Insights into the Crustal Evolution and Tungsten Mineralization of the West Cathaysia Block: Constraints from the Inherited Zircons from the Mesozoic Dengfuxian and Paleozoic Tanghu Plutons, South China
, Youyue Lu 1,*, Lei Liu 4,*, Jianming Fu 1, Guofeng Xu 4, Qianhong Wu 4, Shengxiong Yang 2, Xiaofei Qiu 1 and Zunzun Zhang 1
Round 1
Reviewer 1 Report
This is a solid article reporting high-quality analytical studies of zircons from representative granitic samples which build on previous dating of crustal formation in the West Cathaysia Block. It is mainly of regional interest to those who study the geology and mineralization of South China, but also has international interest for the general conclusion that multiple crustal reworking events favour the formatioin of globally-significant tungsten mineralization.
There is scope for improvement. One issue is that the article does not specify numbers of zircon crystals studied from each location. This should be included in the abstract as well as in the Methods. The abstract is missing numbers, indicated on line 26 as 'XX to XX'. Another flaw is that the tungsten mineralization is not shown on the geology maps and the reader cannot see the spatial association between the sampled granites and the occurrence of mineralization. Also, information on the tungsten ore deposits is presented near the end of the Discussion; this should be placed early in the article as part of the Introduction.
Here are further comments, mostly relating to improvements in language, which the authors should address toi improve the paper:
Line 44: 'thermos-tectonic events' should be thermo-tectonic
Line 49: delete 'the knowledge on'
Line 67: 'will host crucial message on' is poor English, rephrase to 'will elucidate'
Line 96: 'related to the giant Cu-Au-W polymetallic mineralization' - 'giant' is an expression usually applied to an ore deposit, not to just mineralization. Can the authors be specific on the ore deposits referred to here?
Line 100: Figure 1 caption - add that dashed-line box outlines indicate the positions of Figure 2 and 3.
Line 116: 'metamorphic basalts,' should be 'metamorphosed basalts, ...'
Line 118: delete 'been'
Line 127: same issue as stated for line 96
Line 145: delete 'a series of'
Line 148: Figure 2 - the ore field is not indicated on the map; can this be added as a superimposed stipple? In which case, add the symbol to the legend. In the caption, add that the map area is located in Figure 1.
Line 163: in the caption, add that the map area is located in Figure 1.
Line 166: the authors should state the number of zircon crystals prepared for dating from each of the two granites. It is not clear whether the dates represent a single analysis from each crystal, or more than one analysis from different zones?
Lines 222-231: reduce the number of references to Figure 4, as their are too many and they are not all necessary.
Line 229: delete 'show' and combine this sentence with the next sentence.
Line 232: Figure 4 should be much larger, occupying at least half a page: reconfigure each set to display 3 zircons in a row x 3 rows
Line 236: same point as for line 166, we need to know the numbers of zircon crystals in the dataset!
Lines 252-265: the text on the Tanghu zircons is structured the same as for the Dengfuxian zircons lines 236-248; although systematic, this is does not appeal to the reader. Can the authors vary the sentence structure to make it more appealing to the reader?
Line 295: replace 'universal' with 'other planetary'
Line 335: 'indicating a mantle origin for these zircons' change to 'indicating a mantle origin for the magma from which these zircons crystallised'
Line 354: 'Previous study by [99]' insert 'Wang et al. (2018)' before '[99]'
Line 390: add to the caption a link to the Supplementary Material in which the compilation is available
Line 412: replace 'summed' with 'inferred'
Line 422: delete 'To our knowledge that'
Line 424: replace 'a certain size of' with 'economically significant'
Line 426: rephrase 'can host superior solubility'
Line 427: replace 'would get' with 'becomes'
Line 434: delete 'event'
Line 435: insert 'economically valuable' before 'lithophile'
Lines 437-443: move this text to the Introduction, around line 96 where the 'giant Cu-Au-W polymetallic mineralization' is first mentioned
Lines 451-454: delete the sentence starting 'Consequently,' as this is repetition, and is stated again in the Conclusions
Line 459: replace 'these' with 'the'
Line 463: replace 'are in favor of the tungsten mineralization' with something like 'are enriched in the metalliferous lithophile elements W, Sn, U, and Nb'
Author Response
Replies to Reviewers:
First of all, thanks a lot for the constructive suggestions and comments from the anonymous reviewers. We believe that this manuscript can not be perfect without valuable comments and suggestions. We have tried our best to modify the text based on the constructive comments. Great changes were made in responding to these valuable comments. The detailed point-by-point responses are as follows:
Reviewer 1
Comment 1: One issue is that the article does not specify numbers of zircon crystals studied from each location. This should be included in the abstract as well as in the Methods.
Response: Thanks for the valuable suggestion and comments. We have added the related data in the Methods Section as well as in the abstract as suggested.
Comment 2: The abstract is missing numbers, indicated on line 26 as 'XX to XX'.
Response: We have fulfilled the missing data.
Comment 3: Another flaw is that the tungsten mineralization is not shown on the geology maps and the reader cannot see the spatial association between the sampled granites and the occurrence of mineralization. Also, information on the tungsten ore deposits is presented near the end of the Discussion; this should be placed early in the article as part of the Introduction.
Response: Thanks for the valuable suggestion and comments. We have revised the Figure 2 and the location of W-Sn deposits were added in this figure, trying to show the genetic relationship between the granites and W-Sn mineralization. In terms of the location for the discussion part on the regional tungsten mineralization, we have added the description on the regional mineralization in the Introduction part.
Comment 4: Line 44: 'thermos-tectonic events' should be thermo-tectonic
Response: We have revised this part as suggested.
Comment 5: Line 49: delete 'the knowledge on'
Response: We have revised this part as suggested.
Comment 6: Line 67: 'will host crucial message on' is poor English, rephrase to 'will elucidate'
Response: We have revised this part as suggested.
Comment 7: Line 96: 'related to the giant Cu-Au-W polymetallic mineralization' - 'giant' is an expression usually applied to an ore deposit, not to just mineralization. Can the authors be specific on the ore deposits referred to here?
Response: Thanks for the valuable suggestion and comments. We used the regional instead. In addition, we also added some contents on the Cu-Au deposits in the Tongling and Chating ore clusters in China.
Comment 8: Line 100: Figure 1 caption - add that dashed-line box outlines indicate the positions of Figure 2 and 3.
Response: We have revised the Figure 1 as suggested.
Comment 9: Line 116: 'metamorphic basalts,' should be 'metamorphosed basalts, ...'
Response: Thanks for the valuable suggestion and comments. We have revised this part as suggested.
Comment 10: Line 118: delete 'been'
Response: We have revised this part as suggested.
Comment 11: Line 127: same issue as stated for line 96.
Response: We used the regional instead.
Comment 12: Line 145: delete 'a series of'
Response: We have deleted these words as suggested.
Comment 13: Line 148: Figure 2 - the ore field is not indicated on the map; can this be added as a superimposed stipple? In which case, add the symbol to the legend. In the caption, add that the map area is located in Figure 1.
Response: We have revised this part as suggested. Detailed response refers to the Response 3.
Comment 14: Line 163: in the caption, add that the map area is located in Figure 1.
Response: We have added the related content as suggested for the captions of Figure 2 and 3.
Comment 15: Line 166: the authors should state the number of zircon crystals prepared for dating from each of the two granites. It is not clear whether the dates represent a single analysis from each crystal, or more than one analysis from different zones?
Response: The spots for U-Pb isotopic dating in this study were analyzed on single zircon grains. The detailed number for the analyses were listed in the main text.
Comment 16: Lines 222-231: reduce the number of references to Figure 4, as their are too many and they are not all necessary.
Response: We have revised this part as suggested.
Comment 17: Line 163: in the caption, add that the map area is located in Figure 1.
Response: We have added the related content as suggested for the captions of Figure 2 and 3.
Comment 18: Line 166: the authors should state the number of zircon crystals prepared for dating from each of the two granites. It is not clear whether the dates represent a single analysis from each crystal, or more than one analysis from different zones?
Response: The spots for U-Pb isotopic dating in this study were analyzed on single zircon grains. The detailed number for the analyses were listed in the main text.
Comment 19: Line 229: delete 'show' and combine this sentence with the next sentence.
Response: We have revised the part as suggested.
Comment 20: Line 232: Figure 4 should be much larger, occupying at least half a page: reconfigure each set to display 3 zircons in a row x 3 rows.
Response: This figure has been modified as suggested by the reviewer.
Comment 21: Line 236: same point as for line 166, we need to know the numbers of zircon crystals in the dataset!
Response: We have revised the part as suggested.
Comment 22: Lines 252-265: the text on the Tanghu zircons is structured the same as for the Dengfuxian zircons lines 236-248; although systematic, this is does not appeal to the reader. Can the authors vary the sentence structure to make it more appealing to the reader?
Response: We have revised the part as suggested.
Comment 23: Line 295: replace 'universal' with 'other planetary'
Response: This figure has been modified as suggested by the reviewer.
Comment 24: Line 335: 'indicating a mantle origin for these zircons' change to 'indicating a mantle origin for the magma from which these zircons crystallised'
Response: We have revised the part as suggested.
Comment 25: Line 354: 'Previous study by [99]' insert 'Wang et al. (2018)' before '[99]'
Response: We have revised the part as suggested.
Comment 26: Line 390: add to the caption a link to the Supplementary Material in which the compilation is available
Response: I am not sure whether it is suitable for the Journal, but I can further communicate with the editor. We appreciate the kind suggestion from the reviewer.
Comment 27: Line 412: replace 'summed' with 'inferred'
Response: We have revised the part as suggested.
Comment 28: Line 422: delete 'To our knowledge that'
Response: We have deleted this sentence as suggested.
Comment 29: Line 424: replace 'a certain size of' with 'economically significant'
Response: We have revised the part as suggested.
Comment 30: Line 426: rephrase 'can host superior solubility'
Response: We have revised the part as suggested.
Comment 31: Line 427: replace 'would get' with 'becomes'
Response: We have revised the part as suggested.
Comment 32: Line 434: delete 'event'
Response: We have revised the part as suggested.
Comment 33: Line 435: insert 'economically valuable' before 'lithophile'
Response: We have revised the part as suggested.
Comment 34: Lines 437-443: move this text to the Introduction, around line 96 where the 'giant Cu-Au-W polymetallic mineralization' is first mentioned
Response: We have revised the part as suggested.
Comment 35: Lines 451-454: delete the sentence starting 'Consequently,' as this is repetition, and is stated again in the Conclusions
Response: We have revised the part as suggested.
Comment 36: Line 459: replace 'these' with 'the'
Response: We have revised the part as suggested.
Comment 37: Line 463: replace 'are in favor of the tungsten mineralization' with something like 'are enriched in the metalliferous lithophile elements W, Sn, U, and Nb'
Response: We have revised the part as suggested.
Reviewer 2 Report
I was interested to read about the crustal history of this region, about which I knew little. The age patterns of zircons from your two samples are usefully detailed, and you have supported the patterns seen in inherited zircon with other data from detrital zircons. Although this region is important for its tungsten mineralization, there is not much you can add in this respect because your study does not treat the chemistry of the granitoids, other than to observe the apparent extent of “reworking” crustal material, meaning re-melting of older crust, which may increase the concentration of lithophile elements.
The abstract could be made clearer and strengthened. I was confused by a number of statements: line 15: why emphasize explosive magmatism? Line 24, ‘forming age’: I presume you mean formation age, or more strictly crystallization age. Line 26 is missing the age range of the inherited zircons. Line 28: should say ‘in contrast to’ E Cathaysia – the history is not ‘totally different’, only one major age peak differs. Line 30: ‘it was proposed’ – isn’t this your own conclusion? So it should be ‘it is proposed …’. Lines 32–37: these complex, awkward sentences could be shortened to
‘The long duration of crustal reworking in the West Cathaysia Block resulted in the enrichment of lithophile elements (e.g. W, Sn, Nb and Ta) in the crust of that region. Therefore, the Jurassic granites in the Nanling Range, which are mainly derived from partial melting of Proterozoic basement rocks, became associated with large-scale tungsten polymetallic mineralization.’
You have a very large number of citations – are they all necessary? Even so, you could be more helpful in the way you cite them in the text. For example, the citations 32 to 35 in line 66 cover very different topics and could have been inserted at more relevant points, not all left to the end of the sentence. Refs 32 and 33 refer to crustal growth (line 64); 34 is about fractionation and enrichment (line 65), while 35 is a specific link to metallogeny in the Cathaysia Block.
Your Figures may need some work, and the figure captions could be more informative.
Figure 1 is referred to as 1a and 1b in the text, but is a single figure. The description in the text is hard to relate to the figure. 1a may refer to the small inset map. The Qin-Hang belt may be what is outlined in dashed blue lines on Fig.1, but neither the legend nor caption refer to it or to the blue dashed-line ornament
Figure 2: (b) Is evidently an outcrop, not hand specimens; is the pale finer-grained rock the same as that sampled? It is a sheet, and it does not look porphyritic, unlike the Triassic host. And why ‘granites’ (plural)? Fig. 2(c) is too dark to be useful in judging texture. If the scale bar is accurate, which I doubt, the rock is very fine grained, even the K-feldspar would be <1mm. The rock does not appear to be porphyritic.
Figure 3: the latitude and longitude values are attached to the wrong labels E and N, and should be transposed. (b) again, this looks like an outcrop photograph, not a hand specimen.
Figure 4: Labels and numbers are not explained. I infer that the upper ones identify the zircon crystal, and the lower numbers are the ages in Ma. This I can check in Table 1, but I see that you quote the 206/238 age for younger zircons, but the 207/206 age for older grains. I have seen this practice elsewhere, but you do not explain it, or say at what age you change the reported value.
Hadean age, line 258: Table 1 has 401 ages listed, not 403. This Hadean age is not listed, nor is the other c. 4.0 Ga Hadean age. They are also missing from Fig.6. Were these analyses discarded? It makes the later discussion of Hadean zircons rather less relevant to your study if you have no reliable, documented ages >4.0 Ga.
Section 5, Discussion, is incorrectly numbered: all parts of the Precambrian evolutionary history (section 5.1) should be renumbered 5.1.1. (Hadean), 5.1.2. (Archean), 5.1.3. (Paleoproterozoic), 5.1.4. (Meso-Neoproterozoic).
Section 5.2.1. (5.1.1) In relation to the comment about Hadean zircons above, I don’t see the need for a long discussion about Hadean rocks and zircons. You could cut out the first paragraph, and simply report some facts about the few records of ancient zircons in the South China Block.
You could provide some more helpful explanation of the Hf model age patterns as shown on Figures 9 and 10. Some of your readers may see the very large peak at c. 1.6 Ga on Figure 9(b) and assume that this was a major episode of crustal growth. While there is some clustering of inherited and detrital zircons around this time, in practice it’s likely that the major crustal additions were at c. 2.5 Ga and 1.0 Ga, i.e. around the time of the two peaks on Figure 11(a). Later intracrustal melting events (‘reworking’) may sample these crustal reservoirs in different proportions. However, it would seem that both the rocks you investigated, which are from the same part of the Nanling Range, sampled these reservoirs in very similar proportions, leading to clustering of the zircon model ages. The dense part of the array of c. 1 Ga detrital zircons on Figure 11 covers the full range of epsilon (Hf) from +11 to -10, giving potential ‘model ages’ distributed from 1.1 to 2.5 Ga, but these may just reflect more variable mixing of discrete crustal reservoirs.
Line 329 mentions ‘abundant information on Archean rocks’. Is this fair? The three cited papers seem focussed on Proterozoic rocks and the possibility of existence of Archean rocks, not on substantive observations.
The array of zircon ages around 2.5 Ga (yours and the detrital set) is interesting and important, but could be better explained. Yes, many have +ve epsilon Hf, but they may still be second-stage melts. They form a range from DM to negative values (around -10). The plausible hypothesis is that the many granitic and detrital zircons around 2.5 were crystallized from crustal melts of material derived from the mantle between 3.6 and 2.5 Ga. We can’t tell how many Archean crust formation/addition events were responsible for generating this array, but you have a small number of analyses falling on/near DM up to c. 3.6 Ga. That’s good. A lot of >3.0 Ga Archean crustal additions are likely to have been too mafic to have much zircon, which may become abundant only in the products of re-melting mafic or TTG crust (as in your 2.9–2.5 Ga arrays).
What’s also very interesting is that this Archean signal has largely disappeared, at least from your samples, after 1.0 Ga, as if this older source is largely hidden or lost in the crust from this point in time onwards. There may now be Archean remnants down below, but it seems they are rare, and most of the younger granites and other crustal material you might sample are a product of Paleo- to Mesoproterozoic crustal additions, perhaps as I suggested above, signalling the importance of the Rodinia-forming processes.
The format of your discussion, by concentrating on the individual periods, i.e. Archean, Paleoproterozoic, Meso-Neoproterozoic, seems to obscure some of these interesting features. It might help to finish section 5.1 with an overview of the whole pattern that puts these features into a more integrated context.
The conclusions section is short and not very informative, and does not do justice to your data patterns.
Minor things
The bottom half of Table 2 has data columns in a different order (and these are unlabelled) compared to the top half.
l. 44; should be thermo-tectonic
l. 48; Badu Group … … oldest rock unit (not ‘rocks’)
l. 67; replace ‘will host crucial message’ with ‘will hold important information’
l. 78; ‘amalgamation of two blocks’. You refer to Yangtze and Cathaysia, so I guess this should read ‘amalgamation of these two blocks’
l. 85; Kongling Group … … oldest exposed rock unit (not ‘rock’)
l. 244; should be five populations, not three
l. 305; Eco should be Eon
l. 412; ‘it is summed’. What should this be? ‘It is assumed’?
l. 421; Implication to …, should be ‘Implications for’
l. 448; ‘unravelling’. What should this be? ‘Implying’, ‘suggesting’?
Author Response
Replies to Reviewers:
First of all, thanks a lot for the constructive suggestions and comments from the anonymous reviewers. We believe that this manuscript can not be perfect without valuable comments and suggestions. We have tried our best to modify the text based on the constructive comments. Great changes were made in responding to these valuable comments. The detailed point-by-point responses are as follows:
Reviewer 2
Comment 1: I was confused by a number of statements: line 15: why emphasize explosive magmatism? Line 24, ‘forming age’: I presume you mean formation age, or more strictly crystallization age. Line 26 is missing the age range of the inherited zircons. Line 28: should say ‘in contrast to’ E Cathaysia – the history is not ‘totally different’, only one major age peak differs. Line 30: ‘it was proposed’ – isn’t this your own conclusion? So it should be ‘it is proposed …’. Lines 32–37: these complex, awkward sentences could be shortened to
Response: Thanks for the valuable suggestion and comments. 1) The south China is famous for the widespread intermediate acid magmatic rocks. In addition, these granitic rocks (mostly the Mesozoic granites) are genetically related to the region W-Sn polymetallic mineralization. So we emphasize explosive magmatism in this study. 2) Other comments on the expressions were revised as commented.
Comment 2: You have a very large number of citations – are they all necessary? Even so, you could be more helpful in the way you cite them in the text. For example, the citations 32 to 35 in line 66 cover very different topics and could have been inserted at more relevant points, not all left to the end of the sentence. Refs 32 and 33 refer to crustal growth (line 64); 34 is about fractionation and enrichment (line 65), while 35 is a specific link to metallogeny in the Cathaysia Block.
Response: We have revised this part as suggested by the reviewer. The citations were as following: As currently known that granitic rocks not only play an extremely important role in the evolution of the Earth’s crust [32-34] but also are commonly accompanied by mi-gration and/or enrichment of elements and formation of intense tungsten polymetallic mineralization [34-35].
Comment 3: Figure 1 is referred to as 1a and 1b in the text, but is a single figure. The description in the text is hard to relate to the figure. 1a may refer to the small inset map. The Qin-Hang belt may be what is outlined in dashed blue lines on Fig.1, but neither the legend nor caption refer to it or to the blue dashed-line ornament
Response: Thanks for the valuable suggestion and comments. We have revised the Figure 1 as suggested. In addition, the related description was added in the caption.
Comment 4: Figure 2: (b) Is evidently an outcrop, not hand specimens; is the pale finer-grained rock the same as that sampled? It is a sheet, and it does not look porphyritic, unlike the Triassic host. And why ‘granites’ (plural)? Fig. 2(c) is too dark to be useful in judging texture. If the scale bar is accurate, which I doubt, the rock is very fine grained, even the K-feldspar would be <1mm. The rock does not appear to be porphyritic.
Response: Thanks for the valuable suggestion and comments. We have revised the related contents in the main text to agree with the Figure 2. In addition, the title of this figure was also revised as commented.
Comment 5: Figure 3: the latitude and longitude values are attached to the wrong labels E and N, and should be transposed. (b) again, this looks like an outcrop photograph, not a hand specimen.
Response: We have revised this figure. In addition, the caption of this figure was also revised as commented.
Comment 6: Figure 4: Labels and numbers are not explained. I infer that the upper ones identify the zircon crystal, and the lower numbers are the ages in Ma. This I can check in Table 1, but I see that you quote the 206/238 age for younger zircons, but the 207/206 age for older grains. I have seen this practice elsewhere, but you do not explain it, or say at what age you change the reported value.
Response: We have revised this figure as commented. In addition, we also added the explanation for using the age data in the figure caption. Since the young ages (lower than 1000 Ma) and old ages (higher than 1000 Ma) are commonly used 207Pb/236U ages and 207Pb/206Pb ages, respectively.
Comment 7: Hadean age, line 258: Table 1 has 401 ages listed, not 403. This Hadean age is not listed, nor is the other c. 4.0 Ga Hadean age. They are also missing from Fig.6. Were these analyses discarded? It makes the later discussion of Hadean zircons rather less relevant to your study if you have no reliable, documented ages >4.0 Ga.
Response: Thanks for the valuable suggestion and comments. We hold the point to keep this section on the Hadean Eon. Hadean is an important period for the Cathaysia Block, since several Hadean zircon ages have been reported. Although we did not report the Hadean zircon grains, we found a we found a zircon grain core (spot no. 13D40-4-96) with U-Pb isotopic age of 1051 Ma and with TDMC age of 4061 Ma, indicating that this zircon was sourced from Hadean crustal material.
Comment 8: Section 5, Discussion, is incorrectly numbered: all parts of the Precambrian evolutionary history (section 5.1) should be renumbered 5.1.1. (Hadean), 5.1.2. (Archean), 5.1.3. (Paleoproterozoic), 5.1.4. (Meso-Neoproterozoic).
Response: We have rearranged the sequences of the Section.
Comment 9: Section 5.2.1. (5.1.1) In relation to the comment about Hadean zircons above, I don’t see the need for a long discussion about Hadean rocks and zircons. You could cut out the first paragraph, and simply report some facts about the few records of ancient zircons in the South China Block.
Response: Thanks for the valuable suggestion and comments. We have shorten this paragraph as suggested.
Comment 10: You could provide some more helpful explanation of the Hf model age patterns as shown on Figures 9 and 10. Some of your readers may see the very large peak at c. 1.6 Ga on Figure 9(b) and assume that this was a major episode of crustal growth. While there is some clustering of inherited and detrital zircons around this time, in practice it’s likely that the major crustal additions were at c. 2.5 Ga and 1.0 Ga, i.e. around the time of the two peaks on Figure 11(a). Later intracrustal melting events (‘reworking’) may sample these crustal reservoirs in different proportions. However, it would seem that both the rocks you investigated, which are from the same part of the Nanling Range, sampled these reservoirs in very similar proportions, leading to clustering of the zircon model ages. The dense part of the array of c. 1 Ga detrital zircons on Figure 11 covers the full range of epsilon (Hf) from +11 to -10, giving potential ‘model ages’ distributed from 1.1 to 2.5 Ga, but these may just reflect more variable mixing of discrete crustal reservoirs.
Response: Thanks for the insightful comments on this issue. It is true that a peak of ca. 1.6 Ga is marked in Figure 9b. But this age peak does not indicate this period is a major episode of crustal growth in South China. It truly shows that these granites were mainly originated from the source rocks (ca. 1.6 Ga). Besides, it is true that these two granites in this study were both located in the Nanling range of South China, therefore, they might have similar source rocks as indicated by the reviewer.
It is also true that the dense part of the array of c. 1 Ga detrital zircons on Figure 11 covers the full range of epsilon (Hf) from +11 to -10 as indicated by the reviewer. It is indicated that the ca. 1.0 magmatism has variable source (both mantle and/or crust). But in figure 12, we can see that the samples were mostly plotted below the crustal reworking evolutionary line, showing that the ca. 1.0 Ga magmatic rocks were mainly caused by the remelting of the previously formed rocks (mantle and/or crustal rocks).
Comment 11: Line 329 mentions ‘abundant information on Archean rocks’. Is this fair? The three cited papers seem focussed on Proterozoic rocks and the possibility of existence of Archean rocks, not on substantive observations.
Response: We revised this expression as commented.
Comment 12: The array of zircon ages around 2.5 Ga (yours and the detrital set) is interesting and important, but could be better explained. Yes, many have +ve epsilon Hf, but they may still be second-stage melts. They form a range from DM to negative values (around -10). The plausible hypothesis is that the many granitic and detrital zircons around 2.5 were crystallized from crustal melts of material derived from the mantle between 3.6 and 2.5 Ga. We can’t tell how many Archean crust formation/addition events were responsible for generating this array, but you have a small number of analyses falling on/near DM up to c. 3.6 Ga. That’s good. A lot of >3.0 Ga Archean crustal additions are likely to have been too mafic to have much zircon, which may become abundant only in the products of re-melting mafic or TTG crust (as in your 2.9–2.5 Ga arrays).
What’s also very interesting is that this Archean signal has largely disappeared, at least from your samples, after 1.0 Ga, as if this older source is largely hidden or lost in the crust from this point in time onwards. There may now be Archean remnants down below, but it seems they are rare, and most of the younger granites and other crustal material you might sample are a product of Paleo- to Mesoproterozoic crustal additions, perhaps as I suggested above, signalling the importance of the Rodinia-forming processes.
Response: Thanks for the explanation from the kind reviewer. We learn a lot from reviewer. Although the Cathaysia Block is one of the oldest cratons in the world, no Archean rocks were exposed in this block. In addition, the Archean zircon grains were also limited found. As stated by the reviewer, several geologists believe that the unexposed Archean continental fragment might be preserved in the deep Cathaysia Block.
Comment 13: The format of your discussion, by concentrating on the individual periods, i.e. Archean, Paleoproterozoic, Meso-Neoproterozoic, seems to obscure some of these interesting features. It might help to finish section 5.1 with an overview of the whole pattern that puts these features into a more integrated context.
Response: Thanks for the valuable suggestion. We have revised the conclusion part and finish the whole crust evolutionary pattern in this section as suggested.
Comment 14: The conclusions section is short and not very informative, and does not do justice to your data patterns.
Response: We have revised the Conclusion part as commented.
Comment 15: The bottom half of Table 2 has data columns in a different order (and these are unlabelled) compared to the top half.
Response: We have revised this issue as commented.
Comment 16: l. 44; should be thermo-tectonic
Response: We have revised this word as suggested.
Comment 17: l. 48; Badu Group … … oldest rock unit (not ‘rocks’)
Response: We have revised this word as suggested.
Comment 18: l. 67; replace ‘will host crucial message’ with ‘will hold important information’
Response: As commented by the reviewer, we have used “elucidate” instead.
Comment 19: l. 78; ‘amalgamation of two blocks’. You refer to Yangtze and Cathaysia, so I guess this should read ‘amalgamation of these two blocks’
Response: We have revised the part as suggested.
Comment 20: l. 85; Kongling Group … … oldest exposed rock unit (not ‘rock’)
Response: We have revised the part as suggested.
Comment 21: l. 244; should be five populations, not three
Response: We have revised the number as suggested.
Comment 22: l. 305; Eco should be Eon
Response: We have revised the word as suggested.
Comment 23: l. 412; ‘it is summed’. What should this be? ‘It is assumed’?
Response: We have revised the part as suggested.
Comment 24: l. 421; Implication to …, should be ‘Implications for’
Response: We have revised the part as suggested.
Comment 25: l. 448; ‘unravelling’. What should this be? ‘Implying’, ‘suggesting’?
Response: We have revised the part as suggested.
Reviewer 3 Report
The reviewed manuscript presents a large set of zircon U-Pb isotopic ages as well as Lu-Hf isotopic analyses of inherited zircons from S-type granitoids from West Cathaysia Block, south China. Based on these results authors made constrains the emplacement ages and reworking history of these rock sources. The manuscript is generally clear, quite well written and conclusions are well argued.
However I have several comment for sample description and U-Pb isotope data presentation.
1. I would suggest authors to provide more careful zircon morphology description with indication in the text exact position of LA-ICP MS analyses (core or rims). This information will help to discern grains with inherited cores (typical for S-granite) and those regarded as xenogenic. Presented data don’t allow to distinguish it and more over one can even conclude that all Archaean a Proterozoic zircon are not from the inherited cores but presented by the whole grains that a rather strange and needs more interpretation. If the most inherited grains don’t reveal magmatic153 Ma and 442 Ma rims respectively its hard to exclude laboratory contamination etc. The important point for interpretation is Zr context in the rock composition, this information will help for interpretation.
2.Nessesary to perform more U-Pb data reduction used to age calculation. It would be more correct if you will use data with age discordance <10% for age calculations. Also, please, add the D, % in the Table 1 and make trimming. Please dont use unprofessional term like "low harmony degree" despite correct "discordance degree" etc.
In summary, I support the publication of this paper with moderate revisions.
Author Response
Replies to Reviewers:
First of all, thanks a lot for the constructive suggestions and comments from the anonymous reviewers. We believe that this manuscript can not be perfect without valuable comments and suggestions. We have tried our best to modify the text based on the constructive comments. Great changes were made in responding to these valuable comments. The detailed point-by-point responses are as follows:
Reviewer 3
Comment 1: 1. I would suggest authors to provide more careful zircon morphology description with indication in the text exact position of LA-ICP MS analyses (core or rims). This information will help to discern grains with inherited cores (typical for S-granite) and those regarded as xenogenic. Presented data don’t allow to distinguish it and more over one can even conclude that all Archaean a Proterozoic zircon are not from the inherited cores but presented by the whole grains that a rather strange and needs more interpretation. If the most inherited grains don’t reveal magmatic153 Ma and 442 Ma rims respectively its hard to exclude laboratory contamination etc. The important point for interpretation is Zr context in the rock composition, this information will help for interpretation.
Response: Thanks for the valuable suggestion and comments. We have specified the number and analytical locations on these zircon grains as suggested by the reviewers. In this study, the single zircon grains were analyzed for one spot (rims and cores) to avoid the laboratory contamination and the mixing ages. In addition, it can be seen from the Table 1, the rims were mostly yield ages of ca. 150 Ma and ca. 440 Ma for the Dengfuxian and Tanghu granites, respectively.
In terms of the Zr contents in the granites, we found some references on the Dengfuxian granites, however, no geochemical compositions were reported for the Tanghu granites. It was reported that the Dengfuxian Jurassic granites contain variable contents of Zr (19-133 ppm; Cao et al., 2019). The low contents of Zr might indicated low temperatures for the melt, which will explain the abundant xenocrystic zircon cores in these zircons of the Dengfuxian Jurassic granites.
Comment 2: 2. Nessesary to perform more U-Pb data reduction used to age calculation. It would be more correct if you will use data with age discordance <10% for age calculations. Also, please, add the D, % in the Table 1 and make trimming. Please dont use unprofessional term like "low harmony degree" despite correct "discordance degree" etc.
Response: We have revised this part as suggested by the reviewer. In addition, we added the concordance for the age data in Table 1.
Reviewer 4 Report
The objectives of the work are well substantiated, the geological description of the objects and the petrography of the rocks are described in full. Methods are presented correctly. The article incorporates a large amount of analytical data, correctly processed. The article contains a rather fascinating survey material on the geological history of the studied objects. In the opinion of the reviewer, the article lacks a clearer and more detailed rationale for the occurrence of all zircon age peaks
Author Response
Replies to Reviewers:
First of all, thanks a lot for the constructive suggestions and comments from the anonymous reviewers. We believe that this manuscript can not be perfect without valuable comments and suggestions. We have tried our best to modify the text based on the constructive comments. Great changes were made in responding to these valuable comments. The detailed point-by-point responses are as follows:
Reviewer 4
Comment 1: The objectives of the work are well substantiated, the geological description of the objects and the petrography of the rocks are described in full. Methods are presented correctly. The article incorporates a large amount of analytical data, correctly processed. The article contains a rather fascinating survey material on the geological history of the studied objects. In the opinion of the reviewer, the article lacks a clearer and more detailed rationale for the occurrence of all zircon age peaks
Response: Thanks for the valuable suggestion and comments from the reviewer. In this study, we mainly focus on the crustal evolution of the west Cathaysia Block, which host two major age peaks of ca. 1.0 Ga and 2.5 Ga, respectively. So we did not carry out in-depth discussion on the crustal evolution of the east Cathaysia Block, although the east Cathaysia Block host several age peaks, e.g., 2.5 Ga, 1.8 Ga, 0.8-0.9 Ga, and ca. 1.0 Ga.
Round 2
Reviewer 2 Report
As for the first review, I think your contribution provides useful data on the setting of granite suites and crustal evolution in the West Cathaysia Block, especially in relation to the inherited zircons, and you have slightly improved the link to important tungsten deposits. However, some other aspects have not been fully resolved.
I am still unsure why you highlight ‘explosive magmatism’ in the first sentence of the Abstract. To me this means violent volcanism. Are you specifically considering the types of magmatism that involve fluid/vapour saturation and exsolution, and may form magmatic-hydrothermal deposits? If this is the case, it would help the readers’ understanding if you put this phrase after mentioning the ore deposits.
I cannot understand why you are still discussing Hadean zircons. Now you highlight the one extreme example with a crystallization age of 1051 Ma, (and epsilon(t) of -35), extrapolated back to DM at 4061 Ma, using the fixed ‘crustal’ ratio 176Lu/177Hf of 0.015. This is unsound – it is not appropriate to place significance on this single result (especially since two other anomalous results with T(DMc) >4.5 Ga have been justifiably ignored). The crystallization age and epsilon value are so remote from the DM curve that the model age, dependent on the actual but unknown 176Lu/177Hf of the source rock, is highly uncertain (see Vervoort, 2014, Encyclopedia of Scientific Dating Methods). Indeed, the uncertainty on the actual Lu/Hf ratio is so large that the model age could be anywhere between about 3 and 5 Ga. Moreover, if the source is felsic, an Archean TTG crust is understood to have a lower Lu/Hf than modern ‘average crust’ (e.g. Gardiner et al. 2018, Precamb. Res.), which would lower the T(DMc) age of this and perhaps other Proterozoic zircons that have negative Hf epsilon(t).
You should certainly remove the reference to Hadean crust in the Conclusions (Item 1), and I see no need for a detailed section 5.1.1. on Hadean crust, because it is barely relevant to the patterns in your own data, is not relevant at all to the tungsten mineralization, and comes to no satisfactory conclusion.
Crustal incubation time is a useful concept, but again, it embodies the uncertainty in T(DMc), so it should be used cautiously.
I have noted several discrepancies in zircon ages between text, figures and supplementary tables. This mainly relates to the older ages. The abstract gives the oldest zircon as 3651 Ma, which does not appear on the plots. Supplementary Table 1 shows it is highly discordant, so the age has little meaning, and you should quote the oldest concordant age of 3395 Ma.
Line 277 also needs changing from 3651 to 3395 Ma, because 3651 failed the concordance filter.
In the histogram of Figure 6, the data bars for the Tanghu granite zircon ages do not appear to correspond to the numbers of grains in either of the tables.
Figure 1 is still referred to in the text as Fig. 1a and fig. 1b. But the caption has been fixed.
Figure 2: the caption has been modified, but the text on the figure (2b) itself has not been changed from ‘granites’ to ‘granite’. It is not clear if the sample was taken from this outcropping sheet. If the scale bar on the micrograph is indeed correct (did you check?) then this is a microgranite; in its setting I would call it an aplite. Is it representative of the sample used in the study?
Figure 3: caption and coordinates fixed; ‘micrographs’ should be ‘micrograph’.
Figure 4 caption: in new text, the young ages are stated incorrectly to be “207Pb/236U” ages when they are 206Pb/238U ages.
The heading for Section 5.2. (Implications for the regional tungsten mineralization) has become attached to the caption for Fig. 12.
Table 2 has not yet been corrected in the version I downloaded from the journal site. The bottom half of the table has data columns in a different order (and these are unlabelled) compared to the top half.
You will need to check the text again very carefully for missing words and other minor errors. I did not have time to make a detailed list.
Author Response
Replies to Reviewers:First of all, thanks a lot for the constructive suggestions and comments from the anonymous reviewers. We believe that this manuscript can not be perfect without valuable comments and suggestions. We have tried our best to modify the text based on the constructive comments. Great changes were made in responding to these valuable comments. The detailed point-by-point responses are as follows:
Reviewer 1
Comment 1: I am still unsure why you highlight ‘explosive magmatism’ in the first sentence of the Abstract. To me this means violent volcanism. Are you specifically considering the types of magmatism that involve fluid/vapour saturation and exsolution, and may form magmatic-hydrothermal deposits? If this is the case, it would help the readers’ understanding if you put this phrase after mentioning the ore deposits.
Response: Thanks for the valuable suggestion and comments. The aim to highlight explosive magmatism is that it can cause the formation of the magmatic-hydrothermal deposits. But in this version, we delete the the expression, due to the concern of the reviewer.
Comment 2: I cannot understand why you are still discussing Hadean zircons. Now you highlight the one extreme example with a crystallization age of 1051 Ma, (and epsilon(t) of -35), extrapolated back to DM at 4061 Ma, using the fixed ‘crustal’ ratio 176Lu/177Hf of 0.015. This is unsound – it is not appropriate to place significance on this single result (especially since two other anomalous results with T(DMc) >4.5 Ga have been justifiably ignored). The crystallization age and epsilon value are so remote from the DM curve that the model age, dependent on the actual but unknown 176Lu/177Hf of the source rock, is highly uncertain (see Vervoort, 2014, Encyclopedia of Scientific Dating Methods). Indeed, the uncertainty on the actual Lu/Hf ratio is so large that the model age could be anywhere between about 3 and 5 Ga. Moreover, if the source is felsic, an Archean TTG crust is understood to have a lower Lu/Hf than modern ‘average crust’ (e.g. Gardiner et al. 2018, Precamb. Res.), which would lower the T(DMc) age of this and perhaps other Proterozoic zircons that have negative Hf epsilon(t).
Response: Thanks for the valuable suggestion and comments. We accept the valuable suggestion from the kind reviewer to deleted the Section 5.1.1. In addition, the section sequences were rearranged.
Comment 3: You should certainly remove the reference to Hadean crust in the Conclusions (Item 1), and I see no need for a detailed section 5.1.1. on Hadean crust, because it is barely relevant to the patterns in your own data, is not relevant at all to the tungsten mineralization, and comes to no satisfactory conclusion.
Response: Thanks for the valuable suggestion and comments. These references related to the section 5.1.1 of the former version were removed in this revised version as suggested by the kind reviewer. In addition, the reference sequences and the citation in the main text were also revised.
Comment 4: Crustal incubation time is a useful concept, but again, it embodies the uncertainty in T(DMc), so it should be used cautiously.
Response: Thanks for the kind reminding.
Comment 5: I have noted several discrepancies in zircon ages between text, figures and supplementary tables. This mainly relates to the older ages. The abstract gives the oldest zircon as 3651 Ma, which does not appear on the plots. Supplementary Table 1 shows it is highly discordant, so the age has little meaning, and you should quote the oldest concordant age of 3395 Ma.
Comment 6: Line 277 also needs changing from 3651 to 3395 Ma, because 3651 failed the concordance filter.
Comment 7: n the histogram of Figure 6, the data bars for the Tanghu granite zircon ages do not appear to correspond to the numbers of grains in either of the tables.
Response: We have revised this part as suggested. In addition, after assessing the role of the Figure 6, we decided to remove this figure, since the highest peak of the ages in the histogram are ca. 440 Ma which conceals the other peaks of ages.
Comment 8: Figure 1 is still referred to in the text as Fig. 1a and fig. 1b. But the caption has been fixed.
Response: We have revised this part as suggested.
Comment 9: Figure 2: the caption has been modified, but the text on the figure (2b) itself has not been changed from ‘granites’ to ‘granite’. It is not clear if the sample was taken from this outcropping sheet. If the scale bar on the micrograph is indeed correct (did you check?) then this is a microgranite; in its setting I would call it an aplite. Is it representative of the sample used in the study?
Response: Thanks for the valuable suggestion and comments. The granites in this studies is typical in the Dengfuxian pluton. We also checked our data, we are sure about that. From the micrograph, we can conclude that the minerals in this granites have small size as shown in Figure 2c of the main text, but its minerals assemblage is similar to the granite which contain quartz, potassium feldspar, plagioclase, muscovite and so on. Due to the small mineral size, we mostly call them fine-grained granites. But as stated by the reviewer, the aplite should be also correct.
Comment 10: Figure 3: caption and coordinates fixed; ‘micrographs’ should be ‘micrograph’.
Response: We have revised the related content as suggested.
Comment 11: Figure 4 caption: in new text, the young ages are stated incorrectly to be “207Pb/236U” ages when they are 206Pb/238U ages...'
Response: Thanks for the valuable suggestion and comments. We have revised this part as suggested.
Comment 12: The heading for Section 5.2. (Implications for the regional tungsten mineralization) has become attached to the caption for Fig. 12.'
Response: We have revised this part as suggested.
Comment 13: Table 2 has not yet been corrected in the version I downloaded from the journal site. The bottom half of the table has data columns in a different order (and these are unlabelled) compared to the top half.
Response: The Table 2 has been fixed as commented.
Comment 14: You will need to check the text again very carefully for missing words and other minor errors. I did not have time to make a detailed list.
Response: Thanks for the valuable suggestions and insightful comments on this work. We have checked the whole text and the errors were fixed using the revision mode function of the Word software.
