Geochemistry, Zircon U–Pb Geochronology, and Geological Significance of Late Mesozoic Magmatic Rocks in Guangxi Region (Southeastern China)

Round 1

Reviewer 1 Report

In this manuscript, the authors presented new Zircon U-Pb geochronology and geochemistry data from the Liuwang pluton, to discuss the petrogenesis of these rocks and tectonic evolution of South China. The new data in this manuscript are high quality. I think that the topics of this manuscript are interesting and deserve to be published. However, several (moderate) issues need to be fixed before it can be accepted:

General comments:

1. The relationship between Petrogenesis and tectonic setting. As we know, granitic rocks can generated from different tectonic setting. Although most granitoids have arc like geochemical features, we can not give a conclusion that they were formed in arc setting. Besides, the Pearce diagram is not suitable for discrimination of tectonic setting as proved by lots of works. So how do you get the genetic link between Petrogenesis and tectonic setting?

2. Geological setting is too simple. Actually, the distribution of magmatic rocks, the age and geochemical trends on the regional scale will be helpful for discrimination of tectonic setting. I believe there are lots of data had been published in Guangxi and South China. However, I do not see any introduce for these regional works. Besides, a figure with previous data marked is welcome, which will make it easy to see the spatial and temporal distribution of regional magmatic rocks.

3. The chapters are not well organized. Such as 3. 2.1. Liuwang granodiorite and 2.2. Liuwang quartz porphyry should not belong to 2. Geological setting but a new chapter or section named “Field observations and sample descriptions”. Besides, no granodiorite and quartz porphyry in Figure 2.

4. Please provide the GPS location for the dating samples

5. There are several models about the setting of Jurassic and Cretaceous magmatic rocks as listed in the introduction section. However, there has no thoroughly discussion about it. At least I do not see how to exclude the effect of Tethyan subduction, intracontinental delamination and lithospheric extension.

6. There are some spelling and other small mistakes in MS, such as Figure 8 twice in pages 18 and 19. Please check them thoroughly.

Specific comments:

Line 11. focal point, bad English.

Line 16 add some words about the field relationship between Liuwang granodiorite and quartz porphyry

Line 18 replace “granodiorite is” to granodiorites are

Line 19 rock to rocks

Line 20 and depletion to but depletion

Line 21 granodiorite also exhibits, to granodiorites also exhibit

Line 24 with depletion to and depletion

Line 51 Multiple subduction models, but the specific models listed include collision and intracontinental setting.

Line 65 Change foundation to model or process.

Line 69 boasts. Something would be wrong.

Table 1, replace 10-6 to ppm

There are many plots in Figure 5 and lines in Figure 6 but only marked two samples (CX14-N1, CX15-N1). The same problems in Figure 7&8

Line 402 (Zhang, 2017a; Zhang et al., 2017b) should be Zhang (2017a) and Zhang et al. (2017b)

References list is in a confused order.

see above

Author Response

Reviewer 1

Reviewer 2 Report

1. In the Fig. 1, the colours chosen for the Upper Cretaceous and Cenozoic are very similar and difficult to distinguish. Please, change it.

2. The petrographic characteristics of granodiorite and also quartz porphyry is insufficient. It should be supplemented with the characteristics of chemical composition of the main rock-forming minerals and also include them in the classification.

3. In the image No. 3c mineral labelled Pl is amphibol and not plagioclase.

4. In the Fig. 11, the tectonic position of the studied granodiorites, and conversaly, quartz porphyry should be clearly marked. The picture is then unclear.

Only minor ediding of English language is required.

Author Response

The colors for the Upper Cretaceous and Cenozoic epochs have been modified to easily distinguishable hues. Descriptions of accessory minerals and other compositional components have been added to the rock descriptions. Microscopic images have been revised, and in Figure 12 (original Figure 11), the structural locations of the studied rocks have been marked.

Author Response File: Author Response.docx

Reviewer 3 Report

Report on the manuscript Minerals - 2644836

"Zircon U–Pb geochronology, geochemistry, and geological significance of late Mesozoic magmatic rocks in southeastern Guangxi, South China”

 by Qing-Gang Mao, Sai-Sai Li, Xing-Yuan Liu, Jiang-bo Wu, Chun-Jiang Yan, Kun Liu and Wen-Qiang Huang

Dear Authors,

I appreciated your research work although there are some fundamental points in which to intervene.

SUGGESTIONS TO IMPROVE THE MANUSCRIPT

I believe that for the final publication it is necessary to implement the manuscript following these indications:

·       I propose this title as an alternative to the one proposed:

"Geochemistry, Zircon U–Pb geochronology, and geological significance of Late Mesozoic magmatic rocks in Guangxi Region (Southeastern China)"

·       The paper is not properly organized:

It is always necessary to keep the presentation of data clearly distinct from their discussion and interpretation. At present in the manuscript these two important sections are mixed. I suggest the following organization of the paragraphs in order to keep the different parts of the manuscript distinct:

1. Introduction

2. Geological framework

2.1 Regional Geology with Figs 1,2 – Please, this paragraph is too brief, it needs to be implemented

2.2 Sampling with Fig.3 (outcrop and hand samples)

3. Analytical Methods

Optical petrography, XRF whole rock, Zircon separation, Zircon chemistry, Image analysis (SEM/CL) of zircons, U-Pb dating.

It is necessary to describe the methods used in the order in which the data will then be presented

4. Results

4.1. Petrographic features with Fig. 4 (only microphotos)

4.2. Geochemistry

4.2.1 Major Elements

4.2.2 Trace Elements

4.2.3 REE

4.3 Zircon data

4.3.1 Zircon imaging and chemistry

4.3.2 Zircon U-Pb Geochronology

Please, I advise you to keep separate the data concerning the study of the internal textures, the trace element characterization and finally the isotopic data !!!

5 and 5.1…..Discussion organization is ok

Conclusions (par. 6): to improve, please.

3. Analytical Methods

The indication of the percentage of U-Pb discordance and the considered cut off used for the age filtering are recommended (in the text)!

Also in the U-Pb data table (as supplementary material) the %U-Pb discordance and U-Pb data for the standards must be indicated following the recent paper published in Minerals (see supplementary material files):

Fornelli, A., Festa, V., Micheletti, F., Spiess, R., & Tursi, F. (2020). Building an Orogen: Review of U-Pb Zircon Ages from the Calabria–Peloritani Terrane to Constrain the Timing of the Southern Variscan Belt. Minerals, 10(11), 944.

4. Zircon data

The characterization of internal pattern zoning of zircon crystals deserves more attention and detail.

Please refer to the paper:

Corfu, F., Hanchar, J. M., Hoskin, P. W., & Kinny, P. (2003). Atlas of zircon textures. Reviews in mineralogy and geochemistry, 53(1), 469-500.

and

Fornelli, A., Piccarreta, G., Micheletti, F. (2014). In situ U-Pb dating combined with SEM imaging on zircon–an analytical bond for effective geological reconstructions. Geochronology–Methods and Case Studies, 109-39, Edited by Mörner, N. A.

·        For better constrained the significance of Th/U ratios (Zircon U-Pb ages Paragraph), please refer to these papers:

Rubatto, D. Zircon: The Metamorphic Mineral. Rev. Mineral. Geochem. 2017, 83, 261–295.

·       Figure 1: To facilitate the reading of the geological schemes and the thematic map I suggest these modifications: (a) a very schematic map of the Asian continent with the insert (b) indicating the Guangxi Region in which (c) will show the study area in detail.

·       The captions relative to the Figs 1,2,3 must be implemented, they are too concise.

In conclusion,

I think that the manuscript can be accepted for publication after major revisions in an international journal as Minerals.

 Best regards

Comments for author File: Comments.pdf

Minor spelling errors

Author Response

I have already changed the title as per your suggestion and restructured the content of the article according to your requirements. I have added relevant data on concordance behind the zircon age data table and provided a description of concordance. The conclusion regarding the Th/U ratio is consistent with the conclusion from the reference article you provided. I am not sure about the specific modifications required for the last point regarding the figures. Could you please provide more detailed clarification?

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Dear Authors,

Dear authors, I noted that most of the suggestions given in order to improve the presentation of the data and the manuscript as a whole were carried out.

However, there are still some details to be finalized:

-       The schematic map of China should be included in figure 1 in such a way as to allow the reader to immediately identify the study area;

-       for completeness of data it is necessary to add among the data available online the uranium lead data carried out on the standards that it seems to me but also still;

-       I don't think the bibliography has been sufficiently updated, neglecting to cite fundamental articles on the study of zoning patterns and the geochemistry of zircons such as those from Corfu, Rubatto, Fornelli.

best regards

In conclusion,

I think that the manuscript can be accepted for publication after minor revisions in an international journal as Minerals.

Best regards

2023 October 14   

Reviewer

noun

Author Response

I have incorporated your feedback regarding Figure 1 and inserted the references you mentioned

in the text.

Round 3

Reviewer 3 Report

Good job!

best regards