Guangzhou Institute of Geochemistry
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On-land evidence for subduction of the proto-South China Sea beneath northern Borneo and tectonic reconstruction of Southeast Asia during the early Permian-Oligocene
No full textThe development of the Mesozoic proto- South China Sea was closely related to the tectonic evolution of the Tethys and Paleo-Pacific domains and may have been a key driving mechanism for the opening of the South China Sea. Despite its importance, direct geologic evidence for the proto-South China Sea remains limited, and its development is debated between two primary models: intraoceanic subduction and oceanic-continental subduction. Here, we present petrographic, geochronologic, and geochemical data from tuffs and Eocene-Pliocene sedimentary records in Sabah, northern Borneo. The results reveal that these tuffs, formed ca. 28 Ma, possess geochemical characteristics indicative of oceanic arc origins. Combined with changes in sediment provenance since the Oligocene and various subduction timelines around Borneo, we suggest that these tuffs resulted from the subduction of the proto-South China Sea. This oceanic arc, along with Eocene mid-ocean-ridge-like mafic rocks in Sabah, indicates that a younger oceanic basin had formed within the proto-South China Sea. This aligns with observations in Palawan, Philippines, illustrating the transition from an oceanic spreading center to a subduction zone and indicating the proto-South China Sea extended from eastern Sabah to Palawan. In addition, inherited zircons (ca. 280 Ma) in the tuffs exhibit geochemical signatures typical of continental arcs. Combined with the Permian-Cretaceous arc-related igneous rocks in Southeast Asia, this suggests that southern Sabah was part of the Paleo-Tethys Ocean before integrating into the Paleo-Pacific domain since the Triassic. By shedding light on these processes, our research provides critical insights into the existence, extent, and evolution of the proto- South China Sea and reconstructs the multiphase transitions between different tectonic domains in Southeast Asia
Enrichment and fractionation of rare earth elements (REEs) in ion-adsorption-type REE deposits: Constraints of an iron (hydr)oxide-clay mineral composite
No full textIon-adsorption-type rare earth element (REE) deposits are the source of more than 90% of global heavy REEs (HREEs). Thus, understanding the ore genesis of REEs, particularly the distribution characteristics and enrichment mechanisms of HREEs, is vital for efficient exploration and mining of ion-adsorption-type REE deposits worldwide. The characteristics and petrogenesis of bedrock and the aqueous mobility of REEs are known to be important factors controlling REE accumulation and fractionation in the weathering crust of REE deposits. However, the effect of REE adsorption on secondary minerals, a crucial step in deposit formation, remains poorly understood. This problem was addressed by the study described herein, which involved a systematic analysis of the complete weathering profile (78 m) of the Renju ion-adsorption-type REE deposit in South China and a simulated adsorption experiment. Clay minerals and iron (Fe) (hydr)oxides are the dominant REE adsorbents in the weathering crust and most are micro-to-nanosizedparticles. Thus, the fine-particle fraction (<2 mu m) was separated from field samples to disclose better their effects on the concentration and redistribution of REEs. Phase compositions and morphologies were characterized by X-ray diffraction, M & ouml;ssbauer spectrometry, and scanning/transmission electron microscopy (SEM/TEM), which revealed that various clay minerals and Fe (hydr)oxides form composites along the profile of the deposit. Composites of ferrihydrite-kaolinite, goethite-kaolinite/halloysite, and hematite-kaolinite/halloysite were found to be distributed in the semi-weathered, completely weathered, and topsoil layers, respectively, with different sizes and shapes. The concentrations and partition patterns of REEs in different occurrence states were distinguished after sequential extraction. Ion-exchangeable-REEs were the major state and enriched in the upper completely weathered layer. These species were found to be adsorbed onto kaolinite and halloysite via electrostatic attraction without obvious fractionation. Fe (hydr) oxides were determined to comprise ca. 20% of REEs at most depths and over 50% of REEs in the topsoil and semi-weathered layer. It was found that Fe (hydr)oxides scavenge REEs through complexation and oxidation, resulting in HREE enrichment and a positive cerium (Ce) anomaly, respectively. In addition, compared with crystalline Fe (hydr)oxides, amorphous Fe (hydr)oxides immobilize more REEs but exhibit weaker preferential adsorption of HREEs. The above-described findings are consistent with the results of simulated experiments for REE adsorption onto a clay mineral-Fe (hydr)oxide composite (Bt-60d), which was obtained from hydrothermal processing of biotite. Furthermore, the distributions and stabilities of LREEs and HREEs were distinguished by TEM-energy-dispersive spectroscopy (EDS) of Bt-60d before and after REE extraction by ammonium sulfate. The phase transformation pathways of clay minerals and Fe (hydr)oxides and their different enrichment and fractionation characteristics in REEs were also discussed in terms of the structure and surface properties of minerals, adsorption mechanisms, and variations in chemical properties across the REE group. The results shed new light on how clay minerals and Fe (hydr)oxides affect the enrichment and fractionation of REEs in ion-adsorption-type deposits
Influences of synoptic circulations on regional transport, local accumulation and chemical transformation for PM 2.5 heavy pollution over Twain-Hu Basin, central China
No full textThe Twain-Hu Basin (THB), located in Central China, serves as a key juncture where the northerly "polluted" airflows of the East Asian winter monsoon meet the southerly warm and humid airflows. Using the T-PCA (T-mode Principal Component Analysis) objective synoptic pattern classification, Flexible Particle-Weather Research and Forecasting (FLEXPARTWRF) model, and Random Forest model, we investigate the influences of synoptic circulations on regional transport, local accumulation, and chemical transformation of PM 2.5 during heavy air pollution over the THB in January of 2015-2022. The results show that the transport-type synoptic pattern accounts for 65.16% of heavy PM 2.5 pollution, indicating that regional transport of PM 2.5 dominates the THB's heavy air pollution. The PM 2.5 /CO ratio is higher in the transport-type pattern and positively correlated with PM 2.5 concentrations, reflecting a higher efficiency of chemical transformation to secondary PM 2.5 in transport-type pollution compared with the accumulation-type pollution. Transport-type heavy PM 2.5 pollution is predominantly influenced by upstream anomalous northerly and easterly airflows at the bottom of the high-pressure system, converging with the southern wind in the receptor area over the THB. Accumulation-type heavy pollution exhibits weak wind anomalies in central and eastern China under the control of a uniform pressure field. Furthermore, thermally-induced vertical circulations with sinking airflows in the middle and lower troposphere suppress the vertical air pollutant dispersions. The relative contributions of atmospheric factors for transport-type PM 2.5 heavy pollution events are 38.0% for dynamical driver, 26.8% for thermal driver, and 35.1% for chemical transformation, while in accumulation-type, the contribution rates are 33.9%, 36.3%, and 29.7%, respectively. This study elucidates the influences of synoptic patterns on regional transport, local accumulation, and chemical transformation of PM 2.5 for heavy air pollution, with implications for understanding changes of air quality in the receptor region of regional transport. (c) 2025 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V
A continental record of Early Cretaceous (Aptian) vegetation and climate change based on palynology and clay mineralogy from the North China Craton
No full textThe Early Cretaceous Aptian Stage (121.4-113.0 Ma) witnessed significant climate changes and environmental perturbations including Ocean Anoxic Event 1a; however, reconstructions of paleoclimate have predominantly relied on marine records. In this paper, we report palynological and clay mineralogical data from a continuous core (YSDP-4) in the Kazuo Basin of Northeast China to produce a high-resolution terrestrial Aptian record that is correlated with the marine record. In the lowermost part of the Aptian succession (similar to 121 to similar to 120 Ma), vegetation types were dominated by bisaccate conifers (>75%), while smectite and illite clay minerals were co- dominant (each similar to 40-50%), indicating cool and semi-humid to semi-arid conditions with a tendency towards aridity. This was followed by an exceptionally dry and hot climatic event, from similar to 120 Ma to similar to 117.5 Ma, marked by a rapid increase in drought-resistant plants including members of the Cheirolepidiaceae (>60%). During the transition from the early Aptian to the late Aptian (similar to 117.5 to similar to 114 Ma), the clay mineral composition exhibited a complex pattern containing chlorite and kaolinite, and the proportion of vegetation representing relatively cool and moist conditions increased, indicating a gradual transition to a humid climate. By the end of the late Aptian (similar to 114 to similar to 112 Ma), climate became cooler and more humid, as indicated by a sharp increase in Taxodiaceae pollen (similar to 50%). Based on the similar patterns of vegetation and sedimentary records observed in the Kazuo Basin and across the Tethyan Realm, we propose that the early Aptian hot/dry climatic event was synchronous with Oceanic Anoxia Event 1a. The findings of our study provide an important terrestrial sedimentary reference section for future integration of Cretaceous climatic events and biological evolution across the marine-terrestrial spectrum
Frequency of Synoptic-Scale Precipitation Events Recorded by Daily Resolved δ<SUP>18</SUP>O of Land Snail Shells
No full textLand snails exhibit the potential for capturing synoptic-scale precipitation events through the delta O-18 records of their shells (delta(18)Oshell), but the application is hindered by the absence of a practical methodology for tracking these events. Here, we developed a statistical methodology to track the synoptic-scale precipitation events from daily resolved snail body fluid delta O-18 (delta O-18(BF)) record. We further tested and verified our approach using daily resolved delta(18)Oshell records of modern Cathaica fasciola from the Chinese Loess Plateau (CLP). The reconstructed 3-day-timescale precipitation events frequencies using first derivations of delta 18OBF and delta 18Oshell shows strong agreement with instrumental data (>85% detection accuracy). The strong correlation between precipitation days in snail-growing-season and annual precipitation amounts across the CLP also permits the reconstruction of synoptical precipitation frequency for investigating the interannual variability of precipitation. Our study paves the avenue in paleoweather study, enabling quantitative reconstructions of past synoptic-scale precipitation events
Estimating wastewater emissions and environmental levels of typical organic contaminants based on regionalized modelling
No full textOrganic contaminants (OCs) are released into the environment through effluent discharges from wastewater treatment plants (WWTP), posing risks to environment health. However, emissions from various source, particularly large-scale investigations across different industries, remain poorly understood. Based on both sampling and statistical data, this study estimates the emissions of 10 OCs, including perfluorooctane acid (PFOA), perfluorooctane sulfonate (PFOS), 4-nonylphenol (4-NP), 4-tert-octylphenol (4-t-OP), dibutyl phthalate (DBP), di-iso-butyl phthalate (DIBP), dimethyl phthalate (DMP), butyl benzyl phthalate (BBP), di(2-ethylhexyl) phthalate (DEHP), and bisphenol A (BPA), from the effluents of 160 factories across 8 industries, 541 municipal wastewater treatment plants (MWWTPs), and 8 waste treatment plants (WTPs) in the upper Yangtze River Basin. A level III fugacity multimedia model was used to assess the impacts of these emissions on local watersheds. Among the 8 industries, paper production was the largest contributor, accounting for over 80% of total OC emissions, which amounted to 89.1 kg/yr. The contributions of domestic and industrial sources were 91.5% and 8.5%, respectively, underscoring the predominance of domestic sources in the release of the 10 OCs. PFOA emerged as the most dominant compound, with total emissions amounting to 4464 kg/yr from domestic sources and 170 kg/yr from industrial sources. The predicted concentrations of OCs in the receiving rivers closely aligned with values reported in existing literature, differing by no more than one order of magnitude. To our knowledge, this is the first comprehensive report on emissions from various sources in the upper Yangtze River Basin
Distribution of bacterial 3-OH-FAs in Chinese saline lakes and its implication for paleoclimate reconstruction
No full textMicrobial communities in saline lakes are sensitive to environmental changes and showed promise for paleoclimate reconstruction. However, how the Gram-negative bacterial communities and their related membrane lipids, 3-hydroxy fatty acid (3-OH-FA), adapt to salinity change is still unclear. Here, we report the potential impacts of salinity and pH on 3-OH-FA distributions, based on saline lake samples, including lacustrine sediments and surrounding soils, collected from the Balikun Lake of the Xinjiang Province and 12 shallow lakes of the Inner Mongolia Province, China. Our results revealed that 3-OH-FAs in saline lakes are mainly derived from in situ production. The 3-OH-FA distributions are sensitive to salinity and pH variations. Specifically, in brackish lakes (< 30 parts per thousand), salinity and pH dominated the distribution of 3-OH-FAs. However, in hypersaline lakes, salinity predominated the 3-OH-FA distributions. Moreover, multiple linear regression has been used to explore the potential salinity proxies based on 3-OH-FAs. The result revealed the promising potential of using 3-OH-FAs for paleoenvironment reconstruction, which provides alternative tools for investigating the paleoclimate changes in saline environments
Identification of intermediate-silicic cumulates in the Emeishan large igneous province, SW China
No full textGeochemical signatures of crystal accumulation in silicic igneous rocks are subtle and difficult to discern. However, the presence of silicic cumulates is required to explain the formation of silicic magmas by fractionation-dominated mechanisms. In large igneous provinces, such rock records are scarce if ever reported. In this study, we document a case example of identifying intermediate-silicic cumulates in the end-Guadalupian (similar to 260 Ma) Emeishan large igneous province, SW China. We demonstrate that syenitic rocks associated with the Panzhihua intrusion have textures and trace element geochemistry consistent with origins involving both crystal accumulation and melt extraction. Micro-X-ray fluorescence mapping shows that the rocks are either supported by a framework of interconnected, relatively large crystals of alkali feldspar, or by a fine- to medium-grained matrix. The former has relatively low SiO2, relatively high TiO2, Fe2O3, CaO, Na2O, Sr and Ba, and a characteristic positive Eu anomaly, whereas the latter has essentially the opposite features. All studied rocks have restricted initial Sr-Nd-Pb isotopic ratios that are similar to mafic rocks of the Panzhihua intrusion, requiring minimal contamination by the Precambrian basement of the Yangtze block. Because of delayed zircon saturation, Zr and Zr/Hf are less promising compared with Eu/Eu* and Ba in identifying cumulates in the studied rocks, a view that might hold in other intraplate magmatic systems. Our results, combined with available data, improve the current understanding of volcanic-plutonic connection concerning silicic magma types of the Emeishan large igneous province
Fractionation of radiogenic Pb isotopes in meteorites and their components induced by acid leaching
No full textIn this study we test the possibility that radiogenic 207Pb/206Pb ratios (207Pb*/206Pb*) in meteorites can be fractionated during partial dissolution, and explore the consequences of this fractionation for Pb-isotope chronology of meteorites. We report the results of experiments tailored to detect Pb-isotope fractionation, induced by partial dissolution through acid leaching, in plutonic angrite Northwest Africa (NWA) 4801 and ungrouped achondrites NWA 10132 and Erg Chech (EC) 002. We also re-examine previously published U-Pb data for other achondrites and for Ca-Al-rich refractory inclusions (CAIs), to seek evidence of such fractionation. We observe that, in primitive achondrite NWA 10132, differences in 207Pb*/206Pb* ratios, corresponding to the age bias of ca. 1-2 Ma, exist between the 0.5 M hydrofluoric acid leachates of pyroxene or crushed rock, and the residues after such leaching. In angrite NWA 4801, similar acid treatment of pyroxene separates did not cause a resolvable age bias. In EC 002, three steps of partial dissolution in 0.2 M - 5 M HF caused irregular 207Pb*/206Pb* fractionation between leaching steps, and generally higher 207Pb*/206Pb* ratios in the residues than in HF leachates. These age biases were observed in leaching pairs with highly radiogenic Pb, and cannot be explained by mixing between radiogenic Pb, primordial Pb, and Pb introduced by terrestrial contamination. Instead, the observed isotope fractionation is attributed to the combined effects of the size difference between alpha-recoil tracks in the decay chains of 238U and 235U, and exsolution of primary pigeonite, leading to the formation of a lamellar structure consisting of augite and low-Ca pyroxene by either slow-cooling or subsequent metamorphic reactions. Where extensive acid leaching intended for removal of non-radiogenic Pb causes fractionation of radiogenic Pb isotopes, its detrimental effect can be reversed by performing a numeric recombination of partial leachate and residue data. Currently, it is unclear how common leaching-induced isotopic fractionation is in Pb-isotopic chronology to meteoritic materials. Acid leaching is an essential step for removal of non-radiogenic Pb in the precise Pb-isotopic dating of meteorites, which currently does not have viable alternatives. However, it is important to be aware of its possible side effects, and to continue search for new non-radiogenic Pb removal techniques that do not cause radiogenic 207Pb* and 206Pb* fractionation
Metamorphic evidence of the Kuunga orogeny in South China: Highpressure pelitic granulites and gneisses from the Gaozhou Complex
No full textThe role of the South China Block in the Kuunga orogeny, a pivotal event marking the assembly of the Gondwana supercontinent, remains a subject of debate. This study investigates high-pressure (high-P) granulitefacies metamorphism in the Yunkai orogen of eastern South China to shed light on this controversy. Recently,highP pelitic granulites with a mineral assemblage of garnet, K-feldspar, and sillimanite pseudomorph replacing earlier kyanite were identified in the Gaozhou Complex. Petrographic observations, phase equilibria modeling, geothermobarometry, and laser ablation-inductively coupled plasma-mass spectrometry (LAICP-MS) zircon U-Pb dating have revealed a four-stage metamorphic evolution. The peak P stage (M1) is characterized by highP conditions of 10-11.8 kbar/760-830 degrees C in the kyanite and rutile stability fields. This is followed by the peak temperature (T) metamorphism (M2) at slightly lower pressures and higher temperatures of 7.8-9.5 kbar/840-870 degrees C, which suggests a subsequent period of thermal relaxation. Subsequent decompression and cooling (M3) led to the formation of cordierite + spinel coronae, which reflects a change in P-T conditions to 4.5-5.3 kbar/730-790 degrees C. The final retrogression (M4) occurred under lower-grade conditions of 3.7-4.4 kbar/600-640 degrees C. Consequently,highP pelitic granulites in this region have undergone a clockwise P-T path, which indicates a continental collision setting. Zircon U-Pb dating from thehighP granulites and gneisses yielded multistage metamorphic ages of ca. 520 Ma, ca. 440 Ma, and ca. 240 Ma, which correspond to the Pan-African, Caledonian, and Indosinian tectono-thermal events, respectively. These metamorphic ages, coupled with the clockwise P-T path, reveal a history of polymetamorphism associated with a longlived subduction-continental collision event during the assembly of Gondwana and the subsequent Indosinian overprinting. These multiple orogenic processes provide significant insights into the tectonic evolution of the South China Block. Our findings contribute to the evidence of the Kuunga orogeny in South China during the assembly of Gondwana and offer a robust framework for interpreting the complex metamorphic histories of orogenic belts