# Polycyclic Andean-type orogenic evolution of the Dunhuang block in NW China: A result of Paleozoic reconfiguration of oceanic subduction systems

Jérémie Soldner, Karel Schulmann, Pavla Štípská, Yingde Jiang, Robert

Anczkiewicz, Chao Yuan, Zongying Huang

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Jérémie Soldner, Karel Schulmann, Pavla Štípská, Yingde Jiang, Robert Anczkiewicz, et al. Polycyclic Andean-type orogenic evolution of the Dunhuang block in NW China: A result of Paleozoic reconfiguration of oceanic subduction systems. Earth-Science Reviews, 2025, 261, 10.1016/j.earscirev.2024.104984. insu-05082256

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# Polycyclic Andean-type orogenic evolution of the Dunhuang block in NW China: A result of Paleozoic reconfiguration of oceanic subduction systems

Jérémie Soldner<sup>a</sup>, Karel Schulmann<sup>c,d,**</sup>, Pavla Štípská<sup>d</sup>, Yingde Jiang<sup>b,*</sup>, Robert Anczkiewicz<sup>a</sup>, Chao Yuan<sup>b</sup>, Zongying Huang<sup>b</sup>

<figure><img src="image_3.png" /></figure>

## ARTICLE INFO

### Keywords:

- Dunhuang block

- HP-HT metamorphism

- CAOB

- Hot orogen

- Andean-type convergence

## ABSTRACT

Despite numerous studies of metamorphic and magmatic rocks from the Dunhuang block, its protracted Cambrian to Permian geodynamic evolution as well as its role in the final amalgamation of the Tarim–North- China Craton Collage during the Pangea assembly, remain controversial. In order to understand the evolution of the Dunhuang block in the frame of Paleozoic plate tectonics, we review and synthetize recently published P–T data along with geochronological and geochemical data for its northern, central and southern mountain ranges, which we placed in the context of structural observations. Zircon and monazite U–Pb ages combined with P–T constraints determined for Ordovician to Devonian metamorphic rocks reveal that M₁ and M₂ metamorphic events define a clockwise P–T evolution and distinctly hot metamorphic gradients. Ordovician to Devonian protracted garnet growth evidenced by low (Yb/Gd)N ratios in metamorphic zircon and monazite, together with low Th/U ratios, negative εHF(t) and Eu anomalies in magmatic and metamorphic zircon, mark a period of continuous metamorphism accompanied by crustal reworking during thickening of a previously thermally softened crust. Zircon and monazite U–Pb ages suggest that the early Paleozoic D₁–M₁ and D₂–M₂ events started ca. 10 m.y. earlier and lasted longer in the northern and central ranges compared to the southern range con- sisting of significantly older crustal basement components. In all three mountain ranges, the formation of an E-W trending steep cleavage related to D₃–M₃ event was concomitant with emplacement of numerous late Devonian to Carboniferous diorites and I-type granitoids. The negative εHF(t) of magmatic zircon and high (Yb/Gd)N ratios in metamorphic zircon and monazite show that a magma-assisted N-S-directed shortening event responsible for further crustal reworking started in the late Devonian and lasted over 60 m.y. The latest Permian M₄ meta- morphic event, restricted mainly to the southern range, defines anticlockwise P–T paths associated with the emplacement of high-K calc-alkaline granitoids. This event is characterized by the increasing from negative to positive zircon εHF(t) values, suggesting input of juvenile crustal and mantle-derived material. High metamorphic gradients and the petrogenesis of magmatic arc-related rocks intruding a Precambrian basement suggest that the Dunhuang block developed as a supra-subduction continental hot orogenic system formed above subducting oceanic plates similar to the northern and southern margins of the American Cordillera. Our data show that its evolution was related to two kinematically independent early to middle and late Paleozoic orogenic cycles. In the context of plate tectonic reconstructions, the revised chronology of events points to the kinematic interplay between the continental blocks moving within the Proto-Tethys oceanic domain in association with the south- dipping Panthalassa, Paleo-Asian, and north-dipping Paleo-Tethys oceanic subduction systems.

<footnote><sup>a</sup> Institute of Geological Sciences, Polish Academy of Sciences, Senacka 1, 31-002 Kraków, Poland</footnote>

<footnote><sup>b</sup> State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China</footnote>

<footnote><sup>c</sup> Université de Strasbourg, CNRS, ITES UMR 7063, 5 rue René Descartes, 67084 Strasbourg Cedex, France</footnote>

<footnote><sup>d</sup> Centre of Lithospheric Research, Czech Geological Survey, Klárov 3, 118 21 Praha, Czech Republic</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>** Corresponding author at: Université de Strasbourg, CNRS, ITES UMR 7063, 5 rue René Descartes, 67084 Strasbourg Cedex, France.
E-mail addresses: schulmann.karel@gmail.com (K. Schulmann), jiangyd@gig.ac.cn (Y. Jiang).</footnote>
# 1. Introduction

The Central Asian Orogenic Belt (CAOB) is considered to be one of the largest Phanerozoic accretionary orogens on Earth formed from ca. 600 Ma to 250 Ma (e.g. Zonenshain, 1973; Khain et al., 2003; Wilhem et al., 2012). The CAOB was recently interpreted as a supercollage consisting of three collages characterized by distinct tectonic histories: the Mongolian Collage in the northeast, the Kazakhstan Collage in the

northwest and the Tarim–North-China Craton Collage (TNCC) in the south (Xiao et al., 2015) (Fig. 1a). In the last decades, significant progress has been made in the understanding the late Proterozoic to early Mesozoic tectonic evolution of the Mongolian and Kazakhstan Collages and their attachment to the Siberian Craton (e.g. Buslov et al., 2004; Donskaya et al., 2013; Wilde and Zhou, 2015; Huang et al., 2018; Xiao et al., 2018).

However, there is a controversy on the tectonic evolution of the

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** a) Tectonic map of central Asia with the principal tectonic zones indicated (modified after Guy et al., 2020). The black and white lines correspond to tectonic and state boundaries, respectively. b) Tectonic map of the Dunhuang block and adjacent areas showing the distribution of high-grade metamorphic rocks (colored stars) in the Tarim–North-China Collage, the Tethyan domains and the Beishan Orogen in the southern CAOB. Satellite image Google Earth and Landsat/Copernicus.</figcaption></figure>
southerly TNCC and its interaction with the Tethyan oceanic domains and incorporation into the CAOB. Recently, it has been proposed that likewise the other East Asian blocks, the Tarim, North-China, Dunhuang and Alxa blocks collided with the northern margin of Gondwana either at 500–420 Ma (Han et al., 2016; Zhao et al., 2018) or at ca. 400 Ma (Li et al., 2018). The corresponding accretionary-collisional processes between oceanic and continental units currently forming the northern part of the Tibetan plateau were interpreted as a result of the subduction of the Proto-Tethys Ocean (e.g. Xiao et al., 2009; Li et al., 2018; Song et al., 2018; Zhao et al., 2018). The subsequent dispersion of the TNCC continental blocks and their drift away from the northeastern Gondwana were related to the subduction of the Paleo-Asian Ocean and the concomitant opening of the Paleo-Tethys Ocean (Li et al., 2018; Zhao et al., 2018; Metcalfe, 1994, 2021). However, the relative position of these blocks during dispersal and potential existence of a single or multiple independent subduction zones remain elusive, giving rise to contrasting tectonic models (e.g. Buslov et al., 2001; Zhou et al., 2010; Zuza and Yin, 2017; Eizenhöfer and Zhao, 2018; Li et al., 2018; Zhao et al., 2018; Dong et al., 2021; Allen et al., 2023).

As part of the TNCC, the Dunhuang block is located in a proximal position to both the late Carboniferous to Triassic Tianshan-Beishan-Solonker suture zones to the north (e.g. Xiao et al., 2015) and the early Paleozoic Proto-Tethyan sutures to the south (e.g. Zhao et al., 2018). It therefore holds a critical position at the junction of two large Phanerozoic orogenic systems. The Paleozoic tectono-thermal evolution of the Dunhuang block has been inferred from middle Ordovician to early Carboniferous HP metamorphism (e.g. Zong et al., 2012; He et al., 2014; Wang et al., 2017a, 2017b, 2017c, 2018b, 2022; Zhang et al., 2020; Si et al., 2022; Soldner et al., 2023). The duration of this protracted Paleozoic metamorphism is generally compatible with other examples of large hot Precambrian to Paleozoic collisional orogens (e.g. Chardon et al., 2011; Clark et al., 2015; Guergouz et al., 2018). However, numerous middle Cambrian to late Carboniferous magmatic arc rocks have been reported in the Dunhuang block over the last decade, suggesting even longer orogenic processes (Wang et al., 2016a, 2016b; Zhao et al., 2015a, 2015b; Zhao et al., 2017; Zhu et al., 2014, 2020; Gan et al., 2020b, 2021a, 2021b; Kang et al., 2023). Based on both metamorphic and igneous rock geochronology data, a long-lasting oceanic subduction-accretion evolution has been proposed to explain crustal architecture and presence of HP rocks in the southern part of the Dunhuang block (Wang et al., 2022 and references therein). These authors interpreted the apparent block-in-matrix features and hairpin-shaped P–T trajectories as diagnostic of typical Franciscan mélanges (Ernst, 1988). However, similar P–T paths were also identified in typical continental collisional settings (Carswell and Zhang, 1999; Festa et al., 2010, 2012; Catlos et al., 2018; Goscombe et al., 2018). In addition, the presence of large amounts of Precambrian basement rocks (e.g. He et al., 2013; Xin et al., 2013; Zhao et al., 2019b, 2022; Zong et al., 2013; Long et al., 2014; Gan et al., 2020a; Lv et al., 2020) and dominantly continental type sediments of the Dunhuang block (Wang et al., 2013; Zhao et al., 2017, 2019c, 2020) contradict a Franciscan-type oceanic mélange architecture characterized by blueschist, eclogite and gabbro blocks enclosed in a sedimentary matrix and serpentinites.

In order to address these controversial issues, we collected and synthesized the metamorphic P–T and geochronological data for early to late Paleozoic high-grade metamorphic rocks from three individual, NE-SW trending mountain ranges of the Dunhuang block. In particular, the significance of recently acquired and previously unpublished metamorphic P–T data for early and late Paleozoic rocks combined with zircon and texturally controlled monazite U–Pb dating (Soldner et al., 2022, 2023, 2024) are discussed. These data are synthesized for the whole Dunhuang block and correlated with the Paleozoic magmatic evolution of the adjacent blocks in order to bring a coherent view of its protracted tectono-thermal evolution. By doing this, we argue that the Dunhuang block does not resemble typical peri-Pacific accretionary, Franciscan-type subduction or Tibetan-type collisional orogen. In

contrast, it shows features typical for hot supra-subduction belts characterized by alternating periods of orogenic extension and contraction. The newly identified early and late Paleozoic orogenic cycles are discussed in the frame of recent full-plate tectonic models for East Asian Blocks (Domeier and Torsvik, 2014; Domeier, 2018; Merdith et al., 2021). The combination of structural, metamorphic and magmatic records with plate tectonic models for the Dunhuang block allows robust linkage with neighboring orogenic and hypothetical oceanic systems that existed during the dispersal of the north Gondwanan blocks and their amalgamation with the CAOB during Paleozoic times.

## 2. Geological setting and regional structural patterns

### 2.1. Geological setting

The Dunhuang block forms a narrow NE-SW trending segment of the Tarim–North-China Collage (TNCC) in northwestern China, located north of the Tibetan plateau (Fig. 1a). It is bounded by the Tarim Craton to the west and by the Alxa (or Alashan) block in the east (Fig. 1b). The northern termination of the Dunhuang block is separated from the Beishan Orogen by the Ordovician to Permian Shibanshan arc (e.g. Xiao et al., 2010; Tian and Xiao, 2020), whereas in the south it is bounded by the Altyn-Tagh fault (Fig. 1b).

The Dunhuang block is mostly covered by Quaternary sediments. The basement rocks crop out in three roughly NE-SW striking mountain ranges (referred to as ranges hereafter) with lengths varying 60–250 km each: the Qiaowan, Xiaowan, Sanweishan, Duobagou, Kalashitage sections in the northern range (Fig. 2a), the Mogutai, Dongbatu and Changshanzi sections in the central range and the Hongliuxia, Qinshigou and Chijin sections in the southern range (Fig. 2a,b). The northern range is structurally dominated by the top-to-the-north thrust, namely the Main Sanweishan fault system along its 140 km-long northern margin (Cunningham et al., 2016). Together with the Altyn-Tagh fault system, these three ranges represent a regional asymmetric half-flower structures related to late Cenozoic sinistral transpressive restraining bend (Cunningham et al., 2016). The rocks exposed in the region mainly consist of metamorphic, magmatic and sedimentary rocks that are either Mesoarchean to Paleoproterozoic, early Paleozoic or early Mesozoic in age (Fig. 2c).

Precambrian rocks consist of extensive tonalite-trondhjemite-granodiorite (TTG)-like gneisses and supra-crustal metasediments (Fig. 2c; BGMRG, 1989; Lu et al., 2008). The supracrustal metamorphosed rocks involve micaschists, marbles and quartzites enclosing bodies of high-grade metabasites (eclogite, granulite and amphibolite), which are either referred to as the Dunhuang Group, the Milan Group (e. g. BGMRG, 1989; Mei et al., 1997; Lu et al., 2008) or as the khondalite series (Yu et al., 1998). Gneisses and supra-crustal rocks are strongly deformed and throughout the Dunhuang block they are either intruded by Paleozoic magmatic rocks or show sharp fault contacts with these intrusions. In the southern Dunhuang block, metabasite layers alternate with gneisses and micaschists or occur as lenses enclosed in marble (Wang et al., 2014; Zhang et al., 2012). The TTG-like gneisses were formed at 3.0–3.3 Ga (Fig. 2b) (Zhao et al., 2015a) and 2.74–2.50 Ga (Xin et al., 2013; Zhao et al., 2013; Long et al., 2014). Paleoproterozoic metamorphism constrained at 2.00–1.82 Ga has been recognized in both the TTG-like gneisses and metabasites (Fig. 2b) (Zhang et al., 2012; Zong et al., 2013; Zhao et al., 2015a).

In the northern range, weakly metamorphosed late Sinian to Cambrian sandstones and psammites (Kang et al., 2021; Soldner et al., 2022) and late Silurian to early Devonian volcanoclastic sediments (Shi et al., 2020) have been intruded by Paleozoic granitoids and covered by layered volcanics (Kang et al., 2021). Throughout the Dunhuang block, early to late Paleozoic granitoids were variably deformed and affected by overprint locally reaching anatexis (Soldner et al., 2022). In the northern range, undeformed granites host Paleozoic metabasites and metapelites (Li et al., 2021).
<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Geological map of (a) the northern (blue dashed line), central (green dashed line) and southern (red dashed line) mountain ranges and (b) the Chinji area (southern range) of the Dunhuang block modified after Zhao et al. (2017) and Wang et al. (2023). (c) Geological map of the Dunhuang block showing the occurrence and ages of Paleoproterozoic metamorphic and magmatic rocks. Satellite images Esri and EarthStar Geographics. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

Generally undeformed late Paleozoic granitoids, granitic veins and diabase dykes intrude both the early Paleozoic magmatic and metamorphic rocks (e.g. Zhang et al., 2020, 2022; Gan et al., 2021b). In the central and southern ranges, deformed Permo-Triassic pyroclastic sediments are intercalated with amphibole-biotite gneiss (Zhang et al., 2022; Wang et al., 2023).

## 2.2. Regional structural patterns

### 2.2.1. The northern and central ranges

Previous petro-structural studies revealed that the northern and central ranges of the Dunhuang block are characterized by multiple Paleozoic deformational-metamorphic fabrics (Zhang et al., 2020; Wang

et al., 2022; Soldner et al., 2023). Three principal metamorphic fabrics have been identified (Soldner et al., 2023). The oldest sub-horizontal S₁ fabrics are preserved in cores of garnet- and pyroxene-rich mafic granulite lenses in the Sanweishan and Mogutai sections (Figs. 3a and 4). In general, the S₁ fabric is parallelized to a steep amphibolite facies S₂ foliation represented by leucosome-rich retrograde migmatitic amphibolite rims of granulite lenses (Figs. 3d,e and 4). In metapelite and migmatitic metapelite, the N-S striking subvertical S₂ fabric is characterized by leucocratic bands alternating with layers rich in garnet, biotite and kyanite (Fig. 3 a,b,f). The S₂ foliation also occurs in amphibolite lenses, where it intersects at high angle with the main regional sub-vertical E-W striking S₃ foliation (Fig. 3g in Wang et al., 2022). The symmetric, nearly vertical, close to isoclinal F₃ folds show steep west-
<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Field photographs and typical structural relationships in the northern, central and southern ranges of the Dunhuang block. **Northern range:** (a) Preserved S₁ relics in granulite core and S₂-parallel leucosomes developed in retrograde migmatitic amphibolite and metapelite. (b) F₃ open folds deforming S₂ schistosity in metapelites. (c) Penetrative subvertical S₃ fabric in an amphibolite layer, with metamorphic age of 462.4 ± 3.4 Ma (Soldner et al., 2022 (1)). **Central range:** (d) Metabasite lens consisting of granulite core and amphibolite rim enclosed in migmatitic metapelite (Soldner et al. (2023) (2)). (e) Granulitic layers and S₂-parallel leucosomes in amphibole-rich retrograde fabric. (f) Preserved S₂ fabric in retrograde amphibolite lens enclosed in migmatitic metapelite showing cleavage S₃. **Southern range:** (g) Metabasite lens consisting of a granulite core and a amphibolite rim enclosed and injected by leucosomes. (h) F₃ folds reworking the S₂ fabric in (i) paragneiss sample 19HLX17 enclosing an amphibolite lens. (j) Marble hosting an elongated amphibolite boudin with a metamorphic age of 1611 ± 6 Ma (Wang et al. (2013) (3)).</figcaption></figure>

plunging fold axes and E-W striking axial planes (Soldner et al., 2023) (Figs. 3b and 4). The D₃ deformation and F₃ folding are associated with almost complete transposition of all previous fabrics into a ubiquitous S₃ fabric in both the gneisses and amphibolite lenses of the northern range (Fig. 3c) and in the migmatitic metapelite of the central range (Fig. 3f). These amphibolite-facies fabrics have also been observed in the Dong-batu section and interpreted as related to a reverse shearing event by Feng et al. (2018). There, the sub-vertical S₃ fabric is reworked by late Permian-middle Triassic dextral shearing (Feng et al., 2018).

### 2.2.2. *The southern range*

The S₂ and S₃ fabrics are dominant in the southern range (Fig. 3) (Wang et al., 2017b, 2018b, 2023; Soldner et al., 2023). There, mafic granulite and amphibolite occur as metric to plurimetric lenses or layers within orthogneiss, metapelite or marble (Fig. 3g-j) and are often intruded by Paleozoic granitic plutons. In the Hongliuxia section, cores of granulitic boudins are coarse-grained and show isotropic texture (Fig. 3g). However, the relics of the earliest fabric S₁ are locally preserved in form of rootless folds in metasediments (Wang et al., 2017b and Fig. 2e in Wang et al., 2018b). In these rocks, the steep S₂ fabric is mostly defined by leucosome-rich migmatitic amphibolite rims in layered granulite (Fig. 4g in Wang et al. (2016c)) and by folded quartz

bands that are alternating with garnet-, biotite- and kyanite-rich layers preserved in low-strain domains in metasediments (Fig. 3h,i). Despite the local presence of mm-size quartz veins, garnet-free amphibolites rarely preserve evidence of the S₂ fabric and are usually fine-grained and isotropic (Fig. 3h). Similarly to the northern and central ranges, the F₃ folds are mostly vertical, symmetric, and isoclinal with steeply plunging fold axes and generally E-W striking and S-dipping axial planes (Figs. 3h and 4) (Soldner et al., 2023; Wang et al., 2023). Likewise in the northern range, the S₃ fabric is penetrative in both the gneisses and the amphibolite lenses (Fig. 3c in Wang et al. (2016c)). There, the sub-vertical S₃ fabric is reworked by shear zones responsible for the formation of F₄ tight folds, σ-type clasts and S-C fabrics, interpreted as reflecting top to the NW or NE thrust motion (Wang et al., 2022). However, in contrast to the northern and central ranges, numerous mafic granulite and amphibolite of Paleoproterozoic metamorphic age (Zhang et al., 2012; Wang et al., 2014, 2017c) occur within metasediments and marble affected by S₃ (Fig. 3j).

## 3. Methodology

We compiled a data set of thermobaric (T, P) data along with zircon and monazite U-Pb ages (t) of Paleozoic to early Mesozoic metamorphic
<figure><img src="image_7.png" /><figcaption>Fig. 4. Stereonets of poles to planar structures and corresponding insert sketches showing the deformational evolution of the Dunhuang block during the D₁, D₂ and D₃ events. The structural data is compiled from Soldner et al. (2023) and Soldner et al. (2024).</figcaption></figure>

rocks from the Dunhuang block. This is further complemented with a compilation of metamorphic zircon and monazite trace-element data. We also compiled zircon U–Pb age (t) and trace-element data for Paleozoic to early Mesozoic magmatic rocks from the Dunhuang block. In order to complete the above-mentioned data compilation, amphibolite sample 17JS44 from the northern range (40°22′29.09″N, 95°49′15.00″E) as well as metapelite sample 19HLX17 (39°47′57.17″N, 95°31′59.14″E) and orthogneiss sample 19HLX48 (39°42′41.51″N, 95°23′25.40″E) both from the southern domain have been chosen for petrography, mineral composition analysis and chemical mapping, zircon U–Pb dating and trace-element analysis as well as texturally controlled monazite U–Pb dating and trace-element analysis.

Back-scattered electron (BSE) images, compositional analyses and element mapping of monazite for sample 19HLX17 were carried out using a JEOL JXA-8230 Electron Probe Micro-analyzer (EPMA) at the Key Laboratory of Mineralogy and Metallogeny (KLabMM) at GIGCAS. BSE images, compositional analyses and element mapping of selected minerals for samples 17JS44, 19HLX17 and 19HLX48 were carried out using a JEOL SuperProbe JXA-8230 electron microprobe at the Laboratory of Critical Elements AGH-KGHM at the AGH University of Science and Technology (Kraków, Poland). Mineral chemical compositions are given in Table S1. Chemical maps of monazite are given in Supplementary Fig. S4. Chemical maps and major-element compositional profiles of garnet are given in Supplementary Fig. S6.

Cathodoluminescence (CL) images of zircon were obtained using a JEOL JSM-6510A scanning electron microscope (SEM) and MiniCL detector at the Chongqing Yujin Technology Co., Ltd, China, and a Hitachi Su 3500 SEM with a CL detector at the Polish Geological Institute-National Research Institute, Warsaw. Zircon U–Pb dating of sample 19HLX48 was performed using an ELEMENT XR (Thermo Fisher Scientific) ICP-SF-MS coupled with a 193-nm (ArF) Resonetics RESOlution M-50 laser ablation system in the SKLaBIG at GIGCAS. The detailed experiment procedure and data reduction strategy are described in Zhang et al. (2018). Laser condition was set as following: beam size, 33 µm; repetition rate, 6 Hz; energy density, ~4 J cm⁻². Laser ablation ICP-MS U–Pb zircon dating of sample 19HLX17 was conducted at the Institute of Geological Sciences of the Polish Academy of Sciences (IGSPAS) using an excimer laser (ArF) RESOlution by Resonetics (now Applied Spectra) equipped with double volume S155 Laurine Technic

sample cell. The laser was coupled with Agilent 8900 Triple Quadrupole ICP-MS. Laser condition was set as following: beam size, 18 µm; repetition rate, 5 Hz; energy density, ~3 J cm⁻². Data reduction was performed using Iolite 4 (Paton et al., 2011). Representative CL images of zircon are given in Supplementary Fig. S3c and f. Results of zircon U–Pb and trace-element analysis are given in Table S2. Age calculations and Terra-Wasserburg diagrams were performed using Isoplot/Ex (Ludwig, 2003).

Texturally controlled monazite U–Pb and simultaneous trace-element analysis in thin section were acquired at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan). Sample ablation was performed directly in thin section using an ArF excimer GeoLas 2005 193 µm connected to an Agilent 7500a ICP-MS instrument. The laser spot diameter was 10 µm with a laser fluence was 6 J cm⁻² at a repetition rate of 3 Hz. Age calculations and Terra-Wasserburg diagrams were performed using Isoplot/Ex (Ludwig, 2003). Results of texturally controlled monazite U–Pb and trace-element analysis are given in Table S3 and Supplementary Fig. S5.

In order to constrain the *P*–*T* evolution of amphibolite 17JS44 and paragneiss 19HLX17 samples, the textural relationships, observed mineral assemblages and measured mineral compositions were compared with calculated *P*–*T* pseudosections, all available in the Supplementary material S1. Phase equilibria were calculated using the PerpleX version 6.8.1 software package (Connolly, 2005) with the upgraded thermodynamic database DS6.22 from Holland and Powell (2011). Pseudosections were calculated in the MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O (MnNCKFMASHTO) chemical system. Details of the petrological and metamorphic studies together with the results from mineral compositional analyses phase diagram calculations for samples 17JS44 and 19HLX17 can be found in the Supplementary Figs. S1 and S2 and Table S1 of the Supplementary material S1. Mineral abbreviations are after Whitney and Evans (2010).

Details of all the analytical procedures and methodologies are given in the Supplementary material S1.
## 4. Paleozoic metamorphism in the Dunhuang block: Petrology, P–T constraints, metamorphic ages and isotopic data

The detailed descriptions of the petrology, P–T data, geochronology and Hf isotopic data of the metamorphic rocks from the Dunhuang block are given hereafter and are summarized in Figs. 5, 6 and 7 and in Table 1. The data synthesis suggests that these features can be used to distinguish contrasting metamorphic evolutions for rocks outcropping in the northern, central and southern ranges.

New petrological, geochronological and metamorphic P–T investigations are carried out on samples from the northern and southern ranges to complete the existing dataset (Fig. 2a). In the Xiaowan section of the northern range, amphibolite sample 17JS44 displays the oldest middle Ordovician metamorphic age (Soldner et al., 2022) (Fig. 3c). Hence, petrographic investigations and P–T calculations are performed on this sample to constrain the nature of the earliest Paleozoic metamorphism (Supplementary Figs. S1 and S6). Recently, studies based on garnet Sm–Nd ages showed that metamorphic reequilibration occurred in the Carboniferous (Si et al., 2022) but P–T data characterizing the late Paleozoic metamorphism are generally lacking. Petrochronological investigations based on zircon and texturally controlled monazite U–Pb geochronology and P–T calculations are therefore conducted on paragneiss sample 19HLX17 from the Hongliuxia section of the southern range in order to address this issue (Supplementary Figs. S2 and S3–S6). This is complemented with zircon U–Pb geochronological investigations of the protolith of orthogneiss sample 19HLX48 from the same section that provides an upper age limit for the late Paleozoic deformation D₃.

### 4.1. The northern range

In the Sanweishan and Kalashitage sections, metabasites consist of: i) HP mafic granulite or amphibolite lenses or layers within gneiss, metapelite or marble (Zhao et al., 2016; Zhang et al., 2020; Wang et al., 2022), ii) enclaves or xenoliths in pegmatites or granites (Zhao et al., 2016; Li et al., 2021). In mafic granulite, the prograde, peak and retrograde metamorphism are characterized by mineral assemblages of Hbl-Pl-Qz-Ilm ± Cpx ± Ep (M₁), Grt-Cpx-Hbl-Pl-Qz-Rt ± Ilm ± Ttn ± Ap (M₂) and Hbl-Pl-Qz ± Cpx ± Mag (M₃), respectively. Amphibolites enclosed within metasediments are commonly characterized by the peak metamorphic mineral assemblage (M₂) Grt-Amp-Pl-Qz ± Cpx ± Ep with rutile, titanite, ilmenite and apatite occurring as accessory phases (Fig. 5a,b) (Zhao et al., 2016; Li et al., 2021). In contrast, pyroxenite xenoliths in granites are characterized by the peak metamorphic assemblage (M₂) Grt-Cpx-Rt-Ttn-Ap, with the preservation of both high-Al titanite and rutile exsolution lamellae in garnet interpreted as evidence of ultrahigh-pressure (UHP) conditions (Li et al., 2021). Generally, both mafic granulite and amphibolite display Pl-Hbl symplectites at the rims of garnet porphyroblasts or replacing matrix clinopyroxene (Zhang et al., 2020; Wang et al., 2022; Li et al., 2021). The peak metamorphic assemblage M₂ in the host gneiss mainly consists of Grt-Hbl-Pl-Qz-Ap ± Ep ± Bt (Zhang et al., 2020; Wang et al., 2022).

Two contrasting clockwise P–T evolutions have been determined for metabasites from the northern range. Three suites of metamorphic stages with large P and T ranges have been determined for mafic granulite and amphibolite using thermobaronetry: 458–720 °C and 0.52–1.56 GPa (prograde metamorphism M₁), 590–920 °C and 0.67–1.62 GPa (peak metamorphism M₂) and 557–815 °C and 0.43–1.17 GPa (retrograde metamorphism M₃) (Fig. 6b; Table 1). Alternatively, phase equilibria calculations have been used to constrain M₁, M₂ and M₃ P–T conditions of mafic granulite from the Kalashitage and Duobagou sections at 510–800 °C and 0.85–1.30 GPa and 810–850 °C and 1.39–1.60 GPa and 750–785 °C and 1.13–1.17 GPa, respectively (Fig. 6b; Table 1). These P–T metamorphic conditions are compatible with those calculated in this study for the amphibolite from the Xiaowan section, with the M₂ stage constrained at ~825 °C and 0.9–1.0 GPa and

the M₃ stage constrained at ~750 °C and 0.75–0.85 GPa (Fig. 6b). In contrast, P–T conditions of the pyroxenite xenoliths in the Sanweishan section have been constrained at 662–692 °C and 0.54–0.72 GPa (M₁), 789–918 °C and 2.8–4.1 GPa (M₂) and 621–669 °C and 0.46–0.60 GPa (M₃) using thermobarometry (Fig. 6b; Table 1).

Zircon U–Pb data for amphibolites from the Sanweishan section yield metamorphic ages of 441 ± 3 Ma, 410–403 Ma and 370 ± 2 Ma with the early Devonian ages interpreted as reflecting amphibolite-facies metamorphism (Fig. 6a,c) (Meng et al., 2011; Zhao et al., 2016) (Table 1). In the Kalashitage, Duobagou and Xiaowan sections, zircon U–Pb data of mafic granulite and amphibolite yield metamorphic ages of ca. 462 Ma, 431–415 Ma and 398–389 Ma (Zhang et al., 2020; Soldner et al., 2022; Wang et al., 2022) (Fig. 6a,c; Table 1). Zhang et al. (2020) interpreted the two younger age groups as dating peak M₂ and retrograde M₃ metamorphism, respectively. This is compatible with low (Yb/Gd)N ratios of 445–394 Ma zircons in amphibolite suggesting that zircon crystallised together with garnet from 445 Ma (Soldner et al., 2022). Moreover, generally positive ε<sub>Hf</sub>(t) values (14.8 to –5.8) and T<sub>DM2</sub> ages from 1.11 to 0.87 Ga for metamorphic and magmatic zircons in amphibolite reflect the juvenile character of its protolith (Soldner et al., 2022).

### 4.2. The central range

In the Mogutai and Changshanzi sections, lenses and layers of HP mafic granulite and amphibolite are enclosed in metasediments (Zong et al., 2012; He et al., 2014; Pham et al., 2018; Wang et al., 2018a; Soldner et al., 2023) or migmatitic amphibolites (Soldner et al., 2023). For mafic granulite, prograde, peak and retrograde metamorphism are characterized by the assemblages: Cpx-Hbl-Pl-Qz-Ilm ± Ep ± Bt (M₁) included in garnet, Grt-Cpx-Pl-Qz-Rt ± Hbl ± Ilm ± Ttn ± Ap (M₂), and Hbl-Pl-Qz ± Cpx ± Mag (M₃) (Fig. 5c). Amphibolites are characterized by the Grt-Hbl-Pl-Qz ± Rt ± Ilm ± Ttn ± Ap peak metamorphic assemblage M₂ (Wang et al., 2018a; Pham et al., 2018; Soldner et al., 2023). All samples display Pl-Hbl symplectites around garnet rims or replacing matrix clinopyroxene (Zong et al., 2012; He et al., 2014; Wang et al., 2018a; Pham et al., 2018; Soldner et al., 2023) (Fig. 5c). These three metamorphic stages are locally supplemented by late retrograde metamorphic stage characterized by chloritization (He et al., 2014; Soldner et al., 2023). In metapelites and gneisses, prograde and peak metamorphism are represented by the PlBt-Qz-Ilm assemblage M₁ included in garnet and the Grt-Ky-Pl-Bt-Qz-Rt matrix assemblage M₂ (Zong et al., 2012; Wang et al., 2018a; Pham et al., 2018). In migmatitic metapelite, prograde, peak and retrograde metamorphism are defined by the assemblages Bt-Ms-Ky-Pl-Qz-Ilm-Rt (M₁), Grt-Bt-Ky-Pl-Kfs-Qz-Rt ± Sil ± Ms. (M₂) and Grt-Sil-Bt-Ms Pl-Kfs-Ilm-Qz (M₃) (Soldner et al., 2023) (Fig. 5d).

Metabasites and host rocks from the central range are characterized by clockwise P–T evolutions. Results from thermobarometry suggest that HP mafic granulite and amphibolite reached three metamorphic stages at 584–656 °C and 0.32–1.09 GPa (M₁), 720–896 °C and 0.98–1.76 GPa (M₂) and 520–710 °C and 0.32–0.72 GPa (M₃) (Fig. 6b; Table 1). Based on phase equilibria calculations, He et al. (2014) constrained prograde metamorphism M₁ at 720–750 °C and 1.10–1.30 GPa, peak metamorphism M₂ at 760–800 °C and 1.40–1.60 GPa, retrogression M₃ through 690–900 °C and 0.8–1.1 GPa and until <640 °C and 0.6 GPa. In contrast, Soldner et al. (2023) constrained prograde to peak-P metamorphism M₁ from 770–780 °C and ~1.15 GPa to 1.35 GPa and ~850 °C, peak-T metamorphism M₂ at 0.8–1.1 GPa and 850–900 °C and retrogression M₃ at ~0.8 GPa and ~625 °C. In the Duobagou section, results from phase equilibria calculations suggest that amphibolites reached lower peak P–T metamorphic conditions of 610–800 °C and 0.93–1.08 GPa (M₂) (Wang et al., 2018a; Si et al., 2022). Results from thermobarometry indicate that metapelites reached lower peak P–T metamorphic conditions of 635–860 °C and 0.60–0.99 GPa (M₂) (Wang et al., 2018a; Pham et al., 2018; Si et al., 2022) (Table 1). In the Mogutai section, migmatitic metapelite recorded three metamorphic stages at
<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Microphotographs of representative samples from the northern, central and southern ranges of the Dunhuang block. **Northern range:** (a) Garnet porphyroblast in the M₂ matrix in amphibolite 17JS44. (b) Clinopyroxene within the Amp-Pl-Qz M₂ matrix in amphibolite 17JS44. Epidote replacing plagioclase. **Central range:** (c) Garnet porphyroblast in the M₂ matrix in granulite. Amp-Pl symplectites replacing matrix clinopyroxene and Amp-Pl kelyphites around garnet. (d) Representative S₂ Ky-, Sil- and Bt-bearing fabric in melanosomes in migmatitic metapelite. **Southern range:** (e) Garnet, biotite and white micas in the S₃ matrix in paragneiss 19HLX17. (f,g) Sillimanite in quartz-plagioclase bands in paragneiss 19HLX17. (h) Fractured garnet in the S₃ matrix in orthogneiss 19HLX48. (i) Massive and isotropic texture of the matrix Grt-Amp-Ep-Pl-Qz-Ttn-Ilm assemblage in amphibolite, with Amp-Pl kelyphites around garnet and tabular epidote in the matrix.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 6.** (a) Geological maps of the Dunhuang block showing the occurrence and ages of Paleozoic metamorphic rocks from the northern (in blue), central (in green) and southern (in red) ranges. Numbers correspond to reference numbers in Table 1. Symbols correspond to data compiled from different geochronometers. (b) Summary of the *P*–*T* paths determined for the early and late Paleozoic rocks from the northern, central and southern ranges. (c) Relative probability density plots of Paleozoic metamorphic zircon ages in the northern, central and southern ranges. Satellite images Esri and EarthStar Geographics. Abbreviations: UHP, ultrahigh-pressure; UHT, ultrahigh-temperature; E-HPG, eclogite-high-pressure granulite; G, ganulite; A, amphibolite; BS, blueschist. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

760–810 °C and 0.90–1.25 GPa (M₁), 760 °C and 0.7 GPa (M₂) and 675 °C and 0.5–0.6 GPa (M₃) (Soldner et al., 2023).

Zircon U–Pb data of HP mafic granulite yield metamorphic ages of 444–428 Ma, 420–412 Ma and 403 ± 3 Ma (Fig. 6a,c; Table 1). The 444–428 Ma and ca. 403 Ma zircon ages have been interpreted as related to HP granulite-facies and retrograde amphibolite-facies metamorphism, respectively (Zong et al., 2012; He et al., 2014; Soldner et al., 2022). Their overall negative zircon $ε_{Hf}(t)$ values (–1.7 to –9.7) reflect the contribution of evolved crustal components (Soldner et al., 2022). Garnet Lu–Hf and Sm–Nd ages of 421.6 ± 1.2 Ma and 385.3 ± 4.0 Ma for mafic granulite have been interpreted as reflecting HP metamorphism and early cooling during exhumation, respectively (Soldner et al., 2023). Amphibolites from the *Mogutai and Changshanzi sections* systematically yield younger zircon U–Pb metamorphic ages of 408–399 Ma, 394 ± 1 Ma and 249 ± 4 Ma (Fig. 6a,c; Table 1). Zircon U–Pb data of metapelites yield metamorphic ages of 435–429 Ma, 418.5 ± 3 Ma and 372.4 ± 4 Ma, all interpreted as corresponding to peak metamorphism (Zong et al., 2012; Wang et al., 2018a; Pham et al., 2018). Garnet Lu–Hf and Sm–Nd ages of 409.7 ± 2.3 Ma and 356 ± 11 Ma for migmatitic metapelite have been interpreted as dating peak–T metamorphism and cooling below 700 °C, respectively (Soldner et al., 2023). Monazite U–Pb data yield a metamorphic age of 366 ± 3 Ma in metapelites (Zhao et al., 2020) (Fig. 6a). Granulite and amphibolite yield hornblende $^{40}$Ar–$^{39}$Ar ages ranging from 258 to 253 Ma (Fig. 6a) (Zhang et al., 2022).

### 4.3. *The southern range*

Block-in-matrix features represented by metabasite lenses enclosed in host metapelite, paragneiss and marble have been described throughout the southern range (Wang et al., 2016c, 2017a, 2017b; Wang et al., 2018a, 2018b, 2018c; Si et al., 2022). Metabasites mainly include HP mafic granulite and amphibolites (Wang et al., 2016c, 2017b; Wang et al., 2018a, 2018b, 2018c), whereas one eclogite boudin has been reported in the *Hongliuxia section* (Wang et al., 2017a) (Figs. 2a and 6a). Mafic granulites recorded prograde, peak and retrograde metamorphism characterized by the mineral assemblages Hbl-Pl-Qz-Ilm ± Cpx (M₁), Grt-Cpx-Hbl-Pl-Qz ± Rt ± Ilm ± Ttn (M₂) and Hbl-Pl-Qz ± Opx ± Mag (M₃), respectively (Wang et al., 2016c, 2017a, 2017b). Eclogite also preserves prograde, peak and retrograde metamorphic stages in the form of the mineral assemblages Cpx-Omp-Hbl-Pl-Qz-Kfs–Bt-Ep (M₁) included in garnet, and Grt-Omp-PlBt-Qz ± Rt ± Ilm ± Mg (M₂) and Hbl-Pl-Qz-Bt (M₃) in the matrix (Wang et al., 2017a). Amphibolites are composed of the peak metamorphic assemblage Grt-Hbl-Pl-Qz-Ilm ± Cpx ± Bt ± Rt ± Ttn ± Ap (M₂) (Fig. 5i) (Wang et al., 2017a, 2017b, 2018a; Si et al., 2022). All metabasites show Pl-Hbl symplectites rimming garnet porphyroblasts and replacing matrix clinopyroxene (Wang et al., 2017a, 2017b, 2018a; Si et al., 2022). In metapelites, prograde metamorphism is preserved in the form of the Bt-Pl-Qz-Ilm ± Ep assemblage M₁ included in garnet whereas peak metamorphism is characterized by the Grt-Bt-Pl-Qz-Ilm ± Ms ± Ky ± Sil (M₂) mineral assemblage (Wang et al., 2017a, 2017b) (Fig. 5e–g). In the *Chijin section*,
Magmatic rocks

<figure><img src="image_10.png" /><figcaption>**Fig. 7.** (a) Geological maps of the Dunhuang block showing the occurrence and ages of Paleozoic magmatic rocks from the Dunhuang block. Numbers correspond to reference numbers in Table 2. Relative probability density plots of Paleozoic magmatic zircon ages for the (b) northern, (c) central and (d) southern ranges. The vertical dashed lines correspond to garnet Lu-Hf and Sm-Nd ages from Soldner et al. (2023) (in green) and Si et al. (2022) (in red) for metabasites. Satellite image Esri and EarthStar Geographics. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

greenschist-facies metavolcanics occur together with interlayered schists, gneisses and migmatites characterized by the mineral assemblages Grt-Bt-Pl-Qz-Ilm ± Rt (M₂) and Grt-Bt-Pl-Qz-Ilm ± Kfs ± Ep (M₃) (Wang et al., 2023).

In contrast to the other ranges, metamorphic rocks from the southern range record both the clockwise and anti-clockwise *P*-*T* evolutions. A first group of rocks from the *Hongliuxia section* comprises eclogite, HP mafic granulite, amphibolite and their host metapelite, which record clockwise *P*-*T* evolutions. Results from thermobarometry suggest that eclogite reached conditions of ~830 °C and ~2.42 GPa during peak M₂, and ~652 °C and ~0.72 GPa during retrograde metamorphism M₃ (Wang et al., 2017a) (Fig. 6a,b; Table 1). In contrast, mafic granulite recorded three metamorphic stages at 568–756 °C and 0.76–1.06 GPa (M₁), 678–874 °C and 0.93–1.77 GPa (M₂) and 598–706 °C and 0.44–1.23 GPa (M₃) (Wang et al., 2016c, 2017a, 2017b) (Fig. 6a,c; Table 1). Phase equilibria calculations for paragneiss 19HLX17 presented in this study yield *P*-*T* conditions 0.45–0.65 GPa and 650–700 °C (M₂) and 0.30–0.35 GPa and 475–500 °C (M₃) (Figs. 6a,b and S2). A second group of rocks that comprises gneisses and metapelites from the *Chinji section* records anti-clockwise *P*-*T* evolutions. For these samples, prograde, peak and retrograde metamorphism have been constrained using thermobarometry and phase equilibria calculations at 440–610 °C and 0.41–0.48 GPa (M₁), 544–730 °C and 0.61–0.87 GPa (M₂) and 400–500 °C and 0.50–0.60 GPa (M₃) (Wang et al., 2023) (Fig. 6a,b;

Table 1).

Zircon U-Pb data for eclogite and mafic granulite yield metamorphic ages of 411.3 ± 1.7 Ma and 413–409 Ma, respectively, interpreted as the age of metamorphic peak (Wang et al., 2016c, 2017a) (Fig. 6a, Table 1). In these rocks, the upper intercepts of ca. 1.32 Ga and ca. 1.68 Ga possibly reflect the crystallization age of their protoliths. Amphibolites are characterized by i) zircon U-Pb metamorphic ages ranging from 417 to 351 Ma (Table 1), with the upper intercept ages at ca. 1.50 Ga, ca. 1.64 Ga and ca. 1.84 Ga possibly representing the crystallization ages of their protoliths (Wang et al., 2016c; Wang et al., 2017a, 2017b), ii) hornblende <sup>40</sup>Ar–<sup>39</sup>Ar ages of 406.9 ± 4.9 Ma and 397.3 ± 2.4 Ma that have been used to constrain the timing of amphibolite-facies metamorphism (Wang et al., 2017b) and iii) a garnet Sm-Nd age of 333.5 ± 4.0 Ma representing metamorphic reequilibration of 1.82–1.85 Ga Paleoproterozoic rocks (Fig. 6a) (Si et al., 2022). Metapelites and paragneiss yield zircon U-Pb ages of 413.7 ± 2.5 Ma (Wang et al., 2017a) and 408.1 ± 2.3 Ma (Supplementary Fig. S3e), monazite U-Pb ages of 276 ± 18 Ma (Delville et al., 2001) and 307.5 ± 2.1 Ma (Supplementary Fig. S5b), and <sup>40</sup>Ar–<sup>39</sup>Ar ages of 458–414 Ma and 217 ± 4 Ma (Sobel and Arnaud, 1999; Delville et al., 2001; Wang et al., 2005; Liu et al., 2007). Metapelites and paragneisses characterized by anticlockwise *P*-*T* evolutions yield biotite and hornblende <sup>40</sup>Ar–<sup>39</sup>Ar ages ranging from 252 to 237 Ma (Fig. 6a,c) (Wang et al., 2023).
<table><caption>**Table 1**
Summary of geochronological data for Paleozoic metamorphic rocks from the Dunhuang block.</caption><thead><tr><th>Location</th><th>Rock</th><th>Mineral</th><th>Method</th><th>Metamorphic age</th><th>P-T constraints°</th><th>Shape</th><th>References</th><th>#**</th></tr></thead><tbody><tr><td colspan="9"><strong>Northern range</strong></td></tr><tr><td>Sanweishan</td><td>Garnet amphibolite</td><td>Zircon</td><td>U-Pb</td><td>441 ± 5 Ma<br>441 ± 3 Ma</td><td>-</td><td></td><td>Meng et al. (2011)</td><td>10</td></tr><tr><td>Sanweishan</td><td>Granulite, amphibolite</td><td>Zircon</td><td>U-Pb</td><td>410–403 Ma<br>370 ± 2 Ma</td><td>¹458–548°C, 1.14–1.55 GPa</td><td>CW</td><td>Zhao et al. (2016)</td><td>13</td></tr><tr><td>Duobagou</td><td>Amphibolite<br>plagiogneiss</td><td>Zircon</td><td>U-Pb</td><td>442 ± 2 Ma<br>425 ± 31 Ma</td><td>-</td><td></td><td>Wang et al.<br>(2018b)</td><td>19</td></tr><tr><td>Kalashitage</td><td>Granulite, amphibolite</td><td>Zircon</td><td>U-Pb</td><td>431–418 Ma</td><td>¹840–920°C, 0.62–1.26 GPa</td><td>CW</td><td>Zhang et al. (2020)</td><td>20</td></tr><tr><td>Kalashitage</td><td>Amphibolite</td><td>Zircon</td><td>U-Pb</td><td>398–389 Ma</td><td>²~850°C, ~1.6 GPa</td><td>CW</td><td>Zhang et al. (2020)</td><td>20</td></tr><tr><td>Duobagou</td><td>Granulite</td><td>Zircon</td><td>U-Pb</td><td>460.5 ± 6.8 Ma</td><td>¹730–820°C, 0.86–1.17 GPa</td><td>CW</td><td>Zhang et al. (2020)</td><td>20</td></tr><tr><td>Kalashitage</td><td>Amphibolite</td><td>Zircon</td><td>U-Pb</td><td>431–415 Ma</td><td>¹~830°C, ~1.39 GPa</td><td>CW</td><td>Zhang et al. (2020)</td><td>36</td></tr><tr><td>Mogutai</td><td>Granulite</td><td>Zircon</td><td>U-Pb</td><td>388.8 ± 7.4 Ma</td><td>¹560–630°C, 0.62–0.96 GPa</td><td>CW</td><td>Zhang et al. (2020)</td><td>36</td></tr><tr><td>Xiaowan</td><td>Amphibolite</td><td>Zircon</td><td>U-Pb</td><td>430.3 ± 2.5 Ma<br>462.4 ± 3.4 Ma</td><td>¹~685°C, ~1.1 GPa</td><td></td><td>Soldner et al.<br>(2022)</td><td>37</td></tr><tr><td>Sanweishan</td><td>Clinopyroxenite</td><td>Zircon</td><td>U-Pb</td><td>389–370 Ma<br>253 ± 1 Ma</td><td>²790–920°C, 2.8–4.1 GPa</td><td>CW</td><td>Li et al. (2021)</td><td>38</td></tr><tr><td>Sanweishan,<br>Hanxia</td><td>Clinopyroxenite,<br>amphibolite</td><td>Zircon</td><td>U-Pb</td><td>437–432 Ma,<br>362 ± 4 Ma</td><td>-</td><td>CW</td><td>Zhao et al. (2020)</td><td>40</td></tr><tr><td>Kalashitage</td><td>Granulite, amphibolite</td><td>Hornblende</td><td>Ar–Ar</td><td>258–253 Ma</td><td>-</td><td></td><td>Zhang et al. (2022)</td><td>46</td></tr><tr><td colspan="9"><strong>Central range</strong></td></tr><tr><td>Changshanzi</td><td>Granulite, amphibolite</td><td>Zircon</td><td>U-Pb</td><td>419–417 Ma</td><td>¹790–874, 1.32–1.37 GPa<br>¹684–874, 0.97–1.14 GPa<br>¹740–860, ~0.90 GPa</td><td>CW</td><td>Pham et al. (2018)</td><td>18</td></tr><tr><td>Dongbatu</td><td>Amphibolite gneiss</td><td>Zircon</td><td>U-Pb</td><td>249 ± 4 Ma<br>406 ± 5 Ma</td><td>-</td><td></td><td>Feng et al. (2018)</td><td>7</td></tr><tr><td>Mogutai</td><td>Granulite</td><td>Zircon</td><td>U-Pb</td><td>431 ± 2 Ma<br>403 ± 3 Ma</td><td>²760–800°C, 1.4–1.6 GPa</td><td>CW</td><td>He et al. (2014)</td><td>12</td></tr><tr><td>Mogutai</td><td>Granulite</td><td>Zircon</td><td>U-Pb</td><td>444 ± 5 Ma</td><td>¹~800°C, 1.4–1.7 GPa</td><td>CW</td><td>Zong et al. (2012)</td><td>11</td></tr><tr><td>Mogutai</td><td>Micaschist</td><td>Zircon</td><td>U-Pb</td><td>435 ± 4 Ma</td><td>-</td><td></td><td>Zong et al. (2013)</td><td>16</td></tr><tr><td>Dongbatu</td><td>Trondjemite</td><td>Zircon</td><td>U-Pb</td><td>417 ± 6 Ma</td><td>-</td><td></td><td>Zong et al. (2013)</td><td>16</td></tr><tr><td>Dongbatu</td><td>Clinopyroxenite,<br>amphibolite</td><td>Zircon</td><td>U-Pb</td><td>412–408 Ma<br>374 ± 3 Ma</td><td>-</td><td></td><td>Zhao et al. (2019a)</td><td>25</td></tr><tr><td>Dongbatu</td><td>Granulite</td><td>Zircon</td><td>U-Pb</td><td>417–397 Ma</td><td>-</td><td></td><td>Zhao et al. (2019a)</td><td>25</td></tr><tr><td>Mogutai</td><td>Amphibolite</td><td>Zircon</td><td>U-Pb</td><td>372.4 ± 4.0 Ma<br>420–412 Ma</td><td>²~610°C, ~0.93 GPa<br>²~740°C, ~0.95 GPa</td><td>CW</td><td>Wang et al.<br>(2018a)</td><td>26</td></tr><tr><td>Mogutai</td><td>Metapelite</td><td>Garnet</td><td>Lu–Hf<br>Sm–Nd</td><td>421.6 ± 1.2 Ma<br>385.3 ± 4.0 Ma</td><td>²~850°C, ~1.35 GPa</td><td>CW</td><td>Soldner et al.<br>(2023)</td><td>35</td></tr><tr><td>Mogutai</td><td>Granulite</td><td>Garnet</td><td>Lu–Hf<br>Sm–Nd</td><td>409.7 ± 2.3 Ma<br>356 ± 11 Ma</td><td>²760–810°C, 0.9–1.25 GPa</td><td>CW</td><td>Soldner et al.<br>(2023)</td><td>35</td></tr><tr><td>Mogutai,<br>Dongbatu</td><td>Metapelite</td><td>Monazite<br>Zircon</td><td>U-Pb<br>U-Pb</td><td>366 ± 3 Ma<br>338 ± 53 Ma</td><td>-</td><td>CW</td><td>Zhao et al. (2020)</td><td>40</td></tr><tr><td>Dongbatu,<br>Mogutai</td><td>Tonalite, amphibolite</td><td>Titanite</td><td>U-Pb</td><td>409–390 Ma<br>354–352 Ma</td><td>-</td><td></td><td>Wang et al.<br>(2021b)</td><td>39</td></tr><tr><td>Dongbatu</td><td>Amphibolite</td><td>Titanite<br>Apatite</td><td>U-Pb</td><td>345.4 ± 2.7 Ma<br>300 ± 10 Ma</td><td>¹780–807°C, 0.99–1.18 GPa</td><td>CW</td><td>Si et al. (2022)</td><td>34</td></tr><tr><td colspan="9"><strong>Southern range</strong></td></tr><tr><td>Duobagou</td><td>Granulite, amphibolite</td><td>Zircon</td><td>U-Pb</td><td>412–400, ~365 Ma</td><td>¹~861°C, ~1.69 GPa</td><td>CW</td><td>Wang et al.<br>(2016c)</td><td>24</td></tr><tr><td>Altyn-Tagh</td><td>Orthogneiss</td><td>Muscovite,<br>biotite</td><td>Ar–Ar</td><td>454–414 Ma</td><td>-</td><td></td><td>Sobel and Arnaud<br>(1999)</td><td>41</td></tr><tr><td>Altyn-Tagh</td><td>Micaschist</td><td>Muscovite<br>Monazite</td><td>Ar–Ar<br>U-Pb</td><td>227 ± 4 Ma<br>276 ± 18 Ma</td><td>-</td><td></td><td>Delville et al.<br>(2001)</td><td>42</td></tr><tr><td>Hongliuxia</td><td>Amphibolite</td><td>Zircon<br>Amphibole</td><td>Ar–Ar</td><td>417–416 Ma<br>407–397 Ma</td><td>¹~680°C, ~1.54 GPa</td><td>CW</td><td>Wang et al.<br>(2017b)</td><td>15</td></tr><tr><td>Hongliuxia</td><td>Eclogite<br>Granulite</td><td>Zircon</td><td>U-Pb</td><td>411 ± 2 Ma<br>413 ± 2 Ma</td><td>¹~830°C, ~2.62 GPa<br>¹735–744°C, 1.71–1.77 GPa</td><td>CW</td><td>Wang et al.<br>(2017a)</td><td>14</td></tr><tr><td>Hongliuxia</td><td>Amphibolite<br>Metapelite</td><td>Zircon</td><td>U-Pb</td><td>409 ± 2 Ma<br>414 ± 2 Ma</td><td>¹~652°C, ~1.02 GPa<br>¹700–708°C, 1.02–1.07 GPa</td><td>CW</td><td>Wang et al.<br>(2017a)</td><td>14</td></tr><tr><td>Shuixiakou</td><td>Amphibolite</td><td>Zircon</td><td>U-Pb</td><td>412–398 Ma</td><td>¹720–750°C, 1.34–1.47 GPa</td><td>CW</td><td>Wang et al.<br>(2018b)</td><td>8</td></tr><tr><td>Chijin</td><td>Paragneiss, micaschist</td><td>Muscovite<br>Biotite</td><td>Ar–Ar</td><td>252–237 Ma</td><td>²580–650°C, 0.65–0.68 GPa</td><td>ACW</td><td>Wang et al. (2023)</td><td>33</td></tr><tr><td>Shuixiakou</td><td>Amphibolite</td><td>Garnet<br>Apatite</td><td>Sm–Nd<br>U-Pb</td><td>333.5 ± 4.0 Ma<br>236.6 ± 4.3 Ma</td><td>²780–807°C, 0.99–1.18 GPa</td><td>CW</td><td>Si et al. (2022)</td><td>34</td></tr><tr><td>Hongliuxia<br>Shuixiakou</td><td>Amphibolite,<br>orthogneiss</td><td>Titanite<br>Zircon</td><td>U-Pb<br>U-Pb</td><td>409–390 Ma<br>323–309 Ma<br>439 ± 38 Ma<br>317 ± 20 Ma</td><td>-</td><td></td><td>Wang et al.<br>(2021b)</td><td>39</td></tr></tbody></table>

(continued on next page)
<table><caption>**Table 1 (continued)**</caption><thead><tr><th>Location</th><th>Rock</th><th>Mineral</th><th>Method</th><th>Metamorphic age</th><th>P-T constraints<sup>a</sup></th><th>Shape</th><th>References</th><th>#**</th></tr></thead><tbody><tr><td rowspan="2">Hongliuxia</td><td rowspan="2">Paragneiss</td><td>Zircon</td><td>U-Pb</td><td>404 ± 15 Ma</td><td rowspan="2">2650-710°C, 0.9-1.0 GPa</td><td rowspan="2">CW</td><td rowspan="2">Soldner et al. (2024)</td><td rowspan="2">43</td></tr><tr><td>Monazite</td><td>U-Pb</td><td>406-391</td></tr><tr><td rowspan="2">Hongliuxia</td><td rowspan="2">Paragneiss</td><td>Zircon</td><td>U-Pb</td><td>408.1 ± 2.3 Ma</td><td rowspan="2">2650-700°C, 0.45-0.65 GPa</td><td rowspan="2">CW</td><td rowspan="2">This study</td><td rowspan="2">50</td></tr><tr><td>Monazite</td><td>U-Pb</td><td>307.5 ± 2.1 Ma</td></tr><tr><td>Altyn-Tagh</td><td>Schist, orthogneiss</td><td>Muscovite, biotite</td><td>Ar-Ar</td><td>454-445 Ma</td><td>-</td><td>-</td><td>Liu et al. (2007)</td><td>44</td></tr><tr><td>Altyn-Tagh</td><td>Schist, granite, pegmatite</td><td>Muscovite, biotite</td><td>Ar-Ar</td><td>458-442 Ma</td><td>-</td><td>-</td><td>Wang et al. (2005)</td><td>45</td></tr></tbody></table>

Abbreviations: CW, clockwise; ACW, anti-clockwise.

* Peak metamorphism P-T constraints based on conventional geothermobarometry (1) and/or pseudosection modelling (2).

** Reference numbers correspond to numbers in Fig. 6.

# 5. Paleozoic magmatism in the Dunhuang block

The Paleozoic magmatic rocks from the northern, central and southern ranges (Fig. 2a) can be distinguished based on their emplacement ages and petrogenesis that are described hereafter and summarized in Fig. 7 and Table 2.

## 5.1. The northern range

Paleozoic magmatic rocks form the largest fraction of the exposed crust in the northern range (Figs. 2a and 7a,b). The first group of magmatic rocks corresponding to the oldest Paleozoic magmatic rocks exposed in the *Xiaowan section* consists of 519–509 Ma I-type granitoids from a continental arc (Gan et al., 2020b; Kang et al., 2023) and coeval subduction-related metabasalts (Soldner et al., 2022). Altogether the positive zircon $\epsilon_{Hf}(t)$ values (1.4 to 14.7) of granitoids and metabasalts, and a positive whole-rock $\epsilon_{Nd}(t)$ value of a metabasalt sample (5.5) have been interpreted as reflecting the input of juvenile crust (Gan et al., 2020b; Soldner et al., 2022). The second group corresponding to slightly younger magmatic rocks consists of i) composite plutons and volcanics resembling subduction-related continental arc rocks and ii) S-type granites (Fig. 7a). The composite plutons include high- to middle-K calc-alkaline I-type granitoids (Wang et al., 2016b; Zhao et al., 2017; Gan et al., 2021a), granite-granodiorite-diorite suites (Zhu et al., 2020; Zheng et al., 2021; Gan et al., 2021a, 2021b, 2023b), TTG and amphibole-rich meta-igneous rocks (Zhang et al., 2009; Wang et al., 2018b), all emplaced between 462 and 380 Ma (Fig. 7a,b; Table 2). Their geochemical signatures suggest that they were possibly generated with an amphibolite- to eclogite-facies residue (e.g. Zhang et al., 2009; Zhu et al., 2020), and their negative to positive whole-rock $\epsilon_{Nd}(t)$ (–15.0 to 3.0) (Wang et al., 2018b; Gan et al., 2021a, 2021b) and zircon $\epsilon_{Hf}(t)$ (–18.7 to 12.4) (Wang et al., 2016b; Zhao et al., 2017; Gan et al., 2021a, 2023b) were interpreted as reflecting a mixed magma source of depleted mantle materials with various proportions of Archean–Mesoproterozoic continental crust. Minor andesitic-dacitic-rhyolitic tuffs deposited at 424–414 Ma also display calc-alkaline signature of volcanic arc sediments (Shi et al., 2020). In the *Sanweishan section*, 457–434 Ma S-type granites display negative zircon $\epsilon_{Hf}(t)$ (–8.6 to –0.9) (Wang et al., 2016b), suggesting that they originated from melting of late Paleoproterozoic to early Mesoproterozoic rocks (Wang et al., 2016b). Other younger plutons occurring in the northern range consist either of high-K calc-alkaline granitoids and tholeiitic plagiogranites or dacite porphyry with emplacement ages of 390–380 Ma, 367–362 Ma, ca. 303 Ma and 276–274 Ma and ca. 246 (Fig. 7 a,b) (Feng et al., 2012; Zhao et al., 2015b, 2017; Wang et al., 2021a; Gan et al., 2021a, 2023a). The former granitoids are considered to be subduction-related arc rocks or post-collisional rocks originating from mixed source of mafic crustal material and different proportions of mantle derived magmas as exemplified by their positive to negative zircon $\epsilon_{Hf}(t)$ values (–6.05 to 12.4) (Feng et al., 2012; Zhao et al., 2017; Gan et al., 2021b) and whole-rock negative $\epsilon_{Nd}(t)$ values (–0.73) (Gan et al., 2021b). In contrast, plagiogranites display positive zircon $\epsilon_{Hf}(t)$ (3.1 to 8.8) and are considered as formed in a nascent oceanic back-arc basin (Zhao et al., 2015a, 2015b).

## 5.2. The central range

Magmatic and volcanic rocks from the central range were emplaced during four distinct periods: in the late Ordovician–early Silurian, late Devonian, early Carboniferous and early Permian–middle Triassic (Fig. 7a,c; Table 2). Early Silurian metabasalts from the *Mogutai section* were emplaced before 445 Ma and their geochemical signature has been interpreted as reflecting formation in a typical back-arc setting (Soldner et al., 2022). Their progressive increase in whole-rock $\epsilon_{Nd}(t)$ from late Ordovician to early Silurian suggests that the source of the metabasalts progressively evolved from an enriched lithospheric mantle to a depleted asthenospheric mantle. Late Devonian magmatic rocks from the *Mogutai and Dongbatu sections* crystallized at 367–362 Ma (Fig. 7a,c) (Zhao et al., 2017; Gan et al., 2023a; Soldner et al., 2023). There, low-K tholeiite to high-K calc-alkaline I-type granites were generated with an amphibolite- to eclogite-facies residue and originated from a mixed magma source composed of depleted mantle materials mixed with an old continental crust as inferred from their positive to negative zircon $\epsilon_{Hf}(t)$ values (–5.3 to 14.7) (Zhao et al., 2017). Early Carboniferous magmatic rocks mainly consist of granitic dykes exposed in the *Dongbatu section* that yield crystallization ages of 349 ± 9 Ma and 326 ± 7 Ma (Feng et al., 2018). Late Permian to middle Triassic magmatic rocks occurring in the *Dongbatu section* consist of undeformed granite and monzogranite as well as mylonitic granite that crystallized at 284–238 Ma (Feng et al., 2018). These rocks are considered as subduction-related arc rocks that belong to the high-K calc-alkaline I-type series generated from mixing of juvenile materials with Mesoproterozoic continental crust (Feng et al., 2020).

## 5.3. The southern range

Magmatic rocks from the southern range were emplaced from late Silurian to early Triassic times (Fig. 7a,d; Table 2). A first group of magmatic rocks displaying the oldest Paleozoic ages consists of granitic plutons emplaced at 431 ± 5 Ma and 360 ± 3 Ma in the *Hongliuxia section* (Wang et al., 2016a). They consist of S-type granites derived from Paleoproterozoic to Mesoproterozoic crust metagrewacke and meta-pelite displaying zircon $\epsilon_{Hf}(t)$ values ranging from –12.3 to –5.5 (Wang et al., 2016a). A second group of magmatic rocks are gneisses from the *Qinshigou and Hongliuxia sections* with granitic to dioritic protoliths emplaced at 382 ± 4 Ma and 358–317 Ma (Zhu et al., 2014; Wang et al., 2016a; Bao et al., 2017; Zhao et al., 2017) (Figs. 5h, 7a,d and S3a,b; Table 2). Geochemical data suggest that these intrusive rocks were possibly produced with a granulite-facies residue and display high Sr/Y ratios typical of adakitic rocks (Zhu et al., 2014; Bao et al., 2017). Together with their negative zircon $\epsilon_{Hf}(t)$ (–26.2 to –4.9) (Zhu et al., 2014; Wang et al., 2016a; Bao et al., 2017; Zhao et al., 2017) and whole-rock $\epsilon_{Nd}(t)$ values (–9.4 to –11.0) (Zhu et al., 2014), these features have been interpreted as reflecting partial melting of a thickened continental crust. Other minor granitic and dioritic intrusions in the *Hongliuxia and Chijin sections* (Wang et al., 2014, 2018a, 2023) display geochemical
<caption>**Table 2**</caption>

Summary of geochronological data for Paleozoic magmatic rocks from the Dunhuang block.

<table><caption>**Table 2 (continued)**</caption><thead><tr><th>Location</th><th>Rock</th><th>Crystallization/ metamorphic age</th><th>References</th><th>#*</th></tr></thead><tbody><tr><td colspan="5"><strong>Northern range</strong></td></tr><tr><td>Duobagou</td><td>Biotite plagiogneiss</td><td>436 ± 5 Ma</td><td>Wang et al. (2018c)</td><td>19</td></tr><tr><td rowspan="2">Sanweishan</td><td>Volcanic tuff</td><td>424–414 Ma</td><td>Shi et al. (2020)</td><td rowspan="2">9</td></tr><tr><td>Dacitic porphyry</td><td>364 ± 1 Ma</td><td></td></tr><tr><td>Sanweishan</td><td>Granite</td><td>462–434 Ma</td><td>Wang et al. (2016b)</td><td>4</td></tr><tr><td>Kalashitage</td><td>Granitic dyke</td><td>244 ± 2 Ma</td><td>Zhang et al. (2020)</td><td>20</td></tr><tr><td>Xiaowan</td><td>Granite</td><td>552–542 Ma<br>511–509 Ma</td><td>Gan et al. (2020b)</td><td>17</td></tr><tr><td rowspan="2">Kalashitage</td><td>Diorite</td><td>448 ± 2 Ma<br>436 ± 3 Ma</td><td>Zhu et al. (2020)</td><td rowspan="2">23</td></tr><tr><td></td><td></td><td>Zhang et al. (2009)</td></tr><tr><td rowspan="2">Sanweishan</td><td>TTG</td><td>440 ± 12 Ma</td><td></td><td rowspan="2">1</td></tr><tr><td></td><td></td><td>Zhao et al. (2015b)</td></tr><tr><td>Sanweishan, Xiaowan</td><td>Granite, diorite, monzodiorite</td><td>430–410 Ma</td><td>Zhao et al. (2017)</td><td>6</td></tr><tr><td>Xiaowan</td><td>Granite, diorite</td><td>391–380 Ma<br>367 ± 4 Ma</td><td>Gan et al. (2021b)</td><td>27</td></tr><tr><td>Xiaowan</td><td>Monzogranite</td><td>455 ± 3 Ma<br>431 ± 3 Ma</td><td>Gan et al. (2021a)</td><td>28</td></tr><tr><td>Xiaowan</td><td>Diorite</td><td>443–440 Ma</td><td>Gan et al. (2023b)</td><td>29</td></tr><tr><td rowspan="2">Qiaowan</td><td>Diorite</td><td>455–429 Ma</td><td>Zheng et al. (2021)</td><td rowspan="2">30</td></tr><tr><td></td><td></td><td>Feng et al. (2012)</td></tr><tr><td rowspan="2">Qiaowan</td><td>Granite</td><td>303.7 ± 2.4 Ma</td><td></td><td rowspan="2">31</td></tr><tr><td></td><td></td><td>Kang et al. (2023)</td></tr><tr><td>Xiaowan</td><td>Granite, granodiorite</td><td>480–473 Ma</td><td></td><td rowspan="2">32</td></tr><tr><td>Xiaowan</td><td>Granite</td><td>517.3 ± 2.9 Ma</td><td>Soldner et al. (2022)</td></tr><tr><td>Xiaowan</td><td>Basalt</td><td>519.3 ± 3.2 Ma</td><td>Gan et al. (2023a)</td><td>37</td></tr><tr><td>Xiaowan</td><td>Granodiorite</td><td>363 ± 4 Ma</td><td>Zhang et al. (2022)</td><td>49</td></tr><tr><td>Kalashitage</td><td>Granite, syenite, dacite</td><td>273–242 Ma</td><td></td><td>46</td></tr><tr><td>Duobagou</td><td>Granite</td><td>276–274 Ma<br>246 ± 1 Ma</td><td>Wang et al. (2021a)</td><td>47</td></tr><tr><td colspan="5"><strong>Central range</strong></td></tr><tr><td rowspan="2">Dongbatu</td><td>Pegmatite, granite</td><td>349–326 Ma</td><td>Feng et al. (2018)</td><td rowspan="2">7</td></tr><tr><td>Dioritic porphyry</td><td>247–238 Ma</td><td></td></tr><tr><td rowspan="2">Dongbatu</td><td>Gneiss</td><td>445.4 ± 3.4 Ma</td><td>Feng et al. (2020)</td><td rowspan="2">48</td></tr><tr><td>Granite, monzogranite</td><td>284–238 Ma</td><td></td></tr><tr><td rowspan="2">Mogutai</td><td>Granite, diorite, granodiorite</td><td>363–360 Ma</td><td>Zhao et al. (2017)</td><td rowspan="2">6</td></tr><tr><td>monzodiorite</td><td></td><td></td></tr><tr><td rowspan="2">Mogutai</td><td>Orthogneiss</td><td>360.2 ± 1.5 Ma</td><td>Soldner et al. (2023)</td><td rowspan="2">35</td></tr><tr><td>Basalt</td><td>445.4 ± 3.4 Ma</td><td>Soldner et al. (2022)</td></tr><tr><td rowspan="2">Mogutai</td><td>Granodiorite</td><td>366–365 Ma</td><td>Gan et al. (2023a)</td><td rowspan="2">49</td></tr><tr><td>Syenogranite</td><td>274 ± 2 Ma<br>239 ± 2 Ma</td><td>Zhang et al. (2022)</td></tr><tr><td colspan="5"><strong>Southern range</strong></td></tr><tr><td>Hongliuxia</td><td>Granite</td><td>~431 Ma<br>360–340 Ma</td><td>Wang et al. (2016a)</td><td>5</td></tr><tr><td>Hongliuxia</td><td>Adakite</td><td>335–315 Ma</td><td>Zhao et al. (2017)</td><td>6</td></tr><tr><td>Qingshigou</td><td>Diorite</td><td>335 ± 2 Ma</td><td>Zhu et al. (2014)</td><td>21</td></tr><tr><td rowspan="2">Qingshigou</td><td>Adakite</td><td>382 ± 4 Ma<br>358 ± 4 Ma</td><td>Bao et al. (2017)</td><td rowspan="2">22</td></tr><tr><td></td><td>332 ± 2 Ma</td><td></td></tr></tbody></table>

<table><thead><tr><th>Location</th><th>Rock</th><th>Crystallization/ metamorphic age</th><th>References</th><th>#*</th></tr></thead><tbody><tr><td>Hongliuxia</td><td>Granite</td><td>404 ± 3 Ma<br>399 ± 3 Ma</td><td>Wang et al. (2014)</td><td>2</td></tr><tr><td rowspan="2">Shuixiakou</td><td>Granite, monzogranite</td><td>412 ± 1 Ma<br>402 ± 1 Ma<br>313 ± 1 Ma</td><td>Wang et al. (2018b)</td><td>8</td></tr><tr><td></td><td>243.6 ± 2.2 Ma</td><td>Wang et al. (2023)</td><td>33</td></tr><tr><td>Hongliuxia</td><td>Orthogneiss</td><td>325.7 ± 2.6 Ma</td><td>This study</td><td>50</td></tr></tbody></table>

* References numbers corresponds to numbers in Fig. 7.

signatures similar to high-K calc-alkaline series resembling volcanic arc rocks (Wang et al., 2018a). Their positive to negative zircon $\epsilon_{Hf}(t)$ values (–13.5 to 4.6) indicate that they originate from both juvenile and reworked older crustal materials (Wang et al., 2014).

# 6. Discussion

## 6.1. General features of Paleozoic metamorphism in the Dunhuang block

A polyphased metamorphic evolution can be recognized based on spatial occurrences, structural relationships, peak P–T evolutions and metamorphic ages. It is defined by an early to middle Paleozoic metamorphism $D_1–2–M_1–2$ recorded in all three ranges but predominant in the northern and central ones, followed by continuation of $M_3$ metamorphism throughout the Carboniferous and ended by the Permian metamorphic phase $M_4$ mainly recorded in the southern range.

### 6.1.1. Early to middle Paleozoic metamorphism

A characteristic feature of the whole Dunhuang block is a systematic relationship between deformation and metamorphism (Soldner et al., 2023, 2024). It was shown that the $M_1$ assemblage related to the subhorizontal $S_1$ fabric is preserved in core of granulite lenses in the central range where it defines a poorly preserved $D_1–M_1$ stage. However, in the northern and southern ranges the $S_1$ is not visible due to the isotropic texture of equigranular granulite that probably reflects extensive post-deformational annealing. The $M_2$ metamorphism was always related to vertical upright folds $F_2$ and N-S trending penetrative foliation $S_2$, which are locally preserved around granulite lenses or in other low-strain domains. The mineral assemblages related to this fabric define a thermal peak that can be assigned to $D_2–M_2$ compressive phase. The $D_3$ reworks all the previous structures at high angle and is dominant in all three ranges. The E-W trending $F_3$ vertical folds and penetrative foliation $S_3$ associated with $M_3$ retrogression, still at high temperature, can be assigned to $D_3–M_3$ phase, kinematically independent from $D_1–M_1$ and $D_2–M_2$ phases. This indicates that the three metamorphic fabrics result from three distinct tectono-metamorphic stages albeit the $D_1–M_1$ and $D_2–M_2$ can be regarded as a result of continuous orogenic process.

In the northern, central and southern ranges, early Paleozoic HP metamorphic rocks are characterized by clockwise P–T paths with the following metamorphic conditions: 450–610 °C and 0.4–0.8 GPa for prograde metamorphism $M_1$, 544–890 °C and 0.7–1.7 GPa for peak metamorphism $M_2$ and 400–500 °C and 0.5–6.0 GPa for retrograde metamorphism $M_3$ (Figs. 6b and 8a; Table 1). Only two outliers consisting of pyroxenite xenoliths preserved in granite intrusions from the northern range and an eclogite from the southern range display significantly different P–T metamorphic conditions of 2.9–4.2 GPa and 700–840 °C and ~2.4 GPa and ~820 °C, respectively (Figs. 6b and 8a; Table 1). Two main features can also be deduced from the P–T data obtained from thermobarometry and phase diagram calculations: 1) data for $M_1$, $M_2$ and $M_3$ metamorphism clearly plot in distinct P–T regions defining different metamorphic gradients (Fig. 8a). With the exception of outliers, metamorphic gradients for $M_1$ (14–33 °C/km) are characterized by a median value of ~21 °C/km suggesting that hot P–T
<figure><img src="image_11.png" /><figcaption>**Fig. 8.** (a) Summary of the M₁ (yellow), M₂ (orange) and M₃ (red) *P*–*T* conditions calculated for high-grade metabasic and metasedimentary rocks from the Dunhuang block. Colour-filled black circles correspond to data for metasediments. (b) Metamorphic gradient (°C/km) boxplots for the M₁, M₂ and M₃ *P*–*T* conditions. (c) Age vs. *T/P* ratios for recorded by high-grade metabasic and metasedimentary rocks from the Dunhuang and Alxa blocks, and age boxplots for peak M₂ metamorphism for the northern, central and southern ranges. For the box plot diagrams, the line across the box represents the median value of the data and ranges are the interquartile ranges (differences between third and first quartile, Q3–Q1). Data sets in *P*–*T*, box-plot and age vs. *T/P* diagrams are from references given in Table 1. White circles correspond to data from the Alxa block (Chen et al., 2015; Jiang et al., 2021; Zhang et al., 2023). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

conditions prevailed at the beginning of the early Paleozoic (Fig. 8b). Metamorphic gradients for M₂ (9–24 °C/km) are characterized by a median value of ~16 °C/km, and are therefore colder than the ones for M₁ (Fig. 8b). Metamorphic gradients for M₃ (16–52 °C/km) are characterized by a median value of ~29 °C/km, suggesting that hot metamorphic conditions prevailed during retrograde metamorphism

(Fig. 8b). Altogether, the corresponding intermediate to high *T/P* ther-
mobaric ratios accurately reflect the overall petrology dominated by
high-temperature (HT)–HP upper amphibolite- to granulite-facies
metamorphic rocks (Fig. 8b) (Brown and Johnson, 2018). 2) Meta-
basites systematically display higher *P* conditions than metasediments
that seemingly did not reach *P* conditions exceeding ~1.25 GPa (Figs. 6b
<figure><img src="image_12.png" /><figcaption>Fig. 9. Summary of *P*–*T* evolutions for representative metamorphic samples from the northern, central and southern ranges of the Dunhuang block with corresponding relative probability density plots for M₁, M₂ and M₃ metamorphic ages. Available age constraints on metamorphic stages are given. Numbers in brackets correspond to references in Table 1.</figcaption></figure>

and 9a; Table 1).

An important feature revealed by the metamorphic zircon age plots is a longer duration of metamorphism in the northern and central ranges compared to the southern range (Figs. 6c and 8b). In fact, the metamorphic zircon age distribution for the northern and central ranges presents different age peaks: the ca. 429 Ma peak is associated with the M₁ metamorphic stage, 422–407 Ma peaks are associated with M₂ and 378–318 Ma peaks are related to M₃ (Fig. 9). In contrast, only one ca. 411 Ma zircon age related to eclogite-facies metamorphism has been recorded in the southern range (Fig. 9). Metamorphic monazite age distribution presents different age peaks at ca. 401 Ma, ca. 391 Ma and 377–354 Ma that reflect the distinct M₂a (Pmax), M₂b (Tmax) and M₃ stages, respectively (Fig. 9). This is supported by zircon U–Pb age data compiled individually for the northern, central and southern ranges (Fig. 6a,c). In the northern range, zircon U–Pb ages are continuously ranging from 463 to 371 Ma, with one major age peak at ca. 420 Ma (Fig. 6c). In the central range, zircon U–Pb ages are continuously ranging from 461 to 318 Ma, with two peaks at ca. 430 Ma and ca. 407 Ma, and one minor peaks at ca. 377 Ma (Fig. 6c). In the southern range, zircon U–Pb ages are characterized by one major peak at ca. 410 Ma (Fig. 6c), as exemplified by the zircon U–Pb concordia age of 408.1 ± 2.3 Ma for paragneiss 19HLX17 (Supplementary Fig. S3e). This confirms that metamorphic peak M₂ occurred at least 10 to 20 m.y. earlier in the northern and central ranges compared to the southern range (Figs. 8b and 9). Metamorphic monazite age distributions for the southern range further support an overall younging age trend in metamorphism, with Devonian (M₁-M₂) and Carboniferous (M₃) metamorphic events (Fig. 9).

Previous studies assigned the 407–370 Ma zircon U–Pb and ⁴⁰Ar–³⁹Ar ages to M₃ retrograde metamorphism in metabasites (He et al., 2014; Zhao et al., 2016; Wang et al., 2017b; Zhang et al., 2020). However, recent metamorphic *P*–*T* and age data revealed that M₃ metamorphic reequilibration operated continuously until ca. 310 Ma in the central and southern ranges (Zhao et al., 2020; Wang et al., 2021b; Si et al., 2022). The continuation of D₃-M₃ till Carboniferous is supported by i) Carboniferous ages of metamorphic rocks from the central and southern ranges yielding minor zircon U–Pb age peaks ranging from 350 to 318 Ma (Fig. 6c) and ca. 356 Ma and ca. 305 Ma monazite age

peaks (Fig. 10a), ii) ductile deformation of the garnet-bearing orthogneiss 19HLX48 crystallized at ca. 326 Ma (Supplementary Fig. S3a,b) and iii) M₃ *P*–*T* conditions of 475–500 °C and 0.3–0.35 GPa at calculated for the ca. 308 Ma paragneiss 19HLX17 (Supplementary Fig. S2). The metamorphic age vs. (Yb/Gd)N ratio diagram indicates that high (Yb/Gd)N ratios characterize both metamorphic zircons ((Yb/Gd)N mostly >8) and monazite ((Yb/Gd)N > 0.010) (Figs. 10b and 11a), thereby indicating that only limited garnet growth occurred during their (re)crystallization. Carboniferous zircon and monazite also generally display relatively negative Eu anomalies (0.2–0.7 and 0.5–1.0, respectively) (Figs. 10c and 11b). The negative correlation between zircon Eu anomalies and (Yb/Gd)N ratios suggest that negative Eu anomalies may reflect decompression with or without presence of melt. Together with structural evidence, all these data indicate that the D₃-M₃ cannot be regarded as a continuum of the D₁–₂M₁–₂ metamorphic cycle.

### 6.1.2. *Arguments for hot protracted thermal evolution of the Dunhuang block*

Metamorphic rocks from the northern, central and southern ranges yield continuous monazite U–Pb ages in the range of 431–353 Ma, with two minor age peaks at ca. 401 Ma and ca. 390 Ma (Fig. 10a). Both zircon and monazite confirm that the three ranges altogether recorded protracted late Ordovician to early Devonian metamorphism. The monazite and zircon metamorphic age vs. (Yb/Gd)N ratio diagrams reveal that the lowest (Yb/Gd)N ratios correspond to the 432–381 Ma monazites (mostly (Yb/Gd)N < 0.015) and to the 450–390 Ma zircons (mostly (Yb/Gd)N < 8) (Figs. 10a, 11a and S3g). Although dependent of crystallization temperatures, zircons showing flat heavy rare-earth elements (HREEs) distribution in chondrite-normalized diagrams (low (Yb/Gd)N) are usually interpreted as a result of crystallization in equilibrium with garnet (e.g. Schaltegger et al., 1999; Rubatto, 2002; Rubatto and Hermann, 2007). A similar interpretation is proposed for monazite depleted in HREEs (e.g. Rubatto et al., 2013). From the low (Yb/Gd)N ratios of the early Paleozoic zircon and monazite can be inferred that garnet growth started as early as ca. 450 Ma and was not significantly destabilized on the orogenic scale until 390–380 Ma (Figs. 10b and 11a). The 430–410 Ma zircons and 420–390 Ma monazites display large
<figure><img src="image_13.png" /><figcaption>**Fig. 10.** (a) Relative probability density plots of Paleozoic metamorphic monazite from the Dunhuang block. The vertical dashed lines correspond to garnet Lu-Hf and Sm-Nd ages from Soldner et al. (2023) (green lines) and Si et al. (2022) (red line) for metabasites. (b) (Yb/Gd)N and (c) Eu anomaly vs. metamorphic age diagrams for monazite from metamorphic rocks. The Eu anomaly is defined as the ratio EuN/Eu* where Eu* = √(SmN x GdN). Data sets from references given in Table 1. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

variations in Eu anomalies (0.4–1.3 and 0.40–1.97, respectively) (Figs. 10c and 11b). Negative Eu anomalies (<1) in zircon and monazite have been used to infer the behavior of feldspars in igneous and metamorphic systems (e.g. Murali et al., 1983; Rubatto, 2002; Prent et al., 2019). For instance, the negative Eu anomalies could be related to plagioclase crystallization during symplectite development at the expense of garnet or pyroxene (Fig. 5c). This would imply a negative correlation between Eu anomalies and (Yb/Gd)N ratios. However, the negative incursion in zircon Eu anomalies at 430–410 Ma is not correlated with an (Yb/Gd)N increase in zircon (Fig. 11), whereas no Eu anomalies systematics are observed for monazite in the early Paleozoic (Fig. 10c). The negative Eu anomalies in 430–410 Ma zircons can also be interpreted as reflecting the presence of melt in metabasites and their host rocks. Indeed, leucosomes distributed along S2 fabrics in metabasites and host metapelites and intruding granitoids are commonly reported in the Dunhuang block (e.g. Zhang et al., 2020; Soldner et al.,

2022). Altogether, negative Eu anomalies in zircon and monazite suggest that the importance of melt presence increased from ca. 460 Ma until 360 Ma (Figs. 10c and 11b).

The early Paleozoic metamorphism characterized by clockwise P–T paths together with the generally low (Yb/Gd)N ratios at 460–390 Ma and negative zircon Eu anomalies at 430–410 Ma indicates that HP–HT conditions lasted ca. 50 m.y. in the Dunhuang block. Such time scale has been previously proposed by Wang et al. (2022) and matches the duration of metamorphism commonly described in Paleozoic and Paleoproterozoic HT and ultrahigh-temperature (UHT) metamorphic belts. In UHT orogens, the duration of metamorphism may have reached even 100 m.y. (Clark et al., 2015, 2018; Harley, 2016). The duration of ca. 50 m.y. for the Dunhuang block Paleozoic metamorphism is more compatible with typical hot orogens worldwide (e.g. Chardon et al., 2011; Clark et al., 2015; Guergouz et al., 2018). In contrast to orogens that formed during continental collision, the numerous middle Cambrian to late Carboniferous magmatic arc rocks in the Dunhuang block favor a supra-subduction setting (Wang et al., 2016b; Zhao et al., 2015a, 2015b; Zhao et al., 2017; Zhu et al., 2014, 2020; Gan et al., 2020b, 2021a, 2021b; Kang et al., 2023). Wolfram et al. (2019) suggested that the >50 m.y. of HT conditions require a sustained heat source to keep high background temperatures as exemplified by backarc regions. Such a long duration of hot supra-subduction conditions is also a characteristic feature for modern supra-subduction Andean system, where HT conditions are maintained from Maastrichtian to recent times (Büttner et al., 2005; Finch et al., 2017).

### 6.1.3. Late Paleozoic metamorphism

The late Paleozoic event is recorded in the central and southern ranges of the Dunhuang block where mostly vertical foliations and subvertical to subhorizontal lineations have been interpreted as a result of regional deformation. Zircon U–Pb metamorphic ages support the prevalence of Permian metamorphic rocks in the central and southern ranges and their virtual absence in the northern range (Figs. 6c and 11). Metamorphic rocks from the southern range characterized by anti-clockwise P–T paths yield metamorphic gradients ranging from ~23 to ~37 °C/km suggesting that hot P–T conditions also prevailed in the Permian (Wang et al., 2023). The metamorphic age vs. (Yb/Gd)N ratio diagram indicates that high (Yb/Gd)N ratios characterize Permian metamorphic zircons with (Yb/Gd)N mostly >6 (Fig. 11a), thereby suggesting that only limited garnet growth occurred during their (re) crystallization.

## 6.2. Implications for the Paleozoic tectono-thermal evolution of the Dunhuang block

The systematic evaluation of age and P–T data for rocks from the northern, central and southern ranges is used to discriminate the tectonic affinity of the Dunhuang block and reveals the existence of two groups of long-lived, early and middle-late Paleozoic metamorphic events, leading up to a relatively shorter Permian metamorphic event. The two earlier groups differ in their respective durations, the nature of the P–T evolutions and their spatial extents. These differences are further correlated with the Paleozoic magmatic history in order to better characterize the tectono-thermal evolution of the Dunhuang block.

### 6.2.1. Paleozoic tectonic affinity of the Dunhuang block

In the last decade, two main tectonic models based on P–T data and zircon U–Pb geochronology have been proposed to interpret tectono-metamorphic evolution of early Paleozoic metabasites from the Dunhuang block: continental collision (Zong et al., 2012; He et al., 2014; Zhang et al., 2020) and oceanic subduction-accretion process (e.g. Wang et al., 2017a, 2017b; Wang et al., 2018a, 2018b, 2018c; Wang et al., 2022). Early Paleozoic magmatic arc rocks were mainly emplaced in the northern and central ranges of the Dunhuang block from the Cambrian to late Devonian (e.g. Zhao et al., 2015b, 2017; Gan et al., 2020b, 2021a,
<figure><img src="image_14.png" /><figcaption>**Fig. 11.** (a) (Yb/Gd)N and (b) Eu anomaly vs. metamorphic age diagrams for zircon from metamorphic rocks from the Dunhuang block. The Eu anomaly is defined as the ratio EuN/Eu* where Eu* = √(SmN x GdN).</figcaption></figure>

2021b) supporting the existence of a southward oceanic subduction. The distribution of such magmatism thus precludes a model in which the Dunhuang block collided with the northerly Beishan Orogen (Fig. 1b). The block-in-matrix relationships typical for oceanic subduction-accretion model were proposed by Wang et al. (2017a, 2022). Further arguments supporting this model include hairpin-shaped P–T path (Wang et al., 2022) and E-MORB and volcanic arc-type geochemical signatures for metabasites throughout the block (Zhao et al., 2016; Shi et al., 2021; Wang et al., 2022). UHP pyroxenites occur as xenoliths in granites of the northern range of the Dunhuang block (Li et al., 2021). Given their position in the magmatic arc rocks and the calculated peak P–T conditions corresponding to low metamorphic gradients, the origin of UHP pyroxenites is compatible with the southward oceanic subduction. In contrast to HP granulites from the Dunhuang block, low metamorphic gradients recorded by eclogite from the southern range (Wang et al., 2017a) are also compatible with a hypothetical oceanic subduction located to the south. For other metamorphic rocks, the P–T data synthesized in this paper highlight a general increase in metamorphic gradients during exhumation (for M2–M3 from ~16 °C/km to ~29 °C/km; Figs. 8b,c) together with consistent 389–365 Ma exhumation ages throughout the Dunhuang block. The absence of evidence for multiple burial-exhumation events indicates different tectonic process compared to that of the typical Franciscan-type oceanic subduction systems (Ernst,

1988; Wakabayashi, 2015). Elevated geothermal gradients have also been recognized in other subduction-accretion systems such as the Sambagawa belt, where they were assigned to subduction of hot and young lithosphere or ridge subduction (Aoya et al., 2003; Endo et al., 2012). However, such tectonic evolution does not account for concomitant but distinct metamorphic gradients recorded in individual ranges of the Dunhuang block, i.e. HP granulite-facies metamorphism in the northern and central ranges (Wang et al., 2018a; Zhang et al., 2020) and eclogite-facies metamorphism in the southern range (Wang et al., 2017a). The presented metamorphic and geochronological data are also not compatible with collisional environments responsible for the formation of UHP rocks like in the Norwegian Caledonides (Andersen et al., 1991), the European Variscan belt (Schulmann et al., 2014) or the Western Alps (Chopin, 2003). In addition, the synthesis of P–T data for early Paleozoic metamorphic rocks throughout the Dunhuang block reveals that the metasediments systematically reached lower peak pressure conditions compared to the metabasites (Fig. 9a), which is seemingly not compatible with the Franciscan mélange architecture. Altogether, the data may reflect an upper plate configuration, in which metabasites originally occurred in deep lower crust and metasediments formed shallower crust level, prior to their tectonic juxtaposition.

The other important argument is based on systematic presence of Paleoproterozoic basement exposures throughout the Dunhuang block
(Fig. 2c). In addition, negative zircon $\epsilon_{Hf}(t)$ values of Paleozoic metamorphic and magmatic rocks plotting on the crustal evolution trend defined by Mesoarchean to Paleoproterozoic zircons indicate dominant presence of old crust (Fig. 13a). Zircons from the Devonian granitoids from the southern range generally display negative $\epsilon_{Hf}(t)$ values and Paleoproterozoic two-stage Hf model ($T_{DM2}$) ages (Wang et al., 2016a; Bao et al., 2017; Zhao et al., 2017) compared to more positive values for the northern range (e.g. Zhao et al., 2017; Gan et al., 2021a, 2023b) (Fig. 13c,d). As already pointed out by Gan et al. (2023a), decreasing negative zircon $\epsilon_{Hf}(t)$ together with corresponding old $T_{DM2}$ ages in the southern range compared to the northern and central ranges indicate a higher proportion of the Paleoproterozoic basement involved in the orogeny (Fig. 13c,d). This is further supported by the Devonian reworking of the Paleoproterozoic metamorphic rocks such as amphibolites (Fig. 3j) and paragneiss sample 19HLX17 from the southern range (Supplementary Fig. S3d). Finally, E-MORB, N-MORB and volcanic arc signatures of metabasalts used as proxies of oceanic crust face the fact that such geochemical signatures can also characterize metabasites derived from continental mafic crust (e.g. Jahn, 1998; Zhang et al., 2017a). In reality, ubiquitous inherited Paleoproterozoic to Meso-proterozoic zircons possibly representing their protolith ages (Meng et al., 2011; Wang et al., 2017a, 2022; Zhao et al., 2019a, 2020; Si et al., 2022) combined to zircons plotting in the continental crust field in the U/Yb vs. Hf and Y discrimination diagrams (Fig. 14a,b) (Grimes et al., 2007) favor a continental origin of these metabasites.

Altogether, the synthesized P–T data, metamorphic and magmatic ages and geochemistry of Paleozoic rocks from the Dunhuang block are compatible with hot orogenic system associated with the subduction of an oceanic plate beneath a continental one. Similar massive involvement of crystalline basements or accreted Precambrian continental blocks is best exemplified by modern north and south American Cordillera margins (e.g. Coney, 1980; Ramos, 2008). Our data are also compatible with progressive younging of the orogenic activity towards south together with a higher volume of Precambrian crust involved in orogeny. This system resembles Andean-type orogeny in Peru and northern Chile where early thickening occurred on the contact with pro-wedge subducting oceanic plate while the younger orogenic activity was localized at the retrowedge orogenic side represented by the Precambrian Brazilian shield. Such an Andean-type evolution of the hot supra-subduction system of the Dunhuang block is presented in the schematic cartoon in Fig. 15.

### 6.2.2. Early to middle Paleozoic long-lived thermal regime

#### 6.2.2.1. Arc magmatism, crustal melting and upper plate extension.
The Dunhuang block recorded semi-continuous magmatism from 569 Ma to 212 Ma with two major periods of magmatic quiescence at 390–372 Ma and 310–280 Ma (Fig. 7b–d). Paleozoic magmatism in the northern range can be distinguished from magmatism in the central and southern ranges by: i) the occurrence of subduction-related I-type magmatism as early as ca. 519 Ma (Fig. 7a; Table 2), and ii) an intense magmatic flare-up at ca. 439 Ma (Fig. 7b–d). Cambrian magmatic zircons displaying positive zircon $\epsilon_{Hf}(t)$ and whole-rock $\epsilon_{Nd}(t)$ point towards subduction-related magmatism derived from remelting of juvenile crust (Gan et al., 2020b; Soldner et al., 2022) that dominated at the time, as also depicted by the overall high Th/U ratios (>0.5; Fig. 12). Also, a possible presence of forearc and back-arc basins was inferred from the deposition age of 519–489 Ma for sandstones and psammites sourced from the neighboring arc (Kang et al., 2021; Soldner et al., 2022).

In the northern range, the initiation of the metamorphism at ca. 463 Ma is concomitant with significant increase in magmatic activity (Figs. 6c, 7b and 12). This magmatic event was represented by the emplacement of numerous I-type and S-type granitoids (Wang et al., 2016b) as well as underplating of back-arc basalts until 445 Ma (Soldner et al., 2022). Altogether, the high crustal temperature related to arc magmatism, crustal extension and associated mantle upwelling affected the crust of the northern and central ranges at the time (Fig. 15a). The presence of both juvenile materials and Paleoproterozoic crustal rocks as potential sources of Ordovician to early Silurian intrusive rocks is supported by positive to negative zircon $\epsilon_{Hf}(t)$ (Fig. 13b) and whole-rock $\epsilon_{Nd}(t)$ values (Gan et al., 2021b; Soldner et al., 2022). The consistently elevated average Th/U ratios (>0.4) of the corresponding zircons are compatible with a tectono-thermal regime still dominated by magmatic input at the time, until the peak of magmatic activity reached at 445–439 Ma (Figs. 7b,c and 12; Table 2). This magmatic flare up was associated with emplacement of diorites and monzogranites in the northern and central ranges (Fig. 7a). Low (Yb/Gd)$_N$ ratios in coeval metamorphic zircons indicate that this important thermal event resulted in garnet growth since ca. 450 Ma (Fig. 11a).

#### 6.2.2.2. Silurian to early Devonian Andean-type moderate thickening – The Sanweishan phase.
Continuous emplacement of I-type magmatic rocks in the northern and central ranges during the Silurian reflected supra-subduction conditions until ca. 410 Ma (Zhao et al., 2017; Shi et al.,

<figure><img src="image_15.png" /><figcaption>**Fig. 12.** Th/U vs. age diagram of Paleozoic zircons from metamorphic and magmatic rocks from the Dunhuang block. The dashed line corresponds to the 0.5 threshold between divergent and convergent tectonics defined by McKay et al. (2018).</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>**Fig. 13.** Hf isotopic evolution diagram for metamorphic and magmatic zircon from the Dunhuang block for (a) the Precambrian to Paleozoic and (b) the Paleozoic. The vertical dashed lines correspond to garnet Lu-Hf and Sm-Nd ages from Soldner et al. (2023) (in green) and Si et al. (2022) (in red) for metabasites. Histograms and average values (dashed lines) for (c) zircon $\epsilon_{Hf}(t)$ and (d) corresponding $T_{DM2}$ ages from the northern, central and southern ranges of the Dunhuang block. The evolution trend of average felsic crust with $^{176}_{173}\text{Lu}/^{177}\text{Hf}$ ratio = 0.0093 from Vervoort and Patchett (1996). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

2020) (Table 2). The prevalence of high thermal regime until 430 Ma is supported by high metamorphic gradients ranging from 14 to 33 °C/km for prograde metamorphism $M_1$ in the central range (Figs. 6b and 8b), as also depicted by the P–T conditions calculated for amphibolite 17JS44 (Supplementary Fig. S1). From 430 Ma to 410 Ma, significant decrease in average Th/U ratios (<0.4) and $\epsilon_{Hf}(t)$ of magmatic and metamorphic zircons marks a progressive change in the style of deformation from crustal thinning to $M_1$-$D_1$ thickening (Figs. 12 and 13b). The subhorizontal metamorphic fabric $S_1$ and MP conditions are compatible with burial and horizontal flow of deep crust as proposed in the “inverse ductile thinning” model of Jerábek et al. (2012) (Fig. 15b). A good

agreement between the ca. 422 Ma garnet Lu–Hf age and the ca. 420 Ma zircon age peak for $M_1$-$S_1$ in the central range (Fig. 6c) both corresponding to gradients of ~16 °C/km is used to define the timing of crustal thickening called here the Sanweishan phase (Figs. 8b and 15b). The $M_1$ P–T conditions are compatible with crustal thicknesses of 50–55 km further supported by high La/Yb ratios in contemporaneous granitoids exposed in these ranges (Gan et al., 2021a). The combined negative Eu anomalies in metamorphic zircons (Fig. 11b) and negative $\epsilon_{Hf}(t)$ values of both magmatic and metamorphic zircons (Fig. 13b) support partial melting of old crustal components in the moderately thickened crust.
<figure><img src="image_17.png" /><figcaption>Fig. 14. (a) Hf vs. U/Yb and (b) Y vs. U/Yb discrimination diagrams from Grimes et al. (2007) for magmatic and metamorphic zircons from metabasic and metasedimentary rocks from the Dunhuang block.</figcaption></figure>

### 6.2.2.3. Early Devonian continental underthrusting and exhumation – The Hongliuxia phase.
The southward younging $M_2$ metamorphism associ-ated with vertical $S_2$ fabric can be interpreted as a result of progressive migration of crustal deformation during $D_2$ (Fig. 15b,c). A recent P–T–t–D study showed that the $D_2$ shortening dated at ca. 407 Ma in the central range (Soldner et al., 2023) is almost contemporaneous with eclogite-facies metamorphism reported in the southern range (Wang et al., 2017a) (Fig. 15c). There, 400–391 Ma $D_2$-$M_2$ metamorphism recorded in Paleoproterozoic paragneiss was interpreted in terms of northward continental underthrusting beneath the crust of the central and northern ranges (Soldner et al., 2024) (Fig. 15c). In such a model, the rare eclogite-bearing tectonic mélange characterized by ‘Alpine-type’ carbonate and siliciclastic matrix (Ernst, 1988) potentially devel-ed in the southern Dunhuang block (Wang et al., 2017a, 2017b, 2017c). In this context, the subduction of back-arc oceanic crust beneath a moderately thickened hot crust may well explain the preservation of a colder geotherm (Dymkova et al., 2016).

### 6.2.2.4. Late Devonian–Carboniferous orogenic cycle $D_3$-$M_3$. As recog-nized by Gan et al. (2021b), the Dunhuang block underwent a period of relative magmatic quiescence at 400–370 Ma (Fig. 7), with only minor granitoids emplaced in the northern range and characterized by gener-ally positive whole-rock $\varepsilon_{Nd}(t)$ and zircon $\varepsilon_{Hf}(t)$ (Fig. 13b). Together with eclogite formation and migration of deformation in the retro-arc during underthrusting, Devonian tectono-thermal events can be inter-preted in terms of typical Cordilleran orogenic cycle. There, episodes of lithospheric recharge by underthrusting of continental lithosphere concomitant with waning magmatism alternate with episodes of foun-dering of sub-arc eclogitic roots and high-flux magmatic events (e.g. DeCelles et al., 2009). Although the formation and loss of a sub-arc eclogitic root in the Devonian in the Dunhuang block remains debat-able, the 390–380 Ma minor magmatism originating from partial melting of juvenile lower crust with addition of minor mantle materials may be explained by asthenospheric upwelling. This can be achieved by partial or complete loss of an eclogitic root. Alternatively, this magmatic episode can also be explained by asthenospheric upwelling related to convective lithospheric thinning that is associated with crustal thick-ening that is typical for Cascadia-Andean type orogens (Hyndman, 2019), or by break-off of an oceanic slab related to continental under-thrusting (Duretz and Gerya, 2013). The ca. 385 Ma garnet Sm–Nd age and corresponding $M_3$ P–T conditions in mafic granulite from the central range suggest the persistence of a high thermal regime until middle Devonian (Fig. 15d) (Soldner et al., 2023). High (Yb/Gd)$_N$ ratios char-acterizing concomitant (re)crystallized zircon and monazite (Figs. 10b and 11a) associated with the 378–371 Ma age peaks (Figs. 6c and 9) are generally consistent with the 389–365 Ma exhumation ages in the cen-tral and southern ranges (Li et al., 2021; Soldner et al., 2023, 2024; Wang et al., 2016c; Zhang et al., 2020). Altogether, the exhumation event $D_3$ initiated in the late Devonian occurred along hot metamorphic

gradients of ~29 °C/km (Figs. 9a and 12) (Fig. 15e). It was followed by a late Devonian magmatic resurgence revealed in all three ranges (Fig. 7d, f,h), an increase in overall zircon average Th/U ratios (>0.5; Fig. 12) and a continuous decrease in zircon $\varepsilon_{Hf}(t)$ values (Fig. 13b). These data, together with I-type granitoids exposed in the central range (Zhao et al., 2017) and early Carboniferous adakites (Zhu et al., 2014; Wang et al., 2016a; Bao et al., 2017; Zhao et al., 2017) indicate that the Dunhuang block represented an active continental margin at the time. This evo-lution was responsible for ubiquitous formation of the $S_3$ subvertical fabrics in the Dunhuang block. The timing of late $D_3$ crustal reworking event has been constrained between 362 Ma and 300 Ma using i) the deformation of granitic dykes and orthogneiss (Fig. 5h and supple-mentary Fig. S3a–c) (Feng et al., 2018; Soldner et al., 2023) as well as titanite, garnet, monazite and zircon ages (Si et al., 2022; Wang et al., 2021b; Zhao et al., 2020) (Figs. 6b, S4 and S5). This age of the event is supported by the 350–318 Ma zircon and monazite metamorphic age (Fig. 6c) and 368–315 Ma magmatic zircon age peaks (Fig. 7b–d). Altogether, the synthetized data indicate that Carboniferous magmatism was accompanied by long-lasting metamorphic re-equilibration and crustal deformation of the central and southern ranges of the Dunhuang block (Fig. 15e). It can be inferred that the N-S $D_3$-$M_3$ shortening (in current coordinates) operated in a time scale longer than 60 m.y. and did not result from metamorphic continuum typical for subduction-exhumation cycles in subduction and collisional orogens (e.g. Gerya et al., 2002; Maierová et al., 2021).

### 6.2.3. Permian metamorphism $M_4$

The late stages of the late Paleozoic tectono-thermal evolution of the Dunhuang block are marked by two Permian magmatic events, coeval with the emplacement of high-K calc-alkaline continental arc rocks (Table 2; Fig. 7b–d). The corresponding increase in zircon Th/U ratios (up to 1.5) (Fig. 12) and $\varepsilon_{Hf}(t)$ values is compatible with the existence of the supra-subduction magmatic underplating of juvenile rocks and asthenospheric upwelling (Feng et al., 2020; Wang et al., 2021a, 2023). This magmatic event may be responsible for the existence of anti-clockwise P–T paths and corresponding metamorphic gradients of ~23–37 °C/km in the southern range (Wang et al., 2023). In contrast, greenschist-facies conditions have been determined for late Permian to early Triassic dextral strike slip post-accretionary/collisional deforma-tion in the central range (Feng et al., 2018). Both the above-mentioned features can be correlated with the crystallization of high (Yb/Gd)$_N$ ca. 252 Ma zircon (Figs. 11a) as well as the 258–252 Ma and ca. 227 Ma $^{40}$Ar–$^{39}$Ar ages from the northern and southern ranges (Table 1).

## 6.3. Geodynamic evolution at the interface of interior to exterior oceanic domains

Numerous paleogeographic and geological reconstructions suggest that the Tarim and North-China Cratons as well as their neighboring
<figure><img src="image_18.png" /><figcaption>**Fig. 15.** Polyphase early to late Paleozoic tectono-metamorphic evolutionary model of the Dunhuang block. **Left panel:** crustal structures developed in the northern and central ranges (Sanweishan phase) and the southern range (Hongliuxia range). **Right panel:** P–T paths of representative metamorphic samples from Soldner et al. (2023, 2024) and Wang et al. (2017a).</figcaption></figure>

Dunhuang and Alxa blocks were distributed along the northern margin of Gondwana in the Cambrian to early Ordovician (e.g. Metcalfe, 1988; Li et al., 2018; Zhao et al., 2018). The timing of separation of individual blocks from the Gondwana margin range from the Ordovician (Li et al., 2018; von Raumer et al., 2015), to Silurian (Zhao et al., 2018) and Carboniferous (Metcalfe, 2013). Recent reconstructions based on quantitative paleomagnetic data and geologic and paleobiologic observations advocate that extensive northward dispersion of NE Gondwana

already occurred before late Cambrian (Domeier, 2018; Cocks and Torsvik, 2021; Merdith et al., 2021). The plate positions presented in this work have been reconstructed using the GPlates open-source computer software designed to work with full-plate reconstructions (Boyden et al., 2011). GPlates-compatible global plate models of Domeier (2018) (DOM18 hereafter) combined with those of Domeier and Torsvik (2014) (DT14 hereafter) were used with specific focus on the constituting blocks of the TNCC (Fig. 16). Three main features characterize the
<figure><img src="image_19.png" /><figcaption>**Fig. 16.** Position of the Dunhuang block in the early to late Paleozoic in the full-plate models of Domeier (2018) (DOM18) combined to Domeier and Torsvik (2014) (DT14), reconstructed using GPlate software (Boyden et al., 2011). Plate and terrane abbreviations: Al, Alxa; Am, Amuria; An, Annamia; Ba, Baltica; BC, Boshekul-Chingiz; D, Dunhuang; KO, Kazakhstan collage; MC, Mongolian collage; NC, North China; NT, North-Tianshan; SC, South China; Sib, Siberia; T, Tarim. Ocean abbreviation: MO, Mongol-Okhotsk Ocean; Tu, Turkestan Ocean; Ran, branch of the Rheic Ocean. Exterior and interior oceans are indicated in light and dark blue, respectively. Yellow lines in (a), (c) and (e) correspond to the locations of crustal cross-sections (A–A') in Fig. 17. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

DOM18 model in the Cambrian: i) the dispersion of northern Gondwana into several independent blocks, ii) the existence of large interior oceanic domains (dark blue) bounded by NE Gondwana, Siberia and Baltica and iii) the northerly exterior Panthalassa-Paleo-Pacific Ocean (light blue) (Fig. 16a).

Recent geological reconstructions placed the Dunhuang block, together with Tarim, the Alxa block and Proto-Tethyan continental blocks (Altyn-Qaidam-Qilian-Kunlun) in the vicinity of the NE Gondwana margin (Li et al., 2018; Zhao et al., 2018; Dong et al., 2021). The Cambrian active margin setting of the Dunhuang block precludes a

position near the northern passive margin of Tarim at the time but is compatible with the subduction of the Proto-Tethys Ocean as shown in the reconstructions of Fig. 16a (e.g. Yu et al., 2021; Fu et al., 2022). This corroborates late Ordovician–Devonian arc-related magmatic rocks interpreted as products of a south-dipping subduction beneath the northern margin of the Alxa block (Liu et al., 2016). The initiation of subduction of the Proto-Tethys Ocean is also indicated by HP–UHP metamorphism in the Qilian and Qaidam belts (e.g. Zhang et al., 2017b and references therein). Silurian–Devonian metamorphism reported in both the Dunhuang and Alxa blocks support their close position at the time (Fig. 8c) (e.g. Chen et al., 2015; Wang et al., 2017a). In addition, the ca. 2.5–2.3 Ga magmatic and ca. 1.86–1.82 Ga metamorphic events recorded in gneisses in the Dunhuang block (Fig. S3d) have also been recognized in the Alxa block (e.g. Fan et al., 2010; Zhang et al., 2013), thereby coining a possible similar Precambrian evolution of both the blocks.

In the reconstructions of DOM18, the important retreat of a SE dipping Proto-Tethyan subduction zone led to the northward drift of the Dunhuang, Alxa and Proto-Tethyan blocks towards the North-China Craton. In the northern Dunhuang block, this event is marked by the increase in magmatic activity corresponding to I-type and S-type magmatism (Wang et al., 2016a, 2016b; Gan et al., 2021a), basaltic underplating and crustal thinning (Soldner et al., 2022), and coincides with the inception of HT metamorphism from ca. 463 Ma (Figs. 7c–f and 17a).

The late Silurian (ca. 420 Ma) stage is marked by i) final amalgamation of the Dunhuang, Alxa and Proto-Tethyan blocks possibly along the western margins of the North-China Craton, and ii) by the position of the newly formed continental assemblage above the south-dipping Panthalassan peripheral subduction system (Fig. 16b). This is compatible with the persistence of arc magmatism in the northern range and with the simultaneous thickening of the supra-subduction margin of the Dunhuang block (Fig. 17b).

From the middle Devonian (390 Ma), both the Dunhuang and Alxa blocks faced the Panthalassa subduction zone with coeval initiation of the Paleo-Tethys subduction zone under the Proto-Tethyan blocks (Fig. 16b). In the Dunhuang block, this event corresponds to the end of an Andean-type cycle marked by a period of metamorphic rock exhumation and magmatic quiescence (Fig. 15). In the reconstructions of DOM18, the continuous northward subduction of the Paleo-Tethys Ocean operated from the Ordovician to Carboniferous without significant change in plate configurations. In the light of the currently available data showing the prevalence of Devonian–Carboniferous deformational-metamorphic features in the central and southern range of the Dunhuang block, it can be argued that the N-S directed compressional D₃ event mainly reflected the subduction of the Paleo-Tethys Ocean (Fig. 17c).

In the late Carboniferous (310 Ma), the closure of the Turkestan interior Ocean coincided with the westward growth of the Paleo-Asian Ocean north of the TNCC in DT14 (Figs. 16c and 17c). The supra-subduction setting of the Dunhuang block is compatible with M₃ metamorphism as well as magmatism in a thickened crust characterized by continuously decreasing negative zircon $\epsilon_{Hf}$(t) values (Fig. 13b). From the Permian to Triassic, oceanic subduction led to the eastward closure of the Paleo-Asian domain between the Alxa-North-China blocks and Amuria (Eizenhöfer and Zhao, 2018). Overall, both the Carboniferous and Permian high T/P metamorphism recorded in the Dunhuang block are well-explained by its supra-subduction setting between two opposing subduction systems (Figs. 16c and 17c).

## 7. Conclusions

A comprehensive compilation of recently published metamorphic P–T data, metamorphic and magmatic U–Pb ages, zircon Hf isotopic and geochemical data for early to late Paleozoic rocks from the northern, central and southern ranges of the Dunhuang block is presented in this contribution. This compilation is supplemented by new P–T constraints
<figure><img src="image_20.png" /><figcaption>**Fig. 17.** Interpretative crustal scale cross-section (A–A') through the Dunhuang-Alxa-Qilian-Qaidam-Kunlun continental assemblage for the DOM18 and DT14 paleogeographic reconstructions in the (a) Cambrian–Ordovician, (b) Silurian–Devonian and (c) Carboniferous–Permian.</figcaption></figure>

and analyses of zircon and monazite U–Pb ages of Paleozoic meta-
morphic rocks. Major conclusions are:

1) The Ordovician to Devonian metamorphic rocks define a clockwise P–T evolution with M₁, M₂ and M₃ characterized by distinct hot metamorphic gradients.

2) Low (Yb/Gd)N ratios in metamorphic zircon and monazite from metabasites and metapelites suggest that garnet growth occurred as early as 450 Ma in concomitance with the emplacement of 460–432 Ma S-type granitoids. Silurian HP metamorphism, together with low Th/U ratios and negative εHf(t) in magmatic and metamorphic

zircons, clearly mark a period of significant crustal reworking related to thickening of a previously thermally softened crust.

3) The succession of metamorphic stages M₁–M₃ with higher meta-
morphic gradients during late Devonian exhumation, the occurrence of Precambrian crystalline rocks and the continental geochemical signature of zircons from metabasites suggest that a Franciscan-type subduction channel architecture of the region is unlikely. Instead, the Paleozoic tectono-thermal evolution of the Dunhuang block resembles hot orogenic systems typical of supra-subduction active margins involving crystalline basement rocks similar to the north and south American Cordillera margins.
4) The kinematically independent D₃-M₃ event that operated over 60 m. y. did not result from a metamorphic continuum with M₁-M₂. In contrast, it was characterized by metamorphic reequilibration and long-lasting magmatic input that lead to crustal thickening of the central and southern ranges of the Dunhuang block.

5) The short-lived Permian magmatic events and anticlockwise P–T metamorphism can be attributed to a magmatic underplating event in the context of continuous oceanic subduction.

6) The two orthogonal deformation and metamorphic cycles reflect plate re-organization during amalgamation of the Dunhuang, Alxa and Proto-Tethyan blocks with the North China Craton. The early stages reflected subduction of the Proto-Tethys Ocean, while the latter involved the dynamics of the Pthalanlassa–Paleo Asian oceans opposed to the Paleo-Tethys Ocean.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.earscirev.2024.104984.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We gratefully acknowledge the financial supports of the National Natural Science Foundation of China projects (42372240, 42372225) and the International Partnership Program of Chinese Academy of Sciences (Grant no. 132744KYSB20190039). JS was supported by the project No. 2021/43/P/ST10/02996 co-funded by the National Science Centre and the EU H2020 research and innovation program under the MSCA GA No. 945339. For the purpose of Open Access, the author has applied a CC-BY public copyright license to any Author Accepted Manuscript (AAM) version arising from this submission. KS and PS acknowledge the support of the Czech National Grant Agency, GACR 19-27682×. We are grateful to Cao Yonghua, Zhang Le, Matyszczak Milena, Kozub-Budzyń Gabriela, Włodek Adam and Sun Mingqi for helping with the EPMA, LA-ICPMS and SEM analyses. Constructive comments of two anonymous reviewers and guest editor Wenjiao Xiao to the earlier version of this manuscript are gratefully acknowledged. We thank Yilirim Dilek for his editorial work.

Data availability

The data that supports the findings of this study are available in the supplementary material of this article

References

Allen, M.B., Song, S., Wang, C., Zeng, R., Wen, T., 2023. An oblique subduction model for closure of the Proto-Tethys and Paleo-Tethys oceans and creation of the Central China Orogenic Belt. Earth Sci. Rev. 104385.

Andersen, T.B., Jamtveit, B., Dewey, J.F., Swensson, E., 1991. Subduction and eduction of continental crust: Major mechanisms during continent-continent collision and orogenic extensional collapse, a model based on the south Norwegian Caledonides. Terra Nova 3 (3), 303–310.

Aoya, M., Uehara, S.I., Matsumoto, M., Wallis, S.R., Enami, M., 2003. Subduction-stage pressure-temperature path of eclogite from the Sambagawa belt: Prophetic record for oceanic-ridge subduction. Geology 31 (12), 1045–1048.

Bao, W.H., Long, X.P., Yuan, C., Sun, M., Zhao, G.C., Wang, Y.J., Guan, Y., Zhang, Y.Y., 2017. Paleozoic adakitic rocks in the northern Altyn Tagh, northwest China: evidence for progressive crustal thickening beneath the Dunhuang Block. Lithos 272–3273, 1–315.

BGMRG (Bureau of Geology and Mineral Resources of Gansu Province), 1989. Regional Geology of Gansu Province. People's Republic of China, Ministry of Geology and Mineral Resources. Geological Memoirs, Series 1, No. 19. Geological Publishing House, 8–9 pp. Beijing (in Chinese with English abstract).

Boyden, J.A., Müller, R.D., Gurnis, M., Torsvik, T.H., Clark, J.A., Turner, M., IveyLaw, H., Watson, R.J., Cannon, J.S., 2011. Next-generation plate-tectonic reconstructions using GPlates. In: Keller, G.R., Baru, C. (Eds.), Geoinformatics: Cyberinfrastructure for the Solid Earth Sciences: Cambridge. Cambridge University Press, UK, pp. 95–113.

Brown, M., Johnson, T., 2018. Secular change in metamorphism and the onset of global plate tectonics. Am. Mineral. 103 (2), 181–196.

Buslov, M.M., Saphonova, I.Y., Watanabe, T., Obut, O.T., Fujiwara, Y., Iwata, K., Semakov, N.N., Sugai, Y., Smirnova, L.V., Kazansky, A.Y., 2001. Evolution of the Paleo-Asian Ocean (Altai-Sayan Region, Central Asia) and collision of possible Gondwana-derived terranes with the southern marginal part of the Siberian continent. Geosci. J. 5, 203–224.

Buslov, M.M., Fujiwara, Y., Iwata, K., Semakov, N.N., 2004. Late Paleozoic-early Mesozoic geodynamics of Central Asia. Gondwana Res. 7 (3), 791–808.

Bütner, S.H., Glodny, J., Lucassen, F., Wemmer, K., Erdmann, S., Handler, R., Franz, G., 2005. Ordovician metamorphism and plutonism in the Sierra de Quilmes metamorphic complex: Implications for the tectonic setting of the northern Sierras Pampeanas (NW Argentina). Lithos 83 (1–2), 143–181.

Carswell, D.A., Zhang, R.Y., 1999. Petrographic characteristics and metamorphic evolution of ultrahigh-pressure eclogites in plate-collision belts. Int. Geol. Rev. 41 (9), 781–798.

Catlos, E.J., Lovera, O.M., Kelly, E.D., Ashley, K.T., Harrison, T.M., Etzel, T., 2018. Modeling high-resolution pressure-temperature paths across the Himalayan Main Central Thrust (Central Nepal): Implications for the dynamics of collision. Tectonics 37 (8), 2363–2388.

Chardon, D., Jayananda, M., Peucat, J.J., 2011. Lateral constrictional flow of hot orogenic crust: Insights from the Nearchean of South India, geological and geophysical implications for orogenic Plateaux. Geochem. Geophys. Geosyst. 12 (2).

Chen, Y., Wei, C., Zhang, J., Chu, H., 2015. Metamorphism and zircon U-Pb dating of garnet amphibolite in the Baoyintu Group, Inner Mongolia. Sci. Bull. 60 (19), 1698–1707.

Chopin, C., 2003. Ultrahigh-pressure metamorphism: tracing continental crust into the mantle. Earth Planet. Sci. Lett. 212 (1–2), 1–14.

Clark, C., Healy, D., Johnson, T.E., Collins, A.S., Taylor, R.J., Santosh, M., Timms, N.E., 2015. Hot orogens and superconti-nent amalgamation: a Gondwanan example from southern India. Gondwana Res. 28 (4), 1310–1328.

Clark, C., Taylor, R.J.M., Kylander-Clark, A.R.C., Hacker, B.R., 2018. Prolonged (>100 Ma) ultrahigh temperature metamorphism in the Napier complex, East Antarctica: a petrochronological investigation of Earth’s hottest crust. J. Metamorph. Geol. 36, 1117–1139.

Cocks, L.R.M., Torsvik, T.H., 2021. Ordovician paleogeography and climate change. Gondwana Res. 100, 53–72.

Coney, P.J., 1980. Cordilleran suspect terranes. Nature 288, 329–333.

Connolly, J.A.D., 2005. Computation of phase equilibria by linear programming: a tool for geodetic modelling and its application to subduction zone decarbonation. Earth Planet. Sci. Lett. 236, 524–541.

Cunningham, D., Zhang, J., Li, Y., 2016. Late Cenozoic transpressional mountain building directly north of the Altyn Tagh fault in the Sanweishan and Nanjieshan, north Tibetan foreland, China. Tectonophysics 687, 111–128.

DeCelles, P.G., Ducea, M.N., Kapp, P., Zandt, G., 2009. Cyclicity in Cordilleran orogenic systems. Nat. Geosci. 2 (4), 251–257.

Delville, N., Arnaud, N., Montel, J.M., Roger, F., Brunel, M., Tapponnier, P., Sobel, E., 2001. Paleozoic to Cenozoic deformation along the Altyn Tagh fault in the Altun Shan massif area, eastern Qilian Shan, northeastern Tibet, China. Geol. Soc. Am. Mem. 194, 269–292.

Domeier, M., 2018. Early Paleozoic tectonics of Asia: Towards a full-plate model. Geosci. Front. 9 (3), 789–862.

Domeier, M., Torsvik, T.H., 2014. Plate tectonics in the late Paleozoic. Geosci. Front. 5, 303–350.

Dong, Y., Sun, S., Santosh, M., Zhao, J., Sun, J., He, D., Shi, X., Hui, B., Cheng, C., Zhang, G., 2021. Central China orogenic belt and amalgamation of East Asian continents. Gondwana Res. 100, 131–194.

Donskaya, T.V., Gladkochub, D.P., Mazukabzov, A.M., Ivanov, A.V., 2013. Late Paleozoic–Mesozoic subduction-related magmatism at the southern margin of the Siberian continent and the 150 million-year history of the Mongol-Okhotsk Ocean. J. Asian Earth Sci. 62, 79–97.

Duretz, T., Gerya, T.V., 2013. Slab detachment during continental collision: Influence of crustal rheology and interaction with lithospheric delamination. Tectonophysics 602, 124–140.

Dymkova, D., Gerya, T., Burg, J.P., 2016. 2D thermomechanical modelling of continent–arc continent collision. Gondwana Res. 32, 138–150.

Eizenhöfer, P.R., Zhao, G., 2018. Solonker Suture in East Asia and its bearing on the final closure of the eastern segment of the Paleo-Asian Ocean. Earth Sci. Rev. 186, 153–172.

Endo, S., Wallis, S.R., Tsuboi, M., Aoya, M., Uehara, S.I., 2012. Slow subduction and buoyant exhumation of the Sanbagawa eclogite. Lithos 146, 183–201.

Ernst, W.G., 1988. Tectonic history of subduction zones inferred from retrograde blueschist PT paths. Geology 16 (12), 1081–1084.

Fan, H.R., Yang, K.F., Hu, F.F., Wang, K.Y., Zhai, M.G., 2010. Zircon geochronology of basement rocks from the Bayan Obo area, Inner Mongolia, and tectonic implications. Acta Petrol. Sin. 26, 1342–1350.

Feng, J.C., Zhang, W., Wu, T.R., Zheng, R.G., Luo, H.L., He, Y.K., 2012. Geochronology and geochemistry of granite pluton in the north of Qiaowan, Beishan Mountain, Gansu province, China, and its geological significance. Acta Sci. Nat. Univ. Pekin. 48 (1), 61–70.

Feng, L.M., Lin, S.F., Davis, D.W., van Staal, C.R., Song, C.Z., Li, L.M., Li, J.H., Ren, S.L., 2018. Dunhuang Tectonic Belt in northwestern China as a part of the Central Asian Orogenic Belt: Structural and U-Pb geochronological evidence. Tectonophysics 747–748, 281–297.
Feng, L., Lin, S., Li, L., Davis, D.W., Song, C., Li, J., Ren, S.L., Ge, Y.P., Lu, K., 2020. Constraints on the tectonic evolution of the southern central Asia orogenic belt from early Permian-middle Triassic granitoids from the Central Dunhuang orogenic belt, NW China. *J. Asian Earth Sci.* 194, 104283.

Festa, A., Pini, G.A., Dilek, Y., Codegone, G., 2010. Mélanges and mélange-forming processes: a historical overview and new concepts. *Int. Geol. Rev.* 52 (10–12), 1040–1105.

Festa, A., Dilek, Y., Pini, G.A., Codegone, G., Ogata, K., 2012. Mechanisms and processes of stratal disruption and mixing in the development of mélanges and broken formations: Redefining and classifying mélanges. *Tectonophysics* 568, 7–24.

Finch, M.A., Weinberg, R.F., Hasalová, P., Becchio, R., Fuentes, M.G., Kennedy, A., 2017. Tectono-metamorphic evolution of a convergent back-arc: the Famatian orogen, Sierra de Quilmes, Sierras Pampeanas, NW Argentina. *GSA Bull.* 129 (11–12), 1602–1621.

Fu, D., Huang, B., Johnson, T.E., Wilde, S.A., Jourdan, F., Polat, A., Windley, B.F., Hu, Z. C., Kusky, T., 2022. Boninitic blueschists record subduction initiation and subsequent accretion of an arc–forearc in the northeast Proto-Tethys Ocean. *Geology* 50 (1), 10–15.

Gan, B., Diwu, C., Yan, J., Wang, T., Li, J., 2020a. Formation and stabilization of the Dunhuang Block, NW China: Constraints from the Late Paleoproterozoic A-type granitoids of the Dunhuang Complex. *Precambrian Res.* 346, 105791.

Gan, B., Li, Z., Song, Z., Li, J., 2020b. Middle Cambrian granitoids in the Dunhuang Block, NW China mark the early subduction of the southernmost Paleo-Asian Ocean. *Lithos* 105654.

Gan, B., Diwu, C., Lai, S., Wang, T., Wu, L., 2021a. Petrogenesis of early Paleozoic granitoids in the Dunhuang Block, NW China: Insights into magma evolution and crustal thickening. *Lithos* 402, 106233.

Gan, B., Diwu, C., Wu, L., Wang, T., 2021b. Geochronology, geochemistry, and Sr-Nd-Pb
Hf isotopes of the late Paleozoic Dongshuiyou composite pluton in the Dunhuang
Block, southernmost Central Asian Orogen: Petrogenesis and implications for crustal
growth. *Lithos* 384, 105970.

Gan, B., Tang, J., Safonova, I., Qin, L., Diwu, C., 2023a. Devonian continental magmatism in the southern Central Asian Orogenic Belt: evidence from the Dunhuang Block, NW China. *Geosci. Front.* 14 (6), 101643.

Gan, B., Diwu, C., Wang, T., Pei, Q., Wang, S., 2023b. Early Paleozoic intermediate igneous rocks in the Dunhuang Block, southern Central Asian Orogenic Belt: geochronology, petrogenesis, and implications for tectonic evolution. *J. Geol. Soc. Lond.* 180 (1), 2021–2178.

Gerya, T.V., Stöckhert, B., Perchuk, A.L., 2002. Exhumation of high-pressure metamorphic rocks in a subduction channel: a numerical simulation. *Tectonics* 21 (6), 6–1.

Goscombe, B., Gray, D., Foster, D.A., 2018. Metamorphic response to collision in the Central Himalayan Orogen. *Gondwana Res.* 57, 191–265.

Grimes, C.B., John, B.E., Kelemen, P.B., Mazdab, F.K., Wooden, J.L., Cheadle, M.J.,
Schwartz, J.J., 2007. Trace element chemistry of zircons from oceanic crust: a
method for distinguishing detrital zircon provenance. *Geology* 35 (7), 643–646.

Gougrouz, C., Martin, L., Vanderhaeghe, O., Thébau, N., Fiorentini, M., 2018. Zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the Ivrea-Verbano and Strona-Ceneri Zones, NW Italy. *Lithos* 308, 1–18.

Guy, A., Schulmann, K., Soejono, I., Xiao, W., 2020. Revision of the Chinese Alta-east Junggar terrane accretion model based on geophysical and geological constraints. *Tectonics* 39 (4) e2019TC006026.

Han, Y., Zhao, G., Cawood, P.A., Sun, M., Eizenhöfer, P.R., Hou, W., Zahng, X.R., Liu, Q., 2016. Tarim and North China cratons linked to northern Gondwana through switching accretionary tectonics and collisional orogenesis. *Geology* 44 (2), 95–98.

Harley, S.L., 2016. A matter of time: the importance of the duration of UHT metamorphism. *J. Mineral. Petrol. Sci.* 111 (2), 50–72.

He, Z., Zhang, Z., Zong, K., Dong, X., 2013. Paleoproterozoic crustal evolution of the Tarim Craton: Constrained by zircon U-Pb and Hf isotopes of meta-igneous rocks from Korla and Dunhuang. *J. Asian Earth Sci.* 78, 54–70.

He, Z.Y., Zhang, Z.M., Zong, K.Q., Xiang, H., Klemd, R., 2014. Metamorphic P–T–t evolution of mafic HP granulites in the northeastern segment of the Tarim Craton (Dunhuang block): evidence for early Paleozoic continental subduction. *Lithos* 196–197, 1–13.

Holland, T.J.B., Powell, R., 2011. An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids. *J. Metamorph. Geol.* 29, 333–383.

Huang, B., Yan, Y., Piper, J.D., Zhang, D., Yi, Z., Yu, S., Zhou, T., 2018. Paleomagnetic constraints on the paleogeography of the East Asian blocks during Late Paleozoic and Early Mesozoic times. *Earth Sci. Rev.* 186, 8–36.

Hyndman, R.D., 2019. Mountain building orogeny in precollision hot backarcs: north American Cordillera, India-Tibet, and Grenville Province. *J. Geophys. Res. Solid. Earth* 124 (2), 2057–2079.

Jahn, B.M., 1998. Geochemical and isotopic characteristics of UHP eclogites and ultramafic rocks of the Dabie orogen: Implications for continental subduction and collisional tectonics. In: When Continents Collide: Geodynamics and Geochemistry of Ultrahigh-Pressure Rocks. Springer Netherlands, Dordrecht, pp. 203–239.

Jérabek, P., Lexa, O., Schulmann, K., Plasienka, D., 2012. Inverse ductile thinning via lower crustal flow and fold-induced doming in the West Carpathian Eo-Alpine collisional wedge. *Tectonics* 31 (5).

Jiang, L., Zhang, J.R., Tang, S., Wei, C.J., Chu, H., 2021. Geochemistry,metamorphism and geochronology characteristics of the garnet amphibolites in the Baoyintu Group, central-western Inner Mongolia. *Acta Petrol. Sin.* 37 (12), 3759–3780.

Kang, L., Li, T.H., Wang, J., Ji, W.H., Wang, T., Chen, F.N., Liu, X.J., Zhang, C., 2021. Discovery of Late Sinian-Early Cambrian sedimentary strata in Dunhuang area and

its tectonic significances. *Acta Petrol. Sin.* 37 (7), 2103–2122 (in Chinese with abstract English).

Kang, L., Wang, T., Li, T.H., Ji, W.H., Wang, J., Dong, H.Q., Zhang, Y., Zhang, C., 2023. Cambrian-Early Ordovician intrusive bodies in Dunhuang Block: Records of Paleo-Asian Ocean subduction and implications for regional Early Paleozoic tectonic evolution. *Acta Petrol. Sin.* 39 (3), 823–844.

Khain, E.V., Bibikova, E.V., Salnikova, E.B., Kröner, A., Gibler, A.S., Didenko, A.N., Degtyarev, K.E., Fedotova, A.A., 2003. The Paleo-Asian Ocean in the Neoproterozoic and early Paleozoic: new geochronologic data and paleotectonic reconstructions. *Precambrian Res.* 122, 329–358.

Li, S., Zhao, S., Liu, X., Cao, H., Yu, S., Li, X., Somerville, I., Suo, Y., 2018. Closure of the Proto-Tethys Ocean and early Paleozoic amalgamation of microcontinental blocks in East Asia. *Earth Sci. Rev.* 186, 37–75.

Li, Z., Wang, H., Zhang, Q., Shi, M.Y., Lu, J.S., Liu, J.H., Wu, C.M., 2021. Ultra-high pressure metamorphism and geochronology of garnet clinopyroxenite in the Paleozoic Dunhuang Orogenic Belt, northwestern China. *Minerals* 11 (2), 117.

Liu, Y.J., Neubauer, F., Genser, J., Ge, X.H., Takasu, A., Yuan, S.H., Chang, L.H., Li, W. M., 2007. Geochronology of the initiation and displacement of the Altyn Strike-Slip Fault, western China. *J. Asian Earth Sci.* 29 (2-3), 243–252.

Liu, Q., Zhao, G., Sun, M., Han, Y., Eizenhöfer, P.R., Hou, W., Zhang, X., Zhu, Y., Wang, B., Liu, D., 2016. Early Paleozoic subduction processes of the Paleo-Asian Ocean: insights from geochronology and geochemistry of Paleozoic plutons in the Alxa Terrane. *Lithos* 262, 546–560.

Long, X.P., Yuan, C., Sun, M., Kröner, A., Zhao, G.C., 2014. New geochemical and combined zircon U–Pb and Lu–Hf isotopic data of orthogneisses in the northern Altyn Tagh, northern margin of the Tibetan plateau: implication for Archean evolution of the Dunhuang Block and crust formation in NW China. *Lithos* 200–201, 418–431.

Lu, S.N., Li, H.K., Zhang, C.L., Niu, G.H., 2008. Geological and geochronological evidence for the Precambrian evolution of the Tarim Craton and surrounding continental fragments. *Precambrian Res.* 160, 94–107.

Ludwig, K.R., 2003. Isoplot 3.00: A Geochronological Toolkit for Microsoft Excel, 4. Berkeley Geochronology Center Special Publication, p. 70.

Lv, P., Peng, Y., Zhang, J., Xie, W., Jiang, X., Gao, X., Ji, W.T., Li, S., Liu, Y., 2020. Paleoproterozoic multiple magmatic-metamorphic events in the Dunhuang Block, eastern Tarim Craton: Implications for assembly of the Columbia supercontinent. *Precambrian Res.* 351, 105949.

Maierová, P., Schulmann, K., Štěpská, P., Gerya, T., Lexa, O., 2021. Trans-lithospheric diapirism explains the presence of ultra-high pressure rocks in the European Variscides. *Commun. Earth Environ.* 2 (1), 56.

McKay, M.P., Jackson Jr., W.T., Hessler, A.M., 2018. Tectonic stress regime recorded by zircon Th/U. *Gondwana Res.* 57, 1–9.

Mei, H.L., Yu, H.F., Li, Q., 1997. Preliminary litho-tectonic framework of early Precambrian rocks in Dunhuang–Beishan Section, Gansu, West China. *Prog. Precambrian Res.* 20, 47–54 (in Chinese).

Meng, F.C., Zhang, J.X., Xiang, Z.Q., Yu, S.Y., Li, J.P., 2011. Evolution and formation of the Dunhuang Group in NE Tarim basin, NW China: evidence from detrital-zircon geochronology and Hf isotope. *Acta Petrol. Sin.* 27, 59–76 (in Chinese).

Merdith, A.S., Williams, S.E., Collins, A.S., Tetley, M.G., Mulder, J.A., Blades, M.L., Young, A., Armistead, S.E., Cannon, J., Zahirovic, S., Müller, R.D., 2021. Extending full-plate tectonic models into deep time: linking the Neoproterozoic and the Phanerozoic. *Earth Sci. Rev.* 214, 103477.

Metcalf, I., 1988. Origin and assembly of south-east Asian continental terranes. *Geol. Soc. Lond. Spec. Publ.* 37 (1), 101–118.

Metcalf, I., 1994. Gondwanaland origin, dispersion, and accretion of East and Southeast Asian continental terranes. *J. S. Am. Earth Sci.* 7 (3–4), 333–347.

Metcalf, I., 2013. Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys. *J. Asian Earth Sci.* 66, 1–33.

Metcalf, I., 2021. Multiple Tethyan Ocean basins and orogenic belts in Asia. *Gondwana Res.* 100, 87–130.

Murali, A.V., Parthasarathy, R., Mahadevan, T.M., Das, M.S., 1983. Trace element characteristics, REE patterns and partition coefficients of zircons from different geological environments—a case study on Indian zircons. *Geochim. Cosmochim. Acta* 47 (11), 2047–2052.

Paton, C., Hellstrom, J., Paul, B., Woodhead, J., Hergt, J., 2011. Iolite: Freeware for the visualisation and processing of mass spectrometric data. *J. Anal. At. Spectrom.* 26 (12), 2508–2518.

Pham, V.T., Wang, H.Y.C., Zhang, Q.W.L., Liu, J.H., Shi, M.Y., Li, Z., Wu, C.M., 2018. Metamorphic evolution and geochronology of the Changshanzi area, Dunhuang Orogenic Belt, Northwest China. *Acta Petrol. Sin.* 34 (9), 2773–2792 (in Chinese with English abstract).

Prent, A.M., Beinlich, A., Morrissey, L.J., Raimondo, T., Clark, C., Putnis, A., 2019. Monazite as a monitor for melt-rock interaction during cooling and exhumation. *J. Metamorph. Geol.* 37 (3), 415–438.

Ramos, V.A., 2008. The basement of the Central Andes: the Arequipa and related terranes. *Annu. Rev. Earth Planet. Sci.* 36, 289–324.

Rubatto, D., 2002. Zircon trace element geochemistry: partitioning with garnet and the link between U-Pb ages and metamorphism. *Chem. Geol.* 184, 123–138.

Rubatto, D., Hermann, J., 2007. Experimental zircon/melt andzircon/garnet trace element partitioning and implications for the geochronology of crustal rocks. *Chem. Geol.* 241, 38–61.

Rubatto, D., Chakraborty, S., Dasgupta, S., 2013. Timescales of crustal melting in the Higher Himalayan Crystallines (Sikkim, Eastern Himalaya) inferred from trace element-constrained monazite and zircon chronology. *Contrib. Mineral. Petrol.* 165, 349–372.

Schaltegger, U., Fanning, C.M., Gunther, D., Maurin, J.C., Schulmann, K., Gebauer, D., 1999. Growth, annealing and recrystallization of zircon and preservation of
monazite high-grade metamorphism: conventional and in situ U-Pbisotope, cathodoluminescence and microchemical evidence. Contrib. Mineral. Petrol. 134, 186-201.

Schulmann, K., Lexa, O., Janousek, V., Lardeaux, J.M., Edel, J.B., 2014. Anatomy of a diffuse cryptic suture zone: an example from the Bohemian Massif, European Variscides. Geology 42 (4), 275-278.

Shi, M., Hou, Q.L., Wu, C.M., Yan, Q.R., Wang, H.Y.C., Cheng, N.N., Zhang, Q.W.L., Li, M.G.Z., 2020. Paleozoic Sanweishan arc in the northern Dunhuang region, NW China: the Dunhuang block is a Panherozoic orogen, not a Precambrian block. J. Asian Earth Sci. 103954.

Shi, M., Hou, Q., Wu, C., Yan, Q., Cheng, N., Zhang, Q.W., Wang, H.Y., 2021. Origins of the meta-mafic rocks in the southern Dunhuang Block (NW China): Implication for tectonic framework of the southernmost Central Asian Orogenic Belt. Geol. J. 56 (8), 3959-3973.

Si, Y., Ge, R., Zhou, T., Wang, Y., 2022. Decoupling of metamorphic zircon U-Pb ages and PT paths in the Dunhuang metamorphic complex, northwestern China. Precambrian Res. 379, 106783.

Sobel, E.R., Arnaud, N., 1999. A possible middle Paleozoic suture in the Altyn Tagh, NW China. Tectonics 18, 64-74.

Soldner, J., Yuan, C., Schulmann, K., Jiang, Y.D., Stípská, P., Zhang, Y.Y., Huang, Z.Y., Wang, X.Y., 2022. Early Paleozoic Cascadia-type active margin evolution of the Dunhuang block (NW China): geochemical and geochronological constraints. Bulletin 134, 2503-2530.

Soldner, J., Stípská, P., Schulmann, K., Yuan, C., Anczkiewicz, R., Jiang, Y., Koziarska, M., Zhang, L., Zhang, Y., Wang, X., 2023. P-T-t-D records of Early Palaeozoic Andean-type shortening of a hot active margin: The Dunhuang block in NW China. J. Metamorph. Geol. 1-38.

Soldner, J., Jiang, Y., Stípská, P., Schulmann, K., Yuan, C., Huang, Z., Zhang, Y., 2024. Devonian Andean-type convergence in the southern Dunhuang block (NW China): Petro-structural, metamorphic P-T and geochronological constraints. J. Metamorph. Geol. 1-38.

Song, S., Bi, H., Qi, S., Yang, L., Allen, M.B., Niu, Y., Su, L., Li, W., 2018. HP-UHP metamorphic belt in the East Kunlun Orogen: final closure of the Proto-Tethys Ocean and formation of the Pan-East-China Continent. J. Petrol. 59 (11), 2043-2060.

Tian, Z., Xiao, W., 2020. An Andean-type arc transferred into a Japanese-type arc at final closure stage of the Paleo-Asian Ocean in the southernmost of Altaids. Geol. J. 55 (3), 2023-2043.

Vervoort, J.D., Patchett, P.J., 1996. Behavior of hafrnium and neodymium isotopes in the crust: constraints from Precambrian crustally derived granites. Geochim. Acta 60 (19), 3717-3733.

von Raumer, J.F., Stampfli, G.M., Arenas, R., Sánchez Martínez, S., 2015. Ediacaran to Cambrian oceanic rocks of the Gondwana margin and their tectonic interpretation. Int. J. Earth Sci. 104, 1107-1121.

Wakabayashi, J., 2015. Anatomy of a subduction complex: Architecture of the Franciscan complex, California, at multiple length and time scales. Int. Geol. Rev. 57 (5-8), 669-746.

Wang, Y., Zhang, X., Wang, E., Zhang, J., Li, Q., Sun, G., 2005. 40Ar/39Ar thermochronological evidence for formation and Mesozoic evolution of the northern-central segment of the Altyn Tagh fault system in the northern Tibetan Plateau. Geol. Soc. Am. Bull. 117 (9-10), 1336-1346.

Wang, Z., Han, C., Su, B., Sakyi, P.A., Malaviarachchi, S.P.K., Ao, S., Wang, L., 2013. The metasedimentary rocks from the eastern margin of the Tarim Craton: petrology, geochemistry, zircon U-Pb dating, Hf isotopes and tectonic implications. Lithos 179, 120-136.

Wang, Z.M., Han, C.M., Xiao, W.J., Wang, B., Sakyi, P.A., Ao, S.J., Zhang, J.E., Song, D. F., 2014. Petrology and geochronology of Paleoproterozoic garnet-bearing amphibolites from the Dunhuang Block, Eastern Tarim Craton. Precambrian Res. 255, 163-180.

Wang, N., Wu, C.L., Ma, C.Q., Lei, M., Guo, W.F., Zhang, X., Chen, H.J., 2016a. Geochemical zircon U-Pb geochronology and Hf isotopic characteristics for Granite in southern Dunhuang block. Acta Petrol. Sin. 32, 3753-3780 (in Chinese with English abstract).

Wang, N., Wu, C.L., Ma, C.Q., Lei, M., Guo, W.F., Zhang, X., Chen, H.J., 2016b. Geochemistry, zircon U-Pb geochronology and Hf isotopic characteristics for granites in Sanweishan section, Dunhuang block. Acta Geol. Sin. 90, 2681-2705 (in Chinese with English abstract).

Wang, H.Y.C., Chen, H.X., Lu, J.S., Wang, G.D., Peng, T., Zhang, H.C.G., Yan, Q.R., Hou, Q.L., Zhang, Q., Wu, C.M., 2016c. Metamorphic evolution and SIMS U-Pb geochronology of the Qingshigou section, Dunhuang block, NW China: Tectonic implications of the southernmost Central Asian Orogenic Belt. Lithosphere 8, 463-479.

Wang, H.Y.C., Chen, H.X., Zhang, Q.W.L., Shi, M.Y., Yan, Q.R., Hou, Q.L., Zhang, Q., Kusky, T., Wu, C.M., 2017a. Tectonic mélange records the Silurian Devonian subduction-metamorphic process of the southern Dunhuang terrane, southernmost Central Asian Orogenic Belt. Geology 45, 427-439.

Wang, H.Y.C., Wang, J., Wang, G.D., Lu, J.S., Chen, H.X., Peng, T., Zhang, H.C.G., Zhang, Q.W.L., Xiao, W.J., Hou, Q.L., Yan, Q.R., Zhang, Q., Wu, C.M., 2017b. Metamorphic evolution and geochronology of the Dunhuang orogenic belt in the Hengliuxia section, northwestern China. J. Asian Earth Sci. 135, 51-69.

Wang, Z.M., Han, C.M., Xiao, W.J., Su, B.X., Ding, J.X., 2017c. Paleoproterozoic subduction-related magmatism and crustal evolution of the Dunhuang Block, NW China. J. Asian Earth Sci. 134, 13-28.

Wang, H.Y.C., Zhang, Q.W.L., Lu, J.S., Chen, H.X., Liu, J.H., Zhang, H.C.G., Pham, V.T., Peng, T., Wu, C.M., 2018a. Metamorphic evolution and geochronology of the tectonic mélange of the Dongbatu and Mogutai blocks, middle Dunhuang orogenic belt, northwestern China. Geosphere 14 (2), 883-906.

Wang, H.Y.C., Zhang, Q.W.L., Chen, H.X., Liu, J.H., Zhang, H.C.G., Pham, V.T., Peng, T., Wu, C.M., 2018b. Paleozoic subduction of the southern Dunhuang Orogenic Belt, Northwest China: metamorphism and geochronology of the Shuixiakou section. Geodin. Acta 30, 63-83.

Wang, Z.M., Han, C.M., Xiao, W.J., Sakyi, P.A., 2018c. Paleozoic subduction-related magmatism in the Duobagou section, Dunhuang block: Constrained by zircon U-Pb geochronology and Lu-Hf isotopes and whole-rock geochemistry of metaigneous rocks. Lithosphere 9, 1012-1032.

Wang, Z., Zhang, Y., Yu, X., Guo, Z., 2021a. Duobagou Permian-Triassic granites from the Dunhuang orogenic belt, NW China: implications for the tectonic evolution of the southernmost Central Asian Orogenic Belt. Geol. Mag. 158 (4), 656-672.

Wang, T., Diwu, C., Yan, J., Gan, B., 2021b. Reworked early Precambrian basement of the Dunhuang Block (NW China) as revealed by titanite U-Pb dating. Lithos 384, 105963.

Wang, H., Xiao, W., Windley, B.F., Zhang, Q.W.L., Tan, Z., Wu, C., Shi, M., 2022. Diverse P-T-t paths reveal high-grade metamorphosed forearc complexes in NW China. J. Geophys. Res. Solid Earth 127 e2022JB024309.

Wang, H., Xiao, W., Li, R., Chen, H., Tan, Z., Mao, Q., Shi, M., 2023. High-grade complexes record the Late Permian-Middle Triassic arc metamorphism in the southernmost Altaids: Implications for the final closure of the Paleo-Asian Ocean. Lithos 442, 107054.

Whitney, D.L., Evans, B.W., 2010. Abbreviations for names of rock-forming minerals. Am. Mineral. 95, 185-187.

Wilde, S.A., Zhou, J.B., 2015. The late Paleozoic to Mesozoic evolution of the eastern margin of the Central Asian Orogenic Belt in China. J. Asian Earth Sci. 113, 909-921.

Wilhem, C., Windley, B.F., Stampfli, G.M., 2012. The Altaids of Central Asia: a tectonic and evolutionary innovative review. Earth Sci. Rev. 113 (3-4), 303-341.

Wolfram, L.C., Weinberg, R.F., Nebel, O., Hamza, K., Hasalová, P., Miková, J., Becchio, R., 2019. A 60-Myr record of continental back-arc differentiation through cyclic melting. Nat. Geosci. 12 (3), 215-219.

Xiao, W., Windley, B.F., Yong, Y., Yan, Z., Yuan, C., Liu, C., Li, J., 2009. Early Paleozoic to Devonian multiple-accretionary model for the Qilian Shan, NW China. J. Asian Earth Sci. 35 (3-4), 323-333.

Xiao, W.J., Mao, Q.G., Windley, B.F., Han, C.M., Qu, J.F., Zhang, J.E., Ao, S.J., Guo, Q.Q., Cleven, N.R., Lin, S.F., Shan, Y.H., Li, J.L., 2010. Paleozoic multiple accretionary and collisional processes of the Beishan orogenic collage. Am. J. Sci. 310 (10), 1553-1594.

Xiao, W., Windley, B.F., Sun, S., Li, J., Huang, B., Han, C., Yuan, C., Sun, M., Chen, H., 2015. A tale of amalgamation of three Permo-Triassic collagen systems in Central Asia: Oroclines, sutures, and terminal accretion. Annu. Rev. Earth Planet. Sci. 43, 477-507.

Xiao, W., Windley, B.F., Han, C., Liu, W., Wan, B., Zhang, J.E., Ao, S., Zhang, Z., Song, D., 2018. Late Paleozoic to early Triassic multiple roll-back and oroclastic bending of the Mongolia collage in Central Asia. Earth Sci. Rev. 186, 94-128.

Xin, H.T., Liu, Y.S., Luo, Z.H., Song, S.C., Wang, S.Q., 2013. The growth of Archean continental crust in Aqtashtagh section of Southeast Tarim, China: constraints from petrology and chronology about Milan Group and TTG-gneiss. Earth Sci. Front. 20, 240-259 (in Chinese).

Yu, H.F., Mei, H.L., Li, Q., 1998. The Characteristics of Archean Khondalite Series in Dunhuang, Gansu Province. Prog. Precamb. Res. China 21, 19-25 (in Chinese with English abstract).

Yu, S., Peng, Y., Zhang, J., Li, S., Santosh, M., Li, Y., Liu, Y.G., Gao, X.Y., Ji, W.T., Lv, P., Li, C.Z., Jiang, X.Z., Qi, L.L., Xie, W.M., Xu, L., 2021. Tectono-thermal evolution of the Qilian orogenic system: Tracing the subduction, accretion and closure of the Proto-Tethys Ocean. Earth Sci. Rev. 215, 103547.

Zhang, Z.C., Guo, Z.J., Zou, G.Q., Feng, Z.S., Li, J.F., 2009. Geochemical characteristics and SHRIMP U-Pb age of zircons from the Danghe reservoir TTG in Dunhuang, Gansu Province, and its significations. Acta Petrol. Sin. 25, 495-505 (in Chinese).

Zhang, J.X., Gong, J.H., Yu, S.Y., 2012. 1.85Ga HP-Granulite facies metamorphism in the Dunhuang block of the Tarim Craton, NW China: evidence from U-Pb zircon dating of mafic granulites. J. Geol. Soc. Lond. 169, 511-514.

Zhang, J., Gong, J., Yu, S., Li, H., Hou, K., 2013. Neoarchean-Paleoproterozoic multiple tectonothermal events in the western Alxa block, North China Craton and their geological implication: evidence from zircon U-Pb ages and Hf isotopic composition. Precambrian Res. 235, 36-57.

Zhang, L., Chen, R.X., Zheng, Y.F., Hu, Z., Xu, L., 2017a. Whole-rock and zircon geochemical distinction between oceanic-and continental-type eclogites in the North Qaidam orogen, northern Tibet. Gondwana Res. 44, 67-88.

Zhang, J., Yu, S., Mattinson, C.G., 2017b. Early Paleozoic polyphase metamorphism in northern Tibet, China. Gondwana Res. 41, 267-289.

Zhang, Q.W.L., Wang, H.Y.C., Liu, J.H., Shi, Y.M., Chen, C.Y., Li, Z.M.G., Wu, C.M., 2020. Diverse subduction and exhumation of tectono-metamorphic slices in the Kalatashage section, western Paleozoic Dunhuang Orogenic Belt, northwestern China. Lithos 360-361, 10543.

Zhang, Q.W., Chen, Y.C., Shi, M.Y., Li, Z.M., Liu, J.H., Wu, C.M., 2022. Permian-Triassic magmatic and thermal events in the Dunhuang orogenic belt: implications for subduction records of the Paleo-Asian Ocean. Int. Geol. Rev. 64 (16), 2306-2329.

Zhang, L., Ren, Z.Y., Xia, X.P., Wang, C., Qian, S.P., 2018. An improved U-Pb age dating method for detrital zircon by LA-MC-ICP-MS. Geochem. J. 52 (5), 433-439.

Zhang, J., Tang, S., Wei, C., Xu, W., Chu, H., Jiang, L., 2023. Metamorphic evolution and zircon ages of a Barrovian metamorphic series in central-western Inner Mongolia, China: Insights into the tectonic evolution of the Central Asian Orogenic Belt. J. Asian Earth Sci. 250, 105649.

Zhao, Y., Diwu, C.R., Sun, Y., Zhu, T., Wang, H.L., 2013. Zircon geochronology and Lu-Hf isotope compositions for Precambrian rocks of the Dunhuang complex in Shuixiakou
section, Gansu Province. Acta Petrol. Sin. 29, 1698-1712 (in Chinese with English abstract).

Zhao, Y., Diwu, C.R., Ao, W.H., Wang, H.L., Zhu, T., Sun, Y., 2015a. Ca. 3.06 Ga granodioritic gneiss in Dunhuang block. Chin. Sci. Bull. 60, 75-87 (in Chinese).

Zhao, Y., Diwu, C.R., Zhu, T., Wang, H.L., Sun, Y., 2015b. Discovery of the late Devonian plagiogranite in the Sanweishan are Dunhuang Gansu Province and its geological implications. Acta Petrol. Sin. 31, 1855-1869.

Zhao, Y., Sun, Y., Diwu, C.R., Ao, W.H., Zhu, T., 2016. The Dunhuang block is a Paleozoic Orogenic Belt and part of the Central Asian Orogenic Belt (CAOB), NW China. Gondwana Res. 30, 207-223.

Zhao, Y., Sun, Y., Diwu, C.R., Zhu, T., Ao, W.H., Zhang, H., Yan, J.H., 2017. Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt. J. Asian Earth Sci. 138, 562-587.

Zhao, G., Wang, Y., Huang, B., Dong, Y., Li, S., Zhang, G., Yu, S., 2018. Geological reconstructions of the East Asian blocks: from the breakup of Rodinia to the assembly of Pangea. Earth Sci. Rev. 186, 262-286.

Zhao, Y., Ao, W.H., Yan, J.H., Zhai, M.G., Zhang, H., Wang, Q., Sun, Y., 2019a. Paleozoic tectonothermal event in Mt. Dongbatu, Dunhuang terrane, southernmost Central Asian Orogenic Belt (CAOB): Implications for petrogenesis and geological evolution. Lithos 326, 491-512.

Zhao, Y., Ao, W., Zhang, H., Wang, Q., Zhai, M., Sun, Y., 2019b. Latest Paleoproterozoic (ca. 1.8-1.6 Ga) extensional tectonic setting in the Dunhuang terrane, NW China: evidence from geochronological and geochemical investigations on A-type granite and metamafic rock. Lithosphere 11 (6), 834-854.

Zhao, Y., Sun, Y., Ao, W., Zhang, H., Zhu, T., 2019c. Depositional age, provenance and tectonic significance of Precambrian metasedimentary rocks from the Dunhuang Complex, NW China: Evidence from field investigation, zircon U-Pb geochronology and whole-rock geochemistry. Precambrian Res. 326, 272-294.

Zhao, Y., Ao, W., Zhang, H., Wang, Q., 2020. Possible imprints of late Paleoproterozoic orogeny in the Dunhuang terrane, NW China: Constraints from igneous and metapelitic rocks. Precambrian Res. 350.

Zhao, Y., Ao, W., Zhu, T., Hu, Y., Tian, Z., Zhang, R., Zhao, J., 2022. Paleoproterozoic (ca. 2.1-1.9 Ga) dioritic-granitic magmatism in the Dunhuang Terrane, Northwestern China: Implications for petrogenesis and tectonic evolution. Lithos 432, 106915.

Zheng, R., Li, J., Zhang, J., Xiao, W., 2021. A prolonged subduction-accretion in the southern Central Asian Orogenic Belt: Insights from anatomy and tectonic affinity for the Beishan complex. Gondwana Res. 95, 88-112.

Zhou, J.B., Wilde, S.A., Zhao, G.C., Zhang, X.Z., Wang, H., Zeng, W.S., 2010. Was the easternmost segment of the Central Asian Orogenic Belt derived from Gondwana or Siberia: an intriguing dilemma? J. Geodyn. 50 (3-4), 300-317.

Zhu, T., Wang, H.L., Xu, X.Y., Chen, J.L., Ma, Z.P., Li, Z.P., Zhu, X.H., Li, P., 2014. Discovery of adakitic rocks in south margin of Dunhuang block and its geological significance. Acta Petrol. Sin. 30 (2), 491-502 (in Chinese with English abstract).

Zhu, T., Wang, H.L., Zhao, Y., Xu, X., Li, Z.P., 2020. Paleozoic diorites form the south-western Dunhuang terrane, MW China: Constraints on the tectonic evolution of southernmost CAOB. Geol. J. 1-19.

Zonenshain, L.P., 1973. The evolution of central Asiatic geosynclines through sea-floor spreading. Tectonophysics 19 (3), 213-232.

Zong, K.Q., Zhang, Z.M., He, Z.Y., Hu, Z.C., Santosh, M., Liu, Y.S., Wang, W., 2012. Early Paleozoic high-pressure granulites from the Dunhuang block, northeastern Tarim Craton: constraints on continental collision in the Central Asian Orogenic Belt. J. Metamorph. Geol. 30, 753-768.

Zong, K.Q., Liu, Y., Zhang, Z., He, Z., Hu, Z., Guo, J., Chen, K., 2013. The generation and evolution of Archean continental crust in the Dunhuang block, northwestern China. Precambrian Res. 235, 251-263.

Zuza, A.V., Yin, A., 2017. Balkatach hypothesis: a new model for the evolution of the Pacific, Tethyan, and Paleo-Asian oceanic domains. Geosphere 13, 1664-1712.