Yuegao Liu

Magmatic anhydrite has long been regarded as diagnostic of oxidised intermediate–felsic magmas in porphyry Cu deposits. Here we report the world’s first occurrence of mantle-derived magmatic anhydrite in ultramafic rocks. The age of the clinopyroxenite and hornblendite hosting the anhydrite in the Langmuri magmatic platinum group elements (PGEs) sulfide deposit is 409 ± 2 Ma, shortly younger than the Paleozoic Oxygenation Event (POE). The anhydrite coexists with igneous carbonate minerals and Ca-O-C-Fe-S isotopes indicate oxidation of the mantle source by recycled oxidised surface-derived carbonates due to the POE. After the POE, the more oxidised supra-subduction mantle is coupled with the emergence of magmatic sulfide deposits in the orogen during the Late Paleozoic (410–270 Ma) and a rapidly increased frequency of porphyry Cu deposits worldwide. Our results further suggest that high-Mg basaltic magma, typically considered to be the parent magma of magmatic sulfide deposits in orogen, can evolve into PGE-enriched porphyry Cu deposit systems. This requires sufficiently high oxygen fugacity in magma after POE to retain sulfur predominantly as sulfate and thereby suppress sulfide saturation after olivine differentiation. Our findings link atmospheric oxygenation to deep Earth redox evolution, recording secular changes in Earth's redox state that fundamentally controlled the evolution of strategic metal sulfide deposits.

The search for new phases is an important direction in materials science. The phase transition of sulfides results in significant changes in catalytic performance, such as MoS₂ and WS₂. Cubic pentlandite [cPn, (Fe, Ni)₉S₈] can be a functional material in batteries, solar cells, and catalytic fields. However, no report about the material properties of other phases of pentlandite exists. In this study, the unit‐cell parameters of a new phase of pentlandite, sulfur‐vacancy enriched hexagonal pentlandite (hPn), and the phase boundary between cPn and hPn are determined for the first time. Compared to cPn, the hPn shows a high coordination number, more sulfur vacancies, and high conductivity, which result in significantly higher hydrogen evolution performance of hPn than that of cPn and make the non‐nano rock catalyst hPn superior to other most known nanosulfide catalysts. The increase of sulfur vacancies during phase transition provides a new approach to designing functional materials.

In the solar system, oldhamite (CaS) is generally considered to be formed by the condensation of solar nebula gas. Enstatite chondrites, one of the most important repositories of oldhamite, are believed to be the representative of the material which formed Earth. Thus, the formation mechanism and the evolution process of oldhamite are of great significance to the deeply understanding about the solar nebula, meteorites, the origin of Earth, and the C-O-S-Ca cycles of Earth. To date, no report about the oldhamite in the mantle exists. However, here we show the formation of oldhamite through the reaction between sulfide-bearing orthopyroxenite and molten calcite at 1.5 GPa/1510 K and 0.5 GPa/1320 K. Surprisingly the oxygen fugacities in our experiments are within the range of mantle conditions, which is 6 orders of magnitude higher than that of the solar nebula mechanism. Oldhamite is easily oxidized to calcium sulfate. Both low oxygen fugacity of magma and extreme low oxygen content of atmosphere are necessary for existence of oldhamite on the surface of a planet; otherwise, anhydrite or gypsum will exist in large quantities. The widespread existence of oldhamite on the planet surface indicates the planet is definitely not habitable because of the scarcity of oxygen. The formation and oxidation of oldhamite are accompanied by the production of carbon dioxide and the consumption of oxygen, which may have an impact on the Earth atmosphere before the Great Oxidation Event and during the Permian-Triassic Boundary.

In the solar system, oldhamite (CaS) is generally considered to be formed by the condensation of solar nebula gas. Enstatite chondrites, one of the most important repositories of oldhamite, are believed to be representative of the material that formed Earth. Thus, the formation mechanism and the evolution process of oldhamite are of great significance to the deep understanding of the solar nebula, meteorites, the origin of Earth, and the C–O–S–Ca cycles of Earth. Until now, oldhamite has not been reported to occur in mantle rock. However, here we show the formation of oldhamite through the reaction between sulfide-bearing orthopyroxenite and molten CaCO₃ at 1.5 GPa/1510 K, 0.5 GPa/1320 K, and 0.3 GPa/1273 K. Importantly, this reaction occurs at oxygen fugacities within the range of upper-mantle conditions, six orders of magnitude higher than that of the solar nebula mechanism. Oldhamite is easily oxidized to CaSO₄ or hydrolysed to produce calcium hydroxide. Low oxygen fugacity of magma, extremely low oxygen content of the atmosphere, and the lack of a large amount of liquid water on the celestial body's surface are necessary for the widespread existence of oldhamite on the surface of a celestial body otherwise, anhydrite or gypsum will exist in large quantities. Oldhamites may exist in the upper mantle beneath mid-ocean ridges. Additionally, oldhamites may have been a contributing factor to the early Earth's atmospheric hypoxia environment, and the transient existence of oldhamites during the interaction between reducing sulfur-bearing magma and carbonate could have had an impact on the changes in atmospheric composition during the Permian–Triassic Boundary.

Zircon (ZrSiO₄) provides a good pressure-holding environment for ultra-high-pressure metamorphic minerals during crust exhumation due to its high incompressibility and chemical stability. At high pressure, the zircon can transform to reidite. Previous studies show much higher phase-transition pressures at room temperature than those at high temperature (>1000 K) due to kinetic hindrance. To further investigate the kinetics of the zircon–reidite phase transition at relatively low temperatures, the phase boundary at 298–800 K was determined using a diamond anvil cell combined with in situ Raman spectra. The results show that reidite becomes thermodynamically more stable compared with zircon at 8 GPa at room temperature, and the slope of the phase boundary at 298–800 K abruptly differs from that of previous studies at 1100–1900 K. Compared with the equilibrium phase boundary calculated by the density functional theory, it indicates that the kinetic effect of the zircon–reidite phase transition is obvious, and there exists a sufficiently large energy driving force provided by an overpressure to overcome the activation energy barrier below a critical temperature of approximately 880 K. The temperature dependence of overpressure is about 0.023 GPa/K.

Antigorite is the main carrier of water in Earth’s subduction zones. The dehydration processes of antigorite were investigated by carrying out in situ phase transition experiments using a dynamic diamond anvil cell, with a time-resolved Raman scattering system, at 0.3–10 GPa and 396–1100 K. Three typical phase transformation reactions occurred within the P–T range of this study, corresponding to three reaction products. At low pressures (8.6 GPa), the products of the dehydration phase transition of antigorite are consistently clinoenstatite and phase A. Compared with the previous studies carried out by large-volume presses (such as a multi anvil press and a piston-cylinder press), the reaction to produce phase A occurs at higher P–T conditions, and the stable temperature region for talc as a dehydration product is narrower. Moreover, large quantities of pores with 5–10 μm in diameter formed in dehydration products, supporting the hypothesis that intermediate-depth earthquakes may result from dehydration embrittlement. The precise phase boundary determined by this in situ study provides a better understanding of the dehydration phase transition behavior and geological phenomena exhibited by antigorite under different pressure and temperature conditions.

Extensive crustal anatexis is common during the decompressional exhumation of deeply subducted continental crust and the delamination of a collision‐thickened orogenic lithosphere, indicating that determining the timing of partial melting can provide insights into the possible tectonic evolution during orogenic processes. An integrated study of petrology, zirconology and whole-rock geochemical compositions from migmatites and pegmatites in the Nageng, Langmuri and Wulonggou area of the East Kunlun Orogenic Belt, is presented in this study. The protoliths of these migmatites include Tonian sedimentary rocks and ca. 440 Ma arc-related dioritic rock. Together with previous studies, an extensive crustal anatexis event recorded by anatectic zircons occurred after ca. 410 Ma. In addition, hafnium isotope analyses indicate that the anatectic zircons may or may not inherit their Hf isotope compositions from protolith zircons during partial melting, depending on whether or not the garnet Hf contributes to the Hf budget of anatectic melt. Thus, the most reasonable method to trace the source of granite is to compare the Hf isotope composition of anatectic zircon in migmatite and magmatic zircon in contemporaneous granite. By such method, anatectic melt produced by migmatites in this study could account for both penecontemporaneous A- and I-type granites with high magmatic zircon ε_Hf(t) values and S-type granites with low magmatic zircon ε_Hf(t) values. As the extensive crustal anatexis is later than both metamorphic peak and amphibole-facies retrogression of high-pressure and ultrahigh-pressure (HP-UHP) metamorphic rocks, it is reasonable that post-collision orogenic collapse of the collision‐thickened orogenic lithosphere as a result of delamination and asthenospheric upwelling occurred after ca. 410 Ma, which is also supported by contemporaneous granulite-facies metamorphism, molasse deposition, and magmatic events including Xiarihamu mafic-ultramafic intrusions, A-type granites, and mafic dykes formed in the continental rifting setting.