Discovery of 2.45 Ga trondhjemitic gneiss in Eastern Hebei, North China Craton: A constraint on Precambrian crustal evolution

Jing, Jiahao; Liu, Qian; Han, Yigui; Yao, Jinlong; Zhang, Donghai; Sun, Chenyang; Zheng, Jiakang; Zhao, Guochun

doi:10.5194/egusphere-2025-5595

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https://doi.org/10.5194/egusphere-2025-5595

Preprints

23 Jan 2026

| 23 Jan 2026

Discovery of 2.45 Ga trondhjemitic gneiss in Eastern Hebei, North China Craton: A constraint on Precambrian crustal evolution

Jiahao Jing, Qian Liu, Yigui Han, Jinlong Yao, Donghai Zhang, Chenyang Sun, Jiakang Zheng, and Guochun Zhao

Abstract. The early Paleoproterozoic era (2.45–2.20 Ga), known as the Tectono-Magmatic Lull (TML), is characterized by a decline in global magmatic activity. This study first identifies ca. 2.45 Ga trondhjemitic gneiss (2446 ± 15 Ma) in Eastern Hebei of the Eastern Block, North China Craton. These rocks exhibit adakitic geochemical characteristics, marked by high SiO₂, Al₂O₃, and Sr contents, with low MgO, Y, and Yb contents. Their low MgO, Cr, and Ni contents, along with slightly high zircon δ¹⁸O (5.96–6.53 ‰) and positive ε_Hf(t) (3.3–4.9) values, indicate that they originated from partial melting of a juvenile thickened lower crust. All samples show low concentrations of Y, Yb, Ti, Nb, and Ta, coupled with their high (La/Yb)_N and Nb/Ta ratios, suggesting that they formed at a high-pressure condition, with garnet and rutile as residues. In combination with our new data and published zircon U-Pb ages in the region, we have identified multiple stages of magmatism (3.84–3.64 Ga, 3.53–3.22 Ga, 3.12–2.80 Ga, and 2.61–2.45 Ga) and metamorphism (3.50–3.23 Ga, 3.18–2.80 Ga, ~2.50 Ga, ~2.45 Ga, ~1.82 Ga) in Eastern Hebei. Based on a compilation of these magmatic zircon U-Pb ages and Hf isotope data, Eoarchean to early Paleoproterozoic crustal evolution processes in Eastern Hebei is established. The Eoarchean is dominated by Hadean crustal reworking, and the Paleoarchean is primarily characterized by crustal reworking with a minor contribution of crustal growth. Both crustal growth and reworking occurred during Mesoarchean time, with the proportion of crustal growth increasing from the Paleoarchean to the Mesoarchean. The late Neoarchean represents a major period of crustal growth with minor crustal reworking. The ca. 2.45 Ga trondhjemitic gneiss discovered in this study was probably a continuation of the late Neoarchean magmatism and the crustal growth persisted into this period.

Received: 12 Nov 2025 – Discussion started: 23 Jan 2026

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Jiahao Jing, Qian Liu, Yigui Han, Jinlong Yao, Donghai Zhang, Chenyang Sun, Jiakang Zheng, and Guochun Zhao

Status: final response (author comments only)

RC1:
'Comment on egusphere-2025-5595', Patrice Rey, 09 Feb 2026

The paper’s title, abstract, and introduction are not well aligned with its actual scientific content, and should be revised accordingly. In my view, the core contribution of the paper is a detailed synthesis of the Hadean–Archean magmatic evolution of Eastern Hebei within the North China Craton. In contrast, the discovery of a 2.45 Ga trondhjemitic gneiss and its implications for the 2.45–2.20 Ga tectono‑magmatic lull (TML), although interesting in their own right, are of secondary importance.
First, an age of 2.45 Ga lies at the commonly accepted boundaries of the TML, and therefore does not directly address the lull sensu-stricto. Second, high‑grade metamorphism (∼990 °C at ~850 MPa) at ~2.49 Ga, syn‑tectonic granitoid emplacement at ~2.47 Ga, and associated crustal thickening have already been documented in the region. Against this background, the occurrence of a 2.45 Ga trondhjemitic gneiss is not unexpected, and in my opinion does not warrant being highlighted in the title as a primary finding.
The introduction is particularly problematic, as it focuses almost exclusively on the tectono‑magmatic lull, creating a mismatch between the framing of the study and the core of the paper. This emphasis is confusing, given that the bulk of the manuscript is devoted to earlier Hadean–Archean crustal growth and reworking processes. It is also remarkable that the introduction tends to discredit the existence of this lull.
I therefore recommend that, i) the title be refocused on Hadean–Archean crustal evolution of the Eastern Hebei region; ii) that the introduction be rewritten to reflect this central theme, and iii) that the 2.45 Ga magmatic event should be presented as a subsidiary observation rather than the conceptual anchor of the study, or alternatively extracted from this paper and put into a shorter paper solely focusing on this discovery (the discussion about the petrogenesis of the trondjemite is interesting and nicely written, but a bit outside the main scope of the paper). Such relative minor revisions would significantly improve the coherence and impact of the manuscript.

The core of the paper is easy to follow, and it presents a comprehensive synthesis of the magmatic and metamorphic evolution of Eastern Hebei.
Minor points: 1/ The trondjhemite shows a strong, pervasive foliation. What is this fabric related to? Is there any metamorphic zircon or overgrowth which could be dated? 2/ The paper refers to Yao et al., 2017, which should be Yao and Zhang (2017).
Kind regards,
Patrice F. Rey

Citation: https://doi.org/10.5194/egusphere-2025-5595-RC1
- AC2:
  'Reply on RC1', Qian Liu, 11 Apr 2026
  Responses to the comments of Prof. Patrice Rey:
  The paper’s title, abstract, and introduction are not well aligned with its actual scientific content, and should be revised accordingly. In my view, the core contribution of the paper is a detailed synthesis of the Hadean–Archean magmatic evolution of Eastern Hebei within the North China Craton. In contrast, the discovery of a 2.45 Ga trondhjemitic gneiss and its implications for the 2.45–2.20 Ga tectono‑magmatic lull (TML), although interesting in their own right, are of secondary importance.
  First, an age of 2.45 Ga lies at the commonly accepted boundaries of the TML, and therefore does not directly address the lull sensu-stricto. Second, high‑grade metamorphism (∼990 °C at ~850 MPa) at ~2.49 Ga, syn‑tectonic granitoid emplacement at ~2.47 Ga, and associated crustal thickening have already been documented in the region. Against this background, the occurrence of a 2.45 Ga trondhjemitic gneiss is not unexpected, and in my opinion does not warrant being highlighted in the title as a primary finding.
  The introduction is particularly problematic, as it focuses almost exclusively on the tectono‑magmatic lull, creating a mismatch between the framing of the study and the core of the paper. This emphasis is confusing, given that the bulk of the manuscript is devoted to earlier Hadean–Archean crustal growth and reworking processes. It is also remarkable that the introduction tends to discredit the existence of this lull.
  I therefore recommend that, i) the title be refocused on Hadean–Archean crustal evolution of the Eastern Hebei region; ii) that the introduction be rewritten to reflect this central theme, and iii) that the 2.45 Ga magmatic event should be presented as a subsidiary observation rather than the conceptual anchor of the study, or alternatively extracted from this paper and put into a shorter paper solely focusing on this discovery (the discussion about the petrogenesis of the trondjemite is interesting and nicely written, but a bit outside the main scope of the paper). Such relative minor revisions would significantly improve the coherence and impact of the manuscript.
  The core of the paper is easy to follow, and it presents a comprehensive synthesis of the magmatic and metamorphic evolution of Eastern Hebei.
  Response: Many thanks to the reviewer for these thoughtful and constructive comments. After careful consideration, we fully agree with you that a comprehensive synthesis of the Hadean–Archean geochronological framework and crustal evolution of Eastern Hebei is of great scientific significance, as it would provide a critical window into the early tectonic evolution of the North China Craton. Actually, the current conclusions of the crustal evolution of Eastern Hebei are mainly based on previous research findings, and this study has made little contribution. In the revised manuscript, we have removed the Eoarchean to Mesoarchean crustal evolution that was based largely on previous studies, and retained the late Neoarchean to early Paleoproterozoic crustal evolution which is closely linked to the studied 2.45 Ga rocks. In future work, we plan to improve this part by incorporating additional new data and integrate them with the existing data. This will allow us to present a more comprehensive and self-contained synthesis of the crustal evolution of Eastern Hebei, which we intend to publish as a separate paper.
  In addition to the crustal evolution, another focus of this paper is the newly recognized ca. 2.45 Ga trondhjemite in Eastern Hebei. Our study has shown that the 2.45 Ga trondhjemite shows similar whole-rock geochemical and zircon Hf-O isotopic characteristics to the late Neoarchean (ca. 2.55 Ga) thickened lower crust-derived TTG rocks, combined with their close spatial association, indicating a close petrogenetic link between the two rock types. A complete rock record from 2.55 to 2.45 Ga is of great significance for understanding the tectonic transition from the Archean to the Paleoproterozoic in the North China Craton. Another reviewer suggested that we should focus on the origin of the 2.45 Ga trondhjemite and its relationship with late Neoarchean magmatism.
  After careful consideration and taking both reviewers’ comments into account, we have decided to refine the part of crustal evolution and publish it separately, while this study focuses on the ca. 2.45 Ga trondhjemite and its link to the 2.55 Ga magmatism. The specific revisions are as follows:
  (1) Title revision: The title has been changed to “Discovery of 2.45 Ga gneissic trondhjemite in Eastern Hebei, North China Craton”.
  (2) Introduction revision: The introduction has been completely rewritten to focus on the late Neoarchean and early Paleoproterozoic rock records of the North China Craton.
  (3) Abstract and Discuss revision: The part of TML, geochronological framework, and Eoarchean to Mesoarchean crustal evolution have been removed. In contrast, the petrogenetic link between the ca. 2.45 Ga trondhjemite and ca. 2.55 Ga TTG rocks were added.
  We thank the reviewer again for the insightful guidance, which has greatly helped us improve the focus and quality of the present manuscript.
  
  Minor Comments：
  The trondjhemite shows a strong, pervasive foliation. What is this fabric related to? Is there any metamorphic zircon or overgrowth which could be dated?
  
  Response: Many thanks for the reviewer’s comment. The pervasive foliation observed in the trondhjemite is interpreted as a secondary feature related to post-magmatic metamorphic overprinting, rather than a primary magmatic fabric. The zircon grains from the trondjhemite sample exhibit distinct core-rim textures in the CL images (Fig. 4). The cores preserve oscillatory zoning typical of an igneous origin, whereas the rims are bright and featureless, consistent with a metamorphic origin. These observations collectively indicate that the rock has indeed undergone a subsequent metamorphic event. However, the metamorphic rims are too narrow to be reliably targeted for zircon U-Pb dating. Consequently, precise metamorphic ages of the studied trondhjemite are not presented (see Lines 133-135 and revised Fig. 4).
  The paper refers to Yao et al., 2017, which should be Yao and Zhang (2017).
  
  Response: Sorry for our negligence and thanks for reminder. The citation has been corrected to “Yao and Zhang (2017)” as suggested (see Lines 71-72).
  
  Citation: https://doi.org/10.5194/egusphere-2025-5595-AC2
RC2:
'Comment on egusphere-2025-5595', Jinhai Yu, 25 Feb 2026

I fully agree with Dr. Rey's comments on this manuscript. The core contribution of this paper is a detailed synthesis of the Hadean–Archean magmatic evolution of Eastern Hebei, North China. However, these conclusions are based on previous research findings, and this study has made little contribution. On the other hand, as stated in the manuscript, the 2.45 Ga magmatic activity is a continuation of the 2.55 Ga magmatic event, rather than the beginning of the TML. So, this study does not contribute much to the TML. Thus, there seems to be too much commentary on the TML in the introduction. I suggest that the paper focuses on the origin of the 2.45 Ga trondhjemite and its relationship with 2.55 Ga magmatic activity. Although the ~2.45 Ga trondhjemites have Hf-O isotope compositions similar to those 2.55 Ga TTG, suggesting similar source, the ~2.45 Ga trondhjemites show different compositions from the most 2.55 Ga TTG (Figs. 5, 9, 10 and 11), implying different melting conditions (melting degree) and magmatic differentiation process (fractional mineral assemblage and extent). Why are there these differences? What factors lead to these differences? The formation of the trondhjemites is consistent with an important metamorphic peak age (Fig. 8b), what is the inherent connection between them? Thus, this manuscript is suggested to make major revision before it is considered to accept for publishing in this journal.

Other specific comments:
Line 1, because this study focuses on the origin of trondhjemite, rather than their metamorphic process, it is best to directly use "trondhjemite" or "gneissic trondhjemite", instead of "trondhjemitic gneiss". The 2.45 Ga is the crystallization age of trondhjemite, not the metamorphic age of gneiss.
Line 50, it is not advisable to attribute the lack of the early Paleoproterozoic magmatic records to preservation bias! because older rocks are widely preserved in the study area!
Line 91, TTG belong to granitoid, and they are not in a parallel relationship.
Line 96, change “and” to “or”.
Line 100, metamorphic ages listed here are inconsistent with those in line 92.
Lines 155-168, 210-211 and figure 4b, the “inherited” and “magmatic” zircons have similar REE patterns (Fig. 4b), they are continuous changes on the Concordia diagram (Fig. 4a) and also cannot be easily separated in CL images (Fig. 4a). Therefore, this classification is artificial and lacks enough evidence (e.g., element and/or isotope compositions and inner structure) to support it. These “magmatic zircons” may be only outer layers of the zircon grains and have suffered slightly more Pb loss.
Line 162-163, those two grains with discordance > 5% should be kept in supplementary Table S2 and S3 and plot in the Concordia diagram. Hf-O isotopic compositions of “inherited zircons” should be listed in Table S5.
173, delete “contents”.
187, change “slight” to “little”.
225-249, this part of discussion is too verbose, and not need to list the location of each rock.
228, “Labahsan” to “Labashan”.
232, “Zhao et al., 2025” to “Zhao et al., 2025b”.
254-255, 259-261 and 266-267, delete these citations, they have been cited in the caption of this diagram (Fig. 8).
257, start a new line from “It”.
277, but low Th, U, Rb contents suggest that some trace elements of these samples may be affected by granulite-facies metamorphism.
284-285, it is evidently illogical to combine samples with different ages and from different locations and plutons together to discuss their differentiation (Fig. 9)! In this diagram, the 2.45 Ga trondhjemites show little change！Additionally, there are issues with the image itself. Different minerals have different partition coefficients for highly and moderately incompatible elements. The CH/CM of magma cannot remain constant during fractional crystallization!
286, change “gneiss” to “magma”;
298, change “trondhjemitic gneiss” to “gneissic trondhjemite”;
299, delete “further”, and add “source” behind “crust”;
299-300, why can higher zircon d¹⁸O support a juvenile source? This is contradictory!
309, 318, delete “gneiss”;
314-316, the “rutile vector” in Fig. 11b may be problematic! Because Ta is more compatible in rutile than Nb, and Nb is more compatible than La, more residual rutile in the source will lead to a decrease in both the Nb/Ta and Nb/La ratios of the magma, rather than the Nb/La ratio remaining unchanged as shown in the figure. On the other hand, the 2.45 Ga trondhjemites have low Nb/Ta, inconsistent with more rutile residual in the source.
321-322, it is necessary to carefully distinguish whether the low Dy and Er contents of the 2.45 Ga trondhjemites are caused by the fractional crystallization of amphibole or by more amphibole residual in the source during the partial melting.
327, change “the protolith of the 2.45 Ga trondhjemitic gneiss” into “the parental magma of the 2.45 Ga trondhjemites”.
348-352, delete this sentence.
352, in fact, some 3.07-3.51 Ga zircons have 4.4-4.0 Ga Hf-isotope model ages, suggesting their host rocks originated from the same old source as those 3.84-3.64 Ga magmatic rocks, supporting a deep-seated Hadean basement in the Eastern Hebei.
Figure 12, add several Hf isotopic evolution lines with ¹⁷⁶Lu/¹⁷⁷Hf = 0.015 (average crust) or 0.022 (for mafic source);
354, 3.53-3.22 Ga? but there are not any 3.13-3.38 Ga rocks in Eastern Hebei (see Figure 12).
359, Why from the recycling of TTG rocks?
360, change “a” to “more”;
377-379, delete these parenthetical citations. Many citations throughout the text are redundant.
380-382, this viewpoint is incorrect, because the formation ages of magmatic rocks are consistent with their Nd-Hf isotope model age, suggesting the juvenile crustal growth, rather than crustal reworking.
399-400, this understanding is inaccurate. The occurrence of massive late Neoarchean felsic magmatic rocks, including TTG, suggesting strong crustal reworking. Crustal reworking may involve both juvenile crusts, generating high eHf(t) granitoids, and ancient crust, producing low eHf(t) granitoids. So the proportion of crustal growth and reworking cannot be determined solely by Nd-Hf model age.
401-405, the formation of 2.45 Ga trondhjemite indicate a crustal reworking event, and the reworked source is likely to be the juvenile crust produced by 2.67-2.77Ga, similar to those 2.55 Ga TTG. Also see above comment.
401, 405, 407, 414, change “2.45 Ga trondjemitic gneiss” to “2.45 Ga trondhjemite”.
415, that is reworking, but not the crustal growth!

Citation: https://doi.org/10.5194/egusphere-2025-5595-RC2
- AC1:
  'Reply on RC2', Qian Liu, 11 Apr 2026
  Responses to the comments of Prof. Jinhai Yu:
  I fully agree with Dr. Rey's comments on this manuscript. The core contribution of this paper is a detailed synthesis of the Hadean–Archean magmatic evolution of Eastern Hebei, North China. However, these conclusions are based on previous research findings, and this study has made little contribution. On the other hand, as stated in the manuscript, the 2.45 Ga magmatic activity is a continuation of the 2.55 Ga magmatic event, rather than the beginning of the TML. So, this study does not contribute much to the TML. Thus, there seems to be too much commentary on the TML in the introduction.
  I suggest that the paper focuses on the origin of the 2.45 Ga trondhjemite and its relationship with 2.55 Ga magmatic activity. Although the ~2.45 Ga trondhjemites have Hf-O isotope compositions similar to those 2.55 Ga TTG, suggesting similar source, the ~2.45 Ga trondhjemites show different compositions from the most 2.55 Ga TTG (Figs. 5, 9, 10 and 11), implying different melting conditions (melting degree) and magmatic differentiation process (fractional mineral assemblage and extent). Why are there these differences? What factors lead to these differences? The formation of the trondhjemites is consistent with an important metamorphic peak age (Fig. 8b), what is the inherent connection between them?
  Thus, this manuscript is suggested to make major revision before it is considered to accept for publishing in this journal.
  Response: We sincerely thank the reviewer for these thorough and constructive comments. Following the reviewer’s suggestions, we have substantially revised the manuscript, and the focus is now on the petrogenesis of the ca. 2.45 Ga trondhjemite and its relationship with the ca. 2.55 Ga TTG rocks in Eastern Hebei.
  Our most recent work has divided the 2.55 Ga TTG rocks into two groups based on their geochemical and isotopic signatures (Jing et al., 2026). The first group is characterized by high SiO₂ and low MgO, Ni, and Cr contents, with positive zircon ε_Hf(t) values and within or slightly higher zircon δ¹⁸O values than mantle zircon, indicating a magma source of the juvenile thickened lower crust. Comparatively, the second group shows moderate to high SiO₂ and high MgO, Ni, and Cr contents, with a wide range of zircon ε_Hf(t) and δ¹⁸O values, suggesting that they were derived from partial melting of subducted oceanic crust, with some inputs of ancient crust material. In the revised Figs. 5, 7, 9, and 10, the 2.45 Ga trondhjemite shows similar whole-rock geochemical and zircon Hf-O isotopic characteristics to the first group of thickened lower crust derived TTG rocks, suggesting that were derived from the same magma source, i.e., the juvenile thickened lower crust formed at ca. 2.77–2.67 Ga (see Lines 261-270). The geochemical and zircon Hf-O isotopic characteristics differences between the ca. 2.45 Ga trondhjemite and the second group 2.55 Ga rocks primarily result from distinct magma sources (a mixed source of oceanic crust and ancient continental crust vs. thickened lower crust).
  The crystallization age of the ca. 2.45 Ga trondhjemite is consistent with the 2.45 Ga metamorphic peak age in Eastern Hebei. We propose that the metamorphism likely induced partial melting of the thickened lower crust, generating the ca. 2.45 Ga trondhjemitic magma. The metamorphism provided the heat source, while the thickened crust supplied the source material. This interpretation is consistent with experimental petrology results showing that adakitic melts can be produced by partial melting of metabasaltic rocks under high-pressure (>1.5 GPa) and high-temperature (> 900°C) conditions.
  We thank the reviewer again for these invaluable comments.
  Reference:
  Jing, J.H., Liu, Q., Han, Y.G., Yao, J.L., Zhang, D.H., Sun, C.Y., Wang, C., Zheng, J.K., Zhao, G.C., 2026. Petrogenesis of late Neoarchean tonalite-trondhjemite- granodiorite and dioritic gneisses in Eastern Hebei: Implications for coexisting vertical and horizontal geodynamic regime in the eastern North China Craton. Geoscience Frontiers, 17(4), 102305, https://doi.org/10.1016/j.gsf.2026.102305.
  
  Other specific comments:
  Line 1, because this study focuses on the origin of trondhjemite, rather than their metamorphic process, it is best to directly use “trondhjemite” or “gneissic trondhjemite”, instead of “trondhjemitic gneiss”. The 2.45 Ga is the crystallization age of trondhjemite, not the metamorphic age of gneiss.
  
  Response: Many thanks for this careful and constructive comment. We fully agree with the referee’s point that the term “trondhjemitic gneiss” is not suitable for a study focused on the origin of trondhjemite. Accordingly, we have revised the manuscript to use “gneissic trondhjemite” throughout. This change has been made in the revised manuscript (see Lines 1, 12, 17, 19, 46, 47, 83, 89, 158, 185, 217, 223, 239, 248, 251-252, 261, 268).
  Line 50, it is not advisable to attribute the lack of the early Paleoproterozoic magmatic records to preservation bias! because older rocks are widely preserved in the study area!
  
  Response: Many thanks for this comment. We have thoroughly revised the “Introduction” following the reviewer’s suggestions. The updated “Introduction” no longer focuses on the tectono-magmatic lull (TML), and this sentence has been removed.
  Line 91, TTG belong to granitoid, and they are not in a parallel relationship.
  
  Response: We thank the reviewer for this correction. We agree that TTG is a subset of granitoid, and the original phrasing incorrectly implied a parallel relationship. Accordingly, we have revised the text to use “granitoid gneisses” to encompass all such rocks. This revision has been incorporated in the updated manuscript (see Line 70).
  Line 96, change “and” to “or”.
  
  Response: We have changed “and” to “or” in the revised manuscript (see Line 75).
  Line 100, metamorphic ages listed here are inconsistent with those in line 92.
  
  Response: We thank the reviewer for pointing out this discrepancy. The ages in Line 92 refer to the metamorphic ages of the granitoid gneisses in Eastern Hebei, whereas the ages in Line 100 are the metamorphic ages of the supracrustal rocks. These two rock units record different geological histories. In Eastern Hebei, the early Paleoproterozoic metamorphic event is only recorded in the supracrustal rocks, not in the granitoid gneisses. Therefore, the two sets of ages are intentionally different (see Lines 70-71 and 75).
  Lines 155-168, 210-211 and figure 4b, the “inherited” and “magmatic” zircons have similar REE patterns (Fig. 4b), they are continuous changes on the Concordia diagram (Fig. 4a) and also cannot be easily separated in CL images (Fig. 4a). Therefore, this classification is artificial and lacks enough evidence (e.g., element and/or isotope compositions and inner structure) to support it. These “magmatic zircons” may be only outer layers of the zircon grains and have suffered slightly more Pb loss.
  
  Response: Thanks for the reviewer’s careful comment on the classification of “inherited” and “magmatic” zircons. We have carefully re-evaluated our zircon data and clarify the subdivision as follows. (1) The two age populations are statistically distinct and regionally significant. Although the 28 analyses seem to show a continuous range of ²⁰⁷Pb/²⁰⁶Pb ages from 2569 to 2389 Ma, they statistically define two weighted mean ages: 2549 ± 29 Ma (n=5, MSWD=0.3) and 2446 ± 15 Ma (n=23, MSWD=0.5). The probability of overlap between these two populations is extremely low (<5%). More importantly, both ca. 2.55 Ga magmatism and ca. 2.45 Ga metamorphism are well documented in Eastern Hebei. Thus, the two age populations are not statistical artifacts but correspond to the known regional magmatic episodes. (2) The characteristics of Pb loss are not clearly observed in the studied magmatic zircons. Pb loss causes data point to plot below the concordial line (discordance > 5%). All 23 analyses defining the 2446 Ma age are concordant within 5%, with most showing discordance < 3%. In addition, the magmatic zircons have high Th/U ratios (0.4–1.2) and retain sharp oscillatory zoning in CL images, both of which are inconsistent with significant Pb loss or fluid alteration.
  Line 162-163, those two grains with discordance > 5% should be kept in supplementary Table S2 and S3 and plot in the Concordia diagram. Hf-O isotopic compositions of “inherited zircons” should be listed in Table S5.
  
  Response: We thank the reviewer for this careful check. Following the suggestion, we have added the zircon U-Pb dating results and rare earth element (REE) concentrations of the two discordant analyses (see revised Table S1 and S2). They are also plotted in the concordial diagram (see revised Fig. 4a). Besides, the study did not perform Hf-O isotope analyses (Table S4) on the “inherited zircons”.
  173, delete “contents”.
  
  Response: We have deleted “contents” as suggested (see Line 151).
  187, change “slight” to “little”.
  
  Response: We have changed “slight” to “little” in the revised manuscript (see Line 165).
  225-249, this part of discussion is too verbose, and not need to list the location of each rock.
  
  Response: Following the reviewer’s comment, we have deleted this part of the discussion in the revised version.
  228, “Labahsan” to “Labashan”.
  
  Response: Sorry for our negligence and thanks for reminder. The spelling of “Labahsan” has been corrected to “Labashan” in the revised manuscript (see Line 73).
  232, “Zhao et al., 2025” to “Zhao et al., 2025b”.
  
  Response: Thanks for pointing out the missing label. The citation has been corrected to “Zhao et al., 2025b” in the revised manuscript (see Line 75).
  254-255, 259-261 and 266-267, delete these citations, they have been cited in the caption of this diagram (Fig. 8).
  
  Response: We thank the reviewer for this careful observation. These duplicate citations have been removed in the revised manuscript.
  257, start a new line from “It”.
  
  Response: Following the reviewer's main comment, we have deleted the section of the geochronological framework of Eastern Hebei.
  277, but low Th, U, Rb contents suggest that some trace elements of these samples may be affected by granulite-facies metamorphism.
  
  Response: We thank the reviewer for this insightful comment. We agree that some trace elements, such as the Th, U, and Rb, might have been affected by granulite-facies metamorphism, and our original statement that the geochemical characteristics were “not significantly changed” was overly broad. However, the key elements used for petrogenetic interpretation, including the HFSEs and REEs, are generally considered less mobile during high-grade metamorphism. Additionally, we have revised the text to acknowledge the potential mobility of fluid-mobile elements while maintaining that the HFSEs and REEs are reliable for petrogenetic discussion. The revised sentences see Lines 187-191.
  1 284-285, it is evidently illogical to combine samples with different ages and from different locations and plutons together to discuss their differentiation (Fig. 9)! In this diagram, the 2.45 Ga trondhjemites show little change！Additionally, there are issues with the image itself. Different minerals have different partition coefficients for highly and moderately incompatible elements. The CH/CM of magma cannot remain constant during fractional crystallization!
  
  Response: We appreciate the reviewer’s careful and constructive comments.
  The ca. 2.55 Ga TTG and ca. 2.45 Ga trondhjemite are spatially associated in Eastern Hebei and share similar geochemical and zircon Hf-O isotopic characteristics. We discuss their geochemical evolution for comparison. The limited variation of the 2.45 Ga trondhjemite in revised Fig. 8 is due to the small number of samples.
  In revised Fig. 8, the concentrations and ratios of highly incompatible (C_H) and moderately incompatible (C_M) elements are used to distinguish partial melting and fractional crystallization (Schiano et al., 2010). During partial melting, C_H are preferentially incorporated into the melt, whereas C_M are comparatively retained in the residue, leading to a pronounced positive correlation as both the C_H and C_H/C_M ratio increase simultaneously. During fractional crystallization, although different minerals have different partition coefficients for CH and CM, the much lower distribution coefficients of CH compared to CM (D_M ≫ D_H) mean that, following the Rayleigh distillation law, CH/C_M remains nearly constant with increasing crystallization degree. This results in a horizontal trend, which is distinctly different from the steep trend of partial melting.
  The studied samples display a clear positive correlation in Fig. 9, consistent with partial melting and distinct from the horizontal trend expected for fractional crystallization. This interpretation is further supported by the absence of coeval mafic rocks and cumulates in Eastern Hebei (see revised Fig. 8).
  In addition, given the potential mobility of Rb and Sr during post-magmatic alteration, we have replaced the Rb/Sr vs. Rb diagram with the more robust Ce/Zr vs. Ce diagram. As relatively immobile HFSEs and LREEs, Ce and Zr are less affected by secondary processes and provide more reliable constraints on magmatic evolution (see revised Fig. 8).
  Reference:
  Schiano, P., Monzier, M., Eissen, J. P., Martin, H., and Koga, K. T.: Simple mixing as the major control of the evolution of volcanic suites in the Ecuadorian Andes, Contrib. Mineral. Petrol., 160, 297-312, 10.1007/s00410-009-0478-2, 2010.
  286, change “gneiss” to “magma”.
  
  Response: We have changed “gneiss” to “magma” in the revised text (see Line 204).
  298, change “trondhjemitic gneiss” to “gneissic trondhjemite”.
  
  Response: We thank the reviewer for this terminological refinement. We have changed “trondhjemitic gneiss” to “gneissic trondhjemite” (see Line 216-217).
  299, delete “further”, and add “source” behind “crust”.
  
  Response: Many thanks for these two helpful suggestions. This sentence has been deleted in the revised manuscript.
  299-300, why can higher zircon δ¹⁸O support a juvenile source? This is contradictory!
  
  Response: We thank the reviewer for this insightful comment, which prompted us to reconsider the relationship between zircon δ¹⁸O and magma source. The 2.45 Ga trondhjemite positive ε_Hf(t) values (+3.3 to +4.9) and slightly higher zircon δ¹⁸O values than mantle zircon (5.96–6.53 ‰), with corresponding T_DM2 ages varying from 2769 to 2671 Ma, indicating that they represent a crustal reworking of the juvenile crust produced by 2.67–2.77Ga (see Lines 216-219).
  309, 318, delete “gneiss”.
  
  Response: The term “trondhjemitic gneiss” has been revised to “gneiss trondhjemite” in the updated manuscript (see Lines 223, 239).
  314-316, the “rutile vector” in Fig. 11b may be problematic! Because Ta is more compatible in rutile than Nb, and Nb is more compatible than La, more residual rutile in the source will lead to a decrease in both the Nb/Ta and Nb/La ratios of the magma, rather than the Nb/La ratio remaining unchanged as shown in the figure. On the other hand, the 2.45 Ga trondhjemites have low Nb/Ta, inconsistent with more rutile residual in the source.
  
  Response: We appreciate the reviewer’s careful comment on the revised Fig.10b.
  Extensive experimental studies have demonstrated that Ta is more compatible in rutile than Nb (Foley et al., 2002; Schmidt et al., 2004; Xiong et al., 2006, 2011; John et al., 2011). During partial melting with residual rutile in the source, Ta is preferentially retained in the residue relative to Nb, resulting in melts with elevated Nb/Ta ratios (see revised Fig. 10b).
  As a representative element of LREEs, La is highly incompatible in rutile, with a distribution coefficient orders of magnitude lower than that of Nb (Klemme et al., 2005). When rutile is present as a residual phase, Nb is moderately retained in the residue, whereas La is almost completely incorporated into the melt, resulting in a significantly low Nb/La ratio in the melt. With increasing residual rutile, the Nb/La ratio shows little variation and remains roughly constant, consistent with the rutile vector in revised Fig. 10b.
  Collectively, the 2.45 Ga trondhjemite displays low concentrations of Nb and Ta, coupled with their high Nb/Ta and low Nb/La ratios, indicating that the rutile was residual in the source (see Lines 228-237).
  Reference:
  (1) Foley, S., Tiepolo, M., and Vannucci, R.: Growth of early continental crust controlled by melting of amphibolite in subduction zones, Nature, 417, 837-840, 10.1038/nature00799, 2002.
  (2) Schmidt, M. W., Dardon, A., Chazot, G., and Vannucci, R.: The dependence of Nb and Ta rutile–melt partitioning on melt composition and Nb/Ta fractionation during subduction processes, Earth Planet. Sc. Lett., 226, 415-432, https://doi.org/10.1016/j.epsl.2004.08.010, 2004.
  (3) Xiong, X., Adam, J., Green, T. H., Niu, H., Wu, J., and Cai, Z.: Trace element characteristics of partial melts produced by melting of metabasalts at high pressures: Constraints on the formation condition of adakitic melts, Sci. China Earth Sci., 49, 915-925, 10.1007/s11430-006-0915-2, 2006.
  (4) Xiong, X., Keppler, H., Audétat, A., Ni, H., Sun, W., and Li, Y.: Partitioning of Nb and Ta between rutile and felsic melt and the fractionation of Nb/Ta during partial melting of hydrous metabasalt, Geochimica et Cosmochimica Acta, 75, 1673-1692, https://doi.org/10.1016/j.gca.2010.06.039, 2011.
  (5) John, T., Klemd, R., Klemme, S., Pfänder, J. A., Elis Hoffmann, J., and Gao, J.: Nb–Ta fractionation by partial melting at the titanite–rutile transition, Contrib. Mineral. Petrol., 161, 35-45, 10.1007/s00410-010-0520-4, 2011.
  (6) Klemme, S., Prowatke, S., Hametner, K., and Günther, D.: Partitioning of trace elements between rutile and silicate melts: Implications for subduction zones, Geochim. Cosmochim. Ac., 69, 2361-2371, https://doi.org/10.1016/j.gca.2004.11.015, 2005.
  321-322, it is necessary to carefully distinguish whether the low Dy and Er contents of the 2.45 Ga trondhjemites are caused by the fractional crystallization of amphibole or by more amphibole residual in the source during the partial melting.
  
  Response: Many thanks to the reviewer for this constructive comment. The 2.45 Ga trondhjemites have low Y and Yb contents and high (La/Yb)_N ratios, suggesting that garnet is the main residual mineral in the magma source. In addition, they show low concentrations of Ti, Nb, and Ta, coupled with their high Nb/Ta and low Nb/La ratios, indicating that the rutile was also residual. Notably, our samples show extremely high Sr/Y values (637–1248), combined with their flat patterns of MREEs/HREEs and positive Eu anomalies, supporting that they have undergone amphibole fractional crystallization during the magma evolution (Tiepolo et al., 2007).
  To sum up, we interpret the low Dy and Er contents as primarily resulting from amphibole fractional crystallization rather than source residue (see Lines 228-237, 243-245).
  Reference:
  Tiepolo, M., Oberti, R., Zanetti, A., Vannucci, R., and Foley, S. F.: Trace-Element Partitioning Between Amphibole and Silicate Melt, Rev. Mineral. Geochem., 67, 417-452, 10.2138/rmg.2007.67.11, 2007.
  327, change “the protolith of the 2.45 Ga trondhjemitic gneiss” into “the parental magma of the 2.45 Ga trondhjemites”.
  
  Response: We have changed “the protolith of the 2.45 Ga trondhjemitic gneiss “to “the parental magma of the 2.45 Ga trondhjemite” as suggested (see Lines 204).
  348-352, delete this sentence.
  
  Response: We have deleted the sentence as suggested.
  352, in fact, some 3.07-3.51 Ga zircons have 4.4-4.0 Ga Hf-isotope model ages, suggesting their host rocks originated from the same old source as those 3.84-3.64 Ga magmatic rocks, supporting a deep-seated Hadean basement in the Eastern Hebei.
  
  Response: We thank the reviewer for this valuable addition. The Hf model ages (4.4–4.0 Ga) of the ca. 3.51–3.07 Ga zircons suggest that their host rocks were derived from an ancient source that formed in the Hadean. In addition, Hadean zircons have been identified in Eastern Hebei, supporting the existence of Hadean crustal materials in this region. However, the Paleoarchean crustal evolution is not the main focus of this study, and this sentence has been removed from the revised manuscript.
  Figure 12, add several Hf isotopic evolution lines with 176Lu/177Hf = 0.015 (average crust) or 0.022 (for mafic source);
  
  Response: We thank the reviewer for this suggestion. We have added the Hf isotopic evolution lines with ¹⁷⁶Lu/¹⁷⁷Hf = 0.015 (average crust) to revised Figure 7a as recommended.
  354, 3.53-3.22 Ga? but there are not any 3.13-3.38 Ga rocks in Eastern Hebei (see Figure 12).
  
  Response: We thank the reviewer for this observation. We confirm that ca. 3.38–3.13 Ga rocks do exist in Eastern Hebei (Dong et al., 2025). However, these rocks lack corresponding Hf isotope data, and therefore they are not shown in Figure 12. Nevertheless, this issue is not the central focus of our paper, and the relevant discussion has been omitted from the revised manuscript. Nevertheless, the revised manuscript no longer contains the content on the Paleoarchean rocks of Eastern Hebei.
  Reference: Dong, C., Li, P., Nutman, A. P., Xie, H., Liu, S., Li, Y., Liu, D., and Wan, Y.: New discovery of Paleoarchean-Mesoarchean magmatic rocks in eastern Hebei, North China Craton: Petrogenesis and tectonic environment, Precambrian Res., 427, 107870, https://doi.org/10.1016/j.precamres.2025.107870, 2025.
  359, Why from the recycling of TTG rocks?
  
  Response: Many thanks to the reviewer for pointing this out. The inaccurate statement has been corrected by deleting it from the revised version.
  360, change “a” to “more”.
  
  Response: We have deleted this inappropriate statement from the revised manuscript.
  377-379, delete these parenthetical citations. Many citations throughout the text are redundant.
  
  Response: We have removed the redundant citations. We also went through the rest of the manuscript and deleted other unnecessary duplicate citations.
  380-382, this viewpoint is incorrect, because the formation ages of magmatic rocks are consistent with their Nd-Hf isotope model age, suggesting the juvenile crustal growth, rather than crustal reworking.
  
  Response: Many thanks to the reviewer. This valuable comment enhanced our understanding of the crustal growth and reworking. The magmatic rock with similar formation ages and Nd-Hf isotope model age might represent the juvenile crustal growth, rather than crustal reworking (see Lines 272-274).
  399-400, this understanding is inaccurate. The occurrence of massive late Neoarchean felsic magmatic rocks, including TTG, suggesting strong crustal reworking. Crustal reworking may involve both juvenile crusts, generating high eHf(t) granitoids, and ancient crust, producing low eHf(t) granitoids. So the proportion of crustal growth and reworking cannot be determined solely by Nd-Hf model age.
  
  Response: We thank the reviewer for this insightful comment, which help us clarify our thinking. Crustal reworking can involve both juvenile crust (generating high ε_Hf(t) granitoids) and ancient crust (generating low ε_Hf(t) granitoids), and therefore the proportions of crustal growth and reworking cannot be determined solely by Nd-Hf model ages. Following this comment, we have re-examined our data and conclude that the ca. 2.45 Ga trondhjemite in this study represents crustal reworking rather than crustal growth. The reworked source is likely to be the juvenile crust produced by 2.77–2.67Ga (see Lines 216-219).
  401-405, the formation of 2.45 Ga trondhjemite indicate a crustal reworking event, and the reworked source is likely to be the juvenile crust produced by 2.67-2.77Ga, similar to those 2.55 Ga TTG. Also see above comment.
  
  Response: We fully agree with the reviewer. The ca. 2.45 Ga trondhjemite represents a crustal reworking event, and its source was the juvenile crust formed at ca. 2.67–2.77 Ga. This has been clarified in the revised manuscript (see Lines 216-219).
  401, 405, 407, 414, change “2.45 Ga trondjemitic gneiss” to “2.45 Ga gneiss trondhjemite”.
  
  Response: We appreciate the reviewer’s careful reading. Following this suggestion, we have checked the entire manuscript and changed “2.45 Ga trondhjemitic gneiss” to “2.45 Ga gneiss trondhjemite” in the revised version (see Lines 239, 248, 251-252, 261, 268, 288).
  415, that is reworking, but not the crustal growth!
  
  Response: We thank the reviewer for this correction. We have revised the manuscript, and the ca. 2.45 Ga magmatism is now interpreted as a crustal reworking event, not crustal growth (see Lines 216-219, 285-286).
  
  Citation: https://doi.org/10.5194/egusphere-2025-5595-AC1

Jiahao Jing, Qian Liu, Yigui Han, Jinlong Yao, Donghai Zhang, Chenyang Sun, Jiakang Zheng, and Guochun Zhao

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Jiahao Jing, Qian Liu, Yigui Han, Jinlong Yao, Donghai Zhang, Chenyang Sun, Jiakang Zheng, and Guochun Zhao

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Short summary

This study first identifies ca. 2.45 Ga trondhjemitic gneiss (2446 ± 15 Ma) in Eastern Hebei of the Eastern Block, North China Craton. Geochemical analysis reveals that it originated from partial melting of a juvenile thickened lower crust, with garnet and rutile as residues. In combination with our new and collected zircon U-Pb age and Hf isotopic data in Eastern Hebei, the Precambrian geochronological framework and crustal evolution processes of Eastern Hebei have been established.


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