Solid Buffer Research Articles

Chemo-enzymatic synthesis of key intermediates (S)-γ-hydroxymethyl-α,β-butenolide and (S)-γ-hydroxymethyl-γ-butyrolactone via lipase-mediated Baeyer–Villiger oxidation of levoglucosenone

Baeyer–Villiger oxidation of levoglucosenone with CAL-B and solid buffers provided valuable lactones in high yields in only 2 hours while allowing enzyme recyclability.

THE CONTENT OF FATTY ACIDS IN INDONESIA’S FISH OIL

Study of fatty acid content was conducted in six Indonesian fish oils taken from Surabaya, Sorong, Garut, Banyuwangi, and fish oil standard. The acid and peroxide values were a main parameters which affecting the quality of the fish oil. These parameters were set using the method stated on the SNI No. 01-3555-1998. The oil containing omega-3 such as EPA and DHA is beneficial for health. The study of fatty acid content in six fish oils were analyzed by GCMS Shimadzu QP 2010 ULTRA with FID Detector. RTX-5 were used as a column (diphenyl dimethyl polysiloxane as a solid buffer, size length 30 m, diameter 0,25 mm, and He as a gas mobile phase). The results showed that acid values for oil 1, 2, 3, 4, 5, and 6 were 0.55%, 0.50%, 0.48%, 0.55%, 0.48%, and 0.58%, respectively. While the peroxide values were 5.67, 4.72, 4.45,5.01, 4.85, and 5.27 meq/kg, respectively. GCMS analysis showed that fish oil 1, 2, 3, and 4 very dominant containing squalene of 29.45%, 32.34%, 21.07%, and 43.49%, respectively. While oil 6 contained EPA of 8.97% and DHA 6.56%, and that was the highest compared with other oils. However, oil 6 also contained a trans fatty acids i.e., elaidic acid of 26.8% and trans-13-docosanoic acid of 0.9%. For comparison, natural oil 5 was rich of linoleic acid (39.58%). The GCMS's analysis results proved that the oil 6 made from lemuru had a big potency to be developed for an Indonesian fish oil export comodity. Keywords: fish oil, EPA, DHA, squalena, GCMS, acid value, peroxide value

THE CONTENT OF FATTY ACIDS IN INDONESIA’S FISH OIL

<p>Study of fatty acid content was conducted in six Indonesian fish oils taken from Surabaya, Sorong, Garut, Banyuwangi, and fish oil standard. The acid and peroxide values were a main parameters which affecting the quality of the fish oil. These parameters were set using the method stated on the SNI No. 01-3555-1998. The oil containing omega-3 such as EPA and DHA is beneficial for health. The study of fatty acid content in six fish oils were analyzed by GCMS Shimadzu QP 2010 ULTRA with FID Detector. RTX-5 were used as a column (diphenyl dimethyl polysiloxane as a solid buffer, size length 30 m, diameter 0,25 mm, and He as a gas mobile phase). The results showed that acid values for oil 1, 2, 3, 4, 5, and 6 were 0.55%, 0.50%, 0.48%, 0.55%, 0.48%, and 0.58%, respectively. While the peroxide values were 5.67, 4.72, 4.45,5.01, 4.85, and 5.27 meq/kg, respectively. GCMS analysis showed that fish oil 1, 2, 3, and 4 very dominant containing squalene of 29.45%, 32.34%, 21.07%, and 43.49%, respectively. While oil 6 contained EPA of 8.97% and DHA 6.56%, and that was the highest compared with other oils. However, oil 6 also contained a trans fatty acids i.e., elaidic acid of 26.8% and trans-13-docosanoic acid of 0.9%. For comparison, natural oil 5 was rich of linoleic acid (39.58%). The GCMS's analysis results proved that the oil 6 made from lemuru had a big potency to be developed for an Indonesian fish oil export comodity.</p> <p>Keywords: fish oil, EPA, DHA, squalena, GCMS, acid value, peroxide value</p>

Chloride partitioning and solubility in hydrous phonolites from Erebus volcano: A contribution towards a multi-component degassing model

We present results from a series of experiments on the partitioning of chlorine between a hydrous fluid phase and a phonolitic melt that we then use to model specific aspects of volcanic degassing. Experiments were performed from 250 to 10MPa on a phonolite from Erebus lava lake, Antarctica, at 1000°C near the QFM solid buffer. Only one of 48 experimental samples shows coexistence of low-density vapour and high-density brine in the fluid phase while 35 samples are unambiguously in the vapour field. Large uncertainties in the H2O–NaCl phase diagram at the P–T considered do not allow us to assign reliable phase behaviour to the remaining samples. We select a vapour-dominated subset of our dataset to establish an empirical HCl solubility law valid at low pressures and salinities. This law is incorporated into a thermodynamical model of degassing, which we use to compute equilibrium temperatures from gas measurements made at Erebus in 2010. The quiescent lake activity features cyclic temperature variations between 1000 and 1050°C, which is consistent with thermal convection within the shallow plumbing system. Backward tracking of representative gas compositions and temperatures shows the evolution with pressure of the molar ratio of SO2/HCl in the gas, a quantity that is often measured in volcanic plumes. Model outputs suggest that this ratio can vary by up to an order of magnitude when the pressure changes from atmospheric to 100MPa, depending on degassing style (coupled vs. decoupled ascent of gas and melt).

Tungsten diffusion in olivine

Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1atm furnaces for times ranging from 45min to several weeks, at temperatures from 1050 to 1450°C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS).The following Arrhenius relation is obtained for W diffusion in forsterite:DW=1.0×10-8exp(-365±28kJmol-1/RT)m2s-1Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity.The slow diffusivities measured for W in olivine indicate that Hf–W ages in olivine–metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

Oxidation in CSPV experiments involving H2O-bearing mafic magmas: Quantification and mitigation

A difficulty in performing high-temperature (>900 °C) experiments on near-liquidus hydrous mafic melts in gas-medium cold-seal pressure vessels (CSPV) is the tendency for H 2 O in the fluid phase to dissociate and H 2 to diffuse through capsule material, leading to progressive oxidation of sample material. Negative consequences include premature stabilization of Fe-Ti oxide phases and commensurate deviation of the liquid line of descent toward silica enrichment. Moreover, time-variance of an intensive variable equal in importance to temperature or total pressure is an unwanted feature of any experimental study. Methodologies commonly employed to mitigate the oxidation problem, not without their own drawbacks, include incorporating CH 4 into the pressurizing gas, limiting run duration to 24 h, enclosing samples in Au-alloy capsules, and incorporating solid buffering assemblages to serve as indicators of f O₂ excursion. Using the Co-Pd-O system as a f O₂ sensor, we investigated progressive oxidation of basaltic andesite at 1010 °C and P H₂O = 150 MPa. Our time-series of 12, 24, 36, 48, and 60 h run durations reveals that oxidation occurs at a very high rate (~3-4 log unit change in f O₂ in 48 h). Both the variability of f O₂ and magnitude of dehydration-oxidation are considered unacceptable for phase equilibria work. Incorporation of additional CH4 serves only to offset the progressive oxidation trend toward a lower absolute range in f O₂ . Ultimately, rapid oxidation in CSPV hinders the chemical equilibration of experimental charges. To mitigate the issue, we propose the following solution: Incorporation of a substantial mass of Ni metal powder as an O 2 getter to the outer capsule successfully: (1) slows down oxidation; (2) stabilizes f O₂ at the nickel-nickel oxide (NNO) buffer after ~20 h; and (3) allows compositions to approach equilibrium. Runs much longer than 48 h may require one or more steps involving quenching and re-filling the pressure system with CH 4 .

Storage conditions and eruptive dynamics of central versus flank eruptions in volcanic islands: The case of Tenerife (Canary Islands, Spain)

We report the results of phase equilibrium experiments on a phonolite produced during one of the most voluminous flank eruptions (ca. 1km3) of the Teide–Pico Viejo complex (Tenerife Island). Combined with previous experimental and volcanological data we address the factors that control the structure of the phonolitic plumbing system of Teide–Pico Viejo stratovolcanoes. The Roques Blancos phonolite erupted ca 1800BP and contains ~14wt.% phenocrysts, mainly anorthoclase, biotite, magnetite, diopside and lesser amounts of ilmenite. Crystallization experiments were performed at temperatures of 900°C, 850°C and 800°C, in the pressure range 200MPa to 50MPa. The oxygen fugacity (fO2) was varied between NNO+0.3 (0.3 log units above to the Ni–NiO solid buffer) to NNO-2, whilst dissolved water contents varied from 7wt.% to 1.5wt.%. The comparison between natural and experimental phase proportions and compositions, including glass, indicates that the phonolite magma was stored prior to eruption at 900±15°C, 50±15MPa, with about 2.2wt.% H2O dissolved in the melt, at an oxygen fugacity of NNO-0.5 (±0.5). The difference in composition between the rim and the cores of the natural anorthoclase phenocrysts suggests that the phonolite was heated by about 50°C before the eruption, upon intrusion of a hotter tephriphonolitic magma. The comparison between the storage conditions of Roques Blancos and those inferred for other phonolites of the Teide–Pico Viejo volcanic complex shows that flank eruptions are fed by reservoirs located at relatively shallow depths (1–2km) compared to those feeding Teide central eruptions (5km).

Experimental Constraints on Parameters Controlling the Difference in the Eruptive Dynamics of Phonolitic Magmas: the Case of Tenerife (Canary Islands)

We have performed phase equilibrium experiments to determine the pre-eruptive conditions of the explosive eruption of Montana Blanca (2020 BP) that occurred from a satellite vent located in the east flank of Teide volcano (Tenerife Island). Crystallization experiments were performed using a phonolitic obsidian from the fall out deposit that contains 5 wt% anorthoclase, diopside and magnetite with minor amounts of biotite and ilmenite, set in a glassy matrix that contains microlites of Ca-rich alkali feldspars. Temperature was varied between 850oC and 800oC, and pressure between 200MPa to 50 MPa. The oxygen fugacity (fO2) was varied between NNO+0.2 (0.2 log units above to the Ni-NiO solid buffer) to NNO-2, whilst dissolved water contents varied from 7 to 1.5 wt%. Comparison between natural and experimental phase proportions and compositions indicates that the main body of phonolite magma was stored at 850±15oC, 50±20MPa, 2.5±0.5wt% H2O at an fO2 around NNO-0.5 prior to eruption, equivalent to depths between 1 to 2 km below the surface. Some clinopyroxene hosting H2O-rich melt inclusions possibly originates from intermittent supply of phonolitic magma stored at somewhat deeper levels (100 MPa). The Ca and Fe-rich composition of alkali feldspar phenocrysts rims and microlites attests to the intrusion of a mafic magma in the reservoir just prior to eruption, as borne out by banded pumices appearing in the later products of the eruptive sequence. The comparison with other phonolitic magmas from Tenerife and elsewhere (e.g., Vesuvius, Laacher See) shows that differences in the eruptive dynamic of phonolitic magmas can be correlated to differences in storage depths, along with variation in pre-eruptive volatile contents.

Oxygen fugacity control in piston-cylinder experiments

The main goal of this study was to develop and test a capsule assembly for use in piston-cylinder experiments where oxygen fugacity could be controlled in the vicinity of the QFM buffer without H2O loss or carbon contamination of the sample material. The assembly consists of an outer Pt-capsule containing a solid buffer (Ni–NiO or Co–CoO) plus H2O and an inner AuPd-capsule, containing the sample, H2O and a Pt-wire. No H2O loss is observed from the sample, even after 48 h, but a slight increase in H2O content is found in longer runs due to oxygen and hydrogen diffusion into the AuPd-capsule. Oxygen fugacity of runs in equilibrium with the Ni–NiO (NNO) and Co–CoO (CoCO) buffers was measured by analyzing Fe dissolved in the Pt-wire and in the AuPd-capsule. The second method gives values that are in good agreement with established buffer values, whereas results from the first method are one half to one log units higher than the established values.

The electrical conductivity of dry polycrystalline olivine compacts at high temperatures and pressures

AbstractThe electrical conductivity of dry polycrystalline olivine compacts (hot-pressed and sintered pellets) was measured at pressures of 1.0–4.0 GPa, at temperatures of 1073–1423 K, and at different oxygen fugacities via the use of a YJ-3000t multi-anvil press. Oxygen fugacity was controlled successfully by means of five solid buffers: Fe3O4-Fe2O3, Ni-NiO, Fe-Fe3O4, Fe-FeO and Mo-MoO2. Within the selected frequency range of 102–106 Hz, the experimental results indicate that the grain interior conduction mechanism is characterized by a semi-circular curve on an impedance diagram. As a function of increasing pressure, the electrical conductivity of polycrystalline olivine compacts decreases, whereas the activation enthalpy and the temperature-independent pre-exponential factors increase slightly. The activation energy and activation volume of polycrystalline olivine compacts were determined to be 141.02±2.53 kJ/mol and 0.25±0.05 cm3/mol, respectively. At a pressure of 4.0 GPa, electrical conductivity was observed to increase as a function of increasing oxygen fugacity, and the relationship between electrical conductivity and oxygen fugacity can be described as log10 (σ) = (2.47±0.085) + (0.096±0.023)×log10fO2 + (–0.55±0.011)/T, which presents the exponential factor q (˜0.096). Our observations demonstrate that the primary conduction mechanism for polycrystalline olivine compacts is a small polaron.

REE diffusion in olivine

Diffusion of rare earth elements has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. Experiments were prepared by enclosing source material [mixtures of rare-earth element (La, Dy, or Yb) aluminate and synthetic forsterite powders in 3:1 proportions] and polished forsterite in platinum capsules. For buffered experiments on natural olivine, samples were placed with the source in AgPd capsules, sealed under vacuum in silica glass ampoules with a solid buffer (NNO, IW, or graphite ). In some experiments, ground natural olivine was also incorporated into the source material. Prepared capsules were annealed in 1 atm furnaces for one hour to several weeks at 850 to 1300 °C. REE distributions in olivine were profiled by Rutherford backscattering spectrometry (RBS).

Magma storage conditions of the last eruption of Teide volcano (Canary Islands, Spain)

Phase equilibrium experiments were performed to determine the pre-eruptive conditions of the phonolitic magma responsible for the last eruption (about 1,150 yr B.P.) of Teide volcano. The Lavas Negras phonolite contains 30 to 40 wt% of phenocrysts, mainly anorthoclase, diopside, and magnetite. We have investigated pressures from 100 to 250 MPa, temperatures from 750 to 925°C, water contents from 1.3 to 10 wt%, at an oxygen fugacity (fO2) of 1 log unit above the Ni-NiO solid buffer. Comparison of the natural and experimental phase proportions and compositions indicates that the phonolite was stored at 900 ± 20°C, 150 ± 50 MPa, 3 ± 0.5 wt% dissolved H2O in the melt. The fO2 was probably close to the fayalite-magnetite-quartz solid buffer judging from results of other experimental studies. These conditions constrain the magma storage depth at about 5 ± 1 km below current summit of Teide volcano. Given that the island has not suffered any major structural or topographic changes since the Lavas Negras eruption, any remaining magma from this event should still be stored at such depth and probably with a similar thermal and rheological state.

Electrical conductivity of pyrope-rich garnet at high temperature and high pressure

Garnet is one of the important constituent minerals in the upper mantle and the transition zone of the Earth's mantle. However, there were very few previous works on its electrical conductivity. We have measured the electrical conductivity of single crystal of pyrope-rich garnet (∼Py 73-Alm 14-Grs 13) under the conditions of 4–16 GPa, 873–1473 K and frequency range from 10 −2 to 10 6 Hz, with a range of water content (from less than 10 to 7000 H/10 6 Si). A KAWAI-type multi-anvil apparatus and a Solarton-1260 Impedance/Gain Phase analyzer were used in this study. The impedance spectra showed two circles correspondent to the intrinsic resistivity of the crystal and to the effects of charge accumulation at the electrodes. The DC electrical conductivity was determined by the impedance spectroscopy. Molybdenum and molybdenum oxide solid buffer was used to control the oxygen fugacity. Results on hydrous and anhydrous samples were compared to determine the influence of water content on the electrical conductivity of single crystal garnet. Under anhydrous conditions, the electrical conductivity of garnet increases with temperature and decreases with pressure. When we used a thermal activation parameterization, we obtain the following relationship: σ = A exp(−( E * + PV *)/ RT), A = 1036(±236) (1 − 0.044(±0.007) P(GPa)) S/m or A = exp[7.16(±0.37) (1 − 0.012(±0.009) P(GPa))] S/m, E * = 128 ± 6 kJ/mol and V * = 2.50 ± 0.48 cm 3/mol. Hydrous garnet crystals have significantly higher electrical conductivity with different temperature and pressure sensitivity, and the conductivity in these samples increases with the water content. The results can be summarized as σ = A ⋅ C w r exp [ − ( E * + P V * ) / R T ] with A = 1950 (+870, −600) S/m, r = 0.63 ± 0.19, E * = 70 ± 5 kJ/mol and V * = −0.57 ± 0.05 cm 3/mol. These results are similar to those obtained by Wang et al. [Wang, D.J., Mookherjee, M., Xu, Y.S., Karato. S., 2006. The effect of water on the electrical conductivity of olivine. Nature 443, 977–980] for olivine, Huang et al. [Huang, X.G., Xu, Y.S., Karato, S., 2005. Water content in the transition zone from electrical conductivity of wadsleyite and ringwoodite. Nature 434, 746–749] for wadsleyite and ringwoodite and we suggest that the mechanism of hydrogen conduction is likely common to these minerals. We conclude that hydrogen enhances the electrical conductivity of pyrope-rich garnet and its effect increases with pressure but decreases with temperature. At a typical pressure and temperature in the upper mantle, the influence of water is substantial.

Experimental constraints on pre-eruptive conditions of phonolitic magma from the caldera-forming El Abrigo eruption, Tenerife (Canary Islands)

We have performed phase equilibrium experiments to determine the pre-eruptive conditions of the largest caldera-forming eruption (∼ 20 km 3 of DRE) that has occurred on Tenerife (Canary Islands). The Abrigo ignimbrite is phonolitic and was erupted during the last caldera-forming episode (ca. 190 ka), prior to the construction of the Teide–Pico Viejo active central complex. The Abrigo phonolite contains low amounts of phenocrysts (ca. 7 vol.%), mainly sanidine, biotite, clinopyroxene, and magnetite, with minor amounts of titanite, apatite, and haüyne. We have investigated pressures from 50 to 250 MPa, temperatures of 700–900 °C, water contents in the melt from 1.5 to ca. 10 wt.%, and oxygen fugacity ( fO 2) from 1 log unit above the Ni–NiO solid buffer to Quartz–Magnetite–Fayalite. Comparison of the natural and experimental phase proportions and compositions indicates that the phonolite at the roof of the Abrigo magma reservoir was at 130 ± 50 MPa (corresponding to ca. 4–5 km below the surface), 825 ± 25 °C, with 3 ± 1 wt.% dissolved H 2O and fO 2 at the Ni–NiO buffer ± 1 log unit. This shows that the magma that produced the largest ignimbrite on Tenerife was stored at relatively shallow depths but was water-undersaturated, and its eruption was probably triggered by input of fresh mafic magma. Comparison of the Abrigo phase equilibrium results with those obtained in other phonolitic magmas (e.g., Eifel, Kerguelen, Somma-Vesuvius) shows that the major element and probably fluid composition (H 2O, Cl and S) may have a strong effect on the presence or absence of phases and their compositions. Extrapolating phase equilibria results obtained on a specific phonolite to constrain the pre-eruptive conditions of other phonolites should be done with care.

The electrical conductivity of upper-mantle rocks: water content in the upper mantle

The electrical conductivity of upper-mantle rocks—dunite, pyroxenite, and lherzolite—was measured at ∼2–3 GPa and ∼1,273–1,573 K using impedance spectra within a frequency range of 0.1–106 Hz. The oxygen fugacity was controlled by a Mo–MoO2 solid buffer. The results indicate that the electrical conductivity of lherzolite and pyroxenite are approximately half and one order of magnitude higher than that of dunite, respectively. A preliminary model involving water and iron content effects on the electrical conductivity was derived and is summarized by the relation: $$ \sigma = 10^{{5.2\,\pm\,0.4}} \,C^{{0.67\,\pm\,0.07}}_{W} \,\exp{\left( { - \frac{{(183\,\pm\,9){\text{kJ}}/{\text{mol}}}} {{RT}}} \right)}\,\exp {\left( {X\,\frac{{(79\, \pm\,3){\text{kJ}}/{\text{mol}}}} {{RT}}} \right)}.$$ The results also indicate that pyroxenes dominate the bulk conductivity of upper mantle in hydrous conditions and suggest the maximum water content in oceanic upper mantle is as high as ∼0.09 wt%.

Zr and Hf diffusion in rutile

Chemical diffusion of Zr and Hf under anhydrous conditions has been measured in synthetic and natural rutile. The sources of diffusant used were hafnon or zircon powders or a hafnon–rutile mixture. Experiments were run in crimped Pt capsules in air, or in sealed silica glass capsules with solid buffers (to buffer at NNO or QFM). Rutherford Backscattering Spectrometry (RBS) was used to measure Zr and Hf diffusion profiles. From these measurements, the following Arrhenius relations were obtained: For Zr diffusion parallel to c, over the temperature range 750–1100 °C D Zr¦c = 9.8 × 10 − 15 exp(− 170 ± 30 kJ mol − 1 /RT) m 2 s − 1 For Hf diffusion parallel to c, over the temperature range 800–1000 °C D Hf¦c = 9.1 × 10 − 15 exp(− 169 ± 36 kJ mol − 1 /RT) m 2 s − 1 For Hf diffusion normal to c, over the temperature range 750–1050 °C D Hf⊥c = 2.5 × 10 − 12 exp(− 227 ± 62 kJ mol − 1 /RT) m 2 s − 1 Diffusivities for experiments buffered at QFM and NNO are similar to those run in air. Diffusivities in synthetic and natural rutile are likewise similar, indicating that these findings can be applied directly in determining Zr diffusivities in rutile in natural systems. These data indicate that rutile should be moderately retentive of Zr chemical signatures, with Zr diffusivities within an order of magnitude of those for Pb in rutile over most geologic conditions. When applied in evaluation of the relative robustness of the recently developed Zr-in-rutile geothermometer [T. Zack, R. Moraes, A. Kronz, Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer, Contributions to Mineralogy and Petrology 148 (2004) 471–488., E.B. Watson, D.A. Wark, J.B. Thomas, Crystallization thermometers for zircon and rutile, Contributions to Mineralogy and Petrology 151 (2006) 413–433.], these findings suggest that Zr concentrations in rutile will be somewhat more likely to be affected by later thermal disturbance than the geothermometer based on Zr concentrations in titanite [L. Hayden, E.B.Watson, D.A. Wark, A thermobarometer for sphene, Abstract, 16th V.M. Goldschmidt Conference (2006).], and much less resistant to diffusional alteration subsequent to crystallization than the Ti-in-zircon geothermometer [E.B. Watson, D.A. Wark, J.B. Thomas, Crystallization thermometers for zircon and rutile, Contributions to Mineralogy and Petrology 151 (2006) 413–433., E.B.Watson, T.M.Harrison, Zircon thermometer reveals minimum melting conditions on earliest Earth, Science 308 (2005) 841–844.].

Rare earth element diffusion in natural enstatite

Chemical diffusion coefficients of La, Nd, Eu, Gd, and Yb in natural enstatite have been measured at 850–1250 °C and 1 atm. Anhydrous diffusion experiments were run in Pt capsules in air, or in sealed silica glass capsules under an iron–wüstite (IW) solid buffer. The sources of diffusant were pre-reacted mixtures of synthetic enstatite powder and microcrystalline rare-earth aluminate garnet. Rutherford Backscattering Spectrometry (RBS) was used to measure diffusion profiles. For Gd diffusion in air over the temperature range 1000–1250 °C, the following Arrhenius relation is found for diffusion normal to (210): D Gd,air = 2.55 × 10 - 9 exp ( 321 ± 85 kJ mol - 1 / RT ) m 2 s - 1 . There is no significant difference between Gd diffusion in air and under IW-buffered conditions. Behavior similar to Gd is also noted for Nd. The Arrhenius relationship for Eu diffusion in enstatite, normal to (210) and at 850–1150 °C and IW-buffered conditions, is D Eu,IW = 6.93 × 10 - 6 exp ( - 384 ± 29 kJ mol - 1 / RT ) m 2 s - 1 . For Eu diffusion in air over the temperature range 1000–1200 °C for the same orientation, the following Arrhenius relation is found: D Eu,air = 1.70 × 10 - 8 exp ( - 350 ± 42 kJ mol - 1 / RT ) m 2 s - 1 . For Eu diffusion under IW-buffered conditions and for experiments run in air, diffusivities normal to (001) are similar to those for diffusion normal to (210). Eu diffusion under IW-buffered conditions is more than an order of magnitude faster than Eu diffusion in air. It is likely that majority of Eu is in the divalent state for diffusion under IW-buffered conditions, but Eu is in the trivalent state for diffusion in air. In the case of Nd and Gd, where valence state does not change under the investigated fO 2 conditions, diffusivities measured for experiments run both in air and under IW-buffered conditions are comparable to those obtained for trivalent Eu. Further, measurements of La, Nd, Eu +3, Gd, and Yb diffusion suggest that diffusion of trivalent REE in enstatite is not sensitive to ionic size, in contrast to that observed for REE diffusion in diopside [Van Orman, J.A., Grove, T.L., Shimizu, N., 2001. Rare earth element diffusion in diopside; influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates. Contrib. Mineral. Petrol. 141, 687–703]. These differences in diffusive behavior of REE between diopside and enstatite, as well as Eu 2+ and Eu 3+ in enstatite, can result in significant REE fractionation between coexisting pyroxenes during partial melting, melt migration, and subsolidus reequilibration processes in the Earth’s mantle and that of the Moon.

Zr diffusion in titanite

Chemical diffusion of Zr under anhydrous, pO2-buffered conditions has been measured in natural titanite. The source of diffusant was either zircon powder or a ZrO2–Al2O3–titanite mixture. Experiments were run in sealed silica glass capsules with solid buffers (to buffer at NNO or QFM). Rutherford Backscattering Spectrometry (RBS) was used to measure diffusion profiles. The following Arrhenius parameters were obtained for Zr diffusion parallel to c over the temperature range 753–1,100°C under NNO-buffered conditions: D Zr = 5.33 × 10−7 exp(−325 ± 30 kJ mol−1/RT) m2 s−1 Diffusivities are similar for experiments buffered at QFM. These data suggest that titanite should be moderately retentive of Zr chemical signatures, with diffusivities slower than those for O and Pb in titanite, but faster than those for Sr and the REE. When applied in evaluation of the relative robustness of the recently developed Zr-in-titanite geothermometer (Hayden and Watson, Abstract, 16th V.M. Goldschmidt Conference 2006), these findings suggest that Zr concentrations in titanite will be less likely to be affected by later thermal disturbance than the geothermometer based on Zr concentrations in rutile (Zack et al. in Contrib Mineral Petrol 148:471–488, 2004; Watson et al. in Contrib Mineral. Petrol, 2006), but much less resistant to diffusional alteration subsequent to crystallization than the Ti-in-Zircon geothermometer (Watson and Harrison in Science 308:841–844, 2005).

Experimental measurement of the electrical conductivity of pyroxenite at high temperature and high pressure under different oxygen fugacities

Electrical conductivities of pyroxenite were measured between frequencies of 10−1 and 106 Hz in a multi-anvil pressure apparatus using different solid buffers (Ni+NiO, Fe+Fe3O4, Fe+FeO and Mo+MoO2) to stabilize the partial pressure of oxygen. The temperature ranged from 1073 to 1423 K (800 to 1200 °C) and the pressure from 1.0 to 4.0 GPa. We observe that: (1) the electrical conductivity (σ) of pyroxenite depends on frequency; (2) σ tends to increase with rising temperature (T), and Log σ and 1/T obey a linear Arrhenius relationship; (3) under control of the buffer Fe+Fe3O4, σ tends to decrease with rising pressure, nevertheless the activation enthalpy tends to increase. For the first time we have obtained values for the activation energy and activation bulk volume of the main charge carriers, which are (1.60±0.07) eV and (0.05±0.03) cm3/mol, respectively; (4) for a given pressure and temperature, σ tends to rise with increased oxygen fugacity, whereas the activation enthalpy and preexponential factor tend to decrease; and (5) the behaviour of the electrical conductivity at high temperature and high pressure can be reasonably interpreted by assuming that small polarons provide the dominant conduction mechanism in the pyroxenite samples.

Experimental constraints on pre-eruption conditions of pantelleritic magmas: Evidence from the Eburru complex, Kenya Rift

The phase relationships and compositions of a pantellerite from the Eburru complex in the Kenya Rift Valley have been determined at 150 MPa and under reducing conditions, 2 log units below the Ni–NiO solid buffer. The effects of temperature and melt water content on phase relationships have been explored. Alkali feldspar and quartz crystallise alone at temperatures above 700 °C, irrespective of melt water content. Below 700 °C, sodic amphibole and clinopyroxene also crystallise; the amphibole being the liquidus phase under water-rich conditions. The coexistence of amphibole phenocrysts with alkali feldspar and quartz in a crystal-poor pantellerite implies temperatures below 700 °C and melt water contents higher than 4 wt.%, possibly up to 5–6 wt.%. Pantellerites have lower liquidus temperatures than associated comendites, which supports a parent–daughter relationship between the two magma types. The melts produced in the experiments extend the compositional trend displayed by the natural rock series, and reproduce some extreme compositions occasionally observed in alkaline volcanic series, with FeO⁎ contents above 12 wt.% and Na 2O contents approaching 10 wt.%. Pantellerites are therefore the true near-minimum melt compositions of alkaline oversaturated magma series.