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111.
Enthalpies of dissolution in HF solutions have been measured at 323 K for a series of hydrous trachyte glasses. Enthalpies of mixing between water and molten trachyte have then been calculated from heat capacity data for the same set of samples and available enthalpy for pure water. The moderately negative enthalpies of mixing suggested at 1 bar by the measurements made on glasses almost disappear when trachyte liquids and water are referred to the same temperature, and particularly so when enthalpies of mixing are calculated for a few kbars pressure. As found for albite and phonolite liquids, trachyte melts thus appear to mix nearly ideally as far as enthalpy is concerned. These results imply that the enthalpy of exsolution of water from magmas is very small or negligible under the P-T-X conditions relevant to trachytic volcanism, even for complete degassing of up to 5 wt% H2O. Furthermore, the viscosity increase associated with exsolution-driven cooling is negligible compared to the decrease caused directly by water exsolution. 相似文献
112.
Marie-Lise Bernard Jack Molini Rose-Helen Petit Franois Beauducel Gilbert Hammouya Guy Marion 《Journal of Volcanology and Geothermal Research》2006,150(4):395-409
This paper presents the first remote measurements of La Soufrière gas emissions since the fumarolic and seismic reactivation in 1992. The chemical composition of the plumes has been measured from May 2003 to September 2004 using an Open Path Fourier Transform InfraRed (OP-FTIR) spectrometer, up to 15 m downwind the South Crater. HCl is clearly detected (concentration between 2.4 and 12 ppmv) whereas SO2 and H2S generally remain below the detection limit of the OP-FTIR. Direct measurements of SO2 and H2S near the South Crater with a Lancom III analyzer show a fast decrease of their concentrations with the distance. Calculated Cl / S mass ratios are high: from 9.4 ± 1.7 at 15 m from the vent to 2.8 ± 0.6 at 140 m. The enrichment in HCl of the gas emitted at La Soufrière, observed since 1998, corresponds to the degassing of a magma enriched in Cl and depleted in S. This result agrees with isotopic measurements which suggest a magmatic origin of the gases. Readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit. 相似文献
113.
Clifford M. Guy 《GeoJournal》1998,45(4):255-264
This paper reviews current methods used in classifying retail outlets and areas devoted to retailing, in the geographical
and town planning literature. For retail outlets, classifications based upon types of goods sold, and types of shopping trip,
are discussed. This is followed by an analysis of modern large store development which reflects property developers' and retailers'
concerns. Areas devoted to retail uses are subdivided into unplanned ‘retail areas’ and planned ‘shopping centres’. Traditional
classifications based upon central place theory are reviewed for both of these types, and found wanting in the light of recent
changes in retail development practice and consumer behaviour. Classifications based upon physical development characteristics
and type of shopping trip are recommended. Finally, classifications of urban retail location are examined.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
114.
115.
Richard A. Marston Jacky Girel Guy Pautou Herve Piegay Jean-Paul Bravard Chris Arneson 《Geomorphology》1995,13(1-4)
The purpose of this paper is to describe and explain channel metamorphosis of the Ain River in east-central France and the effects of this metamorphosis on floodplain disturbance and vegetation development. The Ain River is a 195 km long stream originating in the Jura Mountains which flows into the Rhône River between Lyon, France, and Geneva, Switzerland. The lower 40 km of the Ain River, beyond the mountain front, are situated in a valley of outwash deposits where the floodplain is 0.2 to 1.2 km wide. A complex mosaic of floodplain landscape units has developed. Maps dating back to 1766 and six sets of aerial photographs dated between 1945 and 1991 were used to document changes in channel pattern. Aerial photos and field surveys were used to compile maps of landscape units based on dominant vegetation life-forms, species, and substrate. Six maps dated between 1945 and 1991 were digitized in ARC/INFO and an overlay was generated to determine the changes in landscape units as related to channel disturbance. Change from a braided to a single-thread meandering channel probably took place in the period 1930–1950. The process of river entrenchment has occurred throughout the Holocene but has accelerated in the present century due to shortening of the river course, construction of lateral embankments, and vegetation encroachment following reservoir construction and cessation of wood-cutting and grazing. The increase in horizontal channel stability coupled with channel entrenchment have decreased floodplain disturbance and lowered the water table by approximately one meter. Pioneer and disturbance-dependent landscape units have experienced a more terrestrial-like succession to an alluvial forest. Abandoned channels have also been replaced by alluvial forests. On poorly drained soils, shrub-swamp communities of willow and hydrophytic herbaceous plants have been replaced by mixed forests of ash, alder, black poplar, and oak. On well drained alluvial soils, ash and oak dominated hardwood forests have declined in favor of mesophytic stands of black poplar. All types of vegetation, but particularly dry grasslands-shrublands, have been cleared for mines, campgrounds, agriculture, and other types of development. Using several measures, landscape diversity decreased between 1945 and 1991. 相似文献
116.
Wallace S. Broecker Rik Wanninkhof Guy Mathieu Tsung-Hung Peng Scott Stine Steve Robinson Andy Herczeg Minze Stuiver 《Earth and Planetary Science Letters》1988,88(1-2)
Since 1957 the 14C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced14C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO2 exchange rate, and (4) biological enhancement of the CO2 exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation.In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity. 相似文献
117.
The transition between blueschists and lawsonite-bearing eclogites based on observations from Corsican metabasalts 总被引:2,自引:0,他引:2
Syntectonic eclogites, associated with blueschist parageneses, have recrystallized in metabasalts from eastern Corsica under very low temperatures (420°C). The evolution of these eclogites is recorded by the order of development of metamorphic minerals, as demonstrated by helicitic inclusions of lawsonite and actinolite in Fe-rich garnets, and the occurrence of fibrous Na-pyroxenes in the pressure shadows and cracks of boudinaged garnets, within a foliated matrix composed of glaucophane, Ca---Fe garnets and lawsonite.
A Schreinemakers analysis has been completed on the lawsonite-ferroglaucophane-actinolite-almandine-grossular-ferro-omphacite-chlorite system in a (T,P,μH2O)-space. The resulting three-dimensional relationships are applied to the studied samples. They are consistent with a prograde increase in temperature at low μH2O, producing eclogites from blueschists, and with a subsequent retrogressive decrease in pressure. 相似文献
118.
Iwan ROELANDTS Guy ROBAYE Panagiotis ALOUPOGIANNIS Georges WEBER Jeanne-Marie DELBROUCK-HABARU 《Geostandards and Geoanalytical Research》1987,11(1):79-80
Eighteen new Chinese standard reference samples (including stream sediments, soils and rocks) have been analysed by an automated proton induced gamma ray emission (PIGE) method for fluorine. Results of determinations are reported and are generally in good agreement with the "usable values" previously published. 相似文献
119.
Guy Libourel Pierre Boivin Gordon M. Biggar 《Contributions to Mineralogy and Petrology》1989,102(4):406-421
One atmosphere liquid-present experiments were carried out in the CMAS system using an ordinary quench furnace apparatus. The runs, including reversal and duplicate experiments, describe the univariant curve l=fo+an+ di between the invariant points Q: l+fo+an=di+sp and F: l+fo=an+di+oen, located respectively at 1245±1° C and 1244±1° C. The thermal divide on this curve M3: l= fo+an+di is located at 1275±1° C and plots well within the silica-saturated field, in agreement with Longhi's (1987) experiments. Along the univariant curve l=fo+an+di, liquid composition evolves away from the thermal divide either toward invariant points Q or F and pierces the silica saturation plane, i.e., the join Di-An-En, in the silica saturated field. In this compositional range, the Al solubility in clinopyroxene changes drastically from one side of the thermal divide to the other, with great increase of Al solubility in the silica-undersaturated field. Four endmembers must be used to describe the complex solid solution of anorthite: CaAl2Si2O8, CaMgSi3O8, MgAl2Si2O8 and [] Si4O8. The last two of these are present only within the silica-saturated field. Unlike clinopyroxene, the Mg content of anorthite is insensitive to the thermal barrier but is only sensitive to silica-saturation plane. Olivine composition can be described by a binary solid solution of forsterite and monticellite with no Ca in the M2 site. As with anorthite, olivine compositions exhibit a marked change with crossing of the silica-saturation plane. The above features imply that the solubility of minor elements in crystalline phases (Al in clinopyroxene, Ca in olivine and Mg in anorthite) selectively respond to only one or another of these particular plane. Results have many important consequences. One is the likelihood of changes in melt speciation depending on position with respect to the thermal divide and the silica-saturation plane. 相似文献
120.
Guy L. Hovis 《Geochimica et cosmochimica acta》1984,48(3):523-525
Glasses in the systems NaAlSi3O8-KAlSi3O8 and NaAlSi3O8-Si4O8 have been studied by means of hydrofluoric acid solution calorimetry at 50°C. Results indicate small negative enthalpies of mixing in the former system and small positive departures from ideality in the latter. 相似文献