A novel lithium metaborate fusion technique using a homemade fusion furnace and graphite crucibles was developed for the determination of major and trace elements in silicate rocks using LA-ICP-MS.

Subduction-driven recycling of crustal materials plays a substantial role in the generation of geochemical and lithological heterogeneities in the Earth’s mantle. Because the distinct compositions and/or mineral-specific equilibrium isotopic fractionation effects are present in eclogitized crustal materials, stable isotopes of major elements that exert significant impacts on geochemical and petrologic properties of the mantle may serve as powerful tracers for linking the geochemical anomaly to lithological heterogeneity within the Earth’s interior. Here we present high-precision Ca isotope data, combined with previously reported Mg-Fe isotopes, for a suite of intraplate basalts with a large contribution from recycled crustal material in their mantle sources. The δ44/40Ca in these potassic basalts are consistently lower (0.66–0.78 ‰) than those of mid-ocean ridge basalt (MORBs; 0.85 ± 0.09 ‰), with an average of 0.72 ± 0.09 ‰. The co-variations of major elements with radiogenic isotopes (e.g., MgO-ɛNd) reflect the mixing of two distinct endmembers, one of which is the low-MgO primitive melts and the other is the lithospheric mantle. The low-MgO, SiO2-rich primitive melts are characterized by low CaO/Al2O3 (<0.4) and high Dy/Yb (>5). Remarkably, the primitive melts exhibit low δ44/40Ca (ca. 0.70 ‰)-δ26Mg (ca. –0.60 ‰), and elevated δ57Fe (ca. 0.30 ‰) relative to MORBs. These features are consistent with their origin as partial melts of eclogitic crustal materials. During ascending to the surface, these melts reacted with the surrounding lithospheric peridotite. This process resulted in a noticeable shift of the Mg-Fe isotopes towards the typical mantle values but very limited δ44/40Ca modification. These results suggest that Ca isotopes largely hold the signature of primary melts and are a promising tracer of eclogite in the mantle source of basalts. We further show that the combined isotopes of Ca-Mg-Fe, which are stoichiometrically incorporated into mantle minerals, offer substantial potential to establish the links between lithological and geochemical heterogeneity in the mantle.

Magma plumbing systems exert strong controls on the formation and evolution of the oceanic crust during crust accretion. However, plumbing system dynamics based largely on mid-ocean ridge basalts (MORBs) are extremely difficult to constrain because the MORBs are aggregated melts and original information may have been blurred. Copper isotopic compositions of lower crustal gabbroic cumulates effectively archive early-stage histories because sulfides constitute the dominant Cu budget of gabbroic cumulates and are largely isolated from subsequent magma filtering processes. Here, we present Cu isotopes of a suite of gabbroic cumulates from the ultraslow-spreading Southwest Indian Ridge (Hole U1473A), and MORBs from the South Mid-Atlantic Ridge and East Pacific Rise. The delta 65Cu of the MORBs from this study (+0.04 %o to +0.19 %o) match those of previous MORB analyses, indicating uniform delta 65Cu at various spreading rates. In contrast, the delta 65Cu of gabbroic rocks vary significantly (-1.14 %o to 0.87 %o), exceeding by far the range known for peridotites. The Cu budget of these gabbroic rocks is hosted in sulfides and the mantle-like S isotopic compositions of sulfides indicate their origin of igneous processes. These results thus suggest that magma accumulation and sulfide segregation would lead to notable Cu isotopic fractionation in the lower oceanic crust. We propose that repeated recharging of primitive melts and efficient mixing of melts within the plumbing system can buffer the removal of early 63Cu-rich sulfides from sulfide-saturated MORBs. The discrepancy in delta 65Cu between lower oceanic crust and MORBs is a natural consequence of continuous replenishment that occurs concurrently with melt-rock interaction, mixing, crystallization and extraction, irrespective of the oceanic settings. The consistent delta 65Cu in MORBs (0.09 +/- 0.08 %o) and komatiites (0.06 +/- 0.06 %o) further indicates that their Cu isotopes reflect the mean mantle source composition, providing a robust delta 65Cu for bulk silicate Earth (BSE) of 0.08 +/- 0.08 %o (2sd). Accordingly, we propose that in open sub-ridge plumbing systems, other incompatible element isotopes and ratios of elements with similar incompatibility in MORBs as Cu isotopes suggest, could also represent mean mantle source compositions.

Iron isotope studies on ocean island basalts (OIBs) and mid-ocean ridge basalts (MORBs) have disclosed the contribution of pyroxenite lithologies in the generation of basaltic magmas. Whether Fe isotopic compositions of continental intraplate basalts can be applied to trace lithological heterogeneity within the mantle source regions remains poorly investigated. To explore the systematics of stable Fe isotopes as a potential probe of lithological heterogeneity in the source of continental intraplate basalts, we present twenty-four Fe isotope data on a suite of well-characterized Cenozoic basalts from SE China. The samples show a large range of Fe isotope values (856Fe = +0.09%o to +0.20%o), which correlate with SiO2, CaO/Al2O3, Ti/Eu, Hf/Hf*, Zr/Nb, Dy/Yb, La/Yb, Nb/Y, K/La, Sr/Ce, 866Zn and estimated equilibrium pressures. The samples with the highest 856Fe values represent early -stage low-silica basalts with moderately enriched Sr-Nd isotope ratios and high 866Zn values, while the late -stage high-silica basalts display a broad 856Fe decrease with increasing 87Sr/86Sr and with decreasing eNd and 866Zn. We demonstrate that the heaviest Fe isotope signatures cannot be derived from a pure peridotite source and require a pyroxenite component in the source. Combined with other geochemical proxies, we show that the heaviest basalt compositions are consistent with low-degree melts produced by the adiabatic decompression of a carbonated pyroxenite-bearing asthenospheric mantle. Mixing of these hybrid melts with melt produced from in -situ melting of the subduction-modified sub-continental lithospheric mantle (SCLM) reproduces the Fe-isotope variability of the late-stage basalts. Our results demonstrate the significance of lithological heterogeneity in the mantle source of continental intraplate basalts and highlight the subsequent imprint of mantle lithosphere in the evolution of their Fe isotope compositions. Finally, this study exemplifies the potential of the Fe-Zn stable isotope pair for mantle geochemistry; coupled with traditional radiogenic isotopes and major and trace element concentrations, they formed an efficient tool to trace the nature and contribution of the mantle source components in the formation of intraplate basalts.

Iron oxide minerals, such as hematite and magnetite, are commonly found in a wide range of geological environments. Their Fe isotopic composition acts as a potent geochemical tracer, finding applications across various realms of Earth sciences. However, natural iron oxide minerals often have a high Cr content up to percentile levels, necessitating correction of isobaric interference caused by 54Cr+ on 54Fe+ to ensure accurate and precise in situ Fe isotopic compositions. In this study, a pure chromium metal with homogeneous isotopic compositions was examined within the analysis sequence to obtain the fractionation factor of Cr (βCr) for isobaric interference correction. A femtosecond laser ablation system combined with wet plasma conditions was used to decrease the matrix effect. We synthesized a series of magnetite and hematite samples with simple matrix as well as natural magnetite samples with complex matrix to evaluate the feasibility of Cr interference correction. By employing our proposed correction method, the deviation caused by the isobaric interference of 54Cr+ was effectively eliminated. The corrected δ56Fe values for hematite and magnetite samples, even with a Cr/Fe ratio of as high as 1.27, exhibited good agreement with the reference values within the long-term reproducibility uncertainty of 0.10‰. These results indicate the robustness of Cr interference correction in obtaining accurate Fe isotopic compositions of Cr-rich iron oxides.

Iron‐titanium oxides such as ilmenite (FeTiO 3 ), titanite (CaTiSiO 5 ) and perovskite (CaTiO 3 ) are the common Ti‐rich mineral phases crystallised during magmatic and metamorphic processes on Earth. Depending on magma types or conditions of phase equilibria, formation of these Ti‐rich minerals can result in Ti isotopic fractionation in the range of ‐1.52‰ to +2.90‰ on δ 49 Ti OL‐Ti (i.e., the per mil difference of 49 Ti/ 47 Ti ratio relative to the OL‐Ti reference material), making the Ti isotope ratios of these minerals potential tracers for conditions of magmatism and metamorphism. Due to their resistance to aqueous alteration, these Ti‐rich accessory minerals are also commonly present as pristine, detrital phases in sedimentary rocks, which offer an opportunity to study the evolution of magmatism and metamorphism throughout the Earth's geological history. Here we have developed a novel technique for in situ Ti isotopic measurement in ilmenite, titanite and perovskite using femtosecond laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (fs‐LA‐MC‐ICP‐MS) under wet plasma conditions. Samples were ablated with different laser spot sizes (15–50 μm) and different laser energy densities (0.6–4.2 J cm ‐2 ) to obtain adequate Ti signal intensity at a fixed laser repetition rate of 2 Hz. When 49 Ti signal intensity of samples ranged from 0.3 to 3.7 V, no significant signal‐dependent Ti isotopic fractionation was observed under wet plasma conditions. Repeated measurements on twelve Ti‐rich minerals using different analytical protocols provided comparable δ 49 Ti OL‐Ti values within uncertainties, confirming the accuracy of the proposed fs‐LA‐MC‐ICP‐MS method. With one exception (i.e., RUS1), all analysed minerals are homogeneous in their Ti isotopic compositions between individual chips with an intermediate precision of ±0.13‰ to ±0.17‰ (2 s ) on δ 49 Ti OL‐Ti . Collectively, these minerals record a significant δ 49 Ti OL‐Ti variation ranging from ‐0.46‰ to +2.12‰. These warrant the suitability of these materials as Ti isotopic reference materials for in situ Ti isotopic measurement.

Dolomite reference material is prepared by pressureless sintering, and the powder particle size and sintering temperature are key factors for isotope homogeneity. No in situ isotope fractionation between synthetic samples and natural dolomites.

Silver (Ag) is a trace metal element in geological rocks and accurate determination of its abundance is very challenging given significant oxide and hydroxide interferences from Zr, Nb, Mo, and Y. Here, we developed a valid method based on inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS), in which NH3 was used as the reaction gas, to determine the Ag content in geological samples. The additional quadrupole analyzer located in front of the collision/reaction cell ensured a simple and controllable reaction in the cell. The first quadrupole (Q1) was set to m/z 107 and 109 to allow Ag+ and its interferences to enter the reaction cell. Ag+ partially reacted with NH3, forming Ag+ and Ag(NH3)(2)(+) as the main products; while the major interferences, ZrO+ and NbO+, reacted strongly and were converted to ZrO(NH3)(4)(+), ZrO(NH3)(5)(+), and NbO(NH(NH3)(3))(+), respectively, and thus no longer affected the measurement of Ag. Consequently, the Ag signals could be detected by both "on-mass" and "mass-shift" methods, where the m/z of Q1-Q2 were 107-107, 109-109 and 107-141, 109-143, respectively. Under the optimized NH3 flow rate (3.5 ml min(-1)), the interference levels of the matrix solution (0.3 mu g ml(-1) Zr and Mo, 0.2 mu g ml(-1) Zn, 0.1 mu g ml-1 Y and Nb, and 0.05 mu g ml(-1) Ga) in four Q1-Q2 mass pairs were negligible and comparable to background signals, and the limits of detection of geological samples were <0.53 ng g(-1). The Ag content of 19 geological reference materials was reported using the proposed ICP-MS/MS method, and the results were consistent with isotope dilution-ICP-MS values. Thus, the proposed method has great potential for the accurate, direct, and high-throughput measurement of Ag in geological samples.

Iron (Fe) isotopic composition is a useful geochemical tracer. Because of the high spatial resolution and simple sample preparation, laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is becoming increasingly popular for Fe isotopic analysis. However, the matrix effect is a challenge for the LA-MC-ICP-MS technique, and external standardization using a matrix-matched reference material is essential. Ilmenite is a common and significant Fe-rich mineral phase in terrestrial and lunar rock, which has variable Cr contents. Herein, four natural ilmenites (RUS10, CZE2, SIN1, and GER16) with Cr contents of 15-2420 mu g g(-1) were characterized for Fe isotopic compositions by both solution nebulization (SN) MC-ICP-MS and LA-MC-ICP-MS. The protocol of isobaric interference correction (Cr-54 on Fe-54) was optimized for in situ Fe isotopic analysis. The precision and accuracy of ns-LA-MCICP-MS measurements are comparable to those of fs-LA-MC-ICP-MS for Fe isotopic analysis. The individual spot internal precision (2SE) of delta Fe-56 was consistently better than 0.08% at Fe-56 signal intensity >= 10 V, and the analytical external precisions (2sd) of delta Fe-56 were in a range from +/- 0.10% to +/- 0.16% in multiple ilmenite fragments by both ns-LA-MC-ICP-MS and fsLA-MC-ICP-MS. The delta Fe-56(IRMM- 014) values of four ilmenites (RUS10, CZE2, SIN1, and GER16) were 0.22 +/- 0.14% (2sd, n=165), 0.14 +/- 0.14% (n=123), 0.00 +/- 0.14% (n=110) and 0.00 +/- 0.14% (n=164), respectively. The four ilmenites, found to be homogeneous in Fe isotopic compositions, are proposed as candidate reference materials to be shared with peers. These ilmenites with different Cr contents and positive Fe isotopic values would certainly be helpful as reference materials for the scientific community.

Plagioclase crystallization is a common process for evolving mafic magmas. Theoretical calculation predicts limited Ca isotopic fractionation of plagioclase from parental magmas (Delta Ca-44/40 < 0.1 %), while natural samples display variable Ca isotopic variation between plagioclase and co-existing matrix (from +0.1 to 1.4%), pointing to the complexity of natural processes. In order to better understand the plagioclase-induced Ca isotope variation during magma evolution, we measured the delta Ca-44/40 of eight pairs of basaltic matrix and giant plagioclase phenocrysts (several centimeters long) in basalts from Emeishan large igneous province, SW China. Most samples are from a thick basalt flow profile (YN, over 200 m in the Daqiao section) and two from another section (ZJ, basaltic layer in Panzhihua intrusion). The plagioclase phenocrysts in two fresh YN samples show chemical as well as Ca isotopic equilibrium (Delta(44/40)CaPl- matrix = 0.01 +/- 0.02% and 0.07 +/- 0.07%, respectively) with their basaltic matrix. Meanwhile, detectable Delta(44/40)CaPl(-matrix) ( 0.13 +/- 0.12% and 0.21 +/- 0.10%, respectively) are observed from the ZJ layered cumulate samples in which plagioclase phenocrysts are captured crystals from the deeper magma chamber. Many plagioclases of the other four YN samples experienced albitization process caused by hydrothermal fluid. They remain the pseudomorphism of plagioclase but show significantly lower CaO content, lower delta Ca-44/40 values (0.09-0.34%) and higher Sr-87/Sr-86 ratio relative to their surrounding matrix (e.g.Delta(44/40)CaPl(- matrix) = -0.29 to -0.57%). The new results thus confirm the negligible equilibrium Ca isotope fractionation between differentiated plagioclases and basaltic melts; however, considerable Ca isotope variation could be caused by complex magma mixing in magma chamber and secondary fluidinduced disturbance. On the other hand, the delta Ca-44/40 value of matrix (0.66 +/- 0.14%, 2sd) from all samples show limited variation regardless of the proportion of plagioclase grains and the degree of secondary effect. Therefore, the matrix could well represent the delta Ca-44/40 of Emeishan high-Ti samples, which is lighter than that of MORBs by similar to 0.2%. The light delta Ca-44/40 of Emeishan basalts reflect the influence of partial melting of garnet-bearing source and slight lower delta Ca-44/40 (0.8 0.9%) of its source region caused by mantle metasomatism at the same time.

Ca isotope geochemistry has great potential for improving our understanding of magmatic systems and for tracing the deep Earth carbon cycle. There are still many open questions, however, regarding the proper application of this relatively novel proxy to the study of mantle-derived magmas, including (i) the possible effects of pressure on mineral-melt Ca isotope fractionation factors, and (ii) the potential for Ca isotopes to be used as tracers of recycled marine carbonates in mantle-derived magmas. Kimberlites are mantle-derived melts that are highly enriched in CO2 and are the deepest-sourced mag-mas (>200 km depth) known to erupt at Earth's surface, providing an excellent opportunity to explore these questions. We present Ca isotope data combined with detailed petrographic observations, bulk -carbonate C-O isotope data, and bulk-rock major element analyses, for a suite of 23 well-characterized kimberlite samples from their type-locality (Kimberley, South Africa). These kimberlites have abundant previous evidence for recycled surface materials in their mantle source, including low S isotope and mod-erately radiogenic Sr isotope compositions, yet display only limited variations in their Ca isotope compo-sitions (844CaBSE of-0.08%degrees to-0.27%degrees), with an average of-0.17 +/- 0.02%degrees (2SE, n = 21). This composition is indistinguishable from average carbonatites [-0.19 +/- 0.03%degrees (2SE, n = 106)] and OIB from recent studies [-0.16 +/- 0.01%degrees (2SE, n = 41)], and slightly lower than average MORB [-0.11 +/- 0.02%degrees (2SE, n = 31)]. Although our samples display a wide range of emplacement styles, alteration conditions, extents of mag-matic differentiation, and degrees of mantle-cargo entrainment (i.e., xenocryst accumulation), we find no correlations between Ca isotopes and any of these factors. Instead, we find that low-degree partial melt-ing of the likely kimberlite source lithology (i.e., carbon-bearing garnet lherzolite) yields modelled melt 844CaBSE values ranging between-0.12%degrees and-0.16%degrees (at 1400-1500 degrees C), in agreement with the mea-sured Ca isotope compositions of the Kimberley kimberlites. This observation, and the lack of heavy car-bon isotope signatures in the examined samples, indicates that kimberlites do not require subducted carbonates in their mantle sources, despite their very high CO2 contents. Although several recent studies have suggested that equilibrium mineral-melt Ca isotope fractionation factors (e.g., 1000lnagrt-melt) could be significantly different at higher pressures (i.e., due to pressure-induced changes in CaAO bond lengths and coordinations), our models successfully reproduce the kimberlite data using pressure-independent predictions for mineral-melt fractionations. It remains possible, however, that differences in isotopic frac-tionation due to the peculiar composition of kimberlite melts (e.g., high CO2, low SiO2) are effectively can-celled out by competing pressure effects, and future work independently targeting these factors will be especially important for our understanding of Ca isotope fractionation in mantle-derived melts and the Ca isotope systematics of Earth's mantle.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Recycling of upper crustal sediments through slab subduction contributes to sub‐continental lithospheric refertilization and heterogeneity. However, the nature of recycled upper crustal components is unclear and direct evidence for sediment melt activity in the sub‐continental lithosphere is lacking. Here, we integrate major and trace elements, zircon U‐Pb dating, Sr‐Nd‐Zn‐Fe isotopic compositions of clinopyroxenites (crust‐mantle boundary) and a “glassy” xenolith from the North China Craton to relate their petrogenesis to the potential recycling of upper continental crust and provide direct insight into the sediment melt‐rock interaction. The clinopyroxenites have relatively uniform δ 56 Fe values (the permil deviation of the 56 Fe/ 54 Fe ratio from the IRMM014; −0.05‰–0.07‰, except for one outlier) and are not affected by melt metasomatism. The clinopyroxenites have highly variable whole‐rock δ 66 Zn values (the permil deviation of the 66 Zn/ 64 Zn ratio from the JMC‐Lyon standard) between 0.04‰ and 0.46‰, that closely correlate with Rb/La, K/U, Ba/Th, and Th/Nb ratios, and generate arrays that trend toward a composition similar to the “glassy” xenolith. The “glassy” xenolith has a high δ 66 Zn value (0.43‰ ± 0.05‰, 2SD) and a significantly low 143 Nd/ 144 Nd ratio (0.510991). This evidence implies that the “glassy” xenolith may represent a quenched sediment melt formed by the melting of carbonate‐bearing terrigenous sediments that may also be responsible for the metasomatism of clinopyroxenite xenoliths. The geochemical evidence from the “glassy” and clinopyroxenite xenoliths provides a direct evidence for the activity of sediment melt with upper continental crust components in the sub‐continental lithosphere.

Lower crustal sulfide-bearing cumulates beneath the convergent plate margins represent a major copper reservoir. However, how Cu is mobilized and migrated in the lower crust is still a matter of debate. Here, we analyzed the Cu elemental and isotopic compositions of well-characterized lower crustal xenoliths from the north margin of the North China Craton to decode Cu mobilization in the lower continental crust beneath cratonic margins. The mafic lower crustal rocks have experienced varying degrees of sulfide accumulation, with Cu contents ranging from 15 to 112 ppm. The majority of lower crustal xenoliths have variable and generally low (compared to the Bulk Silicate Earth) delta Cu-65 (the permil deviation of the Cu-65/Cu-63 ratio from the NIST 976 standard) values ranging from-3.17 parts per thousand to 0.13 parts per thousand (n = 24). Many intragranular and interstitial sulfide grains in these lower crustal xenoliths were partially dissolved and oxidized along the mineral fractures and boundaries. Oxidative dissolution of sulfide will preferentially release Cu-65 into the liquids, leaving the residual sulfides enriched in the light isotope, implying that oxidized melt-rock interactions could account for the light Cu isotopic compositions of the lower crustal xenoliths. Sulfide accumulation and oxidative dissolution are responsible for the enrichment, mobilization, and transfer of Cu in the lower continental crust beneath cratonic margins. (C) 2022 Elsevier Ltd. All reserved.

High-precision and accurate Fe isotopic analyses are essential for various geological processes.In this study, Fe isotopic measurements were optimized on a large-geometry, high-resolution Nu Plasma 1700 MC-ICP-MS instrument, which can distinguish Ar-related interferences completely as opposed to other general-sized MC-ICP-MS instruments.Under the conditions of high mass resolution, complete separation of Ar-related interference can be achieved.We evaluated the type and intensity of all Ar-related interferences.The effects of the acid molarity, concentration mismatch, residual HCl, and matrix elements were also evaluated.The results demonstrate that the molarity of the acid, residual HCl, and Cr significantly affected the precision of the Fe isotopic measurements.Fe was purified by one-step column anion-exchange separation using the anion resin AG-MP-1M.The long-term external precisions of δ 56 Fe and δ 57 Fe were greater than ± 0.03‰ (2SD) and ± 0.06‰ (2SD), respectively.The Fe isotopic compositions of the five geological reference materials measured in this study agreed with previously published data, within uncertainties.

A combination of ultra-fine sulfide powders and a PAS technique to synthesize pyrite and chalcopyrite reference materials for in situ iron and sulfur isotope analysis.

The Triassic-Jurassic boundary is one of the most important geological boundaries in the Earth's evolutionary history. Previous paleoclimate studies focused primarily on Tethys realm at low and middle latitudes, while the northern hemisphere has yet to be studied. Here, we report Mg-Zn-Cu isotopic data for a continuous terrestrial sedimentary section in the southern margin of the Junggar Basin to constrain chemical weathering intensity and climatic change during this critical interval at high latitude. This section is enriched in heavy Mg isotopes with delta Mg-26 ranging from 0.08 parts per thousand to 0.43 parts per thousand. It displays a decreasing Zn isotopic composition with delta Zn-66 ranging from -0.05 parts per thousand to 0.24 parts per thousand, as well as limited Cu isotope fractionation (delta Cu-65 = -0.06 parts per thousand to 0.09 parts per thousand). These isotopic results, combined with major and trace elemental variations, suggest a reduced sedimentary environment and increasingly intensive chemical weathering across the boundary, responding to a warmer and more humid paleoclimate. Compared with other places located around Tethys, this regional climatic change in high latitude areas can be linked to known global climate change during this period. Our study provides new insights from high-latitude Asia to reconstruct the global pattern of climate change at the Triassic-Jurassic boundary.

Multi-isotope systems have shown great application potential in tracing geological and environmental processes. In order to obtain the isotopic composition of multiple elements of interest, the common protocol is to separate each element from the matrix by independent procedures, which has some limitations, including poor efficiency, being time-consuming, requiring large samples and being unsuitable for rare samples (e.g., meteorite, lunar soil and atmospheric aerosol samples). In this study, we present an integrated and optimized one-step method to separate Cu, Fe, Zn and Cd from complex matrix elements using the AG MP-1M anion exchange resin. By experimentally optimizing the resin volume, eluent concentration and eluent amount, these target elements can be effectively separated from the matrix elements, such as Cu separation from Ti and Co, Zn separation from Fe and Cd, and Cd separation from Sn. The recoveries of Cu, Fe, Zn and Cd were 100.1 ± 0.8% (2SD, n = 3), 99.8 ± 0.7% (2SD, n = 3), 100 ± 0.8% (2SD, n = 3) and 99 ± 1% (2SD, n = 3), respectively. Moreover, the resolution (R) between the elements of interest and interfering elements was in the range of 1.8-28.1. The process blanks of Cu, Fe, Zn and Cd were 1-1.6 ng, 62-70 ng, 2.1-3 ng and 66-74 pg, respectively. The obtained isotope ratios for the standard reference materials agreed well with the published values. Meanwhile, we have reported the Cu, Fe and Zn isotope ratios of six soil and sediment standard reference materials, namely NIST 2711a, GSS-1, GSD-5a, GSD-7a, GSD-12 and GSD-23, for the first time. These new data can be used for the intercalibration and quality control of soils and sediments in other laboratories. The one-step separation of Cu, Fe, Zn and Cd shows obvious economic and efficiency advantages, making it suitable for the simultaneous separation of multiple elements of interest in geological samples.

Ocean island basalts (OIBs) with Zn isotopic ratios higher than the normal mantle (delta Zn-66 = 0.17 +/- 0.08%) or mid-ocean ridge basalts (MORBs; delta Zn-66 = 0.27 +/- 0.06%) generally also have an enriched Sr-Nd isotopic signature, suggesting carbonate-bearing eclogites, whose protolith is inferred to be subducting altered oceanic crust, in their mantle source. On the contrary, continental intraplate basalts with high delta Zn-66 usually show depleted Sr-Nd isotopic signatures (i.e., decoupled Zn-Sr-Nd isotopic composition). To elucidate the origin of the decoupled Zn-Sr-Nd isotopic composition in continental intra-plate basalts, we report the discovery of both coupled and decoupled Zn-Sr-Nd isotopic data for a suite of Cenozoic continental intraplate basalts from the Zhejiang province, Southeast China. These basalts display clear spatial and temporal geochemical variations, with early-stage inland low-silica samples presenting moderately enriched Sr-Nd isotopic signatures and high delta Zn-66 (coupled Zn-Sr-Nd isotopic composition, similar to OIBs), and later-stage coastal high-silica samples that dis-play a pronounced 866Zn decrease with increasing SiO2 and Sr-87/Sr-86 and with decreasing alkali contents and Nd-143/Nd-144 (decoupled Zn-Sr-Nd isotopic composition). The early-stage basalts with coupled high Zn-Sr-Nd isotopic signatures are also more enriched in incompatible elements than any other basalts from eastern China reported so far. We explain the spatial and temporal geochemical variations of these basalts as the result of two main melting events: 1) the low-silica early-stage magmatism mostly occurs inland and results from high-pressure partial melting of a carbonated eclogite-bearing asthenospheric mantle. Because of the presence of a thick lithosphere limits the melting of the depleted mantle component, the signature of the Zn-Sr-Nd isotopically enriched, and more fusible carbonated eclogite is preserved. 2) At the later stage, magmatism mostly occurs on the coast where the subcontinental lithosphere is thinner. Hence, decompression melting progresses to shal-lower depth, resulting in an increase of the contribution from the depleted peridotite matrix and a dilution of the signal from the isotopically enriched fusible component. Further upwelling and in-situ melting at the base of the subduction-modified sub -continental lithospheric mantle (SCLM) explains both the decoupled Zn-Sr-Nd isotopic signature of the coastal basalts and their major and trace element variability. We further propose that decompression melting is driven by small-scale convection resulting from variations of lithospheric thickness. Our data highlight the importance of dynamic melting of carbonated eclogite-bearing asthenosphere and subsequent lithospheric melting in preservation and destruction of the coupled enriched Zn-Sr-Nd isotopic signature of carbonated eclogite component and generation of the apparent decoupled Zn-Sr-Nd isotopic signal commonly observed in continental intraplate basalts. (C) 2022 Elsevier Ltd. All rights reserved.

Using boron as a test analyte, laser ablation (LA) solution sampling multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is proposed and validated as a fast method for isotopic analysis in natural liquids and digested samples without any prior purification process. We demonstrated that the solution reference standard can be used as a bracketing standard for in situ δ11B analysis in solids. Based on a sensitivity enhancement of 8- to 9-fold, all testing solutions were diluted in a 5% (v/v) NH3·H2O instead of classical 2% (v/v) HNO3. With a discrete and minimal sample solvent loading by the LA sampling strategy, it produces nearly "dry" plasma conditions that tolerate the sample matrix remarkably. The memory effect, one of the most difficult challenges in boron analysis, was dramatically eliminated with only 15 s wash time; thus, each analysis took less than 100 s. No significant matrix effects were observed for varying 50-100% boron concentrations in the samples and varying 20-60% NH3·H2O matrix used for the dilution, as well as for samples doped with a 1/100 synthetic seawater matrix. The external precision of δ11B measurements in NIST 951a was ± 0.30‰ (2SD). Good agreement with the values described in literature studies was achieved for δ11B measurements in eight geological reference materials, with precisions between 0.4 and 0.7‰ (2SD), confirming the accuracy of the proposed method. The proposed method offers advantages of simple sample preparation, fast analysis, and little use of chemical reagents.

The Dongping gold deposit, located near the northern margin of the North China Craton, contains ore bodies spatially associated with the Devonian Shuiquangou syenite, Cretaceous Shangshuiquan granite, and Archean metamorphic rocks. Major and trace elements and S–Pb isotopes of pyrite from two stages of gold-quartz veins and wall rocks were used to constrain the composition of hydrothermal fluids and metal sources. Stage-1 (early) pyrites are euhedral to subhedral, medium- to coarse-grained, and have low gold contents. Py1a is homogeneous with few fractures, whereas Py1b, which occurs on the edges of Py1a, is porous and has higher metal contents. Stage-2 (late) pyrites are mostly anhedral to subhedral and have smaller grain sizes and higher gold contents than Stage 1. Py2a occurs with sulfide minerals such as galena and chalcopyrite, and Py2b is porous and has the highest gold content (up to 1839 ppm) and smallest grain size. All pyrite samples yield negative δ 34 S values (− 7.5 to − 3.5‰), reflecting oxidized conditions during mineralization. The ~ 2‰ decrease in δ 34 S values from Stage 1 (− 4.3‰, − 4.9‰) to Stage 2 (− 7.0‰, − 6.4‰) may reflect a change in the fluid source and/or an increase in f O 2 . The Pb isotope composition of Stage-1 pyrite is suggestive of a mantle source similar to that of the Shuiquangou syenite, whereas Stage-2 pyrite has more radiogenic Pb isotopic compositions suggestive of an Archean metamorphic source. Combined with previous studies, our trace element and isotopic results indicate that the two stages of pyrite had different sources, with Stage-2 pyrite being more strongly influenced by metasedimentary rocks. We propose that the early stage of low-grade gold mineralization was related to emplacement of the Devonian Shuiquangou syenite, whereas the late stage of high-grade gold mineralization was related to emplacement of the Cretaceous Shangshuiquan granite and leaching of gold from Archean metamorphic rocks.