Oxygen Isotope Shift Research Articles

Fluid chemistry of veining associated with an ancient microearthquake swarm, Benmore Dam, New Zealand

Steeply dipping strata in the vicinity of Benmore Dam, Otago, New Zealand, are complexly deformed metasedimentary rocks of the Torlesse Supergroup (Middle Triassic age). Over an exposed area ∼100 m wide × 25 m high, these strata are disrupted by a fault-fracture mesh comprising conjugate Coulomb shears interlinked by extensional and extensional-shear fractures, all formed in a common stress field and hosting quartz + prehnite ± epidote ± calcite veining. The combined effect of these structures is shortening perpendicular to beddings and subvertical extension so that in their present attitude, they correspond to a set of conjugate thrust faults with associated extension fractures. On the evidence of incremental vein textures, the development of this distributed fault-fracture mesh is interpreted as resulting from a fluid-driven microearthquake swarm, which postdated regional low-grade metamorphism. Mechanical considerations suggest that the migrating hydrothermal fluids were significantly overpressured, possibly to approximately lithostatic values, if the mesh structure developed in its present attitude. Fluid-inclusion microthermometric studies show that Benmore vein quartz contains two-phase aqueous inclusions with salinities between 1.4 and 2.9 wt% NaCl equivalent and homogenization temperatures ( T h ) between 189 and 217 °C. The assemblage quartz + prehnite + epidote suggests trapping temperatures ( T t ) of ∼280 °C, requiring the addition of an ∼70 °C correction to T h values. Late calcite contains inclusions with noticeably lower salinity (0.0–0.9 wt% NaCl) and T h values (129–175 °C). Studies on quartz + pumpellyite ± calcite veins from nearby Lake Aviemore show similar fluid-inclusion salinity and T h values. Fluid-inclusion gas analyses show all the vein samples to be dominated by H 2 O (99.3–99.9 mol%) with few other gases apparent, including CH 4 (≤0.5%), N 2 (≤0.1%), CO 2 (≤0.1%), and C 2 -C 4 hydrocarbons. Cation and anion analyses, when combined with the gas data, show that NaCl dominates the fluid-inclusion salinities. Oxygen isotope results, when combined with calculated T t values, indicate that the water responsible for the deposition of Benmore and Aviemore quartz had δ 18 O compositions of 9.4‰ and 4.8‰, respectively. Calcite δ 13 C values between−25.3‰ and−38.0‰ are indicative of oxidation of CH 4 to CO 2 as a result of hydrothermal fluids interacting with organic- rich sediments. Fluid-inclusion \({\delta}D_{H_{2}O}\) values for Benmore range between −73‰ and −89‰ compared to−109‰ for the one Aviemore sample. This research has demonstrated that (1) water of meteoric origin, probably from subantarctic latitudes, penetrated to ≥6 km depth and underwent an oxygen isotope shift before depositing the Benmore-Aviemore veins; (2) the migrating hydrothermal fluids were likely overpressured well above hydrostatic to near lithostatic values if the mesh structure was active in its present orientation; and, (3) fluid migration was coupled to distributed brittle failure in the prevailing stress field, “self-generating” a permeable fault-fracture mesh.

Paleoproductivity increase at the Eocene–Oligocene climatic transition: ODP/DSDP sites 763 and 592

During the late Eocene–early Oligocene period of rapid climate change (across Oxygen isotope shift Oi-1) productivity showed major changes in the region around Australia (DSDP Site 592 off New Zealand, ODP Site 763 off NW Australia). We estimated paleoproductivity at these sites using benthic foraminiferal accumulation rates, as well as accumulation rates of siliceous and other calcareous microfossils, and carbon isotope data. In the Eocene productivity was generally higher at Site 763, where it reached 4 maxima, but dropped at about 34.3 Ma. At both sites productivity increased strongly at Oi-1 (as recognized in the oxygen isotopic record at the sites), and fluctuted during the early Oligocene at higher levels than in the Eocene. We attribute the difference in Eocene productivity to differences in oceanographic settings: Site 592 was probably under a N–S flowing western boundary current of the Pacific gyre, whereas Site 763 showed periodic high productivity as a result of local upwelling. This upwelling occurred when a warm, N–S flowing current (proto-Leeuwin current) replaced the cold, S–N flowing eastern boundary current of the Indian Ocean gyre. Upwelling ended at the opening of the Tasman Sea. The earliest Oligocene increase in productivity occurred at many other locations in the Southern Oceans, and is accompanied by a strong increase in carbon isotopic values, indicating increased burial of organic matter on a global scale. This productivity increase as well as the increased burial indicates that the oceanic carbon cycle may have been part of the climate change in the earliest Oligocene.

Heat and fluid flow in contact metamorphic aureoles with layered and transient permeability, with application to the Notch Peak aureole, Utah

We have investigated the control of layered and transient permeability structures on fluid flow and thermal evolution in contact metamorphic aureoles using two‐dimensional numerical modeling with petrological and geochemical constraints from the Notch Peak aureole, Utah. The model includes interbedded aquitard and aquifer lithologies on the scale of formations and transient enhancement of permeability due to devolatilization reactions. The results show that a layered permeability structure causes focusing of fluids into aquifer layers, resulting in flow pattern that is strongly time‐dependent and significantly different from the predicted simple convection cells in aureoles with homogeneous permeability. The model predicts temporal development of three distinctive flow regimes: (1) early radial down‐temperature flow due to release of magmatic fluid, (2) small flat convection cells near the pluton‐aquifer contacts during peak metamorphism, (3) late unidirectional down‐temperature flow in the upper aureole and up‐temperature flow in the middle to lower aureole. When the bulk permeability of host rocks is >10−16 m2, heat advection by flowing fluids is significant. At lower bulk permeability, heat conduction dominates, and the effects of detailed permeability structure on the thermal field become negligible. Metamorphic reactions enhance permeability within the inner aureole, localizing fluid convection and increasing fluid flux. The observed spatial distribution of mineral assemblages and oxygen isotopic shifts in the upper part of the Notch Peak aureole is consistent with the predicted time‐integrated fluid flux, which over duration of metamorphism is dominated by the down‐temperature flow of a large amount of water from the pluton into the wall rocks.

Cs–Rb–Ba systematics in phengite and amphibole: an assessment of fluid mobility at 2.0 GPa in eclogites from Trescolmen, Central Alps

Eclogites from Trescolmen that contain abundant hydrous minerals (phengite, amphibole, paragonite, zoisite, talc, apatite) show petrographic evidence for fluid infiltration under conditions of 2.0 to 1.8 GPa, 650 °C. Large ion lithophile elements (LILE, e.g. Cs, Rb, Ba and Sr) were analysed by in-situ techniques in all eclogite mineral phases in order to characterize the behaviour of fluid-mobile elements at high pressure. In-situ analysis of carefully-chosen metamorphic assemblages circumvents the problem of partial late-stage alteration, which can severely influence the calculated element budgets of whole-rock samples. Phengite is the dominant host for Cs, Rb, and Ba in both eclogite and adjacent garnet mica schist samples, and incorporates >90% of the budgets of these elements in whole rocks. LILE contents of phengites in phengite-rich rocks are likely to record the Cs/Rb and Ba/Rb ratios of their host rock protoliths. The LILE patterns of eclogite are consistent with protoliths derived from basalt that underwent seafloor alteration, whereas those of mica schist are almost identical to average upper continental crust. In contrast, LILE patterns of eclogite samples that lack phengite, but do contain amphibole, are unlike any plausible protolith, but are identical to those of amphibole in phengite-bearing samples. This observation points to homogenization of the LILE in different lithologies, which we correlate with petrographic evidence for fluid infiltration. Because phengite in garnet mica schist has a strong capacity to buffer the fluid with respect to Cs, Rb, and Ba, homogenization of amphiboles is best explained by fluid infiltration from the surrounding metapelites into eclogite bodies, implying at least metre-scale fluid mobility. The amphibole homogenization can be most easily modelled by a pervasive open-system fluid flux through the eclogites, possibly facilitated by ductile deformation during the early stages of uplift. Simple calculations give minimum fluid-rock ratios of ~0.001 to 0.004. Demonstration of the mobility of very small volumes of fluid through eclogite is an important prerequisite of many subduction zone models that try to explain across-arc variations in trace element geochemistry. The low fluid-rock ratios from this study are not in contrast with oxygen isotope heterogeneities reported from other eclogite localities. Fluid mobile elements such as Cs, Rb and Ba are more sensitive indicators of small volume, fluid-rock interaction and are therefore potentially valuable for understanding fluid infiltration processes in systems where oxygen isotope shifts are not large enough to be detectable.

Large copper isotope effect on the pseudogap in the high-temperature superconductor HoBa 2 Cu 4 O 8

The copper isotope effect (63Cu vs. 65Cu) on the relaxation rate of crystal-field excitations in the slightly underdoped high-temperature superconductor HoBa2Cu4O8 has been investigated by inelastic neutron scattering. For the 63Cu compound there is clear evidence for the opening of an electronic gap in the normal state at T * ≈ 160 K far above T c = 79.0 K. Upon substitution of 63Cu by 65Cu, T c decreases marginally to 78.6 K, whereas T * is increased to about 185 K. This large copper isotope shift Δ T * ( Cu ) = T * ( 65 Cu ) - T * ( 63 Cu ) ≈ 25 K - together with the corresponding oxygen isotope shift Δ T * ( O ) = T * ( 18 O ) - T * ( 16 O ) ≈ 50 K found in an earlier investigation - suggests that phonons or lattice fluctuations involving both the copper and the oxygen ions are important for the pairing mechanism in high-T c materials.

Argon annealing of the oxygen-isotope-exchanged manganiteLa0.8Ca0.2MnO3+y

We have resolved a controversial issue concerning the oxygen-isotope shift of the ferromagnetic transition temperature ${T}_{C}$ in the manganite ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_{3+y}.$ We show that the giant oxygen-isotope shift of ${T}_{C}$ observed in the normal oxygen-isotope exchanged samples is indeed intrinsic, while a much smaller shift observed in the argon annealed samples is an artifact. The argon annealing causes the ${}^{18}\mathrm{O}$ sample to partially exchange back to the ${}^{16}\mathrm{O}$ isotope due to a small ${}^{16}{\mathrm{O}}_{2}$ contamination in the Ar gas. Such a contamination is commonly caused by the oxygen outgas that is trapped in the tubes, connectors, and valves. The present results thus umambiguously demonstrate that the observed large oxygen isotope effect is an intrinsic property of manganites, and places an important constraint on the basic physics of these materials.

A stable isotope study of multiple species of planktonic foraminifera across sapropels of the Tyrrhenian Sea, ODP Site 974

The planktonic foraminifera Globigerinoides ruber (white variety), Globigerinoides elongatus, Orbulina universa, Globigerina bulloides, Globorotalia inflata, and the fine fraction <38 μm (considered to represent the calcareous nannoplankton association) were sampled for stable isotope analyses across Pleistocene sapropels from Hole 974B in the Tyrrhenian Sea. The aim of this study was to establish if changes in salinity and water column stratification could be observed across the sapropel layers that were recovered at Site 974 in the western Mediterranean during ODP Leg 161. The differences in absolute isotopic compositions of the foraminifera reflect the preferred depth habitats and seasonal distribution of the different species. The magnitudes of the isotope shifts across sapropels are highly variable, but in general more pronounced in the shallow dwelling forms. G. ruber shows an average isotopic shift of 1.3‰ δ 18O and 0.44‰ δ 13C, whereas the isotopic shifts for G. bulloides are −0.85‰ for oxygen and −0.5‰ for carbon. The difference in δ 18O composition between G. bulloides and G. ruber in sapropel layers averages 2.0‰, whereas in non-sapropel times it is 1.8‰. The difference in carbon isotope composition between these two species, on the other hand, is constant at −2.2‰. The larger oxygen isotope shifts observed in the shallow dwelling species G. ruber during sapropel times indicate a more pronounced freshwater influence on the surface waters and/or larger temperature gradients between summer and winter. These data suggest that possibly a stronger water column stratification was present during times of sapropel deposition in the western Mediterranean.

Chemical and Isotopic Constraints for Recrystallization of Sedimentary Dolomites from the Western Canada Sedimentary Basin

Mississippian shoal carbonates of Western CanadaSedimentary Basin are important hydrocarbon hosts.Dolomitization plays a major role in the evolution ofreservoir porosity in these carbonates. This processvaries across the basin and reflects, in part, divergentsources and chemistry of pore fluids. Dolomites fromseveral petroleum reservoirs were analyzed formineralogical, geochemical and isotopic variation. Thedata clearly demonstrate the progressive and complexrecrystallization of dolomite during shallow and deepburial in modified marine, meteoric and burial fluids.These data include: change in crystal size,stoichiometry, cathodoluminscence characteristics,stable oxygen and carbon isotopic shifts and changesin radiogenic Sr isotopic composition. However,regional geology, tectonic history and fluid flowevolution play important roles in the diageneticimprints and the degree of recrystallization. Early microcrystalline dolomite formed in normalmarine and evaporative conditions in Mississippiancarbonates from Western Canada Sedimentary Basinhave undergone variable degrees of recrystallization, frompristine dolomite akin to Holocene sabkha dolomitewith preserved mineralogical and chemical attributesto highly recrystallized mesodolomite, however stillnonstoichiometric, but with highly altered chemicalsignatures. Careful attention should be made to localgeology, hydrodynamics and fluid flow when investigatingdolomite recrystallization in sedimentary basins.

Local vibrational mode spectroscopy of thermal donors in germanium

We report the observation of infrared (IR) vibrational bands related to individual thermal double donors (TDs) in Ge crystals enriched with either 16Oor18O isotopes of oxygen. The TDs were generated by heating the oxygen-doped Ge at 300°C and 350°C. IR absorption spectra were measured at room temperature (RT) and 10K (LT). In the RT spectra two broad bands at about 600 and 780cm−1 are found to develop upon the TD generation. In the LT spectra a splitting of the bands into series of rather sharp bands (up to 9 resolved lines) related to a double-donor (DD) configuration of individual TDs (TD1–TD9) is observed. A manifestation of bistability of the first four TD species (TD1–TD4) is observed in absorption spectra measured at 10K after different cooling conditions. The pairs of lines due to bistable TDs in the DD configuration are detected after cooling under the band-gap illumination. They are found to transform to the sets of three lines after cooling in the dark. These triplets are assigned to the local vibrational modes (LVMs) of a neutral (X) configuration of bistable TDs. Oxygen isotopic shifts of LVMs due to TDs are determined and compared with those for vibrational modes of interstitial oxygen in Ge.

Study of the 1096.9 meV photoluminescent oxygen-related centre in neutron-irradiated CZ-Si: Formation and structure

The creation process and the structure of an oxygen-associated centre in Si are investigated by means of photoluminescence (PL). The centre is formed after annealing between 250°C; and 450°C in neutron-irradiated CZ-Si and is photoluminescent with a bound exciton emission at 1096.9 meV. We show that this PL line as well as the II PL line (1018.2 meV) are the major features of the PL spectra for samples annealed in this temperature range. The comparison of the PL spectra obtained in CZ-Si and FZ-Si crystals indicated that the 1096.9 meV PL line is formed at expenses of II, thus suggesting the associated centre is presumably created by complexing the trigonal II centre with one (or more) interstitial oxygen. Uniaxial stress measurements and the observed oxygen isotopic shift (0.037 meV) show that the PL line is associated with an oxygen centre of monoclinic I symmetry. The thermal activation energy of the binding exciton deduced from the intensity decay, ΔE = 5.1 meV, together with the stress behaviour suggest that the centre probably corresponds to an iso-electronic centre.

A study of oxygen isotopic fractionation during bio-induced calcite precipitation in eutrophic Baldeggersee, Switzerland

In order to better understand environmental factors controlling oxygen isotope shifts in autochthonous lacustrine carbonate sequences, we undertook an extensive one-year study (March, 1995 to February, 1996) of water-column chemistry and daily sediment trap material from a small lake in Central Switzerland. Comparisons between calculated equilibrium isotope values, using the fractionation equation of Friedman and O’Neil, (1977) and measured oxygen isotope ratios of calcite in the sediment-traps reveal that oxygen isotopic values of autochthonous calcite (δ 18O) are in isotopic equilibrium with ambient water during most of the spring and summer, when the majority of the calcite precipitates. In contrast, small amounts of calcite precipitated in early-spring and again in late-autumn are isotopically depleted in 18O relative to the calculated equilibrium values, by as much as 0.8‰. This seasonally occurring apparent isotopic nonequilibrium is associated with times of high phosphorous concentrations, elevated pH (∼8.6) and increased [CO 3 2−] (∼50 μmol/l) in the surface waters. The resulting weighted average δ 18O value for the studied period is −9.6‰, compared with a calculated equilibrium δ 18O value of −9.4‰. These data convincingly demonstrate that δ 18O of calcite are, for the most part, a very reliable proxy for temperature and δ 18O of the water.

Resonance Raman characterization of five-coordinate dioxygen adducts of porphyrinatocobalt(II) complexes formed in low temperature O2 matrices

Resonance Raman (RR) spectra of five-coordinate dioxygen adducts of cobalt(tetramesitylporphine) and cobalt(tetramesopropylporphine) formed in low temperature O2 matrices are reported. For the first time, all three vibrations expected for the Co–O2 fragment, ν(O–O), ν(Co–O2) and δ(Co–O–O), were observed for 16O2 and 18O2 isotopomers. These bands have been assigned based on oxygen isotope shift data as well as normal coordinate analysis of the Co–O2 moiety. This work presents also the first observation of two distinct ν(O–O) bands due to the Co–16O–18O and Co–18O–16O isomers in ‘end-on’ type dioxygen adducts. The mechanism of resonance enhancement, the effect of the axial ligand on the ν(O–O) and ν(Co–O2) frequencies and the differences in metal–O2 bonding between cobalt and iron porphyrins are discussed.

Very strong magnetic-field dependence of the oxygen isotope shift of the charge-ordering transition inLa0.5Ca0.5MnO3

Oxygen isotope effect on the charge-ordering transition was studied in La0.5Ca0.5MnO3 . Upon replacing 16 O with 18 O, the charge-ordering temperature increases by 9 K under zero magnetic field. With an increase of the magnetic field, the oxygen isotope shift increases rapidly and reaches a magnitude of about 40 K under a magnetic field of 5.4 T. The present results cannot be explained by the existing theories of the charge-ordering transition in manganites. @S0163-1829~99!00601-3# It is well known that the observation of the oxygenisotope effect in conventional superconductors is important for the development of the microscopic theory of superconductivity. Recently, Zhao and co-workers 1‐3 have initiated the studies of oxygen isotope effects in the colossal magnetoresistive manganese perovskites. The observed strong oxygen isotope effects in the manganites give clear evidence for the existence of small lattice polarons in these systems. The isotope effects along with many other experimental results 4‐7 strongly support those theoretical models 8,9 where a strong coupling of conduction electrons to local Jahn-Teller distortions is considered to be important for the basic physics in manganites.

New infrared absorption bands related to interstitial oxygen in silicon

In addition to the well-known spectrum of Czochralski-grown silicon, two infrared bands at 560 and 648 cm−1 are found to arise from the interstitial oxygen in silicon. The assignment of the bands is performed using the studies of their oxygen isotope shift and temperature dependence. The 560 cm−1 band is attributed to the hot counterpart of the mode at 518 cm−1 and the 648 cm−1 band to the combination of the far-infrared mode at 29 cm−1 with the Raman active mode at around 600 cm−1.

Superconductivity in BaPb1 − xBixO3 cubic oxide: A coupled charge oscillation with optical phonon model

The nature of pairing mechanism in cubic perovskite BaPbBiO 3 is theoretically investigated. A model potential is developed which includes the Coulomb (e-e), electro-optical phonon (e-ph) as well as electronplasmon (e-pl) interactions to elucidate the superconducting state. The presence of these e-e, e-ph and e-pl interactions allows a coherent interpretation of their properties. The estimated value of the coupling parameter (λ) as 0.73 is consistent with an attractive electron-electron interaction. The screened Coulomb repulsive parameter ( μ * = 0.31 ) suggests poor screening of charge carriers with low concentration and hence reflects the small density of states N( O). The superconducting transition temperature ( T c ) of the system is calculated from the McMillan formulae and is consistent with earlier observations. The reduced energy gap of 2Δ K BT c is found to be 3.53 which is close to the predicted value of BCS weak coupling theory ( 2Δ K BT c = 3.5 ). The oxygen isotope shift of T c is then calculated and the characteristic exponent (α) defined as T c ∞ M − α ( M is the oxygen atomic mass) is evaluated as 0.227. These observations on Ba- Pb 1 − x Bi x O 3 ( x = 0.25) suggest that a weak to moderate coupling exists and the coupling of electrons with the coupled charge oscillation-optical phonon mode could be a reason for the superconductivity.

Geochemistry of the volcano-hydrothermal system of El Chichón Volcano, Chiapas, Mexico

The 1982 eruption of El Chichon volcano ejected more than 1 km3 of anhydrite-bearing trachyandesite pyroclastic material to form a new 1-km-wide and 300-m-deep crater and uncovered the upper 500 m of an active volcano-hydrothermal system. Instead of the weak boiling-point temperature fumaroles of the former lava dome, a vigorously boiling crater spring now discharges / 20 kg/s of Cl-rich (∼15 000 mg/kg) and sulphur-poor ( / 200 mg/kg of SO4), almost neutral (pH up to 6.7) water with an isotopic composition close to that of subduction-type magmatic water (δD=–15‰, δ18O=+6.5‰). This spring, as well as numerous Cl-free boiling springs discharging a mixture of meteoric water with fumarolic condensates, feed the crater lake, which, compared with values in 1983, is now much more diluted (∼3000 mg/kg of Cl vs 24 030 mg/kg), less acidic (pH=2.6 vs 0.56) and contains much lower amounts of S ( / 200 mg/kg of SO4, vs 3550 mg/kg) with δ34S=0.5–4.2‰ (+17‰ in 1983). Agua Caliente thermal waters, on the southeast slope of the volcano, have an outflow rate of approximately 100 kg/s of 71 °C Na–Ca–Cl water and are five times more concentrated than before the eruption (B. R. Molina, unpublished data). Relative N2, Ar and He gas concentrations suggest extensional tectonics for the El Chichon volcanic centre. The 3He/4He and 4He/20Ne ratios in gases from the crater fumaroles (7.3Ra, 2560) and Agua Caliente hot springs (5.3Ra, 44) indicate a strong magmatic contribution. However, relative concentrations of reactive species are typical of equilibrium in a two-phase boiling aquifer. Sulphur and C isotopic data indicate highly reducing conditions within the system, probably associated with the presence of buried vegetation resulting from the 1982 eruption. All Cl-rich waters at El Chichon have a common source. This water has the appearence of a "partially matured" magmatic fluid: condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in S due to anhydrite precipitation. Shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits (Red waters) are Ca–SO4–rich and have a negative oxygen isotopic shift, probably due to ongoing formation of clay at low temperatures.

Copper isotope shifts in Pr and La substituted 123 and 124 cuprate superconductors; comparison with oxygen isotope shifts

Copper isotope shifts of T c have been measured in 123 and 124 cuprate superconductors with partial substitutions by Pr and La to reduce hole concentration. The 123 compositions were Pr x Y 1− x Ba 2Cu 3O 7 ( x=0.2, 0.3, 0.4) and YLa 0.3Ba 1.7Cu 3O 7. The 124 compounds were Pr x Y 1− x Ba 2Cu 4O 8 ( x=0.2, 0.3) and YLa 0.3Ba 1.7Cu 4O 8. Oxygen isotope experiments in materials with these compositions have shown substantial isotope shifts. We find that the Cu isotope shifts are also substantial, but somewhat smaller. Other findings are: (1) the Cu isotope exponent α Cu is positive, (2) α Cu increases rapidly as T c is reduced by substitution, and rises to a substantial fraction of the BCS value, behavior which is similar to that of the oxygen isotope exponent α O, and (3) when T c is reduced by non-isovalent substitution, both O and Cu isotope shifts increase greatly, but the ratio α Cu/ α O remains 0.75±0.1 in both 123 and 124, regardless of the amount and site of the non-isovalent substitution.

Cause of Tc depression in Sr substituted YBaSrCu 3O 7− y examined by isotope studies

We have measured oxygen isotope shifts in YBa 2− x Sr x Cu 3O 7− y . With increasing Sr substitution, T c decreases monotonically, while the oxygen isotope exponent α 0 remains very small. This indicates that the hole concentration in the CuO 2 planes is still optimal, since it is known that high temperature superconductors with non-optimum hole concentration have reduced T c, but large isotope shifts. To confirm this, we carried out hole doping experiments on YBaSrCu 3O 7− y using high pressure O 2 annealing, and also by Ca substitution for Y. In both cases, with the increased holes (overdoping), T c further decreased as expected. Thus, the significant decrease in T c with Sr substitution is not caused by reduced charge transfer into the CuO 2 sheets, but rather is due to decreased ion size, polarizability and/or changes in the phonon spectrum.

Reactions of Laser-Ablated Copper Atoms with Dioxygen. Infrared Spectra of the Copper Oxides CuO, OCuO, CuOCuO, and OCuOCuO and Superoxide CuOO in Solid Argon

Laser-ablated copper atoms react directly with O2 to make CuO (627.7 cm-1), and linear OCuO (823.0 cm-1) which are identified by copper and oxygen isotopic shifts, comparison to earlier work, and DFT frequency calculations. The highest frequency Cu−O vibration (995.3 cm-1) exhibits a resolved copper isotopic triplet appropriate for the vibration of two equivalent copper atoms and oxygen isotopic components consistent with DFT-calculated frequencies for the nearly linear OCuOCuO molecule. Absorptions at 970.0 and 955.1 cm-1 are assigned to CuOCuO isomers. The simple addition product CuOO is characterized by O−O and Cu−O stretching frequencies at 1089.6 and 550.4 cm-1, isotopic shifts, and DFT calculations. The CuOO molecule forms higher complexes (O2)xCuOO readily on annealing the matrix sample.

Stable carbon and oxygen isotope shifts in Permian seas of West Spitsbergen-Global change or diagenetic artifact?

We performed petrographic, cathodoluminescence, electron-microprobe, and isotopic analyses of brachiopod shells from the Permian Kapp Starostin Formation in West Spitsbergen to reevaluate the >9‰ negative shift in δ13C and δ18O values reported in 1989 by M. Gruszczynski, S. Halas, A. Hoffman, and K. Malkowski. The δ13C and δ18O values within shells typically decrease with increasing luminescence, indicating diagenesis. Nonluminescent (NL) shell δ13C and δ18O values are 4.3‰ and 6.2‰ higher, respectively, than those of associated cements and matrix. For the same stratigraphic interval, δ13C and δ18O values of the NL shells are equal to, or substantially greater than, those reported by Gruszczynski et al. For the interval where those authors saw a 10‰ δ13C shift, our mostly NL Spiriferella polaris shells only yield a 1.5‰ shift. Gruszczynski et al. reported a 9‰ δ18O shift, whereas we observe almost none. Our results strongly suggest that the >9‰ isotopic shifts reported in Gruszczynski et al. are diagenetic artifacts. On the other hand, their Kazanian-Tatarian δ13C maximum of 7.5‰ is substantiated by our data. This Late Permian 13C maximum represents the highest spiriferid brachiopod δ13C values in the Phanerozoic and, within stratigraphic uncertainty, correlates with the whole-rock δ13C maximum in East Greenland and northwestern Europe. The δ13C shift may reflect changes in global storage of organic carbon indicated by coal-volume changes in the Late Permian.