Major Element Analyses Research Articles

Identification of the Campanian Ignimbrite in the Dead Sea and consequent time-transgressive hydroclimatic shifts in the Eastern Mediterranean.

Robust chronologies and time equivalent tephra markers are essential to better understand spatial palaeoenvironmental response to past abrupt climatic changes. Identification of well-dated and widely dispersed volcanic ash by tephra and cryptotephra (microscopic volcanic ash) provides time synchronous tie-points and strongly reduces chronological uncertainties. Here, we present the major, minor and trace element analyses of cryptotephra shards in the Dead Sea Deep Drilling sedimentary record (DSDDP 5017-1A) matching the Campanian Ignimbrite (CI). This geochemical identification expands the known dispersal range of the CI to the southeastern Mediterranean, over 2300km from the volcanic source. Due to the CI eruption occurring near-synchronous with North Atlantic ice surge of Heinrich Event 4 (HE4), this tephra provides insights into regional responses to large-scale climatic change in the Mediterranean. In the Dead Sea, the CI layer is associated with wetter climatic conditions. This contrasts with the contemporaneous occurrence of the CI deposition and dry conditions in the central and eastern Mediterranean suggesting a possible climate time-transgressive expansion of HE4. Our finding underscores the temporal and spatial complexity of regional climate responses and emphasises the importance of tephra as a time marker for studying large-scale climatic changes verses regional variations.

The origin of Ordovician siliceous rocks and their deposition settings in the Northwest Tarim Basin, NW China

The siliceous rocks are well developed in Northwest Tarim Basin, which plays an important role in indicating its forming environment. In order to determine the origin of siliceous rock and its deposition settings, the paper studies the petrographic and geochemical characteristics of siliceous rock in well KP 1 and outcrops in Northwest Tarim Basin based on core observation, microscopic section identification and analysis of major and trace elements and rare earth elements. The Ordovician siliceous rocks of Northwest Tarim Basin are mainly developed in the middle and upper Penglaiba Formation and the bottom of the Yingshan Formation. Three types of cherts are identified, including cryptocrystalline silica, microcrystalline quartz and fibrous chalcedony depending on the mineral morphology. The terrigenous source is best evidenced by the high Ti (160∼310 ppm) and Al (1300∼3180 ppm), and positive δ30Si (0.9–3.6‰). Whereas, hydrothermal processes can be inferred from relative high content of V, Ni, Sr, Mo and Ba, and no obvious Ce and Eu anomaly. The chert of well KP 1 and Kuluxi profile is deposited in continental-margin settings, which is evidenced by its Al2O3/(Al2O3 + Fe2O3) (0.58–0.94, average of 0.81) and its Lan/Cen ratio (0.76–1.02, average of 0.93). The continental-margin settings are also evidenced by the close relation between silicification and dolomitization. Silicification is commonly well developed where dolomitization occurs, because the dolomitization mainly occurs in the regression background, where provides more terrigenous source silica to the sea water and results in more silicification. This study highlights the origin of Ordovician siliceous rocks and the outcome from this new contribution may provide useful guidelines for hydrocarbon exploration in the basin and other global analogues.

Application of the Partial Least Squares Discriminant Analysis of major and trace elements of apatites in porphyry deposits

Application of the Partial Least Squares Discriminant Analysis of major and trace elements of apatites in porphyry deposits

Last 150 kyr volcanic activity on Mauritius island (Indian ocean) revealed by new Cassignol-Gillot unspiked K–Ar ages

We present new K–Ar ages extending the volcanic history of Mauritius Island towards the Holocene. Mauritius volcanism is associated with the activity of the Réunion hotspot, the magmatism of which produced the Deccan Traps across the Cretaceous-Tertiary (KT) boundary and continues up to present on Réunion Island. After shield building from before 8.9 Ma to 4.7 Ma, Mauritius Island underwent an unusual volcanic evolution involving two rejuvenation stages (3.5–1.9 Ma and <0.7 Ma) separated by a 1.2 Myr hiatus. The lower bound of the second rejuvenation stage being poorly constrained, it is not clear whether volcanism in this island has come to a rest. Given the occurrence of uneroded, and yet undated strombolian cones in Mauritius, it is important to better constrain the latest activity of this island in order to assess its volcanic hazard. The importance of dating the end of this stage is also enhanced by the fact that most of the surface of Mauritius is covered by the lavas of the rejuvenation stages, hence indicating a recent volcanic activity that needs to be better characterized for risk assessment.We focus here on the last 150 ka interval which lacked precise age controls with only a few whole-rock and groundmass 40Ar/39Ar plateau ages available (Moore et al., 2011), ranging from 138 ± 29 to 40 ± 48 ka (uncertainties are 1 σ). Our six new Cassignol-Gillot unspiked K–Ar ages obtained on plagioclase or groundmass range from 113 ± 7 to 14 ± 3 ka, with much lower uncertainties than previous ages available. Our major and trace element analyses of the dated samples highlight the compositional homogeneity of the lavas erupted in the last rejuvenation stage, showing no geochemical evolution.Our results, with ages as young as 14 ± 3 ka, demonstrate that near-Holocene volcanism is present in Mauritius Island, with no evidence of fading magmatism in the last 150 ka. Our second youngest age at 44 ± 5 ka implies that the latest activity occurred after a ∼30 kyr repose interval, with the consequence that Mauritius volcanism may resume at any time.

On-line quantitative analysis of major elements in phosphate slurry using LIBS assisted by plasma information from orthogonal directions imaging

To solve the lag of chemical element information feedback and realize the on-line analysis of phosphorite flotation, LIBS was used to measure major elements in the phosphate slurry. Plasma images in two orthogonal directions were captured synchronously to describe the irregular plasma. The plasma image projections in different directions were calculated as the features. A spectral correction method with these features was proposed to solve the problems of large signal fluctuations and poor measurement accuracy. The proposed method was first applied in the filed application of phosphate slurry on-line analysis. The RSDs of the characteristic spectral intensity decreased from more than 20 % to less than 3 %, improving the stability of spectra significantly. The method was further combined with the calibration of the concentrations of P2O5, MgO and SiO2. The R2 and MAE of P2O5 were 0.99 and 0.5 %, respectively, meeting the accuracy requirements of online measurements.

Dynamic Climate Influence on Magnesium Isotope Variation in Saline Lacustrine Dolomite: A Case Study of the Qianjiang Formation, Jianghan Basin

The investigation of magnesium (Mg) isotopes in dolomite has mainly focused on marine dolomite environments, leaving a significant gap in the understanding of their dynamics within lacustrine settings, especially in saline lake basins. In this study, a total of 16 sediment core samples from Well BX-7 in the Qianjiang Depression were sequentially selected for scanning electron microscope observation, whole-rock analysis for major and minor elements, and isotopic measurements including δ18Ocarb, δ13Ccarb, δ26Mgdol, and δ26MgSi. In addition, two intact cores were subjected to detailed analysis on the centimeter scale. Sedimentation models were established to elucidate dolomite formation under contrasting climatic conditions, specifically humid climates with a significant riverine Mg input versus relatively dry conditions with a lower Mg input. Furthermore, a quantitative model was developed to assess the magnesium flux and isotopic mass balance within lacustrine systems, simulating the magnesium isotope variations in lake water under different climatic scenarios. The dolomite sample data at a smaller scale (sampling interval ≈ 3~5 mm) demonstrate a consistent trend with the established model, providing additional confirmation of its reliability. Dolomite precipitated under humid climatic conditions exhibits a lower and relatively stable δ26Mgdol, lower δ18O, and higher CIA, indicating higher river inputs and relatively stable Mg isotope values of lake water controlled by river input. Nevertheless, dolomite formed under relatively dry climatic conditions shows a relatively high δ26Mgdol, higher δ18O, and lower CIA, suggesting reduced river inputs and weathering intensity, as well as relatively high magnesium isotope values of the lake water controlled by dolomite precipitation. This study contributes to the understanding of magnesium isotopes in lacustrine dolomite systems.

Formation conditions of Jixian System cherts in the Qishan area, Ordos Basin: Implications for marine redox conditions and paleoecology

Abundant chert bands and nodules are discovered throughout the Mesoproterozoic Jixian System in the Ordos Basin. These cherts faithfully record the Jixian period oceanic conditions and paleoecology. However, the diagenetic mechanism of the cherts remains unclear and controversial. To understand the origin of these cherts, we performed a multitracer study by combining field reconnaissance, petrological analyses, Si isotope analysis, and major and trace element analysis of chert samples from the Qishan section. The results show that Jixian cherts had a high Al/(Al + Fe + Mn) value (~0.48), showed a flat distribution of rare earth elements in seawater, and most of the Fe/Ti values are <20. A weak negative Ce anomaly (~0.97) indicates the contribution of REY to weakly oxygenated seawater. The high isotopic composition of silicon (δ30Si = 0.74 ‰-1.35 ‰) and the average Siex value of 37.52 indicate that there is a source of biological silica, and the relationship between Eu/Eu* and Y/Ho and δ30Si shows that the hydrothermal and volcanic influences were less and correlated with seawater. The chert bands were closely related to biological activities. The chert nodules were influenced by hydrothermal activity. Secondary cherts were related to diagenesis, but the nature of siliceous fluids remains unchanged, still characterized by biogenic activity origins. The sea oxygen concentration in the Jixian period had increased, with periodic variations in the intensity of biological activities affecting the pH of the water body, or biological photosynthesis binding SiO2 colloid in water, affecting chert sediments, leading to frequent interlayering between dolomite and chert bands. Episodic hydrothermal fluids and late-stage diagenetic processes jointly influenced the formation of cherts. This study bears significant significance in enhancing our understanding of the sedimentary environment and the origin of cherts during the Jixian period in the Ordos Basin.

Chemical and boron isotopic compositions of tourmaline from the pegmatite in Ke'eryin rare metal orefield, Eastern Tibet: Implications for pegmatitic evolution

Pegmatites occur widely in the Ke'eryin rare metal orefield. The genesis and evolution of the Ke'eryin pegmatites are still in dispute, and morphological and geochemical studies on tourmalines from the Ke'eryin pegmatites are limited. In this study, in-situ analyses of major and trace elements and B isotope were conducted to uncover the origin of tourmaline and the evolution of related pegmatites. Three types of tourmaline from the Ke'eryin barren pegmatite were identified: elongated columnar or needle-columnar tourmaline (Tur-1 type), isolated, disseminated, irregular, and massive tourmaline (Tur-2 type), and long columnar tourmaline (Tur-3 type). Petrographically, the Tur-1 type crystallized at the early stage of pegmatitic crystallization sequence, the Tur-2 type possibly formed at the early- and/or syn-pegmatitic crystallization sequence, whereas the Tur-3 type likely formed at the relatively late crystallization sequence. Compositionally, most tourmalines belong to the alkali group with a few falling in the vacancy group. All the tourmalines show a schorl composition and are of magmatic origin. Chemical variations from the Tur-1 to Tur-3 tourmalines are controlled by magma fractionation and melt compositions rather than crystal chemical effects. Most tourmalines follow the (Na, Mg)(Xvac, Al)−1, (Mg, OH)(Al, O)−1, and (Ca, Mg2)(Xvac, Al2)−1 exchange vectors. The higher contents of Zn, Sn, Li, Be, Nb, and Ta and negative Eu anomalies in the Tur-3 type indicate that it was likely crystallized at a more evolved stage. In combination with textural evidence and tourmaline chemistry, we suggest that the Tur-1 and Tur-2 types were formed at the relatively earlier stage of pegmatite-forming magma and the Tur-3 type was likely formed closer to the end-stage of barren pegmatite crystallization. The B isotopic compositions are relatively homogeneous and display slightly higher in the Tur-3 type, which were likely caused by fractional crystallization during B-rich magma evolution. It can be inferred that the tourmaline in more evolved and/or Li-mineralized pegmatite with magma evolution should have higher Li, Be, Nb, Ta, and Sn contents, implying that tourmaline chemistry may be used as a potential exploration indicator for rare metal mineralization.

Study on topsoil chemical characteristics in Bao Thang district, Lao Cai province for agricultural development

Researching some chemical characteristics of topsoil in Bao Thang district, Lao Cai province to serve the management, planning, and reasonable use of agricultural land resources is very necessary, especially for identifying areas for growing specialty crops to convert crop purposes and improving local people’s lives. Result analysis of pHsoil, organic carbon (OC), organic matter (OM), major elements and trace elements from 49 topsoil samples taken at depths from 0÷20 cm on different formations in Bao Thang district, Lao Cai province shows that topsoil in Bao Thang district has pH in the slightly acidic to neutral soil group, OM and OC in moderate concentrations. The chemical composition of soil samples shows a relationship with bedrock. The geochemical characteristics of topsoils are high Fe2O3, poor to rich K2O and rich P2O5. Some trace elements in the topsoil of different fomations have lower or equivalent concentrations with those in the world’s soil and are consistent with the safety threshold of National technical regulation on soil quality (QCVN 03:2023/BTNMT), except Cr and Zn. This issue needs to be paid attention to during cultivation and agricultural production.

Revisiting the Tianwen Yellow Pumice (TYP) Eruption of Changbaishan Volcano: Tephra Correlation, Eruption Timing and Its Climatostratigraphical Context

AbstractChangbaishan volcano (China/North Korea) is one of the most active and hazardous volcanic centers in Northeast Asia. Despite decades of intensive research, the eruption history of this stratovolcano remains poorly constrained. One of the major puzzles is the timing of the eruption that produced the Tianwen Yellow Pumice (TYP) deposit at the caldera rim. Here we identify a new cryptotephra layer in sediment core 13PT‐P4 from the East Sea. Grain‐specific major, minor, and trace element analyses of glass shards allow a clear correlation of this distal tephra to the proximal TYP deposit of Changbaishan. Age‐depth modeling using radiocarbon (14C) dates of sediment bulk organic fractions and other tephrochronological markers from the sediment sequence constraints the age of the cryptotephra and thus the TYP eruption to 29,948–29,625 cal yr BP (95.4% confidence interval). Our findings lead to a revision of the history of Changbaishan explosive activity, and show that the volcano has been particularly active during ca. 51–24 ka BP in the last 100 ka. Using high resolution palaeo‐proxy records, we find the TYP tephra almost coeval with regional to hemispheric‐scale climatic changes known as Heinrich Event 3 (H3). With its precise age determination and wide geographic dispersion, the tephra offers a key isochron for dating records of past climatic changes and addressing the phasing relationships in environmental response to H3 across East Asia.

Insights on the origin of oldhamite in enstatite meteorites from Ca stable isotopes

In order to understand the origin of oldhamite (CaS) in enstatite meteorites, we report Ca isotopic compositions (δ44/40Ca) of oldhamite (obtained from water leachate of bulk chondrites and aubrites and mineral separates from the Norton County aubrite) and silicate minerals from different types of enstatite chondrites and aubrite. The δ44/40Ca of the bulk enstatite chondrites range from 1.05 ‰ to 1.24 ‰, with an average of 1.13 ± 0.12 ‰, higher than that of the estimate of the bulk silicate earth (∼0.94 ‰). Major and trace element analyses show that the water leachates of enstatite chondrites are mainly composed of oldhamite, and they take over 20.6–68.5 % Ca of the bulk meteorite Ca budget. The Ca isotope fractionation between oldhamite and residual silicate (Δ44/40Caoldhamite-silicate) for the studied enstatite chondrites is minimum (−0.44 ‰) for Abee (impact-melt breccia) and maximum (+0.16) for St.Marks (EH5). The Ca isotope fractionation between oldhamite (individual mineral grains and leachate) and silicates in Norton County varies from −0.47 ‰ to −0.31 ‰ with an average of −0.41 ‰. These Δ44/40Caoldhamite-silicate correlate well with previous theoretical calculation and suggests that the oldhamites in Norton County are in isotopic equilibrium with co-existing silicates, and therefore were formed during magmatic processes. However, in enstatite chondrites, the large variation on Δ44/40Caoldhamite-silicate and its negative correlation with metamorphic temperature reflects the redistribution and equilibration of Ca isotopes during metamorphism. The variable Δ44/40Caoldhamite-silicate found in unequilibrated chondrites reflect kinetic Ca isotope fractionation between oldhamite and nebular gas and therefore is evidence for the formation of oldhamite by condensation in the solar nebula.

Organic matter accumulation as a convergence response to astronomical forcing: Insights from Milankovitch periods and sea-level fluctuations during the early Cambrian

The accumulation of organic matter (OM) in marine sediments is a vital part of the global carbon cycle today and on ancient Earth, and is driven by a cumulative shift of organic carbon flux through oceans to marine sediments. This shift is a complicated process that is known to be influenced by the biological pump, diagenesis, and thermal alteration, so is affected by oceanic conditions and palaeo-climate, but less attention has been paid to the triggers of OM accumulation. Here, a set of marine sedimentary rocks from the early Cambrian in the southwestern part of the Yangtze Platform in China was used to search for clues to the triggers of OM accumulation. The effect of astronomical forcing, which potentially is a major control on Earth's oceanic conditions, was assessed via frequency analysis based on a high-resolution log dataset from a borehole in Yunnan Province. An astronomical time scale was constructed based on a 405,000 year-tuned filter. Palaeo-oceanic sedimentary conditions and palaeo-climate, which were recorded in the sedimentary rocks, were determined through geochemical analyses of major, trace, and rare earth elements. The mutual influence of astronomical forcing and the early Earth oceanic sedimentary conditions and paleoclimate were examined though Pearson Correlation analyses to provide evidence for the intensity of alteration of sedimentary conditions and the forces impacting the shift of organic carbon in the marine ecosystem. The results show that two convergence responses of OM accumulation were associated with ca. 1.5 and 2.4 million year (Myr) Milankovitch cycles. Fluctuations in sea level establish a connection between Milankovitch forcings and changes in sedimentary conditions, thereby providing evidence for the triggering of a cumulative shift of OM flux to sediments, and the effect of astronomical forcing on the organic carbon cycle.

Olivine in ultramafic rocks from the Polaris Alaskan-type intrusion: A geochemical record of open-system crystallization, diffusional re-equilibration, mantle source, and redox conditions in primitive arc magmas

Olivine in cumulates from the Early Jurassic Polaris Alaskan-type ultramafic-mafic intrusion in the North American Cordillera displays a wide range of textures and compositions produced in a dynamic crystallization environment as part of a transcrustal arc magmatic system. Major, minor, and trace element analyses of olivine were determined using combined electron probe microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to assess the utility of olivine as a petrogenetic indicator in ultramafic intrusions. High forsterite contents (>Fo87) of olivine from dunite, olivine wehrlite, and wehrlite indicate that the parent melts were primitive in composition and that they may represent intrusive analogues to extrusive arc picrites found elsewhere in the Cordillera. Forsterite-Ni systematics (Fo92–80, Ni = 3000–300 ppm) show fractional crystallization-controlled evolution from dunite to olivine wehrlite to wehrlite through olivine clinopyroxenite. Low-Ni olivine (Fo84–80, 500–300 ppm) in magnetite-olivine clinopyroxenite indicates the effects of sulfide melt saturation and Ni-depletion of the residual magma. Entrainment of high-Fo olivine in evolved melts and mixing between fractionated and primitive magmas explains olivine compositions with Ni concentrations (1000–3000 ppm) in excess of those predicted by fractional crystallization models. Extensive subsolidus diffusion of Mg, Fe, Ni, Mn, Ca, Cr, Al, and Li occurred during crystallization and cooling of olivine. Uniform concentrations of Mg, Fe, Ni, and Mn in individual samples and across crystals of olivine indicate complete equilibration in the consolidating cumulate pile. Calcium, Cr, and Al from Polaris olivine (e.g., typically <1000 ppm Ca, <100 ppm Cr and Al), and from plutonic olivine in general, are depleted relative to volcanic olivine as the result of diffusional re-equilibration with interstitial melt and other co-crystallizing phases (Cr-spinel, clinopyroxene). Ratios of first-row transition elements (Mn, Zn, Fe, Co, Ni) in olivine were modified during intracrustal processes (e.g., fractional crystallization, diffusion), however, ratios from the most primitive olivine are indicative of primary mantle signals. Lithium concentrations in olivine (2–12 ppm) show evidence for subsolidus diffusive re-equilibration with Li-enriched melts. Ratios of V/Sc (0.03–0.5) are consistent with relatively oxidized parent magmas and arc mantle sources to Polaris and Alaskan-type intrusions. The Polaris parent magmas ascended through the uppermost mantle and lowermost crust on sufficiently short timescales to avoid significant magmatic differentiation prior to emplacement at a depth of ≤15 km. The findings of this microanalytical study highlight the utility of olivine as a petrogenetic recorder of primary magmatic and high-temperature diffusional processes in ultramafic plutonic rocks and contribute to our understanding of the evolution of primitive arc magmas.

Relationship between the genesis of Changlinggang alkaline rocks and uranium mineralization in the 414U-Th deposit, Jianshui County, Yunnan Province, China

Alkaline rocks identified in the 414 U-Th deposit in Jianshui County, Yunnan Province, exhibit intense spatial correlation with uranium mineralization. However, limited investigations into their genesis have had an adverse impact on our understanding of uranium mineralization. Analyses of major and trace elements, U-Pb chronology, and petrography were conducted on alkaline rocks. The results indicate that anorthosite, which is rich in alkalis, high in potassium, peraluminous, enriched in rare earth elements (U, Th, Rb, and Zr) and deficient in Sr, Ba, Ti, and P, predominates the lithology. The light and heavy rare earth fractionation of the material is readily apparent (LREE/HREE=7.89–46.72), and the presence of Eu negative anomalies (δEu=0.65–0.81) suggests that the region from which the magma originated is a metasomatism-enriched mantle where the source material originates from the transition zone between garnet-lherzolite and spinel-lherzolite in the EMII-enriched lithospheric mantle. This area underwent metasomatization by subduction material from the Paleo-Pacific Ocean and during the ascent process, magma experienced a certain degree of partial melting and a significant degree of crystallization differentiation. The diagenesis of the syenite (186.64 ± 3.76 Ma) occurred after the closure time of the Paleotethys Ocean (237 Ma) in a dynamical context of an intra-terrestrial rift environment following subduction of the oceanic plate. In summary, the U and Th present in the 414 U-Th deposits underwent isomorphism within biotite and feldspars during the hydrothermal mineralization stage of magma evolution, where they were enriched in minerals through the separation and crystallization of alkaline magma.

Geochemistry, Sr-Nd Isotope Compositions, and U-Pb Chronology of Apatite from Kimberlite in Wafangdian, North China Craton: Constraints on the Late Magmatic Processes

Diamondiferous kimberlites occur in the Wafangdian area in the eastern part of the North China Craton (NCC). In order to better constrain their magmatic source and emplacement time, we have investigated apatite from two kimberlites, i.e., the #110 dike kimberlite and the #50 root-zone kimberlite by measuring in situ their U–Pb and Sr–Nd isotopic compositions. The crystallization ages of the #110 and #50 apatites are 460.9 ± 16.8 Ma and 455.4 ± 19.3 Ma, respectively. For the #50 apatite, 87Sr/86Sr = 0.70453–0.70613 and εNd(t) = −2.74 to −4.52. For the #110 apatite, 87Sr/86Sr = 0.70394–0.70478 and εNd(t) = −3.46 to −5.65. Based on the similar distribution patterns of the rare earth elements (REEs) and the similar Sr-Nd isotope compositions of the apatite, it is believed that the #110 and #50 kimberlites have the same source region and the kimberlite magmas in Wafangdian were derived from an enriched mantle source (EMI). The primary magmatic composition has little effect on the emplacement pattern. It is more likely that the geological environment played an important role in controlling the retention and removal of volatile components (H2O and CO2). This led to the different evolutionary paths of the kimberlite magma in the later period, resulting in differences in the major element compositions of the apatite. High Sr concentrations may be associated with hydrothermal (H2O-rich fluid) overprinting events in the later magmatic period; the higher light rare earth element (LREE) concentration of the #50 apatite reflects the involvement of the REE3+ + SiO44− ⇔ Ca2+ + PO43− replacement mechanism. Two emplacement patterns of the #110 dike kimberlite (#110 apatite, low Sr, and high Si) and the #50 root-zone (#50 apatite, high Sr, and low Si) kimberlites were identified via major element analysis of the #110 apatite and #50 apatite.

Mesoarchean–Neoarchean coupled crust–mantle differentiation followed by gravity-driven lithospheric delamination and subduction initiation in the North China Craton

The geodynamic regime that formed Archean silicic continental crust is unclear. The episodic Archean TTGs (tonalite–trondhjemite–granodiorite rocks) and associated granitoids, with emplacement ages of ca. 2.9, 2.7, and 2.5 Ga, occurred in the Jiaobei Terrane, North China Craton (NCC), provide a continuous record of the formation of the Mesoarchean–Neoarchean silicic continental crust. To investigate the crust–mantle differentiation, crustal reworking and recycling, and geodynamic regime associated with formation of the Mesoarchean–Neoarchean silicic continental crust, we undertook zircon U–Pb dating and Hf–O isotope, and whole-rock major and trace element analysis of Archean TTGs and associated granitoids. The episodic Archean TTGs and juvenile crust coexisted spatially–temporally in the Jiaobei Terrane, indicating Mesoarchean-Neoarchean synchronous differentiation of crust and mantle. In addition, the ca. 2.9 and 2.7 Ga TTGs have an identical Mesoarchean juvenile crustal source and similar mantle-like zircon δ18O values, whereas the ca. 2.5 Ga TTGs were derived mainly from younger Neoarchean juvenile crust, indicating removal and replacement of the Mesoarchean juvenile lower crust. Some ca. 2.5 Ga TTGs, granitic gneisses, and sanukitoids have markedly higher zircon δ18O values compared with mantle δ18O values, which are indicative of Neoarchean supracrustal recycling. Consequently, we can constrain the geodynamic processes responsible for the formation of the Mesoarchean–Neoarchean silicic continental crust in the Jiaobei Terrane, NCC. Episodic hot upwelling mantle (or plume)–lithosphere interactions at ca. 2.9, 2.7, and 2.5 Ga resulted in coupled crust–mantle differentiation, which produced the TTGs, juvenile crust, and dense lower crustal restites. Subsequently, lithospheric delamination triggered by gravitational instability occurred followed by continental uplift, subduction of altered oceanic crust, and upwelling of asthenosphere and mantle-derived mafic melts. This resulted in extensive anatexis and metamorphism with anticlockwise P–T paths in the middle to lower crust at ca. 2.5 Ga. Furthermore, following the large-scale melting and cooling of the mantle, a thick, stable, cratonic lithosphere had likely developed by the end of the Neoarchean. The geodynamic processes during the Mesoarchean–Neoarchean were diverse, and episodic hot upwelling mantle (or plume)–lithosphere interactions could have been responsible for the formation of Archean silicic continental crust in the Jiaobei Terrane, NCC.

Textures and Chemistry of Crystal Cargo of the Pleiades Volcanic Field, Antarctica: Potential Influence of Ice Load in Modulating the Plumbing System

Abstract The Pleiades Volcanic Field (PVF) of northern Victoria Land (Antarctica) is made up of a dozen scoria cones whose erupted products present an unusually complete evolutionary trend from alkali-basalt to trachyte. With the aim of reconstructing the evolution of the PVF plumbing system, we have investigated the petrography and chemistry of main mineral phases using scanning electron microscopy (SEM-EDS) coupled with major element analyses using an electron probe microanalyser (EPMA-WDS). We further focussed on clinopyroxene phenocrysts obtaining a more detailed characterization by means of trace laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) element analyses coupled with machine learning thermobarometry. The results indicate that fractional crystallization and magma mixing are the major processes determining the development of the complete evolution trend. While fractional crystallization is a persistently active process in all parts of the plumbing system, mixing among differently evolved magma batches pertaining to the same association is responsible for the formation of intermediate compositions in the differentiation lineage at a specific pressure range (0.4–0.5 GPa). These processes are compatible with significant residence time of magmas at depth, resulting in multiple episodes of magma mixing, as testified by resorption and overgrowth textures in phenocryst assemblage occurring under isobaric conditions. The prolonged residence time likely increased the efficiency of the mixing process, leading to the formation of magmas with intermediate composition. In turn, the build-up of volatiles during the magma differentiation at depth could have favoured the eruption of these (variably differentiated) magmas. Considering that the PVF is situated in a glacial region, a process forcing long magma residence time can be envisaged associated with increased ice loading during glacial stages. This study specifically considers the ice fluctuations in the last 100 ka, theorizing the possibility of a climate-controlled volcano plumbing system.

Constraints on uranium mineralization by chronology and microgeochemical characteristics of monazite in the Datian area of the Kangdian region, China

Monazite, a common U-containing ore-rich mineral found in association with U minerals, has excellent sealing properties after its formation, making it a promising tool for determining the age and genetic type of U mineralization. The Datian area in the Kangdian region of China is an important Neoproterozoic U ore-forming region. It has garnered the attention of researchers owing to the presence of megacrystalline uraninite with well-developed crystal forms. However, most studies conducted on U mineralization in the Datian area have focused on macroscopic observations and uraninite, with limited reports on accessory minerals. In this study, LA-ICP-MS U-Pb chronology and in-situ major and trace element analyses were performed on monazite associated with megacrystalline uraninite in the Datian area metallogenic belt I. The research yielded the following insights: 1) U mineralization in the Datian area was estimated to have occurred approximately 770 million years ago. This age demonstrates a potential correlation with the assembly and fracturing of the Rodinia supercontinent, suggesting a geodynamic context for the mineralization event. 2) The geochemical characteristics of the monazite indicate an igneous rock origin for its genetic type. Combined with previous research findings, it is postulated that U mineralization in the Datian area may be closely linked to the partial melting of deep crustal materials within a metamorphic environment characterized by high temperature and low pressure.

Quantifying denudation rates and sediment recycling of low-relief, high-elevation landscapes using in-situ and meteoric cosmogenic nuclides

Quantifying Earth’s surface denudation rates is crucial for estimating sediment flux and its role in regulating global climate change. The inability of in-situ cosmogenic 10Bein to quantify denudation rates in quartz–free environment has prompted the need for a new proxy–the ratio of meteoric 10Bemet to mineral-weathered 9Be in reactive phase (precipitated in or adsorbed onto secondary minerals). This study utilized 10Bein–26Alin, 10Bemet/9Be, and major element analyses of reactive and mineral phases of bedload sediments to infer basin-wide denudation rates and sediment recycling (reworking of deeply buried sediments) in the Three River Source Region (TRSR) of the central Tibetan Plateau. Results from 10Bein-26Alin analysis of bedload sediments and bedrock samples (quartz grain, 250–500 μm) suggest that the sediments underwent burial events since at least 0.54 ± 0.16 million years ago. Combining paleoclimate records in the central Tibetan Plateau, we interpret the “Great Burial” as most likely the result of climate-controlled deglaciation and denudation at the termination of Naynayxungla glaciation during the MIS 13–15 period. This event marks the first widespread deglaciation on the Tibetan Plateau. The 10Bein-26Alin derived paleo–denudation rates range from 4.2-0.8+0.9 to 151-32+37 mm/kyr, consistent with previous 10Bein–derived modern denudation rates of 10–117 mm/kyr in TRSR. These rates show a moderate positive correlation with regional topography, particularly channel steepness, indicating a decrease in both relief and denudation rates from lower to upper streams. This spatial discrepancy is likely due to enhanced river headward incision and active neotectonic activities in the southeast. Denudation rates derived from the 10Bemet/9Be proxy range from 13 to 248 mm/kyr, alongside a chemical weathering intensity ranging from 43 % to 67 %. These denudation rates are strongly correlated with, but about 1.5 times higher than, the 10Bein–26Alin derived paleo–denudation rates from the same watershed. This suggests that the 10Bemet/9Be extracted from fine grains (<64 μm) may reflect a different sediment recycling pattern compared to 10Bein–26Alin in quartz sediments. Alternatively, the 10Bemet/9Be ratio could indicate a mixture of carbonate rock with a high denudation rate and silicate rock with a lower denudation rate, whereas 10Bein–26Alin reflects a single silicate denudation signal.

Mineralization processes of the Mount Garnet Zinc deposit, NE Queensland (Australia): Insights from garnet geochemistry and U-Pb geochronology

The Mount Garnet Zinc deposit in NE Queensland, Australia, is located in the region of voluminous magmatism associated with the formation of Palaeozoic continental arcs of Gondwana. Ore-forming events of this deposit are related to the intrusion of the Kennedy Igneous Association (KIA) – a large suite of igneous rocks spanning Late Carboniferous to Early Permian in age – into the Silurian limestone (Chillagoe Formation) in the Hodgkinson Province (Mossman Orogen). Petrographic observations and in situ major and trace element analysis reveal the sequence of garnet growth and fluid-rock interaction during skarn formation. Three types of garnets are identified, Grt I (including IA and IB) and Grt II. Grt IB is related to Zn-Pb mineralization. All garnets have elevated Sn and W and the highest levels of W and Sn are observed in Grt II. Garnet U-Pb ages of Grt IB provide the first direct geochronological result of hydrothermal minerals in the Mount Garnet region. New data argues that the base metal mineralization may take place during early Permian period and be sourced from the Claret Creek Supersuite. Sn-W mineralization may be associated with the O’Briens Creek Supersuite.