Early Devonian Slab Melting of the Proto-Tethys Ocean: Insights from Adakitic Granitoids in the Jiayuguan Area, Hexi Corridor (NW China)

The Asian continent was formed by the amalgamation of cratons and the evolution of the Paleo-Asian Ocean and the Tethys Ocean. The Qilian orogen is the northernmost orogenic collage of the Tethyan domain and adjacent to the Central Asian orogenic belt (or Altaids) (Figure 1(a)). The North Qilian orogen is a well-known early Paleozoic to Devonian multiple accretionary orogen [1] and records the evolution and interactions of the Paleo-Asian and Tethys Oceans. Therefore, the North Qilian orogen is key to understanding the evolution of the Asian continent in the early Paleozoic [1-3]. Clarifying the tectonic evolutionary history of the North Qilian orogen will shed light on the tectonics of the Proto-Tethys Ocean and the growth of the Asian continent.

Although the tectonic evolution of the North Qilian orogen has been widely studied and well constrained by the subduction tectonics of the early Paleozoic [2, 4-6], the tectonic settings of the North Qilian in the Devonian (<ca. 440 Ma) have been hotly debated as either post-collisional or subduction settings. The Silurian (<ca. 440 Ma) granitoids have also been suggested to have formed in an arc setting [7, 8], syncollisional setting [9-11], or post-collision setting [12-15]. These uncertainties hamper a better understanding of the tectonic evolution of the Qilian orogen and Proto-Tethyan Ocean.

Adakitic rocks are special intermediate to felsic magmatic rocks that are considered an important parameter for oceanic subduction [16-19], partial melting of the thickened arc and continental crust [18, 20-22], and the assimilation-fractional crystallization (AFC) of the magma [23, 24]. Adakitic rocks extensively emplaced in North Qilian orogen during Cambrian to Devonian [8, 9, 25] is the key parameter to constrain the tectonics of the Qilian orogen. In this study, we report newly discovered Early Devonian adakitic granitoids at Jiayuguan area in the North Qilian orogen, western part of Hexi Corridor, NW China. We present systematic petrology, geochronology, and geochemistry data for these adakitic rocks, which can constrain the evolution of the North Qilian orogen in the Early Devonian.

The Qilian orogen is a WNW-trending tectonic belt separated from the Altaids to the north by the Alxa and North China Craton, from the Tarim Craton to the west by the Altyn Tagh fault and linked to the Qinling orogenic belt to the east (Figure 1(a)). From south to north, the Qilian orogen is generally subdivided into the South Qilian Accretionary Belt, Central Qilian block, and North Qilian Accretionary Belt, based on rock assemblages and WNW-trending thrust faults [1, 2] (Figure 1(b)).

The South Qilian Accretionary Belt is characterized by Neoproterozoic basement to the south, Cambrian to Ordovician Ophiolites and Ordovician oceanic arc to the north [5, 26-30]. They are unconformably covered by the latest Ordovician to early Silurian sedimentary rocks [31, 32]. The Central Qilian block is mainly composed of greenschist- to amphibolite-facies metamorphic rocks and some Paleozoic to Mesozoic sedimentary covered strata [33-37], and Ordovician to Silurian arc-related (I- and S-type) granitic intrusions [9, 33, 38]. The metamorphic sedimentary rocks have maximum depositional ages ranging from late Mesoproterozoic to middle Neoproterozoic [35, 39].

The North Qilian Accretionary Belt consists of Cambrian to Devonian ophiolites, high-pressure/low-temperature metamorphic rocks, arc-related volcanic rocks, turbidites, and minor Carboniferous to Triassic sedimentary rocks [1, 2, 40, 41]. It is subdivided into three subparallel NW-SE-trending tectonic belts, including southern and northern ophiolite belts, and an intra-oceanic arc belt in the middle (Figure 1(b)) [1, 2]. The southern ophiolite belt consists of a Cambrian–Silurian turbidite matrix with ophiolitic blocks and some blueschist and eclogite fragments [1, 2]. The gabbroic blocks have zircon U–Pb ages of ca. 550–490 Ma [2, 42, 43]. The eclogite- and blueschist-facies blocks yield metamorphic ages of ca. 489–463 Ma (zircon U–Pb) [44, 45], whereas glaucophane and phengite ⁴⁰Ar/³⁹Ar ages of ca. 460–410 Ma [46]. The mafic rocks (gabbro and basalt) of the ophiolites and eclogites have N-MORB, E-MORB, and ocean island basalt (OIB) geochemical signatures [2, 47-50]. The arc belt in the middle is composed of ca. 516–446 Ma intermediate-felsic arc-related volcanic rocks, ca. 505–487 Ma boninite and granitoids and pyroclastic rocks and sandstones [2, 9, 41, 51-54]. The northern ophiolitic belt extends from the western Jiugequan to the eastern Laohushan ophiolite and consists of ultramafic rock, gabbro, basalt, chert, and lawsonite-blueschist fragments in the Cambrian–Devonian matrix [2]. The oceanic crustal fragments have magmatic zircon U–Pb ages ranging from 490 Ma to 450 Ma [2, 42, 49, 55-57]. The Jiugequan lawsonite-blueschists yield glaucophane and muscovite ⁴⁰Ar/³⁹Ar ages of 415–413 Ma [58] and the Laohushan blueschists yield phengite and glaucophane ⁴⁰Ar/³⁹Ar plateau age of 455 ± 0.6 Ma and 432–425 Ma [59]. Basalts and gabbros of the ophiolites display N-MOR and SSZ-type ophiolite geochemical characteristics [1, 2, 41, 49, 51, 55]. In addition, early Paleozoic granitoids are widely exposed in the North Qilian ophiolite belt [2, 7, 10, 14, 60, 61].

The Alxa block is the westernmost part of the North China Craton [62] and consists of Archean to Phanerozoic metamorphic basement rocks, Paleozoic sedimentary covers, and ultramafic–mafic–granitic intrusions. The Proterozoic tonalitic/granitic gneisses, amphibolites, and metasedimentary rocks have zircon U–Pb ages of ca. 2.7–1.9 Ga [63-66]. The famous Jinchuan ultramafic intrusion (ca. 827 Ma) in the southern Alxa block [65, 67] was interpreted to have formed by a superplume during ca. 830–750 Ma [68]. The Late Ordovician–early Permian granitoids (458–239 Ma) and associated sedimentary rocks are extensively displaced in the Alxa block [69-73].

The granitic samples were collected from three plutons in the Jiayuguan complex of the northern ophiolite belt in North Qilian Accretionary Belt (Figure 1(c)). As shown in Figure 1(b), the Jiayuguan complex is located westward to Jiayuguan city at the western part of Hexi Corridor, NW China. It is mainly composed of ultramafic, gabbro, basalt, chert, pyroclastic rock, sandstone slices (Figure 1(c)), and minor basic to granitic intrusive rocks that unconformably underlie the Carboniferous and Jurassic–Cretaceous siliciclastic rocks. Ophiolitic slices occur in the northern Jiayuguan complex and contain ultramafic rocks, gabbro, massive basalt, pillow basalt, cherts, and basaltic pyroclastic rocks [74]. The three granites intruded into the flysches of the southern Jiayuguan complex (Figures 1(b) and 1(c)). The 21JYG 26 biotite granite pluton mainly consists of plagioclase (~55%), quartz (~30%), biotite (~5%), and accessory minerals, including apatite, sphene, and zircon (online supplementary Figure S1(a-b)). The 21JYG 27 biotite granite pluton is composed of plagioclase (~50%), quartz (~35%), biotite (~8%), and minor hornblende, apatite, sphene, and zircon (online supplementary Figure S1(c-d)). The 21JYG 28 biotite granite pluton is composed of plagioclase (~50%), quartz (~30%), biotite (~7%), hornblende, and minor apatite and zircon (online supplementary Figure S1(e-f)). The fresh rocks of the three granitic plutons are collected for zircon U–Pb dating and in situ Lu–Hf isotopic analyses, whole-rock geochemical, and Sr–Nd isotopic analyses.

Zircon U–Pb analyses were performed at the Beijing Quick-Thermo Science & Technology Co., Ltd. In situ Lu–Hf isotope was measured using a Thermo Finnigan Neptune-plus MC–ICP–MS fitted with a J-100 femto-second laser ablation system Applied Spectra Inc. at the National Research Center for Geoanalysis, Chinese Academy of Geological Sciences (CAGS), Beijing, China. Major and trace element analyses were conducted by Leeman Prodigy inductively coupled plasma–optical emission spectrometer (ICP-OES) and Agilent-7500a quadrupole inductively coupled plasma–mass spectrometer (ICP-MS) at the Institute of Earth Sciences, China University of Geosciences, Beijing (CUGB), respectively. Whole-rock Sr–Nd isotopic analyses were carried out at National Research Center for Geoanalysis, CAGS, Beijing, China. Detailed information on sample preparation and analytical procedures is available in the Supplementary data Analytical methods.

The zircon U–Pb isotopic dating data of the granites are listed in Table 1. The zircon grains are euhedral prismatic crystal forms with lengths of ca. 100–200 μm. They have clear magmatic oscillatory zones (Figure 2) and high Th/U values (0.28, 0.87). The zircons of the three samples commonly feature significant enrichments in HREEs and Ce but depletions in Eu (Figures 2(b), 2(d), and 2(e)).

For sample 21JYG26, all fifteen analyzed grains are concordant and have ²⁰⁶Pb/²³⁸U ages from 411 to 423 Ma with a weighted age of 402.5 ± 2.9 Ma (MSWD = 1.5; Figure 2(a)). All analyses of sample 21JYG27 yield concordant ages with weighted ages of 413.2 ± 3.9 Ma (MSWD = 2.1, n = 15) (Figure 2(c)). As shown in Figure 2(e), fifteen analyses of sample 21JYG28 yield ²⁰⁶Pb/²³⁸U ages from 402 to 425 Ma with a weighted age of 414.6 ± 4.3 Ma (MSWD = 1.7, n = 15) (Figure 2(e)).

The geochemical and isotopic data of the three intrusions are given in Tables 2-4. The samples are classified as low- and medium-K calc-alkaline magma in a SiO₂-K₂O diagram (Figure 3(b)) with A/NK and A/CNK ratios varying from 1.36 to 1.75 and 0.98 to 1.13 (Figure 3(c)), respectively. They have narrow high contents of SiO₂ (68.01, 70.29 wt%), Al₂O₃ (14.86, 16.98 wt%), Na₂O (4.93, 6.13 wt%, Na₂O/K₂O (4.20, 5.51)>1, Figure 3(d)), and MgO (1.02, 1.87 wt%) and Mg# ratios of 62 to 68. All the samples are characterized by relatively high contents of Sr (583, 904 ppm > 400 ppm), low HREE (e.g. Yb = 0.22–0.70 ppm and Y = 2.80–7.15 ppm), and high ratios of Sr/Y (82–277). The samples also have relatively high Cr (10, 50 ppm), Ni (4.9, 31.02 ppm), and Co (3.6, 8.33 ppm) contents and high Cr/Ni (1.03, 2.08) values. These samples exhibit highly depleted in HREEs [(La/Yb)_N = 7.65–15.16] and negative to positive Eu anomalies (δEu＝0.66–1.83). In the primitive mantle-normalized multi-element diagram [75], they are relatively enriched in Rb, U, Th, K, Ba, Pb, and Sr but depleted in Nb, Ta, and Ti (Figure 4).

The rocks display similar depleted Hf isotopic signatures, as shown in Figure 5(a), including sample 21JYG26 has positive ε_Hf(t) values of +7.9 to +9.9 and TDM ages ranging from 626 Ma to 707 Ma; sample 21JYG27 has ε_Hf(t) values of +6.5 to +11.4 and T_DM ages of 577–772 Ma; and sample 21JYG28 has ε_Hf(t) values of +8.0 to +11.9 and young T_DM ages (564, 719 Ma). However, these granites have relatively high (⁸⁷Sr/⁸⁶Sr)_i values (0.705907, 0.707583), relatively low ε_Nd(t) values of −2.3 to +0.13 (Figure 5(b)). and old T_DM (Ma) ages ranging from 1239 Ma to 1439 Ma.

Adakites are special andesitic to rhyolitic magmatic rocks that are enriched in SiO₂ (≥56%), Na, Al, and Sr but depleted in Y and HREEs (e.g. Yb ≤ 1.9 ppm) and have high Sr/Y (>40) and (La/Yb)_N ratios and MORB-like Sr-Nd isotope signatures [16]. Initially, adakitic rock was suggested to be the product of partial melts of a hot or young subducted oceanic slab under eclogitic-facies or garnet-bearing amphibolite-facies conditions [16, 76, 77]. However, later studies proposed that they can be formed by partial melting of the lower mafic crust of the thickened crust area [18, 20-22] and the AFC of the magma [23, 24]. Tens of 501–403 Ma adakitic granitoids have been reported in the North Qilian orogen in recent decades years (Figure 1(b)), but their origin and tectonic setting are debated and have been proposed as (1) melting of the subduction oceanic slab, e.g. the Kokoli (501 Ma) and Aoyougou plutons (438 Ma) [8, 60]; (2) partial melting of the thickened crust in a collisional setting during ca. 457–441 Ma [10, 12, 13, 15, 25]; and (3) partial melting of the delaminated lower crust in the post-collisional extension setting during ca. 438–424 Ma [9, 11, 12, 15].

The Jiayuguan granitic plutons display the typical geochemical signatures of adakitic rocks (Figures 6(a) and 6(b)), such as SiO₂ [68.01, 70.29 wt.% > 56 wt.%), Al₂O₃ (14.86, 16.98 wt.%), Na₂O/K₂O (4.20, 5.51) > 1], MgO (Mg# = 62–68), high Sr (584, 904 ppm > 400 ppm), very low HREE (e.g. Yb = 0.22–0.70 ppm) and Y (2.80, 7.15 ppm), and high ratios of Sr/Y (82–277) [16, 76]. The three granitic plutons have high SiO₂ contents (68.01, 70.29 wt.%) and can be classified as high-SiO₂ adakites (Figures 6(c) and 6(d)). The Jiayuguan adakitic granitoids are characterized by consistently strong depletions in HREE [(La/Yb)_N = 7.65–15.16)] and Y (2.80, 7.15 ppm) and positive Sr anomalies, suggesting that garnet was a residual mineral in the partial melting processes [77, 78]. Their high Al₂O₃ and Na₂O contents (Na₂O/K₂O > 1) suggest that they are not derived from thickened lower crust-derived magma, which has high K and (Na₂O + K₂O) and low Al₂O₃ contents [18, 22, 78]. Moreover, their high Mg# values (62–68) are quite different to the lower crust derived adakitic rocks (Mg# < 40) [20], indicating that they are derived from the partial melting of oceanic slab (Figure 7(a)) [17]. In the Rb/Sr versus Rb/Ba diagram (Figure 7(b)), the samples plot closely to the basalt, suggesting that they are sourced from the partial melting of the mafic rocks of the subducted oceanic slab. In addition, these adakitic intrusions have relatively high Cr, Ni, Co, and V contents and high Cr/Ni (1.03, 2.08), indicating that they have been modified by the mantle wedge, as shown in Figure 7(c) [6, 16, 79, 80]. The Nb/La versus Nb/Th diagram indicates that the magma may have been contaminated by the arc crust in the emplacement processes (Figure 7(d)).

In general, the Cenozoic slab-derived adakites display depleted isotopic signature liking N-MORB [16, 76]. The Jiayuguan adakitic granitoids have highly positive zircon ε_Hf(t) values (+6.5 to +11.9) (Figure 5), which is consistent with the most Ordovician-Silurian (476, 424 Ma) adakitic granitoids (Figure 1(b)) in the northern Qilian orogen, but lower than the depleted mantle. At the same time, these plutons have relatively low ε_Nd(t) values of +0.13 to −2.3, similar to most Cambrian to Early Devonian adakitic rocks in northern Qilian [8-12, 15], and lower than the ophiolites with ε_Nd(t) values of +2.7 to +8.9 [42, 81], implying the contaminations of continental arc crust. These incompatible Hf and Nd isotopes are similar to those of most adakitic granitoids in the North Qilian orogen [8-12, 15], suggesting that they have similar origins. The incompatible Hf and Nd isotopes could be caused by the mixture or contamination between the mantle source magma and continental arc crust in the emplacement processes. This means that these rocks originated from an arc with continental crust, such as an Andean-type arc or Japanese-type arc [82-84]. In summary, these plutons were sourced from the partial melting of the northern Qilian oceanic slab, similar to Cenozoic slab-derived adakites, but they were contaminated by the continental arc crust in their emplacement processes.

The euhedral crystal form, internal structures, and uniform composition of zircon grains suggest that they are typical of magmatic zircons [85] (Figure 2). According to our calculations, the three granitoids have ages of 402.5 ± 2.9 Ma, 413.2 ± 3.9 Ma, and 414.6 ± 4.3 Ma, respectively, suggesting that the magmatism was emplaced during the Early Devonian (415, 403 Ma). To date, two competing tectonic evolutionary models of the Early Devonian have been proposed for the North Qilian orogen: (1) subduction lasted until the Early Devonian [7, 56] and even to the Late Devonian [1, 70, 73] and (2) the North Qilian Ocean closed prior to ca. 440 Ma, and the North Qilian orogen entered the post-collisional setting from the latest early Silurian to Devonian [2, 9, 37, 86, 87]. Therefore, there are similar disputes about the occurrence of the tectonic setting of the adakitic rocks of the North Qilian orogen, including the subduction setting from 501 Ma to 438 Ma [8, 60]; collisional setting during ~457–441 Ma [10, 12, 13, 15], whereas post-collisional extension setting during ca. 438–424 Ma [9, 11, 12, 14, 15, 87].

This study reveals that the three granitoids are typical low- to medium-K calc-alkaline magmas (Figures 3(a) and 3(b)) and peraluminous granites (Figure 3(c)). They are high-Si adakitic magmas with high SiO₂ contents of 68.01–70.29 wt. %, Na₂O/K₂O ratios (4.20, 5.51) >1 (Figure 3(d)) and Mg# values (62–68). They are typical subduction-related magmatic rocks that are enriched in LREEs, Rb, Sr, Ba, K, Th, U, and Pb and remarkably depleted in Nb, Ta, and Ti [75, 88] (Figure 6). In the discrimination diagrams for granite, the samples also plot in the volcanic arc granite field [89] (Figure 8). All these data suggest that they are subduction-related magmas.

According to existing research data (online supplementary Figure S2 and online supplementary Table S2), the granites and coeval volcanic rocks of the North Qilian orogen have ages of 523–383 Ma and 503–413 Ma [2, 9, 12, 55, 90], respectively. The magmatic activity culminated in the ca. 400–450 Ma; then, magmatic activity decreased from 400 Ma to 380 Ma. Previous geochemical studies have suggested that they have arc-related geochemical signatures [7, 9, 10, 12, 14, 32, 61] (online supplementary Figure S2). Thus, our new study data, together with the spatiotemporal distribution and geochemical data of the granitoids in the North Qilian, indicate that southward subduction lasted until the Early Devonian. This agrees with the arc-related granites that developed from 458 Ma to 390 Ma in the southern Alxa block [70, 73, 90, 91]. These spatiotemporal distributions of the granitoids also agree with our conclusion that subduction in the North Qilian lasted until the Early Devonian.

The North Qilian orogen is a typical accretionary complex with a “matrix-in-blocks” structure. It mainly consists of ophiolite, arc, limestone, blueschist, and eclogite blocks within the sedimentary rock matrix [1, 2, 56, 92]. Although the N-MORB, E-MORB, OIB, and arc-related (SSZ)-type oceanic fragments have ages of ca. 550–450 Ma [42, 56], and the cherts contain abundant Middle Ordovician radiolarians together with rare conodonts [92]. However, the metamorphic ages suggest that the subduction-related eclogites and blueschists uplift and cooled last until the Early Devonian, revealing that the strong subduction-related tectonics, including the following: (1) The eclogites and basic blueschist lenses in the south ophiolite belt have two metamorphic age groups of 489–463 Ma and 424–404 Ma [44, 45, 50, 93]. (2) The glaucophane and phengite from blueschist-facies rocks of the northern ophiolite belt yield ⁴⁰Ar/³⁹Ar ages of ca. 460–410 Ma [46]. (3) The glaucophane and muscovite of the Jiugequan lawsonite-bearing blueschists yield ⁴⁰Ar/³⁹Ar ages of ca. 413–415 Ma [58]. (4) Glaucophane and phengite from the blueschist belt have ⁴⁰Ar/³⁹Ar ages of 400–380 Ma [94].

In summary, together with the ages of ophiolite fragments, metamorphism ages, arc-related intrusions, and our data suggest that the Devonian Jiayuguan adakitic granitoids formed in a subduction setting rather than post-collisional setting.

Several possible tectonic models can be used to interpret slab-melted rocks, including slab break-off, young slab subduction, and ridge subduction. Ridge subduction is an essential mechanism for generating adakites and related magma (e.g. high-Mg andesite, Nb-enriched basalt) and high-temperature metamorphism in the forearc [95-97]. As discussed above, the Jiayuguan adakitic rocks have low K₂O, high Mg# values, high Cr, Ni, Co, and V contents, and high Cr/Ni (1.03, 2.08) and zircon ε_Hf (t) values, indicating they are derived from melts of the young/hot oceanic slab, similar to Cenozoic slab-derived adakites that were formed by the ridge subduction, or young oceanic slab [16, 76, 77]. Considering that these slab melting derived adakitic rocks intruded in the Jiayuguan mélange in the forearc, we proposed that one of the possible tectonic mechanisms is the ridge subduction that formed the Jiayuguan adakitic granitoids in the forearc the accretionary complex liking in Chile ridge subduction area [98, 99]. Integrating with the magmatic activity of the North Qilian orogen and Alxa block was quickly weakening and dying down during the Early Devonian [1, 9, 90](online supplementary Figure S2) and some previous tectonic studies suggest that the North Qilian Ocean close during Early to Middle Devonian [1, 56], we furtherly infer that the ridge subduction occurred during the closed time of the North Qilian Ocean.

Single- and double-side subduction models have been proposed for the North Qilian Ocean; the single model suggests that the Alxa block is a passive continental margin [1, 2, 100], whereas some recent studies suggest a complicated double subduction system that formed the Qilian Japan-type arc and the Alxa continental arc [56]. Therefore, we propose a possible tectonic model for these adakitic granites (Figure 9). These adakitic rocks formed in the accretionary complex of the Alxa continental arc. Previous studies have documented several coeval adakitic granitoids (ca. 417–397 Ma) east of the Jiayuguan adakitic granitoids along the southern margin of the Alxa block [70, 73]. These adakitic granitoids have high K and Si contents, low Mg# values (29-54), and low negative whole-rock ε_Nd(t) (−3.2, −8.9) and zircon ε_Hf(t) (+1.6 to −10.5) values that are different from those of the Jiayuguan adakitic granitoids [70, 73] (Figures 3(d), 5, and 7); therefore, they were proposed to originate from partial melting of the lower mafic crust of the thickened continental arc [70, 73]. The different geochemistry and origins of these adakitic rocks in the southern Alxa block suggest that subduction switched from west to east. Compared with modern subduction zones, we find that this scenario is similar to the Andean subduction zone in southern America, where thickened arc crust-derived adakitic rocks are found in Peru [18], whereas oceanic slab-derived adakites were formed by the subduction of the Chile ridge in the south [98, 99]. Therefore, we suggest that oceanic ridge subduction formed the Jiayuguan adakitic rocks in the Jiayuguan accretionary complex, whereas flat subduction caused the crust of the Alxa continental arc to thicken and melt to form K-enriched adakitic rocks (Figure 9). This interpretation is supported by the typical north-trending subduction kinematic indicators of the accretionary complex in the northern ophiolite belt [56] and the sedimentary characteristics of Alxa [71]. At the same time, southward ridge subduction/young/hot subduction formed Na-rich slab melting-derived adakitic granites in the Nanhuashan Luanduizi area in the eastern parts of the North Qilian Andean-type arc [101] (Figures 1 and 9).

The three adakitic granites intruded into the Jiayuguan accretionary complex during the Early Devonian with zircon U‒Pb ages of 403 ± 3 Ma, 413 ± 4 Ma, and 415 ± 4 Ma.

The three granites are typical subduction-related adakitic rocks with high Sr contents (583, 904 ppm) and significant depletions in HREE and Y geochemical signatures. Their high positive zircon ε_Hf(t) values (+6.5 ‒ +11.9) and ε_Nd (t) values (-2.3 ‒ +0.13) indicate that they are slab-melting derived and were contaminated by the continental arc crust in their emplacement processes. The Jiayuguan adakitic granites and the regional data suggest that subduction of the Proto-Tethys Ocean continued until 403 Ma.

Combined with regional data, we propose that oceanic ridge subduction formed the Na-enriched Jiayuguan adakitic rocks in the western Alxa continental arc, whereas flat subduction and partial melting of the thickened crust form K-enriched adakitic rocks in the eastern Alxa Andean arc.

The data for this study are available in this manuscript and supplementary material.

The authors declare that they have no conflicts of interest.

This study was financially supported by the National Natural Science Foundation of China (42372270), the Science and Technology Major Project of Xinjiang Uygur Autonomous Region, China (2022A03010-1), the Third Xinjiang Scientific Expedition Program (2022xjkk1301), One hundred Talent Program of the Chinese Academy of Sciences (E2250403), and Youth Innovation Promotion Association Chinese Academy of sciences (2022446).

Supplementary data contain the supplementary tables, figures, and analytical methods. Figure S1: Photographs and microphotographs of adakitic granites samples from the Jiayuguan area of the Hexi Corridor, NW China. (a) and (d) 21JYG26; (b) and (e) 21JYG27; (c) and (f) 21JYG28; Pl: plagioclase; Bi: biotite; Qz: quartz. Figure S2: Geochronological age spectra of Paleozoic magmatism in North Qilian orogen. Table S1: REE of the zircon grains for the adakitic granites from the Jiayuguan area of the Hexi Corridor, NW China. Table S2: Age data for the granites and volcanic rocks in North Qilian, NW China. Supplementary Analytical methods: zircon LA-ICP-MS U-Pb dating and Lu-Hf isotope analysis, major and trace element analysis. (Supplementary Materials).