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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.

Geothermobarometry and phase equilibria modeling were conducted for garnet-bearing amphibolite of the Inyoni Shear Zone (ISZ), southwestern Barberton Greenstone Belt, South Africa. The prograde (M1), metamorphic peak (M2) and retrograde (M3) metamorphic P-T conditions were estimated to be ∼560 °C/∼8 kbar, 660–730 °C/7–9.5 kbar and 570–630 °C/5–6 kbar, respectively. The amphibolite records clockwise P-T paths, and the metamorphic peak P-T conditions belong to the medium P/T facies series. The retrograde segment of the P-T path documents near isothermal decompression which may reflect relative fast exhumation. The estimated apparent geotherm is 20–30 °C/km. SIMS U-Pb dating of metamorphic zircon suggests that the metamorphism of the ISZ amphibolite have occurred during ∼3.26–3.22 Ga, and the metamorphic peak might occur at ∼3.24 Ga. Furthermore, 40Ar/39Ar dating of hornblende indicates that the cooling stage might occur at ∼3.20 Ga. It is anticipated that the protolith of the amphibolite of the ISZ may have been involved in a subduction-like tectonic process along with the TTG plutons and was metamorphosed during 3.26–3.22 Ga, then uplifted from within the surrounding TTG plutons at ∼3.20 Ga.

The newly discovered Daxintun Sb-Au deposit (Heilongjiang province, NE China) is located at the north-eastern margin of the Central Asian Orogenic Belt, and it is hosted by Neoproterozoic to Early-Cambrian two-mica schist and marble. The antimony-bearing minerals include stibnite, famatinite, tetrahedrite, boulangerite, freibergite, and minor andorite. Gold occurs largely as native gold microparticles (0.1–20 μm) with high fineness (974–983) accompanied by quartz, stibnite, calcite and pyrite. Fluid inclusions in ore-bearing quartz and calcite phases mainly comprise liquid–vapor and minor CO2-bearing three-phase types, and the gas phases contain CO2, CH4 and H2S. The Daxintun fluid inclusions homogenize at 111.8–353.4 °C and are of low salinity (0.53–12.51 wt% NaCl equiv.). The δ18OSMOW of the Daxintun quartz falls into a wide range (4.2‰–16.9‰), yet the δDSMOW falls into a narrow range (−108.0‰ to −87.3‰), suggesting that the ore-forming fluids formed from metamorphic fluids that mixed with meteoric water. The stibnite δ34S ranges between −0.9‰ and 5.1‰ (mean = 2.8‰). The stibnite has 206Pb/204Pb of 18.234–18.306, 207Pb/204Pb of 15.537–15.561 and 208Pb/204Pb of 38.103–38.227, implying a metamorphic fluid source. The conditions of gold and antimony precipitation are comprised of neutral pH and fluid mixing, with decreasing fS2 and fO2. Zircon U-Pb dating of the fine-grained Daxintun granite yields a Late-Jurassic age (154.0 ± 2.0 Ma), and the Daxintun diorite dike yields a weighted mean age of 122.1 ± 1.3 Ma. Stibnite Rb-Sr dating suggests that the Sb-Au mineralization has an age of approximately 152.8 ± 2.4 Ma. The observed ore deposit geology, as well as new data on the ore-forming fluids, H-O-S-Pb isotopes, and Rb-Sr geochronology, suggest that the Daxintun Sb-Au deposit is best described as an orogenic type gold deposit that formed during subduction of the Palaeo-Pacific and the Mongolia–Okhotsk Oceans during the Late-Jurassic.

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.

Metamorphic evolution and geochronology of pelitic granulites were reported for the first time in the Taihua metamorphic complex, Mts. Huashan area, southern segment of the trans-North China Orogen (TNCO). Three generations of metamorphic mineral assemblages are recognized: (1) the prograde metamorphic mineral assemblages (M1) are represented by mineral inclusions within the garnet porphyroblasts; (2) the metamorphic peak assemblage (M2) are the garnet porphyroblasts and minerals in the matrix (biotite + orthopyroxene + plagioclase + quartz + K-feldspar + ilmenite + zircon + magnetite); and (3) the retrograde metamorphic mineral assemblages (M3) are represented by the symplectic assemblages around the garnet porphyroblasts, resulted from decomposition reactions between garnet rims and neighboring minerals in the matrix. Calculated by both conventional thermobarometry and pseudosection modeling in the NCKFMASHT system using the Perple_X technique, the P–T conditions of these three metamorphic stages are constrained to be of 4–5 kbar/520–530 °C for the M1 stage, 6.8–8.6 kbar/730–810 °C for the M2 stage and 4.1–6.4 kbar/570–740 °C for the M3 stage, respectively. The derived clockwise P–T paths imply that the Mts. Huashan terrane involved in the subduction and subsequent collision between the Eastern and Western Blocks of the North China Craton (NCC) along the Palaeoproterozoic Trans-North China Orogen (TNCO). High resolution SIMS U–Pb dating of metamorphic zircons reveals the metamorphic ages of 1.85–1.82 Ga. Combined with geochronological data from the literature, it is concluded that the tectonothermal evolution between the Eastern and Western Blocks started as early as ∼1.97 Ga and lasted as late as 1.80 Ga. Furthermore, the eastern Taihua complex records older metamorphic ages and higher peak metamorphic pressures than those of the western Taihua complex, possibly suggesting an eastward subduction model for the TNCO.

The Taihua metamorphic complex in the southern part of the North China Craton is composed of tonalite-trondhjemite-granodiorite (TTG) gneisses, amphibolites, metapelitic gneisses, marbles, quartzites, and banded iron formations (BIFs). The protoliths of the complex have ages ranging from ∼2.1 to ∼2.9 Ga and was metamorphosed under the upper amphibolite to granulite facies conditions with NWW-SEE-striking gneissosity. Metapelitites from the Wugang area have three stages of metamorphic mineral assemblages. The prograde metamorphic mineral assemblage (M1) includes biotite + plagioclase + quartz + ilmenite preserved as inclusions in garnet porphyroblasts. The peak mineral assemblage (M2) consists of garnet porphyroblasts and matrix minerals of sillimanite + biotite + plagioclase + quartz + K-feldspar + ilmenite + rutile + pyrite. The retrograde mineral assemblage (M3), biotite + plagioclase + quartz, occurs as symplectic assemblages surrounding embayed garnet porphyroblasts. Garnet porphyroblasts are chemically zoned. Pseudosection calculated in the NCKFMASHTO model system suggests that mantles of garnet porphyroblasts define high-pressure granulites facies P–T conditions of 12.2 kbar and 830 °C, whereas garnet rims record P–T conditions of 10.2 kbar and 840 °C. Integrating the prograde mineral assemblages, zoning of garnet porphyroblasts with symplectic assemblages, a clockwise metamorphic P–T path can be retrieved. High resolution SIMS U−Pb dating and LA−ICP−MS trace element measurements of the metamorphic zircons demonstrate that metapelites in Wugang possibly record the peak or near peak metamorphic ages of ∼1.92 Ga. Furthermore, 40Ar/39Ar dating of biotite in metapelites suggests that the cooling of the Taihua complex may have lasted until ∼1.83 Ga. Therefore, a long-lived Palaeoproterozoic metamorphic event may define a slow exhumation process. Field relationship and new metamorphic data for the Taihua metamorphic complex does not support the previous model in which the Tran-North China Craton (TNCO) was formed through the collision between the East and West blocks.

The Taihua metamorphic complex exposes in the southern Trans-North China Orogen (TNCO) and records at least three episodes of magmatism. The Shanxian TTG gneisses obtained at 2.54–2.48 Ga have high SiO 2 , variable Mg# with high (La/Yb) N and Sr/Y ratios (15.08–93.26 with average of 37.31 and 7.33–115.05 with average of 49.59, respectively). They show negative Nb and Ta but positive Zr and Hf anomalies with low Nb/Ta and Gd/Yb, and high Zr/Hf and Zr/Sm ratios (4.97–18.8, 1.92–6.37, 23.71–50.26, and 29.18–75.23, respectively), and have positive e Hf (t) values (+1.7 to +7.9) and e Nd (t) values (+0.72 to +2.55), indicating that they were possibly produced by partial melting of lower crust derived from metasomatized lithospheric mantle with the residue of minor garnet. The Sihe granitic gneisses recorded at 2.35–2.30 Ga are enriched in silica, Al 2 O 3 contents (13.59–15.33), K 2 O/Na 2 O ratios (1.13–1.7), defined as high-Al TTG. They exhibit high Sr/Y, Zr/Sm and Zr/Hf ratios and low Nb/Ta and Gd/Yb ratios (44.71–83.09, 47.79–62.58, 36.05–37.43, 12.04–16.36, and 2.95–3.68, respectively) with negative Eu anomaly. Combined with Hf and Nd isotopes (−2.5 to +4.7 and −0.74 to +0.36), the Sihe granitic gneiss was possibly generated from partial melting of lower crust with minor ancient material contributions, leaving residual amphibole and minor garnet in the source. The Muce monzonitic gneisses emplaced at 2.17–2.16 Ga have high Mg#, Ni and Cr contents, constant Sr/Y and (La/Yb) N (42.39–50.33, 19.8–41.4, 33.6–74.2, 31.32–34.14, and 15.32–16.7, respectively), with relatively low and constant Dy/Yb ratio (1.82–1.85). Together with Hf and Nd isotopes (−6.5 to −0.9 and −2.07 to −2.86), the Muce monzonitic gneisses might be derived from partial melting of Neoarchean pre-existing crustal materials, possibly in an arc setting. It is therefore found that four episodes of crustal growth and/or reworking in the southern segment of the TNCO have occurred at 2.85–2.72 Ga, 2.57–2.48 Ga, 2.35–2.30 Ga and 2.2–2.0 Ga, respectively, likely to connect with the subduction–collision between the Eastern and Western Blocks along the TNCO in the North China Craton.

Garnet-bearing mafic granulite and amphibolite exposed as lenses, boudins, or interlayers within metasediments in the Qingshigou area, Dunhuang block, southernmost Central Asian orogenic belt, record important information for understanding the tectono-metamorphic evolution of subduction and collision zones in the southern Central Asian orogenic belt during the mid-Paleozoic. Three stages of metamorphic assemblages (M1, M2, M3) are recognized in the high- and medium-pressure mafic granulite and amphibolite. In the high-pressure mafic granulite, the prograde assemblage (M1) is represented by inclusion minerals (hornblende + plagioclase + quartz) preserved in garnet porphyroblasts; the metamorphic peak assemblage (M2) is characterized by garnet porphyroblasts and matrix minerals (garnet + clinopyroxene + plagioclase + quartz ± zircon ± titanite); and the retrograde assemblage (M3) is marked by coronitic symplectite (hornblende + plagioclase + quartz ± magnetite) rimming the garnet porphyroblasts. In the medium-pressure mafic granulite, the prograde assemblage (M1) of hornblende + plagioclase + quartz is included in the garnet porphyroblasts; the peak assemblage (M2) consists of garnet + orthopyroxene + clinopyroxene + plagioclase + quartz ± zircon ± titanite (M2) in the matrix; and the retrograde assemblage (M3) of hornblende + orthopyroxene + plagioclase + quartz (M3) surrounds the garnet porphyroblasts. In the amphibolite, the prograde assemblage (hornblende + plagioclase + quartz + ilmenite) is preserved as inclusions in garnet (M1); the peak assemblage (M2) is composed of garnet + hornblende + plagioclase + quartz ± zircon ± titanite; and the retrograde assemblage (M3), consisting of hornblende + biotite + plagioclase + quartz + epidote + magnetite, rings the garnet porphyroblasts. Geothermobarometric calculations suggest that the metamorphic pressure-temperature paths pass from 568 °C and 8.8 kbar through 607 °C and 10.6 kbar and 861 °C and 16.9 kbar and finally to 598 °C and 4.4 kbar for the high-pressure mafic granulite; from 756 °C and 9.0 kbar through 750–874 °C and 9.3–11.6 kbar to 675 °C and 4.7 kbar for the medium-pressure mafic granulite; and from 686 °C and 7.6 kbar through 715–766 °C and 10.6–11.2 kbar to 671 °C and 5.6 kbar for the amphibolite, and the paths show clockwise pressure-temperature loops typical of an orogenic process. The metamorphic peak of the high-pressure mafic granulite lies in the eclogite facies, which is indicative of a subduction zone environment. High-resolution secondary ion mass spectrometry (SIMS) U-Pb dating of metamorphic zircon indicates that the metamorphism occurred in the Early Silurian (ca. 430 Ma) and lasted for at least 65 m.y. This study reveals a possible southward subduction history of a branch of the Paleo–Asian Ocean, the Liuyuan Ocean, from the Silurian to Late Devonian, which may be an important event in the accretionary history of the Central Asian 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.

Garnet-bearing amphibolites and metapelites of the Luoning metamorphic terrane, Taihua metamorphic complex, southern terminal of the Palaeoproterozoic Trans-North China Orogen (TNCO), preserve different metamorphic mineral assemblages formed at three metamorphic stages in the Palaeoproterozoic. The prograde mineral assemblages (M1) comprise of hornblende + plagioclase + quartz ± biotite inclusions preserved in the garnet porphyroblasts in the amphibolites or quartz + biotite + plagioclase inclusions preserved in the garnet porphyroblasts in the metapelites. The metamorphic peak mineral assemblages (M2) are represented by the garnet porphyroblasts as well as the matrix minerals plagioclase + hornblende ± biotite + quartz in the amphibolites or quartz + biotite + plagioclase ± hornblende in the metapelites, respectively. The retrograde mineral assemblages (M3) are the worm-like, fine-grained “white-eye socket” symplectitic assemblages formed between the relict garnet porphyroblasts and the matrix minerals, consisting of plagioclase + hornblende ± biotite intergrowths in the amphibolites or plagioclase + biotite + quartz intergrowths in the metapelites, respectively. Geothermobarometric computation shows that the Luoning terrane records clockwise P – T trajectories including near isothermal decompression (ITD) processes, from 630–790 °C/5.3–8.9 kbar through 720–820 °C/8.9–10.7 kbar to 690–740 °C/7.1–7.7 kbar. SIMS U–Pb dating of zircons separated from the amphibolites and metapelites presents that the age of the protolith of the amphibolites is ∼2.32 Ga and the metamorphism occurred during 1.97–1.94 Ga, suggesting that the subduction–collision and the subsequent exhumation occurred in the late Palaeoproterozoic. Combined with the literature data of the different discrete terranes within the Trans-North China Orogen, it is further deciphered that the tectono-metamorphic event of the Trans-North China Orogen started as early as 1.97 Ga and lasted as late as 1.80 Ga, suggesting that the tectono-metamorphic event of the orogen is a long and complex history.

At Qianliyan Island, about 80 km East of Qingdao in the northern part of the South Yellow Sea of China, lenses and layers of eclogite and two-mica epidote–plagioclase gneiss occur within granitic gneiss. From the eclogite, peak metamorphic conditions of 775°C, 2.6 GPa were defined using compositions of garnet mantle zones, omphacite inclusions, and homogeneous phengite cores with high Si contents. During exhumation, the eclogite underwent different stages of retrogression, i.e . at amphibolite-facies (740–790°C, 1.60–1.75 GPa,), epidote-amphibolite-facies (640–690°C, 0.8–1.0 GPa), and, finally, at greenschist-facies conditions. Relics of omphacite and garnet in pyrite of the two-mica epidote–plagioclase gneiss, although obliterated in the rock matrix, prove this rock also to have experienced high-pressure (HP) metamorphic conditions. Similar HP metamorphic rocks occur at Sulu and Dabie in the west and at the Hongseong complex of South Korea in the east, enhancing the probability of a coherent HP/(UHP) belt ranging from Qinlin in the west towards the Korean peninsula in the east.

The South Yellow Sea basin in eastern China has experienced a multi-stage tectonic evolution history. The major structures were created when the basin was a foreland basin during the Mesozoic. However the geological evolution of the basin has not yet been corroborated by direct evidence from the underlying basement rocks. Qianliyan Island in the southern Yellow Sea provides an opportunity to study the formation and evolution of the basin by means of direct geochronological and geochemical evidence. On Qianliyan Island, basement rocks are exposed that consist of granitic gneiss, felsic gneiss and minor mylonite, and lenses of eclogite. Major and trace element characteristics of these four types of gneiss indicate that they originated from crustal material, varying in composition from pelite to greywacke. SHRIMP U-Pb zircon dating results of a felsic gneiss sample show that this rock crystallized between 659 and 796 Ma and underwent a metamorphic overprint at 229 ± 4 Ma. This age pattern resembles that of g...

High-resolution SIMS U–Pb dating of metamorphic zircons of the TTG gneisses, gneissic granitoid and amphibolites of the Lushan terrane, Taihua metamorphic complex, suggests that the metamorphism had taken place at least as early as ~1.96–1.86 Ga. These new dates, along with reference data, demonstrate that the southern and middle terranes of the Trans-North China Orogen had been involved in the continent–continent collision between the Western Block and the Eastern Block of the North China Craton. This orogenic process started as early as 1.96 Ga and lasted as late as 1.80 Ga.

Exposed in the southernmost terminal of the Palaeoproterozoic Trans-North China Orogen (TNCO), the garnet-bearing amphibolites in the Mts. Huashan metamorphic complex preserve three generations of mineral assemblages including the prograde, peak and retrograde metamorphic stages. The prograde metamorphic stage (M1) is recognized as inclusion-type mineral assemblages (hornblende + plagioclase + quartz ± biotite ± ilmenite) preserved in the garnet porphyroblasts. The peak metamorphic assemblages (M2) are represented by the garnet porphyroblasts and matrix minerals (hornblende + plagioclase + quartz ± biotite ± ilmenite). The retrograde metamorphic assemblages (M3) are characterized by the symplectitic intergrowth minerals (hornblende + plagioclase + quartz ± orthopyroxene ± biotite ± ilmenite) rimming decomposed, relict garnet porphyroblasts, known as the “white-eye socket” reaction textures. Calculated by geothermometers and geobarometers, the P–T conditions of these three metamorphic stages are estimated to be of 5.7–6.0 kbar/660–760 °C for the prograde stage (M1), 6.6–7.7 kbar/700–820 °C for the peak stage (M2) and 4.5–6.7 kbar/720–760 °C for the retrograde stage (M3), respectively. Therefore, these three metamorphic stages define clockwise P–T paths including nearly isothermal decompression (ITD) processes. Geochronological studies of zircons from the amphibolites indicate that the protolith of the amphibolites formed at ∼2.3 Ga, and the metamorphism occurred at ∼1.87–1.85 Ga, and the metamorphic period was further deciphered to be of 1.96–1.80 Ga when considering our previous reports. It is therefore proposed that the southernmost terminal of the TNCO was also involved in the subduction and collision processes between the Eastern and Western Blocks of the North China Craton at least as early as 1.96 Ga and continued as late as 1.80 Ga, followed by rapid uplift and exhumation. The available data suggest that the Palaeoproterozoic tectono-metamorphic event of the southernmost terminal of the Trans-North China Orogen not only started earlier but also continued longer than the other terranes in the middle and northern sections elsewhere in the orogen.

Garnetiferous amphibolites preserving prograde inclusion assemblages (M1) within garnet porphyroblasts, metamorphic peak assemblages (M2) and post-peak symplectitic assemblages (M3) have been found in the Lushan terrane, Henan Province, Taihua Metamorphic Complex, southernmost section of the NS-striking Palaeoproterozoic Trans-North China Orogen (TNCO). Geothermobarometric computation shows that the M1, M2 and M3 assemblages were formed under the P–T conditions of 650–730 °C/4.9–8.1 kbar, 740–810 °C/9–10.8 kbar and 750–760 °C/5.0–7.7 kbar, respectively, suggesting that these amphibolites record clockwise P–T paths including nearly isothermal decompression (ITD) segments similar to the west-Alpine type P–T paths, indicative of being resulted from an orogenic process. High resolution SIMS U–Pb dating of metamorphic zircons suggests that the metamorphism took place at ca. 1.95–1.75 Ga. These data imply that the Palaeoproterozoic collision between the Eastern and Western Blocks of the North China Craton along the southernmost terminal of the TNCO not only started earlier, but also continued longer, than the middle and north sections of the TNCO.