The calcite-aragonite transition,reinvestigated   总被引：6，自引：0，他引：6  

W. Johannes  D. Puhan 《Contributions to Mineralogy and Petrology》1971,31(1):28-38

The calcite-aragonite equilibrium has been investigated between 200 and 600° C both in a carefully calibrated hydrothermal apparatus and in a piston-cylinder device of high precision. The equilibrium pressure is 5 kb at 180° C, 7 kb at 300° C, 9 kb at 400° C, and 11 kb at 480° C.The calcite-aragonite transition boundary which has been bracketed is continuously curved between 300 and 500° C and is more or less straight above and below this temperature range. It is shown that the calcite I-calcite II reaction is probably a second (and not a first) order transition.The experimental result shows that aragonite may already be formed out of calcite at a depth of 15 km if the temperature is not much higher than 100° C. The calcitearagonite and the albite-jadeite-quartz curves intersect at about 750° C and 20 kb. There is a P-T-field (up to 3.5 kb broad) where aragonite and albite coexist.  相似文献   

Siderit-Magnesit-Mischkristallbildung im system Mg2+-Fe2+-CO 3 2− -Cl 2 2− -H2O     

W. Johannes 《Contributions to Mineralogy and Petrology》1969,21(4):311-318

The formation of the solid solution series MgCO₃-FeCO₃ in the system Mg²⁺-Fe²⁺-CO ₃ ^2? -Cl ₂ ^2? -H₂O has been investigstad between 200° C and 500° C. The experimental results show that the composition of any of these carbonates strongly depends on the temperature: At high temperatures mixed crystals rich in MgCO₃ are formed and low temperatures lead to the formation of FeCO₃-rich carbonates. Thus, at 200° C a Fe-poor (Mg-rich) solution is in equilibrium with a Fe-rich carbonate. At temperatures higher than 350° C a Fe-rich (Mg-poor) solution coexists with a Fe-poor (Mg-rich) solid phase; see Fig. 1. At 350° C a solution with a mole fraction^mFe²⁺/(^mFe²⁺+^mMg²⁺) of 0.20 leads to the formation of magnesite very poor in Fe, whereas at 250° C the same solution is in equilibrium with sideroplesit, containing 80 Mol-% FeCO₃, see Figs. 2 and 3. The importance of the experimental results for the formation of deposits of magnesite and siderite is discussed.  相似文献   

Origin and evolution of a migmatite   总被引：5，自引：0，他引：5  

W. Johannes  L. N. Gupta 《Contributions to Mineralogy and Petrology》1982,79(2):114-123

The development of a stromatic migmatite exposed east and southeast of Arvika (Western Sweden) is described in four stages beginning with the country rock and following evolution through three areas characterized by low, medium and high amounts of leucosomes (areas L, M, and H, respectively).The country rock is a paragneiss composed of thin, alternating fine- and coarse-grained layers. Composition of the layers varies from granitic (fine) to tonalitic (coarse layers).The bulk of the stromatic migmatite is composed of leucocratic layers of magmatic appearance (leucosomes) and darker layers of gneissic aspect (mesosomes). Petrographical and chemical data (given in the form of Niggli values and K₂O/SiO₂ diagrams) show a close relationship between the fine-grained paragneiss layers and the leucosomes on the one hand and between the coarse-grained layers and the mesosomes on the other.At relatively low temperatures only those gneiss layers with a suitable (granitic) composition are transformed into leucosomes. This process is interpreted to be due to recrystallization of the felsic minerals via partial melting and to the separation of biotite.With increasing metamorphism, leucosomes become broader and more frequent due to partial melting of layers with less suitable composition. Contacts between different generations of leucosome can be recognized in the form of relict melanosomes.These observations favour essentially isochemical melting, followed by later in-situ crystallization. This model of an isochemical layer-by-layer transformation is supported by the preferential formation of hornblende in leucosomes and relict melanosomes, as well as by almost identical compositions of migmatite and country-rock plagioclase.  相似文献   

A paleoclimate model of Northern Hemisphere ice sheets     

G.E. Birchfield  Johannes Weertman  Albert T. Lunde 《Quaternary Research》1981,15(2):126-142

A model for predicting the growth and decay of ice sheets based on the astronomical theory of climate change is presented. The purpose of the study in part is to isolate the role of the ice-sheet physics and earth response under varying ice load by simplifying to the extreme the role of the hydrosphere-atmosphere. Ice sheet physics and the response of the lithosphere-asthenosphere under the ice load are modeled explicitly. Insolation anomalies (taken at a fixed latitude) directly force latitudinal displacement of the snow line. Accumulation rate a, and ablation rate a′ evaluated at mean sea level are specificed as external constants; a,a′ decrease linearly with ice sheet elevation. Rough tuning of the model to the general shape of the ice-volume record of the last two major glacials determines the external constants. Model predictions of the ages of several events in the last major glaciation compare well with the radiological ages. The six glacial terminatios (I–VI) over the last 600,000 yr are identified and the predicted ages compare reasonably well with the δ¹⁸O record for two deep-sea cores. A direct comparison of model power spectra of ice volume as a function of period with spectra of the δ¹⁸O record shows apparent underprediction of power near 100,000 yr. When a quantitative but heuristic method for taking into account the “red noise” spectrum evident in the geological records is used, a much more favorable comparison is possible. The model prediction lends support to the hypothesis that the nonlinearity of the ice-sheet physics is responsible for the 100,000-yr periodicity in the geological record of the late Pleistocene.  相似文献   

Stability of phlogopite in granitic melts, an experimental investigation     

B. Grochau  W. Johannes 《Contributions to Mineralogy and Petrology》1997,126(3):315-330

Water-saturated and water-undersaturated experiments (a _{H2 O} = 1.0 and 0.5) were performed in the temperature range 780–1040°C at 2 and 5 kbar in order to determine the upper thermal stability of phlogopite in granitic melts. Starting compositions were: (A) subaluminous mixtures of 20 wt % synthetic phlogopite and 80 wt % synthetic anhydrous haplogranitic glass; (B) peraluminous mixtures (normative corundum  = 4 %) of 20 wt % synthetic phlogopite and 80 wt % synthetic anhydrous peraluminous haplogranitic glass. The molar quartz: albite: orthoclase ratio of the glasses of the 2␣kbar runs was 35:39:26 and that of the 5 kbar runs 30:42:28. In the subaluminous system, phlogopite is stable up to 820°C at a _{H2 O} = 1.0 and up to 780°C at a _{H2 O} = 0.5. At higher temperatures, it is replaced by enstatite. In the peraluminous system phlogopite has a remarkably higher thermal stability (up to 1000°C at 5 kbar and a _{H2 O} = 1.0) and there is a temperature interval of 80°C at a _{H2 O} = 1.0, and 90–100°C at a _{H2 O} = 0.5 between the first appearance of enstatite and the disappearance of phlogopite. In the peraluminous system, phlogopite is a solid solution (ss) of phlogopite, muscovite, talc and eastonite components. The crystalline product of the phlogopite_ss breakdown reaction is an aluminous enstatite. The MgO-content of the melt depends on the normative corundum content of the starting material and the run temperature. It is independent of pressure. In the subaluminous system, the MgO-content ranges between 0.05 and 0.3 wt % in the temperature interval 780–880°C at both investigated water activities. The MgO-content of the peraluminous melts at a _{H2 O} = 1.0 ranges between 0.4 and 1.7 wt % and at a _{H2 O} = 0.5 between 0.2 and 1.4 wt % in the temperature range 780–980°C. Received: 28 August 1995 / Accepted: 6 August 1996  相似文献   

Identification and geochemical modeling of processes controlling leaching of Cr(VI) and other major elements from chromite ore processing residue   总被引：1，自引：0，他引：1  

Jeanine S Geelhoed  Johannes C.L MeeussenStephen Hillier  David G LumsdonRhodri P Thomas  John G FarmerEdward Paterson 《Geochimica et cosmochimica acta》2002,66(22):3927-3942

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Gis-aided land evaluation and decision-making for regulating urban expansion: A South African case study     

Johannes Hendrik Van der Merwe 《GeoJournal》1997,43(2):135-151

A computerised aid to the land use planning process is demonstrated on the urban edge of Cape Town, South Africa. Multi-criteria analysis is performed in the IDRISI GIS package to evaluate development suitability for four land use categories according to appropriately measured and weighted criteria. The four suitability images are then subjected to multi-objective land allocation to demarcate optimum locations for each land use type. The decision-making process entails execution of seven consecutive steps which are discussed in detail and applied in the case study. Technical decisions are rationalised and results displayed. The paper concludes with a call for the development of applications which can incorporate public participation in this type of decision-making process to ensure the wider acceptance of advanced GIS technology as appropriate technology.  相似文献   

Wave-power absorption by parallel rows of interacting oscillating bodies     

Johannes Falnes  Kjell Budal 《Applied Ocean Research》1982,4(4):194-207

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Technical note: Comments on ‘added mass and damping of a sphere section in heave’     

Johannes Falnes 《Applied Ocean Research》1984,6(4):229-230

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Die eigenartigen Verwitterungs- und Landschaftsformen des Dikilitaš-Sandsteines in Nordost-Bulgarien     

Johannes F. Gellert 《International Journal of Earth Sciences》1932,23(3-4):173-178

Ohne Zusammenfassung  相似文献