Equation of state (EoS) plays a crucial role in the prediction of the composition of the outer core. Here, we calculated pressure (P)-volume (V)-temperature (T) data of liquid iron-oxygen alloys (Fe-X wt.% O, X = 0, 2.8, 6.1, and 9.9) under the outer core conditions (∼136–330 GPa, 4000–6000 K) by first-principles molecular dynamics simulations. We established an EoS for liquid Fe-O alloys with parameters including P, T, V, and O concentrations. Consequently, thermodynamic properties of liquid Fe-O alloys such as density (ρ), thermal expansion coefficient, isothermal and adiabatic bulk modulus, and sound velocity (VP) are calculated. To constrain the O content, we predicted the ρ-P and VP-P profiles along the geotherm and compared them with data from the Preliminary Reference Earth Model (PREM). We conclude that the adiabatic T profile as a function of depth affects the prediction of O content dramatically. With several anchored TICB, the composition of Fe-6.1 wt.% O matches the PREM data with an acceptable range of error. But strictly speaking, the distribution in the outer core is probably uneven. In such case, we state that the O content in the outer core cannot be higher than approximately 6.1 wt.%.
Sediments are one of the main carbon sinks in subduction zones, with CaCO3 and SiO2 being the main components in sediments. Their chemical stability plays a significant role in the form of carbon in the Earth’s mantle. Here we report the reactions of CaCO3 with SiO2 in hydrated sediments at 0.8–2.0 GPa, 400–500 ℃ and redox-buffered conditions relevant to shallow subduction zones. Our results show that the reaction CaCO3 + SiO2 = CaSiO3 + C + O2(fluid) occurs under CoCoO and IW buffered conditions to generate wollastonite (CaSiO3) and carbonaceous material (CM). Moreover, wollastonite is formed by the dissolution-crystallization process, which may be significantly affected by oxygen fugacity, leading to distinct crystallization habits (
Ringwoodite is an important mineral in the mantle transition zone, and its cationic disorder can profoundly affect its physicochemical properties, but there is currently much controversy about this disorder. In this study, we investigate the cation disorder states of pure Mg2SiO4-ringwoodite and defective ringwoodite under mantle transition zone conditions through DFT calculations and thermodynamic models. Two stable endmembers are seen, one with normal ringwoodite structure and the other with inverted structure (its Si atoms and half of its Mg atoms have swapped sites). Our results indicate that pure ringwoodite does not invert (swap Mg and Si cations) under normal mantle temperatures but the introduction of a Si-excess, Mg-deficient defect induces a swap at normal mantle temperatures and this swap is likely induced by a wide range of defects including water. Thus, in the presence of such a defect or similar defects the olivine phase transition sequence may then go from olivine to wadsleyite to inverse ringwoodite, and then normal ringwoodite. We calculate the seismic properties of normal and inverse ringwoodite and find significantly slower wave speeds in inverted ringwoodite. Due to this difference the presence of inverse ringwoodite may provide a potential explanation for the discontinuous interface of seismic waves at the depth of ∼560 km.
The bridgmanite (Bgm) to silicate post-perovskite (PPv) phase transition is believed to be the main cause for the distinct seismic features observed in the D'' layer, the lowermost region of the Earth’s mantle. However, the transition depth and elasticity of the PPv phase have been highly debated, as the chemical complexity within the D'' layer can largely affect the Bgm-PPv transition pressure and the associated velocity contrast. Experimental measurements of sound velocities for PPv with different chemical compositions under relevant lowermost-mantle conditions are essential but remain limited. In this study, we have reliably measured both compressional wave velocity (VP), shear wave velocity (VS), and density, for two Fe-bearing PPv compositions [(Mg0.85Fe0.15)SiO3 and (Mg0.75Fe0.25)SiO3] at lowermost mantle pressures using Impulsive Stimulated Light Scattering (ISS), Brillouin Light Scattering (BLS), and X-ray Diffraction (XRD) in diamond anvil cells. Our results indicate that the velocities of Fe-bearing PPv at 120 GPa can be described by the following relationships: VS (km/s) = 7.65–2.8XFe and VP (km/s) = 14.11–3.8XFe, where XFe represents mole fraction of the Fe content. The variations in the Fe content of PPv may provide one of the explanations for the seismic lateral variations observed at the Earth’s core mantle boundary. By comparing our results with the high-pressure velocities of Bgm, our velocity model suggests significant discontinuities across the Bgm-PPv transition, characterized by a reduction in both VP and VΦ, and an increase in VS. These findings highlight the importance of considering the influence of chemical composition, particularly Fe content which could vary significantly at the D'' region, on the seismic properties of the PPv phase. The observed velocity contrasts across the Bgm-PPv transition may contribute to the complex seismic signatures observed in the D'' layer, underscoring the potential role of this phase transition in interpreting the seismic features of the lowermost mantle region.
The comprehension of the composition and physical state of the deep interiors of large planets, as well as the impact events pertinent to planetary formation and evolution, necessitates an understanding of the properties of planetary materials under extreme conditions. Forsterite (Mg2SiO4), a significant geological mineral, has not been fully characterized in terms of its behavior under shock compression due to a lack of consensus among previous experiments and simulations aimed at determining its Hugoniot, as well as the absence of knowledge of sound velocity at high pressures, a critical parameter indicative of phase transformation and melting.
The vibrational and electrical transport properties of natural siderite are systematically investigated by means of in-situ Raman spectroscopy and alternating current impedance spectroscopy under conditions of 0.6–55.6 GPa, 298–873 K and different hydrostatic environments using a diamond anvil cell (DAC). Upon non-hydrostatic compression, all of these observable characteristic variations of siderite including the appearance of three absolutely new Raman peaks (L’, v4′ and v1′), the disappearance of Raman peaks (T, L and v4) and the discontinuity in the pressure-dependent electrical conductivity can provide robust evidence of electronic spin transitions of Fe2+ from high-spin to mixed-spin to low-spin states at the respective pressures of 42.5 GPa and 48.5 GPa. As far as hydrostatic condition, the electronic spin states from high-spin to mixed-spin to low-spin states occurred at the higher pressures of 45.7 GPa and 50.4 GPa, respectively, which implied the highly sensitive hydrostaticity of electronic spin transition pressures. Upon decompression, the reverse electronic spin transitions from low-spin to mixed-spin to high-spin states were detected at the respective pressures of 47.2 GPa and 28.7 GPa under non-hydrostatic condition, and as well as at the pressures of 49.4 GPa and 25.1 GPa under hydrostatic condition, respectively. The huge pressure hysteresis of 13.8 GPa and 20.6 GPa for the electronic spin state transition was revealed under non-hydrostatic and hydrostatic environments, respectively. In order to explore the effect of temperature on the electronic spin transition, a series of electrical conductivity experiments on siderite were performed over the temperature range of 323–873 K under conditions of three typical pressures of 47.7, 49.8 and 51.6 GPa. Furthermore, the functional relationships between the temperature and pressure describing the high-spin to mixed-spin to low-spin transitions for siderite were successfully established: P1 (GPa) = 39.318 + 0.015 T (K) and P2 (GPa) = 41.277 + 0.018 T (K), respectively. In conclusion, our acquired phase diagram of the electronic spin transition on siderite is beneficial to deep insight into the electronic spin behavior for those of iron-bearing carbonate minerals under high-temperature and high-pressure conditions.
The water migration in subduction zones, primarily driven by the phase transition in hydrous minerals, can give rise to hydrated regions with reduced velocity. A fundamental element in comprehending and deciphering these low-velocity zones revolves around acquiring insights into the stability and elasticity of relevant hydrous minerals. As one of the main water carriers in shallow areas, antigorite can dehydrate to form talc, forsterite, and fluid (talc–bearing peridotites) in deep areas of subduction zones, and then the talc thus serves as one of the minerals that can bring water to the deep Earth. Here, the elasticity of talc up to 24 GPa and forsterite up to 12 GPa are calculated by using the first principles method. The result supposes that the talc structure transforming from talc I to talc II is at a pressure between 6 GPa and 8 GPa, impacting the trend of elastic wave velocity in response to pressure. Furthermore, the elastic wave velocity of forsterite can be significantly affected by iron concentration. Meanwhile, a variation velocity model with antigorite consumption and talc content is set up for talc-bearing serpentinized peridotite based on the elastic properties of talc and forsterite in this study, and antigorite in Wang et al. (
Molecular hydrogen (H2) may be an important form of water in nominally anhydrous minerals in the Earth’s mantle and plays a critical role in mantle water cycle, but the transport properties of H2 remain unclear. Here, the diffusion of H2 in Fe-free olivine lattice is investigated at pressures of 1–13 GPa and temperatures of 1300–1900 K by first-principles molecular dynamics. The activation energy and activation volume for H2 diffusion in Fe-free olivine are determined to be 55 ± 8 kJ/mol and 3.6 ± 0.2 cm3/mol, respectively. H2 diffusion in Fe-free olivine is faster than H+ by 1–4 orders of magnitude and therefore it is more favorable for hydrogen transportation under upper mantle conditions. H2 can be carried to the mantle transition zone by subducting slabs without releasing to the surrounding mantle. The upper mantle may act as a lid, preventing the releasing of H2 produced in the deep mantle to the surface.
Since there is a scientific consensus that the energy sector has brought the planet to the tipping point of climate change, transitioning to sustainable energy sources is inevitable to halt foreseeable climatic adversities. This study looks at how promoting green taxation and sustainable energy transition affected the G7 nations’ goal of low-carbon development between 1994 and 2020. This study used Generalized Least Squares Random Effects Regression and Driscoll-Kraay Standard Errors-based Least Sqaures approaches for empirical analysis. The latter approach accounts for cross-sectional dependence, heteroscedasticity, and autocorrelation to provide robust empirical outcomes. The empirical results are as follows: Firstly, through lowering CO2 intensity and greenhouse gas emissions, the environmental tax revenues have enhanced the condition of the environment. The total tax revenues linked to the environment had a greater overall impact than the tax revenues related to the energy industry. Furthermore, compared to CO2 intensity, both of the environmental tax revenue factors contributed considerably more to greenhouse gas emissions. Second, the sustainable energy transition helped to lower greenhouse gas and CO2 intensity. Among covariates, international trade was supportive of low-carbon development, but industrialization and GDP per capita did the opposite. The panel bootstrap causality revealed a unidirectional causal connection from all independent variables, except foreign direct investment, to CO2 intensity and greenhouse gas emissions. These results demonstrated that the G7 nations’ environmental policies supported their commitment to achieving low-carbon development goals. In this respect, the G7 nations’ environmental emission reduction efforts benefited more from the overall environmental tax revenues. To secure the industrial emissions reduction for a future with net-zero carbon emissions, it is thus advised to continue using policies that price environmental emissions, such as the carbon taxation regulations. Additionally, plans for the sustainable energy transition that includes a quick rise in renewable energy sources in the overall energy mix are successful in lowering environmental emissions. For environmental sustainability and low-carbon development, it is thus advised to divert the taxation burden from renewable energy technologies to the fossil fuel industry to enhance the sustainable energy transition phenomenon for achieving Sustainable Development Goals (especially SDG-7 and SDG-13).
The aqueous fluids within subducted slabs have the potential to influence the form of carbonate presence and the carbon cycling process. Experiments were performed on resistive heating diamond anvil cell using siderite crystals and grains with water under conditions of pressure as high as 11.4 GPa and temperatures reaching up to 530 °C. These experiments aimed to simulate geological reactions that may occur within a depth range of 340 km in subducted slabs. Raman spectroscopy was employed to monitor the reactions and microscale phenomena within the sample chamber as pressure and temperature increase. The recovered products were analyzed using scanning electron microscopy and transmission electron microscopy. The results indicate that at 0.8 GPa and 108 °C, a Fischer-Tropsch Type (FTT) reaction occurred on the sample surface, resulting in the formation of organic compound formaldehyde, followed by the observation of formic acid. At higher pressure and temperature (3.5 GPa, 420 °C), the formation of γ-Fe2O3 and γ-FeOOH was observed on the sample surface, accompanied by the release of CO2 and H2. Transmission electron microscope analysis of the quenched product powders indicated that the generated iron oxides were consistent with the phases observed at high pressure and temperature conditions. High pressure and temperature dissolution experiments of siderite in water reveal that carbon may be released into the mantle wedge entirely in the form of CO2 in warm subducted slabs and cold subducted slabs that subduct to depths of 75 km. The released CO2 participates in the carbon cycle of the island arc volcanic systems in the upper mantle at depths of 70–120 km and accelerates the transfer of subducted carbon to the Earth’s surface.
Helium diffusion in carbonates under mantle pressure is crucial for understanding thermal and chemical evolution of mantle. Based on the density functional theory (DFT) and the the climbing image nudged elastic band (CI-NEB) method, we performed first-principles calculations of diffusion characteristics of helium in perfect aragonite crystal under high pressure to 40 GPa. Our results show that He diffusion behaviors are controlled by pressure, temperature and crystal size. The activation energy increases, and the diffusion coefficients decrease significantly under high pressure. Ea[1 0 0] increases from 176.02 kJ/mol to 278.75 kJ/mol, and Ea[0 0 1] increases from 195.89 kJ/mol to 290.43 kJ/mol, with pressure increasing from 20 GPa to 40 GPa. At 700 K, the diffusion coefficients at 40 GPa is 7 orders of magnitude lower than that at 20 GPa; and at 1000 K it decrease 5 orders of magnitude. To ensure that at least 90% helium is not lost, we synthesized the temperature obtained from cooling and heating processes and derive the 'stable temperature range' for helium in aragonite. The obtained results show that the stable temperature range is 22–76 ℃ at 0 GPa and 641–872 °C at 40 GPa, for the crystal of 100–2000 μm size. Besides, the travel time of helium in aragonite under high pressure increases rapidly with pressure increasing. Our calculations indicate that helium can be quantitatively retained in aragonite in the deep mantle as long as the temperature is in the 'stable temperature range'. These results have certain implications for exploring the evolution of mantle and the storage of helium within it.
Hydrous minerals play a critical role in modifying the physical and chemical properties of the Earth’s interior. Among those, epidote is an important hydrous mineral in greenschist and blueschist phases of the metamorphosed subducting crust at shallow depth (30-60 km). Here, we measured the compressional (P) and shear (S) wave velocities of a polycrystalline epidote sample at pressures up to 7 GPa and room temperature by means of ultrasonic interferometry. The obtained sound velocities and elastic moduli of epidote increase monotonically with pressure. Finite strain analysis on those data set yielded the elastic moduli and their pressure derivatives of epidote at ambient condition as follows:
The paleogeographic reconstruction of fragmented and dispersed continents often poses a challenge due to the lack of information regarding the nature of that extend beneath passive margin basins. To define the width of the continental crust beneath passive margin basins and its implications for paleogeographic reconstruction of conjugate continental margins, this study investigates the architecture of the stretched continental crust of the southern South Atlantic conjugate margin. The investigated region encompasses South Africa, Namibia, southern Brazil, and Uruguay, which were formed during the Mesozoic rifting of SW Gondwana. Employing a multi-tool approach combining seismic interpretation, gravity, magnetometry, and U-Pb isotopic data, the research aims to quantify the extension of stretched continental crust and its implications for plate reconstructions. The study reveals that the restored stretched crust spans at least 150 km, emphasizing the significance of considering connections between both margins for realistic paleogeographic reconstructions. Furthermore, the distinct U-Pb zircon age distribution patterns between SW Africa and SE South America reinforce the lack of direct connections despite their Gondwanan origin. The missing link estimated in this study is around 150 km, comparable in size to major mountain ranges such as the Andean or Urals. This work sheds light on critical aspects of Earth’s dynamic crustal evolution and emphasizes the need for comprehensive reconstructions considering stretched and eroded crust in the South Atlantic conjugate margin.
Viscosity is critical for controlling the dynamics and evolution of the Earth’s inner core (IC). The viscosities of hexagonal close-packed (hcp) and body-centred cubic (bcc) Fe were studied experimentally and theoretically under Earth's core conditions. However, Earth’s inner core is mainly composed of Fe-Ni alloys with some light element impurities (Si, S, C, H, O), and the influence of impurities (Ni, Si, S, C, H, and O) on viscosity is still unknown. In this study, the diffusion coefficients of Fe, Ni, Si, S, C, H, and O were calculated under IC conditions using ab initio molecular dynamics (AIMD) and deep learning molecular dynamics (DPMD) methods. Among them, C, H, and O are highly diffusive like liquids in the lattice, while Fe, Ni, Si, and S diffuse through Fe site vacancies. In binary alloys, the influence of these impurities (Ni: 12.5%, S: 3.6%, Si: 3.1%, C: 1.3%, O: 1.7%, H: 0.4% by weight) on viscosity is insignificant. Based on the dislocation creep mechanism, the predicted viscosities of the hcp Fe alloys are 1 × 1014–2 × 1016 Pa·s, which is consistent with the values predicted by free inner core nutation and seismic wave attenuation observations.
Structure and composition of Earth are fundamental importance in exploring the dynamic evolution of the crust and mantle. The Qinling Orogenic Belt (QOB) is located between the North China plate and the South China Plate, and is one of the main orogenic belts in China. To explore the composition and origin of anisotropy and the low wave velocity zone of the QOB, ten rock samples (gneiss and schist) were collected from the five sites of the QOB and the P- and S-wave velocities of these samples were measured under 0.6 to 2.0 GPa and 100 to 550 °C. The wave velocities increase with increasing pressure and decreasing temperature. The VP and VS of the schist and gneiss match the velocity of the middle and lower crust of the QOB, indicating that schist and gneiss are important component of the QOB. All the schist and gneiss samples exhibit obvious seismic anisotropy with 1.64%–17.42% for VS and 2.93%–14.78% for VP under conditions of crust and upper mantle. The CPO/LPO and layering distribution of mica in rock samples are the main reasons for this anisotropy. The VS structures below the five sampled sites from seismic ambient noise tomography were built to explore the effect of schist and gneiss on the composition and structure of the QOB. The results indicate that orientation-arranged gneiss and schist driven by the tectonic stresses might be a new origin of the character of VP/VS, seismic anisotropy, and the low velocity zone in the QOB.
Brucite is a common hydrous mineral on Earth and may contribute to the deep water cycle of the Earth, but its stability and structure under mantle conditions remain uncertain. In this study, we investigated the stability of brucite up to 60 GPa at 800 K and 45 GPa at 1850 K. Within the experiment P-T conditions, no theoretically predicted new phase was observed, and brucite remained in the P
Existing studies provide adequate petrological evidences on ca. 500 Ma ultra-high pressure (UHP) metamorphism in the North Qinling Orogenic Belt (NQOB) in central China, but the genesis of 470–420 Ma multi-phase granulite-facies metamorphism in the NQOB and their relationship with the ca. 500 Ma UHP metamorphism remain controversial, resulting in the early Paleozoic evolution of the Qinling Orogenic Belt (QOB) highly debatable. In this study, we present mafic granulites and host felsic gneisses with a “red-eye socket” texture from the Shuanglong area, eastern NQOB, which recorded two phases of granulite-facies metamorphism superimposing on former eclogite-facies metamorphism. The former eclogite-facies metamorphism is indicated by eclogite-facies zircon trace element patterns and 496–495 Ma zircon ages, which are the same with those of the HP–UHP eclogite-facies metamorphic rocks in NQOB. The first granulite-facies metamorphism occurred at 460–448 Ma is characterized by coarse-grained minerals in matrix. Compositions and zonings of these minerals define an anticlockwise P–T path involving a prograde stage (751–763 °C), a high-temperature peak stage (9.2 kbar and 864 °C), and a near-isobaric cooling retrograde stage (8.3 kbar and 818 °C). The second granulite-facies metamorphism occurred at 422–421 Ma is represented by coronal garnet and coexisting fine-grained mineral aggregates. Coronal garnet compositional zonings suggest a clockwise P–T path consisting of a high-pressure peak stage (9.5–11.2 kbar and 748–783 °C) and a decompressing and heating retrograde stage (9.2–9.5 kbar and 789–800 °C). Combining dating results of leucosomes in these rocks and existing data, we proposed a new model for early Paleozoic tectonic evolution of the NQOB. The North Qinling Terrane (NQT), probably separated from the South China Block (SCB) during the breakup of Rodinia, drifted northwards and underwent UHP metamorphism at 500 Ma and then rapidly exhumed to crust level. Later, the Shangdan Ocean subducted northwards beneath the exhumed NQT at 470–440 Ma, resulting in the first granulite-facies metamorphism and contemporaneous migmatization and magmatism. Finally, the closure of the Shangdan Ocean led to collision between the NQT and South Qinling Terrane/SCB and the second granulite-facies metamorphism and anatexis at 422–418 Ma.
The Meso-Cenozoic geodynamic evolution of northern Türkiye remains a subject of debate primarily due to a lack of systematic geological, geochemical, geochronological, and geophysical investigations. This paper presents comprehensive geochronological and geochemical data on the Late Triassic andesite porphyry, andesite breccia and quartz diorite porphyry, and the Middle Jurassic diabase, and amphibole-poor and amphibole-rich andesite porphyry from Çevrepınar Igneous Complex (Gümüşhane) in the southern part of the Eastern Pontides Orogenic Belt (EPOB), a well-preserved continental arc in the Alpine-Himalayan orogen. Zircon U–Pb geochronology indicates crystallization ages of ∼208–202 Ma (Rhaetian) for the Late Triassic rocks and ∼175–172 Ma (Aalenian) for the Middle Jurassic rocks. Whole-rock geochemical and Sr-Nd-Pb isotopic data, and zircon εHf(t) data indicate that both the Late Triassic and the Middle Jurassic rocks originated by low-degree melting of a spinel lherzolite lithospheric mantle source modified by subduction-related fluids and/or melts. Based on the new and published data, we suggest that the Late Triassic to Middle Jurassic arc magmatism in EPOB occurred as a result of southward subduction of the Paleo-Tethys oceanic lithosphere beneath the northern margin of Gondwana-Land. Late Triassic to Jurassic arc magmatism and basin evolution occurred synchronously in the northern and southern peripheries of the present-day Eastern Black Sea Basin, indicating divergent double subduction of the Paleo-Tethys oceanic lithosphere beneath the northern margin of Gondwana and southern margin of Laurasia during the Early Mesozoic.
The distribution of gold in small acicular arsenopyrite of a pyrite-arsenopyrite association from Suzdal (Eastern Kazakhstan), Olympiada (Yenisei Ridge, Russia) and large pseudorhombic arsenopyrite crystals from Bazovskoe (Yakutia, Russia) orogenic-type deposits were investigated. On orogenic gold deposits in NE Asia, occurring mainly in black shales, two productive stages of ore deposition are distinguished, which correspond to two morphological varieties of arsenopyrite. At the early stage, fine-grained acicular-prismatic arsenopyrite with invisible gold was deposited; at the late stage, tabular arsenopyrite in association with free visible gold was formed. The samples of gold-bearing arsenopyrite were analyzed using Scanning Electron Microscopy, Electron Microprobe Analyses, Atomic Absorption and Laser Ablation Inductively Coupled Plasma Mass Spectrometry in combination with High Resolution 3D X-ray Computed Tomography (HRXCT). HRXCT does not destroy the studied mineral during the investigation. That technique permits to do an estimation of the amount of gold inclusions in minerals or host rocks and draw reasonable conclusions about the gold content of the ores, to study in detail the distribution patterns of metal inclusions (associated with certain minerals, cracks, crystal growth faces, etc.) and to determine the form of the gold. It can be used to understanding of the genesis of productive mineral associations, and to developing optimal technological schemes for gold extraction.
We must persevere to drill through the intact ocean crust to fully address fundamental questions towards completion of the plate tectonics theory. The primary questions include: what is the ocean crust made up of, how thick is it and what is the petrological nature of the crust-mantle boundary (i.e., Mohorovičić discontinuity or Moho)? These questions may sound naive because they are widely believed to be well-understood facts, but they are not. Correctly, our current knowledge remains incomplete, and some popular misperceptions come from interpretations based on convenient assumptions. One assumption is that the ocean crust inferred from seismic data is of magmatic origin. Testing this assumption is a principal motivation of Project Mohole (1957–1966), attempting to drill intact ocean crust across the Moho into the mantle. Project Mohole failed because of its high cost, engineering challenges and insufficient tries, but the technologies developed made subsequent ocean drilling successful. However, answers to the original questions remain unsatisfactory. For example, seismic crust interpreted to be of magmatic origin is shown to have globally uniform thickness of 6.0 ± 1.0 km, but crust with such thickness at many slow-spreading ridge segments is dominated by serpentinized mantle peridotites exposed on seafloors. Therefore, the popular view on ocean ridge magmatism must be re-examined, which needs intact ocean crust drilling into the mantle. Drilling at geologically simple sites in the fast-spreading Pacific seafloor is most promising.
Earth’s free oscillation can provide essential constraints for refining Earth models, inverting seismic source mechanisms, and studying the deep internal structure of the Earth. Large earthquakes can simultaneously excite numerous normal modes. Due to the Earth’s ellipticity, rotation, and internal heterogeneities, these normal modes undergo splitting, with the frequencies of singlets of normal modes becoming very close (only a few µHz apart). This imposes greater demands on the detection of normal modes. This paper introduces a novel method for normal mode detection based on the normal time–frequency transform (NTFT). Compared to classical FT spectrum methods and recent optimal sequence estimation (OSE), the proposed method not only detects more weak normal modes but also reveals the spatial distribution of the phase of each normal mode. Taking the detection of 0S2 as an example, the phase measurements of each singlet are spatially inconsistent. This phenomenon can provide prior information for other methods, such as product spectrum analysis (PSA), spherical harmonic stacking (SHS), multistation experiments (MSE), and OSE. Additionally, understanding the phase distribution patterns contributes to further study of geological structures, offering crucial foundational data and observational support.
As globally important dust source areas, drylands not only have extremely fragile ecosystems that are exceptionally sensitive to global climate change but also have important implications for global warming and carbon cycling. However, the detailed dryland aerosol characteristics are not clear, especially the influence mechanisms of dryland aerosols, which are poorly understood. In this paper, Utilizing the Xinjiang Uygur Autonomous Region (XJ) as a target area, based on high spatial resolution aerosol optical depth (AOD) data, combined with the trend analysis, backward trajectory, source analysis, and machine learning methods, we systematically analyzed the multiscale dynamic characteristics of aerosols in XJ over a long period. Simultaneously, we also quantitatively explored the source distributions of high aerosols at typical sites at different time scales. Furthermore, we discussed the specific effects of natural and anthropogenic factors on aerosols in XJ and its subregions. The results show that 72.45% of the AOD in XJ presents an increasing trend from 2000 to 2019, 27.56% of which passed the significance test, mainly concentrated in northern Xinjiang (NXJ). The AOD in southern Xinjiang (SXJ) is the largest (0.240 ± 0.154), followed by eastern Xinjiang (EXJ) (0.157 ± 0.038), and the AOD in NXJ is the smallest (0.134 ± 0.028); however, the AOD in NXJ has the most obvious increasing trend, peaking in 2011, and the AOD in XJ remains low and stable at 5000 m elevation and above. The backward trajectory shows that nearly half of the potential paths of high AOD in SXJ are from the Taklamakan Desert, most of the potential paths in NXJ are from transboundary transmission, mostly through exposed lake beds, and most of the potential paths in EXJ are from the northwest, with characteristics similar to those of NXJ. The exposed lake beds provide salt dust, which further exacerbates the complexity and hazards of aerosols in NXJ and EXJ. The potential source areas for AOD in SXJ are concentrated in the northeast of the target site, those in NXJ are concentrated in the west of the target site, and those in EXJ are in the northwest and east. The AOD in SXJ (63.92%) and EXJ (74.83%) or XJ (57.77%) is dominated by natural factors, whereas the magnitude of AOD in NXJ (84.01%) is largely explained by anthropogenic factors.
Lock-unlock landslides have thick sliding zones that store a lot of energy. This makes them start quickly, happen suddenly, and have serious consequences. Therefore, it becomes urgent to study the deformation and failure mechanisms of such landslides and develop rational predictive models. Taking the Jiuxianping landslide as an example, this study investigates the regularity of landslide displacement changes using multi-source data, focusing on the abrupt displacement patterns in the unlock phase. Furthermore, employing Transient Release and Inhalation Method tests combined with Geo-Studio’s SEEP/W and SIGMA/W modules for fluid–solid coupled simulation calculations, the evolution process of landslide failure mechanisms and deformation characteristics is analyzed and discussed. Lastly, utilizing data mining analysis of multi-source data, a hybrid optimized machine learning predictive model is established for model prediction comparison. The study reveals that: (1) The rise in infiltration line elevates pore water pressure, affecting the stability of the sliding zone, leading to “unlock effects” and step-like displacement deformation; (2) Simulation shows that YY208 is closer to the actual situation, located at the far bank position, while YY210 is greatly influenced by the “buoyancy effect”, resulting in a slowdown in deformation velocity; (3) After data preprocessing, overall actual displacement prediction performs better than simulation displacement prediction in terms of Mean Absolute Error, Mean Squared Error and Correlation Coefficient, but noise reduction processing can improve the periodic prediction effect of simulation displacement.
Flood is one of the most devastating natural hazards. Employing machine learning models to construct flood susceptibility maps has become a pivotal step for decision-makers in disaster prevention and management. Existing flood conditioning factors inadequately account for regional characteristics of flood in the depiction of topography, potentially leading to an overestimation of flood susceptibility in flat areas. Addressing this gap, this study proposes a novel flood conditioning factor, local convexity factor (LCF), to enhance the accuracy of flood susceptibility modeling. Initially, LCF is computed based on a standard normal Gaussian surface to highlight elevation variations in local terrain. Subsequently, LCF is applied to flood susceptibility modeling using seven machine learning models across four distinct basins. Comparative analysis is conducted between flood susceptibility maps with and without the application of LCF to evaluate its impact on flood susceptibility modeling. The results demonstrate that the proposed LCF can enhance the accuracy of flood susceptibility modeling to varying degrees, across the four basins investigated. The Fujiang basin exhibited the most substantial improvement, with its AUC improved from 0.861 to 0.886, Producer’s Agreement improved from 0.869 to 0.899, and Overall Agreement improved from 0.778 to 0.811. Comparation with hydrodynamic inundation maps shows that particularly in relatively flat terrain areas, flood susceptibility maps incorporating LCF offer more precise delineation between flood-prone and non-flood-prone zones. This research holds potential for widespread application in the prediction of flood susceptibility using machine learning models, providing a novel perspective for enhancing their accuracy.
Against the background of realizing the goal of “carbon peaking and carbon neutrality”, using basaltic rocks for carbon mineralization is one of the most promising approaches to reduce the rise in atmospheric CO2 concentrations. This study conducted a series of experiments to assess carbon mineralization in nine basalt samples from the main terrestrial basalt reservoirs in China within CO2-H2O/brine-rock systems at low temperatures (≤35 °C). The results indicate that the secondary carbonates formed in the CO2-H2O/brine-basalt system are predominantly calcite rather than Mg-carbonate minerals at low temperatures (≤35 °C). Hence, at low temperatures (≤35 °C), basalt rich in Ca-bearing minerals promotes the formation of stable carbonate minerals more effectively than basalt containing Mg-bearing minerals. Furthermore, under conditions of low temperatures (≤35 °C) and pressures of approximately 3 MPa, the results suggest that alkaline olivine basalt, with a higher content of Ca-minerals and typical alkaline minerals (nepheline and Na-sanidine), exhibits the highest pH value and the highest amount of calcite. Hence, the alkaline minerals, nepheline and Na-sanidine, serve as pH buffers to increase the pH and promote the precipitation of calcite within CO2-H2O– basalt systems at low temperatures (≤35 °C). Among the nine evaluated basalts, basalt from the Shandong Linqu-Changle volcanic basin exhibits the highest rate of carbon mineralization at low temperatures (≤35 °C). Hence, Cenozoic alkaline olivine basalt from Shandong Linqu-Changle volcanic basin is one of the most promising basalt reservoirs in China for future in- situ carbonation. As for ex- situ carbonation, compared with olivine, diopside or Ca-plagioclase may be more appropriate for increasing ocean negative emissions.
Magmatic volatiles (H2O, F, Cl), especially water, are critical in the formation of porphyry copper deposit, for its significance as a carrier for metals. However, accurately quantifying the water contents of deep ore-forming magma remain a challenge. Here, we used apatite and forward modelling methods to reconstruct magmatic water evolution histories, with special concern on the control of initial magmatic H2O contents and water saturation threshold to porphyry mineralization. Samples investigated include granitoid rocks and apatite from highly copper-mineralized and barren localities. Generally, our research suggested that both ore-related and ore-barren magma systems are hydrous, the modeled magmatic water contents vary significantly among systems whether mineralized or not, and the major difference lies in the threshold of water saturation (6.0 wt.% for barren, and up to 10.0 wt.% for highly mineralized). Combined with whole rock geochemistry data (high K2O and Sr/Y contents) and modeling result (high modeled water thresholds), we think the ore-related magmas are stored at deeper depth with higher water solubility. In conclusion, we propose that the level of magmatic water saturation plays a crucial role in the formation of porphyry copper systems. Fertile magma has higher water solubility to which deeper storage depth is a critical contributing factor, and can get significantly water enriched upon saturation.
How the subduction direction of the Paleo-Pacific plate beneath the Eurasian plate changes in the Early Cretaceous remains highly controversial due to the disappearance of the subducted oceanic plate. Intraplate deformation structures in the east Asian continent, however, provide excellent opportunities for reconstructing paleostress fields in continental interior in relation to the Paleo-Pacific/Eurasian plate interaction. Anisotropy of magnetic susceptibility (AMS), geological, and geochronological analyses of post-kinematic mafic dykes intruding the detachment fault zone of the Wulian metamorphic core complex (WL MCC) in Jiaodong Peninsula exemplify emplacement of mantle-sourced dykes in a WNW–ESE (301°–121°) oriented tectonic extensional setting at ca. 120 Ma. In combination with the results from our previous kinematic analysis of the MCC, a ca. 21° clockwise change in the direction of intraplate extension is obtained for early (135–122 Ma) extensional exhumation of the MCC to late (122–108 Ma) emplacement of the dykes. Such a change is suggested to be related to the variation in subduction direction of the Paleo-Pacific plate beneath the Eurasian plate, from westward (pre-122 Ma) to west-northwestward (post-122 Ma).
The gold-bearing arsenian pyrite in Carlin-type gold deposits typically grows around the gold/arsenic-poor pyrite core, forming core–rim textured pyrite. However, the causes of rim pyrite precipitation around the early-formed core pyrite and the growth mechanisms of the rim pyrite remain unclear. Here, we combined scanning electron microscopy, electron probe micro-analysis, and nanoscale secondary ion mass spectrometry to investigate the textural and chemical characteristics of core–rim textured pyrite from the giant Shuiyindong and Lannigou gold deposits. Furthermore, we used electron backscattered diffraction and transmission electron microscopy to characterize their crystallographic structure. The results indicated that core–rim textured pyrite is the dominant pyrite type in the ore. This type of pyrite is characterized by the sharp core–rim interfaces, euhedral-subhedral morphology, and oscillating zoning. The gold/arsenic-rich rim and gold/arsenic-poor core formed during the main-ore and pre-ore stages, respectively. Crystallographically, the rim showed that a crystallographic orientation is similar to that of the core along the (0 1 0) crystal facet, indicating that the core pyrite serves as a template for the epitaxial growth of rim pyrite. Textural and chemical features indicate that the epitaxy occurs in the process of direct precipitation of main-ore pyrite over the pre-ore pyrite. As Carlin ore fluids dissolve the iron-bearing carbonates, iron concentrations in the fluids increase, thereby creating a supersaturation environment suitable for the nucleation of main-ore pyrite. Because the minimal lattice misfit would minimize the surface free energy and the (0 1 0) facet of pyrite has a lower surface energy than other facets, the nucleated pyrite would readily grow along the (0 1 0) facet of preexisting pyrite via epitaxy. Our findings highlight that the widespread preexisting pyrite facilitates late-stage pyrite precipitation. For Carlin-type gold deposits, the pre-ore pyrite is essential owing to its promoting the precipitation of gold-bearing pyrite.
The Ordos Basin, located in arid and semi-arid region of China, is famous for its abundant groundwater resources and artesian features. The source of groundwater recharge, whether from local precipitation or external sources, has been debated. This study aims to elucidate the groundwater circulation mechanism in the Ordos Basin through scientific expedition, environmental isotope method, and hydrological drilling exploration, providing valuable insights for other artesian basins. Comprehensive analysis indicates that groundwater in the Ordos Basin is recharged by modern precipitation, primarily from high-elevation areas outside the basin. Deep groundwater from these external sources ascends to the aquifer through basement fault zones. Evidence from hydrogen and oxygen isotopes, hydraulic gradients, and water quantities suggests that the Tibetan Plateau is the most potential recharge source. Based on the distribution of Cenozoic basalt and data from seismic observation wells, we propose that leakage water from the Tibetan Plateau rift valley is transported to the Ordos Basin through fast channels, possibly lava tubes, and then upwelling through basement fault zones. This work provides a new perspective on the mechanism of inter-basin groundwater circulation.
