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Garnet amphibolite is one of the common metabasic rocks exposed in collisional orogenic belt, the metamorphic evolution of which is associated closely with orogenic processes. The Yaganbuyang garnet amphibolites occur as blocks hosted by massive granitic gneiss, and consist mainly of hornblende, garnet, clinopyroxene, plagioclase, biotite, quartz with minor rutile/ilmenite and phengitic muscovite. These garnet amphibolites were interpreted to have experienced decompression-dominated evolution that can be divided into three generations (M1, M2, M3), based on the petrographic observations and phase equilibria modeling calculated by THERMOCALC. The assemblage of the first generation (M1) is inferred to possibly be dominated by garnet + omphacite + rutile + phengite + quartz, which is modeled to be roughly stable at P > 25 kbar and T > 800 °C. The second generation (M2) is characterized by the local symplectites of clinopyroxene + plagioclase produced from omphacite, indicating a near-isothermal decompression from ∼23.8 kbar/875 °C to ∼10 kbar/852 °C. The third generation (M3) is marked by the kelyphitic rims of plagioclase + hornblende around garnet and of hornblende + ilmenite around clinopyroxene, involving the late-stage retrogression from ∼9.8 kbar/848 °C to ∼5.8 kbar/645 °C. Zircon U-Pb dating yielded one group metamorphic age of c. 500 Ma that is interpreted to represent the timing of the peak eclogite-facies metamorphism. A combination of petrography observation, phase modeling results and geochronology data suggests that the Yaganbuyang garnet amphibolites have once undergone eclogite-facies metamorphism by continental subduction rather than crustal thickening. Therefore, the Yaganbuyang area is an eastward extension part of the South Altyn HP-UHP metamorphic belt. [ABSTRACT FROM AUTHOR]

[Display omitted] • Clockwise P–T evolution is recorded by the South Altyn Tagh felsic gneiss. • The felsic gneiss was exhumed from eclogite-facies to granulite-facies within 20 Myr. • HP–HT eclogite-facies records were preserved in the weakly deformed felsic gneiss. • The HP mineralogical records were further eliminated by the strong deformation. Felsic gneisses are usually the dominant rock types in most high-pressure (HP) and ultrahigh-pressure (UHP) terranes, although their peak metamorphic conditions and complete P–T paths are rarely known. This lack of knowledge is attributed to the high variance of mineral assemblages at HP/UHP conditions of the felsic gneisses, or to the effects of retrograde-related overprinting. Thus, it is difficult to distinguish whether felsic gneisses underwent HP/UHP metamorphism. In this paper, we focus on the felsic gneiss that has been previously documented as having formed under HP granulite-facies metamorphism with peak P–T of > 1.15 GPa and > 860 °C from the Danshuiquan locality in the South Altyn HP – UHP belt. The Danshuiquan felsic gneiss is strongly deformed and is spatially associated with weakly deformed garnet-rich felsic gneiss. On the basis of detailed microstructure observations on mineral assemblages and phase equilibria modelling, three stages of metamorphic evolution for the weakly deformed garnet-rich felsic gneiss are identified. The first stage is represented by garnet cores, revealing a prograde P–T path from 1.5 GPa/750 °C to 2.1 GPa/900 °C. The second stage is characterized by garnet mantles with multiphase inclusions, defining HP eclogite-facies metamorphic conditions of 2.2–2.6 GPa/950–1100 °C. The third stage is represented by the composition of garnet rims, biotite, and plagioclase, suggesting an HP granulite to amphibolite facies decompression cooling process to 1.1–1.3 GPa/710–770 °C. In contrast, the strongly deformed felsic gneiss just records a deformation-related decompression process from 1.1 to 1.2 GPa/750–760 °C to 0.87–0.98 GPa/760–770 °C, and finally to 0.83 GPa/740 °C. Zircon U–Pb dating yields c. 920 Ma protolith ages, c. 500 Ma eclogite-facies ages, and c. 480 Ma granulite to amphibolite facies retrograde ages for the Danshuiquan felsic gneisses. Our results show that the Danshuiquan felsic gneisses underwent a similar metamorphic evolution process to that of Yinggelisayi HP–UHP rocks in the eastern segment of the South Altyn Tagh. Most HP mineralogical records tend to be eliminated by the strong deformation at crustal depths (∼30 km), meaning that the peak metamorphic conditions of the studied felsic rocks in UHP metamorphic terranes are previously underestimated. [ABSTRACT FROM AUTHOR]

Newly identified garnet–corundum silica-undersaturated pelitic granulites in the Mianlüe Tectonic Zone of the South Qinling belt, central China, preserve a distinct mineral assemblage of garnet + corundum + biotite + plagioclase ± kyanite + sillimanite + staurolite and are therefore useful for deciphering the metamorphic evolution of the zone. Most of the garnet porphyroblasts preserve prominent major- and trace-element zoning, which provides evidence for two stages of garnet growth, under subsolidus conditions and then fluid-absent conditions, during prograde metamorphism. The distinctive yttrium annuli in garnet grains are most likely the result of the breakdown of xenotime. Four stages in the pressure–temperature (P–T) evolution of the granulites are inferred from the results of P–T pseudosection analysis together with petrographic observations. The first stage records the early prograde evolution, comprising isobaric heating at ~7 kbar from 580 to ~700 °C, and the later-stage prograde evolution with increasing pressure and temperature to the peak-pressure stage. The second stage is marked by the maximum X Grs in the garnet mantle, indicating the peak conditions in the high- P –high- T granulite facies of 830 °C at ~11.7 kbar. The third stage is characterized by a continued increase in pyrope in the garnet rim, suggesting decompression with slight heating from the peak pressure to reach the peak temperature at ~9.4 kbar and ~850 °C. The late retrograde cooling stage is represented by further decompression after the peak temperature, accompanied by the growth of staurolite. 7–13 mol% melt was produced during prograde metamorphism via the reaction sill + bi + pl → g + crn + melt. Although later melt loss reduced the bulk-rock Si and Al, the low-Si and high-Al–Fe bulk compositions of restite were inherited mainly from the protolith, which comprised high-Fe sediments (bauxites) derived from weathering of adjacent mafic rock. U–Pb dating of metamorphic zircon rims yielded two age clusters: ~227 Ma represents the timing close to peak-pressure conditions, and 222–217 Ma represents the timing of post- T max cooling to the solidus. Monazite U–Pb ages of 212–206 Ma are interpreted as the timing of further retrograde cooling under the solidus. The geochronological data and clockwise P – T paths indicate the garnet–corundum pelitic granulites record a complete metamorphic P–T–t history, including crustal thickening during continental collision/subduction and subsequent exhumation and cooling during the early Mesozoic. Combined with recent high-precision early Neoproterozoic data, we proposed that the MTZ was formed as a result of Grenvillian oceanic plate subduction and the assembly of Rodinia during the early Neoproterozoic and that it also records processes related to continental collision/subduction during the early Mesozoic. • irst report of garnet–corundum granulites from Mianlüe Tectonic Zone (MTZ). • Fe Al-rich granulites originated from high-Fe sediments (bauxites). • Clockwise P–T–t evolution is recorded by MTZ granulites. • The MTZ records continental collision/subduction during the early Mesozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mafic granulites in the Kuruksayi area were derived from overprinted eclogites. • Phase modeling suggests that such mafic granulites have undergone UHP metamorphism. • P - T conditions recorded in mafic granulites are comparable to that in HP/UHP eclogites. The South Altyn high-pressure–ultrahigh-pressure (HP–UHP) metamorphic belt in West China records the processes of deep continental subduction (>150–300 km). The HP mafic granulite pods hosted by massive granitic gneiss were for the first time discovered in the Kuruksayi area of the South Altyn Orogen, and they consist mainly of garnet, clinopyroxene, plagioclase, hornblende, biotite, and quartz, with minor rutile, ilmenite, and K-feldspar. The garnets vary in grain size and chemical zoning, and can be divided into three types: subhedral porphyroblastic (g 1), anhedral porphyroblastic (g 2), and neoblastic fine (g 3) grains. Four generations of mineral assemblage (M1–M4) are recognized, and are used to constrain the P–T evolution of the mafic granulites using phase equilibria modeling calculated by THERMOCALC. The first generation (M1) is represented by the core domains of g 1 (g 1C) that have inclusions of rutile and quartz and conspicuous chemical zoning. A pre-peak prograde stage of metamorphism from ~ 15.8 kbar/600 °C to ~ 19.2 kbar/655 °C is recorded by g 1C. The second generation (M2) is inferred to consist of garnet + omphacite + phengite + rutile + quartz and is recorded in the mantle domains of g 1 (g 1M). Modeling suggests that this is representative of conditions that reached a maximum P–T of ~ 36.2 kbar/920 °C. The third generation (M3) is characterized by intergrowths of clinopyroxene + plagioclase and biotite + plagioclase, and this stage is recorded by the compositions of g 2 with modeling suggesting an evolution from ~ 17.8 kbar/820 °C to ~ 11.5 kbar/826 °C, consistent with near-isothermal decompression. The last generation (M4) is characterized by kelyphitic rims of plagioclase + hornblende around garnet and the hornblende coronas that encompass symplectitic clinopyroxene, and is recorded by the compositions of g 3. Modeling suggests evolution from ~ 11.5 kbar/826 °C to ~ 8.7 kbar/735 °C, compatible with near-isobaric cooling. These four stages of metamorphism together establish a clockwise P–T path, which indicates a series of tectonic processes that took the continental slab from subduction to exhumation. Zircon U–Pb dating by LA–ICP–MS yielded two distinct clusters of ages: c. 897 Ma magmatic protolith ages and c. 494 Ma metamorphic ages. The metamorphic ages are interpreted to represent the timing of the eclogite-facies metamorphism, and are similar to the metamorphic ages of other HP/UHP rocks elsewhere in the South Altyn Orogen. Accordingly, we propose that the Kuruksayi mafic granulites underwent UHP metamorphism similar to that recorded in other South Altyn eclogites exposed in Jianggalesayi and Danshuiquan to the west and Yinggelisayi to the east. [ABSTRACT FROM AUTHOR]