Geological Implications Research Articles

Generation of Neoproterozoic granites of the Huangling batholith in the northern Yangtze Block, South China: Implications for the evolution of the Precambrian continental crust

Granites may contain critical information about composition and reworking of continental crust and are widely used to investigate continental crust evolution. Extensive Neoproterozoic granites in the northern Yangtze Block are significant to the Neoproterozoic continental evolution of the Yangtze Block. We investigated the petrology, mineralogy, whole-rock geochemistry, and zircon U–Pb–Hf isotopes of the Neoproterozoic Wuduhe biotite granites and Xiabaoping K-feldspar granites of the Huangling batholith in the northern Yangtze Block to determine their source characteristics and geological implications for the northern Yangtze Block. The Wuduhe biotite granites yielded zircon U–Pb ages of ca. 818–815 Ma. They displayed high SiO2 contents (70.19–74.23 wt%) and Na2O/K2O ratios (1.38–3.35) but low MgO (0.37–0.90 wt%) and CaO (1.49–2.97 wt%) contents, representing calc-alkaline Na-rich I-type granites. They exhibited enriched whole-rock εNd(t) (−19.8 to − 18.8) and zircon εHf(t) values (−41.3 to − 24.2), and had low CaO/Na2O (0.34–0.63), Al2O3/TiO2 (46.6–89.7), Rb/Ba (0.02–0.08), and Rb/Sr (0.04–0.12) ratios, as well as low zircon saturation temperatures (739 − 770 °C), indicating derivation from Na-rich metabasalts of the Archean Kongling complex. The Xiabaoping K-feldspar granites had zircon U − Pb crystallization ages of ca. 816–812 Ma. They displayed high SiO2 (70.82–74.80 wt%), K2O (4.41–6.35 wt%), and Al2O3 (13.46–16.31 wt%) contents, suggesting A2-type affinities. They showed enriched zircon εHf(t) (−44.3 to − 18.4) and whole-rock εNd(t) values (−23.4 to − 18.4) and high zircon saturation temperatures (869–912 °C), indicating formation by anhydrous melting of K-rich felsic rocks from the Archean Kongling complex. The geochemical diversity of these granites from the Huangling batholith was primarily controlled by source heterogeneity of the Kongling complex and distinct melting temperatures. We infer that the northern Yangtze Block underwent significant remelting of ancient continental crust in a subduction background during the Neoproterozoic, induced by continuous upwelling of mantle-derived mafic magmas.

Element Migration of Mineralization-Alteration Zones and Its Geological Implication in the Beiya Porphyry–Skarn Deposit, Northwestern Yunnan, China

Porphyry and the associated skarn-type deposit is one of the most important types of ore deposits worldwide, which usually exhibit significant zoning of mineralization-alteration, but the research on element migration in these mineralization-alteration zones is relatively weak. The Beiya porphyry–skarn gold-polymetallic deposit is a super-large Cenozoic deposit located in the Sanjiang metallogenic belt, northwestern Yunnan, China. In this paper, through a detailed analysis of mineralization and alteration zoning and its element migration regularity, the findings are as follows: (1) Three types of hydrothermal alteration—porphyry alteration, contact alteration, and wall-rock alteration—are developed, and porphyry alteration includes potassic, phyllic, propylitic, and argillic alteration; (2) five types of mineralization—porphyry-type Cu–Au–(Mo), skarn-type Au–Fe–(Cu), hydrothermal vein-type Au–Fe, distal hydrothermal-type Pb-polymetallic, and oxidizing-leaching enriched-type Au—occur in a diversity of forms, which are dominantly controlled by structures and lithologies; (3) concentric-banded mineralization-alteration zones are exhibited centrally from the alkaline porphyry outward or upward, namely [porphyry alteration] potassic → phyllic → propylitic → argillic → [contact alteration] skarnitization–marbleization → [wall-rock alteration] marbleization–silicification–calcitization; (4) porphyry-type mineralization predominantly forms within potassic and phyllic zones, while skarn-type mineralization occurs in contact alteration zones, and proximal and distal hydrothermal (vein)-type mineralization are commonly distributed in marbleization–silicification–calcitization alteration zones; and (5) element migration analysis demonstrates a significantly lateral and vertical zoning in the metallogenic element association of Cu–Mo → Cu–Au → Au–Fe–Cu → Au–Fe → Pb–Zn–Au–Ag–Fe from alkaline porphyry outward to the wall-rock. The mineralization-alteration zoning model indicates the Beiya deposit has similar mineralization and alteration zone characteristics to the typical porphyry copper system; and element migration within mineralization-alteration zones provides new scientific information for understanding the metallogenic regularity and prospecting at Beiya, as well as the similar types of deposits in the Sanjiang metallogenic belt and elsewhere in the world.

Occurrence of Mafic Rocks within Ediacaran Strata in the Aksu Region, NW Tarim Craton, and its Geological Implications

AbstractThe Tarim Craton is an ancient Precambrian continental block, and detailed knowledge of its thermo‐tectonic history is crucial for understanding the early history of continental evolution. Abundant layered mafic rocks, which have commonly been regarded as basalts, occur within the Ediacaran Sugetbrak Formation (Fm.) in the Aksu region of the northwestern Tarim Craton. Clear intrusive features have now been discovered, including mafic rocks truncating Ediacaran sedimentary layers, exhibiting an intrusion‐baked margin where they interact with both the overlying and bottom wall rocks, and displaying a fine‐grained transition zone from their interior to their margins. The new findings demonstrate that these mafic rocks within the Aksu Ediacaran strata were not erupted basalts but instead are intrusive diabase dykes. Therefore, these mafic rocks cannot be used to constrain the timing of the Sugetbrak Fm. in the Aksu area, nor as marker layers for regional stratigraphic correlation. Furthermore, the Ediacaran thermo‐tectonic evolution in this region, deduced from the assumption that the mafic rocks are lavas, needs to be revised.

First documentation of early Silurian conodonts from western Thailand and its geological implications

The early Silurian conodonts are firstly described and illustrated from western Thailand. Samples were collected from the Kroeng Kravia Forest Park area for conodont and lithofacies analyses. An upper Telychian Lower Pterospathodus amorphognathoides amorphognathoides Subzone is recognized for the studied succession. Three lithofacies were identified from the carbonate succession, including stromatolite–thrombolite limestone, nodular limestone, and red limestone. Both analyses on lithofacies and conodont assemblages indicate a deeper marine depositional environment. The conodont fauna in the study area is similar to that from Baoshan of Yunnan Province and Langao of Shaanxi Province in West China and resembles that from similar depositional environments in Australia, Laurentia, and peri-Gondwana, suggesting good connections among these regions by ocean currents.

Outbursts Upon Cooling of Low‐Temperature Binary Mixtures: Experiments and Their Planetary Implications

AbstractFor many binary mixtures, the three‐phase solid‐liquid‐vapor equilibrium curve has intermediate pressures that are higher than the pressure at the two pure triple points. This curve shape results in a negative slope in the high‐temperature region near the triple point of the less volatile component. When freezing mixtures in the negative slope regime, fluid trapped below confined ice has latent heat released with more vapor upon cooling, and thus increases in pressure. If the rising pressure of the confined fluid overcomes the strength of the confining solid, which may be its own ice, it can produce an abrupt outburst of material and an increase in the system's overall pressure. Here, we report experimental results of freezing‐induced outbursts occurring in the N2/CH4, CO/CH4, and N2/C2H6 systems, and provide insight into the phenomenon through a thermodynamics perspective. We also propose other binary systems that may experience outbursts and explore the geological implications for icy worlds such as Titan, Triton, Pluto and Eris as well as rocky bodies, specifically Earth and Mars.

Late Ediacaran to Early Cambrian stratigraphic correlation and its geological implications in the northwestern Sichuan Basin: insights from phosphorus, isotopes, and small shelly fossils

The characteristics of elements, isotopes, and small shelly fossils were investigated for Late Ediacaran to Early Cambrian stratigraphy division and to discuss their geological implications in the northwestern Sichuan Basin. The results reveal that small shelly fossils can be detected in the high-phosphorous section, with the concentration of phosphorus mainly ranging from 2% to 8%, suggesting that this interval belongs to the Early Cambrian, which is also consistent with the carbon isotopic composition results. In addition, the Early Cambrian is denudated in the Sichuan Basin due to tectonic movement, and the characteristics of some isotopes and small shell fossils are different from those in other basins. It can be proposed that P content can support the recognition of lithological boundaries, and the high phosphorus content can be used as a reference to identify the top and bottom boundaries of the Maidiping Formation in the study area. According to the elemental compositions in the Ediacaran Dengying Formation, the variations in Si, Al, Fe, and K contents are similar in the platform area and rift area, suggesting that the third and fourth member of the Dengying Formation are also developed in the Deyang–Anyue Rift. The results suggest that both the Deng-4 member and Maidiping Formation feature contemporaneous deposition of different facies in the northwestern Sichuan Basin. The strata consist of shale intercalated with thin carbonate rock deposits in the Deyang–Anyue Rift, while carbonate rock deposits in the platform. The Deyang–Anyue Rift expanded gradually in the Late Ediacaran and eventually filled in the Early Cambrian. The data in this study illustrate that elemental compositions, isotopes, and small shelly fossils can be combined to correlate the Late Ediacaran to Early Cambrian strata and provide new evidence for Deyang–Anyue Rift evolution. The results offer some new insights for deep oil and gas exploration in the Sichuan Basin and for the tectonic–depositional–environmental–biological synergistic evolution in the Late Ediacaran to Early Cambrian transition.

Geological implications for submarine geohazards, Ulleung Basin, East Sea

Geological implications for submarine geohazards, Ulleung Basin, East Sea

The effect of A-site cations on charge-carrier mobility in Fe-rich amphiboles

Abstract Elucidating the high-temperature behavior of rock-forming minerals such as amphiboles (AB2C5 T8O22W2) is critical for the understanding of large-scale geological processes in the lithosphere and, in particular, the development of high conductivity in the Earth’s interior. Recently, we have shown that at elevated temperatures, CFe-bearing amphiboles with a vacant A site develop two types of charge carriers: (1) small polarons and (2) delocalized H+ ions. To elucidate the effect of A-site cations on the formation and stability of charge carriers within the amphibole structure, here we analyzed synthetic potassic-ferro-richterite as a model Fe-rich amphibole with a fully occupied A site via in situ temperature-dependent Raman spectroscopy. We further compare the results from in situ time-dependent Raman-scattering experiments on pre-heated and rapidly quenched potassic-ferro-richterite and riebeckite as a model Fe-rich amphibole with a vacant A site. We show that the presence of A-site cations (1) reduces the activation temperature of mobile polarons and delocalized H+ cations; (2) decreases the magnitude of the polaron dipole moment; (3) slows down the process of re-localization of electrons on cooling; and (4) makes the electrons inert to rapid change in external conditions, supporting the persistence of a metastable state of pre-activated delocalized electrons even at room temperature. Our results have important geological implications demonstrating that the A-site cations may control the depth of development of high conductivity in subducted amphibole-bearing rocks. Moreover, from the viewpoint of mineral-inspired materials science, our results suggest that the amphibole-structure type has great potential for designing functional materials with tunable anisotropic-conductivity properties.

Spatial and Temporal Distribution of Igneous Sills in the Central Tarim Basin and Their Geological Implications

Interpretation of the seismic reflection profiles associated with borehole data from the petroleum industry offers a novel way to study sill emplacement in sedimentary basins. This study uses this approach to reveal the intrusive part of the Tarim Large Igneous Province (LIP) within the basin, which has not been systematically reported. A large number of igneous intrusions (sills) are identified in the sedimentary layers of the Central Tarim Basin. The burial depth of the sills is 6–8 km, and they are mainly located within the upper Ordovician strata. According to their seismic facies and drilling data, it is inferred that they are dolerite sills. Based on the uplift of the overlying strata above the intrusions, it is concluded that the sills were mainly formed during the depositional period of the middle Permian Kupukuziman Formation and Kaipailezike Formation (early stage), with a few formed during the depositional period of the upper Permian strata (late stage). It is likely that these two stages of sill intrusion correspond to the main basaltic eruptions within the basin and the mafic dike emplacement in the Bachu area of the Tarim LIP, respectively. The study suggests that that the dolerite sills reported in this study are also an important component of the Permian Tarim LIP.

Geochemistry, petrogenesis and geological implication of granitic rocks in Igarra area, southwestern Nigeria

The Igarra area in southwestern Nigeria hosts a diverse suite of granitic rocks that play a significant role in understanding the regional geological framework. This study employs a comprehensive geochemical and petrogenetic approach to unravel these granitic rock’s origin, evolution and geological implications. A comprehensive geochemical analysis was conducted on samples of the granitoids. The results showed moderate to high SiO2, Na2O and K2O, with average compositions of 68.95%, 3.50% and 4.09%, respectively. The total alkalis are characterised by low MgO, CaO, TiO2 and P2O5, consistent with metaluminous to weak peraluminous compositions. The granite primarily falls within the high-K calc-alkaline region, exhibiting distinctive patterns in rare earth elements, with notable depletion in Nb, P and Ti. Geochemical modelling suggests that the granitoids originated from incomplete melting of metasedimentary source rocks under low to moderate pressure conditions, with limited crustal contamination. Trace element discrimination diagrams indicate a collisional tectonic setting for the Igarra granitoids, interpreted to have formed during continental collision. This mixed-source model suggests a complex magmatic system involving both crustal and mantle contributions, with potential interaction between these diverse melt components during the formation of the granites. This study offers fresh perspectives on the evolutional setting of the Igarra granitoids, understanding the geological effect of the Pan-African belt in Southwestern Nigeria and its broader implications.

Spatiotemporal distribution of sediment waves in the northern Gulf of Mexico Basin, USA

The northern Gulf of Mexico basin, known for its hydrocarbon potential and a myriad of geologic structures and processes, has been underexplored to understand deepwater sediment waves. The recent release of a vast amount of both 2D and 3D seismic data by the Bureau of Ocean Energy Management (BOEM) calls for a basin-wide identification of the sediment waves in the Gulf of Mexico.Integrating seismic, well-log, and high-resolution bathymetric data, this study identified sediment-wave fields on the seafloor as well as in the stratigraphic record. These sediment waves have an average wavelength of 798 m and an average wave height of 18 m. On the present-day seafloor, sediment waves are only located on the northwestern continental slope and eastward of the Bryant Fan area (south of Green Knoll). However, in the stratigraphic record, these bedform structures were found to be prevalent across the northwestern continental slope, northeastern continental slope, and continental rise. All of these sediment waves migrate upslope with crests that are perpendicular to the direction of basin-slope (i.e., parallel to the bathymetric contours). Thus, they are interpreted as cyclic-steps bedforms produced by supercritical sediment gravity flow processes. Investigations of these sediment waves have implications for petroleum geology, geohazard studies, oceanography, hydrodynamics, paleoclimate, and coastal engineering.

Carbon isotope fractionation during methane transport through tight sedimentary rocks: Phenomena, mechanisms, characterization, and implications

The phenomenon of carbon isotopic fractionation, induced by the transport of methane in tight sedimentary rocks through processes primarily involving diffusion and adsorption/desorption, is ubiquitous in nature and plays a significant role in numerous geological and geochemical systems. Consequently, understanding the mechanisms of transport-induced carbon isotopic fractionation both theoretically and experimentally is of considerable scientific importance. However, previous experimental studies have observed carbon isotope fractionation phenomena that are entirely distinct, and even exhibit opposing characteristics. At present, there is a lack of a convincing mechanistic explanation and valid numerical model for this discrepancy. Here, we performed gas transport experiments under different gas pressures (1–5 MPa) and confining pressures (10–20 MPa). The results show that methane carbon isotope fractionation during natural gas transport through shale is controlled by its pore structure and evolves regularly with increasing effective stress. Compared with the carbon isotopic composition of the source gas, the initial effluent methane is predominantly depleted in 13C, but occasionally exhibits 13C enrichment. The carbon isotopic composition of effluent methane converges to that of the source gas as mass transport reaches a steady state. The evolution patterns of the isotope fractionation curve, transitioning from the initial non-steady state to the final steady state, can be categorized into five distinct types. The combined effect of multi-level transport channels offers the most compelling mechanistic explanation for the observed evolution patterns and their interconversion. Numerical simulation studies demonstrate that existing models, including the Rayleigh model, the diffusion model, and the coupled diffusion-adsorption/desorption model, are unable to describe the observed complex isotope fractionation behavior. In contrast, the multi-scale multi-mechanism coupled model developed herein, incorporating diffusion and adsorption/desorption across multi-level transport channels, effectively reproduces all the observed fractionation patterns and supports the mechanistic rationale for the combined effect. Finally, the potential carbon isotopic fractionation resulting from natural gas transport in/through porous media and its geological implications are discussed in several hypothetical scenarios combining numerical simulations. These findings highlight the limitations of carbon isotopic parameters for determining the origin and maturity of natural gas, and underscore their potential in identifying greenhouse gas leaks and tracing sources.

Hydrothermal mineral replacement in the apatite-rhabdophane-monazite system: Experiments, reaction mechanisms and geological implications

Apatite, rhabdophane and monazite are actinide- and rare-earth element (REE)-bearing phosphate minerals with diverse geoscientific applications. However, their mineral-fluid reaction mechanisms below 200 °C are understudied. Insufficient understanding as to how these minerals behave during hydrothermal alteration impedes useful interpretations of REE-U-Th mobilisation in regolith profiles, diagenetic environments and low-temperature hydrothermal systems. This work experimentally investigates the replacement of apatite by rhabdophane in a Ce-doped acidic fluid at 30 °C, and of rhabdophane by monazite in REE-barren acidic fluids at 180 °C. Rhabdophane replaced apatite via the coupled dissolution-precipitation mechanism, forming nanoscale prisms clustered into spherulitic aggregates. Interstitial voids that formed between rhabdophane and apatite indicate how rhabdophane precipitation was the rate-limiting step. Void widths varied in response to apatite's anisotropic dissolution; rapid dissolution parallel to the c-axis formed the widest voids (50–125 μm) and thickest rhabdophane layers (20–50 μm), while slow dissolution perpendicular to the c-axis formed narrower voids (< 1 μm) and thinner layers (< 5 μm). At 180 °C, monazite also replaced rhabdophane via the dissolution-precipitation mechanism. Replacement rates increased with increasing phosphate concentrations, implying that monazite precipitation was the rate-limiting step. However, microscale rhabdophane aggregates were pseudomorphically preserved. This is attributed to the shared orientation of rhabdophane prisms (not pseudomorphically preserved) and their intergranular boundaries which, as microreactors, guided monazite precipitation. Both replacement reactions were accompanied by a loss of U to solution, which is attributed to the stabilisation of uranyl-phosphate complexes under acidic conditions. Results indicate that: 1) anisotropic dissolution can govern the extent of rate coupling between dissolution and precipitation during mineral replacement; 2) the pseudomorphic replacement of mineral aggregates can occur when precipitation is the rate-limiting step; 3) rhabdophane is a feasible (and perhaps necessary) metastable precursor to authigenic monazite precipitation in low temperature hydrothermal systems; 4) highly porous aggregates of both rhabdophane and monazite generate insufficient EPMA totals, such that they cannot be differentiated by EPMA alone, and; 5) phosphate complexes can mobilise U under certain hydrothermal conditions, with implications for geochronology, nuclear waste management and the formation of REE deposits.

Characteristics and Deep Mineralization Prediction of the Langmuri Copper–Nickel Sulfide Deposit in the Eastern Kunlun Orogenic Belt, China

The discovery of a Cu-Ni sulfide deposit in Langmuri of the Eastern Kunlun Orogenic Belt holds significant geological implications. This study, based on the examination of the metallogenic geological body, metallogenic structure, and metallogenic process characteristics, suggests that the deposit is a magmatic Cu-Ni sulfide deposit formed in the collision of orogenic and post-extension processes of the Late Ordovician. The early mineralization of the deposit was primarily derived from the differentiation of sulfides in the mafic–ultramafic rock (450–439 Ma) of the Late Ordovician, while the late-stage mineralization underwent significant superimposed modification by the magmatic–hydrothermal activity of crustal-contaminated biotite granite (415 Ma). In addition, this article analyzes the measurements of the geochemical studies of sediments, and the magnetic and gravity measurements carried out in the area, focusing on the geochemical and geophysical anomaly characteristics in the study area, and selects favorable exploration areas, which have been confirmed to have multiple mineral bodies. By integrating comprehensive gravity, magnetic, induced polarization, and audio-frequency magnetotelluric profile measurements, this study analyzes delineated mineralized zones and the deep extensions of surface mineral bodies to assess deep mineralization potential and identify deep ore-finding targets. It suggests that diverse and scattered mafic–ultramafic complexes in the Langmuri mining area have a large-scale distribution of ore-bearing rocks in the deep. Through the analysis and inverse of the geophysical data, a deep mineralization predictive model was established in the basic–ultrabasic rock mass. The study presents prospects for the delineation of the deep-seated mineralization in the Langmuri deposit.

Plant-insect interaction from the Middle Jurassic Haifanggou Formaton in Huludao, western Liaoning and its geological implications

Plant-insect interaction from the Middle Jurassic Haifanggou Formaton in Huludao, western Liaoning and its geological implications

Alkali Trace Elements Observed by MarSCoDe LIBS at Zhurong Landing Site on Mars: Quantitative Analysis and Its Geological Implications

AbstractMars Surface Composition Detector (MarSCoDe) is one of the important payloads carried by the Zhurong rover, China's first Mars exploration mission Tianwen‐1. The laser‐induced breakdown spectroscopy (LIBS) instrument of MarSCoDe is mainly used to detect major and trace elements on the surface of Mars. The quantitative analysis of alkali trace elements, namely lithium (Li), strontium (Sr), and rubidium (Rb), holds significance in unraveling the geological evolution of the Zhurong landing site. This study focuses on establishing univariate calibration models using MarSCoDe LIBS spectra from 84 samples tested in the ground laboratory. The accuracy of these models, within a few parts per million (ppm), was subsequently validated through the analysis of 12 onboard MarSCoDe Calibration Targets (MCCTs). With these models, Li, Sr, and Rb concentrations in the surface targets during the initial 300 sols (Martian days) traverse were determined. These concentrations ranged from 6 to 18, 106–628, and 22–87 ppm, respectively. Our results suggest that Li, Sr, and Rb are mainly related to the igneous rock components in the rocks and soils at the Zhurong landing site. The major secondary minerals in MarSCoDe scientific targets are likely small amounts of sulfates, which appear to have formed from the acidic weathering of recent surface brine. Clay minerals are likely either absent or very sparse in the scientific targets. The surface igneous materials at the landing site likely have originated from the most recent lava flow during the Amazonian epoch.

Gravity Modelling Insights into Crustal Structure: Moho Depth and Subsurface Structures in Central Sulawesi

Abstract The present study examines the underlying structures and Moho depth’s geological implications in Central Sulawesi. Comprehending the underlying features of this area is essential for evaluating seismic risks and geological mechanisms. From the World Gravity Map 2012 (WGM 2012), we used a 2D radially-averaged power spectrum analysis of Bouguer gravity anomalies. The Moho depth is around 31 km in the northwest and northeast, with significant fluctuations in the middle and eastern regions. Although the northeastern and northwestern regions have similar depths, the center region has a lower Moho depth. On the other hand, the Palu-Koro Fault limit is marked by the eastern area, which corresponds to the Matano Fault, mirroring the center region. Furthermore, substantial orogenesis inside the Eastern Tokorondo Complex is suggested by Moho depth thinning, especially in the central, eastern, and southern portions. Our research emphasizes Central Sulawesi’s complicated geological structures, marked by variable Moho depth and underlying formations. With implications for earthquake risk assessment and hazard reduction, these insights advance our knowledge of the region’s geological processes.

Exposure to radon gas in groundwater in southwest Angola (Lubango-Huíla): Implications of geology and climate change

In southern African countries most of the population uses groundwater collected in dug wells for domestic consumption instead of water from public distribution systems. To investigate the impact of natural and human factors on urban groundwater quality, 276 samples were collected in the Lubango region (Angola) in water distribution systems and dug wells ranging from a few meters to almost one hundred meters in depth. Radon concentrations (RC) were determined by liquid scintillation counting according to ISO 13164–4:2015.Geology is the main source of the variability of RC, with median values higher than 100 Bq/L in granitoid units and lower values in mafic and sedimentary units (ranging from 5 to 38 Bq/L). On average, RC was higher in dug wells compared to public water distribution systems. The annual effective dose due to ingestion of radon in water is, on average, ten times lower in the later compared to dug wells. Therefore, from a public exposure perspective, water distribution systems are preferred as means for water distribution. A severe multi-year meteorological drought over the past decade affecting 76–94 % of the population in southern Angola has been linked with climate change. Consequently, a regional lowering of the water table was observed, as well as a reduction in the productivity of shallower wells, leading to a search for water at greater depths. This work demonstrates an increase in median RC from 66 Bq/L in wells shallower than 30 m to values over 100 Bq/L with increasing depth of water extraction and for the same geological unit. The highest RC observed were also observed at the deepest wells. The dose ingested is proportional to RC, being also higher at deeper water extraction depths. The increase in public radiation exposure from radon ingestion due to water extraction at greater depths is attributed to the underlying issue of climate change. Monitoring water quality in terms of radionuclide concentration is advised to ensure the exposure to ionizing radiation remains at acceptable levels in the future.

Uranium(VI) hydrolysis up to 250 °C and its geological implications

The hydrolysis of uranium(VI) has been investigated by solubility experiments conducted on sodium uranate (Na2U2O7) over a pHT range of 4.5–8 at 200 and 250 °C. Equilibrium constants for the UO2OH+, UO2OH20, UO2OH3- and UO2OH42- complexes have all been derived at both temperatures. Alongside this investigation a comprehensive literature review has been conducted to document previous investigations into U(VI) hydrolysis at temperatures above 25 °C. Using the new data reported here alongside those available in the literature, modified Ryzhenko-Bryzgalin equation of state parameters have been generated for the UO2OH+, UO2OH20, UO2OH3- and UO2OH42- complexes along with the polynuclear UO22OH22+ and UO23OH5+ complexes. This permits future works to extrapolate thermodynamic properties for these complexes to pressure–temperature conditions beyond those for which experimental data are available. Results reported here highlight the potential inadequacies of using the Ryzhenko-Bryzgalin and revised Helgeson-Kirkham-Flowers equations of state to extrapolate thermodynamic properties solely from room temperature data, with discrepancies ranging over 2–6 orders of magnitude being observed between extrapolations and the equilibrium constants experimentally derived at 200/250 °C. Using the newly derived properties, we report the results of thermodynamic calculations of uranium solubility and aqueous speciation under hydrothermal conditions relevant to a range of geological systems. These calculations suggest that uranyl hydroxide complexes may be responsible for uranium transport in a wide range of crustal fluids potentially obviating the need for high ligand concentrations.

Earliest Paleoproterozoic arc magmatism in the western Yangtze Block, South China and its geological implications

The Archean – Early Paleoproterozoic tectono-magmatic history of the Yangtze Block is inadequately constrained owing to the scarcity of coeval magmatic outcrops. Herein, we report on the Earliest Paleoproterozoic (2498 ± 17 Ma) meta-diabase dike in the Bajiaojing area of the western Yangtze Block, which may represent the oldest known mafic magmatism in the block. Whole-rock geochemical and mineral chemical proxies (e.g., U/Nb, Sc/Yb, and La/Yb) demonstrated that the Bajiaojing meta-diabase was likely emplaced in a continental arc setting. Positive zircon εHf(t) values (> 8) and incompatible elemental ratios (e.g., Gd/Yb, Sm/Yb, and Lu/Hf) further indicated that the mafic dike was derived from a depleted asthenospheric mantle source, which was modified by fluid and sediment from the subducting slab. The subduction-related modification also accounted for the compositional heterogeneity in the mantle source, which was observed in the wide range of Zr/Nb (1.05–4.38), Ce/Pb (6.11–81.59), and Nb/U (7.96–78.72) values. By combining the Precambrian evolutionary history of the Yangtze Block, we determined that an essential magmatic episode occurred in the Earliest Paleoproterozoic that was likely linked to crustal growth in the block. Therefore, the 2.5 Ga magmatism represented by the Bajiaojing meta-diabase was a potential provenance for the synchronous detrital zircons from Precambrian basement rocks.