The lower mantle occupies over half of Earth's volume, and accordingly, its mineralogy is crucial in determining the structure and dynamics of Earth. Davemaoite, the calcium silicate perovskite, was believed to coexist with bridgmanite in the lower mantle and is considered essential for understanding the chemical evolution and dynamics of Earth's lower mantle. However, the presence of davemaoite is challenged due to the potential for high calcium silicate solubility in bridgmanite. Here we use an ultrahigh-pressure multi-anvil technique to show experimentally that the calcium solubility in bridgmanite is insufficient to eliminate davemaoite under mantle conditions, including typical mantle pressure, temperature and chemical compositions. We conclude that davemaoite has been stable in Earth's lower mantle since its formation. Due to the limited calcium solubility in bridgmanite, davemaoite-enriched domains are expected at the core-mantle boundary. These domains could serve as the principal reservoir for incompatible elements in the lower mantle and may be the source for some ocean island basalts. Furthermore, our study offers an explanation for the observed large low-shear-wave-velocity provinces at the bottom of the lower mantle. These provinces may consist of davemaoite-enriched materials crystallized from basal magma ocean in early Earth history.

Bridgmanite, a magnesium-rich silicate perovskite, is the most prevalent mineral in Earth's lower mantle and contains substantial quantities of ferric (oxidized) iron, even in equilibrium with iron metal. Mixing of oxygen-rich material from the lower mantle could have raised the oxidation state of the upper mantle to its present level after the more reducing conditions during core formation. However, it remains unclear how the lower-mantle oxygen content was established to achieve this level. Here we use high-pressure and temperature multi-anvil experiments at known oxygen fugacities to show that the bridgmanite ferric iron content is independent of pressure but decreases with temperature. Using these data, we build a thermodynamic model to calculate the ferric iron content of the lower mantle as bridgmanite crystallized from a reduced magma ocean in the early Earth. We determine that this ferric iron content would have been sufficient to explain the current upper mantle's ferric iron content after whole mantle mixing.

The phase transformations of MgSiO3 bridgmanite control the structure, dynamics and chemistry of the Earth's mantle. Formation of bridgmanite occurs at a depth of about 660 km causing the strong and abrupt seismic discontinuity. Previous experimental studies have revealed that this discontinuity is caused by ringwoodite dissociation in the average mantle. However, the cause of the 660-km seismic discontinuity beneath hotspots remains unclear. Here we determine the phase relations in the MgSiO3 system near the 660-km seismic discontinuity conditions. At 2,200-2,350 K with decreasing pressure, MgSiO3 bridgmanite first transforms to akimotoite and then to garnet. The akimotoite-bridgmanite boundary has almost no temperature dependence, whereas the garnet-akimotoite transition has a very steep positive boundary slope. Based on these slopes, we calculated the garnet-bridgmanite boundary slope. Depending on the temperature regime, the akimotoite-bridgmanite or the garnet-bridgmanite transition may occur in ascending plume beneath hotspots near the 660 km depth.

Glasses, unlike crystals, are intrinsically brittle due to the absence of microstructure-controlled toughening, creating fundamental constraints for their technological applications. Consequently, strategies for toughening glasses without compromising their other advantageous properties have been long sought after but elusive. Here we report exceptional toughening in oxide glasses via paracrystallization, using aluminosilicate glass as an example. By combining experiments and computational modelling, we demonstrate the uniform formation of crystal-like medium-range order clusters pervading the glass structure as a result of paracrystallization under high-pressure and high-temperature conditions. The paracrystalline oxide glasses display superior toughness, reaching up to 1.99 ± 0.06 MPa m1/2, surpassing any other reported bulk oxide glasses, to the best of our knowledge. We attribute this exceptional toughening to the excitation of multiple shear bands caused by a stress-induced inverse transformation from the paracrystalline to amorphous states, revealing plastic deformation characteristics. This discovery presents a potent strategy for designing highly damage-tolerant glass materials and emphasizes the substantial influence of atomic-level structural variation on the properties of oxide glasses.

Bridgmanite and CaSiO3-perovskite, respectively, are the first and third most abundant minerals in the Earth's lower mantle. The intersolubility of Ca and Mg between these two minerals is still under debate. Some studies indicated limited intersolubility, while others suggested a complete dissolution of CaSiO3-perovskite into bridgmanite at lower mantle conditions. This controversy leads to different explanations of the physical properties of the lower mantle such as density, elasticity, and viscosity, accordingly modifying our understanding of the nature and dynamics of the Earth’s interior. Therefore, it is essential to determine the intersolubility of bridgmanite and CaSiO3-perovskite.The intersolubility of Ca and Mg between bridgmanite and CaSiO3-perovskite can be affected by the temperature, pressure, and bulk compositions of the system. Previous studies showed an increase in intersolubility with temperature, but reported no robust pressure and composition dependence. Because FeAlO3 is the second dominant component in bridgmanite, investigating the effect of FeAlO3 content and pressure dependence is essential to clarify the phase relation of the Earth’s lower mantle.This study determined the pressure and FeAlO3 dependence on the intersolubility of bridgmanite and CaSiO3-perovskite at pressures of 27 to 40 GPa at a constant temperature of 2300 K using a multi-anvil press. Two compositions of MgSiO3:CaSiO3 = 1:1 and MgSiO3:FeAlO3:CaSiO3 = 3:2:5 were examined. SEM images clearly show the existence of two phases in all products. TEM-EDS analyses indicate a decrease in the CaSiO3 content of bridgmanite in both systems with increasing pressure. The FeAlO3 component only slightly enhances the CaSiO3 content of bridgmanite: adding the FeAlO3 component increases the CaSiO3 content of bridgmanite from 0.04(2) to 0.3(2) mol.% at 40 GPa. The MgSiO3 content of CaSiO3-perovskite decreases with increasing pressure from 1.8(7) to 0.06(8) mol.% in the FeAlO3-free system, and from 1.2(5) mol.% mol to an unmeasurably small value in the FeAlO3-bearing system. We conclude that, even with the presence of a FeAlO3 component in bridgmanite, the intersolubility is limited and remains nearly constant at different pressures. Thus, bridgmanite and CaSiO3-perovskite should coexist in the lower mantle, and CaSiO3-perovskite is the host mineral of large lithophile elements such as Ca in the lower mantle.

A better understanding of the kinematics of strike-slip faults in northern Tibet greatly affects our knowledge of the Cenozoic growth of the Tibetan plateau. Despite recent achievements in geometry and slip rate of the modern Altyn Tagh fault as well as the exhumation history of the basement rocks along the fault, how did the Altyn Tagh fault construct through time remains controversial. Here we combined sedimentological and geochronological datasets from the Anxi section in the remote Tula basin to reveal the source to sink system across the western segment of the Altyn Tagh fault through time. Compared with sedimentary records from other two sections (namely Caishiling and Eboliang sections) at the central segment of the Altyn Tagh fault, our study reveals that the Altyn Tagh Range consistently served as the major source of clastic materials for the Tula basin from the Early Jurassic to the Early Miocene, suggesting negligible strike-slip motion along the western segment of the Altyn Tagh fault before Miocene. However, the sediments in both Caishiling and Anxi sections show a consistent variation of composition through time, likely corresponding to the pre-Early Miocene strike-slip faulting along the central segment of the Altyn Tagh fault. Integrated with existing evidence of multistage mountain building process in orogenic belts in the northern Tibet, our inference of the differential initial rupture on different parts of the Altyn Tagh fault highlights a Middle Miocene reorganization of the deformation in the northern Tibetan plateau.

The 660-km seismic discontinuity (D660) is the boundary between the Earth’s lower mantle and transition zone and is commonly interpreted as the dissociation of (Mg,Fe)2SiO4 ringwoodite to (Mg,Fe)SiO3 bridgmanite plus (Mg,Fe)O ferropericlase (post-spinel transition). Prominent features of D660 are significant depressions to 750 km and multiplicity beneath cold subduction zones. Previous high-pressure experiments provided negative but gentle Clapeyron slopes (−1.3 to −0.5 MPa/K) of the post-spinel transition. Thus, the post-spinel transition cannot interpret the D660 depression. Therefore, another phase transition with a steep negative slope is required, and the akimotoite−bridgmanite transition in (Mg,Fe)SiO3 is one candidate. In the current study, we determined the boundaries of the post-spinel (RBP) and akimotoite−bridgmanite (AB) phase transitions in the MgO-SiO2 system over a temperature range of 1250–2085 K using advanced multi-anvil techniques with in situ X-ray diffraction. We judged a stable phase assemblage by observing relative increase/decrease in the ratio of coexisting high- and low-pressure assemblages at spontaneously and gradually decreasing pressure and a constant temperature from diffraction intensities. Since this strategy is strictly based on the principle of phase equilibrium, it excludes problems in determining phase stability caused by sluggish kinetics and surface energy. We found that the RBP boundary has a slightly concave curve, whereas the AB boundary has a steep convex curve. The RBP boundary is located at pressures of 23.2–23.7 GPa in the temperature range of 1250–2040 K. Its slope varies from −0.1 MPa/K at temperatures less than 1700 K to −0.9 MPa/K at 2000 K with an averaged value of −0.5 MPa/K. The slope of the AB boundary gradually changes from −8.1 MPa/K at low temperatures up to 1300 K to −3.2 MPa/K above 1600 K. Based on these findings, we predict that, beneath cold subduction zones, ringwoodite should first dissociate into akimotoite plus periclase, and then akimotoite transforms to bridgmanite with increasing depth; these successive transitions cause the multiple D660. Moreover, the steep negative boundary of the AB transition should result in cold-slab stagnation due to significant upward buoyancy. Our predictions are supported by the seismological observations beneath cold (e.g., Tonga, Izu-Bonin) subduction zones.

The 660-kilometre seismic discontinuity is the boundary between the Earth’s lower mantle and transition zone and is commonly interpreted as being due to the dissociation of ringwoodite to bridgmanite plus ferropericlase (post-spinel transition) 1 – 3 . A distinct feature of the 660-kilometre discontinuity is its depression to 750 kilometres beneath subduction zones 4 – 10 . However, in situ X-ray diffraction studies using multi-anvil techniques have demonstrated negative but gentle Clapeyron slopes (that is, the ratio between pressure and temperature changes) of the post-spinel transition that do not allow a significant depression 11 – 13 . On the other hand, conventional high-pressure experiments face difficulties in accurate phase identification due to inevitable pressure changes during heating and the persistent presence of metastable phases 1 , 3 . Here we determine the post-spinel and akimotoite–bridgmanite transition boundaries by multi-anvil experiments using in situ X-ray diffraction, with the boundaries strictly based on the definition of phase equilibrium. The post-spinel boundary has almost no temperature dependence, whereas the akimotoite–bridgmanite transition has a very steep negative boundary slope at temperatures lower than ambient mantle geotherms. The large depressions of the 660-kilometre discontinuity in cold subduction zones are thus interpreted as the akimotoite–bridgmanite transition. The steep negative boundary of the akimotoite–bridgmanite transition will cause slab stagnation (a stalling of the slab’s descent) due to significant upward buoyancy 14 , 15 .

Two approaches to simulations of phonon properties of solids beyond the harmonic approximation, the self-consistent ab initio lattice dynamics (SCAILD) and decoupled anharmonic mode approximation (DAMA) are critically benchmarked against each other and molecular dynamics simulations using a density-functional-theory description of electronic states, and compared to experimental data for fcc aluminium. The temperature-dependence of phonon dispersion and the phonon density-of-states, heat capacity, and the mean atomic displacement for fcc aluminium are examined with these approaches at ambient pressure. A comparison of results obtained with the harmonic approximation to the ones predicted by SCAILD and DAMA reveal a negligible anharmonic contribution to phonon frequencies, a small, but significant influence on heat capacity, and a strong effect on atomic mean-square displacement. The phase space accessed with SCAILD and DAMA is reduced relative to molecular and harmonic lattice dynamics simulations. In particular the DAMA results are in good agreement with displacement amplitudes determined by the Debye–Waller factor in x-ray diffraction experiments.

Snow preserves fresh water and impacts regional climate and the environment. Enabled by modern satellite Earth observations, fast and accurate automated snow mapping is now possible. In this study, we developed the Automated Snow Mapper Powered by Machine Learning (AutoSMILE), which is the first machine learning-based open-source system for snow mapping. It is built in a Python environment based on object-based analysis. AutoSMILE was first applied in a mountainous area of 1002 km2 in Bome County, eastern Tibetan Plateau. A multispectral image from Sentinel-2B, a digital elevation model, and machine learning algorithms such as random forest and convolutional neural network, were utilized. Taking only 5% of the study area as the training zone, AutoSMILE yielded an extraordinarily satisfactory result over the rest of the study area: the producer’s accuracy, user’s accuracy, intersection over union and overall accuracy reached 99.42%, 98.78%, 98.21% and 98.76%, respectively, at object level, corresponding to 98.84%, 98.35%, 97.23% and 98.07%, respectively, at pixel level. The model trained in Bome County was subsequently used to map snow at the Qimantag Mountain region in the northern Tibetan Plateau, and a high overall accuracy of 97.22% was achieved. AutoSMILE outperformed threshold-based methods at both sites and exhibited superior performance especially in handling complex land covers. The outstanding performance and robustness of AutoSMILE in the case studies suggest that AutoSMILE is a fast and reliable tool for large-scale high-accuracy snow mapping and monitoring.

Segregation of liquid metal from solid silicate is a necessary pathway for core formation in a large rocky planetary body during the planet growth. The mechanism and extent of such process have an ...

Phase relations in the system MgSiO3-Al2O3 were investigated at pressures of 27-45GPa and temperatures of 1700, 2000, and 2300K using sintered diamond and tungsten carbide anvils in a multianvil apparatus. The bulk compositions in the MgSiO3-Al2O3 binary system crystallize a phase assemblage of pyrope and corundum at pressures below 27GPa and an assemblage of bridgmanite and corundum at pressures above 27GPa regardless of temperatures. The solubility of Al2O3 in bridgmanite and that of MgSiO3 in corundum increases significantly with increasing temperature. The solubility of Al2O3 in bridgmanite increases from 6.7mol% at 1700K to 21.8mol% at 2500K under a constant pressure of 27GPa. Bridgmanite becomes more aluminous with increasing pressure from 27 to 45GPa at a given temperature. The MgSiO3 content in corundum increases with increasing pressure at pressure lower than 27GPa, while it decreases at pressure higher than 27GPa. Our results suggest that bridgmanite can incorporate a considerably higher Al2O3 content than that of the pyrope composition (25mol% Al2O3). The present study further suggests that the entire Al2O3 component is accommodated into bridgmanite in the pyrolite lower mantle. However, Al2O3 cannot be fully accommodated into bridgmanite in the coldest parts of subducted slabs in the shallow part of the lower mantle, and therefore, additional phases such as MgAl2O4 with calcium ferrite-type structure are necessary to host the excess Al2O3.Plain Language Summary Here we determined the phase relations in the system MgSiO3-Al2O3 up to 2300K under lower mantle pressures and found that the solubility of Al2O3 in bridgmanite and that of MgSiO3 in corundum increase with increasing temperature. All Al2O3 can be completely accommodated into bridgmanite in the pyrolite composition, while the Al2O3 cannot be fully accommodated into bridgmanite in the coldest parts of subducted slabs, and therefore, additional phases are required to host the excess Al2O3.

We have generated over 40 GPa pressures, namely, 43 and 44 GPa, at ambient temperature and 2000 K, respectively, using Kawai-type multi-anvil presses (KMAP) with tungsten carbide anvils for the first time. These high-pressure generations were achieved by combining the following pressure-generation techniques: (1) precisely aligned guide block systems, (2) high hardness of tungsten carbide, (3) tapering of second-stage anvil faces, (4) materials with high bulk modulus in a high-pressure cell, and (5) high heating efficiency.