Guangzhou Institute of Geochemistry
Institutional Repository of Guangzhou Institute of Geochemistry,CAS(GIGCAS OpenIR)Not a member yet
22838 research outputs found
Sort by
Eocene rhyolites in the Shanglaxiu-Xialaxiu area of north-eastern Qiangtang Block, Tibet: Partial melting of juvenile crust?
No full textMany granitoids and their eruptive equivalents are substantially derived from the uppermost proportion of continental crust, and so their petrogenesis and source are significant in understanding the evolution and characteristics of continental crust. The Eocene felsic rocks in the Qiangtang block (central Tibet) commonly have enriched Nd isotope compositions and have been considered to be related to the recycling of ancient continental crustal material. In this paper we report new data on early Eocene felsic rocks with positive e Nd values in the northeastern Qiangtang block, which can be used to help understand Cenozoic evolution and characteristics of continental crust in the Qiangtang block. These rocks consist of rhyolites and occur in the Shanglaxiu and Xialaxiu areas in the north-eastern Qiangtang block. Zircon U-Pb dating yields ages of 47.8 0.6 and 44.2 +/- 0.7 Ma for the Shanglaxiu and Xialaxiu rhyolites, respectively, and so they represent the earliest record of Eocene magmatism in the Qiangtang block. The Shanglaxiu-Xialaxiu rhyolites have relatively low calculated zircon saturation temperatures (719-819 degrees C), along with high SiO 2 (74.8-83.3 wt%) and K 2 (5.1-7.8 wt%) contents, and low MgO (0.2-0.3 wt%), Cr and Ni contents. They are enriched in light rare earth elements (LREEs), Rb, K, Th, Zr, and Hf, and are depleted in Nb, Ta, Ti, Sr, and P, with moderately negative Eu anomalies. The Shanglaxiu rhyolites have positive whole-rock e Nd (t) (0.3-0.4) and zircon e Hf (t) (1.8-10.4), and variable zircon 8 18 O (6.3-7.3%o). The Xialaxiu rhyolites have slightly different whole-rock e Nd (t) (-1.5 to -1.6), but similar zircon e Hf (t) (2.2-7.7) and 8 18 O (6.7-7.2%o). We propose that the Shanglaxiu-Xialaxiu rhyolites were most probably generated by partial melting of the pre-existing juvenile crust with the addition of minor sedimentary material. This partial melting was possibly triggered by the south-dipping continental subduction of the Songpan-Ganzi block. The pre-existing juvenile crust was probably formed during the subduction of Paleo-Tethyan oceanic slab in Paleozoic-Early Mesozoic
Phosphorus adsorption from aqueous solutions using different types of cement: kinetics, isotherms, and mechanisms
No full textExploring low-cost and high-performance phosphorus (P) adsorbents is key to controlling P contamination in water. This study evaluated the P adsorption performance of three types of cement: Ordinary Portland cement (OPC), Portland slag cement (PSC), and Portland pozzolana cement (PPC). Furthermore, SEM-EDS, XRD, XPS, and FTIR were employed to reveal the adsorption mechanism. The results showed that the pseudo-second-order model exhibited higher regression coefficients than the pseudo-first-order model, indicating that chemisorption dominated the adsorption process. The Langmuir equation fitted the P adsorption data well, with maximum P adsorption capacities of 245.8, 226.1, and 210.0 mg g-1 for OPC, PSC, and PPC at 25 degrees C, respectively. P adsorption capacities decreased gradually with increasing initial pH and reached their maximum values at pH 3. The anions of F-, CO32-, and SO42- negatively affected P adsorption due to the competitive adsorption with Ca2+. The results of XPS, XRD, and FTIR confirmed that Ca-P precipitates (i.e., hydroxyapatite) were the main removal mechanism. A real domestic sewage experiment showed that 0.6 g L-1 OPC effectively reduced the P concentration from 2.4 to below 0.2 mg L-1, with a dosage cost of 0.034 $ per ton. This study indicated that cement, as a low-cost and efficient P adsorbent, has great potential for application in removing P from acidic and neutral wastewater.
This study reveals the potential of cement as a cost-effective and high-capacity adsorbent for removing phosphorus from acidic and neutral wastewaters
Influence of goethite nanophase on rare-earth element patterns and enrichment in marine phosphates during early diagenesis
No full textAlthough rare-earth elements (REEs) in authigenic phosphates and carbonates derived from marine sediments are potential proxies (e.g., REE patterns) for reconstructing paleoenvironmental conditions, the REE patterns appear to be inconsistent. Some marine authigenic phosphates show a "bell-shaped" pattern with an enrichment of the middle REEs (MREEs; Nd - Ho), while others exhibit a "modern seawater-like" pattern characterized by a strong depletion in cerium and an enrichment in heavy REEs (Er - Lu, Y, and Sc). Although the origin of the "bellshaped" pattern in phosphates has been extensively debated, the evidence is often ambiguous; therefore, the origin of the pattern remains unclear. In this study, we investigate the microscale and nanoscale mineralogical and geochemical characteristics of the REE-enriched Early Cambrian phosphorites. In situ elemental analyses reveal that the codeposited phosphates ("bell-shaped" REE pattern) and carbonates ("modern seawater-like" pattern) have different REE patterns. A microscale investigation shows that phosphate grains contain some dispersed goethite nanophase, and a nanoscale investigation using transmission electron microscopy coupled with electron energy-loss spectroscopy shows that Fe 2 + is distributed along the rim of the goethite nanophase, indicating that the goethite were reduced. These findings suggest that the REE pattern and concentration in phosphates could have been influenced by the release of REEs during the reduction of Fe (oxyhydr)oxide in the early diagenetic process before the final deposition. Although additional evidence is required, our results are important for understanding the effects of Fe redox cycling on the REE pattern and enrichment in marine authigenic phosphates. In addition, our results suggest that compared with authigenic phosphates, authigenic carbonates would provide a more reliable reconstruction of paleoenvironmental conditions
Experimental simulation of thermal evolution of nitrogen content and isotopes in source rocks: Implications for nitrogen cycling characterization and oil-source correlation
No full textSedimentary nitrogen isotopes have been widely used to reconstruct the nitrogen cycling and redox characteristics of ancient oceans, but they also have important value in the study of oil genesis, such as oil classification. However, the thermal evolution of nitrogen isotopes in the source rock and associated oil is currently unclear. In this study, the thermal evolution (from the oil generation to the dry gas stage) of three types of low-maturity source rock was simulated. And the content and isotope composition of total organic carbon (TOC) and total nitrogen (TN) of the pyrolyzed source rock, expelled oil and retained oil were measured. In combination with weight-quantitative analyses, the following conclusions can be drawn: (1) During the main oil and gas generation stage, the pyrolyzed source rocks lost 15.1-28.3% of TN, which is much lower than the loss of TOC (26.2-46.1%). This difference may be related to the fact that the TOC content of the generated oil and gas is two orders of magnitude higher than the TN. In addition, TOC loss occurred mainly within the oil generationexpulsion stage, whereas TN loss occurred mainly in the dry gas stage and higher maturity stage. (2) The nitrogen isotope compositions of three types of source rocks and associated kerogens became heavier by 0.5-1.5%o as thermal maturity increased, which is similar to the change of organic carbon isotope compositions. The delta 15N values of pyrolyzed source rocks generally have poor relationships with either the amount of expelled oil and gas or the TN loss, which is different from the delta 13Corg values. The delta 15N fluctuations may be attributed to three processes: oil generation-expulsion, N2 gas generation-expulsion, and inorganic N (like NH4+) expulsion. The bulk nitrogen isotope composition of source rocks is only slightly affected by thermal maturity and can be used to indicate the nitrogen biogeochemical cycle and water redox conditions during the deposition. (3) Similar to delta 13Corg values, delta 15N values of both expelled oil and retained oil increased gradually with enhanced thermal maturity, implying a control of kinetic isotope effect. Among the three types of source rock, two of them having relatively light nitrogen isotope compositions (delta 15N value of -2.5%o) generated and expelled oils with similar nitrogen isotope compositions, while the third type, which has heavy nitrogen isotope composition (delta 15N value of -13.0%o), generated and expelled oils with much lighter nitrogen isotope compositions (by 3-6%o). This finding shows that there may be significant nitrogen isotope fractionation during the generation and primary migration of oil from source rocks. The nitrogen isotopes should be used in oil-source correlation with caution, even though related mechanisms need to be further studied. Nevertheless, using a combination of organic carbon and nitrogen isotopes, the oil generated and expelled by the three types of source rocks could be distinguished. Therefore, the use of nitrogen isotopes for oil-source correlation under geological conditions should be combined with other isotope and molecular indicators
Orbital-paced silicate weathering intensity and climate evolution across the Eocene-Oligocene transition in the southeastern margin of the Tibetan Plateau
No full textThe Eocene-Oligocene transition (EOT, -33.9 Ma), a period of dramatic global cooling marking the onset of the Antarctic ice sheet. However, paleoclimatic reconstructions indicate a notable spatial heterogeneity in both the marine and terrestrial realms. While limited temporal resolution terrestrial records have hindered the precise understanding of short-term climate events and orbital-scale changes during this transition. Here, we present a chemical weathering data sequence from a fluvial-lacustrine deposition from Luhe Basin, which is located at southeastern margin of the Tibetan Plateau. Based on the radioisotope, paleomagnetic and 405 kyr orbital tuning of the elemental datasets, the deposition age of Luhe Basin is dated to -35.5-25.5 Ma. Two weakening stages of the weathering intensity are detected around Eocene-Oligocene boundary: 34.1 to 33.9 Ma and 33.8 to 33.6 Ma, which are temporally equivalent to the two global main climatic steps of EOT (EOT-1 and Oi-1). We find the chemical weathering intensity sequence paced the 1.2 Myr obliquity amplitude modulation and 405 kyr longeccentricity cycles. Notably, the minima of 1.2 Myr obliquity amplitude and 405 kyr eccentricity are synchronous with the Oil-1 event. These patterns highlight the role of orbital forcing in shaping the cooling trend across the EOT and may trigger Antarctic glaciation
Spatiotemporal Variation of the Cretaceous-Eocene Arc Magmatism in Lhasa-Tengchong Terrane
No full textIt was recognized that two magmatic belts in the Lhasa-Tengchong terrane formed due to the Mesozoic-Cenozoic Tethyan evolution. Still, their spatiotemporal variations of magmatic flare-ups/lulls are rarely discussed. Here we use the new U-Pb and Lu-Hf isotopic data of captured zircons and a comprehensive data set to show that the flare-up of northern magmatic belt has peak ages of 110 Ma in central and northern Lhasa and 120 Ma in eastern Tengchong, possibly related to the tectonic transition from Meso- and Neo-Tethyan double subduction to Neo-Tethyan single subduction. For the southern magmatic belt, the flare-ups at 100-85 Ma and 65-45 Ma in eastern southern Lhasa indicate obvious juvenile crustal growth, while flare-ups at 75-45 Ma in western southern Lhasa and Tengchong record ancient crustal reworking. Such flare-up variations in the southern magmatic belt possibly resulted from asynchronous changes in the Neo-Tethyan slab dip.
The Tethyan slab subduction and following collision of India and Asia produced two magmatic belts in the Lhasa-Tengchong terrane. How did the magmatic flare-ups or high-flux episodes and sources spatiotemporally vary? We combine the new U-Pb and Lu-Hf isotopic data of captured zircons (xenocrystic zircons caught by volcanics from country rocks) and a comprehensive data set to show that the peak ages of early Cretaceous flare-up of the northern magmatic belt are ca.10 Ma younger in central and northern Lhasa than in eastern Tengchong, possibly related to the diachronous closure of the Meso-Tethys and flat subduction of the Neo-Tethys. The southern magmatic belt in Tengchong and western southern Lhasa exhibit 75-45 Ma flare-ups featured by the reworking of ancient crust, different from the eastern southern Lhasa with the flare-ups at 100-85 Ma and 65-45 Ma which are dominated by the juvenile crustal growth. Such flare-up variations may be related to changes of the Neo-Tethyan slab dip.
The Neo-Tethyan arc has asynchronous magmatic flare-ups and diverse magmatic sources The spatiotemporal changes of slab dip triggered the asynchronous flare-ups of the Neo-Tethyan ar
Phototrophic Nitrogen Fixation, a Neglected Biogeochemical Process in Mine Tailings?
No full textBiological nitrogen fixation (BNF) has important ecological significance in mine tailing by contributing to the initial accumulation of nitrogen. In addition to chemolithotrophic and heterotrophic BNF, light may also fuel BNF in oligotrophic mine tailings. However, knowledge regarding the occurrence and ecological significance of this biogeochemical process in mine tailings remains ambiguous. The current study observed phototrophic BNF in enrichment cultures established from three primary successional stages (i.e., original tailings, biological crusts, and pioneer plants) of tailings. Notably, phototrophic BNF in tailings may be more active at vegetation stages (i.e., biological crusts and pioneering plants) than in bare tailings. DNA-stable isotope probing identified Roseomonas species as potential aerobic anoxygenic phototrophs responsible for phototrophic BNF. Furthermore, metagenomic binning as well as genome mining revealed that Roseomonas spp. contained essential genes involved in nitrogen fixation, anoxygenic photosynthesis, and carbon fixation, suggesting their genetic potential to mediate phototrophic BNF. A causal inference framework equipped with the structural causal model suggested that the enrichment of putative phototrophic diazotrophic Roseomonas may contribute to an elevated total nitrogen content during primary succession in these mine tailings. Collectively, our findings suggest that phototrophic diazotrophs may play important roles in nutrient accumulation and hold the potential to facilitate ecological succession in tailings
Distribution, chemical, and molecular composition of high and low molecular weight humic-like substances in ambient aerosols
No full textHumic-like substances (HULIS) encompass a continuum of molecular weight (MW) ranges, yet our understanding of how HULIS characteristics vary with MW is still limited and not well established. In this study, a combination of ultrafiltration and solid-phase extraction protocols was employed to fractionate the high MW (HMW; > 1 kDa) and low MW (LMW; C = O). HRMS analysis further unveiled that molecular formulas within HMW HULIS generally featured smaller sizes but higher degrees of unsaturation and aromaticity compared to those within LMW HULIS fractions. This observation suggests the possibility of small molecules assembling to form the HMW HULIS through intermolecular weak forces. Moreover, HMW HULIS contained a higher proportion of CHON but fewer CHO compounds than LMW HULIS. In both HMW and LMW HULIS, the unique molecular formulas were primarily characterized by lignin-like species, yet the former displayed a prevalence of N-enriched and highly aromatic species. Additionally, HMW HULIS contained more unique lipid-like compounds, while LMW HULIS exhibited a distinct presence of tannin-like compounds. These findings provide valuable insights into the distribution, optical properties, and molecular-level characteristics of HULIS in atmospheric aerosols, thereby advancing our understanding of their sources, composition, and environmental implications
Microstructural and compositional evolutions during transformation from biotite to berthierine: Implications for phyllosilicate alteration processes
No full textThe composition and microstructure of phyllosilicates are prone to transformation due to their great sensitivity to surrounding physicochemical changes. Berthierine [(R2+,R3+,)6(Si,Al)4O10(OH)8] ( represents octahedral vacancy) is a typical ferromagnesian phyllosilicate that commonly occurs in ferruginous rocks of shallow-marine habitats and has been used as an indicator of local depositional and/or hydrothermal activity in marine environments. However, little is known about the formation and mineralogy of non-marine berthierine, particularly in volcanic systems. Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), we have identified a berthierine twin structure within weakly altered biotite in a rhyolite from Long Valley, California, U.S.A. The presence of nanoscale Fe-rich layers in the host biotite is revealed by energy-dispersive spectroscopy and electron energy loss spectroscopy (EELS). The HAADF-STEM pictures with atomic resolution demonstrate that the Fe-rich layers are composed of twinning berthierine layers rather than a single chlorite layer. The transformation of biotite to berthierine requires the dissolution of a tetrahedral (T) layer and the introduction of a new TO (O represents octahedral sheet) structure into the biotite stacking sequence, resulting in substituting one biotite layer (i.e., TOT) with two twinning berthierine layers (i.e., TO-OT). Observations based on morphology indicate that the transformation began at biotite defect locations (such as screw dislocation, edge dislocation, and microcleavage fracture), concurrent with the rearrangement of metal cations. During the fluid alteration of biotite, berthierine was produced via an interface-coupled dissolution-reprecipitation process. The EELS analyses further demonstrate that the Fe-rich biotite promotes the production of berthierine as the principal alteration product in low-temperature environments. Additionally, this study suggests that the combination of HAADF-STEM and EELS is effective for identifying nanominerals and elucidating their formation and alteration mechanisms
The Lower Atmospheric Characteristics of Dust Storms Using Ground-Based Sensor Data: A Comparative Analysis of Two Cases in Jinan, China
No full textTwo severe dust storm (DS) events (15-17 March and 28-29 March) hit northern China in 2021 consecutively. The lower atmospheric vertical dynamic and thermal structures during the two cases were compared using the ground-based sensor data from the microwave radiometer and radar wind profiler, combined with the environmental and meteorological observations data in Jinan, China. It was found that both cases occurred under the background of cold vortexes over northeastern China. The dust was transported through the cold air on the northwest route. During the dust period, 2-3 km was the west or northwest airflow, and below 2 km was the northeast wind. The variation in the dynamic structure determined the duration of the DS. During the DS maintenance phase, the vertical wind shear (VWS) below 3 km measured approximately 10 m center dot(s center dot km)-1. The increased VWS during the dust intrusion period facilitated the transportation of dust. In contrast, the more significant VWS was not conducive to the maintenance of DS, and the shift to south wind control in the upper middle layer indicated the weakening of DS. In both cases, we observed a cliff-like decrease in relative humidity as a prominent indicator of dust outbreaks, occurring approximately 2-5 h beforehand. The diurnal difference between the vertical temperature and relative humidity during the dust maintenance period was found to be insignificant