Sr Ratios Research Articles

Fingerprinting Portland cements by means of 87Sr/86Sr and 143Nd/144Nd isotope ratios and geochemical profiles

This study uses conventional 87Sr/86Sr and 143Nd/144Nd isotope and interelement ratios of Ca, Sr, K, Mn, Mg and Ti as fingerprints for provenancing ordinary Portland cements (OPC). Herein, the first database of Sr and Nd isotope ratios investigated in OPCs, stemming from 29 cement plants located worldwide, was created. The results show that the Sr isotope ratios of OPCs are higher than those of seawater from the observed geological period. The spread of 143Nd/144Nd in OPCs is not as large as the spread for 87Sr/86Sr isotope ratios. However, the combination of both Sr and Nd isotope ratios provides the potential for distinguishing between cements of different production sites. Most of the OPCs investigated have measurable differences in their 87Sr/86Sr and 143Nd/144Nd isotope ratios, which can be employed as a valuable analytical fingerprinting tool. In the case of equivocal results, divisive hierarchical clustering was employed to help overcome this issue. The construction of geochemical profiles allowed the computing of suitably defined distances between cements and clustering them according to their chemical similarity. By applying this methodology, successful fingerprinting was achieved in 27 out of the 29 ordinary Portland cements that were analysed.

Structural and physical properties of Sr‐based 3d–5d double perovskites of Sr2Fe0.5Hf1.5O6−δ oxides

AbstractSr‐based 3d–5d double perovskite Sr2Fe0.5Hf1.5O6−δ (SFHO) oxide powders were synthesized via the solid‐state reaction method, and their structural, dielectric, magnetic, optical, and transport properties were investigated. Structural investigations revealed the SFHO powders crystallized in an orthorhombic crystal structure with Pnma space group. Scanning electron microscopy images demonstrated the relatively homogeneous distributions of spherical SFHO powders, and x‐ray energy dispersive spectra gave out the molar ratio of Sr:Fe:Hf equal to 1.94:0.5:1.87, close to the nominal value. XPS spectra confirmed the existence of Sr2+, Fe3+, Hf4+ ions in the SFHO powders, and oxygen appeared in the forms of lattice oxygen and adsorbed oxygen species, respectively. The SFHO ceramics exhibited a relaxor‐like dielectric behavior. Two dielectric abnormities appeared around 518 and 257 K, which were ascribed to the dielectric response of the oxygen vacancies ( activation energy Ea = 0.93 eV and thermal excitation of the electrons with Ea = ∼ 0.02 eV bound weakly to the, respectively. Ferromagnetic behavior was observed in the SFHO powders at 300 and 2 K, and the saturated magnetization at 2 K was 0.67 μB/f.u. Magnetic transition temperature, TC was determined to be 638 K from the temperature dependence of the magnetization under the zero‐field cooling mode. A spin glass‐like behavior was observed around 390 K, which was confirmed by the frequency‐dependent alternating current (ac) susceptibility measurements. The SFHO powders exhibit a butterfly‐like magnetoresistance (MR)–H plot at 2 K, and the MR (2 K, 7 T) is found to be −2.73% owing to the intergranular magneto‐tunneling effect. Temperature dependence of the resistivity of the SFHO ceramics displayed a semiconducting behavior, and the electrical transport properties of the SFHO ceramics were investigated by Mott's variable‐range‐hopping model, thermally activated semiconductor conductivity model, and the adiabatic small polarons hopping model, respectively. UV–vis diffuse‐reflectance spectra of the SFHO powders demonstrated a direct optical bandgap of Eg = 2.62 eV, which was contributed from the electron transfer from the O(2p) orbital to Fe(3d)/Hf(5d) orbitals. A combination of high‐temperature ferrimagnetism and semiconducting nature of the SHFO powders makes them attractive for spintronics and photovoltaics.

Scheelite composition fingerprints pulsed flow of magmatic fluid in the Fujiashan W skarn deposit, eastern China

Abstract Scheelite (CaWO4) is an economically important W mineral in skarns that form when magmatic fluids exsolved from a granitic intrusion react with carbonate wall rocks. In the Fujiashan W skarn deposit, scheelite formed during four stages of the hydrothermal skarn development. We present cathodoluminescence (CL) images and in situ trace element and Sr-O isotope data of scheelite from these four stages, i.e., scheelite in prograde and retrograde skarn, quartz-sulfide veins, and late calcite replacements. Scheelite from prograde skarn and quartz sulfide veins are homogeneous and show oscillatory zoning textures in CL images, whereas scheelite from retrograde skarn and late carbonate stages display dissolution-reprecipitation and patchy textures. The brightness of CL textures decreases with a higher substitution of Mo. Molybdenum-rich scheelite (up to 2.1 wt%) is characterized by relatively high contents of Nb and Ta (up to 156 and 0.9 ppm, respectively), positive Eu anomalies, high-δ18O values (5.2 to 5.9‰), and relatively low-87Sr/86Sr values (0.70661 to 0.70727), and has grown in a system with a continuous supply of magmatic fluid. Molybdenum-poor scheelite (0.2 wt%) has low contents of Nb and Ta, negative Eu anomalies, low-δ18O values (4.2 to 4.3‰), and relatively high-87Sr/86Sr ratios (0.70748 to 0.70804). This type of scheelite formed in a system with a restricted flow of magmatic fluid during scheelite precipitation became increasingly depleted in elements that substitute into scheelite. The continued reaction of the magmatic fluid with the wall rocks and the precipitation of minerals from the fluid resulted in a systematic change of the δ18O and 87Sr/86Sr ratios. Chemical and isotopic variations in scheelite may reflect the pulsed flow of a magmatic fluid and do not require the involvement of different fluids or contrasting redox conditions.

Symmetry control of cation substitution in ‘antizeolite’ borates

‘Antizeolite’ borates are a family of inorganic compounds with structure based on fixed (pseudo)tetragonal [Ba12(BO3)6]6+ sublattice, and various anionic clusters occupying ‘channels’ in the sublattice. An ability to host different anionic clusters provides a convenient way to tune such functional properties of materials based of ‘antizeolite’ borates as dichroism, luminescence etc. We demonstrated the dependence of extent of Sr2+→Ba2+ substitution in the cationic sublattice of antizeolite barium borates on the symmetry of initial compound. The latter is controlled by ‘guest’ anionic clusters in the channels of sublattice. In the case of initially orthorhombic [Ba12-xSrx(BO3)6](BO3)2 solid solution, the structure adapts to the increase in Sr2+ content (up to Sr/(Ba+Sr) ratio of at least 39 wt. %) by tetragonalization of the sublattice. In contrast, in tetragonal [(Ba1-xSrx)12(BO3)6](BO3)[LiF4] solid solution another structural mechanism of Sr2+ accommodation takes place, which results in the (2a,2c) modulation and is limited by maximum Sr/(Ba+Sr) ratio of 10-20 wt. %.

Highly Contrasted Geochemical Pattern in Sediments of the Okavango Delta, Botswana Driven by Dust Supply, Hydrological Heritage and Biogeochemical Reactions

AbstractThe Okavango Delta in North Botswana is a hot‐spot of biodiversity within the semi‐arid central part of the South African plateau. This endorheic ecosystem is highly dependent on the annual flood that brings freshwater from the highlands of Angola to the North. However, in many places, the groundwater of the Delta is saline and contains very high concentrations of metal and metalloid elements, making it toxic to the flora and fauna. These saline waters have been largely studied and their formation is generally explained through evaporation and evapotranspiration processes. However, no studies have investigated the geochemical composition of the sediments that host the aquifers. Here, we provide a complete sedimentological and geochemical investigation (major, traces and rare earth elements, carbon and oxygen stable isotopes ratios, Sr and Nd isotope ratios) of the various geomorphological and ecological compartments that form the landscape of the SW Okavango Delta. We demonstrate that the non‐connected underground aquifer is capped by a clay layer corresponding to a major event of dust deposition from the Makgadikgadi pan. We suggest that this aquifer may extend outside the island, below the floodplain and that the hydrological structure of the Nxaraga area is indeed composed of two non‐connected aquifers of different origins. Challenging the model based on evaporation and evapotranspiration, we propose that the composition of that allochtonous clay and the in situ reactions between sediment, water and organic matter in a confined aquifer explain the geochemical enrichment of the water.

A Record of the Snowball Earth Events? The Parecis Basin May Encompass Three Major Neoproterozoic Glaciations on the Amazonian Craton

The Parecis Basin is an intracratonic basin located at the south-southeast portion of the Amazonian craton. Its stratigraphic units comprise siliciclastic and carbonate rocks that potentially record intense paleoenvironmental changes related to the Sturtian (∼717–660 Ma), Marinoan (∼657–635 Ma), and Gaskiers (∼580 Ma) glaciations. We present novel X-ray fluorescence geochemistry, C, O and Sr isotopic data from carbonate rock samples retrieved from the stratigraphic well 2ANP 0006 MT. The results show two negative excursions of δ13C here correlated to post-Sturtian and Marinoan glaciations, recorded in the Salto Magessi and Mirassol d’Oeste carbonate units, respectively. Both negative excursions were followed by δ13C positive incursions. At the base of the section, Salto Magessi carbonate presents unradiogenic Sr ratios (87Sr/86Sr from 0.70655 to 0.70776) typical of Cryogenian interglacial carbonate rocks found elsewhere. The negative δ13C excursion from Mirassol d’Oeste is associated with radiogenic 87Sr/86Sr ratios (up to ∼0.7186), possibly related to continental influx from the intense erosion generated by the Marinoan deglaciation. Upward, the Nobres Formation displays preserved primary sulfate minerals (gypsum and anhydrite) and isotopically heavy oxygen compositions which point to an evaporative environment and support the scenario of enhanced oxidative weathering during early to middle Ediacaran. Finally, despite the absence of cap carbonate, diamictites related to the Serra Azul Formation occur overlying the Nobres Formation and are associated with the Gaskiers event. Therefore, the 2ANP 0006 MT may record three major glacial events from the Neoproterozoic, representing a promising section for further studies concerning chemostratigraphic and paleoenvironmental reconstructions during the Neoproterozoic Era.

Evaluating the use of Ca/Sr and 87Sr/86Sr ratios to track Ca sources in sugar maple in Ontario

Decades of acidic deposition and timber harvesting have depleted calcium (Ca) stocks in soils, especially at base-poor soils characterized by low base cation weathering rates. One approach to tracking Ca sources from soil is by using Ca/Sr ratios in vegetation, while 87Sr/86Sr ratios have also been used to estimate mineral weathering rates. To evaluate the uses of Ca/Sr ratios and Sr isotopes in identifying Ca sources in sugar maple ( Acer saccharum Marsh.) trees, three base-poor sites on the Canadian Shield and three limestone sites in southern Ontario were sampled for Ca, Sr, and 87Sr/86Sr ratios. Higher Ca/Sr ratios in soil extracts and sugar maple tissues at base-rich sites compared with base-poor sites reflect different minerology among regions, while the Ca/Sr discrimination factor between roots and foliage indicated that internal cycling exerts a major control on Ca/Sr ratios in sugar maple. At the three off-shield sites, 87Sr/86Sr ratios in soil and tree tissues were higher than precipitation but were indistinguishable for off-shield sites. Mixing models using a 1.0 mol L−1 HCl soil extract as the weathering endmember indicated that a lower proportion of weathering Ca compared with other geochemical approaches. One potential explanation is that the extraction method dissolves more recalcitrant minerals to a greater extent than under field conditions, leading to a higher weathering rate endmember value used in the mixing model.

Spontaneous immunomodulation and regulation of angiogenesis and osteogenesis by Sr/Cu-borosilicate glass (BSG) bone cement to repair critical bone defects

Injectable bone biomaterials like bone cement should be designed and fabricated with certain biological criteria, which include: 1) recruitment and polarization of the macrophages from M1 (pro-inflammatory) to M2 (anti-inflammatory) phenotype, 2) enhance vascularization, and 3) activate osteogenic differentiation of bone marrow-derived stem cells to promote bone healing. So far, no injectable biomaterials could spontaneously regulate the entire bone healing process that involves inflammation, angiogenesis, and osteogenesis. Therefore, in this study, we designed bone cement comprised of strontium and copper-incorporated borosilicate glass (Sr/Cu-BSG) in the liquid phase of chitosan to modulate bone healing. In vitro studies showed that the controlled release of Sr and Cu ions up-regulated anti-inflammatory genes(IL-1Ra and TGF-β1) while down-regulating pro-inflammatory genes(IL-1β and IL-6) in macrophages at 3 days. Sr and Cu ions also increased the expressions of angiogenic genes (VEGF and bFGF) in HUVECs at 5 days and osteogenic genes (Runx-2, OCN, and OPN) in hBMSCs at 7, 14, and 21 days. 5Sr3Cu-BSG bone cement exhibited the best anti-inflammatory, angiogenic, and osteogenic properties among the bone cement groups with different Sr and Cu ratios. Short-term and long-term implantation of Sr/Cu-BSGs in femoral condylar bone defects of rats and rabbits confirmed the in vitro results, where the degradation rate of Sr/Cu-BSG matched the bone healing rate. Similar to in vitro, the 5Sr3Cu-BSG group also showed the highest bone formation in vivo. Excellent physical and chemical properties, along with its bone repairing ability, make the Sr/Cu-BSG bone cement a good candidate biomaterial for treating bone defects.

The effects of submarine alteration and phosphatization on igneous rocks: Implications for Sr-, Nd-, Pb-isotope studies

A suite of fresh and variably phosphatized submarine volcanic rock samples from NW Pacific seamounts from the Mid Cretaceous were subject of a detailed trace element and isotopic leaching study to examine the effect of phosphate alteration on the use of Sr-, Nd-, and Pb- radiogenic isotope systems. The study particularly focuses on the behavior of the respective parent/daughter element pairs during phosphatization and leaching in order to evaluate the impact on radiogenic ingrowth correction (“age correction”) for old seafloor samples and their use in geochemical studies. For this purpose, variably intense leaching procedures (no leaching; 2 M HCl at 70 °C for 1 h; 6 M HCl at 130 °C for 3 h) were applied to diverse sample materials (rock powder, rock chips and fresh volcanic glass chips).Phosphatization causes significant modification of isotope ratios and elemental proportions of most trace elements including the rare earth elements. As opposed to common seafloor weathering, Rb/Sr decreases in the lavas with increasing phosphatization, while U/Pb enrichment appears slightly amplified. Mild acid leaching of rock chips, however, generally yields Sr, Nd and Pb isotope ratios largely in accordance with values from fresh glass fractions of the same samples and comparable with the results for similarly leached rock powders. Applying original (non-leached) elemental concentration ratios for the radiogenic age correction of mildly leached sample chips produces mixed results for 87Sr/86Srin but generally agrees with expected 143Nd/144Ndin, 206Pb/204Pbin, 207Pb/204Pbin, and 208Pb/204Pbin values.All residua of strongly leached powders yield significantly more radiogenic 206Pb/204Pbm, 143Nd/144Ndm and higher U/Pb than mildly leached rock chips or powders or even non-leached powder of the respective samples, opposite to what is expected when removing seawater-derived secondary phases by stronger acid leaching. We suggest that this enrichment, after removal of most of the magmatic Pb and Nd, reflects minor refractory components that formed in association with the phosphatization and developed high 206Pb/204Pb ratios by radiogenic ingrowth since the eruption of these lavas in the Mid Cretaceous due to high U/Pb.Utilizing modeled parent/daughter ratios based on magma evolution systematics of associated fresh glass yields no satisfying initial isotopic compositions for the strongly leached samples despite supposed removal of secondary isotopic signals upon leaching. Applying the modeled parent/daughter ratios to age correct mildly leached sample chips and powder otherwise slightly improves the accordance with their respective fresh glass fractions for 208Pb/204Pbin but yields similar results as if using the actual parent/daughter ratios for 143Nd/144Ndin, 86Sr/87Srin, 206Pb/204Pbin, and 207Pb/204Pbin.

Geochemical and radiogenic isotope records of the Weissert Event in south Tethyan sediments

The Cretaceous marine sedimentary record is characterized by time intervals rich in organic matter correlating with positive carbon isotope excursions, often called oceanic anoxic events. The Weissert Event corresponds to the first such event in the Cretaceous during the Valanginian stage. The associated palaeoenvironmental perturbations, which include increasing marine surface water primary productivity, are hypothesized to have been triggered by volcanic activity from large igneous provinces, and the source of nutrients is not well constrained (continental runoff v. oceanic upwelling). We present isotope ratios of Pb, Sr and Nd, together with concentrations of major and trace elements, for sediments from the central Moroccan margin to test these hypotheses. We demonstrate that the nutrient input was dominated by continental weathering. The source of sedimentary material remained stable during the Valanginian interval and originated from an old source, probably the African Sahara region. The radiogenic isotope signatures do not show a significant contribution of volcanic products from any known Valanginian large igneous province to the geochemical budget of sediments deposited on the central Moroccan margin. Although this does not preclude an impact of volcanic activity on the composition of seawater, it demonstrates that the erupted volumes were not sufficient to affect the deposited sediments. Supplementary material: The Supplementary Table contains three sheets: (1) Central Moroccan Margin, the analytical data generated and analysed during this study; (2) Fig. 8 data, large igneous provinces, the data of known Valanginian large igneous provinces used for comparison; and (3) Fig. 9 and S5 data, source areas, the data of potential surrounding source areas used for comparison, available at https://doi.org/10.6084/m9.figshare.c.6333040 .

Preparation of SrZrAl multiple oxide catalyst for produce biodiesel from acidified palm oil

The strontium oxide (SrO) is considered as an efficient heterogeneous catalyst for biodiesel production. However, the resistance of SrO to high free fatty acids (FFAs) in low-quality raw materials is a great challenge. In this study, the SrZrAl multiple oxide catalysts are prepared and applied in transesterification of the acidified palm oi. The preparation of the SrZrAl catalysts is optimized from the aspects of the preparation method and zirconium content, where the co-precipitation method with Sr, Zr and Al molar ratio of 6:6:1.5 is preferentially determined. The microstructure and surface chemical properties of SrZrAl catalyst are thoroughly characterized by XRD, CO2/NH3-TPD, XPS and SEM-EDS. The GA-PSO-BP algorithm is used to optimize the transesterification parameters, where the FAME yield of 94.4% could be achieved with the addition of oleic acid of 5 wt% under the condition of the methanol to oil molar ratio of 16:1 and catalyst amount of 3.8 wt% at 171 °C in 2.6 h. Excellent reusability of the SrZrAl catalyst is demonstrated by the fact that the FAME yield of 80.3% is still obtained at the fifth reuse cycle. In addition, the FAME yield reaches 83.4% even at a high oleic acid addition of 15 wt%.

Petrogenesis and Rb-Sr Isotopic Characteristics of PaleoMesoproterozoic Mirgarani Granite Sonbhadra Uttar Pradesh India: Geodynamics Implication for Supercontinent Cycle

The Rb-Sr whole-rock isochron, age 1636 ± 66 Ma of Mirgarani granite, is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex (CGGC). The initial Sr ratio is 0.715 ± 0.012 (MSWD = 0.11), showing an S-type affinity. The Mirgarani granite has intruded the migmatite complex of the Dudhi Group and forms the Mirgarani formation comparable to the granites of the Bihar Mica Belt around Hazaribagh (1590 ± 30 Ma). The present studies have established the chronostratigraphy of the Dudhi Group and adjoining areas in CGGC. Petro graphic and geochemical studies revealed that the granite is enriched in Rb (271 ppm), Pb (77 ppm), Th (25 ppm), and U (33 ppm) and depleted in Sr (95 ppm), Nb (16 ppm), Ba (399 ppm) and Zr (143 ppm) contents as compared to the normal granite. The Mirgarani granite is a peraluminous (A/CNK = 1.23), high potassic (K2O 6.42%), Calc-Alkalic to Alkali-Calcic {(Na2O+K2O)-CaO = 6.29} S-Type granite, a feature supported by the presence of modal garnet and normative corundum (2.68%). The Mirgarani granite is considered to have been formed by the anatexis of a crustal sedimentary protolith at a depth of approximately 30 km with temperatures ranging from 685-700 °C during the Co lumbian - Nuna Supercontinent.

Effects of La-Co Substitution and Ratio of Ba and Sr on Anisotropic Magnetic Field of Fe<sub>2</sub>-W Ferrites

It is known that the anisotropic magnetic fields are improved by La and Co substitutions for M-type ferrite sintered magnets, and the coercive forces are significantly improved. On the other hand, since W-type ferrites have a crystal structure similar to that of M-type ferrites, it is expected that La-Co substitution would improve magnetic properties in the same way. However, evaluations of the effects of La and Co substitution are difficult because sintered bodies with a single phase of W-type has not been obtained and sintering at high temperatures is required. Recently, a method to determine the anisotropic magnetic fields using the saturation asymptotic law was proposed by T. Kuno et al., J. Jpn. Soc. Powder Powder Metallurgy 63 (2016) 1053, which makes it possible to evaluate the anisotropic magnetic fields. In this study, La-Co substituted W-type ferrite powders in the Ba, Sr and (Ba-Sr) based systems were prepared, and the effects of La-Co substitution and the ratio of Ba and Sr on the anisotropic magnetic fields were investigated.

Numerical Investigation on the Leakage and Rotordynamic Characteristics for a Hole-Pattern Seal in Wet-Gas Conditions

Abstract For turbomachinery working in wet-gas conditions, liquid-phase fluid may worsen the rotordynamic characteristic of an annular seal, which induces a subsynchronous vibration problem and destabilizes the rotor-bearing system. The hole-pattern seal, demonstrated as effective to eliminate synchronous or subsynchronous vibrations for gas turbomachinery, is an ideal seal scheme to increase rotor stability and liquid tolerance capability of wet-gas turbomachinery. In this paper, the leakage and rotordynamic characteristics of a hole-pattern seal are numerically investigated under wet-gas conditions, using a three-dimensional transient CFD-based perturbation method. The accuracy and reliability of the present numerical method are demonstrated based on published experimental data. The rotordynamic force coefficients are presented and compared for the wet-gas hole-pattern seal with various inlet liquid volume fractions (LVF = 0%–20%), rotor speeds (ω = 0–20 krpm), inlet preswirl ratios (Sr = −0.2–0.5), and pressure ratios (Pr = 0.3–0.7). Numerical results show that the hole-pattern seal possesses desired tolerance capability for high inlet liquid volume fraction (LVF) of up to 20%. With inlet LVF increasing from 0 to 20%, the effective damping of the hole-pattern seal increases by about 50%, suggesting an improvement in rotor stability. The leakage flow rate of the oil-air mixture increases by 97.5%, combined with the sharply increasing oil leakage flow rate (by 636%) and decreasing air leakage flow rate (by 40%). The increasing rotor speed and inlet preswirl ratio both result in an obvious increase (by 50%) in the cross-coupled stiffness, yielding a smaller effective damping and worse rotor stability. With the increase in pressure ratio, all the rotordynamic force coefficients show a weaker frequency dependency and smaller magnitudes. The swirl velocity in the seal clearance can cause an accumulation of the liquid component in the hole cavities. With the increase of swirl velocity, more liquid component accumulates in the hole cavities, and the main accumulation position gradually moves upstream.

Structure-dependent luminescence of Eu3+-doped strontium vanadates synthesized with different V : Sr ratios – application in WLEDs and ultra-sensitive optical thermometry

Sr3V2O8:Eu3+ exhibits bi-modal, structure-dependent luminescence, and can be applied as an ultra-sensitive temperature sensor based on its spectral shift.

Enhanced electrical transport properties of polycrystalline La0.67Sr Ca0.23-K0.1MnO3 ceramics through A-site multielement co-doping

Current research on perovskite materials is mainly focused on how to achieve a high temperature coefficient of resistivity (TCR) in anticipation of application in infrared detection. In this study, we report the superior electrical transport properties of polycrystalline La0.67SrxCa0.23-xK0.1MnO3 (LSCKMO) (0.03 ≤ x ≤ 0.13) ceramics produced through the sol-gel process using different Sr doping contents. Based on previous studies, polycrystalline manganite ceramics with a higher TCR at room temperature were obtained by optimising the composition ratio of Sr or Ca. In the process of continuous doping, the crystal structure of the polycrystalline LSCKMO ceramics changed significantly from Pnma to R 3‾ c. The final polycrystalline La0.67Sr0.10Ca0.13K0.1MnO3 ceramic material was obtained with a TCR of 17.16% K-1 and peak TCR temperature of 289.42 K, demonstrating that suitable candidates can be obtained for infrared detection technology.

Mesozoic slab-derived magmas from mid-eastern China: Responses to a ridge-transform fault-ridge subduction system

Distinct thermal states of mid-ocean ridges and adjacent transform faults on subducting plates tend to produce distinct magmatic responses on overlying plates. The origins and spatial distribution of the widespread late Mesozoic adakitic rocks in mid-eastern China may provide critical insights into understanding magmatic responses under various thermal states of the underlying Pacific plates. Among them, the intrusive rocks from the Xu-Huai (Xuzhou-Huaibei) region are spatially important but their petrogenesis remains controversial. These intrusions were proposed to be formed by foundering of an ‘eclogitic’ lower continental crust represented by the mafic xenoliths hosted by these intrusions. By eliminating abundant tiny xenoliths that potentially affect chemical and isotopic compositions of the host rocks, our new data reveal a positive correlation between Sr and Nd isotopic ratios defining two end-members on the EM-I and EM-II arrays respectively, which cannot be explained by a delaminated lower crustal source alone. The radiogenic Pb isotopic ratios of the Xu-Huai intrusions are as high as those of the oceanic crust and marine sediments. Meanwhile, these rocks are sodic with high Na2O/K2O, and have relatively low (La/Yb)N but high (Dy/Yb)N, Sr/La and Sr/Y, resembling those of oceanic adakites. Given the contemporaneous subducting oceanic ridges under mid-eastern China, the Xu-Huai intrusions were most likely derived from partial melting of a hot subducted oceanic crust that was close to the mid-ocean ridge. Consequently, a sandwich-like distribution pattern of Mesozoic adakitic rocks in mid-eastern China can be recognized, and subduction of a ridge-transform fault-ridge system is proposed to explain this observation.

Stable Sr isotope (88Sr/86Sr) fractionation in calcite precious corals

Stable isotope ratios of Sr (88Sr/86Sr) are a novel indicator for identifying terrestrial and oceanic Sr cycling and biological processes. Here we evaluate the temperature dependence of stable Sr isotope ratios (δ88Sr) in the calcite skeletons of precious corals, known as octocorals. High-precision Sr isotope measurements by double spike thermal ionization mass spectrometry were applied to different precious corals (Corallium japonicum, Pleurocorallium elatius, P. konojoi, Corallium sp., Keratoisis sp., and Coralliidae sp.) collected from water depths of 30–1500 m in the Pacific Ocean, corresponding to annual mean water temperatures of 2.5 to 19.5°C. The precious corals showed mean δ88Sr values of 0.101 ± 0.023‰. The magnitude of Sr isotope fractionation between the skeleton and ambient seawater (Δ88Sr) is −0.291 and is about −0.1‰ lower than the value predicted from the precipitation of inorganic calcite. This fractionation is not affected by changes in skeletal Sr/Ca ratio and associated biological effects on δ88Sr are negligible. δ88Sr of precious coral skeleton is an excellent recorder of ambient seawater.

Petrogenesis and tectonic affinity of Early Cretaceous potassic diorites in the northern Taihang Mountain, Trans-North China Orogen

• Early Cretaceous potassic diorites are identified within the central Trans-North China Orogen. • Lithospheric delamination and thermo-mechanical erosion explain lithospheric structures during the Early Cretaceous in the North China Craton. • Early Cretaceous magmatism in the study area was linked to slab sinking and rollback. • The subducted Izanagi plate may be a candidate for carbonated peridotite at ∼140 Ma. Mesozoic mantle-derived potassic magmatic rocks in the Trans-North China Orogen (TNCO) are important for constraining tectonic evolution. However, potassic intermediate plutons in this orogen are rarely reported in literature, despite the significance of such a potassic magmatic event being well understood. Here, we describe the petrography of the Longmen potassic diorites and present zircon U–Pb ages and elemental and Sr–Nd–Mg isotopic compositions for this pluton. The Longmen potassic diorites were emplaced during the Early Cretaceous (ca. 140 Ma), showing shoshonite features with marked depletion of high-field strength elements relative to large ion lithophile elements with a slightly negative Eu anomaly. It possesses restricted ranges of initial 87 Sr/ 86 Sr ratios (0.70592 to 0.70667), ε Nd (t) values (−15.86 to −13.26), and low δ 26 Mg (−0.37 to −0.26‰). Low-degree partial melting of the ancient and enriched mantle, characterised by amphibole-bearing lherzolite in the spinel–garnet transition zone, was the likely mantle source of the evaluated Longmen potassic diorites, resulting from fluid-related metasomatism and upwelling mantle (carbonated) peridotite. Minor crustal materials were present in the lithospheric mantle because of Eastern Block and Western Block subduction/collision during the Paleoproterozoic. Based on our data and previous studies, slab sinking and rollback of the Izanagi plate (Paleo-Pacific plate) may have created an ancient, enriched mantle beneath the East Asian continent, inducing lithospheric thinning and heterogeneity of the lithospheric mantle in the North China Craton and lithospheric extension via thermo-mechanical erosion at 145–110 Ma in the TNCO.

Tracing changes in base cation sources for Arctic tundra vegetation upon permafrost thaw

Upon permafrost thaw, the volume of soil accessible to plant roots increases which modifies the acquisition of plant-available resources. Tundra vegetation is actively responding to the changing environment with two major directions for vegetation shift across the Arctic: the expansion of deep-rooted sedges and the widespread increase in shallow-rooted shrubs. Changes in vegetation composition, density and distribution have large implications on the Arctic warming and permafrost stability by influencing the albedo, the snow accumulation and the litter decomposition rate. A better understanding of these cumulated effects of changing vegetation on warming and permafrost requires assessing the changes in plant nutrient sources upon permafrost thaw, nutrient access being a limiting factor for the Arctic tundra vegetation development. In this study, we determined the influence of permafrost degradation on the base cation sources for plant uptake by using the radiogenic Sr isotope ratio as a tracer of source, along a permafrost thaw gradient at Eight Mile Lake in Interior Alaska (USA). As plants take up Sr from the exchangeable soil fraction with no measurable fractionation, we determined the differences in 87Sr/86Sr ratio of the exchangeable Sr between shallow and deeper soil horizons, and we compared the 87Sr/86Sr ratio of foliar samples for three Arctic tundra species with contrasted rooting depths (Betula nana, Vaccinium vitis-idaea, and Eriophorum vaginatum) upon different permafrost thaw conditions. The higher foliar 87Sr/86Sr ratios of shallow-rooted Arctic tundra shrubs (B. nana, V. vitis-idaea) was consistent with a shallow source of soil exchangeable Sr from surface soil horizons, whereas the lower foliar 87Sr/86Sr ratios of deep-rooted Arctic tundra sedges (E. vaginatum) reflected a source of Sr from deeper soil horizons. There is a shift between poorly and highly thawed soil profiles towards lower foliar 87Sr/86Sr ratios in both deep- and shallow-rooted plant species. This shift supports that micro-landscape variability in the exchangeable base cation reserve with soil depth represents a key source of readily available nutrients for both shallow- and deep-rooted plant species upon permafrost thaw. This study highlights a key change in plant nutrient source to consider upon thaw. This finding lies beyond the common view that nutrient release at the permafrost thaw front preferentially benefits deep-rooted plant species.