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461.
The currently inactive deep-seated gravitational slope deformation (DGSD) Sagspitz in Tyrol, Austria, covers an area of 3 km2 and originated along a glacially over-steepened slope composed mainly of phyllites belonging to the Innsbruck Quartzphyllite
Complex. Past mass movement processes caused the formation of fracture systems and slump bodies which consequently form the
aquifers of relatively large springs in a rock type with generally very low permeability and poor porosity. Analysis of water
chemistry, oxygen isotope, and field parameters of the springs emerging from the DGSD imply that multilevel aquifers exist
and enabled the detection of continuous deep flow paths through the entire length of the mass movement from the main scarp
to the toe of the slope. It is shown that the aquifer boundaries and spring emergences throughout the loosened rock mass can
be correlated to the internal and basal shear zones of the DGSD so that this hydrogeological approach proved to be useful
for evaluating the mass movement structure. 相似文献
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We present new ultra-high precision 142Nd/144Nd measurements of early Archaean rocks using the new generation thermal ionization mass spectrometer Triton. Repeated measurements of the Ames Nd standard demonstrate that the 142Nd/144Nd ratio can be determined with external precision of 2 ppm (2σ), allowing confident resolution of anomalies as small as 5 ppm. A major analytical improvement lies in the elimination of the double normalization procedure required to correct our former measurements from a secondary mass fractionation effect. Our new results indicate that metasediments, metabasalts, and orthogneisses from the 3.6 to 3.8 Ga West Greenland craton display positive 142Nd anomalies ranging from 8 to 15 ppm. Using a simple two-stage model with an initial ε143Nd value of 1.9 ± 0.6 ε-units, coupled 147Sm-143Nd and 146Sm-142Nd chronometry constrains mantle differentiation to 50-200 Ma after formation of the solar system. This chronological constraint is consistent with differentiation of the Earth’s mantle during the late stage of crystallization of a magma ocean. We have developed a two-box model describing 142Nd and 143Nd isotopic evolution of depleted mantle during the subsequent evolution of the crust-mantle system. Our results indicate that early terrestrial protocrust had a lifetime of ca. 0.7-1 Ga in order to produce the observed Nd isotope signature of Archaean rocks. In the context of this two box mantle-crust system, we model the evolution of isotopic and chemical heterogeneity of depleted mantle as a function of the mantle stirring time. Using the dispersion of 142Nd/144Nd and 143Nd/144Nd ratios observed in early Archaean rocks, we constrain the stirring time of early Earth’s mantle to 100-250 Ma, a factor of 5 shorter than the stirring time inferred from modern oceanic basalts. 相似文献
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The logical structure of species richness determinations is outlined in order to explain how their accuracy is affected by nonrandomly distributed populations. The transformation of a species-area curve to a species-range curve is discussed in general terms and conditions required for accurate species richness determinations are given. Applications of the approach to scleractinid coral and pine-tree communities illustrate the method. 相似文献
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