the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jan 2026
Discovery of 2.45 Ga trondhjemitic gneiss in Eastern Hebei, North China Craton: A constraint on Precambrian crustal evolution
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 εHf(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.
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Status: open (until 14 Mar 2026)
- RC1: 'Comment on egusphere-2025-5595', Patrice Rey, 09 Feb 2026 reply
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RC2: 'Comment on egusphere-2025-5595', Jinhai Yu, 25 Feb 2026
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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
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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