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The final subduction and suture of the Paleo-Asia Ocean (PAO) are controversial, and the key to this question is to locate the latest subduction/final suture of the accretionary type orogenic belt....

The Biesituobie A-type batholith in West Junggar in NW China of the Central Asian Orogenic Belt contains metapelite xenoliths derived from the contact metamorphic aureole. These xenoliths could be divided into two types: biotite-muscovite-andalusite hornfels and cordierite-alkaline feldspar-sillimanite-corundum gneiss, indicating prograde metamorphism. The phase equilibrium modeling on the cordierite-alkaline feldspar-sillimanite-corundum gneiss sample yielded a peak condition of P = 3.0−4.0 kbar, T = 760−800 °C. Similarly, the Na-in-cordierite geothermometer yielded a peak condition of T = 771−780 °C. The temperature of the peak metamorphism could be considered as a lower limit of the temperature of the Biesituobie A-type batholith. On the contrary, the Ti-in-zircon geothermometer applied to the Biesituobie A-type batholith zircons yields a mean temperature of 672 ± 22 °C. It suggested that the application of Ti-in-zircon geothermometer on A-type magma may involve a >100 °C underestimation. Zircon U-Pb dating indicates that the age of the contact metamorphism is between 263 and 286 Ma, consistent with the age of the pluton at 274 Ma. The result of 760−800 °C calculated from the contact metamorphic aureole of the Biesituobie batholith put a lower limit on considering the temperature condition of the A-type granite series from a metamorphic constraint.

The comprehensive investigation of orogenic-related litho-structural assemblages, metamorphism, and geochronology in early Precambrian orogens can help us better understand the features of plate tectonics in early Earth. The Paleoproterozoic Aketashitage orogenic belt is located at a key position in northwestern China and connects the North China craton, Tarim craton, Altaids orogen, and Tethys orogen. Garnet-bearing mafic and paragneissic granulite occur as interlayers or blocks preserved within paragneissic matrix, and two to three generations of metamorphic mineral assemblages were identified. Geothermobarometry and pseudosection modeling yielded clockwise metamorphic P-T paths passing from 7.5–8.6 kbar/575–715 °C (M1) through 7.4–12.2 kbar/715–895 °C (M2) and finally to 5.2–7.3 kbar/710–800 °C (M3) for the mafic and paragneissic granulite as well as amphibolite, which is indicative of metamorphic features of subduction/collision zones. Peak metamorphic P-T conditions of all the samples lie in the medium P/T facies series, suggesting that the thermal gradient (∼20–31 °C/km) of this Paleoproterozoic orogenic belt was obviously higher than most of the Phanerozoic subduction zones. Secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of zircon and monazite yielded metamorphic ages of ca. 1.98–1.96 Ga in the eastern part of the orogen, ca. 1.86–1.85 Ga in the western part, and a maximum depositional age of ca. 2.06 Ga for paragneiss. Compared with previous studies, the Aketashitage orogen is composed of unordered juxtaposition of diverse, subduction-related tectono-metamorphic blocks with different protoliths, metamorphic grades, and ages preserved within the paragneissic matrix deposited in the Paleoproterozoic, which is highly similar to Phanerozoic mélange. A Paleoproterozoic subduction-metamorphic-exhumation-accretionary process was deciphered, similar to that found in accretionary/orogenic wedge in Phanerozoic orogens. The juxtaposition of diverse, subduction-related tectonic blocks with contrasting ages and metamorphic features can serve as a marker of early Precambrian orogens and plate tectonics.

Early Palaeozoic evolution of the Kazakhstan orocline in the Central Asian Orogenic Belt (CAOB) is key to reconstructing the Palaeozoic tectonic framework in Central Asia. This study presents field...

Garnet amphibolite and semi-pelitic gneiss preserving three stages of metamorphic mineral assemblages, i.e., the prograde metamorphic inclusion assemblage (M1) preserved in the garnet porphyroblast, metamorphic peak assemblage (M2) and retrograde symplectic assemblage (M3), have been recognized in the Aketashitage area, northwestern China. Geothermobarometric computation shows that the M1, M2 and M3 assemblages record the metamorphic P-T conditions of 600–700 °C/4.2–5.3 kbar, 730–790 °C/6.3–7.1 kbar, and 770 °C/5.6 kbar, respectively. These three metamorphic stages define clockwise P-T paths including nearly isothermal decompression (ITD) process, indicating typical orogenic metamorphism. The peak metamorphic P-T conditions reach the transition zone between the high amphibolite facies and granulite facies, and belong to intermediate P/T facies series. The SHRIMP and LA-ICP-MS U-Pb dating of metamorphic zircon implies that the subduction might occur as early as ∼1.97 Ga and last as late as 1.84 Ga. Combined with literature data, it is concluded that the Aketashitage area was a Paleoproterozoic orogenic belt, which is possibly related to the assembly of the basements of the Columbia supercontinent.

Garnet-bearing mafic granulites occur as lenses within TTG gneiss or metapelite in the Fuping Complex, middle Palaeoproterozoic Trans-North China Orogen. They are composed mainly of garnet, clinopyroxene, orthopyroxene, hornblende, plagioclase, quartz and accessary zircon and titanite. Four stages of metamorphic mineral assemblages have been found in these mafic granulites: (a) the prograde assemblages (M1) are inclusions preserved in the garnet porphyroblasts, including clinopyroxene, hornblende, plagioclase and quartz; (b) the metamorphic peak assemblages (M2) consist of garnet porphyroblasts plus matrix minerals clinopyroxene + orthopyroxene + hornblende + plagioclase + quartz + zircon + titanite; (c) the first retrograde assemblages (M3) are represented by clinopyroxene + orthopyroxene + plagioclase + quartz symplectites rimming the garnets; and (4) the final retrograde assemblages (M4) are hornblende + plagioclase + quartz symplectites rimming or adjacent to the garnets. The retrieved metamorphic P-T paths pass from 530–600 °C/6.5–7.0 kbar (M1) through 680–820 °C/7.2–11.7 kbar (M2) to 730–760 °C/3.2–3.9 kbar (M3) and finally to 600–640 °C/3.2–3.7 kbar (M4). All the P-T paths of the mafic granulites are clockwise, two of these even contain near isothermal decompression (ITD) and subsequent near isobaric cooling (IBC) segments. SHRIMP U-Pb dating of metamorphic zircons of the mafic granulites yields a mean weighted age of ∼1849 ± 9Ma, which is consistent with the metamorphic time of surrounding TTG gneisses. Therefore, the Fuping Complex records the collision event between the Eastern and Western Blocks of the North China Craton that led to the final assembly of this craton during the late Paleoproterozoic.

Mafic and felsic granulite from the Miyun metamorphic complex, northeast Beijing, North China Craton, occur as either interlayers or lenses within the Late Archean TTG gneiss. In the mafic granulite, the metamorphic peak assemblages (M1) are represented by porphyroblast minerals plus matrix minerals (orthopyroxene + clinopyroxene + plagioclase + quartz ± K-feldspar ± hornblende ± biotite) as well as accessory minerals of zircon + apatite + ilmenite ± magnetite, the post-peak assemblages (M2) are characterized by “red-eye socket” symplectites (garnet + clinopyroxene + plagioclase + quartz) rimming the orthopyroxene or clinopyroxene porphyroblast as well as accessory minerals of rutile, and the final retrograde assemblages (M3) are marked by the hornblende-biotite intergrowth. As for the felsic granulite, the peak assemblages (M1) are represented by the porphyroblast and matrix minerals (garnet + orthopyroxene + biotite + plagioclase + quartz ± K-feldspar) as well as accessory minerals in the matrix (zircon + monazite + apatite + pyrite), the post-peak assemblages (M2) are characterized by “red-eye socket” symplectites (garnet + plagioclase + quartz) rimming the orthopyroxene porphyroblast, and the final retrograde assemblages (M3) are marked by the biotite-calcite intergrowth. Geothermobarometric computation suggests that the M1, M2 and M3 assemblages of the mafic granulite were formed under P-T conditions of ∼800 to 860 °C/∼6 to 10 kbar, ∼620 to 700 °C/11 to 12 kbar and ∼590 to 660 °C/4 to 6 kbar, respectively, suggesting that these granulites record anticlockwise P-T paths including final nearly isothermal decompression (ITD) segments, indicative of orogenic process. For the felsic granulite, metamorphic P-T conditions of the M1 and M3 assemblages were estimated to be ∼680 to 750 °C/6–8 kbar and ∼670 to 680 °C/5 kbar, respectively, also including ITD process. The widely penetrative gneissosity of the granulite and these P-T paths, suggest a collisional event of cold nappes overthrusting on hot ones or hot nappes being buried/subducted into cold ones and finally experienced fast tectonic exhumation. High-precision SIMS and LA-ICP-MS U-Pb dating of metamorphic zircon of the granulite suggest that the metamorphism occurred at ∼2.5 Ga. These data confirm that the Miyun metamorphic complex experienced a Neoarchean collisional event within the Eastern Block of the North China Craton.

Ultra-high pressure (UHP) metamorphism is recorded by garnet clinopyroxenite enclaves enclosed in an undeformed, unmetamorphosed granitic pluton, northeastern Paleozoic Dunhuang orogenic belt, northwest China. Three to four stages of metamorphic mineral assemblages have been found in the garnet clinopyroxenite, and clockwise metamorphic pressure-temperature (P-T) paths were retrieved, indicative of metamorphism of a possible subduction environment. Peak metamorphic P-T conditions (790~920 °C/28~41 kbar) of garnet clinopyroxenite suggest that they experienced high pressure to UHP metamorphism, and the UHP metamorphism occurred in the coesite- or diamond-stability field. The UHP metamorphic event is further confirmed by the occurrence of high-Al titanite enclosed in the garnet, along with at least three groups of aligned rutile lamellae exsolved from within the garnet. SIMS U-Pb dating of metamorphic titanite indicates that the post peak, subsequent tectonic exhumation of the UHP rocks occurred in the Devonian (~ 389~370 Ma). These data suggest that part of the Paleozoic Dunhuang orogenic belt experienced UHP metamorphism, and diverse metamorphic facies series prevailed in this orogen in the Paleozoic. It can be further inferred that most of the UHP rocks of this orogen are now buried in the depth.

Amphibolites in the Shuixiakou area of the southern Dunhuang Orogenic Belt, southernmost Central Asian Orogenic Belt (CAOB), occur as lenses within hornblende-biotite-plagioclase gneiss or pelitic schist, exhibiting block-in-matrix feature of tectonic mélange. Three generations of metamorphic mineral assemblages (M1, M2, and M3) have been recognized in the garnet-bearing amphibolite lenses. The metamorphic prograde assemblage (M1) is documented with inclusion trails (hornblende + plagioclase + quartz) within garnet porphyroblasts, and are estimated to be formed under 610–690 °C and 6.5–10.2 kbar. The metamorphic peak assemblage (M2) consists of garnet + hornblende + clinopyroxene + plagioclase + quartz in the matrix and records metamorphic peak P-T conditions of 720–750 °C and 13.4–14.7 kbar. The retrograde assemblage (M3) is represented by the symplectic assemblage (hornblende + plagioclase + quartz ± biotite ± magnetite) rimming the garnet porphyroblast, formed in the decompression stage under P-T conditions of 630–730 °C and 3.8–7.2 kbar. The derived metamorphic P-T paths show similar tight clockwise loops including nearly isothermal decompression processes, typical of orogenic metamorphism. SIMS dating of metamorphic zircons from the amphibolites confirm that the high-pressure metamorphism (M2) occurred at ca. 438–398 Ma.

The discrete mafic granulite and amphibolite enclaves within the Pingyang trondhjemitic pluton, Fuping metamorphic terrane, middle Trans-North China Orogen, ubiquitously record three stages of metamorphic assemblages. For the mafic granulite enclaves, the prograde metamorphic assemblage (M1) is represented by mineral inclusions (clinopyroxene + hornblende + plagioclase + quartz ± apatite) preserved in the garnet porphyroblast, the metamorphic peak (M2) assemblage consists of garnet and matrix minerals of clinopyroxene + orthopyroxene + hornblende + plagioclase + quartz ± magnetite ± ilmenite ± zircon, and the retrograde (M3) stage is represented by symplectite assemblage of orthopyroxene + plagioclase ± clinopyroxene ± hornblende ± quartz rimming the garnet porphyroblast. The metamorphic P-T paths of the mafic granulite enclaves are defined to pass from 560–750 °C/6–9 kbar (M1) through 740–880 °C/11–14 kbar (M2) to 720–800 °C/6–8 (M3), indicative of a collisional orogenic process. The metamorphic P-T path of the amphibolite enclave experienced from 670–730 °C/9.3–11.8 kbar to 710–730 °C/3.9–5.5 kbar, further certify such metamorphic feature of an orogenic belt. SIMS U-Pb dating of zircons of the trondhjemitic gneiss yields the magmatic crystallization age of ∼2.52 Ga, and both the trondhjemitic gneiss and the mafic granulite enclaves yield the metamorphic age of ∼1.89–1.86 Ga. Therefore, it can be concluded that the Fuping terrane was involved in the late Palaeoproterozoic subduction-collision-uplifting tectonic process caused by amalgamation of the Eastern and Western Blocks of the North China Craton along the Trans-North China Orogen.

The Hongliuxia tectonic melange of the southern Dunhuang terrane, northwestern China, southernmost Central Asian Orogenic Belt (CAOB), consists of eclogite, mafic granulite, and amphibolite as puddingstones within a matrix of metapelitic gneiss and marble; these rocks are interpreted to be part of an ancient subduction zone setting. Secondary ion mass spectrometry U-Pb dating of metamorphic zircons obtained from the puddingstones and matrix metapelite suggests that the metamorphism occurred at ca. 428–391 Ma. The metamorphic rocks all record similar clockwise metamorphic pressure-temperature-time ( P - T - t ) paths of the western Alpine type. However, remarkable differences between metamorphic peak P - T conditions ranging from 830 °C and 24.2 kbar for the eclogite puddingstone to 700 °C and 10.2 kbar for the metapelite matrix were found in the melange rocks. This indicates the mixing of rocks from significantly different depths to create a tectonic melange in a subduction channel, possibly juxtaposed during the uplift stage. These data suggest that the southernmost CAOB underwent subduction and subsequent exhumation caused by subduction of the Paleozoic Hongliuxia ocean during the middle Silurian to middle Devonian.

Garnet-bearing mafic granulites and amphibolites from the Hongliuxia area of the southern Dunhuang orogenic belt, northwestern China, commonly occur as lenses or boudinages enclosed within metapelite or marble, which represent the block-in-matrix feature typical of orogenic melange. Three to four generations of metamorphic mineral assemblages are preserved in these rocks. In the high-pressure amphibolites, prograde mineral assemblages (M1) occur as inclusions (hornblende + plagioclase + quartz ± chlorite ± epidote ± ilmenite) preserved within garnet porphyroblasts, and formed at 550–590 °C and 7.7–9.2 kbar based on geothermobarometry. The metamorphic peak mineral assemblages (M2) are composed of garnet + hornblende + plagioclase + quartz + clinopyroxene, as well as titanite + zircon + rutile + apatite as accessory minerals in the matrix, and are estimated to have formed at 640–720 °C and 14.1–16.0 kbar. The first retrograde assemblages (M3) are characterized by “white-eye socket” symplectites (hornblende + plagioclase + quartz ± biotite ± epidote ± magnetite) rimming garnet porphyroblasts, which formed at the expense of the garnet rims and adjacent matrix minerals during the decompression stage under P – T conditions of 610–630 °C and 5.6–11.8 kbar. The second retrograde assemblages (M4) are intergrowths of actinolite and worm-like quartz produced by the breakdown of the matrix hornblendes, and formed under P – T conditions of ∼490 °C and ∼2.8 kbar. For the high-pressure mafic granulites, the prograde assemblages (M1) are represented by plagioclase + quartz preserved within the garnet porphyroblasts. The metamorphic peak assemblages (M2) are garnet + matrix minerals (clinopyroxene + plagioclase + quartz + hornblende + rutile + zircon) and were estimated to have formed at ∼680 °C and ∼15.4 kbar. The retrograde assemblages (M3) are characterized by fine-grained patches of hornblende + plagioclase + quartz rimming the garnet porphyroblasts, as well as hornblende rimming clinopyroxene in the matrix, and were inferred to have formed at ∼620 °C and ∼4.2 kbar. For the metapelitic gneiss, the metamorphic peak assemblages are the garnet porphyroblasts plus the matrix minerals (biotite + plagioclase + quartz + ilmenite + zircon), which were estimated to have formed at ∼630 °C and ∼8.9 kbar. The mafic granulites and amphibolites record fairly similar clockwise P–T paths that include nearly isothermal decompression processes, which suggest that they experienced subduction and subsequent rapid tectonic exhumation. SIMS and LA-ICP-MS U–Pb dating of zircons and 40Ar/39Ar dating of hornblende suggest that the metamorphism occurred at ∼430–390 Ma. Field occurrences, different protolith ages of the mafic granulites and amphibolites, and the considerable gap in peak P – T conditions between the amphibolite and mafic granulite boudinages and their country rock may suggest a melange accumulation process during the Paleozoic caused by the Silurian–Devonian orogeny, which is possibly associated with the closure of the Liuyuan ocean, a branch of the Paleo-Asian ocean near the southern Central Asian Orogenic Belt.

The Trans-North China Orogen has witnessed the assembly of the Western and Eastern blocks of the North China Craton during Late Paleoproterozoic. Numerous studies have focused on the subduction/collision timing and metamorphic evolution of the Trans-North China Orogen, whereas the thermal evolution and exhumation history are still poorly understood. The Fuping and Wutai Complexes are widely exposed of middle- to high-grade metamorphic rocks, which are excellent regions to investigate the thermal evolution and exhumation history of the Trans-North China Orogen. Previous U-Pb geochronological data of metamorphic zircon and monazite suggest that the peak granulite facies metamorphism in the Fuping Complex occurred during 1.92–1.80 Ga, and peak amphibolite facies metamorphism in the northeastern part of the Wutai Complex happened at 1.85–1.82 Ga. Here we report newly obtained hornblende 40Ar/39Ar age of 1813–1806 Ma in the Fuping Complex, and biotite 40Ar/39Ar age of 1802–1786 Ma in the northeastern part of the Wutai Complex, which representing the cooling ages. Combined with previous thermochronological data, the cooling rate of 2.0–8.5 °C/Ma was obtained for the middle to southern segments of the Trans-North China Orogen, possibly suggesting a moderate to fast exhumation relative to other Proterozoic orogens.

The Paleoproterozoic Aketashitage orogenic belt lies in between the two large accretionary orogenic systems, i.e., Paleo-Asian ocean and Paleo-Tethys ocean systems, in northwest China. Previous geochronologic studies reveal widespread Paleoproterozoic orogeny-related magmatism and high-grade metamorphism in this area, determined by the U-Pb dating of zircon and monazite. In this paper, 40Ar/39Ar dating of hornblende of three representative amphibolite samples yielded cooling ages of ∼1.88–1.85 Ga. Comparison of the zircon/monazite U-Pb and hornblende 40Ar/39Ar ages suggests that these amphibolite samples record different exhumation and cooling processes. These new geochronologic data further confirm that the Aketashitage orogenic belt only records Paleoproterozoic metamorphism but no overprint of Paleozoic thermal event. It is thus inferred that the Aketashitage area might act as a continental fragment/terrane which was passively collaged onto the ambilateral Paleozoic orogens but was not involved in the Paleozoic subduction.

The Wutai Complex lies in the middle part of the Trans-North China Orogen, mainly consisting of metamorphosed volcanic-sedimentary rocks (named as “Wutai Group”) and Late Archean TTG gneisses. Garnet biotite schist from the northeastern part of the Wutai Group (lower Shizui Subgroup) mainly consists of garnet porphyroblast plus biotite, staurolite, kyanite, sillimanite/fibrolite, plagioclase, quartz as well as accessory minerals including ilmenite, magnetite, hematite, apatite, monazite and zircon. Petrographic observation and mineral chemistry indicate that these metapelites underwent the sequential prograde (M1), peak (M2) and retrograde (M3) metamorphic stages. Geothermobarometry computation and phase equilibrium modelling show that the representative samples record clockwise P-T paths passing from 3–7 kbar/570–630 °C (M1) through 9–10 kbar/615–660 °C (M2P) to 6–9 kbar/655–680 °C (M2T) and finally to a speculated exhumation stage (M3), indicative of orogenic metamorphism. SRHIMP and LA-ICP-MS U-Pb dating on inherited detrital zircons yielded three age peaks of ~2.7 Ga, ~2.5 Ga and ~2.1 Ga. The youngest 207Pb/206Pb age of 2064 ± 21 Ma of detrital zircon possibly constrains the maximum depositional age of the Shizui Subgroup. SIMS and SHRIMP U-Pb dating of metamorphic monazite and zircon constrain the metamorphic age of the garnet-bearing mica schist to be 1853–1823 Ma. Combined with previous data, the Wutai Complex was demonstrated to have been involved in a prolonged subduction-collision process (1.97–1.82 Ga) between the Western and Eastern Blocks in the Paleoproterozoic.

The Miyun area is located in the western margin of the Eastern Block of the North China Craton (NCC), and granulite- to amphibolite facies tectono-metamorphic events occurred in the Precambrian. In this contribution, high-resolution secondary ion mass spectrometry (SIMS) U-Pb dating of metamorphic zircon from garnet-pyroxene amphibolite yielded the metamorphic age of 2507 ± 4 Ma. SIMS U-Pb dating of monazite from garnet-biotite gneiss yielded the metamorphic ages of 2496 ± 16 Ma and 1834 ± 21 Ma, respectively. Furthermore, 40Ar/39Ar dating of hornblende from amphibolite yielded plateau ages of 1817 ± 41–1795 ± 19 Ma, and the biotite yielded a plateau age of 1744 ± 12 Ma. Combined with previous studies and the closure temperatures of the dating minerals, it is inferred that the Miyun area experienced a late Neoarchean granulite-facies metamorphic event occurred at ~2.50 Ga, followed by a late Paleoproterozoic amphibolite-facies metamorphic event occurred at ~1.83–1.74 Ga. These two tectono-metamorphic events are ascribed to the Precambrian orogenic-related environments.

The Dunhuang region is located to the south of the Central Asian Orogenic Belt and connecting the Tarim Craton westerly and North China Craton easterly, respectively. It is an important position for understanding the geodynamics and tectonic framework of Central Asia. However, the issue about whether it is a Phanerozoic orogen or a Precambrian block is still controversial. Magmatic arcs are the most prominent and laterally persistent structural elements of orogenic belts and used to reconstruct now-disrupted orogenic belts. This paper concerns the petrogenesis and tectonic setting of andesitic-dacitic-rhyolitic volcaniclastic rocks and dacitic porphyries in the Sanweishan area, northern Dunhuang region. Volcaniclastic rocks overlie the metasedimentary rocks by fault and dacitic porphyries intrude into the metasedimentary rocks. The calc-alkaline signature and relative enrichment of large-ion lithophile elements of volcaniclastic rocks and dacitic porphyries seemingly favor a subduction setting. Zircon U-Pb dating results reveal the deposition at 424–414 Ma for volcaniclastic rocks and emplacement at ca. 364 Ma for dacitic porphyries. The coeval granitoid plutons in the Sanweishan area show arc geochemical signature and are originated from partial melting of the subducted sediments based on the available data. Paleozoic volcanic-subvolcanic rocks and plutons in this area probably represent a magmatic arc developed on the accretionary complex, resembling the arc magmatic rocks formed in the Nankai complex, SW Japanese Island arc. Our results provide constraints on the existence of the Paleozoic magmatic arc in the northern Dunhuang region and suggest the so-called “Dunhuang block” is virtually a Phanerozoic orogen rather than a Precambrian block.

High-pressure mafic granulite and garnet amphibolite are identified as small-scale tectonic slices within pelitic or semi-pelitic gneiss in the Kalatashitage area, which is located in the western Paleozoic Dunhuang Orogenic Belt, northwestern China. These rocks retain three generations of metamorphic mineral assemblages: prograde assemblage (M1) preserved as inclusions within garnet porphyroblasts, metamorphic peak assemblage (M2) consisting of matrix minerals and garnet porphyroblasts, and retrograde assemblage (M3) mainly represented by the symplectic minerals surrounding the embayed garnet and the retrograded hornblende rimming matrix-type clinopyroxene. Metamorphic pressure and temperature (P-T) paths of high-pressure mafic granulite, amphibolite, and metapelite retrieved by thermobarometry are all clockwise, passing from 640 to 720 °C/6.2–12.6 kbar (M1) through 840–920 °C/14.6–16.2 kbar (M2) to 750–815 °C/5.5–7.9 kbar (M3) for high-pressure mafic granulite, from ~650 °C/5.7 kbar (M1) through ~750 °C/9.2 kbar (M2) to ~780 °C/8.1 kbar (M3) for amphibolite, and from ~615 °C/7.9 kbar (M1) through 730–820 °C/8.6–11.7 kbar (M2) to 675–740 °C/5.4–8.7 kbar (M3) for pelitic and semi-pelitic gneiss. Furthermore, pseudosection modeling of high-pressure mafic granulite indicates that the growth zonation of garnet porphyroblast exhibits prograde metamorphism in a P-T range of 510–800 °C/8.5–13 kbar and demonstrates peak metamorphic P-T conditions of ~850 °C/16 kbar, which are consistent with the thermobarometric estimates. The significant pressure differences in peak metamorphism observed in different rocks indicate that the rocks initially subducted to remarkably different depths and were subsequently juxtaposed at shallower crustal levels during exhumation. Sensitive high-resolution ion microprobe (SHRIMP) analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U Pb dating of metamorphic zircon indicates that the metamorphic events occurred at ca. 430–420 Ma (M2) and ca. 400–390 Ma (M3), respectively. Metamorphism was followed by the intrusion of granitic dykes at ca. 244 Ma. Moreover, the metamorphic evolution indicates that the Kalatashitage area was involved in the subduction, collision and subsequent tectonic exhumation in the Paleozoic. Combined with previous literature, it is inferred that the discrepant subduction and exhumation of high-grade metamorphic rocks is a universal phenomenon in the Paleozoic Dunhuang Orogenic Belt, supporting the ubiquitous existence of subduction-collision complexes in this orogenic belt.

As a key accessory mineral in metapelite, monazite forms in the metamorphic event and therefore, places important direct constraint on the timing of the tectono-metamorphic event. In this study, we investigate four representative metapelites from different metamorphic terranes in the central-south Trans-North China Orogen (TNCO), applying secondary ion mass spectrometry (SIMS) U–Th–Pb dating on monazite. The dating results reveal that monazite collected from the Huashan, Luoning, Zanhuang and Wutai metamorphic complexes record the metamorphic ages of ~1.83 Ga, ~1.95 Ga, ~1.85 Ga and ~1.91 to 1.83 Ga, respectively. Combined with the literature data of metamorphic geochronology on the discrete terranes within the TNCO, it is suggested that the amalgamation between the Western and Eastern Blocks of the North China Craton along the nearly NS-trending TNCO stared as earlier as ~1.97 Ga and continued to as late as ~1.80 Ga, which was in fact a long-lived tectono-metamorphic event.