Kinetics of crystallization: example of micro-crystallization in basalt lava

The kinetics of crystallization of basalt glass from Kilauea, Hawaii, was investigated to derive time and temperature dependence of growth rates, and to relate these results to crystallization characteristics that develop during in-place cooling of lava and isothermal re-heating in the lab. The choice of temperatures of re-heating was based on observations that pyroxene and Fe-Ti oxide production starts at about 850 °C and plagioclase above 920 °C. Crystallization parameters were determined by the crystal size distribution method (CSD), which allows one to derive growth (G) and nucleation (J) rates, if the residence time within the temperature interval of crystallization is known. For the in-place cooled lava, the residence time was determined from cooling rates that could be derived from literature data of temperature measurements in the upper 2 cm of lava lobes. Re-heating of basalt glass as a function of time shows a linear relationship between log G and log (time): % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabiabaaGcbaGaciiBaiaac+ % gacaGGNbGaam4raiabg2da9iabgkHiTiaadggaciGGSbGaai4Baiaa % cEgacaWG0bGaeyOeI0Iaam4AamaaBaaaleaacaaIXaaabeaaaaa!42ED! logG = - alogt - k₁\log G = - a\log t - k_1 . This observation was possible because the time scale of crystallization was similar to the observational time scale, a condition usually not given for cooling processes. The time dependence of G is shown to correspond to a decrease in G (and J) from the original surface-air interface to the interior of the lava: a change that occurs concomitant with an increase in crystal size and number density. Hence, it is the time dependence of G that explains the hitherto well-observed relationship with cooling rate along a temperature gradient in magmatic bodies. Moreover, the log-linear relationship between time and growth rate is suggested to describe heterogeneous nucleation and growth, which is independent of the process, i.e. cooling or metamorphism. Isothermal re-heating extinguishes the high growth rate signatures of cooling. Temperature dependence of growth rates, carried out at 24 h, shows minimum temperatures of 900-950 °C, which, because of the time dependence of growth, refers to the nucleation and crystallization maximum, and is in agreement with results from differential scanning calorimetry.     

Uranium removal from groundwater using hydroxyapatite

The present work shows that U can be effectively removed from groundwater using permeable reactive barriers with hydroxyapatite (HAP) as reactive material. The main factor influencing the removal processes is the composition of the groundwater, namely the concentration of Ca and carbonate. Sorption of U onto the HAP surface seems to be the dominant removal process with the possibility of remobilisation. Newly formed U-phosphate minerals were detected by ESEM/EDX and XRD in samples with high U content indicating either a dissolution-precipitation mechanism or sorption onto the apatite surface followed by alteration of the structure. The formed U-phosphate minerals are stable under common groundwater conditions and can be remobilised only at high pH-values and high carbonate concentrations.     

Quantification of strain rate in the Western Alps using geodesy: comparisons with seismotectonics

The contrasted seismotectonic regime of the Western Alps is characterized by radial extension in the high chain, combined with local compressive areas at the foothill of the belt, and everywhere occurrence of transcurrent tectonics. Here, we compare this seismotectonic regime to a large-scale compilation of GPS measurements in the Western Alpine realm. Our analysis is based on the raw GPS database, which give the measured velocity field with respect to the so called “stable Europe”, and an interpolated velocity field, in order to smooth the database on a more regular mesh. Both strain rate and rotational components of the deformation are investigated. The strain rate field shows patch-like structure, with extensional areas located in the core and to the North of the belt and compressional areas located in its periphery. Although the GPS deformation fields (both raw and interpolated) are more spatially variable than the seismotectonic field, a good qualitative correlation is established with the seismotectonic regionalization of the deformation. The rotation rate fields (both raw and interpolated) present counterclockwise rotations in the innermost part of the belt and a surprising continuous zone of clockwise rotations following the arc-shape geometry of the Western Alps along their external border. We interpret this new result in term of a counterclockwise rotation of the Apulia plate with respect to the stable Europe. This tectonic scheme may induce clockwise rotations of crustal block along the large strike-slip fault system, which runs in the outer part of the belt, from the Rhône-Simplon fault to the Belledonne fault and Southeastward, to the High-Durance and Argentera fault.     

On weighted total least-squares adjustment for linear regression

The weighted total least-squares solution (WTLSS) is presented for an errors-in-variables model with fairly general variance–covariance matrices. In particular, the observations can be heteroscedastic and correlated, but the variance–covariance matrix of the dependent variables needs to have a certain block structure. An algorithm for the computation of the WTLSS is presented and applied to a straight-line fit problem where the data have been observed with different precision, and to a multiple regression problem from recently published climate change research.     

Best invariant covariance component estimators and its application to the generalize multivariate adjustment of heterogeneous deformation observations

Repeated measurements, like relevelling or periodically observed control networks, e.g., may be adjusted within the Simple Multivariate Gauss-Markov Model if the coefficient matrices are identical at each epoch and if the observations are homogeneous yielding proportional variance-covariance matrices between each two (not necessarily different) epochs. However, when processing data concerning recent crustal movements both conditions are violated, in general, such that the usual approach becomes inapplicable. Therefore, a procedure is proposed for this case which makes a joint adjustment possible within the Generalized Multivariate Regression Model of Heterogeneous Observations and which further coincides with the standard multivariate analysis in the special case.     

Fluid regimes in the deformation of the Helvetic nappes,Switzerland, as inferred from stable isotope data

The stable isotope composition of veins, pressure shadows, mylonites and fault breccias in allochthonous Mesozoic carbonate cover units of the Helvetic zone show evidence for concurrent closed and open system of fluid advection at different scales in the tectonic development of the Swiss Alps. Marine carbonates are isotopically uniform, independent of metamorphic grade, where ¹³C=1.5±1.5 (1 ) and ¹⁸O=25.4±2.2 (1 ). Total variations of up to 2 in ¹³C and 1.5 in ¹⁸O occur over a cm scale. Calcite in pre- (Type I) and syntectonic (Type II) vein arrays and pressure shadows are mostly in close isotopic compliance with the matrix calcite, to within ±0.5, signifying isotopic buffering of pore fluids by host rocks during deformation, and closed system redistribution of carbonate over a cm to m scale. This is consistent with microstructural evidence for pressure solution — precipitation deformation.Type III post-tectonic veins occur throughout 5 km of structural section, extend several km to the basement, and accommodate up to 15% extension. Whereas the main population of Type III veins is isotopically undistinguishable from matrix carbonates, calcite in the largest of these veins is depleted in ¹⁸O by up to 23 but acquired comparable ¹³C values. This generation of veins involved geopressurized hydrothermal fluids at 200 to 350° C where ¹⁸O H₂O=–8 to +20, representing variable mixtures of ¹⁸O enriched pore and metamorphic fluids, with ¹⁸O depleted meteoric water. Calc-mylonites ( ¹⁸O=25 to 11) at the base of the Helvetic units, and syntectonic veins from the frontal Pennine thrust are characterized by a trend of ¹⁸O depletion relative to carbonate protoliths, due to exchange with an isotopically variable reservoir ( ¹⁸O H₂O=20 to 4). The upper limiting value corresponds to carbonate-buffered pore fluid, whereas the lower value is interpreted as ¹⁸O-depleted formation brines tectonically expelled at lithostatic pressure from the crystalline basement. Carbonate breccias in one of the large scale late normal faults exchanged with infiltrating ¹⁸O-depleted meteoric surface waters ( ¹⁸O=–8 to –10).During the main ductile Alpine deformation, individual lithological units and associated tectonic vein arrays behaved as closed systems, whereas mylonites along thrust faults acted as conduits for tectonically expelled lithostatically pressured reservoirs driven over tens of km. At the latest stages, marked by 5 to 15 km uplift and brittle deformation, low ¹⁸O meteoric surface waters penetrated to depths of several km under hydrostatic gradients.     

Field-aligned currents between 400 and 3000 km in auroral and polar latitudes

The polar orbiting magnetically stabilized satellite AZUR measured transverse magnetic variations in auroral and polar latitudes by means of a two component flux-gate magnetometer. Simultaneous measurements of $\text{λ2972}\text{A}\text{?}$ and $\text{λ3914}\text{A}\text{?}$ auroral emissions are related to low-energy zero-pitch-angle electron fluxes, which cause the transverse magnetic disturbances. Power spectra of the magnetic field variations are consistent with those of geomagnetic micropulsations.The sources of the field-aligned currents can be located in the Alfvén layer and in the magnetotail.     

Dépliage 3-D des anticlinaux bordant le synclinal fermé de la vallée des Ponts, Jura central, Suisse

The Ponts valley syncline is a closed basin within the Neuchâtel Jura fold and thrust belt. This syncline, apparently uplifted to an altitude of around 1000m is closed in the SW by an anticline with an oblique WNW-ESE direction. The 3-D geometry of the entire structure is examined and unfolded in detail. This syncline is filled with an unexpectedly thick series (~400m) of Tertiairy Molasse, as revealed by the CS-AMT (controlled source audio-magneto-telluric) and a reflexion seismic line. The latter also documents internal compressional structures within the well layered upper freshwater Molasse series. The 3-D configuration of the top Malm limestones has been constructed for the entire area based on new detailed geologic and structural mapping, hundreds of dip measurements, as well as geophysical data. The Malm marker bed displays three distinct types of structures: 1) Thrust faults with shallow dips, vergent to the NW and/or SE that are associated with folds interpreted as fault bend folds; 2) high angle inverse faults, mostly with a SE vergence are interpreted as inverted normal faults, inherited from a modest Oligo-Miocene extensional phase in a NW-SE direction; and 3) tear faults with a dominant N-S direction, probably inherited from an Oligocene extensional phase in association with the opening of the Rhine and Bresse grabens. Tear faults accommodate important lateral changes in fold geometry during the Late Miocene main folding-and-thrusting phase. All deformations are easily explained in an entirely thin-skinned fashion, taking place above a thick detachment horizon within Triassic evaporite series.Manuscrit reçu le 31 mars 2003 Révision acceptée le 23 juin 2004     

Effect of boron on the water speciation in (alumino)silicate melts and glasses

The investigation of hydrous boro(alumino)silicate melts and glasses with near infrared (NIR) spectroscopy revealed an important effect of boron on the water speciation. In the NIR spectra of B-bearing glasses new hydroxyl-related bands develop at the high frequency side of the 4500 cm⁻¹ peak. In NaAlSi₃O₈ + B₂O₃ glasses this new peak is present as a shoulder at 4650 cm⁻¹, and in NaAlSi₃O₈-NaBSi₃O₈ (Ab-Rd) glasses it appears as a resolved peak at 4710 cm⁻¹. These bands increase with increasing boron concentration, suggesting that they are due to B-OH complexes. Furthermore, the variations in the NIR spectra indicate that with increasing B-content, but constant total water concentration, the amount of structurally bonded hydroxyl groups increases at the expense of molecular H₂O. For example, at a total water concentration of 4 wt.%, pure Rd-glass contains ∼50% more water as hydroxyl groups than pure Ab-glass.In-situ NIR spectroscopy at high P and T using a hydrothermal diamond-anvil cell was used to gain information about the temperature dependence of the water speciation in NaBSi₃O₈ melts. The data demonstrate the conversion of molecular H₂O to hydroxyl groups with increasing temperature. However, a fully quantitative evaluation of the high T spectra was hampered by problems with defining the correct baseline in the spectra. As an alternative approach annealing experiments on a Rd-glass containing 2.8 wt.% water were performed. The results confirm the conversion of H₂O to OH groups with increasing T, but also suggest that the OH groups represented by the 4710 cm⁻¹ peak (B-OH) participate much less in the conversion reaction compared to X-OH, represented by the 4500 cm⁻¹ peak.