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101.
Giuliano F. Panza Stephan Mueller Erhard Wielandt 《Pure and Applied Geophysics》1980,118(2):1191-1191
102.
Summary Existing gravity and seismic refraction data are used to deduce a crustal cross section across the Eastern Alps along the meridian 11°.4 East. The results suggest that a high density body of the Ivrea type is present under the southern margin of the Alps, that the Apennines do not have a crustal root extending to a depth of 50 km and that a profound discontinuity extending to the base of the crust exists between the Apennines and the Po Valley.Lamont-Doherty Contribution No. 1590. 相似文献
103.
The low-temperature heat capacity of magnesioferrite (MgFe2O4) was measured between 1.5 K and 300 K, and thermochemical functions were derived from the results. No heat capacity anomaly
was observed. From our data, we suggest a standard entropy (298.15 K) for magnesioferrite of 120.8±0.6 J mol−1 K−1, which is about 2.4 J mol−1 K−1 higher than previously reported calorimetric studies; but is in rough agreement with predictions from sets of internally
consistent thermodynamic data. 相似文献
104.
The temporal evolution of natural illite du Puy dissolution rates was measured from Si release rates in single-pass flow-through experiments lasting at least 100 days at 25°C and pH ranging from 2 to 12. Si release rates decreased by a factor of five and three at pH 12 and 2, respectively, during the experiments. These observations are interpreted to stem from changes in illite du Puy reactive surface area during these experiments. As the edges of clay minerals dissolve faster than the basal planes, dissolution tends to change clay mineral morphology decreasing the percentage of reactive edge sites. This continuously changing morphology prevents illite dissolution rates from attaining steady state during laboratory experiments lasting 100 to 200 days. A similar temporal decrease in dissolution rates is evident for many different sets of clay mineral dissolution rate data available in the literature. It seems reasonable, therefore, to expect that clay mineral dissolution does not attain steady state in nature, but rather their dissolution rates decrease continuously during their dissolution. 相似文献
105.
106.
107.
Andreas Tennie Radegund Hoffbauer Stephan Hoernes 《Contributions to Mineralogy and Petrology》1998,133(4):346-355
The oxygen isotope fractionation between kyanite and calcium carbonate has been investigated experimentally at four temperatures
in the range between 625 and 775 °C at 13 kbar. Because of low exchange rates, the isotopic reaction was enhanced by polymorphic
transformation of andalusite to kyanite. With this experimental modification a close approach to equilibrium was reached in
all runs. The temperature dependence of the equilibrium fractionation is described by the equation 1000 ln ky-cc=−2.62×106/T
2. Application of the experimental results to natural quartz-kyanite-garnet assemblages indicates the preservation of the oxygen
isotope composition of kyanite acquired during its formation, reflecting its extremely low oxygen diffusivity. This refractory
behaviour restricts the use of kyanite for thermometry but opens the possibility to use its O-isotope composition as an indicator
for recognition of polymetamorphic rock histories and reconstruction of the prograde evolution of a metamorphic sequence.
Received: 8 June 1998 / Accepted: 24 August 1998 相似文献
108.
109.
Pipe G3b is part of the Upper Cretaceous carbonatitic Gross Brukkaros Volcanic Field in southern Namibia. The pipe represents
the root zone of a diatreme and is located 2800 m west of the rim of Gross Brukkaros, a downsag caldera. The pipe is exposed
approximately 550 m below the original Upper Cretaceous land surface. It cuts down into its own feeder dyke, 0.3 m thick.
The pipe coalesced from two small pipes and in plan view is 19 m long and 12 m wide. It consists of fragmented Cambrian Nama
quartzites and shales of the Fish River subgroup. Despite intensive brecciation, the stratigraphic sequence of the country
rocks is almost preserved in the pipe. In addition, the feeder dyke became fragmented too and can be traced in a 2- to 3-m-wide
zone full of carbonatite blocks along the southern margin of the pipe. The void space of the breccia is 30–50% in volume.
Finally, after the disruption of country rocks and feeder dyke, a little carbonatite magma intruded some of the void space.
The breccia of pipe G3b is considered to represent a root zone at the transition from the feeder dyke into a diatreme above.
Formation of the breccia required a shock wave thought to have been associated with a last explosion of the diatreme immediately
above the present level of exposure. The explosion can be shown to have been phreatomagmatic in origin.
Received: 11 October 1996 / Accepted: 6 March 1997 相似文献
110.
In the Upper Cretaceous Gross Brukkaros Volcanic Field, southern Namibia, a radial dyke system surrounds a dome structure
and its 74 closely related carbonatite diatremes. This paper focuses on volcanological features which seem to be typical for
a low-viscosity melt in various settings such as dykes, sills and diatremes. The total or near absence of vesicles in carbonatite
ash grains and lapilli inside the diatremes is evidence against explosive exsolution of volatile phases and in favour of a
phreatomagmatic fragmentation mechanism and thus for a phreatomagmatic eruption mechanism of the carbonatite diatremes.
Received: 15 August 1996 / Accepted: 13 January 1997 相似文献