Late Permian High-Ti and Low-Ti Basalts in the Songpan–Ganzi Terrane: Continental Breakup of the Western Margin of the South China Block

Round 1

Reviewer 1 Report

Comments on ms. # minerals- 1943584

Late Permian High-Ti and Low-Ti Basalts in the Songpan- Ganzi Terrane: Continental Break-up of the Western Margin of the South China Block?

By

Yumeng Shao, Danping Yan, Liang Qiu, Hongxu Mu and Yi Zhang

This article presents geochemical, isotopic and U-Pb radiochronological data on a series of basalt samples from the Dashibao Formation interbedded in folded low grade metasediments of the Songpan- Ganzi Terrane. Dashibao basalts are extremely variable in thickness and occur on top of a Proterozoic –lower Permian platform sequence similar to that of the South China Block. This mostly submarine basalt unit displays some tuffs on top and are overlain by thick Triassic clastic sequence that includes collapse breccia and siliclastic turbidites. Per se, this sequence of events advocates a correlation between basalt eruption and drastic sedimentation change from a carbonate platform into fast-subsiding siliclastic basin. In addition, U-Pb zircon age constraints, major and trace elements and isotope data reveal that volcanic rocks are Late Permian alkaline and continental flood basalts, an association diagnostic of continental rift environments. Thus, it appears that Dashibao basalts are coeval to similar continental basalts of the Emeishan LIP. A correlation is suggested that finally allows the interpretation of the Songpan- Ganzi Terrane as a part of the South China Block rifted during the Late Permian and later re-amalgamated to the South China Block. The ELIP would have triggered the formation of a RRR triple junction, the northeastern branch of which, associated with Dashibao basalts, aborted while the southern and northwestern branches were oceanized as an extension of Tethys Ocean. The rest of the paper is an attempt of interpretation in terms of mechanisms, which sounds somewhat speculative owing to the data presented.

The content of this article is interesting and worth to be published; however, the form is much perfectible and hampers a good understanding. This article contains too many typing errors and repetitions, and some paragraphs should be shortened. Many remarks and suggestions have been directly on the pdf and are hopefully of some help. In short, this article still needs some work but could be acceptable in Minerals provided the suggested corrections.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer:

We have studied your comments carefully and have tried our best to revise our manuscript accordingly and our point-by-point responses are presented below.

（1）Thank you for your careful review. We are very sorry for the mistakes in this manuscript and inconvenience they caused in your reading. We have rectified the mistakes in the manuscript, and it has been thoughtfully reviewed, rewritten and polished by MDPI English editor. We hope it can meet the journal’s standard.

(2) According to your comment, we have made a major revision in the manuscript. We simplified the text by removing some sentences from Sections 5.5 and 5.6, and added some new contents (lines 334-352, Figure 13). In these contents, we comprehensively considered the characteristics of Emeishan basalt in different areas and rock types (low or high titanium basalt), and drew stratigraphic columns of the Emeishan basalt for comparison, which is conducive to support the conclusion.

(3) For your other suggestions, we also have made corresponding revisions in the manuscript, including taking new photomicrographs. Please refer to the revised manuscript for details.

We would like to express our great appreciation to you for your careful comments on our paper. Those helpful comments were critical and would benefit not only the improvement of this paper but also our future work.

Special thanks to you for all your help.

Best wishes,

Yours sincerely,

Yumeng Shao

 

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors,

I went carefully through your very interesting manuscript on petrology, geochemistry and isotopic dating of basaltic magmatism of Permian intracontinental rifting in the South China Block, related to a mantle plum. The obtained new results are clearly reported and supported by suitable graphical documentation in text and supplementary materials. However, I was surprised in finding a lot of mistakes in text and figures which decrease high scientific impact of your ms. Moreover, you often use et al. in reference list. I have suggested some corrections or marked them in red in the ms to be corrected in minor revision. In addition, I put some questions in text or figures.

Kind regards,

 

The Reviewer

 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer:

We have studied your comments carefully and have tried our best to revise our manuscript accordingly and our point-by-point responses are presented below.

（1）Thank you for your careful review. We are very sorry for the mistakes in this manuscript and inconvenience they caused in your reading. We have rectified the mistakes in the manuscript, and it has been thoughtfully reviewed, rewritten and polished by MDPI English editor. We hope it can meet the journal’s standard.

（2）We have revised all the pictures in the manuscript（Figure 1-14）, including the mistakes in Figure 1 and Figure 12.

（3）For your other suggestions, we also have made corresponding revisions in the manuscript. Please refer to the revised manuscript for details.

We would like to express our great appreciation to you for your careful comments on our paper. Those helpful comments were critical and would benefit not only the improvement of this paper but also our future work.

Special thanks to you for all your help.

Best wishes,

Yours sincerely,

Yumeng Shao

 

Author Response File: Author Response.docx

Reviewer 3 Report

This paper presents the new SIMS U-Pb zircon data on the Dashibao basalt from the Songpan-Ganzi Terrane and constrains the duration of the basalt eruption, indicating the relationship between the Emeishan mantle plume and the regional tectonic evolution. However, the current version of manuscript is still not well organized. Therefore, I suggest a major revision before the acceptance for publication in Minerals.

Major comments:

(1) There are many reports on the Dashibao basalts. It is suggested to comprehensively consider the characteristics of the Dashibao basalt in different areas, including thickness, rock types (low Ti or high Ti basalts, whether there is pillow structure), and draw geological sections for comparison, which is conducive to support the conclusion.

(2) In the abstract, "The Dashibao basalts are geochemically classified into  alkaline basalts (Group 1) and tholeiitic basalts (Group 2), which are comparable to the oceanic island basalts (OIB) or continental flood basalts." Whether the basalt in this area is OIB or continental flood basalts?

(3) There are many errors in the figures, such as in Fig.1(legend) and Fig.12(VI?IV?). In addition, the font size is different in some figures and some names of the figures are missing (Fig.1c), and the upper and lower scripts are labeled incorrectly (Fig.6 and Fig.12).

(4) Multiple spelling duplications or errors in Line 246, Line 263, Line 287-289.

(5) Note the number of significant digits.

(6)References should be cited in Analytical Methods.

Author Response

Dear editors:

We have studied your comments carefully and have tried our best to revise our manuscript accordingly and our point-by-point responses are presented below.

（1）There are many reports on the Dashibao basalts. It is suggested to comprehensively consider the characteristics of the Dashibao basalt in different areas, including thickness, rock types (low Ti or high Ti basalts, whether there is pillow structure), and draw geological sections for comparison, which is conducive to support the conclusion.

Based on your comments, we turned to consult many reports on the Dashibao Formation, in which characteristics, thickness and rock types of the basalt of the Dashibao Formation were described. But almost all of these reports focused on the Dashibao sections in Baoxing while there were few reports on the Dashibao Formation sections and pillow basalts in other areas. We compared the Baoxing section with the measured Xindianzi section, and found that their rock characteristics were comparable. In order to make a better comparison, we drew five representative stratigraphic columns of the Emeishan basalt，Results reveal that these areas are all characterized by LT basalt on the bottom and HT basalt on top..and we added corresponding descriptions and pictures（Lines 334-352, Figure 13）. Please refer to the revised manuscript for details.

 

（2）In the abstract, "The Dashibao basalts are geochemically classified into  alkaline basalts (Group 1) and tholeiitic basalts (Group 2), which are comparable to the oceanic island basalts (OIB) or continental flood basalts." Whether the basalt in this area is OIB or continental flood basalts?

The geochemical characteristics of the basalts in Xindianzi area, which are part of Emeishan basalt and belong to continental flood basalts, are similar to OIB basalts. The original sentence has been changed to The Dashibao basalts are geochemically classified into alkaline basalts (Group 1) and tholeiitic basalts (Group 2), which are a part of the Emeishan basalt.

 

• There are many errors in the figures, such as in Fig.1(legend) and Fig.12(VI?IV?). In addition, the font size is different in some figures and some names of the figures are missing (Fig.1c), and the upper and lower scripts are labeled incorrectly (Fig.6 and Fig.12).and (4) Multiple spelling duplications or errors in Line 246, Line 263, Line 287-289.

Thank you for your careful review. We are very sorry for the mistakes in this manuscript and inconvenience they caused in your reading. We have rectified the mistakes in the manuscript, and it has been thoughtfully reviewed, rewritten and polished by MDPI English editor. We hope it can meet the journal’s standard. 

• References should be cited in Analytical Methods.

As your suggestion, we have added more references in the Analytical Methods part.

 

We would like to express our great appreciation to you for your careful comments on our paper. Those helpful comments were critical and would benefit not only the improvement of this paper but also our future work.

 

Special thanks to you for all your help.

 

Best wishes,

 

Yours sincerely,

 

Yumeng Shao

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments on #1943584_V2 (revised version).

The authors have made a great effort in amending the original text and this article is now near to be acceptable. However, there are still a number of  errors that could be easily corrected, especially in the new text parts. Comments and suggestions have been made directly on the pdf.

A few prominent points should be necessarily corrected:

1) Fig. 1a must display the location (outline) of Fig. 2 (geol. map)

2) Fig 1b: the colour of basalt on the stratigraphic columns and caption must be the same

3) Using HT and LT for high- and low-Ti is questionable because these abbreviations are commonly used for high- and low-temperature. It is necessary to use HTi and LTi instead.

The rest of suggested corrections are on the pdf

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you for your careful review. For your suggestions, we have made corresponding revisions in the manuscript, including outlining the location of Fig. 2 in Fig.1a, unifying the color of basalt on the stratigraphic columns and caption in Fig. 1b, Change the LT and HT to the LTi and HTi, and so on. Please refer to the revised manuscript for details.

We would like to express our great appreciation to you for your careful comments on our paper. Those helpful comments were critical and would benefit not only the improvement of this paper but also our future work.

Special thanks to you for all your help.

Best wishes,

Yours sincerely,

Yumeng Shao

Author Response File: Author Response.docx

Reviewer 3 Report

There are some inconformity in the figures, such as legend for basalt in Fig.1b.

There are still many errors such as SiO vs. FeOT/MgO in Fig.6.

Author Response

Dear Reviewer,

Thank you for your careful review. For your suggestions, we have made corresponding revisions in the manuscript, including unifying the color of basalt on the stratigraphic columns and caption in fig.1b, revising the error in Figure 6, and so on. Please refer to the revised manuscript for details.

We would like to express our great appreciation to you for your careful comments on our paper. Those helpful comments were critical and would benefit not only the improvement of this paper but also our future work.

Special thanks to you for all your help.

Best wishes,

Yours sincerely,

Yumeng Shao

Author Response File: Author Response.docx