Guangzhou Institute of Geochemistry
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40 years of theoretical advances in mass-independent oxygen isotope effects and applications in atmospheric chemistry: A critical review and perspectives
No full textThe discovery of chemically induced mass-independent isotope fractionation in ozone formation 40 years ago revealed a new type of isotope effect that was not considered within the conventional framework of singleisotope ratio measurements. Since this landmark discovery, advances to our theoretical understanding of isotopic physical chemistry effects have helped establish numerous new applications in geochemistry and cosmochemistry. Given that many mass-independent isotope effects are linked to gaseous or multiphase (gas-liquidsolid) reactions, such as the ozone effect arising from the basic symmetry-dependent bond-formation reaction and the photochemical effect associated with wavelength-dependent bond-dissociation reactions, they have wide applications in atmospheric sciences and also contribute to enhancing the fundamental knowledge of quantum chemical effects. Within this context, the present review critically elucidates the historical development of research on mass-independent isotope effects over the past four decades, with a particular emphasis on investigation in atmospheric chemistry. We underscore the paramount importance of a deeper mechanistic understanding of mass-independent isotope effects to effectively harness cutting-edge insights from isotope geochemistry in atmospheric chemistry research. With a focus on triple oxygen isotope compositions of oxygenbearing molecules in the modern Earth's atmosphere, we critically identify and appraise key unresolved questions pertaining to mass-independent isotope effects. Addressing these questions in the future may allow new and exciting interdisciplinary discoveries, not solely confined to atmospheric chemistry but also encompassing the realms of earth and planetary sciences, given the existence of analogous intricacies in the highly complex isotope effects related to sulfur and other elements, both in the present and the deep past
Magnesium Isotopes of Carbonate Reveal Seasonal Climate Variation in the Central East Asia During the Middle Eocene
No full textIt is debated whether there was strong climate seasonality during the Eocene, which provides a close geological analogy for near-future scenarios of greenhouse gas emissions. Lithological data suggest the existence of a broad arid zone centered around 30 degrees N paleo-latitude, while a humid climate was supported by palaeobotanic assemblages in East Asia. Here, we report the occurrence of massive primary lacustrine dolomite and magnesite in the central East Asia during the middle Eocene. We provide a novel perspective from magnesium isotopes to link the formation of Mg-carbonates to seasonal dry-wet cycles. Rapid magnesium input during the rainy season and intense evaporation in the dry season likely caused the formation of magnesium carbonates in an enclosed lake. These findings provide insights into hydroclimatic seasonality during the Eocene, contributing to our understanding of the hydrological cycle response to a greenhouse climate.
The Eocene epoch serves as a valuable analog for future climates. While geochemical reconstructions and model simulations have illuminated lower thermal latitudinal gradients and seasonal variations, our understanding of Eocene precipitation patterns lags, encompassing wet-dry conditions and seasonal dynamics. To enhance our understanding of Eocene precipitation patterns, we investigated a 158-m-thick primary dolomite and magnesite deposition in the middle Eocene lacustrine succession of the Lushi Basin, central China. From a novel perspective, we provide evidence from magnesium isotopes to link the formation of Mg-carbonates to climate seasonality. Clumped isotopes (triangle 47) and Mg isotopes provide evidence supporting the formation under specific hydroclimatic conditions. A surge in magnesium input during the rainy season, succeeded by intense evaporation in the dry season, likely led to the development of extensive Mg carbonate layers in an enclosed lake. The prevalence of seasonal variations in precipitation in the central East Asia during the middle Eocene is further substantiated by a compilation of the occurrence of Eocene lacustrine Mg-carbonates in this region. Our findings suggest that while Eocene temperature seasonal variability was weak, significant precipitation seasonality could have coexisted.
Magnesium isotopes of Eocene lacustrine dolomites and magnesites provide insight into the presence of seasonal precipitation variation Mg-carbonate formation was linked to hydroclimatic seasonality characterized by alternation between heavy rainfall and strong evaporation Weak temperature seasonal variation and significant precipitation seasonality could have coexisted in central East Asia during the Eocen
Cultivation and characterization of functional-yet-uncultivable phenanthrene degraders by stable-isotope-probing and metagenomic-binning directed cultivation (SIP-MDC)
No full textHigh-throughput identification and cultivation of functional-yet-uncultivable microorganisms is a fundamental goal in environmental microbiology. It remains as a critical challenge due to the lack of routine and effective approaches. Here, we firstly proposed an approach of stable-isotope-probing and metagenomic-binning directed cultivation (SIP-MDC) to isolate and characterize the active phenanthrene degraders from petroleumcontaminated soils. From SIP and metagenome, we assembled 13 high-quality metagenomic bins from 13C- DNA, and successfully obtained the genome of an active PHE degrader Achromobacter (genome-MB) from 13C- DNA metagenomes, which was confirmed by gyrB gene comparison and average nucleotide/amino identity (ANI/ AAI), as well as the quantification of PAH dioxygenase and antibiotic resistance genes. Thereinto, we modified the traditional cultivation medium with antibiotics and specific growth factors (e.g., vitamins and metals), and separated an active phenanthrene degrader Achromobacter sp. LJB-25 via directed isolation. Strain LJB-25 could degrade phenanthrene and its identity was confirmed by ANI/AAI values between its genome and genome-MB (>99 %). Our results hinted at the feasibility of SIP-MDC to identify, isolate and cultivate functional-yetuncultivable microorganisms (active phenanthrene degraders) from their natural habitats. Our findings developed a state-of-the-art SIP-MDC approach, expanded our knowledge on phenanthrene biodegradation mechanisms, and proposed a strategy to mine functional-yet-uncultivable microorganisms
Transport Model of Rare Earth Elements in Weathering Crusts during Electrokinetic Mining
No full textElectrokinetic mining (EKM) is a novel method for rare earth element (REE) mining that can achieve green and efficient recovery of REEs. However, as yet, there is no accurate model for describing the electrokinetic transport of REEs in weathering crusts, and this hinders the wider application of EKM. The conventional model fails to capture the microscale transport physics occurring in the nanochannels that exist ubiquitously in weathering crusts. Consequently, the existing models cannot distinguish the mobilities of different REEs. Here, we report a new model for a more faithful description of the electrokinetic transport of REEs in weathering crusts that considers the ionic size, which has previously been neglected. We reveal that the electrokinetic transport of heavy REEs (HREEs) is faster than that of light REEs (LREEs) in weathering crusts, which is contrary to the predictions of conventional models. Our model was validated experimentally by measurements of the electrokinetic transport of two LREEs (La and Sm) and an HREE (Er) in weathering crusts. The speed of electrokinetic transport follows the order Er > Sm > La. Our findings suggest that the ionic size is a non-negligible factor affecting the electrokinetic transport of REEs in weathering crusts containing nanochannels. This work offers a constitutive model to describe the electrokinetic transport of REEs in weathering crusts, which promotes both theoretical developments and practical applications of EKM
Timing of India-Asia collision and significant coupling between them around 51 Ma: Insights from the activation history of the Zhongba-Gyangze thrust in southern Tibet
No full textConstraining the timing of tectonic coupling between converging plates is crucial for understanding the transition from continental subduction to continental collision. In the case of the India-Asia collision, thrusting of an accretionary complex onto the Indian continental margin provides the most direct temporal constraint on the early stages of continental collision, as it represents the most immediate upper-crustal fault system corresponding to plate coupling. Here, we used structural analysis combined with K-Ar dating and hydrogen isotopes of authigenic illite and muscovite to unravel the time-progressive development of the Zhongba-Gyangze thrust (ZGT), which represents a tectonic boundary fault in southern Tibet. Our results suggest that the ZGT evolved from its initiation as a single fault zone infiltrated by metamorphic fluids with high delta D values (-47%0 to -55%0) at ca. 80 Ma to multiple deformation localization zones starting around 51 Ma. This latter phase is represented by the development of different generations of authigenic 1 M/1Md illite and significant input of meteoric fluids with delta D values ranging from -71%0 to -98%0 through multiple episodes of brittle fault reactivation. A Late Cretaceous tectono-thermal event related to the subduction of a Neotethyan oceanic ridge may have been responsible for the formation of 2M1 illite/ muscovite at ca. 80 Ma. The oldest (ca. 51 Ma) 1 M/1Md illite age coincides with the first major pulse of shortening in the upper plate after the initial India-Asia contact. Given the synchronous deceleration of India-Asia convergence, the ca. 51 Ma deformation pulse across the Yarlung-Zangbo suture zone demarcates strong coupling (i.e., the onset of continental collision) between India and Asia at this time
Redox control of the partitioning of platinum and palladium into magmatic sulfide liquids
No full textThe partitioning behavior of platinum group elements in magmas is critical for their use as tracers of planetary accretion and in understanding magmatic sulfide deposits. Here we use laboratory experiments to determine sulfide liquid-silicate melt partition coefficients for platinum and palladium at 1.5 GPa, 1400 degrees C, and oxygen fugacity 1.5-2 log units above the fayalite-magnetite-quartz buffer. We find that the partitioning coefficients of these elements are 2.3 x 105 to 1.1 x 106 and are independent of the platinum and palladium concentration in the system. Combined with previous data obtained at oxygen fugacity below the fayalite-magnetite-quartz buffer, this indicates redox-controlled partitioning behavior whereby at oxidizing conditions platinum- and palladium-enrichments are achieved through their dissolution in sulfide liquids, while at reducing conditions the entrapment of platinum- and palladium-rich clusters in sulfide liquids is more critical. This redox-controlled partitioning behavior should be considered when studying crust-mantle differentiation and the formation of magmatic sulfide deposits.
High-pressure and high-temperature experiments suggest a redox-controlled partitioning behavior of platinum group elements between sulfide liquid and basaltic melt, which could help constrain the formation mechanisms of magmatic sulfide deposit
An anomalous rollback process of Mesozoic flat-slab subduction in South China
No full textThe Mesozoic magmatic rocks within the South China Block exhibit a widespread distribution, extending up to 1300 km inland. In order to better understand the Mesozoic tectonic evolution within the interior South China Block, we present new geochronological and geochemical investigations on the Danguanzhang granitic pluton in the region where multiple episodes of Mesozoic magmatism were initiated in South China. The Danguanzhang pluton is primarily composed of Guizhumao granites (168 +/- 1 Ma) as its main body and Gaojian granites (246 +/- 1 Ma) as the eastern part. Both the Guizhumao and Gaojian granites are highly differentiated I-type granite based on their high SiO2 contents (>72 wt%), metaluminous-weakly peraluminous (A/CNK = 0.99-1.12), fractionated rare earth element (REE) patterns ([La/Yb](N) = 1.1-13.3), significantly negative Eu anomalies (delta Eu = 0.02-0.14), and a negative correlation between P2O5 and SiO2. They were derived from the partial melting of Paleoproterozoic metaigneous rocks and show negative whole-rock epsilon(Nd)(t) values (-9.12 to -9.38 and - 9.61 to -9.8, respectively) and zircon epsilon(Hf)(t) values (-7.0 to -12.8 and - 6.8 to -11.8, respectively). The Guizhumao granites exhibit a close affinity with the widely distributed early Yanshanian (165-150 Ma) I-type granites within the interior South China Block, marking the onset of the early Yanshanian magmatism in South China. Conversely, the Gaojian granites, coeval with the Indiosinian magmatism, are associated with inland subduction. A compilation of previously published geochronology data reveals distinct episodes of Mesozoic magmatism within the interior South China Block (250-200 Ma, 195-180 Ma, and 168-150 Ma), which contrast with the typical flat-slab subduction scenario that typically exhibits two episodes of magmatism corresponding to flat subduction and rollback. Therefore, the interior South China Block might have undergone complex deep dynamic processes in the Mesozoic, involving prolonged flat-slab subduction and unique slab rollback caused by slab break-off and foundering in the central part of the subducted slab
Short-lived natural radionuclides as tracers in hydrogeological studies - A review
No full textFundamental approaches to the study of groundwater rely on investigating the spatial and temporal distribution of stable and radioactive isotopes and other anthropogenic compounds in natural waterbodies. The most often used tracers for estimating groundwater flow paths and residence times, groundwater/surface water interaction as well as tracing chemical (contamination) sources include stable isotopes of water (delta 18O and delta 2H), radiocarbon (14C; t1/2 = 5730 a), tritium (3H; t1/2 = 12.43 a) as well as unreactive fluorine -containing gases (e.g., chlorofluorocarbons CCl3F or CFC-11; CCl2F3 or CFC-12; C2Cl3F3 or CFC-113; and SF6). While gas tracers are usually referred to as transient tracers and are appropriate for investigating modern flow systems, the isotopic tracers are often used to investigated paleo or regional flow systems. Stable isotopes of water can also be used to investigate groundwater/surface water interactions. Another, thus far been less frequently used group of groundwater tracers, are cosmo- and geo- genic short-lived radioisotopes. These isotopes are uniquely suited for studying a wide range of groundwater problems that have short time scales including high aquifer vulnerability to quantitative and qualitative impacts and groundwater discharge to surface waters. Here, we discuss and compare the applications of radio -sulphur (35S; half-life t1/2 = 87 d), radio -beryllium (7Be; t1/2 = 53 d), radio -phosphorus (32/33P; combined t1/2 = 33 d), natural tritium (3H; t1/2 = 12.43 a), radon (222Rn; t1/2 = 3.8 d) and short-lived radium (224/223Ra; combined t1/2 = 5.2 d). The paper discusses the principles of the individual tracer methods, focusing on the isotopes' input functions or values, on sampling techniques, and on methods of analyses. Case studies that applied a combined use of the tracers are referred to for readers who wish to learn more about the application of the so far underused cosmo- and geo- genic radioisotopes as aquatic tracers
Oxidation state of Cu in silicate melts at upper mantle conditions
No full textBeyond its economic value, copper (Cu) serves as a valuable tracer of deep magmatic processes due to its close relationship with magmatic sulfide evolution and sensitivity to oxygen fugacity (fO2). However, determining Cu's oxidation state (+ 1 or + 2) in silicate melts, crucial for interpreting its behavior and reconstructing fO2 in the Earth's interior, has long been a challenge. This study utilizes X-ray Absorption Near Edge Structure spectroscopy to investigate the Cu oxidation state in hydrous mafic silicate melts equilibrated under diverse fO2 (- 1.8 to 3.1 log units relative to the Fayalite-Magnetite-Quartz buffer), temperature (1150-1300 degrees C), and pressure (1.0-2.5 GPa) conditions. Our results reveal that Cu predominantly exists as Cu+ across all fO2 conditions, with a minor Cu2+ component. This dominance of Cu+ persists even in relatively oxidized melts, highlighting its limited sensitivity to fO2 under upper mantle conditions. This significantly constrains the utility of Cu as an oxybarometer in hydrous silicate melts in the deep Earth. However, our findings suggest that Cu isotopes primarily reflect the interplay of sulfide segregation/accumulation during magmatic differentiation, shedding light on these fundamental processes in Earth's interior
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