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61.
62.
Bernardo Cesare 《Contributions to Mineralogy and Petrology》1994,116(3):239-246
Metapelitic hornfelses in the contact aureole of the Vedrette di Ries pluton exhibit the terminal decomposition of Zn-poor Fe-staurolite in a muscovite-quartz-free domain. The reaction takes place only within coarsegrained sillimanite that has replaced andalusite porphyroblasts during prograde metamorphism. The product is a gahnite-poor hercynitic spinel, which occurs as very small grains closely associated in space with resorbed staurolite. Microstructural observations indicate that bereynite growth postdates the pseudomorphs of sillimanite after andalusite. The textural evidence for a genetic relationship between hercynite and staurolite is confirmed by the identical Fe/Mg/Zn ratios of the two minerals, which causes the collinearity of hercynite, staurolite and Al2SiO5 in FeO–MgO–ZnO–Al2O3–SiO2–H2O composition space (FMZASH), and indicates hercynite formed by the reaction: Fe-staurolite = 3.85hercynite + 5.1sillimanite + 2.55quartz + 2H2O Staurolite inclusions within andalusite did not break down to form hercynite, indicating a kinetic control, as well as little overstepping of the equilibrium conditions, of the reaction forming hercynite. Assuming overstepping did not occur, modelling of the reaction with existing thermodynamic data in the simplified FASH system suggests that the terminal breakdown of staurolite to form hercynite occurred at 2.5–3.75kbar and 585–655°C. 相似文献
63.
18O/16O and14C analysis of deep-sea cores from the Gulf of Mexico revealed a 2.4% isotopic anomaly between 12,000 and 11,000 years ago. This value, together with estimates of the oxygen isotopic composition of ice meltwater and rates of mixing within the Gulf of Mexico indicates that the average yearly discharge of the Mississippi River was between 100,000 and 230,000 m3/s (as compared to 57,000 m3/s for the peak flood of February 17, 1937), with probable yearly peak floods twice as large. Corresponding sea-level rise was between 1 and 2 m per century. 相似文献
64.
B. Cesare 《Contributions to Mineralogy and Petrology》1995,122(1-2):25-33
Equilibrium C–O–H fluid speciation calculations predict that graphite will precipitate from initially graphite saturated
fluid inclusions during cooling and exhumation of metamorphic rocks. In the case that no mass is gained or lost by the inclusions,
the original X
O ratio [O/(O+H)] of the fluid phase must be maintained. Given this closed system constraint, the down-temperature progress
of graphite precipitation can easily be monitored as a function of the varible X
O, and produces some effects that are of significance to fluid inclusion studies: 1. Variation of the H2O : CO2 : CH4 relationship in the graphite-saturated COH fluid, namely increase of X
H2
O and decrease of the carbonic fraction; 2. Decrease of fluid density due to precipitation of graphite, which is denser than
the residual fluid; 3. Alteration of the CO2 : CH4 ratio of the fluid, depending on the initial O : H ratio of the fluid: for X
O>1/3, fluids increase their CO2 : CH4 ratio with decreasing temperature, and vice-versa. This implies that the CO2 : CH4 ratio measured at room T will not represent the trapping value, which is in any case closer to unity. As a consequence of density reduction, isochores
extrapolated from densities observed at room temperature do not pass through the pressure-temperature conditions at which
the inclusion was trapped, with pressure underestimates of up to 2 kbar. Actual P-T trapping conditions are located along the equilibrium “bulk isochore” (curve of constant-X
O, constant-volume) of the fluid. Alteration of the CO2 : CH4 ratio is a mechanism by which a CO2-rich or CH4-rich carbonic phase can be formed from aqueous fluids that are slightly off the neutral X
O=1/3 value. Subsequent segregation of this phase from the aqueous counterpart may account for the formation of pure CO2 and CH4 fluids in the upper crust.
Received: 15 March 1995 / Accepted: 1 June 1995 相似文献
65.
Governing urban vacancy in post-crash dublin: contested property and alternative social projects 总被引:1,自引:1,他引:0
The scale and severity of property crashes following the global financial crisis has made vacancy a more visible and politically significant feature of cities. Although research has focused on urban experiments in vacant spaces, there has been less emphasis on how the contested property relations around vacancy remake urban governance. In this paper, we argue that debates about vacancy have been a central concern in post-crisis urban governance. In the first part of the paper we draw two conceptual approaches into a dialogue and apply them to an analysis of vacant space: that of Nicholas Blomley on property and Elizabeth Povinelli on “alternative social projects”. In the second part of the paper, we critically analyse how three groups discursively construct the need to “activate” and “re-use” vacant spaces in Dublin: grassroots groups, urban policy-makers, and financial actors. We argue that governing vacancy will be a key feature of post-crisis urbanisation. 相似文献
66.
67.
Cesare Cecchi-Pestellini & David A. Williams 《Monthly notices of the Royal Astronomical Society》1998,296(2):414-418
High brightness temperatures ( T b ) implied by quasar intraday variability may be explained by coherent emission, or else by physically implausible bulk relativistic Lorentz factors Γ ≥ 100. Previous theory asserts that various absorption mechanisms will block escape of such coherent, high-brightness sources. Yet this same theory fails to account for laboratory experiments detecting collective emission. Probably this is because present theory is inadequate, and should not be used to rule out collective radiation processes. 相似文献
68.
Trapping of long water waves that are induced by submarine earthquakes and that attack circular islands is studied by applying a theoretical model (Tinti andVannini, 1994) that is based on the linear shallow water approximation. The solution is computed as the superposition of the eigenmodes of the water basin. The tsunami trapping is seen in terms of the capability of the source to excite the trapped eigenmodes of the basin. The bottom depth dependence around the island is shown to be quite important in determining the trapping capability of the island: a depth profile that is downwardly concave as the distance from the island coasts increases is substantially more efficient in amplifying the incoming waves and in trapping their energy than a profile exhibiting an upward concavity. 相似文献
69.
Shun Nomura Giovanni De Cesare Mikito Furuichi Yasushi Takeda Hide Sakaguchi 《国际泥沙研究》2022,37(3):299-306
A turbidity current is a turbulent, particle-laden gravity current that is driven by density differences resulting from the presence of suspended sediment particles. The current travels downslope, bearing a large amount of sediment over a great distance, and forms fluvial and submarine bedforms. Knowledge of the spatio-temporal deposition profile of turbidity-deposited sediment is important for a better understanding of sediment transport by turbidity currents. In the current study, the depositi... 相似文献
70.
Cesare Cecchi-Pestellini Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2000,313(1):L6-L8
A model is constructed of the material in front of the star Cygnus OB2 no. 12 in which dense cores are embedded in diffuse clumps of gas. The model reproduces the measured abundances of C2 and CO, and predicts a column density of 91010 cm2 for HCO+ . 相似文献