lines?
DONE

 

Line 222 I would simply reference to the development of textures in the samples as CPOs, and not as “fiber distribution”. This is also valid for other instances in the manuscript.

DONE

Line 243 In Figure 6 (and the others) the sample shown is 04STE, not 07STE. Check carefully throughout the manuscript for the right labelling and referencing of the samples.
DONE

I would delete the outline in Figures 2 and 3.

DONE

Table 2 I suggest to use the Greek symbols for omega, phi, chi (and also theta).

DONE

Moreover, I suppose those angles are in degrees, please use the measure unit.

DONE

Finally, avoid abbreviations (i.e. “acq. time”) in the Table.

DONE