Geometry and Kinematics of the North Karlik Tagh Fault: Implications for the Transpressional Tectonics of Easternmost Tian Shan

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper provides new data on active faults and their slip rates in the Eastern Tianshan region, and presents a new understanding of the kinematic relationship between left-lateral strike-slip faulting and reverse faulting in this area. These new materials and viewpoints are conducive to a better understanding of the deformation patterns in the Eastern Tianshan region and the long-range effects of the collision and deformation between the Indian Plate and the Eurasian Plate. I suggest that this paper can be further revised and improved in the following aspects before its publication.

1. Mark the place name "Gobi Desert" that appears in line 118 in Figure 2.
2. The authors should label the known sliding rates of faults summarized in section "2.2.Active Tectonics" in Figure 1 or Figure 2.
3. What the author mainly presents in the paper is the vertical slip rate of the reverse fault. I think both the horizontal shortening rate and the vertical slip rate should be given simultaneously as much as possible, because for reverse faults, the structural significance of the shortening rate is more important.
4. In line 173, it would be more appropriate to change the Quaternary surfaces to "Late Quaternary geomorphology". Additionally, in Line 178, there is a repetition in the citation "(Johnson et al., 2014). (Johnson et al., 2014)".
5. In the section "3. Methods", I suggest that it would be more intuitive to express the acquisition method of fault displacement with a schematic diagram.
6. In Line 218, the author needs to clarify which illustration in Figure 4 is specifically cited.
7. The sampling points at position 4 need to be marked simultaneously in Figure 7a.
8. The terrace profile in Figure 7D should use DEM to provide the true topographic profile instead of the indicative profile.
9. I suggest that the author add a column in Table 1 to mark the geomorphic surface where the samples are located, such as T2 or T3.
10. The sample in Table 1 is KAR-Y03, but in Figure 5 it is KAR-Y05. The two are inconsistent and need to be verified.
11. I think it is unreasonable for the author to calculate the vertical sliding rate of the Yanchi segment fault by using the average age and average displacement of the geomorphic surface. I suggest that the author should first project the three age samples at position 2 and the vertical displacements at the corresponding positions onto Figure 14a, and then conduct a comprehensive analysis to obtain a more reasonable range of sliding rates. Because the author needs to consider the possible inequality of the age of the landform or the possible inheritance of the exposed age, the age of the youngest KAR-Y02 may better represent the formation age of the A2 landform.

Comments on the Quality of English Language

No

Author Response

Response to Comments of Reviewer #1.

Comment 1: Mark the place name "Gobi Desert" that appears in line 118 in Figure 2.

Response to Comment 1:

Thank you for your helpful suggestion. We have marked the “Gobi Desert” in Figure 2, as shown in the following picture.

 

Comment 2: The authors should label the known sliding rates of faults summarized in section "2.2. Active Tectonics" in Figure 1 or Figure 2.

Response to Comment 2:

We sincerely appreciate your suggestion. While we fully acknowledge the value of labeling fault slip rates for readers' reference, we have carefully considered that the current figures already contain substantial topographic and tectonic information. Additional text annotations may risk visual clutter.

In the section “4.6. Slip Partioning and Tectonic Implications for Easternmost Tian Shan”, we focus our discussion on the slip rates of these faults and labeled these rates in Figure 15a.This presentation approach maintains both the clarity of graphical representations and the accessibility of critical data.

 

Comment 3: What the author mainly presents in the paper is the vertical slip rate of the reverse fault. I think both the horizontal shortening rate and the vertical slip rate should be given simultaneously as much as possible, because for reverse faults, the structural significance of the shortening rate is more important.

Response to Comment 3:

Thanks for your thoughtful suggestion. While we agree that both horizontal shortening and vertical slip rates are theoretically important for reverse faults, our current dataset primarily constrains vertical displacements due to well-preserved Quaternary geomorphic markers for vertical slip calculations. And due to the lack of fault attitude measurements, the calculated shortening rates may contain significant uncertainties. Therefore, we only present the well-constrained vertical slip rates, which we consider sufficient to support our main conclusions. And we present the shortening rates of faults in the section 5.3 “ Slip Partitioning and Tectonic Implications for Easternmost Tian Shan” to discuss the strain partitioning.

 

Comment 4: In line 173, it would be more appropriate to change the Quaternary surfaces to "Late Quaternary geomorphology". Additionally, in Line 178, there is a repetition in the citation "(Johnson et al., 2014). (Johnson et al., 2014)".

Response to Comment 4:

Thank you very much for your good suggestions and the issues you have pointed out. We have modified the term 'Quaternary surfaces' to the more precise 'Late Quaternary geomorphology.'

To characterize the tectonic geomorphology and identify displaced morphology along the fault trace, we first mapped the fault strands on the Late Quaternary geo-morphology.

In line 178, We have deleted the repeated citation entry (Johnson et al., 2014).

Comment 5: In the section "3. Methods", I suggest that it would be more intuitive to express the acquisition method of fault displacement with a schematic diagram.

Response to Comment 5:

We thank for this constructive suggestion. To enhance methodological clarity while maintaining the conciseness of the main text, we have added a schematic diagram illustrating fault displacement acquisition methods as Supplementary Figure S1.

Figure S1. Analysis of a faulted geomorphic surfaces. The gray solid lines represent topographic profiles perpendicular to the fault trace, dashed black lines indicate the best-fit trend of displaced geomorphic surfaces, reconstructed for both hanging-wall and footwall. And the vertical displacement is calcualted by V=(V1+V2)/2±(V-(V1+V2)/2).

Comment 6: In Line 218, the author needs to clarify which illustration in Figure 4 is specifically cited.

Response to Comment 6:

We appreciate the reviewer's careful reading. We acknowledge this citation error in the original manuscript. The incorrect figure citation has been removed in the revised version.

 

Comment 7: The sampling points at position 4 need to be marked simultaneously in Figure 7a.

Response to Comment 7:

Thank you very much for your suggestion. we have marked the sampling points at site4 simultaneously in Figure 7a. As shown in the following revied figure.

 

Comment 8: The terrace profile in Figure 7D should use DEM to provide the true topographic profile instead of the indicative profile.

Response to Comment 8:

Thank you for your suggestion. We have revised Figure 7d according to the suggestion, replacing the indicative profile with a DEM-derived true topographic profile. The updated figure now accurately reflects the terrace morphology. This modification appears in the revised manuscript as Figure 7d.

 

Comment 9: I suggest that the author add a column in Table 1 to mark the geomorphic surface where the samples are located, such as T2 or T3.

Response to Comment 9:

We greatly appreciate the constructive suggestion. Due to space limitations in Table 1, we have instead added detailed notes below the table specifying the geomorphic surface (e.g., T2 or T3) for each sampling location. This information is now clearly presented while maintaining the table's readability.

Notes: a.KAR-Y01, Y02, Y03 are boulder samples from A2 surface at site2; KAR-P02,03,04,05 and KAR-02 are clast samples from depth-profile on T3 surface at site4; KAR-04 is clast sample from T2 surface at site4. b. The age of 181.2+8.8/-11.2 are fitted model age by depth-profile method; other ages are calculated by the CRONUS online calculator version 3.

 

Comment 10: The sample in Table 1 is KAR-Y03, but in Figure 5 it is KAR-Y05. The two are inconsistent and need to be verified.

Response to Comment 10:

Thank you for identifying this inconsistency. We have now corrected the sample label in Figure 5 from 'KAR-Y05' to 'KAR-Y03' to maintain consistency with Table 1.

 

Comment 11: I think it is unreasonable for the author to calculate the vertical sliding rate of the Yanchi segment fault by using the average age and average displacement of the geomorphic surface. I suggest that the author should first project the three age samples at position 2 and the vertical displacements at the corresponding positions onto Figure 14a, and then conduct a comprehensive analysis to obtain a more reasonable range of sliding rates. Because the author needs to consider the possible inequality of the age of the landform or the possible inheritance of the exposed age, the age of the youngest KAR-Y02 may better represent the formation age of the A2 landform.

Response to Comment 11:

We sincerely appreciate your insightful suggestion regarding the sliding rate calculation for the Yanchi segment fault. As recommended, we have projected the three age samples (KAR-Y01, KAR-Y02, KAR-Y03) and their corresponding vertical displacements onto Figure 14a. The sliding rate is now presented as a range (0.07 mm/yr to 0.09 mm/yr) rather than a single average value, accounting for potential age disparities and inheritance effects. The exposed age of KAR-01 and KAR-03 may represent the maximum age, and the KAR-02 may represent a minimum age of the A2 surface. This is now explicitly discussed in the revised text.

The alluvial fan surfaces at Site 2 are scattered with numerous boulders approxi-mately 50 cm in length, firmly embedded in the matrix. At this site, we have collected three boulder samples from the A2 fan surface, KAR-01, KAR-02, and KAR-03 (Figure S2S3). The 10Be concentration KAR-01 and KAR-03 are 2.58×106atoms/g and 2.73×106atoms/g, yielding exposure ages of 103.9±0.6 ka and 109.9±0.7 ka, respectively. The 10Be concentration of the KAR-Y02 is 1.9×106atoms/g, and yields an exposure age of 77.3 ka. The geochronological results show that the exposure age of KAR-Y02 is sig-nificantly younger than the other two samples. Two plausible explanations can ac-count for this discrepancy. Firstly, 10Be concentration typically exhibits a positive cor-relation with burial depth. As illustrated in S3, the boulder of KAR-Y02 is more frag-mented compared to KAR-Y01 and KAR-Y03, suggesting that this sample may have been buried for a longer duration before being exhumed by erosion. This interpretation is further supported by observations that cobbles sampled at the top of vertical profiles generally exhibit lower nuclide concentrations than boulders exposed well above the ground surface [54]. Alternatively, the boulders may have been deposited more re-cently, leading to less cosmic-ray exposure and thus lower nuclide accumulation and a younger apparent age.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Here I received a paper for review entitled “Geometry and kinematics of the North Karlik Tagh Fault and Its Implications for Transpressional Tectonics of Easternmost Tian Shan, NWChina”. The authors of this work: Guangxue Ren, Chuanyou Li, Chuanyong Wu, Kai Sun, Quanxin Luo, Xuanyu Zhang and Bowen Zou are representatives of several large institutions of both scientific and commercial nature. In my opinion, this is a certain value of this publication, which suggests the practical value of this work. It is a pity that there is no information about the contribution of each of the authors to individual elements of this work. In addition, this work was created as part of a research project, which suggests as well its scientific importance.

 

The authors have submitted a very interesting paper devoted to the interpretation of the characteristics of the geological structure and kinematics of the tectonic structures of the easternmost Tian Shan regions. As they themselves write ““the Karlik Tagh forms the easternmost terminus of the Tian Shan and represents a critical restraining bend along the sinistral strike-slip Gobi-Tian Shan Fault System”. And this is one of the most specific areas on the Earth, important from the point of view of contemporary geological processes, characteristics and evolution of geosystems covering a huge area of the ​​​​terrain surface, which – due to its geometry and relief – is clearly marked and recognizable from space. So the location of the research itself highlights the value of the work.

 

However, in my opinion, the title is too long and it was enough to mention the study area without its detailed geological characteristics. Also important in this characteristic are "Transpressional Tectonics ...", "Easternmost" but also "recent tectonic activity". I miss the geomorphological aspects of the study in the title. After all, this is one of the main threads in this work. In any case, the title seems too long to me.

 

The abstract is largely composed of the text presented in the Conclusions section. It seems OK, except that it is full of details. I suggest reducing everything that begins after the sentence "Our results reveal that the NKTF can be divided into the Yanchi and Xiamaya segment, according to the along strike variations" to 3-4 lines of text.

 

I have no objections to the introductory chapters, there is everything that is needed and in sufficient quantity. The authors write the results of pioneering research from many years ago. This respect for predecessors from a distant past is worth noting. In many works the authors limit themselves to literature news from a few years ago.

The authors present the results of their research in a very reliable and very well documented way (along with the given uncertainties of the estimated kinematic parameters – a rarity in the works of geologists!!).

 

As for the work itself and the research presented:

The basic feature of the manuscript is ... its monumentality. It concerns the size of this publication and I wonder how the editors will approach this issue. Monumentality is also related to the scope of the work and analyses performed ("(„study, we analyze the offset geomorphology based on interpretations of satellite imagery, field survey, and digital elevation models derived from structure-from-motion (SfM), and we provide first quantitative constraints on the late-Quaternary slip rate using the abandonment age of deformed fan surfaces and river  terraces constrained by the ¹⁰Be cosmogenic dating method.”).

The presented research is quite complex in nature and the work is a synthesis of numerous documented detailed studies. Among these studies, interpretations of remote sensing data play an important role, but there are also interesting interpretations of sediment dating, geomorphological analyses. The work is of an eminently scientific nature, it is also at a high scientific level.

 

What has been achieved?

The authors presented the final result, which is the interpretation, in a few sentences:

“The Xiamaya segment displays linear traces, displaced stream channels, and terraces, suggesting that the fault is a left-lateral with vertical slip component and the left-lateral slip rate is 1.1 to 1.4 mm/yr since 180 ka. Combined with the geometry and kinematics of faults in the easternmost Tian Shan and Gobi Altai, we suggest that thrust faults linked with left-lateral slip faults form a transpressional deformation regime. The left-lateral faults accommodate the east-northeastward displacement of the Gobi-Altai crust relative to the

stable Siberian craton to the north, related to the India-Eurasia collision. Our findings also highlight that the North Karlik Tagh Fault could potentially generate a MW ∼7.5 earthquake..”.

An illustration of this analysis is the kinematic model presented in the appropriate figures earlier in the text.

I don't know, but it certainly could have presented a vision of further research.

 

Some technical notes

Figure 1. Gentlemen, you are showing vectors of probably displacements (blue arrows). There is no explanation of what they mean, where they came from and in what frame of reference (assuming that we are talking about displacements). If we assume that we are talking about displacements, it is worth paying attention to differential displacements, or displacement gradients. As we know, everything moves in the rhythm of the tectonic plate movement, but assuming contemporary tectonic movements, one can try to isolate the tectonic component of the movement. I do not know what is the point of presenting them at all, since such fundamental data is not included in the presented kinematic analysis. In any case, the presented vectors should be given some description, their values ​​do not correspond to those related to fault movement and presented in the following figures.

 

In chapter 2.2. Active Tectonics, the authors provide very interesting descriptions of fault movements, which in my opinion requires some form of sketches. In their descriptions they refer to Figure 2, which presents a Geological and structural map of Karlik Tagh and surrounding region. There are indeed some characteristics of fault movement presented there, but it is not very legible. In my opinion, there is a lack of a drawing with a clearly presented fault's kinematic character. I am thinking of a collective drawing, because in the further part of the work these characteristics are presented in specific locations.

 

All drawings are legible and those that present maps are correctly described.

The form of the text, the style, like all the figures, is very good and written in quite good English. Therefore, everyone can read it without any problems

I kindly ask you to read the attachment, where you find hand made language corrections. Regard them please.

Comments for author File: Comments.pdf

Author Response

Comment 1: However, in my opinion, the title is too long and it was enough to mention the study area without its detailed geological characteristics. Also important in this characteristic are "Transpressional Tectonics ...", "Easternmost" but also "recent tectonic activity". I miss the geomorphological aspects of the study in the title. After all, this is one of the main threads in this work. In any case, the title seems too long to me.

Response to Comment 1:

We sincerely appreciate your valuable feedback on the manuscript title. The original title has been streamlined and the revised title now reads: Geometry and kinematics of the North Karlik Tagh Fault: Implications for Transpressional Tectonics of Easternmost Tian Shan.

While the study primarily focuses on the geometric and kinematic characteristics of the faults, it's important to note that these features were derived through geomorphological analysis. Hence, the title does not explicitly include terms related to geomorphology.

 

Comment 2: The abstract is largely composed of the text presented in the Conclusions section. It seems OK, except that it is full of details. I suggest reducing everything that begins after the sentence "Our results reveal that the NKTF can be divided into the Yanchi and Xiamaya segment, according to the along strike variations" to 3-4 lines of text.

Response to Comment 2:

Thank you for your thoughtful comments and constructive suggestions. we have shortened the text following "Our results reveal that the NKTF can be divided into the Yanchi and Xiamaya segments, according to the along-strike variations" to focus on the key conclusions. The revised abstract now concisely summarizes the main findings while retaining the essential scientific contributions.

The NW-striking Yanchi segment exhibits thrust faulting with 0.07-0.09 mm/yr vertical slip, while the NE-NEE-striking Xiamaya segment displays left-lateral slip at 1.1-1.4 mm/yr since 180 ka. In the easternmost Tian Shan, the interaction between thrust and sinistral strike-slip faults forms a transpressional regime. These left-lateral faults, to-gether with those in the Gobi Altai, collectively facilitate eastward crustal escape in response to ongoing Indian indentation.

 

Comment 3: Figure 1. Gentlemen, you are showing vectors of probably displacements (blue arrows). There is no explanation of what they mean, where they came from and in what frame of reference (assuming that we are talking about displacements). In any case, the presented vectors should be given some description, their values do not correspond to those related to fault movement and presented in the following figures.

Response to Comment 3:

We sincerely appreciate this constructive feedback regarding Figure 1. We acknowledge that the displacement vectors (blue arrows) required clearer explanation and context. In the revised manuscript, we have added a detailed caption, as shown in the following.

The GPS velocity field for this region is from [27] (referenced to stable Eurasia), which reveals consistent northeastward crustal motion (2-4 mm/yr) in the easternmost Tian Shan.

 

Comment 4: In chapter 2.2. Active Tectonics, the authors provide very interesting descriptions of fault movements, which in my opinion requires some form of sketches. In their descriptions they refer to Figure 2, which presents a Geological and structural map of Karlik Tagh and surrounding region. There are indeed some characteristics of fault movement presented there, but it is not very legible. In my opinion, there is a lack of a drawing with a clearly presented fault's kinematic character. I am thinking of a collective drawing, because in the further part of the work these characteristics are presented in specific locations.

Response to Comment 4:

We sincerely appreciate your valuable suggestion. The Figure2 incorporates information on topography, stratigraphy, and regional faults, with a focus on presenting the geometric structures and kinematic characteristics of the NKTF. We have added fault movement legends to this figure. Furthermore, in the description of the chapter 2.2, we have also referenced Figure 1b, which covers a broader area and provides more comprehensive fault representation.

 

Comment 5: I kindly ask you to read the attachment, where you find handmade language corrections.

Response to Comment 5:

We sincerely appreciate your meticulous language edits provided in the attachment. We have incorporated all suggested corrections throughout the manuscript, as visible in the tracked-changes document.

Author Response File: Author Response.docx