ALBERT

Description: Ionospheric disturbances are associated with the propagation of seismic waves generated by earthquakes. We analyze total electron content (TEC) fluctuations from Global Navigation Satellite Systems (GNSS) data. This study investigates the global earthquakes from December 2004 to March 2020 with magnitude (Mw) 4.0 to 9.1. Data of 65 permanent GNSS stations are used to analyze the impacts of these earthquakes on the ionosphere. The experimental data based on the cluster sampling method ensure strict conditions such as accuracy, the distance from the monitoring stations to the epicenter, and the depth of the hypocenter. At least three GNSS stations near the epicenter participate in the analysis of each earthquake. Probability and statistics are applied to remove outliers and rough errors in the input data, to select datasets with similar quality, and to analyze TEC anomalies. The results show that when a strong earthquake occurs, the TEC values calculated at different GNSS stations surrounding the earthquake region tend to exhibit similar variations. Depending on the magnitude, epicenter, and hypocenter depth, these fluctuations can range from ± 3.2 TECU to ± 14.5 TECU for large earthquakes. These TEC fluctuations occur from 30 min to almost two hours before the mainshock of the earthquakes and last to the aftershock period. For earthquakes with a magnitude greater than 6.0 Mw, the TEC fluctuations are significant. The findings of this study contribute to GNSS applications in studying earthquakes in the future.

Description: In deformation analysis, irregularly spaced data, extreme values, and anomalies in time series can lead to misleading simulations for forecast models, such as overfitting and underfitting. Therefore, K-fold cross-validation is one of the hyperparameter tuning techniques used in machine learning (ML) to deal with these problems. In this study, we use data from 22 permanent GNSS stations to predict the motion trajectory of the Earth’s crust. Lag functions and sampling techniques are applied to generate 924-time series samples. Time series standardization techniques are also performed to improve the quality of data. To test the efficiency of the K-fold cross-validation method, we investigate 26 mathematical models based on six ML algorithms. The optimal K values are selected through trial methods. Root mean squared error (RMSE) of validation and test is the basis for determining the overfitting and underfitting models. The investigations show that the optimal intervals of K-fold range from five to ten folds for the GNSS time series with many anomalies, jumps, and significant variations, from three to ten for stable time series. The sensitivity of cross-validation is more effective on the time series of the Up component than those of the North and East components. In addition, cross-validation can also detect effectively overfitting and underfitting for forecast models in motion of permanent GNSS stations.

Description: Understanding the phase behavior and structural properties of salt water at high pressures is essential for understanding the dynamics and physical characteristics of icy planets. In this study, we employed high-pressure experimental and ab initio simulation techniques to investigate the impact of CaCl2 on the structure of ice VII. Our findings reveal that 1.8 mol% CaCl2 can be incorporated into the ice VII structure above 10 GPa. This CaCl2-bearing ice VII (Cb VII) exhibits a lower O-H stretching frequency in the Raman spectra as well as a reduced volume of the unit cell compared to pure ice VII. In contrast to doping ice VII with other salts such as LiCl and NaCl that leads to an increase of the ice VII to ice X transition pressure occurring at 100–150 GPa, CaCl2 doping stands out by reducing the transition pressure. It shifts the transition to a pressure of 52 GPa, which is significantly lower than the transition pressure of 80 GPa in the pure H2O ice system. This notable distinction highlights the unique influence of CaCl2 on the phase behavior of water under high pressure, and we attribute these effects to the phenomenon of chemical pressure induced by CaCl2 within the ice VII structure. Our study suggests that the presence of a modified ice VII phase, contaminated with salt and referred to as Cb VII, may influence the composition, structure, and evolution of planets.

Description: High-resolution thermospheric mass density low Earth orbit (LEO)-based measurements are valuable for accurately estimating short-term atmospheric abrupt disturbances triggered by solar flux forcing. To investigate the enhancing status of solar cycle 25 between August 29 and December 31, 2020, we processed Gravity Recovery and Climate Experiment Follow-on (GRACE-FO) 10-s accelerometer-derived thermospheric mass density (TMD) measurements normalized at 500 km altitude by the NRLMSIS-2.0 empirical model. These 4-month enhancing disturbance observations suggest a shift from relative quiescence to a much more active solar phase, revealing unexpected dependencies on temporal and spatial characteristics. The results indicated that the dominant driver is solar extreme ultraviolet radiation (EUV) during this ascending phase. Density enhancement was symmetric in both hemispheres around the autumn equinox. After the equinox, the neutral density enhancement intensity in the Southern Hemisphere surpasses that in the Northern Hemisphere. Density maxima occurred from high to low latitudes, accompanied by a 2–3 h time lag. The Wygant function was applied to model the response to solar wind geomagnetic field changes and quantify the impact of geomagnetic activities on upper atmosphere density, verifying the time lag of density disturbances. All these findings could potentially improve our understanding of the solar cycle and LEO orbital drag.

Description: Uraninite [UO2] is an increasingly recognized accessory mineral for geochronological studies of the mid to upper crust. Similar to what is seen for zircon and monazite, the U-Pb system of uraninite can become reset under relatively low temperatures in certain domains via the action of fluids through the process of coupled dissolution-reprecipitation. Whether or not the uraninite geochronometer is reset will be dependent on the chemistry of the fluid it interacts with as opposed to being purely dependent on P-T. This makes uraninite a mineral of interest for the dating of low- to mid-temperature, fluid-controlled geological processes. In order to better understand which factors cause the recrystallization and/or metasomatic alteration of uraninite, a set of 5 metasomatism experiments have been performed in cold seal autoclaves on a hydrothermal line involving a natural uraninite from Příbram, Czech Republic and a series of Na-, Ca-, OH-, and F-bearing fluids at 600°C and 200 MPa for 21 days. A second set of the same 5 experiments, to which elemental sulfur was added, were subsequently run at 450°C and 200 MPa for 66 days. Generally, little textural alteration of the starting material was observed in any of the experiments, which was independent of the fluid chemistry and temperature, except for an increase in the apparent porosity of the reacted grains. In the second set of experiments galena formed as small grains in four of the runs, indicating that Pb had migrated out from the uraninite into the solution and reacted with the sulfur to form galena. The excessive depletion of Pb in the metasomatized uraninite to negligible amounts in some of these fluids is especially evident if the solutions were NaF + H2O and 2M NaOH. This suggests that interaction of uraninite with F- or high pH Na-bearing fluids can metasomatically reset the uraninite geochronometer at 450 °C and mid to upper crustal pressures and by analogy to even lower temperatures given sufficient time.

Description: Rare earth elements (REE) include the lanthanides (La–Lu), Y, and Sc which are critical elements for the green energy transition. The REE show a decrease in ionic radii with increased atomic numbers, which results in a so-called lanthanide contraction systematically affecting crystal structures and mineral properties. Here we present a compilation of reference Raman spectra of ten REE sesquioxides (A-, B- and C-type), five REE hydroxides, eight xenotime-structured REE phosphate endmembers and two solid solutions, seven monazite-structured REE phosphate endmembers and two solid solutions and seven rhabdophane endmembers with up to five Ce1−xLREEx rhabdophane solid solutions (LREE = La–Gd). Raman mode assignment is based on a detailed literature review summarizing existing analytical work and theoretical calculations and systematic trends observed in this study by analyzing different REE-bearing solids. The wavenumbers of the main REE-O Raman band systematically increase with decreasing ionic radii forming discrete linear trends within isostructural mineral groups, that can be used to estimate the REE-O mode in other solids with known REE-O coordination numbers. Photoluminescence using 266 nm, 532 nm and 633 nm excitation laser wavelengths for REE-bearing oxides, hydroxides, anhydrous and hydrous phosphates is also presented providing a new framework for identifying REE-phases in phosphate-bearing natural mineral deposits.

Description: Iron oxide-apatite (IOA) deposits generally undergo extensive late-stage metasomatic overprinting that modifies the texture and geochemistry of the magnetite, apatite, and other ore-forming minerals. However, the onset of metasomatism in IOA deposits worldwide generally remains poorly constrained. The Heiyingshan IOA deposit is located in the Beishan area of the Central Asian Orogenic Belt, NW China. Fluorapatite from this IOA deposit has undergone extensive fluid-aided alteration resulting in the formation of numerous monazite inclusions via a coupled dissolution-reprecipitation process (CDRP) in altered domains of the fluorapatite. Petrographic studies show that these monazite grains are mainly subhedral to anhedral in shape, have a topotaxial relationship with the parent fluorapatite, and co-exist with magnetite, xenotime, and other mineral inclusions. The crystallization age of this monazite constrains the metasomatic activity following the original IOA mineralization. This study presents EMPA and trace element LA-ICP-MS analytical data for fluorapatite and monazite from the Heiyingshan IOA deposit. It also includes in-situ U–Pb isotopic data for unaltered, altered domains of fluorapatite, and monazite. U–Pb data obtained for unaltered fluorapatite, altered fluorapatite and monazite inclusions within altered fluorapatite grains have similar U–Pb ages (∼325 Ma), consistent with the regional Carboniferous volcanic rocks. Furthermore, this study also presents Sr–Nd isotopic data for fluorapatite, the unaltered and altered fluorapatite domains in the Heiyingshan IOA deposit have similar initial Sr isotope ratios, 143Nd/144Nd ratios, and εNd(t) values, with the Sr isotope ratios consistent with the regional Carboniferous volcanic rocks. This implies that magmatism, mineralization, and metasomatism in the Heiyingshan IOA deposit were essentially contemporaneous, the metasomatizing fluids were derived from the evolution of mineralizing fluids. A comparison of the results from Heiyingshan with the available geochronological data from other IOA ore deposits reveals a general consistency in the timing between the mineralization and the metasomatism of IOA deposits due to evolved later-stage fluids. In contrast, dating of monazite metasomatically derived from fluorapatite in some older (e.g., Kiirunavaara) IOA deposits indicates that these IOA deposits appear to have undergone additional episodes of metasomatic alteration during various later geological events after the original IOA mineralization. We suggest that the formation age of monazite inclusions within apatite in IOA deposits should be consistent with the timing of the IOA mineralization, as the original formation and subsequent fluid-aided modification of IOA deposit occur in the same magmatic-hydrothermal event/system. However, some IOA deposits may have undergone additional late episodes of metasomatic events.

Description: In high-precision space geodetic techniques data processing, the mapping function (MF) is a key factor in mapping the radio waves from the zenith direction down to the signal incoming direction. Existing MF products, either site-wise Vienna Mapping Function (VMF1 and VMF3) or grid-wise VMF1 and VMF3, are only available at the Earth surface. For overhead areas, height correction is always required, which is becoming increasingly important with growing airborne aircraft activity. In this contribution, we introduce a novel method aimed at providing a large number of MFs to the user in a simple and efficient manner, while minimizing the loss of precision. The approach effectively represents the vertical profile of the MFs from the Earth's surface up to altitudes of 14 km. In addition, the new model corrects for height in the assessment using the fifth generation of the European Centre for Medium-Range Weather Forecasts ReAnalysis (ERA5) ray tracing calculations for a global 5° × 5° grid with 54 layers in the vertical direction, a total of 8 azimuths in the plane, and 7 elevation angles, for each day in 2021. Specifically, for both polynomial and exponential model of order 2 and 3, the relative residuals are 〈 0.3% for the hydrostatic delay MF coefficient , and 〈 1% for the wet delay MF coefficient . The precision of the new model on the Earth’s surface is evaluated using site-wise VMF1 and VMF3 GNSS (Global Navigation Satellite System) products from Technische Universität Wien. The root mean square error of slant hydrostatic delay and slant wet delay at a 3° elevation angle is approximately 4–5 cm and 2–5 cm, respectively.

Description: Radio signals transmitted by Global Navigation Satellite System (GNSS) satellites experience tropospheric delays. While the hydrostatic part, referred to as zenith hydrostatic delay (ZHD) when mapped to the zenith direction, can be analytically modelled with sufficient accuracy, the wet part, referred to as zenith wet delay (ZWD), is much more difficult to determine and needs to be estimated. Thus, there exist several ZWD models which are used for various applications such as positioning and climate research. In this study, we present a data-driven, global model of the spatial ZWD field, based on the Extreme Gradient Boosting (XGBoost). The model takes the geographical location, the time, and a number of meteorological variables (in particular, specific humidity at several pressure levels) as input, and can predict ZWD anywhere on Earth as long as the input features are available. It was trained on ZWDs at 10718 GNSS stations and tested on ZWDs at 2684 GNSS stations for the year 2019. Across all test stations and all observations, the trained model achieved a mean absolute error of 6.1 mm, respectively, a root mean squared error of 8.1 mm. Comparisons of the XGBoost-based ZWD predictions with independently computed ZWDs and baseline models underline the good performance of the proposed model. Moreover, we analysed regional and monthly models, as well as the seasonal behaviour of the ZWD predictions in different climate zones, and found that the global model exhibits a high predictive skill in all regions and across all months of the year.

Description: Tin (Sn) and tungsten (W) behave incompatibly in reduced magmatic systems and may become enriched in late highly-evolved melts. Nonetheless, Sn and W rarely concentrate in the same deposit. In deposits formed by Sn- and W-bearing granites, this separation may be due to the contrasting behavior of Sn and W during exsolution of a magmatic fluid or the scavenging of Sn by silicate minerals. We illustrate the separation of Sn and W for the world-class Zhuxi W skarn deposit (South China). Although tin orebodies have not yet been identified within the Zhuxi deposit, tiny (commonly 〈 20 μm) cassiterite grains are widespread within the endoskarn and the retrogressed exoskarn. We analyzed the W and Sn contents of the magmatic minerals biotite and ilmenite in ore-forming granites and the prograde anhydrous skarn minerals garnet, pyroxene and vesuvianite. Our data show that (i) magmatic ilmenite (65.5–79.1 ppm Sn; 8.7–14.3 ppm W) and biotite (109–120 ppm Sn; 1.3–6.3 ppm W) from biotite monzogranite strongly enrich Sn relative to W, implying that W partitioned more strongly into the magmatic fluids than Sn, (ii) there is 100 Kt non-recoverable Sn within the Zhuxi deposit in addition to the certified 3.44 Mt WO3 reserves, and (iii) W is mainly hosted in scheelite, whereas Sn is dominantly sequestered in prograde skarn minerals, most importantly garnet (76–4086 ppm Sn, 〈 42 ppm W), pyroxene (3–103 ppm Sn, 〈 1 ppm W), and vesuvianite (43–361 ppm Sn, 〈 2 ppm W). The formation of secondary cassiterite requires the release of silicate-bound Sn by alteration of primary skarn minerals, which depends on the availability of magmatic or metamorphic fluids. Deep-seated granites such as those associated with the Zhuxi skarn deposit, which crystallized at 5 km to 12.6 km depth, do not release or mobilize copious amounts of fluid. Therefore, the Zhuxi deposit, like other deep-seated reduced skarn systems shows little alteration and most Sn remains in silicate minerals and is economically non-recoverable. Thus, reduced, deep-seated W skarn systems are unlikely to have associated Sn orebodies even if significant amounts of Sn are present.