Basement Characteristics and Late-Stage Tectonic Evolution of the Qiangtang Terranes Open Access

The Sanjiang area in the eastern part of the Tibetan Plateau, with its intricate tectonic conditions, is the key area on the study of the Tethyan evolution and is also the location of the final convergence between the Laurasia and Gondwana. The Longmu Co-Shuanghu suture zone may be the final disappearance location of the paleo-Tethyan Ocean. Determining the diagenetic ages and provenance regions of the basement rocks on either side of the suture zone holds significant importance for understanding the formation of the Qiangtang terrane. The core of the Tibetan Plateau is primarily comprised of three blocks: the Songpan-Ganzi, the Qiangtang, and the Lhasa blocks [1]. These blocks are bounded and separated by several suture zones, such as the Yalung-Zangpo suture, the Bangong-Nujiang suture, and so on (Figures 1(a) and 1(b)). Traditionally, the Qiangtang terrane has been regarded as an anticlinorium sandwiched by the Jinshajiang suture zone at north and the Bangong-Nujiang suture zone at south [2]. However, recent studies suggest that the Qiangtang terrane consists of two distinct terranes, the North and South Qiangtang terranes, separated by the Longmu Co-Shuanghu paleo-Tethyan suture zone, based on records of arc magmatism, sedimentary basins, mafic dykes, and ophiolites mélange. It is also suggested that the paleo-Tethyan Ocean between these two terranes closed westward through scissor-like motion during the Early Triassic to Late Triassic [3-5].

Presently, there are three main views on the origin of the North and South Qiangtang terranes:

The first model suggests that the Qiangtang terrane is a unified landmass with a cohesive basement originating from the East Gondwana continent before the Late Carboniferous and Permian [2]. In this context, the ophiolitic mélange along the Longmu Co-Shuanghu suture zone is interpreted as an exotic nappe resulting from the Cenozoic Jinshajiang thrusting [2, 6].

An alternative view proposes that the North and South Qiangtang terranes originate from the Gondwana continent and the Cathaysian continent, respectively, and they are separated by the Longmu Co-Shuanghu suture zone [7]. In this model, the South Qiangtang terrane, and its southeastern extension of the Baoshan block, possesses a Pan-African crystalline basement similar to Gondwana, whereas the North Qiangtang terrane has a Rodina basement resembling the Cathaysian continent; in this context, the Longmu Co-Shuanghu suture zone serves as a boundary between the Gondwana and Cathaysian continent [4, 7].

The third competing hypothesis argues that both the North and South Qiangtang terranes are derived from the Cathaysian continent based on their similarities in geochronological characteristics [8]. Therefore, there should be no substantial differences in basement composition between the North and South Qiangtang terranes.

Another approach to solve this debate is to investigate the properties of the Qiangtang terrane, since the characteristics of the crystalline basement and sedimentary cover are two fundamental factors to determine the properties of a terrane [9, 10]. Currently, the North and South Qiangtang terranes are overlain by extensive Mesozoic sediments of the North and South Qiangtang Basin. The crystalline basement is only sporadically exposed along the basin margins, thus receives little attention in previous research [11-14].

In this study, we analyze the geochronology and geochemical characteristics of three groups of samples from the basement of the Qiangtang terrane, including the metamorphosed basement rocks of the Proterozoic Ningduo Group and the Neoproterozoic Jitang Group from the North Qiangtang terrane and the Paleozoic Youxi Group gneisses from the South Qiangtang terrane. We then compare our results with the published data to investigate the interconnections among the North Qiangtang, the South Qiangtang and adjacent blocks, to better constrain the evolution of the basements.

The study area in the northeast Tibetan Plateau straddles the Longmu Co-Shuanghu ophiolitic mélange. The tectonic units in this region consist of the South Qiangtang terrane, the North Qiangtang terrane, and the Songpan-Ganzi terrane from south to north. Proterozoic rocks are distributed within microcontinents or close to suture zones (Figure 1(b)).

The Songpan-Ganzi terrane is bounded by the A'nyemaqen suture zone (Kunlun fault zone) to the north, the Jinshajiang suture zone to the southwest, and the Longmenshan thrust belt to the east (Figure 1(a)). The terrane interior is characterized by Triassic flysch deposits of 5–15 km thick and contemporaneous intrusions [15]. The basement rocks only outcrop at the southern margin of the terrane [16] and share similar age and geochemical characteristics to the basement of the Cathaysian craton [17].

The Jinshajiang suture, a significant branch of the paleo-Tethyan suture zone, separates the Songpan-Ganzi terrane at north and the North Qiangtang terrane at south (Figure 1(a)). It formed through the collision of the two terranes at around 210 Ma [18-20], following the subduction of the paleo-Tethyan oceanic lithosphere prior to 230 Ma. Permo-Triassic igneous rocks associated with the paleo-Tethyan Ocean subduction are present on both sides of the suture zone [21].

The North Qiangtang terrane changes its trending direction from east-west in central Tibet to southeast-northwest in the central-eastern Tibetan Plateau (Figure 1). The cover of the terrane consists of extensive Triassic and Jurassic sedimentary strata, as well as Paleozoic marine sedimentary strata [22]. The Late Paleogene-Triassic paleontological association in this region exhibits a significant presence of warm water fauna that is distinctly different from that found on the Gondwana continent [23]. In addition, Permian-Triassic intrusions are present in the southern part of this terrane, forming a paleo-Tethyan magmatic belt (Figure 2(b)) [15, 24]. The North Qiangtang terrane likely possesses a Proterozoic crystalline basement [25]. Previous studies have documented intermediate- to high-grade metamorphic rock series of the Ningduo Group (Pt_1-2Nd.) and scattered metamorphosed basement fragments of the Jitang Group (Pt_2-3Jt.) [6, 26]. These basement rocks of Ningduo and Jitang groups outcrop along the northeastern part and southern margin of this terrane, respectively [27]. Intrusions within the Ningduo Group include Proterozoic gneiss granite (991 Ma) and Late Triassic monzonitic granite, as well as Paleogene monzonitic granite that is distributed on its western side in an intrusive contact relationship [6]. The southern side of the Jitang Group is intruded by Late Triassic monzonitic granite, and the northern side consists of Mesozoic strata within the Changdu Basin (Figures 2(a) and 2(c)).

The Longmu Co-Shuanghu suture zone represents the primary tectonic boundary of the paleo-Tethyan Ocean basin (Figure 1) [4, 28]. The ophiolites within the mélange zone are dated between middle Ordovician and upper Cambrian based on zircon U-Pb ages (438-497) from their mafic rocks [13], while high-pressure metamorphic rocks, post-orogenic volcanic rocks, and molasse along the suture zone constrain terranes convergence around Early Triassic [1, 3, 12, 19, 29-31]. The metamorphic rocks are interpreted as an extensional core complex derived from the tectonic mélange that was underthrust beneath the Qiangtang terranes during the southward/westward flat subduction of the Jinshajiang oceanic crust [1, 12, 19]. The volcanic rocks arc (named Jiangda–Weixi continental margin arc) formed because of the closure of the Paleo-Tethys and associated continental collision [32].

The South Qiangtang terrane is juxtaposed with the North Qiangtang terrane along the Longmu Co-Shuanghu suture zone. Mesozoic strata are extensively distributed in the terrane, and Precambrian and Paleozoic strata are sporadically exposed along the west side of the suture zone [33]. The sedimentary sequence of glacio-marine sandstone (bearing cold-water biota) interbedded with metamorphosed sandstone, sandy slate, phyllite, and metabasalt can be observed in the Carboniferous-Permian strata [14], and the Youxi Group metavolcanic rocks are part of sedimentary sequence. Sedimentary sequences of slates, bioclastic limestone, metamorphic sandstone, and basic volcanic rocks are found in Permian [4].

To investigate the origins and tectonic histories of the South and North Qiangtang, we collected three samples from both sides of the Longmu Co-Shuanghu mélange zone to conduct geochronological, geochemical, and isotopic geochemical analyses. They are gneisses from the Ningduo Group (sample Y02) and Jitang Group (sample Y03) in the North Qiangtang terrane and a granitic gneiss from the Youxi Group (sample Y04) in the northern margin of the South Qiangtang terrane (Figures 2(a) and 2(b)). Below in this section, we describe the samples and their geological context.

The Ningduo Group is exposed in the northern part of the North Qiangtang terrane adjacent to the Jinshajiang suture zone. It primarily consists of pre-Cambrian Series stratigraphy, with lithologies such as sandstone, shale, mudstone, and limestone. Sample Y02 is a biotite plagioclase gneiss at coordinates 32°31′06″N, 97°05′58″E with an elevation of 4802 m. The rock composition mainly includes plagioclase (~45％), potassium feldspar (~15％), quartz (~25％), biotite (~15％), and a small amount of magnetite (<1％). The plagioclase, potassium feldspar, and quartz are xenomorphic. The polysynthetic twin was observed within the plagioclase. The surface of some plagioclase particles is blurred due to argillation. Compared with plagioclase, the surface of quartz is relatively clean, and local wavy extinction can be seen. Biotite is brown, flaky, and oriented in the rock to form schistosity (Figure 3(c)).

The Jitang Group, situated at the west edge of the North Qiangtang terrane, is close to the Longmu Co-Shuanghu suture zone. Its lithologic combinations are highly diverse, predominantly comprising sandstone, mudstone, shale, and limestone. Spiral shell fossils are common in the limestone. Sample Y03 is a biotite plagioclase gneiss (30°42′26″N, 97°19′56″E; Elev. 3659 m), and it exhibits distinct gneissic and mylonitic characteristics (Figures 3(d) and 3(e)). It is evident that biotite and quartz exhibit pronounced plastic deformation and recrystallized textures, with recrystallized fine-grained minerals (biotite and quartz) surrounding the fragmented feldspar. The feldspar exhibits large grain sizes and displays brittle deformation characteristics such as porphyroclastic texture. It primarily consists of plagioclase (~60％), quartz (~25％), biotite (~15％), and minor amounts of magnetite, apatite, and zircon (<1％) The plagioclase, potassium feldspar, and quartz are xenomorphic. The polysynthetic twin was observed within the plagioclase. The surface of some plagioclase particles is blurred due to argillation. Compared with plagioclase, the surface of quartz is relatively clean, and local wavy extinction can be seen (Figure 3(f)).

The Youxi Group is exposed to the southwest of the Jitang Group. The two groups are separated by Triassic intrusions and the Longmu Co-Shuanghu suture zone. The lithology composition of this rock group is highly diverse, encompassing various stratigraphic units ranging from the Lower Cambrian to the Lower Silurian series, primarily consisting of sandstone, mudstone, shale, and occasionally breccia and conglomerate. Sample Y04 is a banded granitic gneiss from the Youxi Group (32°42′14″N, 97°19′15″E; Elev. 3589 m). It exhibits distinct gneissic and mylonitic characteristics (Figures 3(g) and 3(h)). This sample comprises plagioclase (~45％), quartz (~30％), potassium feldspar (~15％), biotite (~10％), as well as a small quantity of magnetite, apatite, and zircon (<1％). The plagioclases are hypidiomorphic, whereas potassium feldspar and quartz are xenomorphic. The minerals exhibit wavy or concavo-convex boundaries. Quartz perforation within potassium feldspar and vermicular quartz within plagioclase were observed (Figure 3(i)).

For each of the three groups, we selected different parts of the same outcrop. All samples were analyzed for major and trace elements, with the most representative samples (the rocks are fresh, with a great number of zircon grains, and the cracks and inclusions in the zircon grains are less.) undergoing isotopic determinations (e.g. zircon U-Pb dating and Lu-Hf isotope analysis; whole rock Sr-Nd analysis) (Online Supplementary Tables S1–S4). We analyzed 211 zircons from sample Y02, 205 zircons from sample Y03 and 239 zircons from sample Y04 for zircon U-Pb dating (Online Supplementary Table S1). We randomly conducted 125 Lu-Hf isotope analyses on the zircons which had undergone U-Pb dating (40 zircons out of 211 from Y02, 40 zircons out of 205 from Y03, and 45 zircons out of 239 from Y04) (Online Supplementary Table S2). Eight whole-rock analyses of Sr-Nd isotopes were conducted for the three samples, with two analyses for sample Y02, three for sample Y03, and three for sample Y04 (Online Supplementary Table S3). We conducted 26 major and trace element geochemistry analyses for the three samples, with eight analyses for sample Y02, seven for sample Y03, and eleven for sample Y04 (Online Supplementary Table S4).

The laser ablation-inductively coupled plasma mass spectrometry U-Pb dating of 655 zircons was conducted in this study. The experiment took place at the Key Laboratory of Palaeomagnetism and Palaeotectonic Reconstruction, Ministry of Natural Resources of China. Laser Denudation System (LA) employed a GeoLas HD ArF excimer laser manufactured by Coherent Corporation, USA, operating at a wavelength of 193 nm. The detection system utilized an Agilent 7900 inductively coupled plasma mass spectrometer (ICP-MS) produced by Agilent Technologies.

The samples were initially subjected to conventional methods for physical fragmentation, followed by sorting using magnetic and heavy liquid techniques after washing. Subsequently, the samples were examined under a binocular microscope for selection. Next, the zircon grains were placed on an epoxy resin target, and their cores were exposed through grinding and polishing. Finally, the internal structure, genetic type, and optimal analysis point of the zircon were determined through observations and photography of transmission light, reflected light, and cathodoluminescence (CL).

The laser spot denudation parameters were set as follows: beam spot diameter, 32 µm; energy density, 5.0 J/cm²; denudation frequency, 5 Hz; and sample denudation duration, 50 seconds. The signal intensity of the original data was converted into content data using ICP-MS data Cal 10.9. Time drift correction and quantitative calibration were performed on the dating results. Isoplot/Ex (version 4.15) software [34] was utilized for concordant plot, statistical histogram, and weighting calculation. Plešovice zircon served as the signal monitoring standard sample with 1 standard sample added every six measuring points. The mean ²⁰⁶Pb/²³⁸U age of standard zircon Plešovice is determined to be 337.95 ± 0.41 Ma (MSWD = 0.77, N = 232), which aligns with the reported or recommended value of 337.13 ± 0.37Ma.

The Hf isotope analysis point coincided with the zircon U-Pb age testing site. CL photos were utilized for the identification and selection of suitable points. The resolution SE 193 nm laser (Applied Spectra, Inc.) serves as an instrumental laser injection system connected to a multi-receiver plasma mass spectrometer analysis system (NEPTUNE plus, Thermo Fisher Scientific Inc.). The laser spot beam diameter typically measures 38 µm, the stripping length lasts for 26 seconds, the energy density amounts to 7.5 J/cm², the frequency is set at 8 Hz, and helium functions as the carrier gas sent to ICP-MS.

The isotopic ratios ¹⁷⁹Hf/¹⁷⁷Hf = 0.7325 and ¹⁷³Yb/¹⁷¹Yb = 1.132685 [35] were utilized to calculate the mass fractionation coefficients β_Hf and β_Yb for Hf and Yb, respectively. The isotopic ratio ¹⁷⁶Yb/¹⁷³Yb = 0.79639 [35] was employed to correct for the isobaric interference of ¹⁷⁶Yb on ¹⁷⁶Hf. Additionally, the isotopic ratio ¹⁷⁶Lu/¹⁷⁵Lu = 0.02656 [36] was used to account for the minor isobaric interference of ¹⁷⁶Lu on ¹⁷⁶Hf.

To ensure the reliability of the analytical data, the test results were optimized using a combination of three internationally recognized zircon standards: Plešovice, 91500, and GJ-1. The external precision (2SD) for Plešovice, 91500, and GJ-1 is superior to 0.000020. The measured values are in agreement with the recommended values [37] within the margin of error.

The sample pretreatment of whole-rock major element analysis was made by the melting method. The flux used was a combination of lithium tetraborate, lithium metaborate, and lithium fluoride (45:10:5). Ammonium nitrate served as the oxidant, while lithium bromide acted as the release agent. The melting process was carried out at a temperature of 1050°C for a duration of 15 minutes. For analysis, we employed the ZSX Primus II wavelength dispersive X-ray fluorescence spectrometer manufactured by RIGAKU, Japan, equipped with a 4.0 kW end window rhodium target X-ray tube. Test conditions included a voltage set at 50 KV and current adjusted accordingly. All main elements were analyzed using Kα spectral lines, and standard curves were generated based on the national standard material rock series GBW07101-14. Data calibration was performed using the theoretical α coefficient method to achieve a relative standard deviation below 2％.

Whole-rock trace element analysis was conducted on Agilent 7700e ICP-MS at the Wuhan Sample Solution Analytical Technology Co., Ltd., Wuhan, China. The detailed sample-digesting procedure was as follows: (1) Sample powder (200 mesh) was placed in an oven at 105°C for drying of 12 hours; (2) 50 mg sample powder was accurately weighed and placed in a Teflon bomb; (3) 1 mL HNO₃ and 1 mL HF were slowly added into the Teflon bomb; (4) Teflon bomb was put in a stainless steel pressure jacket and heated to 190°C in an oven for >24 hours; (5) After cooling, the Teflon bomb was opened and placed on a hotplate at 140°C and evaporated to incipient dryness, and then 1 mL HNO₃ was added and evaporated to dryness again; (6) 1 mL of HNO₃, 1 mL of MQ water, and 1 mL internal standard solution of 1 ppm In were added, and the Teflon bomb was resealed and placed in the oven at 190°C for >12 hours; (7) The final solution was transferred to a polyethylene bottle and diluted to 100 g by the addition of 2％ HNO₃.

We performed eight analyses for whole-rock Sr and Nd isotope ratio on three samples, employing the German Thermo Fisher Scientific company MC-ICP-MS (Neptune Plus) instrument for simultaneous determination of Nd and Sr isotopes.

The mass spectrometer is equipped with nine Faraday cup receivers (⁸³Kr⁺, ¹⁶⁷Er⁺⁺, ⁸⁴Sr⁺, ⁸⁵Rb⁺, ⁸⁶Sr⁺, ¹⁷³Yb⁺⁺, ⁸⁷Sr⁺, ⁸⁸Sr⁺) for detection and calibration in Sr isotope analysis. The test accuracy exceeds a threshold of better than 2 × 10^-5 (~0.03‰). The measured value of the standard sample NIST-987 for the analysis of the isotopic ratio of ⁸⁷Sr/⁸⁶Sr was determined as 0.710242 ± 14 (2σ, n = 345), which demonstrates consistency with the recommended value of 0.710248 ± 12 (2σ) [37].

The mass spectrometer is equipped with nine Faraday cup receivers (¹⁴²Nd⁺, ¹⁴³Nd⁺, ¹⁴⁴Nd⁺, ¹⁴⁵Nd⁺, ¹⁴⁶Nd⁺, ¹⁴⁷Sm⁺, ¹⁴⁸Nd⁺, ¹⁴⁹Sm⁺, ¹⁵⁰Nd⁺) for detection and calibration in Nd isotope analysis. The test accuracy exceeds the threshold of better than 2.5 × 10⁻⁵ (~0.05‰). The measured value of the standard sample GSB04-3258-2015 for the ratio of isotopes, namely, the analysis result of ¹⁴³Nd/¹⁴⁴Nd, is determined as 0.512440 ± 6 (2σ, n = 31), which demonstrates consistency with the recommended value of 0.512438 ± 6 (2σ) [38].

The ε_Nd(t) value is determined using the modern reference values for the Chondrite Uniform Reservoir (CHUR), with (¹⁴³Nd/¹⁴⁴Nd) _CHUR = 0.512638 and (¹⁴⁷Sm/¹⁴⁴Nd) _CHUR = 0.1967.

Most of the zircon grains in samples Y02 and Y03 exhibit a long column-elliptic shape, while a minor portion is rounded. All grains in sample Y04 exhibit an elliptic-rounded morphology. The grain sizes in samples Y02, Y03, and Y04 range from 90 to 210 µm, 63 to 219 µm, and 78 to 249 µm, respectively. The aspect ratios for these grains vary between 1.1 and 3.4, 1.0 and 2.8, and 1.0 and 3.78, respectively. CL images show that most zircon grains in sample Y02 are incomplete, displaying rims and inherited cores. Only a small portion exhibits well-developed crystals with oscillatory zoning (Figure 4(a)). In sample Y03, most zircons possess a core-rim structure (Figure 4(b)), with some zircons showing excellent crystal morphology and pronounced oscillatory zoning, indicating their magmatic origin. Zircons in sample Y04 predominantly feature core-rim structures, and a few grains contain inherited crystal nuclei (Figure 4(c)). Therefore, the zircons in sample Y02 are predominantly detrital zircons derived from magmatic sources. The zircons in sample Y03 primarily comprise detrital zircons sourced from both metamorphic and magmatic origins. The zircons in sample Y04 are predominantly detrital magmatic zircons.

The obtained age data from Y02 are plotted on or close to the Concordia line, indicating negligible lead loss events in these zircons. Zircon Th/U values range from 0.04 to 2.01. The oldest and youngest zircons are 2889 ± 8 Ma (²⁰⁷Pb/²⁰⁶Pb age) and 263 ± 2 Ma (²⁰⁶Pb/²³⁸U age, Th/U = 0.05), respectively. Most ages are in the range of 500–1500 Ma, with four notable age clusters: (1) 656–699 Ma (n = 9, Th/U_mean = 0.46), (2) 951–998 Ma (n = 32, Th/U_mean = 0.57), (3) 1100–1148 Ma (n = 24, Th/U_mean = 0.65), and (4) 1254–1293 Ma (n = 11, Th/U_mean = 0.71) (Figure 4(a)) (Online Supplementary Table S1).

The obtained age data from Y03 are aligned along the Concordia line, indicating insignificant lead loss events in these zircons. The Th/U values of the zircons range from 0.01 to 1.43. The oldest zircon has an age of 3473 ± 5 Ma (²⁰⁷Pb/²⁰⁶Pb), while the youngest zircon has an age of 225 ± 2 Ma (²⁰⁶Pb/²³⁸U) and a Th/U value of 0.03. Most ages fall within the range of 200–1050 Ma, with five distinct clusters at approximately (1) 226–249 Ma (n = 14, Th/U_mean = 0.06), (2) 603–649 Ma (n = 13, Th/U_mean = 0.42), (3) 705–743 Ma (n = 14, Th/U_mean = 0.39), (4) 952–998 Ma (n = 22, Th/U_mean = 0.45), (5) 1052–1093 Ma (n = 15, Th/U_mean = 0.51) (Figure 4(b)) (Online Supplementary Table S1).

The obtained age data from Y04 are consistent with or close to the Concordia line, suggesting no significant lead loss occurred in the zircon samples. Their Th/U values ranged from 0.05 to 1.82. The oldest zircon yielded a ²⁰⁷Pb/²⁰⁶Pb age of 2618 ± 10 Ma, while the youngest zircon showed a ²⁰⁶Pb/²³⁸U age of 213 ± 2 Ma, with a Th/U value of 0.45. Most ages fall within the range of 200–1150 Ma and are concentrated within three distinct age groups: (1) 213–249 Ma (n = 23, Th/U_mean = 0.38), (2) 402–449 Ma (n = 39, Th/U_mean = 0.60), and (3) 1055–1098 Ma (n = 15, Th/U_mean = 0.45) (Figure 4(c)) (Online Supplementary Table S1).

The 40 ε_Hf(t) values of the biotite plagioclase gneiss (sample Y02) exhibit a wide range, from −20.2 to 7.9. Their two stages models age of Hf isotope (T_DM2(Hf)) span 1297 to 3130 Ma, which concentrate in three age groups: 1734–1789 Ma (n = 5), 1928–1993 Ma (n = 6), and 2104–2287 Ma (n =11) (Figure 4(d)) (Online Supplementary Table S2).

The 40 ε_Hf(t) values of the biotite plagioclase mylonitic gneisses (sample Y03) range from −26.9 to 12.0. Their T_DM2(Hf) ranges from 1128 to 3361 Ma and are predominantly distributed in ranges of 1525–1793 Ma (n = 13), 1901–1999 Ma (n = 7), 2388–2465 Ma (n = 5), and 2883–2996 Ma (n = 5) (Figure 4(e)) (Online Supplementary Table S2).

The 45 ε_Hf (t) values of the banded granitic gneisses (sample Y04) exhibit a broad range from −28.1 to 5.8, and the T_DM2(Hf) span 1337–3214 Ma. The crustal model ages primarily fall into four groups: 1505–1708 Ma (n = 18), 1780–1893 Ma (n = 5), 2038–2133 Ma (n = 7), and 2368–2499 Ma (n = 6) (Figure 4(f)) (Online Supplementary Table S2).

For the sample Y02, the initial ⁸⁷Sr/⁸⁶Sr ratios (I_Sr) yield from the two analyses are 0.698014 and 0.698567, while the ε_Nd (t) values are −8.4 and −8.3, respectively. The crustal model ages (T_DM (Nd)) are estimated to be 2044 and 2028 Ma (Online Supplementary Table S3).

For the sample Y03, the I_Sr values obtained from the three analyses are 0.702721, 0.693916, and 0.695507, respectively. Their ε_Nd (t) values are −11.9, −12.0, and −11.9, respectively. The T_DM (Nd) model ages are 1970, 1974, and 1982 Ma (Online Supplementary Table S3).

For the sample Y04, the I_Sr ratios of three analyses of Y04 are 0.709705, 0.713473, and 0.723841, and ε_Nd (t) values are −7.2, −7.8, and −8.0, respectively. The T_DM (Nd) model ages are 1593, 1626, and 1642 Ma (Online Supplementary Table S3).

The SiO₂ and Na₂O+K₂O contents of the eight analyses from Y02 range from 69.97% to 73.72% and from 4.25% to 5.58%, respectively, indicating low total alkali content. The K₂O/Na₂O ratio ranges from 1.4 to 2.6, indicating a potassium-rich content. CaO and MgO contents are from 1.17% to 1.92%, and from 2.54% to 2.94%, respectively. Al₂O₃ content is high (between 11.50% and 13.54%), surpassing the combined molecular number of K₂O, Na₂O, and CaO, leading to A/CNK ratios ranging from 1.27 to 1.56, implying peraluminous characteristics. Their discriminant function (DF = 10.44 − 0.21 × SiO₂ − 0.32 × Fe₂O₃^T −0.98 × MgO + 0.55 × CaO + 1.46 × Na₂O + 0.54 × K₂O, [39]) values are from −3.20 to −5.80, which indicate a para-metamorphic rock type (Online Supplementary Table S4).

The total rare earth content (ΣREE=157.8–211.4 ppm) of the Y02 analyses exceeds the average value of the upper crust (143 ppm). The (La/Sm)_N values range from 3.44 to 3.89, (La/Yb)_N values from 7.52 to 10.02, and (Gd/Yb)_N values from 1.40 to 1.95, indicating a relative enrichment of LREE and fractionation between LREE and HREE. The analysis results also exhibit negative Eu anomalies with Eu/Eu* ratios ranging from 0.41 to 0.63 (Figure 5(a)). In the spidergrams, these biotite plagioclase gneisses are enriched in Pb and large ion lithophile elements (LILE, e.g. Rb, Th, and K), while Ba, Sr, and high field strength elements (HFSE, e.g. Nb, Ta, P, Ce, and Ti) show negative anomalies (Figure 6(a)) (Online Supplementary Table S4).

Seven analyses from sample Y03, a mylonitic gneiss from Jitang Group, were analyzed. The content of SiO₂ and Na₂O+K₂O is 70.23%–73.64％ and 5.36%%–6.13％, respectively, indicating low total alkali content. K₂O/Na₂O is 1.2–1.4, indicating potassium-rich characteristics. CaO and MgO were 1.29%–1.69％ and 1.61%–2.44％, respectively. Al₂O₃ content is as high as 12.96%–13.85％, A/CNK = 1.23–1.37, with peraluminous characteristics (>1.1). DF value is between −1.65 and −2.75, indicating a para-metamorphic rock type. The Al2O₃/SiO₂ of the results is between 0.18 and 0.20, and relatively rich in iron (FeO^T=3.31%–4.99％) (Online Supplementary Table S4).

The total rare earth content analyses (ΣREE=87.7-229.4 ppm) of the Y03 are predominantly higher than the average value of the upper crust (143 ppm). The values for (La/Sm)_N range from 3.41 to 4.62, (La/Yb)_N ranges from 6.85 to 10.04, and (Gd/Yb)_N ranges from 0.88 to 2.01, indicating a relative enrichment of LREE and fractionation between LREE and HREE elements. Additionally, the results exhibit negative Eu anomalies with Eu/Eu* ratios ranging from 0.38 to 0.67 (Figure 5(b)). On the spidergrams, Pb and LILE display noticeable positive anomalies, whereas Ba, Sr, and HFSE show negative anomalies (Figure 6(b)) (Online Supplementary Table S4).

The SiO₂ content in eleven banded granitic gneiss analyses (Y04) from the Youxi Group ranges from 63.46％ to 79.33％, while the Na₂O+K₂O content ranges from 3.06％ to 8.25％, indicating a low total alkali content. The CaO and MgO contents are between 1.29％ and 1.69％, and between 1.61％ and 2.44％, respectively. Their DF values range from 1.65 to 2.75 (with two analyses values < 0), suggesting an ortho-metamorphic rock nature. The Al₂O₃ content is high, ranging from 12.96％ to 13.85％, which exceeds the sum of K₂O, Na₂O, and CaO molecular numbers, resulting in an A/CNK ratio of between 1.23 and 1.37 (>1.1). The K₂O/Na₂O ratios range from 1.2 to 1.4, indicating moderate-high potassium enrichment characteristics (Online Supplementary Table S4).

The distribution of total rare earth content in eleven analyses from the Y04 exhibits large variations, with ΣREE ranging from 56.7 to 408.2 ppm. The (La/Sm)_N values range from 2.23 to 4.95, (La/Yb)_N from 2.14 to 39.1, and (Gd/Yb)_N from 0.8 to 6.74, indicating a relative enrichment of LREE and fractionation between LREE and HREE elements. Additionally, the analysis results displayed negative Eu anomalies (Eu/Eu* = 0.10–0.86, except for one analysis, which is 1.24) (Figure 5(c)). In the spidergram, Pb and LILE show distinct positive anomalies while Ba, Sr, and HFSE exhibit negative anomalies (Figure 6(c)) (Online Supplementary Table S4).

We calculated the DF index and the P₂O₅/TiO₂ versus MgO/CaO ratio (Figure 7(a)) for each analytical result to differentiate between orthogneisses and paragneisses [40, 41]. In order to distinguish more detailed information about source areas, we further calculated a non-standardized DF F₁-F₂ diagram (Figure 7(b)) and the Chemical Index of Alteration (CIA = 100×Al₂O₃/[Al₂O₃+CaO^*+Na₂O+K₂O], the calculation is determined based on the molecular proportions of major elements) [42, 43].

After determining the rock categories of the gneiss, the geochemical classification diagram of terrigenous sandstone (Figure 8) [44] is utilized to predict the lithology of the paragneiss protolith. To determine the lithology of the orthogneiss protolith, total alkali-silica (TAS) and A/NK-A/CNK diagrams (A/CNK= molar ratio Al₂O₃/[CaO+Na₂O+K₂O] and A/NK= molar ratio Al₂O₃/[Na₂O+K₂O]) are also employed (Figure 9(b)). In addition, La/Th-Hf and tectonic discrimination diagrams (Figure 10(a)) [45] were utilized to ascertain the primary source regions of the meta-sedimentary samples.

Geological data and discrimination diagrams suggest that the Y02 biotite plagioclase gneisses protolith is lithic feldspar greywacke, Y03 biotite plagioclase mylonitic gneisses protolith is felsic lithic greywackes, Y04 granitic gneisses protolith isdisplaying traces of I-type granite. Primary basis for reconstructing their protolith is as follows:

1. Y02 and Y03 exhibit stratiform appearances consistent with the attitude of gneisses and displaying distinct deformation characteristics such as structural lenticle, box fold, and mica fish structures (Figures 3(a), 3(b), 3(d), and 3(e)). The mineral grains are coarse, mainly composed of granular minerals, with a small amount of flake or columnar minerals. The flake minerals exhibit a non-continuous preferred orientation, indicating a high degree of recrystallization. Additionally, the recrystallization phenomenon of quartz is evident, locally exhibiting porphyroblast (Figures 3(c) and 3(f)). Y04 exhibits a massive structure and holocrystalline texture, with prominently visible clumps of light-colored mineral assemblage. The mineral particles are euhedral and epigranular, predominantly composed of light-colored minerals interspersed with intermittent bands of dark-colored minerals (Figures 3(g)–3(i)).

2. In the Y02 and Y03 samples, most zircon grains are detrital zircons exhibiting evident abrasion features, indicative of physical transportation and deposition. As to Y04, most of zircons exhibit strong ablating characteristics indicative of volcanic and subvolcanic rocks, while some possess well-formed crystal shapes and oscillating bands. A small part of detrital zircons displays traces of abrasion.

3. The DF index is negative (−3.20 > Y02 > −5.80; −1.65 > Y03 > −2.75) and the plot on the P₂O₅/TiO₂ versus MgO/CaO discrimination diagram (Figure 7(a)) both suggest that the Y02 and Y03 are classified as para-gneiss [40]. In contrast, nine out of the eleven DF values yield positive results. And the P₂O₅/TiO₂ versus MgO/CaO diagram shows that eight analyses of Y04 exhibit ortho-gneiss rock characteristics (Figure 7(a)).

The Al₂O₃/SiO₂ ratio of the Y02 and Y03 analyses ranges from 0.17 to 0.20. They have relatively high iron contents (FeO^T from 3.68% to 5.34%, average 4.80). The Y02 and Y03 results are plotted in the mature terrigenous sedimentary region based on the non-standardized DF F₁-F₂ diagram (Figure 7(b)). These characteristics are similar to those described by Roser and Korsch [46] for mature continental sandstone equivalents. The CIA index falls within the range of terrigenous sedimentary rocks [42, 43]. In the F₁-F₂ diagram, most results of the Y04 samples are dispersed within the felsic igneous rocks source region, while only one data point is situated in the mature terrigenous sedimentary region (Figure 7(b)). The CIA of the Y04 samples ranges from 50.6 to 52.7, positioning it between Tonalite-Trondhjemite-Granodiorite rock series (~50.0) and granite (~55.4).

The geochemical classification diagram of terrigenous sandstone suggests that the protoliths of Y02 and Y03 are lithic arkose and lithic greywacke, respectively [47] (Figure 8). In the TAS diagram, Y04 most fall within the granite (rhyolite) field, with only one in the syenite (trachyte) area (Figure 9(a)). In conjunction with the phenomenon of well-crystallized at the microscale, the protolith of Y04 should be granite.

The ratio of trace elements serves as a reliable indicator for distinguishing source materials. In the La/Th-Hf diagram [48], all plots align closely with the mean value of the upper continental crust (UCC) (Figure 10(a)), while exhibiting enrichment in LREE, stable HREE content, and a distinct negative Eu anomaly (Figure 5(a)). These observations suggest that the samples originate from the UCC.

During the recycling process of sedimentary rocks, U4⁺ and U6⁺ will undergo oxidation and become soluble, increasing the Th/U ratio of the rocks. Therefore, the Th/U ratio can be used to identify the source type. When the Th/U value is close to 6, it indicates predominantly recycled sedimentary rocks; when the Th/U ratio is around 4.5, it suggests mainly sedimentary rocks that may be mixed with island arc volcanic rocks; when the Th/U ratio ranges from 2.5 to 3.0, it signifies primarily island arc volcanic rocks [49]. The Th/U ratio of Y02 ranges from 3.8 to 6.8 with an average value of 5.4, which indicates that it represents a mixture of recycled sedimentary rock and island arc volcanic rock. The Th/U ratio of Y03 ranges from 6.1 to 8.1, with an average value of 7.5, indicating the characteristics of recycled sedimentary rocks.

Sandstone and mudstone generally inherit the parent rock’s Al₂O₃/TiO₂ ratio. A ratio of 19:28 suggests a felsic rock source for the sediment, while a ratio below 14 indicates a mafic rock origin [50]. The Al₂O₃/TiO₂ in Y02 ranges from 16.1 to 22.2, with an average of 18.5, indicating that the protolith was composed of felsic material. The Al₂O₃/TiO₂ ratio of Y03 varies from 19.0 to 31.0, with an average value of 23.4, which is consistent with the results obtained from the tectonic discrimination diagrams (Figure 10(b)), suggesting that the protolith’s parent rock was previously situated in a continental island arc-active continental margin and was a felsic recycled sedimentary rock.

The Y04 granitic gneiss exhibits high SiO₂ and low TiO₂, FeO^T, and MgO contents, indicating a clear differentiation from the mantle materials [51] but similarity to the average chemical composition of UCC [52]. In terms of trace elements, the significant depletion of Nb element and notable enrichment of Zr and Hf elements further suggest that the original magma shares similarities with crust source magma [51, 52]. Additionally, La/Yb values range from 4.24 to 19.09 with an average value of 12.35, which significantly deviates from magmas derived from the mantle (La/Yb≈0.96).

Additionally, Y04 exhibits a high SiO₂ content (average 72.38%), low FeO^T/MgO ratio (average 2.75), low 10000 x Ga/Al ratio (average 2.38), and low contents of Zr, Nb, Ce, and Y elements. These characteristics differentiate it from A-type granites [47]. According to the zirconium saturation thermometer formula for whole-rock analysis, the calculated saturation temperature for metamorphic acid volcanic rocks T_Zr ranges from 717°C to 852°C, with an average of 790℃. This is inconsistent with the high-temperature nature typically associated with A-type granite (>900°C) [53]. The low P₂O₅ content (average 0.08) further distinguishes it from S-type granites [46]. The A/NK-A/CNK diagram aligns with the characteristics observed in I-type granites (Figure 9(b)).

The formation of the Qiangtang terranes may have been influenced by 0.7–1.1 Ga tectonic events resulting from the assembly and breakup of the Rodinia supercontinent. Additionally, the Pan-African events recorded in Gondwana might have impacted these terranes due to its paleogeographic location [54].

Many models of supercontinents suggest the Qiangtang terranes have maintained a long-term paleogeographical connection with the Cathaysian continent [33]. Throughout various stages of convergence between the Cathaysian continent and the Gondwana continent during the Ediacaran period, as well as the multi-phase, diachronic evolution of the Tethyan Ocean (proto-, paleo-, meso-, and neo), the Qiangtang terranes have consistently occupied a position between the Cathaysian continent and the Gondwana continent as in the model proposed by Li et al. [55] and also by Zhao et al. [56]. There is significant different evolution between the Cathaysian continent and the Gondwana continent in terms of basement composition and cover layer characteristics. Additionally, factors such as Tethyan Ocean evolution (including the closure of proto, paleo-, and meso-Tethyan Ocean) and tectonic events like the Tibetan Plateau uplift (Himalayan orogeny) both influenced the development of Qiangtang terranes [57].

Several studies indicate that the Precambrian basement rocks of the northern Qiangtang terrane were formed during 1048–965 Ma [6, 58] (Figures 11(c) and 11(d)), which aligns with the primary peak age we obtained from the Niduo Group (Y02). Moreover, some scholars have proposed a double-layered structure, suggesting that the basement of the Qiangtang basin comprises both a hard basement and an overlying soft basement [59]. Consequently, it is plausible that the Niduo Group represents Precambrian upper soft basement rocks.

Basement of the South Qiangtang terrane is relatively young. For instance, Dong et al. [60] estimate its formation at approximately 525 Ma (Figure 11(h)), while Zhao et al. [61] suggest during 591–470 Ma (Figure 11(i)). This period is remarkably close to the main peak age of the Youxi Group (426 Ma, Y04), suggesting that the Youxi Group could represent a magmatic intrusion event following the formation of the South Qiangtang basement.

The age distribution of the Youxi Group sample (Y04) predominantly ranges between 200 and 250 Ma, 350 and 500 Ma, and 1050 and 1100 Ma (Figure 11(g)). The analyses from the Youxi Group granite have relatively low zircon saturation temperatures ranging from 727 to 852°C (790°C on average) (Online Supplementary Table S4) [62], close to those of the I-type granites. Besides, we conducted tests on the cores of the zircons. Therefore, the possibility of us obtaining inherited zircon ages has greatly increased. So, we interpret the low proportion older zircons (500, 1100 Ma) as inherited zircons. According to statistics, the proportion of inherited zircons is approximately 30%, which might reflect zircon-rich sources produced by partial melting of magmatic rocks and sediments.

The older age component between 1050 and 1100 Ma correlates with the assembly period of the Rodinia supercontinent (Figure 11(g)). Additionally, zircons within this age range are abundant in the Paleozoic strata of the Tethyan Himalayan terrane, which is in the northern part of Gondwana. This suggests a plausible material source for these zircons.

The prolonged low peak interval of 550–950 exhibits a bimodal feature Ma indicates a stable passive continental marginal sedimentary period for the main source area, where the South Qiangtang terrane received the Pan-African basement material from the Gondwana terranes. This lower peak value can be explained by the paleogeography of the South Qiangtang during the Early Paleozoic. It has been suggested that the South Qiangtang terrane was located at Gondwana’s continental margin [63] and was not significantly impacted by Rodinia supercontinent breakup. Paleogeographic reconstruction reveals that in the Early Paleozoic, the South Qiangtang terrane was located at the Gondwana continent’s northern margin after the Pan-African orogenic event (~470Ma) [8, 64, 65].

The dominant age group is between 350 and 500 Ma (average 426 Ma, Figure 11(g)). The records in the central-Qiangtang metamorphism and uplift between 350 and 500 Ma include the presence of multi-stage ophiolites (480, 520 Ma, 430–460 Ma, 340–370 Ma) [66], Early Carboniferous granite intrusions (352 Ma), and high-pressure granulite facies metamorphism (422, 427 Ma) [67]. Our age data span from the Paleozoic Andean-type orogeny to the breakup [68, 69], which occurred along the northern margin of Eastern Gondwana. This feature is comparable to magmatism in the Himalayan terrane and the south India (Figure 11(g)) [64, 65]. We conclude that the dominant peak (ca. 426 Ma) represents the protolith formation which associated with the southward subduction of the Proto-Tethyan Ocean and (or) the collision between micro-blocks around the northern margin of Gondwana.

Previous studies suggest that zircons of 200–250 Ma in the Bitu ophiolite mélange record the subduction of paleo-Tethys [29]. Our data support the previous interpretation. Because our sample is an ortho-metamorphic rock and the Th/U mean ratio (0.38) of our zircons of 200–250 Ma, we interpret that they form during the metamorphism associated with partial melting of continental crust caused by subduction of paleo-Tethys.

Other discrete ages beyond 1450 Ma lack centrally distributed peaks (Figure 11(g)), exhibit uncertain origins with limited statistical significance, and may potentially originate from the reworking of older sedimentary material, such as the Columbian Period.

The Ningduo Group sample (Y02) exhibits significant differences from the Youxi Group. Detrital zircon ages that are older than 1400 Ma constitute a small portion of all the obtained ages (Figure 11(e)). Ages between 2420 and 2620 Ma form a minor peak on the probability density function plot, which can be correlated with a major age peak of previously reported Cathaysia samples [70]. It suggests that the provenance of the Ningduo Group may contain or recycle from Early Proterozoic basement rocks of the Cathaysia. The source of other zircons older than 1400 Ma is uncertain. They could be recycling zircons formed during the long history (1450, 2300 Ma) of the assembly and breakup of the Columbia supercontinent.

The ages younger than 1300 Ma exhibit a bimodal feature (Figure 11(e)). The main group that ranges from 900 to 1300 Ma has two prominent peaks at approximately 973 and 1118 Ma and a lower peak at 1271 Ma. He et al. [6] obtained a zircon U-Pb age of ~991 Ma for a granite intrusion in the Ningduo Group, providing a minimum depositional age for the Ningduo Group. We interpret that the age peak preceding this intrusion event corresponds to the forming age of basement rock (during 991 to 1118 Ma). This suggests the Ningduo Group association with the Greenville event, which correlated with the assembly of the Rodinia supercontinent. Moreover, these datasets of Ningduo Group are highly similar to the two major peaks of Cathayan terrestrials reported by Yao et al. [71]. This coincidence indicates that North Qiangtang is closely related to Cathaysia. It also has a potential implication that the primary clastic source of the Ningduo Group is from Cathaysia. Therefore, we conclude that the North Qiangtang originates from either the margin of the Cathaysian continent or adjacent areas (e.g. Laurentia).

Weak peaks (600, 750 Ma) can be observed in the age records of the Rodinian break-up and the evolution of proto-Tethyan ocean [72] (Figure 11(e)). Recent studies have depicted the Proto-Tethys as an ocean basin formed during the break-up of the Rodinia supercontinent at 600–750Ma [56]. There has been no Cryogenian to Early Ediacaran igneous rock reported inside the Cathaysian continent or the North Qiangtang terrane, which were related to intra-continental rifts. But the Neoproterozoic magmatism that has been attributed to a mantle superplume over 200 million years (from ca. 750 to 550 Ma) among the Asian Hun superterrane (also known as the Pan-Cathaysian blocks) [72, 73]. Our dataset (600, 750 Ma) is consistent with this plume event, where the heating of the plume caused the metamorphism of the basement. Therefore, we interpret that the Ningduo Group was originally formed during the Greenville period (from 991 to 1118 Ma) and was later overprinted by the magmatism associated with Neoproterozoic plume events (ca. 600 to 750 Ma). This also indicates that the North Qiangtang terrane is located on the margin of the Asian Hun superterrane.

The sample of Jitang Group (Y03) exhibits a broader range of age distribution and a larger peak area of age concentration distribution (Figure 11). This multi-peak characteristic suggests that the sample does not originate from a single source and has experienced multiple tectonic-thermal events. There are three distinctions observed in comparison to the previous two samples (Figure 11(f)), specifically: an increase in the proportion of ancient zircons (older than 1500 Ma); an augmentation in the age components ranging from 750 to 600 Ma; and the identification of metamorphic zircons aged between 226 and 249 Ma.

The oldest zircon grain found within this sample (3473 ± 5 Ma) significantly predates those in other samples, indicating a substantial increase in ancient zircon grain composition. This could potentially be attributed to the introduction of older and deeper materials.

The two prominent peaks between 1100 and 900 Ma align with those observed in the Ningduo Group and the peak within 2500–2350 Ma both indicating distinct Cathayan characteristics. It can be inferred that the Ningduo Group and the Jitang Group have similar provenance regions.

The peak age of 750–600 Ma represents the formation of metamorphic protolith, which is associated with the termination of the Rodinia break-up [74]. The rift basins, developed against this geological background, can provide an excellent sedimentary environment. And we adopt the younger peak age to represent the age of rock formation (618 Ma). Furthermore, it also represents that the North Qiangtang terrane was in the southern margin of the Cathaysian continent during this period.

Additionally, records within the interval of 500–350 Ma all fall within the main peak area of Youxi Group (c. 426 Ma) (Figure 11(f)), suggesting the Jitang and Youxi groups potential shared the influence of the proto-Tethys over multiple periods [75].

The presence of zircons with ages between 226 and 249 Ma is related to the closure of the paleo-Tethyan Ocean (Figure 11(f)) [29]. Additionally, it should be noted that the low Th/U ratio (average 0.06) exhibited by these zircon analyses suggests their involvement in a metamorphic event related to the closure of paleo-Tethys.

Thus, the Jitang Group shares a similar provenance with the Ningduo Group and has undergone comparable tectonic-thermal events as the Youxi Group. Additionally, during the closure of the paleo-Tethyan Ocean, some deep-seated materials were incorporated.

The age distribution of the South Qiangtang terrane is similar to that of adjacent terranes (e.g. Cathaysia, Western Laurentia, Northern India, and Tethyan Himalaya), but there are still some important differences: (1) Age peak from the Indian and the Tethyan Himalayan terranes was absent during the 600–750 Ma period, which is different from our samples of the North Qiangtang (Y02 and Y03) (Figure 11(e) and (f)); (2) The proportion of older zircons (older than 1150 Ma) in Y04 is lower than that in Y02 and Y03 (Figures 11(e)–11(g)); (3) There is no record of less than 500 Ma in Y02 (Figure 11(e)). These distinctions indicate that the North Qiangtang shows close affinity with the Cathaysian continent before c.600 Ma, while the South Qiangtang is similar to the Gondwana terrane.

In the ε_Hf(t) value versus zircon crystallization age diagram (Figure 12), most analytical results of the three samples fall below the chondrite evolution line (CHUR), with a small amount distributed above it. This suggests that the primary source of these rocks is likely ancient material recycled from the crust, with only minor contributions from newer crustal materials.

The T_DM2(Hf) (Figure 12, appendix table 2) results of the Ningduo Group (Y02) are predominantly concentrated around 1.5–2.5 Ga and the εHf(t) value was mainly negative at ~1000 Ma, both corresponding to the crustal reconstruction documented by [76], Cathaysian continent. The T_DM2(Hf) of the Youxi Group (Y04) results primarily cluster around ~1.6 Ga and the ε_Hf(t) values evolved to negative values during 1000–200 Ma, both coinciding with the typical characteristic age observed in Gondwana-related terranes within the Tibetan Plateau [33]. The T_DM2(Hf) of the Jitang Group (Y03) results exhibit both 1.5–2.5 Ga and ~1.6 Ga, with ε_Hf(t) primarily exhibiting negative values, indicating distinct ancient crustal material sources for the Ningduo Group and Youxi Group while suggesting complex material origins for the Jitang Group.

The Nd crustal model ages (T_DM[Nd]) in the whole rock analyses correspond well with the T_DM2(Hf) characteristics [77] (Table 3 in Appendix). The T_DM(Nd) of the Y02 is greater than those of the Y03 and Y04 (Table 3 in the Appendix). This indicates that the formation age of the North Qiangtang terrane is older than the South Qiangtang, and the Y03 consists of a mixture of other two materials. Furthermore, both Sr-Nd isotopic compositions of the Y02 and Y03 fall within an old material region associated with lower crustal rocks similar to Proterozoic metamorphic sedimentary rocks from Cathaysian [78, 79]; whereas for Y04, falls into the upper crust region (Figure 13). These analyses suggest that the Y02 and Y04 basement rocks have undergone distinct crustal evolutionary processes. In comparison to the South Qiangtang terrane, the North Qiangtang terrane suggests a protracted period of crustal recycling.

At the same time, previous studies have demonstrated that the characteristics of sedimentary cover also serve as a significant basis for distinguishing terrane attribution. For instance, Ordovician-Devonian is exclusively present in the north edge of South Qiangtang terrane and exhibits a set of shallow marine carbonate formations with stable continental margin platform sedimentary features [80]. The Late Carboniferous and Early Permian sedimentary structure is characterized by immature clastic rocks interspersed with basic volcanic rocks, indicating an active continental margin environment hosting cold-water species and iceberg deposit anagenite [81]. We found that the Paleozoic sedimentary cover in South Qiangtang and the accretionary wedge on Gondwana’s northern margin record by Zhang et al. [82] are comparable.

There is a typical coral fossil in the Cathaysian continent named Guizhouphyllum-Yuanophyllum assemblage from the Lower Carboniferous Series, which consists of stable platform carbonate formations with well-developed corals, sponges, and other biological reefs [33]. During the same period in the North Qiangtang region, shallow sea and shore-shallow sea carbonate formations prevailed with abundant organisms [83], then in the Late Permian, it transitioned into ocean-land or non-marine environments developed famous Gigantopteris flora along with coal seams [84]. Therefore, considering similar sedimentary, biological, and tectonic characteristics from the Devonian to Permian, the North Qiangtang area shows good affinity with Cathaysian continent in sedimentary cover.

Through our analyses, we identified four significant temporal intervals from Rodinia to paleo-Tethys. In these intervals, the South Qiangtang consistently occupied the northernmost margin of the Great India continent before they are separated, while the North Qiangtang was situated at the southernmost margin of the Cathaysian continent from Rodinia to Proto-Tethys. This is the same view as Wang et al. [54] and Ma et al. [74]. These crucial intervals can be succinctly described as follows: independent developments in the Rodinia period (Figure 14(a)); transoceanic (Proto-Tethys) connection with Gondwana (Figure 14(b)); the paleo-Tethyan Ocean opening (Figure 14(c)); and the closure of paleo-Tethyan Ocean and subsequent collision (Figure 14(d)).

Phase I: In this study, the detrital zircon records from the Ningdo Group show a strong correlation with the Cathaysian continent (1100, 900 Ma). Additionally, there are records on both sides of the North Qiangtang terrane (750, 600 Ma), suggesting that it had been separated from the Cathaysian continent (Figure 11). The fragmentation could be attributed to sustained tectonic activity resulting from the superplume (750, 600 Ma) [85]. The detrital zircons found in the Youxi Group from the South Qiangtang Terrane provide evidence for their association with Gondwana (1150, 1000 Ma). Furthermore, numerous documents support its long-standing position on the northern side of the Gondwana [83].

According to the tectonic affinity and restoration map of Rodinia supercontinent, we propose that the South Qiangtang terrane is situated at the northernmost margin of the Greater India plate, while the North Qiangtang is positioned at the southernmost margin of the Cathaysian continent. In this tectonic configuration, these two regions are likely separated by thousands of kilometers [86] (Figure 14(a)).

Phase II: The reconstruction is based on the peak ages (500, 350 Ma) of the Y03 and Y04. This age range is in the age scale of the proto-Tethyan subduction [87]. During this time, we suggest that Cathaysian and Gondwana may have shared a similar latitudinal value despite not being contiguous, potentially delimited by the Proto-Tethyan Ocean within the Asian Hun superterrane (Figure 14(b)). The break-up of Rodinia in phase I provided a closer position between the North and South Qiangtang terranes. Subsequently, with the emergence of the paleo-Tethyan Ocean, a noticeable disparity in latitude between the Cathaysian continent and Gondwana continent became apparent.

Phase III: The sites of Y03 and Y04 are close to the paleo-Tethyan suture zone, and their zircon age distribution shows that they have been strongly influenced by the evolution of the paleo-Tethyan Ocean (ca. 250 Ma). The geochronological evidence of ophiolite, magmatite, and molasse formation also points to the same closure time of paleo-Tethyan Ocean along the Longmu Co-Shuanghu suture zone [29]. Furthermore, it is close to the evolution time of the Jinshajiang Paleo-Tethyan Ocean [88], suggesting multiple branch ocean basins within the paleo-Tethyan tectonic domain.

Consequently, this tectonic model inevitably leads to the distance between the North Qiangtang terrane and the Cathaysian continent. This resulted in the evolution of a multi-island chain ocean pattern of the paleo-Tethys (Figure 14(c)).

Phase IV: The ongoing expansion of the Neo-Tethyan Ocean and the closure of the Paleo-Tethyan Ocean amalgamated the North and South Qiangtang terranes to the south margin of' the Laurasia continent (Figure 14(d)) [24]. Consequently, the Mesozoic basins within the newly amalgamated Qiangtang terrane exhibit comparable stratigraphic sedimentary characteristics and tectonic evolution paths. The Jitang Group and Youxi Group, both located near the suture zone, effectively document the tectonic event (213, 249 Ma), which is represented by the youngest age peak in all samples.

We have investigated the gneissic rocks in three groups in the Qiangtang terranes through petrology, whole rock geochemistry, and isotope chronology, to examine their protolith characteristics, provenance characteristics, and tectonic evolution. The key findings are as follows:

1. The basement rock sample from Ningduo Group (Y02) has a felsic protolith composed of lithic feldspar greywacke. The provenance for that is probably the Greenville basement of southern Cathaysian. The major sources include recycled sediments and island arc volcanic rocks. And suggest that the North Qiangtang basement underwent the metamorphism induced by mantle plume (656, 699 Ma).

2. The protolith of the Jitang Group sample (Y03) consists of felsic lithic greywacke with hybrid terrigenous sedimentary sources. It potentially has a similar provenance to Ningduo Group. The Jitang Group formed rapidly after the break-up of Rodinia (603, 743 Ma) and subsequently underwent metamorphism during the transition from the proto-Tethys to the paleo-Tethys stages (545, 226 Ma).

3. Located at the southern region of the South Qiangtang terrane, the protolith of the Youxi Group basement rock (Y04) is characterized as I-type granites. These granites are formed by the partial melting of upper crustal materials during the subduction of the Proto-Tethys. Intense metamorphism occurred due to the closure of the paleo-Tethyan Ocean (213, 249 Ma) and subsequent collision orogeny.

4. The analyses (Sr-Nd and Lu-Hf isotopic systems) show that samples Y02 and Y03 have a more prolonged recycling process than Y04 and are associated with the Cathaysian terrane. The primary two age peaks of Y02 and Y03 are identical. But the other peaks suggest that they have experienced distinct metamorphic events. These differences can be attributed to the spatial location of the two groups: Ningduo Group is situated within terrestrial interior and has experienced a lesser impact from oceanic opening and closing as well as orogenic collisions. The Jitang Group is located on the terrane boundary and has been significantly influenced by late tectonic metamorphism.

5. Our study indicates that the South and North Qiangtang terranes should possess distinct tectonic affiliations, the North Qiangtang area is closely linked to the Cathaysian continent, while the South Qiangtang region exhibits connections with the Gondwana continent. Additionally, this study proposes a potential scenario wherein the North Qiangtang was once part of the Cathaysian continent but eventually separated from it during the Neoproterozoic and Paleozoic eras. Consequently, we infer that the Longmu Co-Shuanghu suture zone serves as a primary boundary between the northern margin of the Gondwana and the southern margin of the Cathaysia.

All data in this study are presented in supporting information and can be achieved at https://www.scidb.cn/(data archiving is underway). Furthermore, all data have already uploaded as Supporting Information for review purposes. Published data in the literature (Figure 11): Cathaysia data are available through Yao et al. [62] via https://doi.org/10.1016/j.gr.2011.01.005, Western Laurentia data are available through Hedhli et al. [63] via https://doi.org/10.2113/2022/ 209585729, Northern India data are available through Cawood et al. [67] via https://doi.org/10.1016/j.epsl.2006.12.006, Tethyan Himalaya data are available through Gao et al. [68] via https://doi.org/10.1016/j.sedgeo.2022.106144.

The authors declare that there is no conflict of interest regarding the publication of this article.

This study was financially supported by Xinjiang Science and Technology Department Project（2024B03018-1）and National Science and Technology Major Project (2021YFB2301401-01).

Supplementary information with four tables containing Zircon U-Pb isotope data, zircon Hf isotope data, whole rock Sr-Nd isotope data and whole rock major-trace element data. Large table, upload as separate file, captions only (with files uploaded separately) in this document.

Table S1. Zircon U-Pb isotope data.

Table S2. Zircon Hf isotope data.

Table S3. Whole rock Sr-Nd isotope data.

Table S4. Whole rock major-trace element data.