A Pb-Ra-Th-U study of Klyuchevskoy and Bezymianny volcanoes, Kamchatka

Lavas from Klyuchevskoy and Bezymianny volcanoes, Kamchatka, appear to show a link between the extent of partial melting in their mantle source region and the subsequent degree of fractionation suffered by the magmas during passage through the crust. This fractionation may have occurred on timescales significantly less than 1000 years if observed ²²⁶Ra excesses largely reflect variable residual porosity in the source melting region. Unlike most arc lavas, those with the highest MgO contents and Ba/Th ratios have the lowest ²²⁶Ra excess. Forward models suggest that those portions of the source which had undergone the greatest addition of U by fluids from the subducting plate also underwent the greatest extents of partial melting at the highest residual porosity. At Kluchevskoy, a change from eruption of high-MgO to high-Al₂O₃ basaltic andesites around 1945 is reflected in an increase in size of ²²⁶Ra excess which seems to require a simultaneous decrease in residual porosity and suggests a rapid changes in the melting regime. The eruption of andesites at Bezyminanny, simultaneous with the eruption of basaltic andesites at Klyuchevskoy, further suggests that different degree melts produced at differing residual porosity can be formed and extracted from the melt region at the same time. Thus, the melting processes beneath Klyuchevskoy and Bezyminanny are demonstrably complex. They have clearly been influenced by both fluid addition from the subducting plate and extension and decompression beneath the Central Kamchatka Depression. Finally, the ²¹⁰Pb data are, with one or two exceptions, in equilibrium with ²²⁶Ra, suggesting that there was restricted relative magma-gas movement in this highly productive magmatic system.     

A petrological and geochemical study on time-series samples from Klyuchevskoy volcano,Kamchatka arc

To understand the generation and evolution of mafic magmas from Klyuchevskoy volcano in the Kamchatka arc, which is one of the most active arc volcanoes on Earth, a petrological and geochemical study was carried out on time-series samples from the volcano. The eruptive products show significant variations in their whole-rock compositions (52.0–55.5 wt.% SiO₂), and they have been divided into high-Mg basalts and high-Al andesites. In the high-Mg basalts, lower-K and higher-K primitive samples (>9 wt.% MgO) are present, and their petrological features indicate that they may represent primary or near-primary magmas. Slab-derived fluids that induced generation of the lower-K basaltic magmas were less enriched in melt component than those associated with the higher-K basaltic magmas, and the fluids are likely to have been released from the subducting slab at shallower levels for the lower-K basaltic magmas than for higher-K basaltic magmas. Analyses using multicomponent thermodynamics indicates that the lower-K primary magma was generated by ~13% melting of a source mantle with ~0.7 wt.% H₂O at 1245–1260?°C and ~1.9 GPa. During most of the evolution of the volcano, the lower-K basaltic magmas were dominant; the higher-K primitive magma first appeared in AD 1932. In AD 1937–1938, both the lower-K and higher-K primitive magmas erupted, which implies that the two types of primary magmas were present simultaneously and independently beneath the volcano. The higher-K basaltic magmas evolved progressively into high-Al andesite magmas in a magma chamber in the middle crust from AD 1932 to ~AD 1960. Since then, relatively primitive magma has been injected continuously into the magma chamber, which has resulted in the systematic increase of the MgO contents of erupted materials with ages from ~AD 1960 to present.     

Plagioclase zoning as an indicator of magma processes at Bezymianny Volcano,Kamchatka

Back-scattered electron (BSE)-derived zoning patterns of plagioclase phenocrysts are used to identify magma processes at Bezymianny Volcano, Kamchatka, based on the 2000–2007 sequence of eruptive products. The erupted magmas are two-pyroxene andesites, which last equilibrated at ~915°C temperature, 77–87 MPa pressure, and a water content of ~1.4 wt%. Textural and compositional zoning of individual plagioclase phenocrysts typically includes a repeated core-to-rim sequence of oscillatory zoning (An_50–60) truncated by a dissolution surface followed by an abrupt increase in An content (up to An₈₅), which then gradually decreases rimward. This zoning pattern is interpreted to be the result of frequent replenishments of the magma chamber which cause both thermal and chemical interaction between resident and recharge magmas. The outermost 70- to 150-μm-wide zoning patterns of plagioclase phenocrysts are composed of dissolution surface with a subsequent increase in An and Fe contents. Zoning patterns of the rims exhibit correlation among plagioclase phenocrysts within one eruption. Rims are interpreted as a result of crystallization of a batch of magma in the conduit after recharge event.     

高精度铅同位素比值MC-ICP-MS测试方法及岩石标样铅同位素组成

利用多接收电感耦合等离子体质谱仪（Neptune plus）建立了高精度铅同位素比值MC-ICP-MS测试方法。建立该方法的过程中,重点评估了加入的Tl标准溶液对铅同位素比值测试结果的影响,并最终确定Tl标准溶液的浓度为25 ng/mL,同时样品溶液Pb的浓度应该大于25 ng/mL（即Pb/Tl浓度比应大于1）。利用该方法对铅同位素标准物质SRM 981进行了长期监控（2020年7月—2021年6月）,测试结果为：206Pb/204Pb=16.9415±0.0010、207Pb/204Pb=15.4985±0.0009、208Pb/204Pb=36.7204±0.0023,与统计的文献报道值一致。长期监控的全流程空白均小于0.25 ng,能满足地质样品高精度铅同位素比值测试的需要。同时运用该方法,对4个元素含量标样（BCR-2、AGV-2、BHVO-2和BIR-1a）进行了铅同位素比值测试,测试结果与文献报道的测试结果和精度一致,表明建立的方法是准确、可靠的。     

Mantle components in Iceland and adjacent ridges investigated using double-spike Pb isotope ratios

High precision Sr-Nd isotope ratios together with Pb isotope ratios corrected for mass fractionation using a double spike are reported for an extensive suite of late Quaternary to Recent lavas of Iceland, the Kolbeinsey and Reykjanes Ridges, and a small number of basalts from further south on the Mid-Atlantic Ridge. Compared with global MORB, the Icelandic region is distinguished by having low ²⁰⁷Pb/²⁰⁴Pb for any given ²⁰⁶Pb/²⁰⁴Pb, expressed by negative Δ²⁰⁷Pb (−0.8 to −3.5) in all but four Icelandic samples. Most samples also have elevated ²⁰⁸Pb/²⁰⁴Pb (strongly positive Δ²⁰⁸Pb), which combined with their negative Δ²⁰⁷Pb is very unusual in MORB worldwide. The negative Δ²⁰⁷Pb is interpreted as a consequence of evolution in high-μ mantle sources for the last few hundred Ma. The region of negative Δ²⁰⁷Pb appears to correspond with the region of elevated ³He/⁴He, suggesting that both lithophile and volatile elements in melts from the whole region between 56 and 70°N are dominantly sourced in a plume that has incorporated recycled Palaeozoic ocean crust and unradiogenic He, probably from the deep mantle. At least four mantle components are recognized on Iceland, two with an enriched character, one depleted and one that shows some isotopic affinities to EM1 but is only sampled by highly incompatible-element-depleted lavas in this study. Within restricted areas of Iceland, these components contribute to local intermediate enriched and depleted components that display near binary mixing systematics. The major depleted Icelandic component is clearly distinct in Pb isotopes from worldwide MORB, but resembles the depleted mantle source supplying the bulk of the melt to the Kolbeinsey and southern Reykjanes Ridges. However, an additional depleted mantle source is tapped by the northern Reykjanes Ridge, which with very negative Δ²⁰⁷Pb and less positive Δ²⁰⁸Pb is distinct from all Icelandic compositions. These components must mostly mix at mantle depths because a uniform mixture of three Icelandic components is advected southward along the Reykjanes Ridge.Despite strong covariation with isotope ratios, incompatible trace element ratios of Icelandic magmas cannot be representative of old mantle sources. The observed parent-daughter ratios in depleted and enriched Icelandic lavas would yield homogeneous Sr, Nd, Hf and ²⁰⁶Pb isotope signatures ∼170 Ma ago if present in their sources. The heterogeneity in ²⁰⁷Pb/²⁰⁴Pb is not however significantly reduced at 170 Ma, and the negative present day Δ²⁰⁷Pb cannot be supported by the low μ observed in depleted lavas from Iceland or the adjacent ridges. Since μ is higher in melts than in their sources, it follows that all the depleted sources must be residues from <170 Ma partial melting events. These are thought to have strongly affected most incompatible trace element ratios.     

Ore-forming timing of polymetallic-fluorite low temperature veins from Central Pyrenees: A Pb,Nd and Sr isotope perspective

Vein fluorite deposits (Tebarray, Lanuza, Bielsa-Parzán, Bizielle and Yenefrito) as well as one MVT-style fluorite mineralization (Portalet) in the Central Pyrenees are the focus in this contribution. These deposits are made up of fluorite, barite, base metal sulphides, calcite, and quartz and are hosted in sedimentary rocks and granites of Palaeozoic age. Generally, these mineral occurrences, typically associated with Late Palaeozoic steeply dipping faults are similar with respect to geologic setting, mineralogy and geochemical trends to other fluorite and base metal veins located in the Central Pyrenees. Veins occurring along such faults most likely represent channelways used by mineralizing solutions that were expelled from the basement. Previous work argued for genetic processes involving circulation of mineralising fluids during the Triassic–Lower Cretaceous period, which is often considered to represent a period of heat, fluid, and mass transfers related to rifting events in the western European basins, which is related to the opening of the Atlantic.A major goal of this study was to decipher the timing of fluid flow and ore formation on the basis of Nd–Sm dating of fluorite sampled from a number of deposits sharing a similar geological framework. No precise age(s) could be obtained due to a scatter in data, but results from the Portalet MVT-style deposit point to a mid-Triassic age (around 220 Ma) for this mineralization. The model that best explains the diagenetic stratabound mineralization at Portalet is gravity-driven fluid flow involving basinal brines during a rifting stage. Indeed, the formation of horst and graben structures during Early Alpine extensional tectonics favoured the infiltration of meteoric water into uplifted blocks, followed by fluid migration through the deeper parts of the basins whereby heat and dissolved components were acquired. This model also explains diagenetic changes recorded in the host limestone at Portalet. Also, overall Pb, Sr and Nd isotopic ratios measured in galena and fluorite suggest that differences in host rock and in the lithology of the basement seem to have exerted control on the chemistry of mineralizing fluids providing each deposit with distinctive characteristics.     

Petrography and stable isotope ratios from Archaean stromatolites,Mushandike Formation,Zimbabwe

The Mushandike Sanctuary, near Masvingo (Fort Victoria), Zimbabwe, contains well-preserved, but metamorphosed stromatolitic limestones of Archaean age. Despite the metamorphism, textural preservation is excellent to a scale as fine as c. 100–200μ. Cores recovered from the stromatolites have $\text{δ}{}^{18}\text{O = ?15‰}$ (PDB), approximately, and δ¹³C = 0.0 to 0.5‰ (PDB), in less weathered samples. The results are consistent with a metamorphic history involving volatile loss at 200°C or less, from an original source rock which may have been isotopically similar to the Cheshire stromatolites, Belingwe.     

Deciphering formation processes of banded iron formations from the Transvaal and the Hamersley successions by combined Si and Fe isotope analysis using UV femtosecond laser ablation

To investigate the genesis of BIFs, we have determined the Fe and Si isotope composition of coexisting mineral phases in samples from the ∼2.5 billion year old Kuruman Iron Formation (Transvaal Supergroup, South Africa) and Dales Gorges Member of the Brockman Iron Formation (Hamersley Group, Australia) by UV femtosecond laser ablation coupled to a MC-ICP-MS. Chert yields a total range of δ³⁰Si between −1.3‰ and −0.8‰, but the Si isotope compositions are uniform in each core section examined. This uniformity suggests that Si precipitated from well-mixed seawater far removed from its sources such as hydrothermal vents or continental drainage. The Fe isotope composition of Fe-bearing mineral phases is much more heterogeneous compared to Si with δ⁵⁶Fe values of −2.2‰ to 0‰. This heterogeneity is likely due to variable degrees of partial Fe(II) oxidation in surface waters, precipitation of different mineral phases and post-depositional Fe redistribution. Magnetite exhibits negative δ⁵⁶Fe values, which can be attributed to a variety of diagenetic pathways: the light Fe isotope composition was inherited from the Fe(III) precursor, heavy Fe(II) was lost by abiotic reduction of the Fe(III) precursor or light Fe(II) was gained from external fluids. Micrometer-scale heterogeneities of δ⁵⁶Fe in Fe oxides are attributed to variable degrees of Fe(II) oxidation or to isotope exchange upon Fe(II) adsorption within the water column and to Fe redistribution during diagenesis. Diagenetic Fe(III) reduction caused by oxidation of organic matter and Fe redistribution is supported by the C isotope composition of a carbonate-rich sample containing primary siderite. These carbonates yield δ¹³C values of ∼−10‰, which hints at a mixed carbon source in the seawater of both organic and inorganic carbon. The ancient seawater composition is estimated to have a minimum range in δ⁵⁶Fe of −0.8‰ to 0‰, assuming that hematite and siderite have preserved their primary Fe isotope signature. The long-term near-zero Fe isotope composition of the Hamersley and Transvaal BIFs is in balance with the assumed composition of the Fe sources. The negative Fe isotope composition of the investigated BIF samples, however, indicates either a perturbation of the steady state, or they have to be balanced spatially by deposition of isotopically heavy Fe. In the case of Si, the negative Si isotope signature of these BIFs stands in marked contrast to the assumed source composition. The deviation from potential source composition requires a complementary sink of isotopically heavy Si in order to maintain steady state in the basin. Perturbing the steady state by extraordinary hydrothermal activity or continental weathering in contrast would have led to precipitation of light Si isotopes from seawater. Combining an explanation for both elements, a likely scenario is a steady state ocean basin with two sinks. When all published Fe isotope records including BIFs, microbial carbonates, shales and sedimentary pyrites, are considered, a complementary sink for heavy Fe isotopes must have existed in Precambrian ocean basins. This Fe sink could have been pelagic sediments, which however are not preserved. For Si, such a complementary sink for heavy Si isotopes might have been provided by other chert deposits within the basin.     

Origin and formational history of some Pb-Zn deposits from Alborz and Central Iran: Pb isotope constraints

Several Pb-Zn deposits and occurrences within Iran are hosted by Mesozoic–Tertiary-aged sedimentary and igneous rocks. This study reports new Pb isotope analyses for galena from 14 Pb-Zn deposits in the Alborz and Central Iran structural zones. In general, Pb isotope ratios are extremely variable with data plotting between the upper crustal and orogenic curves in a plumbotectonic diagram. The latter may be attributed to Pb inputs from crustal and mantle end-members. Most of the galena samples are characterized by high ²⁰⁷Pb/²⁰⁴Pb ratios, suggesting significant input of Pb from old continental crust or pelagic sediment. Pb isotope data also indicate that some of the deposits, which are hosted by sedimentary rocks in Central Iran and Alborz, have similar Pb isotopic compositions and hence suggest similar source regions. Most of the galenas yield Pb model ‘ages’ that vary between ~140 and ~250 Ma, indicating that mineralization resulted from the extraction of ore-bearing fluids from Upper Triassic–Lower Jurassic sequences. The similarity in Pb isotope ratios for the Pb-Zn deposits located within these zones suggests analogous crustal evolution histories. Our preferred interpretation is that Pb-Zn mineralization within the sedimentary and igneous rocks of the Central Iran and Alborz tectonic regions occurred following a Late Cretaceous–Tertiary accretionary stage of crustal thickening in Iran.     

Insights into Li and Li isotope cycling and sub-arc metasomatism from veined mantle xenoliths,Kamchatka

Harzburgitic xenoliths cut by pyroxenite veins from Avachinsky volcano, Kamchatka, are derived from the sub-arc mantle and record element transfer from the slab to the arc. Olivine and orthopyroxene in the harzburgites have Li isotopic compositions (δ⁷Li = +2.8 to +5.6) comparable to estimates of the upper mantle (δ⁷Li ~ +4 ± 2). The pyroxenite veins, which represent modal metasomatism and may therefore provide information about the metasomatic agent, have mantle-normalized trace element characteristics that suggest overprinting of their mantle source by an aqueous, slab-derived fluid. These include relative enrichments of Pb over Ce, U over Th and Sr over Nd. Li is enriched relative to the HREE, and ortho- and clinopyroxene from the veins are in Li elemental and isotopic equilibrium with each other and the surrounding harzburgite. Vein samples (δ⁷Li = +3.0 to +5.0) do not record a significant slab-derived δ⁷Li signature. These observations can be reconciled if slab Li diffusively re-equilibrates in the mantle wedge. Modeling demonstrates that Li equilibration of small (1–2 cm width) veins or melt conduits is achieved at mantle wedge temperatures within 10¹–10⁵ years. We conclude that strongly fractionated Li isotopic signatures cannot be sustained for long periods in the sub-arc mantle, at least at shallow (<70 km) depths. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano,Hawaii

Eighteen basalts and some volcanic gases from the submarine and subaerial parts of Kilauea volcano were analyzed for the concentration and isotope ratios of sulfur. By means of a newly developed technique, sulfide and sulfate sulfur in the basalts were separately but simultaneously determined. The submarine basalt has 700 ± 100 ppm total sulfur with δ³⁴S_Σs of $\text{0.7 ± 0.1 ‰}$. The sulfate/sulfide molar ratio ranges from 0.15 to 0.56 and the fractionation factor between sulfate and sulfide is $\text{+7.5 ± 1.5‰}$. On the other hand, the concentration and δ³⁴S_Σs values of the total sulfur in the subaerial basalt are reduced to 150 ± 50 ppm and $\text{?0.8 ± 0.2‰}$, respectively. The sulfate to sulfide ratio and the fractionation factor between them are also smaller, 0.01 to 0.25 and +3.0‰, respectively. Chemical and isotopic evidence strongly suggests that sulfate and sulfide in the submarine basalt are in chemical and isotopic equilibria with each other at magmatic conditions. Their relative abundance and the isotope fractionation factors may be used to estimate the $\text{?o}{}_2$ and temperature of these basalts at the time of their extrusion onto the sea floor. The observed change in sulfur chemistry and isotopic ratios from the submarine to subaerial basalts can be interpreted as degassing of the SO₂ from basalt thereby depleting sulfate and ³⁴S in basalt.The volcanic sulfur gases, predominantly SO₂, from the 1971 and 1974 fissures in Kilauea Crater have δ³⁴S values of 0.8 to 0.9%., slightly heavier than the total sulfur in the submarine basalts and definitely heavier than the subaerial basalts, in accord with the above model. However, the δ³⁴S value of sulfur gases (largely SO₂) from Sulfur Bank is 8.0%., implying a secondary origin of the sulfur. The δ³⁴S values of native sulfur deposits at various sites of Kilauea and Mauna Loa volcanos, sulfate ions of four deep wells and hydrogen sulfide from a geothermal well along the east rift zone are also reported. The high δ³⁴S values (+5 to +6%._o) found for the hydrogen sulfide might be an indication of hot basaltseawater reaction beneath the east rift zone.     

Elucidating microbial processes in nitrate- and sulfate-reducing systems using sulfur and oxygen isotope ratios: The example of oil reservoir souring control

Sulfate-reducing bacteria (SRB) are ubiquitous in anoxic environments where they couple the oxidation of organic compounds to the production of hydrogen sulfide. This can be problematic for various industries including oil production where reservoir “souring” (the generation of H₂S) requires corrective actions. Nitrate or nitrite injection into sour oil fields can promote SRB control by stimulating organotrophic nitrate- or nitrite-reducing bacteria (O-NRB) that out-compete SRB for electron donors (biocompetitive exclusion), and/or by lithotrophic nitrate- or nitrite-reducing sulfide oxidizing bacteria (NR-SOB) that remove H₂S directly. Sulfur and oxygen isotope ratios of sulfide and sulfate were monitored in batch cultures and sulfidic bioreactors to evaluate mitigation of SRB activities by nitrate or nitrite injection. Sulfate reduction in batch cultures of Desulfovibrio sp. strain Lac15 indicated typical Rayleigh-type fractionation of sulfur isotopes during bacterial sulfate reduction (BSR) with lactate, whereas oxygen isotope ratios in unreacted sulfate remained constant. Sulfur isotope fractionation in batch cultures of the NR-SOB Thiomicrospira sp. strain CVO was minimal during the oxidation of sulfide to sulfate, which had δ¹⁸O_SO4 values similar to that of the water-oxygen. Treating an up-flow bioreactor with increasing doses of nitrate to eliminate sulfide resulted in changes in sulfur isotope ratios of sulfate and sulfide but very little variation in oxygen isotope ratios of sulfate. These observations were similar to results obtained from SRB-only, but different from those of NR-SOB-only pure culture control experiments. This suggests that biocompetitive exclusion of SRB took place in the nitrate-injected bioreactor. In two replicate bioreactors treated with nitrite, less pronounced sulfur isotope fractionation and a slight decrease in δ¹⁸O_SO4 were observed. This indicated that NR-SOB played a minor role during dosing with low nitrite and that biocompetitive exclusion was the major process. The results demonstrate that stable isotope data can contribute unique information for understanding complex microbial processes in nitrate- and sulfate-reducing systems, and offer important information for the management of H₂S problems in oil reservoirs and elsewhere.     

Formation processes of compound chondrules in CV3 carbonaceous chondrites: Constraints from oxygen isotope ratios and major element concentrations

We found thirty compound chondrules in two CV3 carbonaceous chondrites. The abundance in each meteorite relative to single chondrules is 29/1846 (1.6%) in Allende and 1/230 (0.4%) in Axtell. We examined petrologic features, major element concentrations and oxygen isotopic compositions. Textural, compositional and isotopic evidence suggests that multiple, different mechanisms are responsible for the formation of compound chondrules.Seven compound chondrules are composed of two conjoined porphyritic chondrules with a blurred boundary. At the boundary region of this type of compounds, a poikilitic texture is commonly observed. This suggests that the two chondrules were melted when they came to be in contact. On the other hand, seventeen compound chondrules consist of two conjoined chondrules with a discrete boundary. The preservation of spherical boundary planes of an earlier-formed chondrule of this type implies that it already solidified before fusing with a later-formed chondrule that was still melted. Six samples out of 17 compound chondrules of this type are composed of two BO chondrules. The BO-BO compound chondrules have a unique textural feature in common: the directions of the barred olivines are mostly parallel between two chondrules. This cannot be explained by a simple collision process and forces another mechanism to be taken into consideration.The remaining six compound chondrules differ from the others; they consist of an earlier-formed chondrule enclosed by a later-formed chondrule. A large FeO enrichment was observed in the later-formed chondrules and the enrichment was much greater than that in the later-formed chondrules of other types of compounds. This is consistent with the relict chondrule model, which envisages that the later-formed chondrule was made by a flash melting of a porous FeO-rich dust clump on an earlier-formed chondrule. The textural evidence of this type of compound shows that the earlier-formed chondrule has melted again to varying degrees at the second heating event. This implies that FeO concentrations in bulk chondrules increases during the second heating event if an earlier-formed chondrule was totally melted together with the FeO-rich dust aggregates.Silicate minerals such as olivine and low-Ca pyroxene in compound chondrules have oxygen isotope compositions similar to those in single chondrules from CV3 chondrites. The oxygen isotope composition of each part of the compound chondrule is basically similar to their chondrule pair, but silicates in some chondrules show varying degrees of ¹⁶O-enrichment down to −15‰ in δ¹⁸O, while those in their partners have ¹⁶O-poor invariable compositions near 0 ‰ in δ¹⁸O. This implies that the two chondrules in individual compounds formed in the same environments before they became conjoined and the heterogeneous oxygen isotope compositions in some chondrules resulted from incomplete exchange of oxygen atoms between ¹⁶O-rich chondrule melts and ¹⁶O-poor nebular gas.     

Compound-specific chlorine isotope ratios of TCE,PCE and DCE isomers by direct injection using CF-IRMS

A method for determining compound-specific Cl isotopic compositions (δ³⁷Cl) was developed for tetrachloroethene (PCE), trichloroethene (TCE), cis-dichloroethene (cis-DCE), trans-dichloroethene (trans-DCE) and 1,1-dichloroethene (1,1-DCE). The isotope ratio mass spectrometry (IRMS) used in this study has nine collectors, including two for m/z 50 and 52 (CH₃Cl) and two for m/z 94 and 96 (CH₃Br). The development of this method is based on the fact that fragments with mass ratios of 94/96, 95/97 and 96/98 are produced from PCE, TCE and DCE isomers during ion bombardment in the source of a mass spectrometer. Using continuous flow isotope ratio mass spectrometry coupled with gas chromatography (GC–CF-IRMS), it is possible to separate these compounds on-line and directly measure the Cl isotopic ratios of the fragments with the specific mass ratios.Both pure phase and aqueous samples were used for Cl isotopic analysis. For pure phase samples, a vapour phase of the chlorinated ethenes was injected directly into the GC, whereas the solid phase micro extraction (SPME) method was used to extract these compounds from aqueous solutions. The precisions of this analytical technique were ±0.12‰ (1σ, n = 30), ±0.06‰ (1σ, n = 30), and ±0.08‰ (1σ, n = 15) for PCE, TCE and DCE isomers, respectively. The limits of quantification (LOQ) for analyzing Cl isotopic composition in aqueous solutions were 20, 5, and 5 μg/L for PCE, TCE and DCE isomers, respectively. This corresponds to 6–9 nano-mole of Cl, which is approximately 80 times lower than the most sensitive existing method. Compared to methods previously available, this new development offers the following advantages: (1) The much lower LOQ make it possible to extract these compounds directly from aqueous solutions using SPME without pre-concentration; (2) The linking of a GC with an IRMS eliminates off-line separation; and (3) Because the fragments used for isotopic ratio measurement are produced during ion bombardment in the mass spectrometer, there is no need to convert chlorinated ethenes to methyl chloride. As a result, this technique greatly enhances the efficiency for isotopic analysis by eliminating procedures for pre-concentration, off-line separation and sample preparation. In addition, it also reduces the potential for isotopic fractionation introduced during these procedures.Compound-specific Cl stable isotope analysis can be used as a tool to study the sources of organic contaminants in groundwater and their behaviour in the subsurface environments. It may also assist in understanding processes such as transport, mixing, and degradation reactions.     

Klyuchevskoy Volcano, Kamchatka, Russia: The Role of High-Flux Recharged, Tapped, and Fractionated Magma Chamber(s) in the Genesis of High-Al2O3 from High-MgO Basalt

Mineral Chemistry, and major and trace element variations ofthe basalts from Klyuchevskoy, the world's most active islandare volcano, are most consistently explained by the persistenceof a non-steady state, erupting, recharging, and fractionatingmagma chamber in which fractionation of a parental high-MgObasalt melt produces high-Al₂O₃ basalt. Although fractionalcrystallization is the dominant controlling mechanism, periodicrecharge with a more primitive high-MgO basalt is also an importantprocess contributing to the chemical evolution of the magmas.Hybrid basalts are the mixed product of high-Al₂O₃ basalt rechargedwith high-MgO basalt. The lavas range in composition from high-MgO, low-Al₂O₃ ( 12wt. % MgO, 14 wt. % Al₂O₃) to high-Al₂O₃, low-MgO ( 18 wt. %Al₂O₃, 4 wt. % MgO). The high-MgO lavas are characterized byphenocrysts of olivine (cores FO_90–80 and rims FO_85–75)with chromite inclusions [Cr/(Cr + Al)0.7], clinopyroxene (Wo_46–42En_48–42Fs_15–7),and the rare occurrence of orthopyroxene (En_72–70). Allthe phenocrysts are normally zoned and set in a groundmass ofplagioclase, pigeonite, clinopyroxene, magnetite, orthopyroxene.The high-Al₂O₃ basalts contain plagioclase (An_85–55),olivine (Fo_80–65), clinopyroxene (Wo_45–30En_50–38Fs_23–11), orthopyroxene (En_72–70) phenocrysts, that preserve bothnormal and reverse zoning in a groundmass of plagioclase, pigeonite,olivine, clinopyroxene, magnetite, orthopyroxene. Hybrid basaltshave characteristics of both high-MgO basalts and high-Al₂O₃basalts and preserve complicated normal-to-reverse, reverse-to-normal,and normally zoned phenocrysts. No hydrous minerals are presentin any of the lavas. The varied basaltic magmas erupted from Klyuchevskoy are derivedfrom a magma chamber(s) located near the base of the Kamchatkacrust (pressures 0.5–0.9 GPa) and characterized by relativelyhigh crystallization temperatures, some in excess of 1150C.Under these conditions, the fractionation of a parental high-MgOmagma, produced principally from the melting of a fluid-fluxed,peridotitic mantle wedge, results in the production of a chemicallydiverse spectrum of basalts ranging from high-MgO, low-Al₂O₃to high-Al₂O₃, low-MgO basalt, traversing the relatively primitiveend of both the calc-alkalic and tholeiitic differentiationtrends.     

Collisional processes at the junction of the Aleutian–Kamchatka arcs: new evidence from fission track analysis and field observations

The Aleutian island arc collides with the Kuril–Kamchatka arc in the area of the Cape Kamchatka peninsula. Field studies of neotectonic structures and apatite fission track analysis provide evidence for crustal plate shortening onshore the Cape Kamchatka peninsula. Tectonic blocks show differential mean exhumation rates varying from 0.18 ± 0.04 mm yr⁻¹ in the north up to 1.2 ± 0.18 mm yr⁻¹ in the south of the peninsula. A few of the fission track length data point to an unsteady exhumation rate. The blocks are separated by major dextral fault zones splaying off from Aleutian island arc fault zones. Across the western segment of the North American–Pacific Plate boundary the strain is partitioned along the fault zones and increases from north to south. Results from this study suggest that indentation and accretion of island arc fragments has recently occurred in the southeastern part of the Cape Kamchatka peninsula.     

Methane production and consumption monitored by stable H and C isotope ratios at a crude oil spill site,Bemidji, Minnesota

Stable isotopic ratios of C and H in dissolved CH₄ and C in dissolved inorganic C in the ground water of a crude-oil spill near Bemidji, Minnesota, support the concept of CH₄ production by acetate fermentation with a contemporaneous increase in HCO₃⁻ concentration. Methane concentrations in the saturated zone decrease from 20.6 mg L⁻¹ to less than 0.001 mg L⁻¹ along the investigated flow path. Dissolved N₂ and Ar concentrations in the ground water below the oil plume are 25 times lower than background; this suggests that gas exsolution is removing dissolved CH₄ (along with other dissolved gases) from the ground water. Oxidation of dissolved CH₄ along the flow path seems to be minimal because no measurable change in isotopic composition of CH₄ occurs with distance from the oil body. However, CH₄ is partly oxidized to CO₂ as it diffuses upward from the ground water through a 5- to 7-m thick unsaturated zone; theδ¹³C of the remaining CH₄ increases, theδ¹³C of the CO₂ decreases, and the partial pressure of CO₂ increases.Calculations of C fluxes in the saturated and unsaturated zones originating from the degradation of the oil plume lead to a minimum estimated life expectancy of 110 years. This is a minimum estimate because the degradation of the oil body should slow down with time as its more volatile and reactive components are leached out and preferentially oxidized. The calculated life expectancy is an order of magnitude estimate because of the uncertainty in the average linear ground-water velocities and because of the factor of 2 uncertainty in the calculation of the effective CO₂ diffusion coefficient.     

微量岩石样品中Rb-Sr和Pb一步分离及高精度热电离质谱测试

采用30 μL Sr特效树脂微柱,一步分离微量岩石样品中Rb-Sr和Pb,其回收率均优于90％,流程试剂用量仅0.75 mL,分离时间约3h,Rb-Sr流程本底优于5 pg,Pb流程本底优于50 pg.本方法具有样品用量少、本底低、回收率高、分离效率高等优点.结合高灵敏度TIMS分析技术,可以实现微量岩石样品高精度Rb...     

Oxygen and strontium isotope ratios in some ejecta from the Alban Hills volcanic area,Roman comagmatic region

CaSO₄ has been investigated at room temperature over the pressure range of 0 to 160 kbar. A reversible, sluggish transition that occurs at about 20 kbar with a volume change of about 4% has been confirmed. The x-ray powder data collected at pressure can be indexed on the monoclinic monazite structure cell (P2₁/n) which is considered to be the most likely model structure for the new HP CaSO₄ phase. The transition is largely distortional and involves rotation and displacement, but essentially preserves the chains of edge shared CaO₈₍₉₎ and SO₄ polyhedra found in the orthorhombic anhydrite (Bbmm) structure.