Acta Geochimica最新文献

Photosynthesis is the most important biochemical reaction on Earth. It has co-evolved and developed with the Earth, driving the biogeochemical cycle of all elements on the planet and serving as the only chemical process in nature that can convert light energy into chemical energy. Some heavy oxygen isotopic (¹⁸O) labeling experiments have “conclusively” demonstrated that the oxygen released by photosynthesis comes only from water and are written into textbooks. However, it is not difficult to find that bicarbonate has never been excluded from the direct substrate of photosynthesis from beginning to end during the history of photosynthesis research. No convincing mechanism can be used to explain photosynthetic oxygen evolution solely from water photolysis. The bicarbonate effect, the Dole effect, the thermodynamic convenience of bicarbonate photolysis, the crystal structure characteristics of photosystem II, and the reinterpretation of heavy oxygen isotopic labeling (¹⁸O) experiments all indicate that the photosynthetic oxygen evolution does not exclude the important role and contribution of bicarbonate photolysis. The recently proposed view that bicarbonate photolysis is the premise of water photolysis, bicarbonate photolysis and water photolysis work together with a 1:1 (mol/mol) stoichiometric relationship, and the stoichiometric relationship between oxygen and carbon dioxide released during photosynthetic oxygen evolution is also 1:1, has excellent applicability and objectivity, which can logically and reasonably explain the precise coordination between light and dark reactions during photosynthesis, the bicarbonate effect, the Dole effect, the Kok cycle and the neutrality of water and carbon in nature. This is of great significance for constructing the bionic artificial photosynthetic reactors and scientifically answering the question of the source of elemental stoichiometric relationships in nature.

The Early Paleozoic tectono-thermal event was a significant orogenic activity during the Phanerozoic era, which had a profound impact on the early crust of the South China Block (SCB) and established the foundation for later tectonic activity. The Wuyi-Yunkai orogenic belt in Southeastern China was extensively exposed to Early Paleozoic magmatism, the genetic mechanism of which remains controversial. To shed light on this issue, detailed petrological, geochemical, and zircon U–Pb–Hf isotopic studies were carried out on two granitoids, namely the Yuntongshan pluton and the Gaoqiao pluton, identified in the central Wuyishan. Zircon U–Pb chronology of the Yuntongshan and Gaoqiao bodies yielded ages of 437 ± 4 Ma (MSWD = 2.2) and 404 ± 2 Ma (MSWD = 12), respectively, indicating that they were emplaced during the Early Silurian and Early Devonian periods. These granitoids are primarily composed of biotite-granite and biotite-monzonitic-granites, with high concentrations of S_iO₂ (73.59–75.91 wt%), K₂O + Na₂O (8.31–8.73 wt%), and low contents of MgO, CaO, Cr, Ni. They are classified as high-K calc-alkaline and weakly metaluminous-strongly peraluminous S-type granites. These granitoids are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs) with arc affinity. The εHf(t) values of − 3.3 to − 15.4 with two-stage Hf model ages ranging from 2829 to 1644 Ma, combined with the presence of Neoproterozoic inherited zircons, suggest that the primary magma of these granitoids was derived from the partial melting of Neoproterozoic crust with a Paleoproterozoic crustal model age. These findings, combined with the spatio-temporal distribution of regional magmatism, reveal that the late Early-Paleozoic granitoids formed in the intraplate orogenic background originating from the subduction of the proto-Tethys Ocean and proto-Pacific Ocean around the margin of the east Gondwana supercontinent.

The rapid development and widespread use of ZnO nanoparticles (nZnO) in various industries have raised concerns about their potential environmental impact. Therefore, understanding the fate and role of nZnO in the natural environment is crucial for mitigating their hazardous effects on the environment and human safety. The purpose of the present study was to provide scientific support for understanding and eliminating the joint risk of nanoparticle and heavy metal pollution in the soil environment by revealing the co-transport characteristics of Cd(II) and ZnO nanoparticles (nZnO) in soil under different ionic strength (IS) and pH. The impacts of different IS and pH on the co-transport of Cd(II) and nZnO in a 20 cm long with an inner diameter of 2.5 cm acrylic column packed with 10 cm high soil samples were investigated in the present study. In the above system, a 500 μg L⁻¹ Cd(II) loaded nZnO suspension pulse with varying IS or pH was introduced into the soil column for leaching over 5 PVs, followed up by 5 PVs background solutions without nZnO. The IS was 1, 10, or 50 mM NaCl, with pH6, or the pH was 6, 7 or 8 with 1 mM NaCl. Meanwhile, Sedimentation experiments for nZnO, adsorption of Cd(II) on soil, and nZnO, DLVO theory calculation for the same background condition were conducted. The presence of nZnO significantly increased the mobility of Cd(II) as a result of its strong adsorption capacity for nZnO-associated Cd(II). However, with the increase of IS, the co-transport of nZnO and Cd(II) was decreased and the retention of nZnO in the soil column due to more nZnO attended to aggregate and sediment during the transport and the decrease in the adsorption capacity of nZnO for Cd(II) by competition of Na⁺. When pH was 6, 7, and 8, the co-transport of nZnO and Cd(II) increased with higher pH due to the lower electrostatic attraction between nZnO and soil under higher pH. Meanwhile, the DLVO theory was fitted to describe the above co-transport process of nZnO and Cd(II). More attention should be paid to the presence of nZnO on the migration of Cd(II) in the natural soil to control the potential risk of nanoparticles and heavy metals to the environment. The risk of co-transport of nZnO and Cd(II) might be controlled by adjusting IS and pH in the soil solution.

Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at 423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series. Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_Nd(t) = (− 3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Post-collisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.

Water in Earth’s mantle plays a critical role in both geodynamic and surficial habitability. Water in the upper mantle and transition zone is widely discussed, but less is known about the water in the lower mantle despite it constituting over half of Earth’s mass. Understanding the water storage in Earth’s lower mantle relies on comprehending the water solubility of bridgmanite, which is the most abundant mineral both in the lower mantle and throughout Earth. Nevertheless, due to limited access to the lower mantle, our understanding of water in bridgmanite mainly comes from laboratory experiments and theoretical calculations, and a huge controversy still exists. In this paper, we provide a review of the commonly employed research methods and current findings concerning the solubility of water in bridgmanite. Potential factors, such as pressure, temperature, compositions, etc., that influence the water solubility of bridgmanite will be discussed, along with insights into future research directions.

Geochemistry, zircon U–Pb geochronology, and Hf isotope data for the Early Paleozoic granites in the Baoshan Block reveal the Early Paleozoic tectonic evolution of the Proto-Tethys. The samples are high-K, calc-alkaline, strongly peraluminous rocks with A/CNK values of 1.37–1.46, are enriched in SiO₂, K₂O, and Rb, and are depleted in Nb, P, Ti, Eu, and heavy rare earth elements, which indicates the crystallization fractionation of the granitic magma. Zircon U–Pb dating indicates that they formed in ca. 480 Ma. The Nansa granites have ε_Hf(t) values ranging from − 16.04 to 4.36 with corresponding T^C_DM ages of 2.10–0.81 Ga, which suggests the magmas derived from the partial melting of ancient metasedimentary with minor involvement of mantle-derived components. A synthesis of data for the Early Paleozoic igneous rocks in the Baoshan block and adjacent (Tengchong, Qiangtang, Sibumasu, Himalaya, etc.) blocks indicates that these blocks were all aligned along the proto-Tethyan margin of East Gondwana in the Early Paleozoic. The Early Paleozoic S-type granites from Nansa were generated in a high-temperature and low-pressure (HTLP) extensional tectonic setting, which resulted from Andean-type orogeny instead of the final assembly of Gondwana or crustal extension in a non-arc environment. In certain places, an expanding environment may exist in opposition to the tectonic backdrop of the lithosphere's thickening and shortening, leading the crust to melt and decompress, mantle-derived materials to mix, and a small quantity of peraluminous granite to emerge.

Ragahama Formation comprises a siliciclastic continental deposits followed by marine carbonates, representing prograding alluvial fans from adjacent high hinterlands seaward into lagoons and fringing reef environments. The present work aimed to document the facies development and sedimentology of the Raghama carbonates exposed along the eastern coastal plain of the Red Sea, northwestern Saudi Arabia. Four stratigraphic sections were measured and sampled (D1–D4) and thin sections and major and trace element analyses were prepared and applied for petrographic and geochemical approaches. The carbonates were subdivided into three successive fore-reef, reef-core, and back-reef depositional facies. Sandy stromatolitic boundstone, microbial laminites, dolomitic ooidal grainstone, bioclastic coralline algal wackestone, sandy bioclastic wackestone, and coral boundstones were the reported microfacies types. Petrographic analysis reveals that the studied carbonates were affected by dissolution, dolomitization, and aggrading recrystallization, which affects both the original micrite matrix and grains or acts as fracture and veinlet filling leading to widespread vuggy and moldic porosity. No evidence of physical compaction, suggesting rapid lithification and recrystallization during early diagenesis and prior to substantial burial and intensive flushing by meteoric waters. Most of the original microstructure of corals were leached and destructed. This is indicated by the higher depletion in Sr and Ca levels and increase in Mg, Na, Fe, and Mn levels, especially in section D1, in comparison with the worldwide carbonates.

The Nigerian oil sands represent the largest oil sand deposit in Africa, yet there is little published information on the distribution and potential health and ecological risks of trace elements in the oil resource. In the present study, we investigated the distribution pattern of 18 trace elements (including biophile and chalcophile elements) as well as the estimated risks associated with exposure to these elements. The results of the study indicated that Fe was the most abundant element, with a mean concentration of 22,131 mg/kg while Br had the lowest mean concentration of 48 mg/kg. The high occurrence of Fe and Ti suggested a possible occurrence of ilmenite (FeTiO₃) in the oil sands. Source apportionment using positive matrix factorization showed that the possible sources of detected elements in the oil sands were geogenic, metal production, and crustal. The contamination factor, geo-accumulation index, modified degree of contamination, pollution load index, and Nemerow pollution index indicated that the oil sands are heavily polluted by the elements. Health risk assessment showed that children were relatively more susceptible to the potentially toxic elements in the oil sands principally via ingestion exposure route (HQ > 1E-04). Cancer risks from inhalation are unlikely due to CR < 1E-06 but ingestion and dermal contact pose severe risks (CR > 1E-04). The high concentrations of the elements pose serious threats due to the potential for atmospheric transport, bioaccessibility, and bioavailability.

Elemental information carried by phytoliths plays a crucial indicative role in geochemical research. For instance, it serves as an indicator of the carbon pool effect in phytoliths and aids in the elucidation of silicon sources. However, early extraction methods for soil phytoliths primarily focused on obtaining their morphological and quantitative information, lacking efficient techniques for quantitative elemental analysis. In this study, we aimed to extract Si/Al information from soil phytoliths. Considering the need for complete extraction of phytolith, six extraction methods were developed and further by alkaline dissolution to determine Si/Al. Six methods were compared in terms of enrichment capacity, the weight of extracted phytoliths, and Si/Al differences. The results indicated that the addition of Ammonia-Catechol in the commonly used heavy liquid flotation method effectively improved phytolith extraction capability and the accuracy of Si/Al results. Additionally, the inclusion of an acetic acid step before alkaline dissolution further removed surface-adsorbed impurities and enhanced the analytical quality of Si/Al in phytolith. The comparison of the data in this study with other published data shows that our method is relatively robust. The improved method proposed in this study can provide a new idea for the quantitative analysis of other elements in soil phytoliths.

The wadi dahab delta is in a dry, arid coastal zone within Egypt's south Sinai Peninsula's eastern portion. The primary water source is the Quaternary coastal alluvial aquifer. The groundwater salinity varies from 890 to 8213 mg/L, with a mean value of 3417 mg/L. The dissolved major ions have been used to calculate the seawater mixing index (SWMI) using a linear equation that discriminates the groundwater mostly affected by water–rock interaction (SWMI 1 >) and other samples mixed with Seawater (SWMI < 1). The isotopic composition of groundwater for specifically chosen groundwater samples ranges from −0.645‰ to +5.212‰ for δ¹⁸O and from − 9.582‰ to + 22.778‰ for δ²H, where the seawater represented by a Red Sea water sample (δ¹⁸O + 1.64‰ − δ²H + 9.80‰) and reject brine water are considerably enriched the isotopic groundwater values. The geochemical NETPATH model constrained by the dissolved significant ions, isotopes, and the rock aquifer forming minerals as phases indicate the mixing percent with the seawater ranges from 9% to 97% of seawater from 91% to 3% of original recharge water. According to the SEAWAT 3-D flow models, seawater has penetrated the Northeastern Dahab delta aquifer, with the intrusion zone extending 1500 m inland. The salt dissolution, upwelling of saline water, recharge from the upstream mountain block, and seawater encroachment are the primary aspects contributing to the deterioration of groundwater quality. These findings may have significance for effective groundwater withdrawal management in arid locations worldwide with similar hydrogeological systems.