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The Kaladawan iron deposit is located in the North Altyn Tagh and exhibits occurrences of iron ore bodies at the contact zone between Ordovician magmatic rocks (basalts, rhyolite, and granodiorite) and marble. However, controversy persists regarding the genetic classification and metallogenic mechanism of this deposit. Through a field investigation, single mineral in situ geochemical analysis, whole-rock geochemical analysis, and Fe isotope determination, the following conclusions are made: (1) Ti-(Ni/Cr) and (V/Ti)-Fe diagrams indicate that the magnetite from all studied rocks underwent hydrothermal metasomatism, while (Ni/(Cr + Mn))-(Ti + V) and (Ca + Al + Mn)-(Ti + V) diagrams suggest a skarn origin for these magnetites. Therefore, it can be inferred that the Kaladawan iron deposit is skarn-type. (2) The iron ore exhibits similar rare-earth-element characteristics to the altered basalt. Additionally, the altered basalts (δ56Fe = 0.024~0.100‰) are more enriched in light Fe isotopes than the unaltered basalts (δ56Fe = 0.129~0.197‰) at the same location, indicating that the ore-forming materials of the Kaladawan iron ore are mainly derived from basaltic rocks. (3) According to the law of mass conservation and the intermediate Fe isotopic composition of the iron ore between the granodiorite and basalt, the hydrothermal fluid for the formation of iron ores was inferred to be derived from the late intrusive granodiorite. [ABSTRACT FROM AUTHOR]

The different olivine fabrics in ultramafic rocks have been widely used to discuss past tectonic settings, given that the olivine fabrics vary with pressure, temperature and water content. However, there are no research related to whether and how the olivine fabrics transform at different metamorphic stages in a natural rock during the process of deep subduction and exhumation. Yinggelisayi garnet lherzolites from South Altyn have experienced deep continental subduction and exhumation. The garnet lherzolites contain well‐preserved residual protolith minerals, and near‐peak (M1), granulite‐facies retrograde (M2), and amphibolite‐facies retrograde (M3) metamorphic mineral assemblages. Olivine grains in M1 formed at P‐T conditions of 2.52–3.08 GPa, 1,095–1,136°C and low water contents (183–213 ppm H/Si), and showed [010] axes sub‐normal to the foliation and [001] axes subparallel to the lineation, which is characteristic of B‐type fabric ((010)[001]). Olivine grains in M2 formed at P‐T conditions of 1.31–1.80 GPa, 851–893°C and also low water contents (93–139 ppm H/Si), and exhibited [010] axes sub‐normal to the foliation and [100] axes subparallel to the lineation, which is characteristic of A‐type fabric ((010)[100]). These observations suggest that olivine fabrics in high pressure‐ultrahigh pressure metamorphosed ultramafic rocks are different in the near‐peak and retrograde metamorphic stages, and also that the olivine fabrics can be transformed during deep continental subduction and exhumation. Therefore, the dispersed or no clear olivine fabric is probably caused by multi‐stage deformation and metamorphism, and the distinct olivine fabrics can also be used as a clue to identify geological processes and better understand metamorphism and deformation during subduction and exhumation. Plain Language Summary: According to the previous research that different olivine fabrics developed under various temprerature, pressure, stress and water content, we try to discuss the transformation of olivine fabric at different metamorphic stages with different P‐T conditions in metamorphic ultramafic rocks. The Yinggelisayi garnet lherzolites from South Altyn, NW China contain residual protolith minerals, and three stages of metamorphic minerals which include the near‐peak (M1), granulite‐facies (M2) retrograde, and amphibolite‐facies (M3) retrograde metamorphic minerals base on the petrography and mineral composition. And then, we analyzed olivine fabrics in the near‐peak (M1) and early retrograde metamorphic stages (M2). Results showed that the olivine in M1 during deep subduction of the continental crust developed the B‐type olivine fabric and the olivine in M2 during exhumation developed the A‐type olivine fabric. Key Points: Yinggelisayi garnet lherzolites contain residual protolith inclusions and three stages of metamorphic mineralsOlivine in the garnet lherzolites exhibited different fabrics during deep subduction and exhumation of the continental crustOlivine fabrics will be dispersed at multi‐stage deformation and metamorphism [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]

[Display omitted] • Magmatism formed during the initial stage (ca. 480Ma) and advanced stage (ca. 450Ma) of exhumation of subducted continental crust have been recognized in South Altyn western China. • Two stages of magmatism exhibits evidence for the partial melting of subducted continental crust during differential exhumation process of South Altyn in Palaeozoic. The early Palaeozoic continental subduction–collisional belt in South Altyn (SA) western China distributes a large amount of (ultra)-high-pressure ((U)HP) metamorphic and granitic rocks associated with subduction, collision, and exhumation. In this study, four granitic rocks were collected from Bashenwake located in eastern SA. The ages of the garnet-bearing alkali-feldspar granite (GAFG), garnet-bearing granitic gneiss (GGG), alkali-feldspar granite (AFG), and syenogranite (SG) are 458.0 ± 4.1, 483.0 ± 4.1, 450.0 ± 2.4, and 482.0 ± 4.9 Ma, respectively. Whole-rock major and trace elements and Sr–Nd–Pb isotope, and zircon Hf isotope compositions for all samples exhibit characteristics of a continental crustal source. Based on partial melting modeling, the source temperature of the GGG, GAFG, AFG and SG was concluded as 750–780 °C, 730–760 °C, 730–770 °C and ca. 800 °C, respectively. The source pressure was estimated as ca. 0.8 GPa for the GGG, GAFG and AFG, and ca. 1.2 GPa for SG. Combined with studies on (U)HP metamorphic rocks in SA, this study reveals that GGG is formed by metamorphism while SG is formed from partial melting of upper crustal rocks heated by upwelling mantle during the initial stage of exhumation (ca. 480 Ma) of subducted continental crust in SA. During further stage of exhumation of the subducted continental crust at ca. 450 Ma, the GAFG and AFG were formed from partial melting of GGG as a result of decreased pressure and further mantle upwelling. Consequently, the exhumation age of subducted continental crust in eastern SA is ca. 30 Myr earlier than that in western SA. Thus, the geochronology and petrogenesis of four granitic samples in this study exhibit one of very few evidence for partial melting of subducted continental crust during the exhumation and also provide magmatism exhibits evidence for the differential exhumation model of eastern SA in Palaeozoic. [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]

The Qilian orogeny formed by subduction of the proto-Tethyan ocean along the northern margin of Gondwana. In this paper we report geochemical, zircon U-Pb-Hf, and mapping data of the Duoruonuoer volcanic rocks from the western Qilian Orogen. Based on distinct geochemical compositions, four melt types can be distinguished: boninite-like basalt, OIB-like basalt, MORB, and high-K to shoshonitic volcanic rocks (HKSV). Field relationships show a compositional change from HKSV, MORB, OIB to boninite-like basalt, from north to south. The boninite-like basalt is low to medium-K calc-alkaline, with low TiO 2 (0.13–0.18 < 0.5 wt%) and high CaO/Al 2 O 3 ratio (0.72–0.80), similar to high-Ca back-arc boninite. The geochemical characteristics of Duoruonuoer OIB-like basalt, MORB, and HKSV are similar to those of the Izu-Bonin (IB) back-arc magmatic assemblages. Boninite-like basalt is enriched in LILEs, and has low Ce/Pb, and high Sr/Nd, Ba/Nb ratios, indicating an addition of a shallow subduction-derived fluid phase. Inferred pressures of magma segregation are 0.9–1.4 GPa with temperatures of 1200–1370 °C consistent with melting of a highly depleted, low pressure hydrous mantle source. The MORB-like rock formed by mixing of depleted mantle and a subduction component, and is identical to back-arc basin floor basalt (BABB). The HKSV, dated at 475 Ma, shares the characteristics with lava from the IB back-arc seamount chains (rear-arc). Their low Ce/Pb and high Th/Yb and Th/Nb ratios are compatible with contributions from melts of deep subducting sediment and oceanic crust. High pressure (1.8–2.0 GPa) may reflect sourcing from a mantle melt at the base of thickened arc crust. The OIB-like basalts have high TiO 2 , Zr/Yb, Nb/Yb and Ce/Pb ratios, suggesting an enriched component from partial melting of the asthenosphere. The high-Fe 8 and Ti 8 composition of the Duoruonuoer OIB-like basalt is produced by fractional melting, similar to a spreading ridge segment developed a deeper source. The variety of Duoruonuoer back-arc magmatism highlights the importance of changes to the melt source region linked to replenishment of the mantle wedge by material extracted from the subducting slab and influx of more fertile mantle material. It is also controlled by evolution of the mantle wedge over time in the building of the back-arc basin. These findings provide evidence for c.475 Ma back-arc basin developed on a thickened arc lithosphere at the western Qilian Orogen. [ABSTRACT FROM AUTHOR]