| 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.
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