The metamorphic evolution of the Higher Himalayan rocks in southern Tibet has been characterized through detailed studies of metapelites, whereas the associated amphibolites remain largely unexplored. In this paper, we describe detailed petrography, mineral chemistry, phase-equilibrium modeling, and zircon U-Pb ages of garnet-bearing amphibolites in the Cona area, southern Tibet. The rocks record three distinct metamorphic stages M1, M2, and M3. Prograde stage (M1) is defined by a mineral assemblage of garnet with amphibole, biotite, and plagioclase, crystallized under pressure-temperature (P-T) conditions of 9.5 kbar and 720 degrees C. Peak metamorphic stage (M2) is characterized by the existence of garnet, amphibole, biotite, plagioclase, quartz, ilmenite, and rutile, with P-T conditions of 12 kbar and 810 degrees C. Retrograde stage (M3) comprising garnet, K-feldspar, plagioclase, and quartz, stable at 8.5 kbar and 710 degrees C. U-Pb ages of zircon indicate that these amphibolites experienced anatectic metamorphism between 28 and 15 Ma. There is an increase in the metamorphic thermobaric ratios from 675-835 degrees C/GPa to 875 degrees C/GPa, rising the geothermal gradients from 18.2 degrees C/km to 24.8 degrees C/km. Integrating our results with previous studies, it is concluded that the Cona amphibolites underwent peak HP metamorphism, followed by a decompressional path similar to that of Cona metapelites during the Miocene, reflecting a phase of post-collisional rapid exhumation.

The Prydz Bay region of East Antarctica holds critical information regarding the assembly of both Rodinia and Gondwana. This study documents the discovery of high-pressure metapelitic granulites from the Søstrene Island, SW Prydz Bay, which are characterized by a two-stage decompression texture. Integrated petrological analyses, thermobarometric calculations and phase equilibria modeling reveal a clockwise P–T path with peak P–T conditions of 11.5–13.0 kbar and 850–900 °C, followed by two-stage decompression to 4.5–5.5 kbar and 760–820 ℃. Zircon, monazite and rutile U-Pb petrochronology constrains this metamorphic event to ∼1000 Ma, with sedimentary precursors deposited prior to this time. These findings refute the earlier hypothesized existence of a Neoproterozoic basin along the Prydz Bay, and provide robust petrological evidence for the involvement of the Prydz Bay region in the Rayner Orogeny. Coupled with published data, we propose that the ∼1000 Ma high-pressure granulite facies metamorphic event was likely related to the collision between the Indian Craton and Australo-Antarctica during Rodinia assembly. Subsequent transpressional movement facilitated Rayner’s southward drift and collision with Antarctica at 590–500 Ma, forming part of East Gondwana. We speculate that the Gondwana-forming suture lies near the Bunger Hills, extending into the hinterland of Antarctica. This study underscores the dual tectonic imprints of first the ∼1000 Ma Rayner Orogeny associated with the assembly of the supercontinent Rodinia, and then the Gondwana amalgamation that together shaped the crustal architecture of the Prydz Bay region, offers new insights into the spatiotemporal complexity of supercontinent assembly process.

Accurate quantification of energy deposition under ultra-high linear energy transfer (LET) is critical for predicting heavy-ion radiolysis outcomes. This study presents a calibration scheme for chemical dosimeters, validated using a 450 MeV/u 112Sn33+ beam (LET ≈ 1000 eV/nm) at the Heavy Ion Research Facility in Lanzhou (HIRFL). Pulse and steady-state radiolysis experiments were performed using potassium thiocyanate (KSCN) and potassium dichromate (K2Cr2O7) dosimeters, respectively. The measured radiation chemical yields (G-values, in molecules/100 eV)were GSCN2·-=0.371±0.025 and G-Cr2O72-=0.400±0.015. Experimental results were cross-referenced with gMicroMC simulations to validate the response mechanisms. The observed consistency between experimental results and theoretical predictionsvalidates the applicability for dosimetry calibration in ultra-high LET regimes.

Greywacke is a rock type pervasively present in orogens, and anatexis of greywackes is a pivotal process for crustal differentiation and granitoid formation. However, it remains challenging to characterize pristine compositions of anatectic melts derived from diverse lithologies. This study investigates nanogranitoids (i.e. crystallized melt inclusions) in metagreywackes from the Rauer Islands, eastern Prydz Bay, East Antarctica. This is the first study to recognize nanogranitoids in metagreywackes dominated by Bt dehydration melting. Results from phase equilibrium modeling and Zr-in-rutile thermometry indicate that the peak metamorphic P-T conditions were similar to 0.95 GPa and similar to 850 degrees C, and that the melts were trapped under near-peak conditions. Zircon and monazite dating suggests that the granulite facies metamorphism and anatexis occurred during the Pan-African orogeny. Nanogranitoids (2 to 40 mu m in size) occur in garnet and are composed of cryptocrystalline daughter phases including phlogopite, muscovite, cristobalite, quartz, plagioclase, kokchetavite, and kumdykolite. They were experimentally re-homogenized under 850 degrees C, with the glass showing silicic (SiO2 = 74.2 +/- 3.1 wt %), peraluminous (aluminum saturation index = 1.1-1.6), K-enriched (K/Na = 1.1-2.6), and low-maficity (FeO + MgO = 1.7-4.1 wt %) compositions. Micro-Raman spectroscopy suggests that H2O contents in the melts vary from 0.44 to 1.08 wt %, with an average value of 0.75 +/- 0.2 wt %. Compared with bulk rock compositions, the investigated melts show enrichment in Rb, Cs, and U, depletion in Ce and Sr, and elevated Rb/Sr ratios (3.8-13.7). From these geochemical characteristics of nanogranitoids, we conclude that (1) K2O and Rb enrichment in melts points to incongruent melting involving dehydration of biotite; (2) depletion of Sr reflects moderate melting degrees (i.e. plagioclase is still abundant at peak stage); and (3) zircon saturation temperatures (775-837 degrees C at 1.0 GPa) imply disequilibrium melting of accessory minerals during high-temperature anatexis. Physical properties of the melt (2.43 +/- 0.06 g/cm(3) density, and similar to 3.5 mu W/m(3) heat production) suggest that anatexis of metagreywackes would facilitate efficient melt extraction and redistribution of some large ion lithophile elements (Rb and Cs) and heat-producing elements (K and U). A detailed comparison between published data suggests that biotite dehydration melting usually generates granitic melts with high heat production values. Considering the wide distribution and efficient melt production, anatexis of metagreywackes may have a remarkable contribution to chemical differentiation across crustal sections, prompting stabilization of the crust.

The Taihua Complex, located on the southern margin of the Trans-North China Orogen (TNCO), North China Craton, is a critical region for decoding tectonic evolution of the TNCO. In this study, an integrated investigation of petrology, phase equilibrium modelling and LA-ICP-MS zircon U-Pb dating is undertaken for the staurolite-bearing metapelitic schist in the Lushan Taihua Complex. Petrographic observations reveal a four-stage metamorphic evolution, including: (1) A pre-peak (M1) assemblage consisting of the garnet core and its mineral inclusions of staurolite, plagioclase, biotite, quartz, ilmenite and rutile; (2) The pressure peak (M2) assemblage represented by the inclusions of plagioclase, biotite, quartz, ilmenite and rutile within garnet rims, and the presence of kyanite pseudomorphs after sillimanite, which is confirmed by the Raman spectra; (3) The decompression stage (M3) characterized by the transformation from kyanite to sillimanite as well as partial replacement of rutile by ilmenite; and (4) the final stage (M4) marked by the fine-grained assemblage of biotite + plagioclase + quartz +/- sillimanite, locally surrounding the garnet porphyroblasts. Phase equilibrium modelling results suggest that the metapelitic schist experienced the high-amphibolite facies metamorphism, with P-T conditions approaching 654 similar to 661 degrees C/8.7 similar to 9.1kbar (M1) and 751 similar to 766 degrees C/10.7 similar to 11.1 kbar (M2), followed by a decompression with minor heating to 778 similar to 795 degrees C/7.2 similar to 7.9 kbar (M3), and finally, the rocks underwent a cooling process until 699 similar to 702 degrees C/7.1 similar to 7.2 kbar (M4). Thus, a clockwise P-T path is retrieved. Zircon U-Pb dating yields a weighted mean Pb-207/Pb-206 age of 1883 +/- 9 Ma, interpreted as the time of the post-peak cooling. Therefore, it can be inferred that the Taihua Complex has been involved in the collision between the Western and Eastern Blocks of the NCC in the late Paleoproterozoic. Based on previously published data, we propose that the Taihua Complex records the pressure peak metamorphic ages of ca. 1.95 Ga and cooling ages of ca. 1.93(1.92) similar to 1.80 Ga. The main crustal thickening process possibly occurs at ca. 1.95 Ga, followed by uplifting, and final cooling from ca. 1.93(1.92) - 1.80 Ga.

The Irtysh tectonic belt lies on the southern margin of the Chinese Altai Orogen. Several secondary shear zones with NW-SE strikes have developed in this tectonic belt, and the deformation processes are of great significance to understanding the tectonic regime of the Altai Orogen in the Late Paleozoic. The Tuerhongshate ductile shear zone is located in the eastern Irtysh tectonic belt with obvious deformed structures. The felsic rocks are strongly mylonitized, exhibiting S-C fabrics, asymmetric rotational porphyroclasts, and bookshelf structures of the plagioclases, indicating a sinistral shear sense. The deformation mechanisms, lattice preferred orientations (LPOs) of quartz, and opening angles of quartz c-axis suggest that the deformation temperatures range from 400 to 500 °C, consistent with higher-greenschist to lower-amphibolite facies conditions. The calculated kinematic vorticity values (Wk) of the studied samples range from 0.53 to 0.89 and indicate general shear to simple shear, based on rotational rigid porphyroclast method and oblique grain-shaped/quartz c-axis fabric method. The U-Pb ages of magmatic zircons in felsic mylonites indicate that the sinistral shear occurred after 296.7 ± 3.0 Ma (Early Permian) in the Tuerhongshate shear zone and persisted for approximately 13 Ma. Combined with the tectonic setting and the observed sinistral strike-slip shear indicators in the mylonite zone, these features demonstrate that the Irtysh tectonic belt was in a post-orogenic and strike-slip environment following the closure of the Irtysh Ocean.

Scientific diamond drilling into the Purang massif, located in the western Yarlung-Zangbo suture zone, Southwest Tibet, provides critical insights into the petrographic and geochemical evolution of Neo-Tethyan suprasubduction zone ophiolites. This study integrates structural, geochemical, and petrological data to reconstruct the formation and subsequent evolution of peridotites and associated lithologies, with implications for broader geodynamic processes. The massif predominantly consists of harzburgite, along with subordinate lherzolite, pyroxenite, and dunite (ca. 130 Ma), all of which are variably serpentinized (loss on ignition [LOI] of up to similar to 11 wt%). Geochemical features, including high MgO (42.68-46.24 wt%), low Al2O3 (0.7-1.18 wt%), and U-shaped rare earth element patterns, point to initial formation in a mid-ocean ridge setting with similar to 10%-15% partial melting, which produced Cr- and Mg-enriched residues (Cr# 0.3-0.4; Mg# 0.88-0.92). Subsequent interactions with hydrous melts in a suprasubduction zone environment, combined with distal subduction components, led to the formation of high-Cr chromitites (Cr2O3 <= 60%), dunite pods, and clinopyroxene-bearing harzburgite. Re-Os isotopic data (Os-187/Os-188: 0.12479-0.12846; gamma Os: -2.74 to 0.12) and pressure-temperature estimates (2.0-2.7 GPa, 745-1067 degrees C) suggest a polyphase genesis involving melt percolation and mantle interaction. Platinum-group element (PGE) patterns show Pt and Pd depletion and enrichment in iridium-group PGEs in dunite, which reflects fractionated melts. Additionally, Mg isotopic data (delta Mg-26: -0.67 parts per thousand to -0.22 parts per thousand) emphasize the role of metasomatic processes, which indicates interaction with isotopically light fluids during subduction and mantle modification. This study provides compelling evidence of the multiphase genesis of the Purang peridotites, and shows they were shaped by mid-ocean ridge extension, subduction dynamics, plume-induced lithospheric modification, and detachment faulting. These findings refine models of mantle evolution, oceanic lithosphere formation, and subduction zone dynamics, and highlight how detachment faulting, coupled with the emplacement of the Purang ophiolite, contributed to the evolution of oceanic lithosphere in the Neo-Tethyan realm.

Metamorphic thermobaric ratios are used to interpret the evolution of convergent plate margins and to understand the evolution of the Higher Himalayan Crystalline Sequence. To better understand changes in pressure (P) and temperature (T) with time (t), we examine the metamorphic petrology, mineral chemistry, phase equilibrium modeling, and geochronology of the metapelites from the Cona area in the eastern Himalayan orogen. Based on this integrated approach, three metapelites were selected to study the Miocene metamorphism. Our results reveal that the metapelites preserve a peak garnet-kyanite-K-feldspar-bearing high-grade metamorphic mineral assemblage, and a post-peak sillimanite-bearing assemblage, and underwent the granulite-facies metamorphism and associated partial melting under P-T conditions of ca. 10 kbar and 725-775 degrees C, followed by isothermal decompression and isobaric cooling. Zircon dating indicates that these rocks experienced metamorphism between 24 and 14 Ma, accompanied by an increase in geothermal gradients from 21 degrees C/km (780 degrees C/GPa) to 29 degrees C/km (1190 degrees C/GPa), and finally to 32 degrees C/km (1250 degrees C/GPa). Thus, there is an increase in the thermobaric ratio and geothermal gradient along the north-south transect, concurrent with a decrease in elevation and age. We argue that these extreme gradients are a consequence of the active tectonic processes and ongoing deep crustal magmatism in the eastern Himalaya, whereas the decreasing trend of P-T conditions of peak metamorphism and younging of exhumation ages southward from the upper to lower Higher Himalayan Crystalline Sequence is well matched with a critical taper model.

The Siberian Craton is one of the most renowned stable cratons in the world, and its lower crustal metamorphic evolution history is crucial for understanding continental dynamics. There has been an ongoing academic debate regarding the tectonic mechanisms responsible for the modification and reconstruction of the lower crust during the Paleoproterozoic, including vertical and horizontal tectonic accretion. This study focuses on the Paleoproterozoic granulite xenoliths from the Udachnaya kimberlite pipe in the Siberian Craton. Through petrographic observations, mineral chemistry analysis, various geological thermobarometers and P-T pseudosection modeling, we have constrained the P-T conditions of different metamorphic stages recorded in the granulites. In this study, three distinct metamorphic stages of the granulites are identified as: (1) the early prograde stage (M1), characterized by the mineral assemblage of garnet, clinopyroxene, plagioclase, rutile, and quartz inclusions, with P-T conditions of 740 similar to 770 degrees C and 1.04 similar to 1.12GPa; (2) the peak metamorphic stage (M2), with the assemblage of matrix garnet, clinopyroxene, amphibole, plagioclase, rutile, and melt, with exsolved acicular rutiles in garnet porphyroblasts, with P-T conditions of 900 similar to 912 degrees C and 1.37 similar to 1.39GPa; and (3) the retrograde stage (M3), characterized by the symplectite of amphibole+quartz developed at the rims of garnet and clinopyroxene, with P-T conditions of 832 similar to 850 degrees C and 0.9 similar to 0.95GPa. The above P-T conditions and phase equilibrium modeling results indicate that they experienced a peak high-pressure and ultrahigh-temperature metamorphism, with a clockwise P-T path of prograde heating and pressure-up followed by post-peak isothermal decompression (ITD), recording the crust thickening caused by continent-continent collision and subsequent rapid exhumation processes. Combined with the previous chronological results of others, it suggests that the transformation and reconstruction of the lower crust of the Siberian Craton in the Paleoproterozoic may be related to the contemporaneous assembly of the Columbia Supercontinent (1.9 similar to 1.8Ga). This result highlights the significance for understanding the tectonic evolution history of the Siberian Craton and the initiation time of plate tectonics.

The Erentaolegai silver deposit is located within the Derbugan metallogenic belt in the eastern segment of the Central Asia–Mongolia giant orogenic belt. The ore bodies are primarily hosted in the volcanic rocks of the Middle Jurassic Tamulangou Formation of the Mesozoic. The mineralization process of the deposit is divided into three stages: Stage I: Pyrite–Quartz Stage; Stage II: Sulfide–Quartz Stage; Stage III: Quartz–Manganese Carbonate Stage. This paper discusses the ore-forming fluids, ore-forming materials, and deposit genesis of the Erentaolegai silver deposits using fluid inclusions microthermometry, laser Raman spectroscopy, and H-O-S isotope analyses. Fluid inclusion microthermometry and laser Raman spectroscopy analyses indicate that the Erentaolegai silver deposit contains exclusively fluid-rich two-phase fluid inclusions, all of which belong to the H2O-NaCl system. Homogenization temperatures of fluid inclusions in the three stages (from early to late) ranged from 257 to 311 °C, 228 to 280 °C, and 194 to 238 °C, corresponding to salinities of 1.91 to 7.86 wt%, 2.07 to 5.41 wt%, and 0.70–3.55 wt% NaCl equivalent, densities of 0.75 to 0.83 g/cm−3, 0.80 to 0.86 g/cm−3 and 0.85 to 0.89 g/cm−3. The mineralization pressure ranged from 12.2 to 29.5 MPa, and the mineralization depth was 0.41 to 0.98 km, indicating low-pressure and shallow-depth mineralization conditions. H-O isotope results indicate that the ore-forming fluid is a mixture of magmatic fluids and meteoric water, with meteoric contribution dominating in the late stage. The δ34S values of metallic sulfides ranged from −1.8 to +4.0‰, indicating that the metallogenic material of the Erentaolegai silver deposit was dominated by a deep magmatic source. This study concludes that meteoric water mixing and subsequent fluid cooling served as the primary mechanism for silver mineral precipitation. The Erentaolegai silver deposit is classified as a low-sulfidation epithermal silver deposit.

The Cretaceous gold deposits along the margins of the North China Craton (NCC), which formed in a craton destruction setting, display geological characteristics similar to traditional orogenic gold deposits typically associated with accretionary orogeny. These deposits, known as Jiaodong-type gold deposits, have attracted considerable attention. However, the lithospheric controls and formation mechanisms of these deposits remain unclear, as they cannot be fully explained by the supracrustal metamorphic genetic model commonly applied to classic orogenic gold deposits. In this study, the compiled S-Hg-Pb isotope ratios of gold deposits on different NCC margins display compatible variations to the Sr-Nd-Hg isotope ratios of mafic dikes spatial-temporally associated with the deposits. This implies that mantle lithosphere, metasomatized by variable proportions of oceanic and continental crust, was the source for both gold deposits and mafic dikes. Increase of oxygen fugacity and zircon εHf(t) from pre- to syn-gold granites suggests continuous basic magma underplating, which could induce concentrations of Au-rich sulfides and contribute additional Au to auriferous CO2-rich fluids derived from metasomatized mantle lithosphere and basic magma. Localization of gold deposits was controlled by craton-margin sinistral shearing induced by clockwise rotation of the craton coincident with distal emplacement of metamorphic core complexes. Thus, the Cretaceous Jiaodong-type orogenic gold deposits were derived from fertilized mantle lithosphere through such crust-mantle processes within a lithosphere thinning background.

The timings and geodynamic controls of Mo, Au, and Au-Mo deposits in the Xiaoqinling Orogen (> 630 t Au and 115, 000 t Mo), a rare Au-Mo province globally, are addressed by a combination of mineral parageneses, crystalline mineralogy, geochemistry, and Re-Os and U-Pb geochronology in the Dahu, Qinnan, and Yangzhaiyu deposits. The Xiaoqinling Orogen comprises an E-W-trending fold and thrust system with repeated structural reactivation and the Mo or Au orebodies in these deposits are dominantly controlled by E-W-trending and NW-SE-trending shear zones. Molybdenum mineralization related to Kfeldspar alteration comprises early molybdenite, pyrite, rutile, and monazite within gray quartz veins plus late molybdenite and pyrite within white quartz veins in the Dahu and Qinnan Au-Mo deposits. Early and late Au mineralization events have similar mineral assemblages of pyrite, native gold +/- Au-A g-Te minerals, rutile, and monazite associated with quartz-sericite alteration at Yangzhaiyu. The early disseminated molybdenite is characterized by rhombohedral polytype and oscillatory Re zoning, in contrast to the late molybdenite with a coexistence of rhombohedral and hexagonal polytypes and irregularly distributed Re. The early molybdenite has a Re-Os isochron age of 222.5 +/- 1.3 Ma, compatible with a monazite U-Pb age of 224 +/- 6.1 Ma, whereas late molybdenite provides a Re-Os isochron age of 185.0 +/- 12 Ma, with the implication that the 3R-polytype molybdenite with oscillatory Re zoning is more suitable for high-precision dating. The early and late Au mineralization have a pyrite Re-Os age of 202. 0 +/- 5.9 Ma and U-Pb age of 124.0 +/- 1.3 Ma, respectively. In accordance with its complex geodynamic setting, geological and geochronological studies record a complicated 100-million-year mineralization history with multiple magmatic-hydrothermal Mo and orogenic Au mineralization events that formed within a structural framework of multiply reactivated shear zones. (c) 2025 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Detailed structural studies and dating of mineralization define two discrete gold mineralization events during formation of the Chaihulanzi gold deposit. This complexity in gold mineralization resulted from overlap of two distinct orogenic events on the northern margin of the North China Craton. The earlier gold lodes are hosted by NW-SE-trending thrusts and ENE-WSW-trending extensional faults that formed under far-field sub-horizontal NE-SW-trending compression. These lodes comprise pyrite, pyrrhotite, chalcopyrite, sphalerite, tellurides, and native gold associated with quartz-sericite alteration. The later gold veins are controlled by steeply dipping NW-SE-and NE-SW-trending faults that formed under far-field sub-horizontal E-W-trending compression. These veins comprise pyrite, pyrrhotite, and native gold associated with quartz-carbonate or quartz-sericite alteration. The quartz in the earlier and later veins has c-axes with preferred orientations that are sub-parallel and sub-perpendicular to the ore-controlling fault plane, respectively. U-Pb ages of magmatic zircons from the diorite and granite that host later gold ores are dated at ca. 265 Ma. In situ U-Pb dating of hydrothermal rutile and monazite intergrown with goldbearing pyrite in both earlier and later aurif erous quartz veins indicates that the two gold events were at ca. 290 Ma and ca. 170 Ma. These two discrete gold events are related to crustal shortening during subduction of the Paleo-Asian oceanic plate and crustal rotation during subduction of the Paleo-Pacific oceanic plate. The recognition of two gold mineralization events that occurred more than 100 m.y. apart in the Chaihulanzi deposit has implications for district-scale gold exploration in tectonically complex terranes.

The Chaihulanzi gold deposit, located along the northern margin of the North China Craton, is an example of detecting the controls on the complexity of orogenic gold systems. This deposit consists of a series of gold lodes hosted in graphite-schist, gneiss, and porphyrite and is controlled by NW- to NWW-directed faults. The graphite- schist-hosted gold lodes contain pyrite-arsenopyrite-dominated polymetallic sulfides, whereas the gneiss- and porphyrite-hosted lodes are characterized by pyrite-pyrrhotite-dominated polymetallic sulfides. Despite variations in ore-minerals, these lodes exhibit similar quartz-sericite +/- carbonate-chlorite alteration. In the dilatational faults, the S34S values of pyrite from graphite-schist-hosted lodes from + 0.4 to + 6.5 %o , whereas pyrite from gneiss-hosted lodes have S34S values ranging from-3.5 to + 8.5 %o . In the compressional faults, pyrite from porphyrite-hosted lodes shows S34S values between + 2.3 to + 4.4 %o . The broader range of S34S values from dilatational-lodes compared to compressional-lodes can be attributed to varying fluid-rock interactions and fluid pressure fluctuations. The contrasting ore minerals and sulfur isotope are linked to the interaction of ore-forming fluids with different host rocks in complex structural and lithological settings. Specifically, the relatively positive S34S in pyrite from graphite-schist-hosted lodes may result from the fluid reduction due to reaction with graphite- schist. The Pb isotope of pyrite with 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of 18.51-22.13, 15.69-16.54, and 37.92-43.59, respectively, support the hypothesis of Pb contamination of the host rocks. This study underscores the detailed influence of structural settings and lithologies on the complexity of ore-forming fluid compositions and provides valuable insights for guiding regional exploration.

The role of the South China Block in the Kuunga orogeny, a pivotal event marking the assembly of the Gondwana supercontinent, remains a subject of debate. This study investigates high-pressure (high-P) granulitefacies metamorphism in the Yunkai orogen of eastern South China to shed light on this controversy. Recently,highP pelitic granulites with a mineral assemblage of garnet, K-feldspar, and sillimanite pseudomorph replacing earlier kyanite were identified in the Gaozhou Complex. Petrographic observations, phase equilibria modeling, geothermobarometry, and laser ablation-inductively coupled plasma-mass spectrometry (LAICP-MS) zircon U-Pb dating have revealed a four-stage metamorphic evolution. The peak P stage (M1) is characterized by highP conditions of 10-11.8 kbar/760-830 degrees C in the kyanite and rutile stability fields. This is followed by the peak temperature (T) metamorphism (M2) at slightly lower pressures and higher temperatures of 7.8-9.5 kbar/840-870 degrees C, which suggests a subsequent period of thermal relaxation. Subsequent decompression and cooling (M3) led to the formation of cordierite + spinel coronae, which reflects a change in P-T conditions to 4.5-5.3 kbar/730-790 degrees C. The final retrogression (M4) occurred under lower-grade conditions of 3.7-4.4 kbar/600-640 degrees C. Consequently,highP pelitic granulites in this region have undergone a clockwise P-T path, which indicates a continental collision setting. Zircon U-Pb dating from thehighP granulites and gneisses yielded multistage metamorphic ages of ca. 520 Ma, ca. 440 Ma, and ca. 240 Ma, which correspond to the Pan-African, Caledonian, and Indosinian tectono-thermal events, respectively. These metamorphic ages, coupled with the clockwise P-T path, reveal a history of polymetamorphism associated with a longlived subduction-continental collision event during the assembly of Gondwana and the subsequent Indosinian overprinting. These multiple orogenic processes provide significant insights into the tectonic evolution of the South China Block. Our findings contribute to the evidence of the Kuunga orogeny in South China during the assembly of Gondwana and offer a robust framework for interpreting the complex metamorphic histories of orogenic belts.

Garnet-orthopyroxene granulites from the Rauer Islands (East Antarctica) provide a spectacular example to investigate the late fluid evolution, metamorphic duration, and behavior of monazite and zircon in response to metamorphic reactions and fluid-rock interaction. Here, we characterize the secondary fluid inclusions in peritectic garnet and orthopyroxene, which occur as multiphase inclusions along micro-fractures. Inclusions are composed of siderite, pyrophyllite, calcite, quartz and residual CO2, representing stepdaughter phases resulting from the interactions between C-O-H fluid and its hosts at variable temperatures during retrogression. Zircon grains show clear core-rim structure, which yield Pb-206/U-238 ages of 540-507 Ma and 527-490 Ma, respectively. Index inclusions and internal structures suggest that the cores document the timing of peak and post-peak decompression while the growth of rims corresponds to melt crystallization during the final cooling. The U-Pb systems in zircons are considered to have not been obviously affected by fluid or melt-mediated modification. The unusual formation of monazites in garnet-orthopyroxene granulites may be linked with the elevated phosphorus budget as a result of apatite dissolution during the prograde melting of the rocks. Detailed investigations suggest that the crystallization of monazites occurred both at peak and post-decompression stages, whose isotopic systematics has been completely reset due to melt-mediated dissolution-precipitation. The spurious dates for monazites (522-495 Ma) are highly coinstantaneous with the dating results for zircon rims, further supporting this view. Therefore, we conclude that the late carbonic fluid influx cannot result in marked U (-Th)-Pb resetting in zircon and monazite. Instead, anatectic melt may have played an important role in the disturbance of isotopic systematics in monazites, especially for long-lived high-grade metamorphic terranes. Combined with previously published data, we propose that the Pan-African metamorphic event in the Rauer Islands may have reached the peak at around similar to 540 Ma, followed by a protracted post-peak evolution that lasted for at least similar to 50 Myr. This study highlights the importance of an integrated investigation of fluid and index mineral inclusions, as well as the chemical signatures of zircon and monazite, to interpret chronological data correctly.

The Vestfold Block, a typical polymetamorphic Archean terrane in East Antarctica, is a key area to understand amalgamations of Rodinia and East Gondwana continents. However, multiphase overprinting makes it difficult to determine the timing and nature of each tectonothermal event. In this study, we present P-T estimates, zircon, monazite U(-Th)-Pb and biotite/K-feldspar Rb-Sr isochron ages of paragneisses from the SE Vestfold Block. One paragneiss sample, which is assigned to the Chelnok Paragneiss, has experienced a protracted metamorphism from the Neoarchean to the early Paleoproterozoic. Phase equilibria modeling constrained the peak P-T conditions to 7.2-9.6 kbar and 850-880 degree celsius, and the post-peak metamorphism to 4.2-5.6 kbar and 720-790 degree celsius, respectively. On the other hand, a paragneiss sample close to the ice sheet documented a high-grade metamorphic event at 918 +/- 23 Ma, with peak P-T conditions of 6.0-8.0 kbar and 860-880 degree celsius. Biotite/K-feldspar Rb-Sr dating for these two samples yields isochron ages of 474 +/- 12 and 442 +/- 7 Ma, respectively, representing the cooling ages of the Pan-African reworking. Collectively, an integrated application of diverse chronometers, combined with published data, indicates that the Vestfold Block may have experienced at least three major thermal events with variable intensities and extents. Initially, the supracrustal rocks in this region pervasively underwent a protracted high-grade thermal event from the Neoarchean to the early Paleoproterozoic, which formed the backbone of the block. Thereafter, the southern Vestfold Block experienced a Grenvillian granulite facies metamorphism, indicating that the Vestfold Block has been locally involved in the Rayner orogeny (i.e. the late Mesoproterozoic/early Neoproterozoic collision between the Indian craton and East Antarctica). Ultimately, the whole Vestfold Block may have been reworked under relatively low temperatures during the Pan-African Prydz tectonic event.

Precise constraints on the compositions of melts generated by anatexis under ultrahigh temperature (UHT) conditions are critical for understanding processes of partial melting and differentiation of the Earth's crust. Here we reveal geochemical and physical signatures of anatectic melts preserved as nanogranitoids (i.e. crystalized melt inclusions) within sapphirine-bearing UHT metapelitic granulites from the Mather Peninsula, East Antarctica. Their coexistence with high-Al orthopyroxene as inclusions in garnets strongly suggests that the investigated melts were at least partially UHT in origin. The nanogranitoids are enriched in SiO2 (69.9-75.6 wt.%), strongly peraluminous (ASI values = 1.2-1.6) and potassic to ultrapotassic (Na2O + K2O = 7.1-9.5 wt.%, K/Na = 2.2-9.3). When compared to the granulitic restite, the melts are enriched in Li, Cs, Rb, Ta, Sm, Nd, Zr, U and Pb, and depleted in Ce, Th, Ba, Sr and Nb. Their geochemical characteristics are consistent with biotite-dehydration melting in the absence of plagioclase. Our calculation results indicate that these hot crustal melts have low densities of 2.47 & PLUSMN; 0.07 g/cm(3), low viscosities of 10(4.9 & PLUSMN; 1.2) Pa & BULL;s and high heat production values of & SIM;2.8 & mu;W/m(3). Therefore, such melts are mobile and susceptible to be extracted from the source, and consequently their flow and removal from the deep crust may greatly affect the chemical and thermal structure of the continental crust. Secondary C - O - H fluid inclusions within garnet and orthopyroxene have also been detected. These inclusions contain magnesite, pyrophyllite, corundum, with or without residual CO2. The minerals within the fluid inclusions are interpreted as stepdaughter minerals, which were produced by the reaction of the fluid with its host. The metamorphic timing of the investigated rocks is still a matter of debate. Zircon U-Pb dating results obtained in this study suggest that the metapelitic granulites may have undergone two separated thermal events at & SIM;1000 and & SIM;530 Ma, respectively. The presence of fluid inclusions indicates that fluid infiltration and Pan-African reworking may have played an important role in obscuring chronological information of the early thermal scenario in poly-metamorphic terranes.

Mafic granulites from the Rauer Islands (East Antarctica) provide a spectacular example to investigate the behavior of monazite and zircon in response to metamorphic reactions and fluid–rock interaction. Previous studies have shown that these rocks experienced ultrahigh–temperature (UHT) metamorphism, followed by two stages of post–peak decompression and a final cooling stage. We characterized the secondary fluid inclusions in peritectic garnet and orthopyroxene, which occur as multiphase inclusions along micro–fractures. They consist of siderite, pyrophyllite, calcite, quartz and residual CO2, representing stepdaughter phases resulting from the interaction of C–O–H fluid with its hosts at variable temperatures during retrogression. Zircon grains show clear core–rim structure. The Dark–CL cores yield 206Pb/238U ages ranging from 540 ± 8 Ma to 507 ± 7 Ma, with a weighted mean age of 519 ± 3 Ma. Geochemical signatures and index mineral inclusions (i.e., such as garnet) in zircon cores suggest that these ages reflect the timing of the decomposition of garnet and therefore, the second stage of decompression. Dating for the bright–CL rims of the zircon grains shows that the final crystallization of anatectic melts occurred between 491 ± 7 Ma and 427 ± 9 Ma. The presented data provide novel and robust constraints on the timing of the post–peak evolution of the Rauer Islands. We also report on the occurrence of monazite in the Rauer UHT mafic granulites for the first time, which we propose formed during the first stage of decompression. Pre–peak melting of the rocks was accompanied by the dissolution of apatite. This may lead to the saturation of P in the melt, which was possibly responsible for the crystallization of the monazite. These monazite grains show texture–unrelated dates of 522–495 Ma, with a weighted mean value of 510 ± 3 Ma. These dates are at least ~20 Myr younger than their formation ages and therefore, are considered to have been disturbed. As monazite is more susceptible to fluid alteration than zircon, we conclude that the dates for monazite most likely reflect the timing of the influx of C–O–H fluid in the lower crust in the Cambrian (~510 Ma). This study highlights the importance of an integrated investigation of fluid and index mineral inclusions, as well as the chemical signatures of zircon and monazite, to interpret chronological data correctly.

Partial melting of granulites generates melts, which causes the modification of continental crust. However, the detailed mechanisms of this partial melting and related magmatic processes are debated. In this study, we investigated how crustal melting of granulites generated late Miocene (ca. 6.0 Ma) silicic volcanic rocks in the Chibuzhangcuo area of the Qiangtang Block, Tibet. Various peritectic textures (e.g., quartz inclusions in clino-pyroxene and fluorhydroxyl phlogopite) suggest that the pyroxenes were derived from a residual granulite phase and peritectic reactions, and were then entrained into the partial melts. The F-rich mica, granulite mineral as-semblages, and high titanomagnetite-ilmenite (811-975 degrees C) and zircon saturation (836-867 degrees C) temperatures indicate the silicic magmas were high-temperature and water-poor. The geochemical and isotopic compositions of the silicic volcanic rocks are similar to those of middle-lower crustal intermediate-mafic granulite xenoliths in Cenozoic volcanic rocks in the Qiangtang Block. We suggest that these volcanic rocks were generated by partial melting of hydrous mineral-bearing granulites, triggered by an underlying thermal anomaly associated with the high crustal heat-flow of the central Tibetan Plateau. This work indicates that the occurrence of restitic hydrous mineral and perturbation of thermal anomaly are the primary conditions to cause the partial melting of granulite. As the melting went on, the residual granulite phase and peritectic minerals were likely to be preferentially entrained into the melt due to the erosion effect caused by the continued melt flow at the sites of melting.