To expand the newly developed ARM glasses as reference materials for in situ microanalysis of isotope ratios and iron oxidation state by a variety of techniques such as SIMS, LA‐MC‐ICP‐MS and EPMA, we report Li‐B‐Si‐O‐Mg‐Sr‐Nd‐Hf‐Pb isotope data and Fe 2+ /ΣFe ratios for these glasses. The data were mainly obtained by TIMS, MC‐ICP‐MS, IR‐MS and wet‐chemistry colorimetric techniques. The quality of these data was cross‐checked by comparing different techniques or by comparing the results from different laboratories using the same technique. All three glasses appear to be homogeneous with respect to the investigated isotope ratios (except for B in ARM‐3) and Fe 2+ /ΣFe ratios at the scale of sampling volume and level of the analytical precision of each technique. The homogeneity of Li‐B‐O‐Nd‐Pb isotope ratios at the microscale (30–120 μm) was estimated using LA‐MC‐ICP‐MS and SIMS techniques. We also present new EPMA major element data obtained using three different instruments for the glasses. The determination of reference values for the major elements and their uncertainties at the 95% confidence level closely followed ISO guidelines and the Certification Protocol of the International Association of Geoanalysts. The ARM glasses may be particularly useful as reference materials for in situ isotope ratio analysis.
A new natural chalcopyrite reference material TC1725 is prepared for in situ Cu isotope measurement by femtosecond laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (fsLA‐MC‐ICP‐MS). Detailed textural examination and major element determination suggest the TC1725 chalcopyrite grains have no growth rim or zoning. The chalcopyrite grain is homogeneous with respect to Cu isotopes based on a large number of measurements performed by bulk solution nebuliser (SN)‐MC‐ICP‐MS, single‐grain SN‐MC‐ICP‐MS and fsLA‐MC‐ICP‐MS. The traditional bulk isotope analyses by SN‐MC‐ICP‐MS yielded a mean δ 65 Cu value of −0.06 ± 0.03‰ (2 s , n = 132). Randomly selected single chalcopyrite grain of TC1725 determined by SN‐MC‐ICP‐MS without column chromatography gave a mean δ 65 Cu value of −0.06 ± 0.04‰ (2 s , n = 188). The intermediate measurement precision for four measurement sessions was better than 0.04‰ (2 s ), suggesting TC1725 chalcopyrite is suitable as a microanalysis reference material for Cu isotope measurement. The mean δ 65 Cu value determined by fsLA‐MC‐ICP‐MS analyses on different individual chalcopyrite mounts and strips was −0.06 ± 0.03‰ (2 s , n = 393), consistent with the bulk isotope composition within uncertainty. The recommended mean δ 65 Cu value for this chalcopyrite reference material is −0.06 ± 0.03‰ (2 s , n = 132) as determined by bulk SN‐MC‐ICP‐MS.
The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks (greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile‐brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids (Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple‐collector inductively coupled plasma mass spectrometry (MC–ICP–MS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore‐forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks (Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions. Zartman's plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the Δβ‐Δγ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction‐zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ 34 S values of the sulfides range from 3.90 to 8.50‰ (average 6.80‰), with a pronounced mode at 5.00‰–8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the ore‐forming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.
ARTICLE I NFO Early Cretaceous alkaline picrites and high-magnesium basalts from the North China craton provide evidence for recycling of continental lithosphere by density foundering. Both the picrites and basalts contain xenocrystic olivines with high Fo92-93 and low CaO (b0.10%), consistent with the lavas' derivation from, or interaction with Archean mantle lithosphere. Most importantly, both the picritic and basaltic lavas contain unusual, reversely zoned clinopyroxene phenocrysts whose cores have low MgO, high Na2O (up to 2.4 wt.%, or 17.3 mol% Jd), and frequently contain ilmenite exsolution lamellae, consistent with their crystallization from an eclogite-derived melt (tonalite or trondhjemite). In contrast, the clinopyroxene exteriors have low Na2 O( b0.92 wt.%, or b6.5 mol% Jd) and are lamellae-free, suggesting crystallization from a mantle-derived melt (picrite or basalt). Both the cores and exteriors have high Al2O3 contents (up to 6.9 wt.%). These features reflect crystallization of the cpx from an aluminous melt at mantle depths, with the cores forming at a significantly greater depth (≥2.5 GPa) than the surrounding cpx (≥1.5 GPa). Calculated primary melt compositions further constrain the magmas' formation at 3-4 GPa, in the presence of garnet. The unusually low CaO, high Ni/MgO and low 100Mn/Fe of primary melts indicate derivation of both the picritic and basaltic lavas from pyroxenite sources containing limited or no olivine. High Sr/Y, LaN/YbN and Th/U and low Lu/Hf, together with radiogenic initial 87 Sr/ 86 Sr and 187 Os/ 188 Os ratios and negative eNd values implicate contributions from melts derived from foundered eclogitic lower continental crust. Modelling suggests that the basalt source region contained a variable proportion (30-40%) of eclogite-derived component whereas the source of the picrites, on average, likely contained a generally higher proportion (60-70%) of a different eclogite-derived component. Collectively, these results suggest that both the basaltic and picritic lavas originated by partial melting of Archean lithospheric mantle that was variably hybridised by melts derived from foundered lower crustal eclogite. Together with previous studies, these findings provide new evidence that thinning of the North China craton was caused by the removal of the lower lithosphere (mantle and lower crust). Recycling and melting of eclogitic lower crust may contribute more to mantle heterogeneity than has previously been recognized.
Three zircon synthesis techniques (synthesis, high-temperature and high-pressure sintering and fast hot-pressing sintering) for the preparation of reference materials for Hf isotope analysis of zircon by LA-MC-ICP-MS were compared.
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