Petrogenesis and Tectonic Implications of Early Paleozoic Magmatism in Awen Gold District, South Section of the Truong Son Orogenic Belt, Laos

Round 1

Reviewer 1 Report

The manuscript entitled ‘Petrogenesis and Tectonic Implications of the Caledonian Magmatism in Awen Gold District, South Section of the Truong Son Orogenic Belt, Laos’ by Shang et al., presents new data to discuss the petrogenesis and tectonic implications of the Caledonian magmatism in the Awen gold district. This is a readable paper on the geochemistry of mafic to felsic rocks. However, this manuscript also has obvious defects. In my opinion, the paper can be published in minerals with moderate modification. At the moment, the prose is not reader-friendly. Language polishing with native speaker is also preferred and necessary.

 

Major issues:

1.      After I have been through the paper, I think that the authors are not good at tectonic dynamics and some inaccurate discussions were made. For example, we can't constrain the tectonic evolution of an old ocean just only by using the little magmatism; the tectonic process must not be that simple, and also the strata and structural conditions, etc. For example, we can combine whether there is a corresponding passive continental margin deposition.

2.      The quality of the English is not good enough for minerals readership. There are too many grammatical mistakes in the paper, for example some long and complex sentences. It is very hard to follow and even to understand in places. Thus, authors had better ask a native speaker/colleague or professional editing service to assist in the editing.

3.      In 2. Geological background and petrography part, firstly, the outcrop pictures of samples should be added, which are fundamental to identify the rock type. Secondly, for Figure 3 Representative photomicrographs (cross-polarized light) of thin sections, I cannot identify the mineral. Thus, author should provide more clear pictures. Thirdly, in Line 96-122, authors should add the volume % content of each mineral for olivine-basalt, quartz-monzonite, granodiorite, and tonalite samples. For example, for gabbro (LHJT), the major minerals are plagioclase (??%), pyroxene (??%) and a small amount of amphibole and biotite (??%). Fourthly, add QAPF modal diagram for samples and use these names for your samples in the paper.

4.      When discussing the rock type, authors should integrate the mineralogy contents rather than only relying on the geochemical diagrams. For example, in Line 448-451, authors described the tonalite as I-type granite only by the geochemical data. In fact, many S-type granites also could have these similar characteristics. Besides, some geochemical discrimination diagrams are misused in the paper. In fact, every discrimination diagram has its conditions. For example, for Figure 11, these diagrams of Th/Yb vs. Ba/La and La/Yb vs. Ba/La are suitable for mantle-derived samples. Thus, the felsic samples cannot plot in these diagrams. Many similar misuses still have existed in the paper, and please check other diagrams one by one. Finally, many diagrams should add legend explaining symbols.

5.      I suggest that authors should add the in-situ mineral isotope content, such as zircon Lu-Hf isotope. Because whole rock Sr and Nd Isotopes stand for a mixed composition, which are inaccurate to constrain the magma source region.

6.      In Conclusions part, some conclusive points cannot obtain after I pass through the paper several times. Firstly, in Line 597, how do you conclude that these rocks are related to the northward subduction of the Tamky-Phuoc Son Ocean?? In fact, in 5.3. Tectonic Setting and Geodynamics part, you should solve the question by your data, but you not. Secondly, in Line 603-604, you say that the granitoid in this stage is closely associated with gold mineralization in the Awen gold district. But no evidence has been supported in the discussion part. I cannot find the contents about the relationship between granitoid rocks and gold mineralization.

 

Specific points:

1.      Line 13: In the TSOB

2.      Line 32: bimodal volcanic associations? The paper discuss on mafic to felsic intrusive rocks. Why are volcanic associations?

3.      Line 32: TSOB is a proper noun. Please add definite article ‘the’ before.

4.      Line 32: the Tamky-Phuoc Son suture zone (TPSSZ) which was separated from…….

5.      Line 34: ……were mainly formed in the Early Paleozoic.

6.      Line 41: thought should be argued

7.      Line 47-48: Please rewrite the sentence.

8.      Line 50-53: There is the grammatical mistake in the long and complex sentence. Please rewrite the sentence.

9.      Line 55: Delete ‘Complementing previous studies,’

10.   Line 55: ……and further constrain these events in this region.

11.   in the Southeast Asia

12.   Line 81: Cenozoic volcanic rocks are outcropped in ……

13.   Line 93: add the scale in the Fig. 2.

14.   Line 102: The major minerals are plagioclase (volume %), pyroxene (volume %) and a small amount of amphibole and biotite (volume %).

15.   Line 105: Phenocryst is primarily composed of olivine (volume %) and plagioclase (volume %).

16.   Line 106: I cannot identify the mineral in Figure 3. Please provide more clear pictures.

17.   Line 111: Quartz is granular and mainly……

18.   Line 119: delete ‘are’

19.   Line 124: Geologic sketch map modified after[2] and sample locations.

20.   Line 131-144: I was unable to find information about the secondary standard used during the period of analyses to confirm the accuracy of the data set, which is a crucial component of these types of secondary analyses.

21.   Line 145: add one standard analyzed by this lab and also detection limits.

22.   Line 167: ….. were analyzed for zircon U-Pb dating in this study.

23.   Line 168: The zircon U-Pb data are shown….

24.   Line 170: These grains are 70-120 μm in length with…..

25.   Line 220: Please support the calculated formula of Mg#

26.   Line 233: Please delete the space between 65.35 and symbol %. % is just a symbol not the unit.

27.   Line 235: Please support the calculated formula of δEu

28.   Line 265-271: The validity of using two-stage model ages, rather than one-stage model ages for olivine-basalt or other mantle-derived samples should be elucidated.

29.   Line 276-278: There is the grammatical mistake in the long and complex sentence. Please rewrite the sentence.

30.   Line 282:….. range from 428 to 449 Ma.

31.   Line 293-297: Delete these content ‘Due to few samples available in previous studies, directly resulted in the scarcity of 293 magma crystallization ages and further induced the geochronological framework could 294 not be well established. The Caledonian magmatism in TSOB is still unclear. In the explo- 295 ration of the Awen gold deposit in recent years, a mass of mafic to felsic magmatic rocks 296 were disclosed in drill holes. Nine fresh samples of magmatic rocks were systematically 297 collected and dated by LA-ICP-MS method.’ They are meaningless content.

32.   Line 299: ……yield an intrusive age of 507 Ma. Please delete the decimal point for the LA-ICP-MS age.

33.   Line 316: reaches the peak in the collision stage??? The collision stage is a compressional setting and little magma can be produced. Please check these age data.

34.   Line 324: You say that the Caledonian magmatism in the TSOB can be further subdivided into four different stages. What is your evidence? Only the different ages? Please add more evidence, e.g., rock association in different stages.

35.   Line 324: These four stages correspond to specific period of the subduction of the Tamky-Phuoc Son Ocean?? Only the subduction stage?? Why do you say these rocks form in different stage including subduction, collision and post collision in the conclusion part.

36.   Line 331-331: Delete the sentence ‘The relationship between magmatism and geodynamic settings can be probed through in-depth research on the petrogenesis of magmatic rocks.’ It is meaningless content.

37.   Line 362:which show arc signatures (ref.)

38.   Line 416: The quartz-monzonite is a kind of dioritic rock that cannot depict it as the I-type granite. Please rewrite the petrogenesis of quartz-monzonite.

39.   Line 425: bimodal volcanic rocks？？ Where are the volcanic rocks? Please use the accurate terminology.

40.   Line 427: Please add the mineralogical content when you discuss the granite type.

41.   Line 430-431: You cannot describe the felsic rock as EM1 or EM2.

42.   Line 441: high differentiated granite? Please add more evidence.

43.   Line 488:  For 5.3. Tectonic Setting and Geodynamics part, authors have not prepared the evidence, especially the regional strata evidence. Besides, it is difficult to follow the changes of the indistinct discussion. So, please rewrite this part. Finally, the paper focuses on the evolution of a paleo ocean, so the regional geochemical data also should added.

44.   Line 511: delete ‘We have been researching the TSOB for many years. ‘

45.   Line 544: Middle Cambrian

46.   Line 561: The stage name should add in Cartoonic illustration of Figure 18.

 

 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors,

thank you very much for this interesting work.

I put some comments along the text.

As I suggested, make one or two clearer Figures for the geodynamic framework, and fournish some comparison with similar settings in other parts of the world. 

I also suggest an English colleague revise the manuscript.

Best regards

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

Dear Authors,

Your manuscript demonstrates international importance, novelty, and rigor. It sheds light on the Early Paleozoic evolution of the notable, but still poorly-known sector of the planet. Indeed, it is suitable to “Minerals”, although some changes are necessary. I draw your attention to the recommendation to put your findings into the frame of the modern plate tectonic reconstructions.

1)      Title: may be to replace Caledonian by Early Paleozoic? Caledonian sounds confusing when applied outside of Europe.

2)      Introduction: some information can be moved to the next section. In Introduction, you need to demonstrate the international importance of your study.

3)      Section 2 to be titled “Geological Setting”.

4)      You cite the works by Hutchison and Metcalfe – great! However, please, note that these specialists updated their tectonic reconstructions, and, thus, you need to refer to their fresher works.

5)      Figure 1, legend: Tertiary and Quaternary -> Cenozoic.

6)      Section 3 should start with a section explaining your sampling.

7)      Figure 8: the geological time scale MUST be justified to the developments of the International Commission on Stratigraphy. See stratigraphy.org

8)      Your subsections 5.2 and 5.3 should form a new section titled “Discussion”.

9)      Discussion: writing about tectonic interpretations, you MUST consider and cite the works by G. Stampfli, C. Scotese, D. Mueller, T. Torsvik, C. Hutchison, and I. Metcalfe. Please, consider their freshest works. Although many of them are planetary-scale, you have to “attach” your developments to what is shown on the plate tectonic reconstructions there. I do not exclude that you can question the reliability of some of these reconstructions.

10)  Discussion: are you sure there was Caledonian orogeny in SE Asia? May be to use local orogeny name(s) if available?

11)  The writing is clear, but the quality of English needs improvement. May be you can ask any native-speaking colleague to help?

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

This is a good paper based in geological, petrographical, geochemical, and isotopical data.

- I suggest a detailed spell check by a native English-speaker.

Author Response

Dear reviewer, thanks for your suggestion, this manuscript has been revised.