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61.
62.
The Lippmann diagram for the system(Ba, Sr)SO4-H2O was computed at 25 °Cby determining the solid-phase activity coefficientsfrom first principles calculations. Directcalculations of the mixing properties of thebarite-celestite series indicate this solid solutionbehaves as non-ideal and non-regular. At 25 °C,the enthalpy of mixing shows a minimum around 50 mole% SrSO4 due to an ordering tendency. Thefree energy of mixing shows two minima that delimit awide and symmetric miscibility gap (from 2.1 to 97.9 mole% SrSO4) at this temperature. The excessfree energy of mixing requires a Guggenheim expansionseries of 5 terms to be described, where the termswith odd exponents are null as a consequence of thesymmetric distribution of the mixing properties withcomposition. The Lippmann diagram shows a peritecticpoint that corresponds to the composition of an aqueoussolution which is simultaneously at equilibrium withthe two extremes of the miscibility gap. The largedifference between the solubility products of theendmembers involves a strong preferential partitioningof the less soluble endmember towards the solid phase,which explains the extremely Ba-poor composition ofthe aqueous solution (aqueous activity fraction forBa2+ = 0.000446 ) at the peritectic point. 相似文献
63.
The Ardara pluton as part of the Donegal batholith was intruded into Neoproterozoic metasediments and metadolerites at mid-crustal
levels. The emplacement mechanism of the Ardara granite is very controversial, and mechanisms ranging from diapirism, ballooning
and stoping followed by nested diapirism have been proposed. Magnetic fabrics, rock fabrics and K/Ar dating of micas are used
here to constrain the emplacement history. The compositional zoning of the Ardara pluton is clearly reflected in the different
bulk magnetic susceptibilities between the outer quartz monzodiorite and the central granodiorite, whereas the intervening
tonalite is of intermediate nature. The magnetic carriers are characterized by the anisotropy of the magnetic susceptibility
(AMS), thermomagnetic measurements and through high field analyses (HFA). The separation of the ferrimagnetic and paramagnetic
contributions revealed that biotite and magnetite control the AMS in the quartz monzodiorite. Both minerals are oriented in
such a way that their summed contribution is constructive and originates from the shape fabric of magnetite and the texture
of biotite. Biotite is responsible mainly for the AMS in the tonalite and granodiorite. The magnetic foliation can be directly
related to the macroscopic foliation and also to the D4 structures in the country rocks. The foliation is consistent with
the geometry of the roughly circular shape and has a mostly steep to vertical dip. Towards the central granodiorite the magnetic
foliation dies out, although plagioclase texture measurements indicate a weak magmatic shape fabric. With the exception of
the tail, the Kmax axes (magnetic lineation) vary from steeply to gently plunging. The so-called lineation factor is approximately 1.01 and
therefore points to a less significant axial symmetry. These observations coincide with strain estimates on mafic enclaves
that show a very consistent pattern of K ∼0 flattening strain. Texture analyses of biotite and quartz additionally support
the observations made by the strain analyses and the magnetic fabric data. Microstructural investigations give evidence that
the fabrics are associated with the emplacement over a range of temperatures from truly magmatic to high-temperature solid-state
conditions. The age of the intrusion is still under discussion, but a new cooling age was determined by K/Ar dating of biotite
at 403.7±8 Ma corresponding to a temperature range between 450 and 300°C. For a mylonite along the southern contact between
the Ardara pluton and the country rock a K/Ar muscovite age of 378.8±7 Ma indicates a minimum age for the shear zone when
the Ardara pluton must have already been cooled down below 350±50°C.
Received: 28 January 1999 / Accepted: 28 December 1999 相似文献
64.
Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials
and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms
in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the
insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these
minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion
will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. 相似文献
65.
S. Siegesmund H. Jelsma J. Becker G. Davies P. Layer E. van Dijk L. Kater M. Vinyu 《International Journal of Earth Sciences》2002,91(1):20-34
In order to constrain the temporal relationship between granite (sensu lato) emplacement and metamorphism, isotope work was carried out on the minerals zircon and apatite (U-Pb), garnet (Pb-Pb) and hornblende (Ar-Ar) from wall rock samples in the Shamva area in Zimbabwe. The area, encompassing parts of the Chinamora and Murehwa batholiths and a wedge-shaped greenstone belt segment in between, is commonly quoted in the literature as an example illustrating pluton emplacement processes and deformational models for the Archean. New U-Pb dating of apatite from a boudinaged pegmatite within mafic schists in the batholith-greenstone contact zone has yielded an age of 2619 +28/-24 Ma. This age is interpreted as the best estimation of the intrusion age of this unit, depending on the assumed closure temperature, and provides an upper age limit for the syntectonic emplacement of the now gneissic granites. Pb-Pb dating of late kinematic garnets in cordierite-bearing rocks within the greenstone belt wall rocks gives an age of 2623NJ Ma. Together, this timing of relatively late, syntectonic plutonism and metamorphic mineral growth at ca. 2.62 Ga compares well with existing zircon crystallization ages for felsic volcanics (2645dž Ma, 2643NJ Ma) and post-tectonic porphyritic monzogranites (2601ᆢ Ma). Ar-Ar hornblende ages for mafic schists from different areas within the greenstone belt wall rocks range between 2621 and 2498 Ma and have been interpreted to indicate mixing between metamorphic ages and cooling ages. The data support a geological model whereby volcanism and sedimentation are associated with an early phase of regional deformation at ca. 2.64 Ga, which may have started earlier and lasted longer, and evolves into the voluminous emplacement of granites (now gneissic granites) in the batholiths at approximately 2.62 Ga. Emplacement of post-tectonic tabular monzogranites takes place at ca. 2.60 Ga. 相似文献
66.
Summary Monthly precipitation trends of 160 stations in China from 1951–2002 have been analysed and interpolated. The Mann-Kendall trend test was applied to examine the monthly precipitation data. Significant positive and negative trends at the 90, 95, and 99 percent confidence levels were detected for numerous stations. The number, distribution, and direction of the trends varied from month to month.The detected trends were spatially interpolated by applying the Inverse Distance Weighted (IDW) interpolation method. The spatial presentation of the detected precipitation trends gives a better understanding of climatic changes or variations in China during the last 50 years. This is especially the case for highlighting the spatial structure of precipitation trends.A clustering of trends is observed in certain months, including distinct trend belts especially in east and north-east China. Nevertheless, positive as well as negative monthly trends can be noted simultaneously in different areas. The spatial interpolation of precipitation trend analysis results is a useful approach to give further understanding of the regional pattern of precipitation trends in China. 相似文献
67.
68.
M. Merck A. Karle S. Martinez F. Arqueros K. H. Becker M. Bott-Bodenhausen R. Eckmann E. Faleiro J. Fernandez P. Fernandez V. Fonseca V. Haustein G. Heinzelmann I. Holl F. Just F. Krennrich M. Kühn E. Lorenz H. Meyer N. Müller R. Plaga J. Prahl M. Probst M. Rozanska M. Samorski H. Sander K. Sauerland C. Sesea W. Stamm 《Astroparticle Physics》1996,5(3-4):379-392
A precise knowledge of the angular resolution of scintillator arrays used to observe extended air showers (EAS) is of key importance in the search for VHE/UHE γ point sources. Four independent methods have been used to determine the mean resolution for which a value of ΔΘ63 of 0.8°(1.0°) at a proton threshold of 50 (40) TeV has been found for the HEGRA EAS-array. 相似文献
69.
70.
Hans Becker 《International Journal of Earth Sciences》1937,28(5):385-406
Ohne Zusammenfassung 相似文献