Mixed H2O CO2 Research Articles

Theoretical insight into the competitive effect of CO2 and additive H2O in coke gasification

To reduce CO2 emissions, hydrogen-rich fuels are widely used in ironmaking, which significantly increases H2O amounts in blast furnace. Recent works have mostly focused on the coke gasification with CO2 or H2O alone, but lacked the interaction between two gases and the microscopic mechanism. This work combines particulate coke reaction experiments and theoretical calculations to explore the competitive effects of CO2 and additive H2O during coke gasification from a microscopic perspective. Experimental results indicate that the coke gasification rate with H2O is dramatically higher than that with CO2, and that H2O inhibits the reaction between CO2 and coke. Both the orderly stacking of carbon layers and the proportion of graphitic carbon are more obviously increased upon the addition of H2O. Reactive force fields simulations reproduce the experimental phenomena and provide the reaction network from elementary reactions·H2O molecules react with carbon layers in the form of OH radicals. Based on density functional theory, OH-oxidation reactions at all reactive sites of the carbon layer (wrinkled sites, edges, and defects) are confirmed to have relatively low activation energies, and some are even barrierless processes. The oxidation rate by OH radical is much higher than that by CO2, thus significantly inhibiting the oxidation by CO2. In contrast, OH radicals are also inactivated by CO2 in gas phase. Furthermore, atoms at edges and defects of carbon layers are hydrogenated by H2O, promoting the reconstruction and orderly stacking of carbon layers. This work explains the coke gasification mechanism in a mixed CO2-H2O atmosphere and competitive effects between CO2 and the additive H2O in blast furnace, and would provide theoretical support for determination and optimization of hydrogen-rich blast furnace technology.

Non-destructive analysis of a mixed H2O–CO2 fluid in experimental noble-metal capsule by means of freezing and high-energy synchrotron X-ray diffraction

High-pressure high-temperature syntheses that involve volatile-bearing aqueous fluids are typically accomplished by enclosing the samples in gas-tight welded shut noble-metal capsules, from which the bulk volatile content must be extracted to be analyzed with mass spectroscopy, hence making the analysis non-replicable. Here we describe a novel non-destructive method that ensures the identification and the quantitative estimate of the volatiles directly in the sealed capsule, focusing on fluid H2O–CO2 mixtures equilibrated with graphite at conditions of geological interest (1 GPa, 800 °C). We used a high-energy (77 keV) synchrotron X-ray radiation combined with a cryostat to produce X-ray diffraction patterns and X-ray diffraction microtomographic cross-sections of the volatile-bearing samples down to –180 °C, thus encompassing the conditions at which crystalline phases-solid CO2 and clathrate (CO2 hydrate)-form. The uncertainty of the method is < 15 mol%, which reflects the difference between the volatile proportion estimated by both Rietveld refinement of the diffraction data and by image analysis of the microtomograms, and the reference value measured by quadrupole mass spectrometry. Therefore, our method can be reliably applied to the analysis of frozen H2O–CO2 mixtures and, moreover, has the potential to be extended to experimental fluids of geological interest containing other volatiles, such as CH4, SO2 and H2S.

Dry and Wet CO2 Capture from Milk‐Derived Microporous Carbons with Tuned Hydrophobicity

AbstractPore size distribution and surface chemistry of bio‐derived (milk) microporous dominated carbon “MDC” is synergistically tuned, allowing for promising carbon capture in a dry CO2 atmosphere and in mixed H2O–CO2. The capture capacity is attributed to the synergy of a large total surface area with an ultramicroporous and microporous texture (e.g., Stot 1889 m2 g−1, Smic 1755 m2 g−1, Sultra 1393 m2 g−1), and a high content of nitrogen and oxygen heteroatom moieties (e.g., 5 at% N, 10.5 at% O). Tailored two‐step low‐temperature pyrolysis‐chemical activation is employed to take advantage of the intrinsic properties of the precursor, allowing for this unusual textural properties‐heteroatoms combination. For example, tested at 1 bar and 295 or 273 K, MDCs adsorb up to 22.0 and 29.4 wt% CO2, respectively. MDCs are also tailored to be hydrophobic, with CO2/H2O adsorption selectivity even after prolonged cycling. Maximum working capacities of 10.8 wt% for pure CO2 and 3.5 wt% for a flue gas simulant (15% CO2, 85% N2) are measured using temperature swing adsorption with dynamic purge gases, while being minimally affected by humid conditions. This work is directly aligned with the United Nation’s Sustainable Development Goal 13, take urgent action to combat climate change and its impacts.

Neogene Metasomatism in the Subcontinental Lithosphere beneath SE Asia—Evidence from Modal and Cryptic Phosphorus Enrichment in Peridotites and Pyroxenites from Southern Laos

AbstractMetasomatism is the prime process to create compositional heterogeneity of the upper mantle. Mineralogical and mineral chemical changes of the mantle triggered by metasomatism can be used to deduce the nature of the metasomatic agent(s) and to constrain the timing of metasomatism. This information is vital for an understanding of the secular evolution of a given mantle segment and the magmatic processes occurring therein. For this study spinel-lherzolites and -websterites were collected from ∼16 Myr old alkali-basaltic lava flows that were extruded on the Bolaven Plateau in south–central Laos. These xenoliths are fragments of the shallow continental lithosphere of the SE Asian peninsula and originate from a mantle segment that acted as source for Cenozoic basaltic volcanism in the wake of the India–Asia collision. In both rock types modal metasomatism formed apatite ± whitlockite ± phlogopite ± calcic amphibole ± calcite ± orthopyroxene. The principal metasomatic phase is apatite, which appears in three varieties. Type-I apatite is ±inclusion-free and associated with phlogopite, calcic amphibole, calcite and lamellar orthopyroxene. It is high in Na and low in P and shows low analytical totals indicating a type-B carbonate–apatite component. Type-I apatite presumably precipitated from a P-alkali-rich mixed H2O–CO2 fluid with low large ion lithophile element (LILE)–light rare earth element (LREE) contents. Type-II apatite shows a spongy texture and has lower Na and higher P contents with higher analytical totals. Crosscutting discontinuous zones of type-II characteristics within type-I apatites indicate type-II formation through an exchange Na+ + CO32– = PO43– + Ca2+ by a later fluid with lower aCO2. REE-rich type-III apatite is the youngest type and formed by infiltration of basaltic melts as part of spongy rims around clinopyroxene. One lherzolite contains whitlockite in addition to apatite. Whitlockite formation is ascribed to a short-lived metasomatic event involving a fluid with extremely low aH2O. Disequilibrium between whitlockite and the bulk assemblage is indicated by hydrous silicates in the immediate vicinity of whitlockite and by substantial H2O contents of 250–370 µg g–1 in clinopyroxenes and 170–190 µg g–1 in orthopyroxenes. High-density (1·15–≥1·17 g m–3) CO2–fluid inclusions in the whitlockite-bearing sample provide evidence for the presence of low-aH2O fluids at mantle depths. The spinel-herzolites may also show cryptic metasomatism evidenced by P zoning in olivine, which is characterized by P-poor (&amp;lt;20–130 µg g–1) cores and P-rich (170–507 µg g–1) rims, the latter in part with oscillatory zoning on a µm scale. Element correlations indicate [4]Si4+ + [6](Mg, Fe)2+ = [4]P5+ + [6]Li+, 2 [4]Si4+ + 4 [6](Mg, Fe)2+ = 2 [4]P5+ + 3 [6](Mg, Fe)2+ + [6]vac and/or 5 [4]Si4+ = 4 [4]P5+ + [4]vac as major P incorporation mechanisms. High P–T experiments conducted at 2 GPa and 950–1050 °C yield apatite-saturated P contents of olivine in the range ∼360–470 µg g–1. Most P concentrations in olivines from the xenoliths including those in the P-rich rims, however, are significantly lower than the apatite-saturated values, which indicates disequilibrium uptake of P during growth of the P-rich rims by dissolution–reprecipitation. Diffusion modeling indicates that the P zoning must have formed within decades prior to the eruption of the host basalts. This is consistent with the preservation of Li disequilibrium partitioning between olivine and pyroxenes in some of the xenoliths. All metasomatic phenomena were assigned to two metasomatic events, both of which were in close temporal relation with the eruption of the xenolith host basalts: an older event-1 formed type-I apatite, hydrous silicates, calcite and orthopyroxene and caused the modification of type-I apatite composition towards that of type-II. It is also likely to be responsible for whitlockite formation and P zoning in olivine. A younger event-2 comprises all paragenetic, textural and compositional modifications of the xenolith assemblages associated with the infiltration of basaltic melts.

H2O–CO2 solubility in alkali-rich mafic magmas: new experiments at mid-crustal pressures

Volatile solubility in magmas depends on several factors, including composition and pressure. Mafic magmas with high concentrations of alkali elements are capable of dissolving larger quantities of H2O and CO2 than subalkaline basalt, which possibly contributes to large explosive eruptions. Existing volatile solubility models for alkali-rich mafic magmas are well calibrated below ~ 200 MPa, but at greater pressures the experimental data are sparse. To fill in this gap, we conducted a set of mixed H2O–CO2 volatile solubility experiments between 400 and 600 MPa at 1200 °C in six mafic compositions with variable alkali contents (Stromboli, Etna, Vesuvius, Erebus, Sunset Crater, and the San Francisco Volcanic Field). Results from our experiments indicate that existing volatile solubility models for alkali-rich mafic magmas, if extrapolated beyond their calibrated ranges, do not accurately describe CO2 solubility at mid-crustal pressures. We adapt an existing thermodynamic model to reflect our higher-pressure experimental data by determining model parameters $$\Delta {\text{V}}_{r}^{0,m}$$ (partial molar volume change of CO2 reaction) and K0 (equilibrium constant) for each studied composition. In these compositions, $$\Delta {\text{V}}_{r}^{0,m}$$ is found to vary between ~ 15 and ~ 25 cm3 mol−1, while ln K0 ranges from − 14.9 to − 14.0. The calculated solubility curves show good agreement with CO2 solubility data from the experiments and provide a more accurate description of CO2 solubility than purely empirical fits. These new experiments indicate while CO2 solubility is increased in alkali-rich mafic magmas, it is not simply controlled by total alkali content but rather the full multicomponent magma composition.

CO2–H2O solubility in K-rich phonolitic and leucititic melts

The solubility of CO2 and H2O in phonolitic and leucititic melts from Vesuvius and Colli Albani was investigated experimentally at 1250 °C and pressures between 50 and 300 MPa as a function of CO2–H2O fluid composition. Quenched glasses were analyzed for their volatile contents by thermogravimetry, carbon–sulfur analysis, and Fourier transform infrared (FTIR) spectroscopy, which enabled the determination of the absorption coefficients of the H2O- and CO2-related IR bands at 5200 cm−1 (H2O molecules), 4500 cm−1 (OH groups), and the carbonate doublet at 1510 and 1430 cm−1. No molecular CO2 was detected in our phonolitic and leucititic glasses. Leucititic glasses with elevated CO2 concentrations (approaching total absorption in transmission FTIR measurements) were also analyzed quantitatively by micro-ATR (attenuated total reflection) IR spectroscopy. While the water solubility in both melts is quite similar for pure H2O as well as for mixed CO2–H2O fluids (at given $$ f_{{{\text{H}}_{ 2} {\text{O}}}} $$ ), the CO2 solubility depends strongly on melt composition. In the range of 100–300 MPa, the solubility of pure CO2 increases from 580 to 1800 ppm in the phonolite melt and from 2950 to 8460 ppm in the leucitite melt. For the leucitite melt, we observe a single power law trend of CO2 solubility as function of $$ f_{{{\text{CO}}_{ 2} }} $$ , regardless if the melt was equilibrated with pure CO2 or mixed CO2–H2O fluids, indicating that water acts as diluent of the fluid phase. However, for the phonolite melt, we observe for mixed CO2–H2O samples a positive solubility deviation from the power law trend defined by the data for pure CO2 solubility. This effect seems to increase with increasing water content and pressure. Our interpretation is that this enhanced CO2 solubility is caused by melt depolymerization induced by water and is more apparent in the relatively polymerized phonolitic melt compared to the relatively depolymerized leucititic melt.

Argon behavior in basaltic melts in presence of a mixed H2O-CO2 fluid at upper mantle conditions

The behavior of argon in H2O-CO2 bearing basaltic melts was experimentally investigated in the pressure range 1–5GPa and at temperatures between 1350 and 1600°C. Our experimental data simulate the partitioning of argon between an Ar-H2O-CO2 bearing fluid and a silicate melt occurring during magma ascent and degassing. The experimental results show several features:-At a pressure of 1GPa the variation of H2O from 0.35 to about 2wt.% (at constant CO2 content) does not induce any systematic variation of argon dissolved in basaltic melt. For higher water contents (>2wt.%) we observe a positive effect of water on argon solubility.-In the range of 3–5GPa, we did not observe any systematic variation of the argon content in the basalt melt for water concentration from 0.35 to 5.3wt.% and at CO2 content <0.5wt.%. For CO2 content >0.5wt.%, argon concentration in basalt melt decreases from about 3800 to 2400ppm when the CO2 content increases from 0.5 to 0.8wt.%.-At all pressures investigated in the present study, a negligible effect of CO2 for concentration<5000ppm on argon content in the silicate melt is observed.-More importantly (despite all these variations) it seems that the effect of pressure in the range of 1 to 5GPa is the dominant parameter on argon solubility in basaltic melt. Pressure has a positive effect on argon incorporation in the H2O-CO2 bearing basaltic melt reaching at 3GPa a concentration of ~0.38wt.%. This maximum of ~0.38wt.% corresponds to 6.8×10−5cm3g−1bar−1 at standard temperature and pressure, a value of the same order of magnitude as that derived from volatiles free basaltic melts equilibrated with argon. The experimental data can be well described by a thermodynamic model assuming mixing of volatile species and oxygen in the silicate melt. The results can be applied for a better understanding of the fractionation noble gas/noble gas and noble gas/CO2 occurring in degassing processes during magma ascent.

Evolution of the Chilka Lake granulite complex, northern Eastern Ghats Belt, India: First evidence of ~ 780 Ma decompression of the deep crust and its implication on the India–Antarctica correlation

High-grade para- and orthogneissic rocks near the Chilka Lake granulite complex, northern part of the Eastern Ghats Belt show complex structural and petrological history. Based on field and petrographic characters, five (M1–M5) metamorphic events could be identified. The earliest metamorphic event (M1) produced amphibolite grade mineral assemblage which produced the peak granulite (M2) assemblages at 900–950°C, 8.5–9.0kbar. The third metamorphic event caused decompression of the deeper crust up to 700–800°C, 6.0–6.5kbar. This was followed by cooling (M4) and subsequent thermal overprinting (M5). Fluid-composition during M3 was dominated by high-density CO2 and changed to low-density mixed CO2–H2O during the M3. Zircon U–Pb SHRIMP data suggest 781±9Ma age for M3 event. Texturally constrained monazite U–Th–Pb EPMA data, on the other hand, yield a group age of 988±23Ma from grain interior, which can signifies the age of M2 event. Few spots with younger dates in the range of 550–500Ma are also noted. This interpretation changes the existing tectonothermal history of northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories. While the central Domain 2 evolved through early anticlockwise P–T path culminating in ultrahigh temperature, the northern Domain 3 evolved through a clockwise P–T path. It appears that the Domain 3 was contiguous to East Antarctica and became part of the Eastern Ghats Belt during the assembly of Gondwana. The ca. 780Ma decompression event in the northern Eastern Ghats Belt opens up new possibilities for interpreting the breakup of Rodinia.

A glimpse into Augustine Volcano's Pleistocene past: Insight from the petrology of a massive rhyolite deposit

Activity at Augustine Volcano, Alaska, has been characterized by intermediate composition domes, flows, and tephras during the Holocene. Erosive lahars and pyroclastic flows associated with the 2006 eruption revealed large exposures of voluminous rhyolite pumice fall beneath glacial tills; the massive rhyolite deposit is evidence of anomalously large prehistoric eruptions. The rhyolite is petrologically and mineralogically different from more recent eruptive products, with abundant amphibole (calcic amphiboles and cummingtonite) and quartz. Three texturally and chemically distinct lithologies are present. Fe–Ti oxide equilibria suggest temperatures of ~765°C and oxygen fugacities of NNO+1.5. Melt inclusions indicate that magma representing the stratigraphically lowest lithology was crystallizing at ~260MPa with a contemporary mixed H2O–CO2 fluid phase becoming progressively more H2O-rich. Magma forming the other lithologies crystallized in the presence of this H2O-dominated fluid, as demonstrated by the presence of cummingtonite and little to no CO2 in melt inclusions. Amphibole and quartz–feldspar–melt equilibria models yield results indicating a range of crystallization pressures from ~400MPa to ~175MPa. Apatites and melt inclusions have lower chlorine contents than more recently erupted material at Augustine suggesting that the composition of Augustine's volatile phase has changed over time. Reheating textures in melt inclusions and phenocrysts, as well as the presence of xenocrysts of olivine and clinopyroxene containing mafic melt inclusions, signify the likelihood of mixing and/or mingling of magmas as an eruption trigger. The unique qualities of this Pleistocene rhyolite and the potential hazard of a similarly large eruption in modern times indicate that further study is warranted.

Melt inclusion CO2 contents, pressures of olivine crystallization, and the problem of shrinkage bubbles

The H2O and CO2 contents of melt inclusions can potentially be used to infer pressures of crystallization and inclusion entrapment because the solubility of mixed H2O-CO2 vapor has been determined experimentally for a wide range of melt compositions. However, melt inclusions commonly develop a shrinkage bubble during post-entrapment cooling and crystallization because these processes cause a pressure drop in the inclusion. This pressure drop causes a vapor bubble to nucleate, leading to exsolution of low-solubility CO2 from the trapped melt. To investigate the loss of CO2 into such bubbles, we experimentally heated large, naturally glassy melt inclusions in olivine (Fo contents of 88.1 ± 0.2) from a Mauna Loa picrite to rehomogenize the inclusions. Rapid heating to 1420 °C using a hightemperature heating stage dissolved the shrinkage bubbles into the melt. CO2 contents measured by FTIR spectroscopy and recalculated for melt in equilibrium with the olivine host are 224-505 ppm (n = 11) for heated inclusions, much higher than the CO2 contents of naturally quenched inclusions from the same sample (38-158 ppm; n = 8). Pressures of inclusion entrapment calculated from the H2O and CO2 data for the heated inclusions range from 0.5 to 1.1 kbar, indicating that Mg-rich olivine crystallized at very shallow depths beneath the surface of Mauna Loa. Our results indicate that 40-90% (average 75%) of the original CO2 dissolved in the melt at the time of inclusion entrapment can be lost to the shrinkage bubble during post-entrapment cooling. We show that the computational method of Riker (2005), which predicts the pre-eruption shrinkage bubble size as a function of the difference between trapping temperature and pre-eruption temperature, successfully reproduces our experimental results. Our results demonstrate that the mass of CO2 contained in shrinkage bubbles must be considered to accurately infer original pressures of crystallization for melt inclusions. However, the effect is expected to be smaller for more H2O-rich melt inclusions than those studied here because the vapor bubble in such inclusions will have lower mole fractions of CO2 than the low-H2O inclusions in our study.

A high-pressure high-temperature setup for in situ Raman spectroscopy of supercritical fluids

A high-pressure/high-temperature cell dedicated to Raman spectroscopy is presented. The P and T ranges are optimized for the study of supercritical fluids (T≤975K, P≤200MPa); the P and T parameters are controlled independently. The autoclave was adapted from a previous cell (designed for X-ray absorption and scattering spectroscopies) to answer the specific requirement of Raman spectroscopy. Original high pressure windows and sample cell have been developed to ensure both pressure resistance and transparency for the optical laser and Raman scattering beams. An optical integration of the autoclave in the Raman spectrometer setup was designed to perform in situ Raman experiments on fluids. The spectroscopic measurements can be combined with visual observation, which is particularly useful for the study of multi-phasic systems. As examples of the efficiency of the set-up and its scientific opportunities, we present Raman measurements on water, carbon dioxide and mixed H2O–CO2 system obtained from ambient to supercritical conditions.

Contrasting compositional trends of rocks and olivine-hosted melt inclusions from Cerro Negro volcano (Central America): implications for decompression-driven fractionation of hydrous magmas

Melt inclusions in olivine Fo83–72 from tephras of 1867, 1971 and 1992 eruptions of Cerro Negro volcano represent a series of basaltic to andesitic melts of narrow range of MgO (5.6–8 wt %) formed by ~46 wt % fractional crystallization of olivine (~6 wt %), plagioclase (~27 wt %), pyroxene (~13 wt %) and magnetite (<1 wt %) from primitive basaltic melt (average SiO2 = 49 wt %, MgO = 7.6 wt %, H2O = 6 wt %) as it ascended to the surface from the depth of about 14 km. The crystallization occurred at increasing liquidus temperature from 1,050 to 1,090 °C in the pressure range from 400 to 50 MPa and was induced by release of mixed H2O–CO2 fluid from the melt at decreasing pressure. Matrix glass compositions fall at the high-Si end of the melt inclusion trend and represent the final stage of melt crystallization during and after eruption. The bulk compositions of erupted Cerro Negro magmas (tephras and lavas) range from high- to low-MgO (3–10 wt %) basalts, which form a compositional array crossing the trend of melt inclusions so that virtually no rock from Cerro Negro has composition akin to true melt represented by the inclusions. The variations of the bulk magma (rocks) and melt (melt inclusions) compositions can be generated in a dyke connecting a deep primitive magma reservoir with the Cerro Negro edifice. While the melt inclusions represent the compositional trend of instantaneous melts along the magma pathway at decreasing pressure and H2O content, occurrence of low-Mg to high-Mg basalts reflects the process of phenocryst re-distribution in progressively evolving melt. The crystallization scenario is anticipated to operate everywhere in dykes feeding basaltic volcanoes and can explain the predominance of plagioclase-rich high-Al basalts in island arc as well as typical compositional variations of magmas during single eruptions.

A novel high pressure column flow reactor for experimental studies of CO2 mineral storage

The objective of this study was to design, build, and test a large scale laboratory high pressure column flow reactor (HPCFR) enabling experimental work on water–rock interactions in the presence of dissolved gases, demonstrated here by CO2. The HPCFR allows sampling of a pressurized gas charged liquid along the flow path within a 2.3m long Ti column filled with either rock, mineral, and/or glass particles. In this study, a carbonated aqueous solution (1.2M CO2(aq)) and basaltic glass grains was used. Given the pressure and temperature rating (up to 10MPa at 90°C) of the HPCFR, it can also be used with different gas and/or gas mixtures, as well as for supercritical fluid applications. The scale of the HPCFR, the possibility of sampling a reactive fluid at discrete spatial intervals under pressure, and the possibility of monitoring the evolution of the dissolved inorganic carbon and pH in situ all render the HPCFR unique in comparison with other columns constructed for studies of water–rock interactions. We hope that this novel experimental device will aid in closing the gap between bench scale reactor experiments used to generate kinetic data inserted into reactive transport models and field observations related to geological carbon sequestration. A detailed description and testing of the HPCFR is presented together with first geochemical results from a mixed H2O–CO2 injection into a basalt slurry whose solute concentration distribution in the HPCFR was successfully modelled with the PHREEQC geochemical computer code.

The P-T-X(fluid) evolution of meta-anorthosites in the Eastern Granulites, Tanzania

Meta-anorthosite bodies are typical constituents of the Neoproterozoic Eastern Granulites in Tanzania. The mineral assemblage (and accessory components) is made up of clinopyroxene, garnet, amphibole; scapolite, epidote, biotite, rutile, titanite, ilmenite and quartz. Within the feldspar-rich matrix (70–90% plagioclase), mafic domains with metamorphic corona textures were used for P–T calculations. Central parts of these textures constitute high-Al clinopyroxene – which is a common magmatic mineral in anorthosites – and is therefore assumed to be a magmatic relict. The clinopyroxene rims have a diopsidic composition and are surrounded by a garnet corona. Locally the pyroxene is surrounded by amphibole and scapolite suggesting that a mixed CO2–H2O fluid was present during their formation. Thermobarometric calculations give the following conditions for the metamorphic peak of the individual meta-anorthosite bodies: Mwega: 11–13 kbar, 850–900 °C; Pare Mountains: 12–14 kbar, 850–900 °C; Uluguru Mountains: 12–14 kbar, 850–900 °C. The P–T evolution of these bodies was modelled using pseudosections. The amount and composition of the metamorphic fluid and <0.5 mol.% fluid in the bulk composition is sufficient to produce fluid-saturated assemblages at 10 kbar and 800 °C. Pseudosection analysis shows that the corona textures most likely formed under fluid undersaturated conditions or close to the boundary of fluid saturation. The stabilities of garnet and amphibole are dependent on the amount of fluid present during their formation. Mode isopleths of these minerals change their geometry drastically between fluid-saturated and fluid-undersaturated assemblages. The garnet coronae developed during isobaric cooling following the metamorphic peak. The cooling segment is followed by decompression as indicated by the growth of amphibole and plagioclase. The estimated of the metamorphic fluid is ∼0.3–0.5. Although the meta-anorthosites have different formation ages (Archean and Proterozoic) they experienced the same Pan-African metamorphic overprint with a retrograde isobaric cooling path. Similar P–T evolutionary paths are known from the hosting granulites. The presented data are best explained by a tectonic model of hot fold nappes that brought the different aged anorthosites and surrounding rocks together in the deep crust followed by an isobaric cooling history.

Estimation of pre-eruptive magmatic water fugacity in the Phlegrean Fields, Naples, Italy

We estimated the water fugacity (fH(2)O) in the trachytic magma of Phlegrean Fields using the biotite-magnetite-sanidine equilibrium. We confirm that the partly ionic model is the most appropriate to estimate annite activity (a(annite)) for the experimental biotite. Crystallization experiments were carried out on a representative sample of trachytic Breccia Museo eruption, Naples, Italy. Experiments were performed in the temperature and pressure range or 725-870 degrees C and 50-200 MPa, and redox conditions ranging from NNO (nickel- nickel oxide) + 1 (+/- 0.2) to FMQ (fayalite + magnetite + quartz). Most experiments were done under conditions of H2O saturation (P-water = P-total). Few experiments were done using a mixed H2O-CO2 fluid phase. The pre-eruptive fH(2)O of the Phlegrean Fields magma is estimated at 735 bars, which compares well with available melt inclusion constraints. Our results confirm that this geohygrometer can be used in any magmatic systems bearing the worked assemblage.

Amorphous Materials: Properties, structure, and Durability: Oxidation state of iron in hydrous phono-tephritic melts

The oxidation state of Fe in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed H2O-CO2 fluids was studied experimentally at 1200 and 1250 °C and pressures from 50 to 500 MPa. The oxygen fugacity (fO₂) varied from NNO-2.9 to NNO+2.6 in log fO₂, relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The Fe redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the Fe2+/ΣFe ratio of milligram-sized samples within ±0.03 (2σ). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The Fe2+/ΣFe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on Fe2+/ΣFe at given fO₂ was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of Fe was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower Fe2+/ΣFe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher K2O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in FeOT (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between log fO₂ and Fe3+/Fe2+ for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as H2O or K2O, on the redox state of Fe in silicate melts.

New experimental data on biotite + magnetite + sanidine saturated phonolitic melts and application to the estimation of magmatic water fugacity

New experimental data are presented that allows the biotite–magnetite–sanidine equilibrium to be used for estimating water fugacity (ƒH2O) in hydrous phonolitic magmas. It is also demonstrated that the partly ionic model gives the best estimate for the annite activity (aannite). Crystallization experiments were carried out on a representative sample of peralkaline, phonolitic obsidian of Montana Blanca (MB) pumice deposit, Tenerife, Canary Islands. Experiments were performed from 720–810 °C and 50–250 MPa. Redox conditions were varied between NNO (nickel + nickel oxide) + 1 (±0.2) and FMQ (fayalite + magnetite + quartz). The majority of the experiments were done under H2O saturation conditions (Pwater = Ptotal). Several experiments were done using a mixed H2O-CO2 s uid phase whereas in other experiments 10 or 20 wt% powdered alkali feldspar was added to the starting material. The pre-eruptive ƒH2O of the Montana Blanca magma is estimated at 676 ± 200 bars. The pre-eruptive ƒH2O for the Fish Canyon tuff (753–2978 bars) and Bishop tuff rhyolite (1065–2440 bars) were also calculated, as well as ƒH2O for metamorphic biotite from Au Sable Forks (≈ 130 bars). The results of this study suggest that this geohygrometer can be used in any magmatic system in which biotite–magnetite–sanidine is a stable assemblage.

Single photon ionization of van der Waals clusters with a soft x-ray laser: (CO2)n and (CO2)n(H2O)m

Pure neutral (CO2)n clusters and mixed (CO2)n(H2O)m clusters are investigated employing time of flight mass spectroscopy and single photon ionization at 26.5 eV. The distribution of pure (CO2)n clusters decreases roughly exponentially with increasing cluster size. During the ionization process, neutral clusters suffer little fragmentation because almost all excess cluster energy above the vertical ionization energy is taken away by the photoelectron and only a small part of the photon energy is deposited into the (CO2)n cluster. Metastable dissociation rate constants of (CO2)n+ are measured in the range of (0.2-1.5) x 10(4) s(-1) for cluster sizes of 5< or =n< or =16. Mixed CO2-H2O clusters are studied under different generation conditions (5% and 20% CO2 partial pressures and high and low expansion pressures). At high CO2 concentration, predominant signals in the mass spectrum are the (CO2)n+ cluster ions. The unprotonated cluster ion series (CO2)nH2O+ and (CO2)n(H2O)2+ are also observed under these conditions. At low CO2 concentration, protonated cluster ions (H2O)nH+ are the dominant signals, and the protonated CO2(H2O)nH+ and unprotonated (H2O)n+ and (CO2)(H2O)n+ cluster ion series are also observed. The mechanisms and dynamics of the formation of these neutral and ionic clusters are discussed.

Effects of temperature, pH and NaCl on protease activity in digestive tract of young turbot,Scophthalmus maximus

Isochemical conversion of garnet-biotite bearing paragneiss to charnockite in the Precambrian Khondalite belt of southern Kerala is described from Ponmudi area. Petrographic evidences indicate the formation of hypersthene by the breakdown of biotite in the presence of quartz following the reaction: Biotite + quartz → hypersthene + K-feldspar + vapour. The estimated pressure — temperature conditions of metamorphism are around 5–7 kbars and 750° ± 40°C. Presence of CO2-rich, mixed CO2-H2O and H2O-rich inclusions were noticed in gneiss as well as in charnockites. Charnockites contain abundant CO2-rich inclusions.

Reactive flow of mixed CO2–H2O fluid and progress of calc‐silicate reactions in contact metamorphic aureoles: insights from two‐dimensional numerical modelling

AbstractPrevious models of hydrodynamics in contact metamorphic aureoles assumed flow of aqueous fluids, whereas CO2 and other species are also common fluid components in contact metamorphic aureoles. We investigated flow of mixed CO2–H2O fluid and kinetically controlled progress of calc‐silicate reactions using a two‐dimensional, finite‐element model constrained by the geological relations in the Notch Peak aureole, Utah. Results show that CO2 strongly affects fluid‐flow patterns in contact aureoles. Infiltration of magmatic water into a homogeneous aureole containing CO2–H2O sedimentary fluid facilitates upward, thermally driven flow in the inner aureole and causes downward flow of the relatively dense CO2‐poor fluid in the outer aureole. Metamorphic CO2‐rich fluid tends to promote upward flow in the inner aureole and the progress of devolatilization reactions causes local fluid expulsion at reacting fronts. We also tracked the temporal evolution of P‐T‐XCO2conditions of calc‐silicate reactions. The progress of low‐ to medium‐grade (phlogopite‐ to diopside‐forming) reactions is mainly driven by heat as the CO2 concentration and fluid pressure and temperature increase simultaneously. In contrast, the progress of the high‐grade wollastonite‐forming reaction is mainly driven by infiltration of chemically out‐of‐equilibrium, CO2‐poor fluid during late‐stage heating and early cooling of the inner aureole and thus it is significantly enhanced when magmatic water is involved. CO2‐rich fluid dominates in the inner aureole during early heating, whereas CO2‐poor fluid prevails at or after peak temperature is reached. Low‐grade metamorphic rocks are predicted to record the presence of CO2‐rich fluid, and high‐grade rocks reflect the presence of CO2‐poor fluid, consistent with geological observations in many calc‐silicate aureoles. The distribution of mineral assemblages predicted by our model matches those observed in the Notch Peak aureole.