Experimental study of bubble coalescence in rhyolitic and phonolitic melts     

Jessica F Larsen  Marie-Helene Denis 《Geochimica et cosmochimica acta》2004,68(2):333-344

We have experimentally studied the process of bubble coalescence in rhyolite and phonolite melts of natural composition. The experiments involved decompression of water-saturated melts equilibrated at pressures and temperatures from 100 to 150 MPa and 775 to 840 °C in vertically oriented, rapid-quench capable, cold seal pressure vessels. One type of experiments (rhyolite MCR-100, 120, 150 and phonolite LSP-120 series') approximates a “static” bubble coalescence case, where we held the decompressed samples for ∼5 seconds to 4320 minutes (3 days) before quenching. The second type (rhyolite LPC-100 series) replicates an “expanding” bubble coalescence environment, where we continually decompressed the experiments at a rate of 0.5 MPa/s, examining samples quenched at ending pressures between 10 and 80 MPa. Our “static” case (MCR-100, 120, and 150, and LSP-120) results show significant increases in the modal bubble sizes and in the sizes of the largest bubbles, corresponding to measurable broadening in the size distributions. Their bubble number densities (N_V) decrease as a function of hold time at their final pressures (P_F), and can be fit well by power law functions. Our “expanding” case experiments (LPC-100) show a significant drop in N_V during the duration of the experiments that can be fit by an exponential equation as N_V vs. either time or P_F. Average estimates of bulk coalescence rates indicate a ∼1 order of magnitude drop in N_V for “static” case rhyolites in a 2-3 day period, and ∼2 orders of magnitude for phonolites within a 3 day period. Despite a ∼2 order of magnitude difference in viscosity, coalescene in the phonolite is only slightly faster than the rhyolite. The “expanding” case experiments show a ∼1 order of magnitude drop in N_V over 180 seconds. Thus, N_V's decrease 4 orders of magnitude faster in expanding vs. static bubbly rhyolite melts. Our results imply that significant bubble coalescence can occur in rhyolite magmas at relatively fast (∼20 m/s) ascent rates in the conduit. Thus, bubble interconnectivity, leading to high permeability, is possible during ascent. Bubble coalescence may occur during second boiling in magma bodies that are stalled in the crust. The timescales over which this occurs is much faster than the estimated rise rates for bubbles to reach the top of the magma chamber.  相似文献   

Heterogeneous bubble nucleation on Fe-Ti oxide crystals in high-silica rhyolitic melts     

James E. Gardner  Marie-Hélène Denis 《Geochimica et cosmochimica acta》2004,68(17):3587-3597

The nucleation of H₂O bubbles in magmas has been proposed as a trigger for volcanic eruptions. To determine how bubbles nucleate heterogeneously in silicate melts, experiments were carried out in which high-silica rhyolitic melts were hydrated at 740-800°C and 50-175 MPa, decompressed by 20-70 MPa, and held at the lower pressures for ≥10 s before being quenched. The hydration conditions were subliquidus, and all samples contain blocky magnetite + needle-shaped hematite ± plagioclase. Magnetite is abundant at 800°C and high pressures, whereas hematite becomes more abundant at lower temperatures and pressures. Bubbles nucleated in a single event in all samples, with the number density (N_T) of bubbles varying between 2 × 10⁷ and 1 × 10⁹ cm⁻³. At low degrees of supersaturation, one to a few bubbles nucleate on faces of magnetite, but at medium to high degrees of supersaturation, multiple bubbles nucleate on single magnetite grains. On hematite, one to a few bubbles nucleated at the ends of the needle-shaped crystals at medium supersaturations, but formed along their entire lengths at high supersaturations. N_T increases as water diffusivity decreases, indicating that the number of bubbles nucleated is influenced by their growth, which depletes the melt with respect to H₂O and lowers supersaturation. If volcanic eruptions are triggered by bubble formation in magmas stored in shallow-level magma chambers, then the supersaturations needed for heterogeneous nucleation suggest that only small amounts of crystallization are needed, whereas homogeneous nucleation is unlikely to trigger eruptions.  相似文献   

Methods for computing internal flattening, with applications to the Earth's structure and geodynamics     

C. Denis  M. Amalvict  Y. Rogister  & S. Tomecka-Sucho&#; 《Geophysical Journal International》1998,132(3):603-642

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A Chemical Equilibrium Model for Natural Waters   总被引：7，自引：0，他引：7  

Frank J. Millero  Denis Pierrot 《Aquatic Geochemistry》1998,4(1):153-199

This paper reviews the present status of the Pitzer chemical equilibrium model, which can be used to characterize the one-atmosphere activity coefficients of ionic and non-ionic solutes in natural waters as a function of temperature and ionic strength. The model considers the ionic interactions of the major seasalt ions (H, Na, K, Mg, Ca, Sr, Cl, Br, OH, HCO₃, B(OH)₄, HSO₄, SO₄, CO₃, CO₂, B(OH)₃, H₂O) and is based on the 25 °C model of Weare and co-workers. The model has been extended by a number of workers so that reasonable estimates can be made of the activity coefficients of most of the major seasalt ions from 0 to 250 °C. Recently coefficients for a number of solutes that are needed to determine the dissociation constants of the acids from 0 to 50 °C (H₃CO₃, B(OH)₃, H₂O, HF, HSO ₄ ^- , H₃PO₄, H₂S, NH ₄ ⁺ etc.) have been added to the model. These results have been used to examine the carbonate system in natural waters and determine the activity of inorganic anions that can complex trace metals. The activity and osmotic coefficients determined from the model are shown to be in good agreement with measured values in seawater. This model can serve as the foundation for future expansions that can examine the activity coefficient and speciation of trace metals in natural waters. At present this is only possible from 0 to 50 °C over a limited range of ionic strengths (<1.0) due to the limited stability constants for the formation of the metal complexes. The future work needed to extend the Pitzer model to trace metals is discussed.  相似文献   

Trace and major element models of granitoid genesis in the Pampean Ranges,Argentina     

Carlos W. Rapela  Denis M. Shaw 《Geochimica et cosmochimica acta》1979,43(7):1117-1129

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Sur lesStaurastrum du lac Léman     

Dr Jacques Naef  Prof. Dr Pierre Bourrelly  Paul Martin  Denis Mack 《Aquatic Sciences - Research Across Boundaries》1978,40(1):51-59

Among the Desmids which have been observed in the plankton of the lake of Geneva, organisms having 4 processes have been discovered. Their frequency in the water samples and the results of in vitro studies on their progeny when cultivated in several environmental conditions, allow us to consider these organisms as a form ofStaurastrum sebaldi. The triradiate organisms have been incorrectly named and one must now consider three different species.   相似文献   

Lithium in spilites     

Denis M Shaw  Nicole Vatin-Pérignon 《Geochimica et cosmochimica acta》1977,41(11):1601-1607

During spilitisation the abundance of Li increases from about 12 ppm in normal basaltic rocks to an average of 75 ppm, with some spilites containing up to 190 ppm. This is relatively far greater than the increase of <50% in Na. Also the ratio CaO/Al₂O₃ decreases from about 1.0 to <0.1 and the H₂O content increases markedly.Alteration of this kind requires waters rich in both Na and Li, with the material added having a ratio 10⁵ Li/Na of about 750: the ratio for seawater is 1.8 but most subsurface waters have higher ratios and are more likely agents of spilitisation.Volcanic hydrothermal brines have suitable Li and Na abundances and are known to have reacted with fresh basalts to produce spilitic alteration: in cases of spilitisation of volcanogenic sediments, reaction with non-volcanic brines may have occurred. In both cases the waters must initially have high CO₂ and low Ca activities.  相似文献   

Physics and chemistry of the Earth,Vol. 10, No. 3, 1977, Chemistry of the Moon: (Edited by L. H. Ahrens), annual subscription $78 (6 issues), Pergamon Press,Oxford     

Denis M. Shaw 《Geochimica et cosmochimica acta》1977,41(12):1879

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Helen Margaret (Elliott) Roberts,née Westcott     

Denis M. Shaw  Lynn Falkiner  Linda Hillier 《Geochimica et cosmochimica acta》1985,49(4):iii

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Additional estimates of continental surface Precambrian shield composition in Canada     

Denis M Shaw  Jaroslav Dostal  Reid R Keays 《Geochimica et cosmochimica acta》1976,40(1):73-83

New trace element analyses have been made on the composite Canadian Precambrian shield samples reported in 1967.The overall mean abundance of Cr has been revised to 35 ppm (from 99). New abundances similar to 1967 values are (in ppm): Ni, 19; Co, 12; Cu, 14; Zr, 300; Sr, 315; Ba, 1070; Rb, 110: individual 1967 Rb values were erroneous.Elements not previously determined have the following overall mean values (in ppm): Zn, 52; Sc, 7.0; Nb, 26; Hf, 6.9; La, 32; Ce, 65; Nd, 26; Sm, 4.5; Eu, 0.94; Gd, 2.8; Tb, 0.48; Ho, 0.62; Yb, 1.5; Lu, 0.23; Y, 21; Pb, 17; values in ppb are: Ir, 0.02; Au, 1.8; Tl, 520.Clear positive correlations among Mg-Cr-Ni-Ir-Au appear for all rock-types, marble and quartzite as well as mafic igneous. Regional differences are apparent for several elements: e.g. higher Au, Ir, Cr, Ni in Baffin Island and Northern Quebec composites, compared with Saskatchewan and Southwestern Quebec; high Ti, Zn, Nb, Zr, Hf, REE, Y, Sr, K/T1 abundances and negative Eu anomalies in Southwestern Quebec.The overall REE abundances (omitting Southwestern Quebec) differ from other surface continental crustal rock estimates.  相似文献