Guangzhou Institute of Geochemistry
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Dual-pressure pyrolysis apparatus unravelling how fluid and lithostatic pressure matter in hydrocarbon expulsion
No full textImprovement in thermal simulation technology will increases the accuracy of predictive geochemistry. A dual- pressure pyrolysis apparatus was developed, to precisely control the fluid pressure and lithostatic pressure during simulated source rock maturation. Two series of pyrolysis experiments were carried out, simulating the same generation process but different expulsion fluid pressure condition. Episodic hydrocarbon expulsion from source rocks under controlled lithostatic pressure and fluid pressure was for the first time observed through thermal simulation experiments. The results were applied to (1) hydrocarbon expulsion efficiency (HEE) analysis, and (2) compositional analysis of oil and gas expelled under different pressures. Results show that HEE is strongly influenced by both fluid and lithostatic pressures. If the oil discharged during depressurization and normal pressure is taken into account, the calculated HEE was 2-31 times the HEE that only considers the high fluid pressure expelled oil. Compared with previous experimental results, HEE under controlled dual pressure is also lower. Therefore, before applying the results of thermal simulation experiments to unconventional and deep oil/gas evaluation, sufficient attention should be paid to the pressure conditions of the experiments. Within the oil window, when the temperature and hydrostatic pressure of source rocks are dropped due to tectonic events such as uplift, they can discharge more oil and gas than before uplift, as a consequence of adjustment of overpressured fluid to re-equilibrate to the adjacent hydrostatic conditions. In addition, during pressure and temperature reduction, the expelled fluids have a higher gas to oil ratio. This helps to indicate that sedimentary basins that experienced tectonic events still have great exploration potential. The temperature program, pressure setup, expulsion conditions in the two-series experiments is a tentative work tested on a representative source rock from the Triassic Yanchang Formation (Ordos Basin), indicating that control of fluid and lithostatic pressure are essential for improving the accuracy of thermal simulation predictions. The dual-pressure pyrolysis apparatus has high exploration relevance, particularly when quantitative results are integrated with the depositional, tectonic and thermal histories of specific source rocks
Early miocene adakitic porphyries in the Chagai arc, Pakistan: Petrogenesis, tectonic setting and implications for porphyry Cu-Au mineralization
No full textNumerous porphyry Cu-Au deposits were formed in the Chagai arc, western Pakistan, but their origin remains debated. To address this issue, we conducted zircon U-Pb dating, zircon Hf-O and plagioclase Sr isotopic analyses, and geochemical characterization of ore-bearing biotite granitic porphyries (BGP) from the Saindak area in the Chagai arc. These BGP, formed during the early Miocene (21.9-21.7 Ma), exhibit adakite-like geochemical characteristics, including high SiO2 (60.5-67.9 wt%) and low Y (6.41-9.13 ppm) contents, coupled with high Sr/ Y (26.2-116) ratios. The depleted Hf (epsilon Hf(t) = 2.42-9.73) and mantle-like O (delta 18O = 4.99-6.06 parts per thousand) isotopic compositions of zircon grains, along with depleted Sr ((87Sr/86Sr)i = 0.70297-0.70482) isotopic compositions and high anorthite (An = 56.5-69.4 %) contents of plagioclase crystals, suggest that these BGP rocks were derived from an oceanic slab. Slab melting may cause the exceptionally high Cu (667-3060 ppm, average of 1416 ppm) contents of the studied BGP samples, which facilitates the formation of porphyry Cu-Au deposits
Mineralogical fingerprints of crustal silica contamination in the Bayan Obo carbonatite
No full textCarbonatites are carbonate-rich and silica-undersaturated igneous rocks. The presence of various silicates in carbonatites has sparked discussions about the source of silica. In this study, abundant fluorbritholite-(Ce) and humite group minerals are identified in the No. 1 carbonatite dike at the Bayan Obo REE-Nb-Fe deposit. These silicates are relatively rare and poorly understood in carbonatite systems. Mineral textures, in situ EPMA, and LA-ICP-MS analyses have been combined to constrain the mineral genesis in the carbonatite. Fluorbritholite-(Ce), a member of the apatite super-group, occurs as euhedral to subhedral crystals in the dike. They are characterized by remarkably high concentrations of REE2O3 (56.0-63.7 wt%), SiO2 (19.6-21.2 wt%), and F (2.47-3.47 wt%), along with relatively lower P2O5 (0.25-3.69 wt%) and CaO (10.3-14.2 wt%) contents compared to common fluorapatite species. Additionally, their high-Y (961-3435 ppm) and low-Sr/Y (0.59-2.70) values suggest a hydrothermal origin from a fluid rich in SiO2, REE, and F. Humite group minerals, mainly chondrodite and humite, display irregularmineral textures. They also exhibit elevated SiO2 (32.5-34.7 wt%) and F content (3.59-7.32 wt%) with notably low TiO2 content (0.02-0.08 wt%), indicating a hydrothermal origin induced by fenitization in the shallow crust. Our results favor a model of crustal silica contamination for the fenitization fluids enriched in F, LREE, and SiO2. More importantly, the fluid-assisted silica contamination from wall rocks within carbonatites is likely to be a critical trigger of REE deposition in the carbonatite ore-forming systems
Meteorological effects on sources and future projection of nitrogen deposition to lakes in China
No full textLake ecosystems are extremely sensitive to nitrogen growth, which leads to water quality degradation and ecosystem health decline. Nitrogen depositions, as one of the main sources of nitrogen in water, are expected to change under future climate change scenarios. However, it remains not clear how nitrogen deposition to lakes respond to future meteorological conditions. In this study, a source-oriented version of Community Multiscale Air Quality (CMAQ) Model was used to estimate nitrogen deposition to 263 lakes in 2013 and under three RCP scenarios (4.5, 6.0 and 8.5) in 2046. Annual total deposition of 58.2 Gg nitrogen was predicted for all lakes, with 23.3 Gg N by wet deposition and 34.9 Gg N by dry deposition. Nitrate and ammonium in aerosol phase are the major forms of wet deposition, while NH 3 and HNO 3 in gas phase are the major forms of dry deposition. Agriculture emissions contribute to 57% of wet deposition and 44% of dry deposition. Under future meteorological conditions, wet deposition is predicted to increase by 5.5% to 16.4%, while dry deposition would decrease by 0.3% to 13.0%. Changes in wind speed, temperature, relative humidity (RH), and precipitation rates are correlated with dry and wet deposition changes. The predicted changes in deposition to lakes driven by meteorological changes can lead to significant changes in aquatic chemistry and ecosystem functions. Apart from future emission scenarios, different climate scenarios should be considered in future ecosystem health evaluation in response to nitrogen deposition. (c) 2024 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V
Controlling factors and geological applications of the drimane-skeleton compound content and composition of crude oils in complex petroleum systems: New insights from the Western Pearl River Mouth Basin, South China Sea
No full textCrude oils generally contain drimane-skeleton compounds, but the uncertainty of the main factors controlling drimane distributions limits their effective geological applications, especially in complex petroleum systems. In this study, the drimane-skeleton compound composition and the relative content of each drimane-skeleton compound to C 30 hopane (CDSC) were systematically studied for crude oils in different structural regions of the Western Pearl River Mouth (WPRM) Basin, South China Sea. The results show that the C DSC of crude oil is mainly controlled by its organic sources. Higher C DSC values in crude oil indicates a greater contribution from terrigenous organic matter to their source rocks. For crude oils from source rocks with similar biotic inputs, the C DSC values are controlled mainly by the depositional environment. Higher C DSC values in crude oil correspond to higher concentrations of clay minerals and lower salinities. In addition, the drimane-skeleton compound composition of crude oil is largely controlled by its maturity. The ratios of drimane to homodrimane (Dr/HDr), total rearranged drimane to total drimane and homodrimane (TRDr/TDr), and 8-rearranged drimane to 9-rearranged drimane (8RDr/9RDr) synchronously increase with increasing maturity. These ratios can effectively characterize the maturity of various types of crude oils. The maturity range characterized by the drimane maturity parameters is greater than that characterized by conventional maturity parameters. Correlation diagrams based on drimane parameters and other organic geochemical parameters can be used to classify crude oils and reveal their sources and origins, which has great application potential in complex petroliferous basins, especially in deep and ultra-deep petroleum systems with abundant light oil/condensate
Protracted post-eruptive basaltic weathering of the Emeishan large igneous province constrained by U-Pb CA-ID-TIMS geochronology
No full textThe post eruptive basaltic weathering of the Emeishan large igneous province is proposed to cause early Wuchiapingian cooling globally. However, the endpoint of this cooling event has not been evaluated yet, preventing the further understanding of long-term interaction between climate and weathering. In this study, abundant thick and highly weathered basaltic paleosols at the Emeishan volcanic landscapes have been identified, providing direct evidence for intense post-eruptive basaltic weathering. By using CA-TIMS zircon U-Pb dating on paleosols and adjacent tuffs, the onset and the termination of the intense weathering are constrained to similar to 259.6 Ma and similar to 253.4 Ma, respectively. The onset of intense weathering is coincident with the early Wuchiapingian cooling, supporting the CO2-forced cooling model triggered by the post-eruptive basaltic weathering of the Emeishan large igneous province. Moreover, the temporal correlation between the long-term weathering and the paleoclimate and carbon isotope records indicate that this cooling is possible persisting until at similar to 253.4 Ma
Daytime Production of Airborne Pollutants Including Brown Carbon by NO<sub>2</sub> Interaction With Surface Microlayer of Lake Water in Southwestern China
No full textSurface microlayer at freshwater (rivers, lakes, ponds, streams, and groundwater) and seawater is abundant with organic compounds compared to subsurface water. These organics adsorbed at the air-water interface can interact with the atmospheric oxidants and influence the exchange of organic materials between the water and the atmosphere. Here, we assess the chemical interaction between gaseous NO2 and authentic surface microlayers collected at the lake water (Dianchi Lake) situated in China. The formation of the gas-phase product compounds was evaluated in real time using a novel secondary electrospray ionization ultrahigh-resolution quadrupole Orbitrap mass spectrometer (SESI-UHR-MS) upon exposure of surface microlayer to gaseous NO2 (20 or 50 ppb) in dark and under simulated sunlight irradiation at two different temperatures: 5 degrees C and 25 degrees C. The obtained results revealed that the sampling sites of the lake impacted by human activities (municipal sewage and agricultural activities) significantly impact the number and the composition of the formed gas-phase product compounds. The formation of nitrogen (N)-containing compounds was observed as well, which contain most likely nitro or amino functional groups, or alternatively, they could be aromatic compounds. The observed N-containing compounds may contribute to the "brown carbon" which act as light-absorbing compounds, thus influencing the radiative forcing of aerosols in the atmosphere
Extensional settings favour initial REE enrichment in the parent granites of ion-adsorption REE deposits: implications from Late Permian to Triassic granites in South China
No full textTo understand the generation of ion-adsorption REE deposits it is important to clarify the mechanism of REE enrichment in granites. We investigated Late Permian to Triassic granites from South China to investigate these issues. Ore-related granites with high REE contents (192-467 ppm) intruded in the Late Permian have high K2O and Zr + Ce + Nb + Y contents, high Ga/Al and K/Na ratios and low CaO contents, and are classified as aluminous A-type granite derived from melting of felsic igneous rocks in a high-temperature extensional setting. Ore-unrelated Triassic Pingtian granite with relatively low REE contents (81.7-127 ppm) is peraluminous with occurrence of muscovite, indicating an S-type affinity. Its high Rb/Sr and low CaO/Na2O ratios indicate magma origin from a metapelitic source related to a compressional setting owing to continental collision. In extensional settings in South China, the high-temperature conditions promoting melting of REE-rich accessory minerals and F-rich conditions improving the solubility of REE in the melts could be the reasons for the initial REE enrichment in these granites. Given that parent rocks for ion-adsorption REE deposits are all generated in extensional settings, it is considered that multiple tectonic stages and long-term extensional setting in South China contributed to generation of the specific ion-adsorption REE deposits in South China
Mantle induced hydration and oxidation of intracontinental granite sources in the North China Craton
No full textArc magmatism is typically highly oxidized, due to the influx of oxidizing aqueous fluids released from the subducting plate. The observation that some intracontinental A- and I-type granites also exhibit high oxidation presents a significant challenge in igneous petrology and geodynamics. This is particularly true for regions such as the North China Craton (NCC), situated over 1000 km from the trench. In this study, we measured water content, oxygen fugacity (fO2), and O-Hf isotopes in zircons from the late Mesozoic granites from the NCC. The results reveal positive correlations between water content and f O 2 , and between water content and epsilon Hf(t), indicating the predominant control of primary magma composition, rather than magmatic differentiation, on water content andfO2 of zircon. The Early Cretaceous A-type and I-type granites, which involved greater amount of mantle-derived melts, exhibit more elevated water, Nb, Ta, and f O 2 than the Jurassic granites. This suggests that the hydration and oxidization of intracontinental granitoids of the NCC are strongly influenced by the ingress of mantle-derived oxidized hydrous melts/aqueous fluids to the granitoid source, which were likely released from the Paleo-Pacific plate at a greater depth than the sub-arc mantle. The proposed model involves significant water in intracontinental crustal melting, thereby challenging the paradigm of intraplate A- and I-type granite genesis and shedding light on the crustal and mantle processes during cratonic destruction
Unraveling the link between worldwide adakite-like rocks and porphyry Cu deposits
No full textAdakite-like rocks, as an important recorder of magmatic evolution in mantle and crust, are closely associated with major porphyry Cu deposits. However, the underlying mechanism connecting these associations remains insufficiently elucidated. This study compiles ca. 7000 whole-rock geochemical data from Phanerozoic adakitelike rock samples and from ore-forming porphyries in porphyry Cu deposits. Machine learning investigations are performed to characterize the geochemical variations of adakite-like rocks from various orogenic or cratonic systems and investigate any geochemical similarities with rocks associated with porphyry ore systems. Principal component analysis (PCA), along with t-distributed Stochastic Neighbor Embedding (t-SNE), highlights elemental distinctions between adakite-like rocks formed in mature and juvenile crust and the similarities of rocks from porphyry Cu-Mo deposits with the former and rocks from porphyry Cu-Au deposits with the latter. Extreme Gradient Boosting (XGBoost) and Support Vector Machine (SVM) analyses are applied to the original dataset and the PCA data derived from the dataset to discriminate adakite-like rocks from various geodynamic settings from each other and from rocks associated with porphyry ore deposits. Our models show that XGBoost and SVM can identify the tectonic regions of adakite-like rocks and rocks from porphyry copper systems with high efficiency and confidence e.g., accuracy = 0.88-0.94 and area under curve (AUC) = 0.69-0.86. The application of SHapley Additive exPlanations (SHAP) values is employed to elucidate the parameters that discriminate the different environments, providing insight into the underlying petrogenetic processes, including diverse levels of formation depth and extent of mantle interaction. Additionally, when examining ore-forming porphyries and adakite-like rocks, the incorporation of heatmaps into taxonomic classification (HTC) provides significant distinguishing factors with substantial geological implications. These findings suggest potential geological processes (e.g., remelting of Cu-sulfide-bearing cumulates or flotation of Cu-sulfide phases attached to vapor bubbles) that may enrich the source magma of ore-forming porphyries beyond the conventional geological processes responsible for adakite-like rock formation, which could serve as an exploration indicator