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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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 (M 1 ) are represented by mineral inclusions within the garnet porphyroblasts; (2) the metamorphic peak assemblage (M 2 ) 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 (M 3 ) 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 M 1 stage, 6.8–8.6 kbar/730–810 °C for the M 2 stage and 4.1–6.4 kbar/570–740 °C for the M 3 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Clockwise ITD P–T paths were retrieved from the Mts. Huashan amphibolites. [•] U–Pb geochronology of metamorphic zircons demonstrates the metamorphism occurred during ca. 1.96–1.80Ga. [•] Metamorphism of the southernmost Trans-North China Orogen started earlier and lasted longer than other terranes in the TNCO. [ABSTRACT FROM AUTHOR]

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 (M 1 ) includes biotite + plagioclase + quartz + ilmenite preserved as inclusions in garnet porphyroblasts. The peak mineral assemblage (M 2 ) consists of garnet porphyroblasts and matrix minerals of sillimanite + biotite + plagioclase + quartz + K-feldspar + ilmenite + rutile + pyrite. The retrograde mineral assemblage (M 3 ), 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Clockwise P- paths were retrieved from the Lushan amphibolites. [•] SIMS U–Pb dating of zircons demonstrates that the metamorphism took place at ca. 1.95–1.75Ga. [•] Metamorphism of the southernmost TNCO started earlier and continued longer than other terranes in the TNCO. [Copyright &y& Elsevier]