Carboniferous-Triassic rise and fall of continental arc recorded by retro-arc shifts of basin-infill and climate in the Hexi Corridor

Zhang, Junxiang; Sun, Jiaopeng; Dong, Yunpeng; Han, Xiaofeng; Yang, Xiangyang; Qi, Yukun

doi:10.5194/egusphere-2026-4406

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https://doi.org/10.5194/egusphere-2026-4406

Preprints

04 Sep 2026

| 04 Sep 2026

Status: this preprint is open for discussion and under review for Solid Earth (SE).

Carboniferous-Triassic rise and fall of continental arc recorded by retro-arc shifts of basin-infill and climate in the Hexi Corridor

Junxiang Zhang, Jiaopeng Sun, Yunpeng Dong, Xiaofeng Han, Xiangyang Yang, and Yukun Qi

Abstract. The Hexi Corridor inboard the Andean-type North China Continental Arc preserves pivotal records of basin transition and dynamic change in Carboniferous-Triassic. This work provides an integrated study on strata in the Eastern Hexi Corridor Belt (EHCB) and western Ordos. Provenance analyses show that Carboniferous strata in the southern EHCB were sourced from the Central Qilian, evidenced by north-direct paleoflow data and age profiles mainly of Paleozoic and Neoproterozoic clusters. The northern EHCB samples have age spectra with dominance of ca. 2700–1700 Ma ages, implying sources from the Ordos basement, which is compatible with south-direct paleoflow. Crustal thinning and mantle-derived magmatism indicate an extension setting for the EHCB. Shallow-water deposition in the EHCB was terminated at ca. 295 Ma. The late Permian strata were fed by the intensely raised Nuru-Langshan Continental Arc (NLCA), given occurrence of >80 % number of Paleozoic-age zircons in forearc and retroarc samples. Crustal thickening and negative ε(Hf) values for plutons demonstrate raising of the NLCA, cratonward expansion of which constructed a retroarc foreland system in the western Ordos and EHCB. The ~3±0.5 km high relief of the IMCA triggered orographic rain shadow and retroarc aridification, expressed by changing of mudstone color from black to red. The Paleo-Asian Ocean closure at early Triassic induced uplift of the NLCA basement and left-lateral strike-slip of the Bayanwula Fault, providing a swath of zircons of ca. 2700–1700 Ma ages to the retroarc. Paleodrainage reorganized, as fluvial-delta systems in the western Ordos commenced routing to the southeast.

Received: 22 Jul 2026 – Discussion started: 04 Sep 2026

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Junxiang Zhang, Jiaopeng Sun, Yunpeng Dong, Xiaofeng Han, Xiangyang Yang, and Yukun Qi

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RC1:
'Comment on egusphere-2026-4406', Anonymous Referee #1, 18 Sep 2026 reply
General summary
The authors conducted a provenance analysis combining paleo-flow analysis, petrological characterisation, and zircon geochronological and isotopic characterisation, to decipher the dominant tectonic regimes and basin evolution in the Eastern Hexi Corridor Belt and western Ordos (China) during Carboniferous to Triassic.
The article is lengthy, supported by a substantial number of references and combines new data acquisition with previous data interpretation to contrast and assess the research hypotheses. However, it displays a few inconsistencies along the text, and the amount of information provided makes the argumentation difficult to follow. Sometimes it is difficult to decipher whether the information comes from previous studies or from newly collected data. The manuscript focuses on solid, well-known concepts and ideas, providing new data to an already large corpus of evidence from previous research. It constrains and narrows the timing of deposition for some units, and the paleogeographic interpretation of the area.
The work contributes to the understanding of the orogenic structuring and evolution of the southern Central Asia Orogenic Belt, one of the most complex and long-lived accretionary orogens in the world.
General comments
Figures, especially graphs, are generally dense, and the legibility would benefit from enlarging some figures, or even dividing them in more than one figure (ex: Figs 10 to 12, and encapsulated graphs within Concordia plots)

Figure captions sometimes lack detailed description of figure labels, acronyms, etc. and would be necessary to ensure that figures are self-explicative enough, otherwise consider extending figure captions.

Sometimes the terminology of the various structural units is confusing, as different names appear to be used interchangeably (ex. nº1: do “western NCB”, “NLCA”, “IMCA”, or “western Ordos” correspond to equivalent areas? ex. nº2: is “Eastern Hexi Corridor Belt” -in the text- referring to the same structural unit as “Eastern Hexi Corridor retroarc” – in Figure 15 and discussion section-?). Please ensure strict consistency or, if needed, define terminology upon first use, to facilitate reading to an international audience.

Please ensure that all acronyms are formally defined upon their first appearance.

Supplementary figures are missing.

Grammar should be checked as there are several pitfalls and grammatical errors throughout the text.

Some structural units and regions of primary importance in the evolution of the area are directly presented in the discussion section (ex: Quagan Qulu back-arc basin, Solonker suture) making it difficult to follow the discussion, as well as to understand location and significance of such units. Ensure all structural units and terminology are properly introduced and located in a map or figure.

The discussion chapter is at times a bit confusing regarding which findings are new observations from this work and which are previous findings from other studies. Some assertions by other authors appear in the discussion without being introduced beforehand in the tectonic setting or previous data sections. This makes it difficult to follow the discussion and to track the novel contributions of the presented work. I would recommend ensuring a clear separation between new and previous evidence to improve readability.

Specific comments
Figure 1: Consider adding a global location map to make it easier to locate the study area.

Figure 2. and section 4.1. It is not entirely clear to the referee that the paleocurrent data cluster around the areas stated by the authors. For example, the authors state that Triassic paleo-flows in EHCB show “unimodal southeastward direction”. However, Fig. 2 shows a rather dominant southward direction, or even south-southward in some cases. Given this discrepancy, describing it as a “general southward direction” might be more accurate that “unimodal southeastward”. Furthermore, the authors state that Triassic paleocurrents in western Ordos are “southeastern directed”, but Fig. 2 shows a high degree of dispersion. While it is true that the SSE quadrant might be dominant, and that dispersion is consistent with alluvial fan deposition, I would recommend explain section 4.1. in more detail. Doing so, it would significantly improve the clarity of the text and the solidity of observations, especially considering that paleocurrent data play an important role in the discussion of the results.

Section 3. “Chang” members are introduced as Triassic stratigraphic units in Ordos basin, but they do not appear in Fig. 3., nor in other sections of the text. Please ensure all units are properly introduced and shown in maps and/or figures.

Figure 9 c.: This figure illustrates the composition of lithic fragments, which subsequently supports the provenance analysis together with other evidence. In section 5.1.1. the authors state that Permian samples are dominated by volcanic lithic fragments. However, Fig. 9 c. does not appear to support this affirmation. I would recommend reviewing this interpretation and questioning the affirmations of provenance that rely on these specific data.

Figure 14. Figure caption does not seem to correspond to the figure itself.

Section 5.1.1. It is not entirely clear to the referee whether the section title accurately reflects the content of the section. While the section summarizes paleocurrent data, petrological observations, and previous geochronological data, the section title seems to imply a direct comparison between newly collected and previous findings. I would recommend evaluating the primary objective of this section and, if necessary, rephrase the title or restructuring the text to more clearly compare the new observations against previous ones.

Figure 15. Figure labels are not explained in figure caption. Figure caption is incomplete.

Section 5.3.1. Although the lines of evidence are clearly interlinked, the authors introduce some features that have not been described in precedent sections, such as the existence of diabase sills, or structural features such as normal faults. Moreover, some of these features appear in earlier figures without prior explanation (ex: diabase sills, figure 3, crustal thickness variation, figure 18). For the sake of clarity, I would recommend ensuring all evidence and features used in the discussion are properly introduced and described in the stratigraphy/geologic context section, if needed.

Figure 19, section 5.3.1. Eu/Eu* geochemical analysis was conducted to characterize crustal thickness variations. This methodology appears in the discussion without being properly introduced and described in the methodology section. Please ensure that all data and methods are introduced in the corresponding section.

Permian – Triassic unconformity: In section 5.2.3. the authors state that zircon ages found in Triassic samples of southern EHCB support post-depositional erosion. Later, in section 5.3.2. they indicate that crustal thickening in the NCLA during the Permian produced depositional hiatus in EHCB, which appears to contradict these earlier observations. I would recommend reorganising or rephrasing the discussion section in general, to ensure consistency across statements.

Minor comments:
“Commence of Carboniferous” instead of “Commerce of Carboniferous” (pg. 5)

“Successions” instead of “succussions” (pg. 6)

“Red stars” instead of “Red stars with red words” (pg. 8)

“EHCB show textural immaturity” instead of “EHCB are textural immaturity” (pg. 13)

In Fig. 15, “Ages of potential provenances” instead of “Ages of penitential provenances”

“no time-equivalent” instead of “on time-equivalent” (pg. 25)

“change” instead of “chang” (pg. 26)

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Citation: https://doi.org/10.5194/egusphere-2026-4406-RC1
CC1:
'Comment on egusphere-2026-4406', Beihang Zhang, 19 Sep 2026 reply
This preprint presents an integrated study combining field sedimentology, paleocurrent measurement, sandstone petrography, detrital‑zircon U‑Pb geochronology, and zircon Lu‑Hf isotopes to reconstruct the Carboniferous‑Triassic evolution of the Andean‑type continental‑arc‑retro‑arc basin system in the Eastern Hexi Corridor and western Ordos Basin. The authors establish a three‑stage evolution history tightly linked to the subduction and closure of the Paleo‑Asian Ocean and highlight the orographic rain‑shadow effect triggered by arc uplift, which drove retro‑arc aridification recorded by lithological colour changes in mudstones. This work supplies valuable basin‑fill evidence for tectono‑sedimentary‑climatic coupling in the southern Central Asian Orogenic Belt. Overall, this is a data‑rich and constructive contribution.
Nevertheless, several points deserve revision, and the specific comments are as follows.
Major comments：
Detrital zircons from the Carboniferous and Triassic strata contain a certain proportion of Neoproterozoic ages, whereas those from the Permian strata contain none at all. The Permian provenance was mainly derived from the Nuru–Langshan belt to the north, which is the principal exposure area of Neoproterozoic intrusions in the Alxa region. Why did this belt not provide detrital material to the Permian strata?

Triassic paleocurrent data and detrital zircon ages indicate that the detritus was mainly derived from the north. However, the Triassic was precisely the key period of collision between the North China and South China cratons, which led to the uplift of the Qingling Mountain. Why, then, did the Qilian Mountains and West Qinling Mountain, on the southern side of the Hexi Corridor, not develop into a highland capable of supplying detritus?

Regarding the crustal thickness of the Nuoergong–Langshan tectonic belt during the Middle–Late Permian, additional literature should be cited to support the argument. The following reference is recommended: Hui Jie, Zhang Kai-Jun, Zhang Jin, Qu Junfeng, Zhang Beihang, Zhao Heng, Niu Pengfei. 2021. Middle-late Permian high-K adakitic granitoids in the NE Alxa block, northern China: Orogenic record following the closure of a Paleo-Asian oceanic branch? Lithos, 400-401, 106379.

General comments：
Whether to add "the" before geological time units should be made consistent throughout the manuscript.

Throughout the manuscript, a comma is missing after "et al." in numerous places; please uniformly correct them to "et al.,"

Using Figure 1a to indicate the tectonic location of Figure 1b is somewhat inappropriate, because Figure 1b illustrates present-day geological features, whereas Figure 1a depicts the tectonic framework at ~300 Ma. It is recommended to add or replace it with an appropriate tectonic location map.

Some fault elements in Figure 2 are incomplete. For example, along the eastern margin of the Bayanhala fault, the elements indicating fault kinematics are incomplete. On both sides of the Helan Mountains, multiple isolated arrows or short lines associated with faults appear, but the actual fault traces are missing.

The location of the cross-section in Figure 2b is not clearly indicated in Figure 2a. It is recommended to directly label the two ends of the line segment as B1 and B2 to facilitate correspondence with Figure 2b.

In the Fig.3 caption, “defined in (Cohen et al. 2013)” should be revised to “defined in Cohen et al. (2013)”.

In the Fig. 4 caption, "red star and red text" should be revised to "red star and black text."

“Xiangyang, Yang” in the author list, a comma appears between the given name and the surname, inconsistent with the other author names. Suggested revision: “Xiangyang Yang (delete the comma)”.

“geological harmer” in Fig.5 and Fig.8 content should be revised as “geological hammer”.

Line 72, “Changanchulu” should be revised to “Chaganchulu”.

Line 87, “delimitated” should be revised to “delimited”.

Lines 91, 96, “Terrene” should be revised to “Terrane”.

Line 98, “Commerce” should be revised to “Commencement”.

Line 158, “uncomfortably” should be revised to “unconformably”.

Line 206, “paleodranage” should be revised to “paleodrainage”.

Line 343, “attitude” should be revised to “attribute”.

Reply
Citation: https://doi.org/10.5194/egusphere-2026-4406-CC1

Junxiang Zhang, Jiaopeng Sun, Yunpeng Dong, Xiaofeng Han, Xiangyang Yang, and Yukun Qi

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Short summary

Two basin transition events occurred at ca. 295–265 Ma and ca. 250–240 Ma.
Retroarcbasin evolved from Carboniferous extension to Permian
Retroarcdrainage reorganization in syn-orogenic basin occurred at mid-Triassic.
Retroarcbasin fluctuation coincided with changing tectonic regime of the
An evolving Andean-type arc system across the northern North China was depicted.


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