Guangzhou Institute of Geochemistry
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A Newly Identified "Proto-Kenting Mélange (S. Taiwan)" Represents a Missing Link for a Continuous Early Cretaceous Paleo-Pacific Subduction-Accretion System
No full textMost m & eacute;langes in exhumed subduction-accretion complexes are polygenetic, recording significant information about the nature of geological processes during their formation. Here, we apply micro-chemical analysis and illite K-Ar dating to constrain the deformation mechanism and timing of the pervasively sheared scaly matrix in the accretionary complex rocks presently known as "Kenting M & eacute;lange" in the Hengchun Peninsula (South Taiwan). Our results reveal that parts of the matrix were formed in Cretaceous (96.7 +/- 8.6 Ma and 108 +/- 18.4 Ma) due to pressure solution. These new, older matrix ages suggest that the Kenting M & eacute;lange, which was considered as Cenozoic and interpreted to have been associated with the subduction of the South China Sea, preserves different primary chaotic units (e.g., m & eacute;lange and/or olistostrome). Our findings imply the Kenting M & eacute;lange is actually polygenetic and allow part of Kenting M & eacute;lange that we named the "proto-Kenting M & eacute;lange" to be interpreted as a remnant of a primary m & eacute;lange, which was mixed and/or juxtaposed in the Cenozoic Kenting M & eacute;lange. The block-in-matrix fabric with a pervasively sheared scaly muddy matrix, along with the preservation of slightly older oceanic crust blocks, suggests that the proto-Kenting M & eacute;lange is most likely an ocean plate stratigraphy m & eacute;lange. This unit initially formed near a Paleo-Pacific subduction margin during the latest Early Cretaceous. Our results reveal a nearly 3000-km-long physical archive of latest Early Cretaceous subduction-accretion processes, which took place adjacent to the continental margin of East Asia during the consumption of Paleo-Pacific ocean floor during the latest Mesozoic
Metal-Silicate Partitioning of Si, O, and Mg at High Pressures and High Temperatures: Implications to the Compositional Evolution of Core-Forming Metallic Melts
No full textHigh-pressure and high-temperature experiments were conducted to investigate the partitioning behaviors of Si, O, and Mg between molten Fe-alloys and silicate melts in the Fe-Si-O-Mg system under conditions of 2-72 GPa and 2000-5500 K, using both laser-heated diamond anvil cells and a multi-anvil press. Combing our new experimental results with previously published data, we evaluated the effects of pressure, temperature, and metallic compositions on the partitioning behaviors of Si, O, and Mg. A set of internally consistent interaction parameters between Si, O, and Mg were obtained by the simultaneous fitting of distribution coefficients for all three elements in the Fe-Si-O-Mg system. The composition-dependent distribution coefficients were applied in calculating the compositional evolution of metallic melts during multi-stage core formation. Our results suggest that the core-forming metallic melts would contain more Si and O than previously estimated due to the attractive interactions of light elements in the metal. Compared to the geophysically constrained core composition, these findings imply the exsolution of light elements, likely in the form of SiO2, from the outer core upon cooling
Metal-Silicate Partitioning of Si, O, and Mg at High Pressures and High Temperatures: Implications to the Compositional Evolution of Core-Forming Metallic Melts
No full textHigh-pressure and high-temperature experiments were conducted to investigate the partitioning behaviors of Si, O, and Mg between molten Fe-alloys and silicate melts in the Fe-Si-O-Mg system under conditions of 2-72 GPa and 2000-5500 K, using both laser-heated diamond anvil cells and a multi-anvil press. Combing our new experimental results with previously published data, we evaluated the effects of pressure, temperature, and metallic compositions on the partitioning behaviors of Si, O, and Mg. A set of internally consistent interaction parameters between Si, O, and Mg were obtained by the simultaneous fitting of distribution coefficients for all three elements in the Fe-Si-O-Mg system. The composition-dependent distribution coefficients were applied in calculating the compositional evolution of metallic melts during multi-stage core formation. Our results suggest that the core-forming metallic melts would contain more Si and O than previously estimated due to the attractive interactions of light elements in the metal. Compared to the geophysically constrained core composition, these findings imply the exsolution of light elements, likely in the form of SiO2, from the outer core upon cooling
Nano-Scale Insights into Clay Minerals Regulating the Fe(II)-Catalyzed Ferrihydrite Transformation under Anoxic Conditions
No full textMetastable ferrihydrite nanoparticles and clay minerals always coexist as heteroaggregates in nature due to their abundance, opposite charge, and large interface energy. However, the impact of clay minerals on the transformation of ferrihydrite under anoxic conditions remains elusive. This study systematically investigated the effect of distinct clay minerals on the Fe(II)-catalyzed transformation of ferrihydrite and clarifying the underlying nanoscale mechanisms for the first time. Our results demonstrated that clay minerals could affect the production and recrystallization of labile Fe(III) (an active Fe(III) intermediate species formed by oxidation of Fe(II) at the ferrihydrite surface) by dispersing ferrihydrite aggregates. This modulation led to different transformation rates, higher crystallinity of formed lepidocrocite, and enhanced goethite formation in the heteroaggregates. Importantly, montmorillonite can accommodate Fe(II) and labile Fe(III) within its interlayer spaces, which further led to the inhibited crystallization of Fe(II) to magnetite and long-term preservation of labile Fe(III). Additionally, clay minerals served as templates for forming dendritic goethite and hexagonal magnetite nanoplates. Our findings provide new insights into the complicated roles of clay minerals in controlling the ferrihydrite transformation and other iron (oxyhydr)oxides formation, which is significant for predicting the bioavailability of iron and the fate of other coexisting contaminants
Study on hydrocarbon retention and expulsion of kerogen based on centrifugal swelling method
No full textCentrifugal swelling experiments using n-hexadecane and 1-methylnaphthalene were carried out to explore the connection between hydrocarbon retention and expulsion in type I kerogen. A driving force-hydrocarbon expulsion model was innovatively established through the results of differential centrifugation experiments and low field nuclear magnetic resonance. Additionally, the hydrocarbon expulsion process of kerogen was categorized into three distinct stages based on the driving force, including free, intergranular state and immovable state (adsorption and swelling) hydrocarbon expulsion. A linear correlation also was established between the T1/T2 signal and the liquid hydrocarbon content during the swelling process, revealing that low- field NMR technology could effectively detect the retention of alkane compounds in kerogen. The study revealed that when the driving force is greater than 647.4 g N, most of the shale oil retained in the kerogen is in an immobile state, which cannot be exploited. Additionally, the hydrocarbon expulsion model based on the centrifugal experiment presents several advantages, including low equipment requirements, straightforward operation, and a broad range of applications. This model can effectively support various types of laboratories conducting shale oil retention assessment work, especially those in oilfields with relatively simple experimental setups
Formation and evolution of environmentally persistent free radicals in charcoal and soot generated from biomass materials
No full textEnvironmentally persistent free radicals (EPFRs) are emerging pollutants that are highly reactive and toxic, posing potential health risks. Biomass burning is a significant source of EPFRs, but there has been a notable gap in research regarding the EPFRs present in charcoal and soot produced from the same combustion process. Our study detected EPFRs in both charcoal and soot, but there were significant differences in their characteristics. The EPFR concentrations in charcoal were much higher than that in soot, by approximately 2-4 orders of magnitude, suggesting that charcoal may be more chemically reactive. Differences in the formation mechanisms between charcoal and soot were found to result in variations in the characteristics of EPFRs observed in each material. Furthermore, the ability of EPFRs to generate reactive oxygen species (ROS) differed considerably between charcoal and soot. Charcoal exhibited a strong ability to produce ROS, including O-1(2) and center dot OH radicals, and the abundances of O-1(2) was further enhanced (similar to 1.2-2.1 times) after illumination. In contrast, only the O-1(2) radical was found in soot produced at 300 degrees C. These findings enhanced our understanding of the environmental impact and potential toxicity of EPFRs, offering valuable insights for evaluating the risks associated with wildfires and agricultural burning
The factors affecting mineralization potential of arc magma: Insights from silicate melt inclusions and zircon composition of igneous lava at Eastern Taiwan Island
No full textSubduction-related Cu-(Au) deposits which represent giant geochemical anomalies of metals and S in the upper crust are commonly associated with arc magmas. However, the fundamental differences between barren and fertile magma producing these deposits still remain highly controversial. In this study, we report the chemical compositions of zircon and silicate melt inclusions (SMIs) from barren arc lavas at eastern Taiwan Island aiming to increase our knowledge on the factors that affect the mineralization potential of arc magma systems. The zircon U-Pb dating shows the magmatism occurred at similar to 0.7 Ma and the andesitic lava formed at similar to 900-950 degrees C with a reduced magmatic environment. The plagioclase-hosted SMIs show an andesitic melt composition and variable Cu content features. The calculated H2O content of parental melt is similar to 3-4 wt.%. The evidence presented above suggests that oxidation state (fO(2)) and H2O content are probably the key controls of Cu-(Au) fertility of arc magmas. We interpret that a reduced and relatively dry magma may be a potential hinderance to cause the absence of porphyry Cu deposits at the eastern Taiwan Island
Monitoring of linear alkyl benzenes (LABs) in riverine and estuarine sediments in Malaysia (vol 44, pg 3687, 2022)
No full textDecoupling Temperature and Light Effects on Terpene Emissions From Subtropical Eucalyptus: Insights From Controlled Field Experiments
No full textEmissions of biogenic volatile organic compounds (BVOCs) from plants are significantly influenced by both temperature and light, yet the individual contribution of these factors, particularly for emissions of monoterpenes (MTs) and sesquiterpenes (SQTs) from tropical and subtropical plant species, remain poorly quantified due to their covariant effects. In this study, we conducted in situ and controlled field experiments on subtropical Eucalyptus trees using a portable LI-6800 photosynthesis system to isolate and quantify the temperature and light responses of major MTs. Additionally, we qualitatively assessed the light dependence of minor MTs and SQTs through dynamic chamber measurements. Our results revealed distinct light dependence across different compounds: beta-ocimenes were fully light-dependent but exhibited unexpected suppression under high light conditions, whereas alpha-pinene and 1,8-cineole were light-independent. Temperature response experiments indicated that the temperature sensitivity (beta) for light-dependent beta-ocimenes (0.095 K-1) and light-independent alpha-pinene (0.071 K-1) and 1,8-cineole (0.102 K-1) were similar to the model value (0.1 K-1), but significantly lower than previously reported values from uncontrolled tropical measurements (0.2 K-1), suggesting an influence of light on observed temperature sensitivity. Chamber-based results revealed that acyclic MTs and alpha-phellandrene were fully light-dependent, similar to beta-ocimenes, while cyclic MTs and the SQT alpha-longipinene were light-independent and followed an exponential temperature function. Other SQTs exhibited partial light-dependence and would need a hybrid modeling approach. These results provide valuable insights into the emission mechanisms of various terpene types, with important implications for enhancing predictive models of BVOC emissions
Formation of carbonatite-related giant rare earth element deposits by liquid immiscibility
No full textThe occurrence of sulfate and fluoride minerals in carbonatite-hosted rare earth element (REE) deposits suggests that sulfur and fluorine play important roles in REE mineralization. However, their influence on the partitioning behavior of REEs during the immiscibility process remains poorly understood. This study performed partitioning experiments to explore the impact of sulfur and fluorine on the liquid immiscibility between carbonatitic melt and alkaline silicate melt at 1000-1200 degrees C and 0.5-2.2 GPa. Surprisingly, the experimental results indicate that the addition of sulfur and fluorine does not significantly change the partition coefficients of trace elements between carbonatitic melt and silicate melt. The key factor determining REE partitioning is the structural difference between the two immiscible melts, which can be characterized by the non-bridging oxygen per tetrahedrally coordinated cation of the silicate melt (NBO/T). Partition coefficients tend to decrease as NBO/T increases. Importantly, REE, SO3, and F exhibit similar behaviors, making sulfate and fluoride minerals useful indicators for exploring carbonatite-hosted REE deposits. Additionally, we used rhyolite-MELTS software to simulate crystallization differentiation and liquid immiscibility in alkaline silicate melts. Modeling results show that the initial CO2 content of silicate melt determines the degree of crystallization at which liquid immiscibility occurs. Lower initial CO2 content enhances the enrichment of REEs in the immiscible carbonatitic melt