the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Origin of the Bohai Sea, North China Craton and implication for bi-directional back-arc extension in East Asia continental margin
Abstract. The Bohai Sea in eastern China is located in the back-arc extensional regime due to westward subduction of the Pacific Plate underneath the Eurasian Plate. It is one of the regions with frequent earthquakes. Previous recognition of the origin of the Bohai Sea was limited by the understanding of back-arc extensional mode perpendicular to the subduction zone in eastern Asian continental margin. In this paper, a new model for the genesis of the Bohai Sea is proposed, based on the construction of major fault system and investigation of several main boundaries enclosing the Bohai Sea. Through field investigation and analyses of tectonic landforms and boundary faults on the northwest coast of the Bohai Sea and eastern and western margins of the Liaodong Peninsula, and geological correlation of the Liaodong and Jiaodong Peninsulas and surrounding areas, we revealed a left-lateral strike-slip fault between the northwest coast of the Liaodong Bay and western margin of the Liaodong Peninsula, and proposed a right-lateral strike-slip fault between the eastern margin of the Liaodong Peninsula and northwestern margin of the Jiaodong Peninsula. This mode of movement may have been resulted from the NE stretching which is parallel to the subduction zone in northwestern Pacific margin. Therefore, we suggest that the formation of the Bohai Sea is resulted from the superimposition of the NE extension parallel to the subduction zone on the NW extension perpendicular to the subduction zone. We speculate that the two-direction extension perpendicular and parallel to the subduction zone should be the basic pattern of the back-arc extension with spherical-geometric effect.
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RC1: 'Comment on egusphere-2024-1263', Anonymous Referee #1, 30 May 2024
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The manuscript by Chen and Chen examines the strike-slip faults in East China to talk about the formation of the Bohai Bay basin. Through detailed fieldwork, the authors propose a new two-stage model, namely, the superimposition of the NE extension parallel to the subduction zone on the NW extension perpendicular to the subduction zone. I think it is worth to be published and will attract the attention of the audience in the Solid Earth. Thus, I suggest some revisions before considering accepting for publication.
Meanwhile, I hope my comments and suggestions are useful for your revision.
- In the first paragraph of section 2.1, the authors think of the “Jiaodong and Liaodong Peninsulas” as the key areas. What’s your reason? Please clarify it in detail.
- The figure 3 is too large to see the details of structural features in your study area. I hardly find the faults you studied in this map. I suggest that you also provide a detailed structural map of your study area.
- Some photos, such as Fig. 4A, Fig. 5, and Fig. 9 seem not to relate to the topic authors discussed, even presenting as a single figure. I suggest they should be removed. And I think it’s better to merge Figure 6 with Figure 7.
- There is a logical gap between structure and geodynamics, and I think the bridge is the deformation timing. How do you know the ages of faults you studied, and then correlate them with the opening of the Bohai Bay basin, and even the Paleo-Pacific subduction? I know it is difficult to date the faults, but it’s better to give more interpretations and discussions about the deformation timing.
- Based on a lot of measurements, Paleo-stress analysis is a useful method to study the kinematics of the faults. I suggest that the authors could add related analysis.
- The distribution of the magnetic anomaly is a more direct way to discuss the extensional direction, such as the study of the South China Sea (e.g., Barckhausen et al., 2014 Marine and Petroleum Geology). If you can collect the magnetic anomaly data of the Bohai Bay, it may test your two-stage model.
Citation: https://doi.org/10.5194/egusphere-2024-1263-RC1 -
AC1: 'Reply on RC1', Xuanhua Chen, 12 Jun 2024
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Thanks for your review. Your constructive comments and suggestions are very useful for my revision. So, we modified some sentences and photos, and added some materials, to improve our manuscript. The changes are marked in red color.
(1) In the first paragraph of section 2.1, we list some reasons to explain why the Jiaodong and Liaodong Peninsulas as the key areas for the formation of Bohai Bay.
(2) The figure 3 is separated into two maps, a regional map (figure 3) and a detailed structural map of studied area (figure 4), in order to emphasize the structural features of studied area.
(3) We agree with your comments, some of the pictures do not relate to our topic. We removed these photos, such as Fig. 4A, Fig. 5, and Fig. 9, and merged Figure 6 with Figures 7 and 8.
(4) Really, it is important and difficult to understand the deformation time. We can speculate the faulting time from two aspects. First, previous studies gave us some information about the faulting time. Especially, some of them predicated fault time according to cooling ages in the Luxi area. Second, we have made some logical analysis of fault time. We distinguish fault time according to the relationship between the fault and related strata, especially the effect of the faulting on sedimentary processes. Therefore, we can correlate the normal faulting with the formation of Bohai Bay basin or Bohai Sea. In addition, we can also consider the opening of Bohai Bay basin as the result of the back arc extension of the Paleo-Pacific subduction, despite there are some gaps between structure analyses and geodynamics, and we need more detailed further studies to reduce the inaccuracy.
(5) We have included some preliminary paleo-stress analysis to study the kinematics of the faults, mostly based on previous studies. Further more detailed studies should be conducted in the future.
(6) We have collected data of the magnetic anomaly in the Bohai Sea area, which is modified from Xiong et al., 2015. The data is good evidence for the two-stage model of the studied area.
Citation: https://doi.org/10.5194/egusphere-2024-1263-AC1
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RC2: 'Comment on egusphere-2024-1263', Chen Wu, 30 May 2024
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All looks great, accepted as suggested.
Citation: https://doi.org/10.5194/egusphere-2024-1263-RC2 -
AC2: 'Reply on RC2', Xuanhua Chen, 12 Jun 2024
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Thanks a lot for your kindly review. We have modified the manuscript, in order to improve the writing.
Citation: https://doi.org/10.5194/egusphere-2024-1263-AC2
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AC2: 'Reply on RC2', Xuanhua Chen, 12 Jun 2024
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