Implications of the ongoing rock uplift in NW Himalayan interiors

Dey, Saptarshi; Thiede, Rasmus C.; Biswas, Arindam; Chauhan, Naveen; Chakravarti, Pritha; Jain, Vikrant

doi:https://doi.org/10.5194/esurf-9-463-2021

Articles | Volume 9, issue 3

https://doi.org/10.5194/esurf-9-463-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/esurf-9-463-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 9, issue 3

Research article

|

02 Jun 2021

Research article |

| 02 Jun 2021

Implications of the ongoing rock uplift in NW Himalayan interiors

Saptarshi Dey, Rasmus C. Thiede, Arindam Biswas, Naveen Chauhan, Pritha Chakravarti, and Vikrant Jain

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Final revised paper (published on 02 Jun 2021)
Supplement to the final revised paper
Preprint (discussion started on 18 Jun 2020)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of "Structural variations in basal decollement and internal deformation of the Lesser Himalayan Duplex..."', Stefan Hergarten, 15 Jul 2020
- AC1: 'reply to comments on 'Kishtwar window' paper', Saptarshi Dey, 15 Jul 2020
  - EC1: 'Answers to reviewers', Richard Gloaguen, 15 Jul 2020
    - SC1: 'short comment to editor on 'Kishtwar window'paper', Saptarshi Dey, 15 Jul 2020
RC2: 'Review of "Structural variations in basal decollement and internal deformation of the Lesser Himalayan Duplex trigger landscape morphology in the NW Himalayan interiors"', Adam Forte, 15 Jul 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Saptarshi Dey on behalf of the Authors (14 Sep 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Sep 2020) by Richard Gloaguen

RR by Stefan Hergarten (20 Oct 2020)

Suggestions for revision or reasons for rejection

The revised version has indeed been improved in some points. In particular, the introductory sections and the description of the methods has become clearer. In principle, the results have also been enlarged by including results of luminescence dating.

I must admit that these methods go beyond my area of expertise, so I am afraid that an additional reviewer is needed. I am also afraid that these results raise more new questions than they answer. How does the
hypothesis of changes in the course of the river fit into the picture of the geomorphic analysis?

At least, the new results do not fix the problem that it is very difficult to follow the line how all these results are brought together. There are many interesting results, but these are still somewhat isolated and bringing them together remains vague.

Apart from this general problem, I am a bit concern about some little things. Just to mention a few examples:

- Not all references to the figures are correct, e.g., those to Fig. 2 on page 13 do clearly not refer to Fig. 2., and I do not see where Fig. 3a shows rapids as mentioned in line 483.

- There are still several inconsistent sentences and, e.g., the word ``river'' has been capitalized unsystematically at some occurrences now. This is not really a problem and can easily be fixed, but it gives me the feeling that not all coauthors have read the text thoroughly before submitting.

- The geomorphic data still seem to be not fully consistent. Let us look, e.g., at the channel channel slope and the steepness index ksn in Fig. 6. They are related to each other by the factor A^0.9 where A is the catchment size which increases downstream, i.e., from the right to the left. Let us start from the right-hand edge where the slope increases while ksn immediately decreases to the left. Or look how much the large double peak at x = 10 km is higher than the ksn values at x < 10 km, and how much lower the relative difference in slope is. This is in principle impossible. I am quite sure that this is not a fundamental problem, maybe even only inconsistent smoothing of the data. I think it can be fixed easily, but such things just do not make it easier to trust that everything is technically sound -- although the most importing parts are probably.

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RR by Yann Gavillot (26 Oct 2020)

Suggestions for revision or reasons for rejection

I am listing below my main concerns and recommendations.

1. Throughout the paper the authors are unclear or ambiguous how they characterize and interpret patterns associated with “faulting”, “growth”, or “active surface faulting” across the Kishtwar Window. For instance their cross section and map figures clearly indicate their interpretation of an out-of-sequence surface breaking fault, however, in the text their interpretation is unclear going back and forth between implying active faulting on MHT crustal ramps (no surface faulting), to active duplex growth, to active out-of-sequence deformation (surface faulting) that links to a crustal ramps. The authors need to clarify and revise many of the structural terms and interpretations being used in the text to streamline their interpretations.

2. The authors need to provide more justification in their interpretation that morphometric indices provide evidence for or against active out-of-sequence faulting. In many places, the authors jump to their preferred model but failed to recognize that these morphometric indices or other structural data are non-unique! In other words, the authors do not provide enough justification why or why not the pattern observed can be attributed to a specific deformation pattern. The authors have a tendency to have model-driven interpretations and do not justify why other structural models or non-tectonic controls are not permissible. For instance, many of the arguments used by the authors as “evidence” of an active out-of-sequence fault within the KW are not justified and highly speculative. Many of the observation described by the authors can be equally or more easily explained of the presence of an exhumed duplex floor thrust, and all of the knickpoints pattern are controlled by translation across MHT ramp which require no surface faulting.

3. I believe there would be strong benefits in this paper to recognize that this an open-ended interpretation (active out-of-sequence thrusting versus translation across MHT ramp). A more constructive approach would be to offer two possible viable structural interpretation of the cross section diagrams (out-of-sequence thrust versus and exhumed duplex floor thrust with active deeper ramp along the MHT), and let the reader see how each models can explain some of the observations.

4. Interpretation of duplex or cross section needs revision. There are several keys issues with the cross section listed below:

a. The figure shows an out-of-sequence thrust in the KW core that projects to cut roof thrust. Because the author interprets as an out-of-sequence thrust, it implies it does not join the roof thrust as duplex. Hence this is not consistent with the discussion in the text that there is active/ongoing duplex growth. The diagram imply growth within KW occurs via out-of-sequence thrusting (ramp #1), and translation of above MHT ramp (ramp #2). There is no active/ongoing duplex kinematics as shown in the diagram.
b. This cross section does not appear to be restorable. Even If one would attempt to retro-deform this cross section, it would show no duplex nor significant crustal thickening, but instead a single nappe in the LHS that has been faulted by an out-of-sequence fault.
c. This cross section has major implications at odds with constraints from regional shortening absorbed in the Kashmir Himalaya orogenic wedge. Available long-term kinematics from low-temperature thermochron, Pleistocene-Holocene shortening rates, and geodetic shortening rates across the Kashmir Sub-Himalaya imply that no significant surface faulting within the KW or High Himalaya is needed to account for the total budget of plate convergence absorbed in the Kashmir Himalaya.
d. The cross-section diagram is not consistent with duplex kinematics. Instead this pattern is more aligned with antiformal dome with flexural flow within the structure (~local crustal extrusion model).

5. Calculations and analyses of the shortening rates need substantive improvements. The author makes incorrect assumptions that incision rate deduced west of KT and KW can be translated to a shortening rate on the MCR1 fault ramp within the KW. For instance, if looking at Fig. 8b, slip on the MCR-2 would not be translated with the same geometry to the surface, as the underlying ramp-flat geometry would predict very little rock uplift translated to the surface. I would recommend the author deletes text on the shortening rate, because there is no data of incision rates in the upper plate of the inferred out-of-sequence thrust to justify a calculation of shortening rate, and it is actually not relevant to the main points of the paper. This section appears out of place for this paper.
6. Much of the text and analyses on the OSL ages appear rushed and needs revision. Details of OSL lab methodology ought to be placed in the supplement.

7. There are still many unclear sentences that need revision. At times, there are also odd choices of words and excessive use of unnecessary adjectives.

Referee Report: PDF

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ED: Reconsider after major revisions (26 Oct 2020) by Richard Gloaguen

AR by Saptarshi Dey on behalf of the Authors (07 Dec 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Mar 2021) by Richard Gloaguen

RR by Anonymous Referee #2 (22 Mar 2021)

Suggestions for revision or reasons for rejection

In their revised manuscript, ‘Implications of the ongoing rock uplift in NW Himalayan interiors’ Dey et al., combine topographic analyses with a variety of field observations, dating of Quaternary deposits, and synthesis of previous work to explore the extent to which the surface geology and geomorphology helps to constrain the subsurface structural geometry in the northwestern Himalaya. The paper is improved from the original submission and the authors have addressed some of the questions I had on the first draft. There are still some issues with following the arguments, though mostly all the information is there, there just needs to be a little more thought given to organization or explanation as to where the authors are taking the readers. In a few places the authors need to provide a bit more explanation that was asked for in the previous review as well (e.g., the specific stream power calculation, though ultimately these values are barely used in the paper, so the details might not matter that much).

1. This comment is mainly on the discussion as a whole, but it kind of extends to the results as well. At present, it’s kind of hard to follow the connections between the various data being presented, i.e. what is the relevance of the different parts to each other. You go through some of this in the very beginning of the paper, but by the time a reader gets to the results and discussion, it gets harder to see these connections. You have the start of a description of what you’re going to do near the beginning of your discussion (L483-491), but I think this could benefit from a little expansion and a bit more specificity before you launch into the rest of the discussion.

2. Where every thing comes together is Section 5.5, but as highlighted in some of my line by line comments below, this section is hard to follow and it’s not clear what model you prefer or if you prefer any of them. It seems like you are arguing against the Gallivot duplex model at the beginning, but then you agree with parts of it. In the end, it seems like the data you have assembled can’t discriminate between some of these options or clarify some of the details. This is fine, but you just need to be much more explicit about it, i.e. explain from the beginning that you can’t differentiate on the basis of the data you have and then go through the relevant data and how it does or does not support various models. You tell us this is the case in the introduction, but this final discussion section meanders around this point a bit.

3. Knickpoints vs knickzones: There is some lack of consistency between defining something as knickpoint vs a knickzone which leads to confusion. Both K1 and K2 seem to both be knickpoints and knickzones. In figure 7, they are both (i.e., there are steepened zones highlighted named K1 and K2 and also discrete point named K1 and K2). In the text, K1 is described more as knickzone, but K2 is described as a knickpoint and a knickzone in section 5.1.2. Are the points for K1 and K2 just the upstream beginning of the knickzones? If that is the case, maybe distinguishing them with different names (e.g. K1_s, K2_s or something). It makes it challenging to follow how we are suppose to interpret these features.

Line by line:

L273-283: Could you provide a little more detail on this calculation, kind of just fill in the gaps. Specifically, I assume you use the width measurements from the previous section in your calculation of SSP? How are you estimating discharge? Again, I would assume you’re routing the TRMM rainfall, but saying this is necessary. Do you assume a runoff ratio of 1? Do you have any data that would allow you to estimate if a constant runoff ratio is warranted (regardless of the specific value), etc?

L392-402: Some of this text is repeated from your background section. Maybe keeping the previous observations in the background and your new observations here in the results would be better.

L652-653: It’s not clear which field observations don’t work with the duplex model or what the differences would be. Later (L658) you mention that the Gavillot model suggest no surface-faulting, but in the sentence that precedes this, you describe that the observed deformation could be a product of active faulting, crustal buckling, or internal folding, so the incompatibility of these observations with this model is not clear.

L669-672: This seems out of place and more like something that belongs in your conclusion.

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RR by Stefan Hergarten (23 Mar 2021)

ED: Publish subject to minor revisions (review by editor) (23 Mar 2021) by Richard Gloaguen

AR by Saptarshi Dey on behalf of the Authors (01 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (06 Apr 2021) by Richard Gloaguen

ED: Publish subject to technical corrections (19 Apr 2021) by A. Joshua West (Editor)

Thank you for submitting your work to esurf, and for the effort to see through the repeated revisions necessary to refine your analyses and interpretations to the level acceptable for publication. I am pleased to confirm acceptance of your paper based on the recommendation of the Associate Editor and reviewers, along with my own reading. I recognize that this work will add new data and useful information about the evolution of topography in the Himalaya.

I have marked a number of minor corrections on the attached file. Addressing these now will save time during type-setting and proofing of your paper, and will make sure none slip through the cracks. If you feel strongly about not making these changes, that is at your discretion.

In addition, the following important clarification is needed, though it was unfortunately a comment received after the Associate Editor decision had been made. Please make sure to make this change (the ALL CAPS highlight the new text, though you should put this text in normal capitalization in your revision):

From:
Figure 1: (a) An overview geological map of the western sector of the Indian Himalaya showing 1000 major lithology (modified after Steck, 2003 and Gavillot et al., 2018) .... (b) A balanced cross-section of 1005 the NW Himalaya showing the general architecture of the Himalayan orogenic wedge (modified after Gavillot et al., 2018)....

to:
Figure 1: (a) An overview geological map of the western sector of the Indian Himalaya showing 1000 major lithology (SIMPLIFIED FROM Gavillot et al., 2018 and references therein) .... (b) A balanced cross-section of 1005 the NW Himalaya showing the general architecture of the Himalayan orogenic wedge (SIMPLIFIED FROM Gavillot et al., 2018)….

Thank you again for choosing esurf for this work, and for your patience through the review process.

Josh West

Comments to the Author: PDF

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AR by Saptarshi Dey on behalf of the Authors (25 Apr 2021) Author's response Manuscript

Short summary

Ongoing deformation of the Himalaya is not constrained to its southern extremity. With morphometric analysis using a high-resolution digital elevation model, satellite image analysis, luminescence chronology of fluvial terraces and field observations, we identify a zone of rapid rock uplift in the interior of the Kashmir Himalaya. Our results suggest active tectonic and structural control on the growth of topography in the Himalayan interiors over multi-millennial timescales.