Geothermal Geological Characteristics and Genetic Model of the Shunping Area along Eastern Taihang Mountain

Round 1

Reviewer 1 Report

There are a lot of geothermal resources in the eastern section of Taihang, and understanding the underground geological structure and geothermal origin is of certain significance for the exploration of geothermal resources. The author obtained the underground electrical structure in Shunping area by means of magnetotelluric and gas geochemistry, and established a geothermal genesis model, which is helpful for local economic development and further geological exploration. However, there are still some problems in the article, which have been pointed out below, and I suggest that the article still needs to be revised before reviewing.

 

Main comments:

1. The introduction and abstract are not clear about the scientific problems existing in the research area, and it is recommended to re-edit and raise specific scientific problems.

2. The introduction part summarizes the previous work on thermal storage of geothermal system in the study area, and it is suggested to supplement some predecessors' research work on the underground geological structure in the study area or the research status of other components of the geothermal system.

3. This paper uses the structural analysis method to analyze the development characteristics of thermally controlled structures, but the structural analysis method does not seem to be sufficient as a separate method to be proposed in parallel with MT and gas geochemistry, and separate section 3.3 is established.Wouldn't it be more appropriate to mention it later in the explanation section as a method of analysis and discussion?

4. It is recommended to indicate the measurement point number in the measurement point location map (Figure 2), or the direction of the measurement line in the magnetotelluric interpretation section diagram (Figure 6).

5. The magnetotelluric data processing part is less described. It is recommended to add specific processing details, or to compare with the previous research work in the eastern part of Taihang. Similar electrical structures can increase the reliability of the results.

6. The unit of depth on the ordinate in Figure 6 is "m", but the geological structures such as faults described in this paper can reach "km", and the electrical results at a depth of 20 m cannot explain the geological structure of thousands of meters. In addition, the name and unit of the color scale in Figure 6 is "f/Hz", whether it should be "Rho/Ω·m", please check carefully.

7. The obtained electrical structure interpretation needs more geological and geophysical evidence to support.

8. Is the unit of drilling depth in Table 1 "m"? The drilling data at a depth of several hundred meters is not enough to determine the formation depth of thousands of meters.

9. Figure 11 is a conceptual model diagram of the genesis of geothermal resources, so the specific vertical depth is not marked, but the specific formation thickness obtained from Figure 11 is mentioned later. If the formation thickness is mentioned, it is recommended to specifically mark it in the figure.

Author Response

Dear Editor Dr. Hartono and anonymous Reviewers:

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Geothermal geological characteristics and genetic model of Shunping area along the eastern Taihang Moutain” (ID: minerals-1794303). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked up using the “Track Changes” function in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

 

Responds to the reviewer’s comments.

Reviewer #1:

1. Response to comment: The introduction and abstract are not clear about the scientific problems existing in the research area, and it is recommended to re-edit and raise specific scientific problems.

Response: In order to make the main scientific and technological issues of the paper more pertinent, we have re-written parts of the introduction and abstract according to the Reviewer’s suggestion. For example, some expressions in the abstract have been changed, and some content has been added in the introduction part, including added citations of papers to explain in more detail the previous work and the problem to be solved by this research. Please refer to the revised draft for specific changes.

2. Response to comment: It is suggested to supplement some predecessors' research work on the underground geological structure in the study area or the research status of other components of the geothermal system.

Response: Fully considering the suggestions of reviewers, we have added some previous detailed studies on the geological structures in the study area and surrounding areas. The specific additions are as follows:

“The Taihang Mountain are an extensional orogenic belt composed of tectonic magma belts and metamorphic core complexes. The orogenic belt uplifted rapidly, and a large amount of denuded clasts filled the North China Basin. At the same time, the deep crust-mantle material in the rift basin migrated to the Taihang Mountain uplift area to supplement the space for the lower mantle depression of the orogenic belt and the uplift of mountain systems. And with the continuous development of the orogenic belt, the lithosphere is balanced to form the coupling relationship between the rift basin and the extensional mountains (Liu et al., 2000).

Through the MT profile from the Taihang Mountain in the south of Shijiazhuang to the Jizhong Depression, predecessors have concluded that the lithospheric electrical properties have the characteristics of vertical stratification and horizontal block (Cao et al., 2013). Moreover, the electrical structures of the Taihang Mountains uplift belt and the Jizhong Depression are completely different. The Taihang Mountains uplift belt is a high-resistance body. In the basin area, the electrical properties in the crust are roughly distributed in layers, and low-resistivity layers develop from the surface to a depth of about 7 km. This low-resistivity layer should be the upper Paleogene formation (E-Q) composed of loose sediments.”

3. Response to comment: The structural analysis method does not seem to be sufficient as a separate method to be proposed in parallel with MT and gas geochemistry, and separate section 3.3 is established.

Response: We deleted the section 3.3 structural analysis.

4. Response to comment: It is recommended to indicate the measurement point number in the measurement point location map (Figure 2), or the direction of the measurement line in the magnetotelluric interpretation section diagram (Figure 6).

Response: To make it easier to identify the direction and location of the survey line, we have added direction signs to the MT interpretation section in Figure 6.

5. Response to comment: The magnetotelluric data processing part is less described.

Response: More detailed methods and procedures for MT inversion and interpretation were added in the revised draft as follows:

Obtaining high-quality raw data is the basis for establishing a reasonable three-dimensional electrical structural model. The study area is densely populated, the power grid is dense, and various electromagnetic interferences are strong. The paper adopts the method of combining Robust analysis technology and remote reference technology (single point or multi-point) to process time domain data to obtain apparent resistivity and impedance phase data. "Dead band" distortion correction is performed using Rhoplus analysis technology. Using impedance tensor decomposition technology, the underground geoelectric structure is analyzed, and local distortion analysis and correction are carried out. The curve translation method, the two-dimensional inversion method with terrain and surface inhomogeneity, and the spatial filtering method analyze and correct the static displacement generated by the shallow inhomogeneity, strengthen noise identification and elimination, and improve data quality.

At the same time, the added MT interpretation content in the Geological background part (Cao et al., 2013) also increases the reliability of the research results.

6. Response to comment: The unit of depth on the ordinate in Figure 6 is "m". In addition, the name and unit of the color scale in Figure 6 is "f/Hz", whether it should be "Rho/Ω·m".

Response: We are very sorry for our incorrect writing of “km” as “m” and "Rho/Ω·m" as "f/Hz" in Figure 6. The error markers in Figure 6 have been modified.

7. Response to comment: The obtained electrical structure interpretation needs more geological and geophysical evidence to support.

Response: In order to increase the credibility of the interpretation of the electrical structure, the previous comprehensive interpretation results of geology and geophysics were cited. The specific additions are as follows:

Previous studies have shown that the piedmont fault zone of the Taihang Moun-tain was mainly formed in the Paleogene (Xu et al., 2000). It is basically developed in the upper crust, and most of them are shovel-shaped positive faults with a gentle dip. In particular, the Baoding-Shijiazhuang and other faults in the middle-north section of the fault zone are large and gentle detachment faults, extending horizontally for tens of kilometers on their inclinations. The Taihang Mountain piedmont fault is a large spade-shaped fault, accompanied by right-slip, which controls the formation of the Bo-hai Bay Basin (Cao et al., 2013; Shan, 2018). The Jizhong Depression has formed a tectonic pattern dominated by faults in the west and superposition in the east, as shown in the section in Figure 6.

Meamwhile, the added MT interpretation content in the Geological background part (Cao et al., 2013) also increases the reliability of the electrical structure.

8. Response to comment: The drilling data at a depth of several hundred meters is not enough to determine the formation depth of thousands of meters.

Response: The drilling data in Table 1 was used to support the characterization of cap rocks rather than the geological characteristics of geothermal reservoirs. As has been written in the 4.4 Cap rock” The thickness of the Quaternary to the west of F1 of Taihang Mountain piedmont fault is about 0-200 m, and the thickness of the Quaternary to the east of F1 is about 100- 450 m, which shows an obvious increasing trend from west to east.” Drilling holes from 12.5 meters deep to 450 meters deep and the strata they encountered can better help us understand the distribution law and characteristics of cap rocks in the study area and surrounding areas. Knowing the depth of the cap rock means also knows the starting depth of the geothermal reservoir.

9. Response to comment: Figure 11 is a conceptual model diagram of the genesis of geothermal resources, so the specific vertical depth is not marked, but the specific formation thickness obtained from Figure 11 is mentioned later.

Response: Figure 11 is a conceptual model diagram of the genesis of geothermal resources, so the specific vertical depth is not marked. The specific formation thickness we mentioned in the text is derived from the reference Dai et al., 2019, rather than directly read on the conceptual schema map. We have indicated in the text with a citation format.

 

We would like also to thank you for allowing us to resubmit a revised copy of the manuscript.

We hope that the revised manuscript is accepted for publication in Minerals.

                          Sincerely, Dr. Peng Dai

Reviewer 2 Report

The geothermal geological conditions in the Shunping area along the eastern Taihang Moutain were analyzed by geophysical, geochemical and geological methods, such as magnetotelluric, gas geochemistry and structural analysis. However, It is suggested that authors should give supplement of the geophysical MT 3 D inversion section and result in detail.

Author Response

Dear Editor Dr. Hartono and anonymous Reviewers:

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Geothermal geological characteristics and genetic model of Shunping area along the eastern Taihang Moutain” (ID: minerals-1794303). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked up using the “Track Changes” function in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Responds to the reviewer’s comments.

Reviewer #2:

1. Response to comment: The geothermal geological conditions in the Shunping area along the eastern Taihang Moutain were analyzed by geophysical, geochemical and geological methods, such as magnetotelluric, gas geochemistry and structural analysis. However, it is suggested that authors should give supplement of the geophysical MT 3 D inversion section and result in detail.

Response: Thank you for your summary. We really appreciate your efforts in reviewing our manuscript. In addition, we are sorry that the magnetotelluric 3D inversion process is wrongly marked in Figure 2, but no related work has actually been done in this research area. We corrected the content in Figure 2 to record the actual work being carried out.

 

We would like also to thank you for allowing us to resubmit a revised copy of the manuscript.

We hope that the revised manuscript is accepted for publication in Minerals.

                          Sincerely, Dr. Peng Dai

 

Reviewer 3 Report

Thanks for this interesting study. Unfortunately, I do not have major comments on it to improve it. Please find the following minor ones:

*Figures 3, 6, 8 and 11 should be placed after you mention them in the text.

*Line 193: A type error in the unit.

*Line 202: between fractures or through fractures?

*Line 272, 273: It seems that this sentence is not complete.

*Line 292, 293: Please revise this sentence.

*Table 1: Please check it again, line SNC1.

*Line 316: The:the

*Line 367: It is not clear.

*As you mentioned, there are a lot of parameters which play roles for heat extraction from geothermal reservoirs. However, the importance of them is not comparable. Therefore, for the next steps, focus should be given to the most important ones. For the future studies, it is better to mention these parameters. See these papers for example: Simulations and global sensitivity analysis of the thermo-hydraulic-mechanical processes in a fractured geothermal reservoir; Thermo-hydro-mechanical modeling of an enhanced geothermal system in a fractured reservoir using carbon dioxide as heat transmission fluid-A sensitivity investigation

Author Response

Dear Editor Dr. Hartono and anonymous Reviewers:

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Geothermal geological characteristics and genetic model of Shunping area along the eastern Taihang Moutain” (ID: minerals-1794303). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked up using the “Track Changes” function in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

 

Responds to the reviewer’s comments.

Reviewer #3:

Response to comment: Thanks for this interesting study. Unfortunately, I do not have major comments on it to improve it. Please find the following minor ones:

*Figures 3, 6, 8 and 11 should be placed after you mention them in the text.

*Line 193: A type error in the unit.

*Line 202: between fractures or through fractures?

*Line 272, 273: It seems that this sentence is not complete.

*Line 292, 293: Please revise this sentence.

*Table 1: Please check it again, line SNC1.

*Line 316: The:the

*Line 367: It is not clear.

*For the next steps, focus should be given to the most important ones.

Response: According to the Reviewer’s suggestion, we modified the above issues one by one.

*Figures 3, 6, 8 and 11 should be placed after you mention them in the text.

    The positions of these pictures have been adjusted.

*Line 193: A type error in the unit.

    Corrected in the revised manuscript.

*Line 202: between fractures or through fractures?

    Fractures or fissures. There are no errors in the original text. Fissures are small or relatively fine cracks.

*Line 272, 273: It seems that this sentence is not complete.

    We accidentally missed a word. Corrected.

*Line 292, 293: Please revise this sentence.

Revised. The new expression is as follows:

Conclusions can be drawn by analyzing the source-pathway-reservoir-cap (SPRC) characteristics of geothermal geological conditions in Shunping area.

*Table 1: Please check it again, line SNC1.

    There is no problem in the line SNC1. Unlike the other rows, the number 29 is between Q and N, indicating that both Quaternary and Neogene strata are exposed, with a total thickness of 29 meters.

*Line 316: The:the

    Change the wrong “The” to the correct “the”.

*Line 367: It is not clear.

Revised. The new expression is as follows:

However, due to the shallow covering layer in the Shunping area and the damage by tectonic action, the effect of thermal preservation and water insulation is affected, which limits the practical preservation of underground thermal energy in the Shunping area.

*For the next steps, focus should be given to the most important ones.

We deeply appreciate the reviewer’s suggestions for our future studies, in particular the two very recent findings on coupled thermo-hydro-mechanical (THM) mechanism of the geothermal energy extraction is meaningful for us. It has a good guiding role for our future research. This is also the research direction we are learning and paying attention to.

 

We would like also to thank you for allowing us to resubmit a revised copy of the manuscript.

We hope that the revised manuscript is accepted for publication in Minerals.

                          Sincerely, Dr. Peng Dai

Round 2

Reviewer 1 Report

The author made a detailed modification and explanation in response to the problems raised. The structure of the paper is reasonable, the method is appropriate, and the results are credible. It clarifies the geothermal genetic mechanism of thermal storage in the Taihang Mountains, which is of great significance to the follow-up geothermal research work. I recommend accepting this paper.

Author Response

Dear Editor Dr. Hartono and anonymous Reviewers:

Thank you for your kind letter and for the reviewers’ comments concerning our manuscript entitled “Geothermal geological characteristics and genetic model of Shunping area along the eastern Taihang Moutain” (ID: minerals-1794303). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We revised the manuscript in accordance with the reviewers’ comments，and carefully proof-read the manuscript to minimize typographical, grammatical, and bibliographical errors. Revised portion are marked up using the “Track Changes” function in the paper. Here below is our description on revision according to the reviewers' comments.

 

Responds to the reviewer’s comments.

Reviewer #1:

1. Response to comment: The author made a detailed modification and explanation in response to the problems raised. The structure of the paper is reasonable, the method is appropriate, and the results are credible. It clarifies the geothermal genetic mechanism of thermal storage in the Taihang Mountains, which is of great significance to the follow-up geothermal research work. I recommend accepting this paper.

Response: We really appreciate your review and affirmation of our work. At the same time, we would like to thank you again for your detailed comments in the first round of review, which played an important role in the improvement of our paper.

We hope that the revised manuscript is accepted for publication in Minerals.

                          Sincerely, Dr. Peng Dai

 

Reviewer 2 Report

The authors has a clear description of the geological structure, however,the deep structure requires geophysical work.How can we verify the reliability of the MT inversion results?It is suggested that the author supplement the relevant content of MT inversion.

Author Response

Dear Editor Dr. Hartono and anonymous Reviewers:

Thank you for your kind letter and for the reviewers’ comments concerning our manuscript entitled “Geothermal geological characteristics and genetic model of Shunping area along the eastern Taihang Moutain” (ID: minerals-1794303). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We revised the manuscript in accordance with the reviewers’ comments，and carefully proof-read the manuscript to minimize typographical, grammatical, and bibliographical errors. Revised portion are marked up using the “Track Changes” function in the paper. Here below is our description on revision according to the reviewers' comments.

 

Responds to the reviewer’s comments.

Reviewer #2:

1. Response to comment: The authors has a clear description of the geological structure, however, the deep structure requires geophysical work. How can we verify the reliability of the MT inversion results? It is suggested that the author supplement the relevant content of MT inversion.

Response: Thanks to the reviewer for your kind comments. We agree with the reviewer and have added relevant content of MT inversion. The theme of this paper is to establish a geothermic genetic model by analyzing the characteristics of heat source, water source, migration channel, reservoir and cap rock of geothermal geological conditions. Because the processing method used are all mature technology, and considering the theme of this paper, the relevant content of MT inversion were not explained in detail in the paper. But we also think it is necessary to add this information, so it is added in this revision, as detailed below:

Before MT data inversion, we conducted dimensional analysis and strike analysis. Bahr skew determined that the underground electrical structure is mainly partial to 2D (Bahr, 1988). For a one-dimensional (1D) regional conductivity structure, a single coordinate-invariant phase is equal to a 1D impedance tensor, which is the characteristic of the phase-phase tensor. If the regional conductivity structure is 2D, the phase tensor is symmetric with one of its major axes parallel to the strike axis of the domain structure. In the case of 2D, the dominant values (coordinate invariants) of the phase tensor are the transverse electric and magnetic polarization phases (Caldwell et al., 2004). The phase tensor analysis determined that the geoelectric strike direction is NE35 °. The non linear converge gradients (NLCG) code (Rodi and Mackie, 2001) was used for 2D inversion. The algorithm employs an NLCG scheme to minimize objective functions that penalize data residuals and second-order spatial derivatives of resistivity. After 109 iterations, the inversion was finished and root-mean-square (RMS) misfit is 2.1.

Meanwhile, more detailed processing procedures can be reached at the following three references:

2. Bahr K . Interpretation of the magnetotelluric impedance tensor: regional induction and local telluric distortion[J]. Journal of Geophysics, 1988, 62(2): 119- 127.
3. Caldwell T. G. , Bibby H. . , Brown C . The magnetotelluric phase tensor[J]. Geophysical Journal International, 2004, 158(2): 457-469.
4. Rodi W. L. , Mackie R. L . Nonlinear Conjugate Gradients Algorithm For 2-D Magnetotelluric Inversion[J]. Geophysics, 2001, 66(1): 174-187.

 

We would like to thank you for allowing us to resubmit a revised copy of the manuscript again.

We hope that the revised manuscript is accepted for publication in Minerals.

                          Sincerely, Dr. Peng Dai

 

Round 3

Reviewer 2 Report

 

Authors make full revision according to reviewers, this paper can be accepted  based on the new version