Fractional Crystallization and Liquid Immiscibility Processes in the Alkaline-Carbonatite Complex of Juqui (So Paulo, Brazil)     

BECCALUVA  L.; BARBIERI  M.; BORN  H.; BROTZU  P.; COLTORTI  M.; CONTE  A.; GARBARINO  C.; G.  C.B. GOMES; M.  ACCIOTTA; MORBIDELLI  L.; RUBERTI  E.; SIENA  F.; TRAVERSA  G. 《Journal of Petrology》1992,33(6):1371-1404

The Juqui circular intrusion, which is Cretaceous in age (130–135Ma), crops out in the Precambrian gneissic basement in Brazilover an area of 14 km2. It consists of olivine clinopyroxen-itecumulates (with minor olivine gabbros) in the northeastern sector(74 vol.%), whereas ijolites-melteigites-urtites (4%) and nephelinesyenites with minor essexites and syenodiorites (21%) outlinesubannular concentric patterns with an Mg-carbonatite core (1%), in the southwestern part of the complex. Petrographical, bulk rock, and mineral compositional trendsindicate that the origin of the complex can be largely accountedfor by shallow-level fractional crystallization of a carbonatedbasanitic parental magma. Such a magma was generated deep inthe subcontinental lithosphere by low-degree partial meltingof a garnet-phlogopite peridotite source. Mass-balance calculations in agreement with field volume estimatespermit definition of several fractionation stages of the magmaticevolution under nearly closed-system conditions, with inwarddevelopment of zonally arranged side-wall cumulates. These stagesinvolved: (1) fractionation from basanite to essexite magma(liquid fraction F = 33–5%) by crystallization of olivineclinopyroxenite plus minor olivine alkali gabbro cumulates;(2) derivation of the least differentiated mafic nepheline syenite(F = 5–5 %) from essexitic magma by subtraction of a syenodioriteassemblage; (3) exsolution of a carbonatite liquid (5%) froma CO₂-enriched mafic nepheline syenite magma, which also underwentcontinuous fractionation giving rise to ijolite-melteigite-urtitecumulates. The proportion of cumulus clinopyroxene and biotiteand intercumulus nepheline and alkali feldspar in these lastrocks, as well as the absence of alkalis in carbonatite, maybe attributed, at least in part, to loss of alkali-rich hydrousfluids released during and after the unmixing formation of thetwo conjugate liquids. The KD values determined for Mg-carbonatite/nepheline syeniteare lower (1–4–2–9) for light rare earth elements(LREE) than for REE from Eu to Yb (4–6–7–8),in contrast to recent experimental results (Hamilton et al.,1989). A possible explanation is that Juquia Mg-carbonatiterepresents an alreadydifferentiated magma, which underwent extensivefractionation of LREE-enriched calcite. In this way, the highvariability of K₀ REE patterns observed in several alkaline-carbonatitecomplexes can also be accounted for. The remarkably constant initial ⁸⁷Sr/⁸⁶Sr ratios (mostly between0–7052 and 0–7057) support the interpretation ofthe intrusion as having been generated by fractrional crystallizationand liquid immiscibility from a common parental magma. Iligherisotopic ratios (0–7060–0–7078), found mainlyin dykes and in the border facies of the intrusion, may be dueto contamination by the gecissic basement.  相似文献   

Geological,fluid inclusion and stable isotope studies of Mo mineralization,Galway Granite,Ireland     

V. Gallagher  M. Feely  H. Högelsberger  G. R. T. Jenkin  A. E. Fallick 《Mineralium Deposita》1992,27(4):314-325

Mo mineralization within the Galway Granite at Mace Head and Murvey, Connemara, western Ireland, has many features of classic porphyry Mo deposits including a chemically evolved I-type granite host, associated K- and Si-rich alteration, quartz vein(Mace Head) and granite-hosted (Murvey) molybdenite, chalcopyrite, pyrite and magnetite mineralization and a gangue assemblage which includes quartz, muscovite and K-feldspar. Most fluid inclusions in quartz veins homogenize in the range 100–350°C and have a salinity of 1–13 eq. wt.% NaCl. They display Th-salinity covariation consistent with a hypothesis of dilution of magmatic water by influx of meteoric water. CO₂-bearing inclusions in an intensely mineralized vein at Mace Head provide an estimated minimum trapping temperature and pressure for the mineralizing fluid of 355°C and 1.2 kb and are interpreted to represent a H₂O-CO₂ fluid, weakly enriched in Mo, produced in a magma chamber by decompression-activated unmixing from a dense Mo-bearing NaCl-H₂O-CO₂ fluid. ³⁴S values of most sulphides range from c. 0 at Murvey to 3–4 at Mace Head and are consistent with a magmatic origin. Most quartz vein samples have ¹⁸O of 9–10.3 and were precipitated from a hydrothermal fluid with ¹⁸O of 4.6–6.7. Some have ¹⁸O of 6–7 and reflect introduction of meteoric water along vein margins. Quartz-muscovite oxygen isotope geothermometry combined with fluid inclusion data indicate precipitation of mineralized veins in the temperature range 360–450°C and between 1 and 2 kb. Whole rock granite samples display a clear ¹⁸O-D trend towards the composition of Connemara meteoric waters. The mineralization is interpreted as having been produced by highlyfractionated granite magma; meteoric water interaction postdates the main mineralizing event. The differences between the Mace Head and Murvey mineralizations reflect trapping of migrating mineralizing fluid in structural traps at Mace Head and precipitation of mineralization in the granite itself at Murvey.  相似文献   

The energetics of interaction between oxygen vacancies in sillimanite: A model for the mullite structure     

S. Padlewski  V. Heine  G. D. Price 《Physics and Chemistry of Minerals》1992,19(3):196-202

A microscopic model is introduced to discuss the modulated structure of mullite. The oxygen vacancies of this aluminosilicate are known to play a central role. In particular, a single vacancy strongly orders its surrounding Al/Si tetrahedral sites. It is shown in this work that if two oxygen vacancies approach too closely to one another, their Al/Si dressing overlap. This situation results in repulsive interaction. The field of interaction between the vacancies is estimated with the use of an atomistic computer simulation. We use a Bragg-Williams type of theory to dicuss the ordering pattern of the vacancies. Due to frustration between the two dominant repulsive interactions, our model predicts a modulated phase transition in agreement with observation.  相似文献   

Water-rock interaction in a zone of lateral flow: A natural example from the active geothermal field and gold-mineralized zone of Beppu (Kyushu Island,Japan)     

G. Gianelli  Y. Yusa  S. Battaglia  K. Takemura 《Mineralogy and Petrology》1992,45(3-4):247-259

Summary Beppu is a water-dominated active geothermal system in Kyushu (Japan). Gold mineralization exists in places within altered Pleistocene volcanites in the southernmost part of this field. A shallow 300 m well was drilled in an alluvial fan deposit made up of unsorted volcanic clasts of andesite and dacite. Water and core samples were collected and a temperature log was carried out. In the depth range of 150-230 m and at temperatures of 126-148° C the main authigenic minerals are quartz, calcite, K-feldspar, mixed layers illite/smectite, stilbite and pyrite. The chemical data of the waters indicate that mixing occurs between shallow bicarbonate waters and deep Na-Cl geothermal waters in the outflow zone. The authigenic mineral assemblages found in the well are analogous to those found in the epithermal gold deposits of southern Kyushu. Au concentration data for the hydrothermal springs of Beppu (0.53 g/kg) indicate that the fluids found in the borehole at 148° C could theoretically deposit gold. It is reasonable to hypothesise that a process of mixing between deep Na-Cl fluids and shallow Ca-HCO₃-SO₄ fluids were responsible for massive silicate deposition, accompanied in places by Au mineralizations.

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Wasser-Gesteins-Wechselwirkung in einer Zone lateraler Fließbewegung: ein natürliches Beispiel aus der aktiven Geothermal-Golderz-Zone von Beppu (Kyushu, Japan)

Zusammenfassung Beppu ist ein geothermales System auf der Insel Kyushu, Japan, in der Wasser die dominante Rolle spielt. Goldvererzungen treten stellenweise in umgewandelten pleistozänen Vulkaniten im südlichsten Teil des Gebietes auf. Ein 300 m tiefes Bohrloch wurde in einem alluvialen Sedimentations-Fächer, der aus unsortierten vulkanischen Klasten, aus Andesit und Dazit besteht, niedergebracht. Wasserproben und Kernproben wurden genommen und die Temperaturen im Bohrloch systematisch gemessen. In Tiefen von 150–230 m und bei Temperaturen von 126–148°C sind die wichtigsten autigen gebildeten Minerale Quarz, Calcit, K-Feldspat, Illit/Smectit, Stilbit und Pyrit. Der Chemismus der Wässer zeigt, daß eine Mischung zwischen seichten Bikarbonat-Wässern und aus der Tiefe stammenden Na-Cl geothermalen Wässern erfolgt. Die autigenen Mineralassoziationen in diesem. Bohrloch sind vergleichbar mit denen in epithermalen Goldlagerstätten des südlichen Kyushu. Auf der Basis von existierenden Goldkonzentrationsdaten für die hydrothermalen Quellen auf Beppu (0.53 g/kg) läßt sich zeigen, daß die Fluide, die in dem Bohrloch bei 148 angetroffen wurden, theoretisch Gold absetzen könnten. Daher läßt sich die Theorie vertreten, daß Mischungsvorgänge zwischen einem aus der Tiefe stammenden Na-Cl Fluid und einem oberflächennahen Ca-HCO₃-SO₄ Wasser für die massive Silikatausscheidung verantwortlich waren, die stellenweise von Goldmineralisation begleitet wurden.

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Contribution No 4. Foreign Visiting Scientist Section, Beppu Geophysical Research Laboratory, Kyoto University.

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This paper was presented at the IGCP 291 Project Symposium Metamorphic Fluids and Mineral Deposits, ETH Zurich, March 21–23, 1991.  相似文献   

Analysis of hydrologic relations between Eğirdir-Beyşehir-Suğla lakes system and adjacent basins by means of remote sensing techniques (southern Turkey)     

Mustafa Değirmenci  Gültekin Günay 《Environmental Geology》1992,19(1):41-45

The study area is situated within the complex structure and karst system of the western Taurids. Basinwide interpretation of the structural features, each of which has great importance, will enlighten many complicated hydrogeologic problems encountered in the area. Thus, considering the previous views on the structural geology of the area, an interpretation of the structural and tectonic features of the study area by means of satellite images was undertaken, and based on the data gained, new approaches were suggested to solve the hydrogeological problems. In particular, determination of the recharge-discharge mechanisms of the Olukköprü and Dumanli karst springs, which are the most important karst groundwater discharge points in the region, has been attempted. Within the framework of this study, a tectonic-lineament map of a large area covering Eirdir, Beyehir, and Sula lakes at the north and the basins to the south of these lakes was prepared.  相似文献   

Modeling groundwater quality in an agriculturally used water catchment     

F. Aschenbrenner  G. M. Richter  J. Richter 《Environmental Geology》1992,20(1):43-55

The sulfate pollution in an agriculturally used watershed has been investigated with respect to the transport in the saturated zone and the development of sulfate in the unsaturated zone. Besides of other sources such as acid wet and dry deposition or sulfate input by agricultural activities, most of the sulfate originates from oxidation of pyrite by either NO₃ or O₂. High sulfate concentrations coincided with high nitrate leaching caused by plowing of former grassland or by vegetable crop residues and with former wet lands that have become dry. By using soil water concentration data and maps showing the extension of former wetlands and grassland as well as agricultural land use, it was possible to delineate regions of high sulfate input. The transport of sulfate in the aquifer was analyzed with a modified version of the USGS MOC model, which takes into account the nonlinearity of the underlying equation describing unconfined groundwater flow. The calibration of the transport model showed good agreement between the estimated and modeled sulfate input rates. A prediction of future sulfate concentrations in the aquifer was feasible by using worst-case parameters.  相似文献   

Electrical resistivity structure of the eastern Moroccan Atlas System and its Tectonic implications     

G. Schwarz  H. G. Mehl  F. Ramdani  V. Rath 《International Journal of Earth Sciences》1992,81(1):221-235

The electrical resistivity structure of the crust and upper mantle of the Atlas Mountain System was studied using magnetotelluric and geomagnetic deep soundings. Field experiments were done in eastern Morocco along a traverse from the Anti Atlas to the Rides Rifaines in two campaigns in 1983 and 1988.Zones of very low electrical resistivity could be identified in the various structural settings at different depth ranges, most likely connected directly to the tectonic evolution of the mountain belts. A mid-crustal low resistivity layer with total conductance (thickness-resistivity ratio) of about 2000 Siemens stretches from the southern border of the High Atlas towards the Middle Atlas. This layer seems to characterize the base of crustal detachment, e.g., the plane for large horizontal overthrusting, and supports the idea of thick- and thin-skinned tectonics involved in Atlasic mountain building. In the western Middle Atlas an upper-crustal low resistivity layer (at depth < 10 km) was found in the area where volcanic activity was present, pointing towards a direct relation between low electrical resistivity and volcanic or postvolcanic events. North of the Middle Atlas resistivity structures change totally: The Pre and parts of the Sub-Rif have a highly conductive cover, presumably connected to the molasse basin. Total conductance was calculated to reach 6000 Siemens. No further conductive structures, like, e.g., the ones found beneath the High and Middle Atlas, are seen within the resistive crust, but at much greater depth within the upper mantle.

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Zusammenfassung Im marokkanischen Atlas-System wurde der elektrische Widerstand der Kruste und des oberen Mantels mit magnetotellurischen und erdmagnetischen Tiefen-Sondierungen erkundet. Die Feldmessungen wurden in den Jahren 1983 und 1988 im östlichen Marokko entlang einer Traverse vom Anti Atlas bis in das Rif durchgeführt.In den einzelnen strukturellen Einheiten wurden in unterschiedlichen Krustentiefen Schichten sehr kleiner elektrischer Widerstände entdeckt, die direkt mit der tektonischen Entwicklung des Atlasgebirges verknüpft zu sein scheinen. Zwischen dem Südrand des Hohen Atlas und dem Mittleren Atlas im Norden erstreckt sich eine Zone sehr kleiner Widerstände (integrierte Leitfähigkeit etwa 2000 Siemens) in mittleren Krustentiefen. Diese Schicht scheint einen Bereich krustaler Ablösung zu kennzeichnen und kann als Basis einer weitspannigen Überschiebung angenommen werden. Diese Form der »thick- & thin-skinned« Tektonik scheint wesentlich am Prozess der Gebirgsbildung im Atlas beteiligt zu sein. Im westlichen Mittleren Atlas, im Bereich des jungen Vulkanismus, wurde eine gutleitende Zone in der oberen Kruste (Tiefe < 10 km) gefunden. Diese Beobachtung legt einen direkten Zusammenhang zwischen erhöhter elektrischer Leitfähigkeit und vulkanischen bzw. postvulkanischen Ereignissen nahe. Nördlich des Mittleren Atlas ändern sich die Widerstandsstrukturen sehr stark: Im Prä- und teilweise auch noch im Sub-Rif liegt eine sehr gut leitende Deckschicht (integrierte Leitfähigkeit etwa 6000 Siemens) über einem hochohmigen Basement. In der Kruste des Rif werden keine weiteren, tieferliegenden Schichten erhöhter Leitfähigkeit gefunden, wie sie z.B. unter dem Hohen Atlas vorliegen. Dagegen gibt es Hinweise auf Zonen hoher Leitfähigkeit im oberen Mantel.

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Résumé Dans l'Atlas marocain la résistivité électrique de la croûte et du manteau supérieur a été étudiée à l'aide des sondages magnétotelluriques et géomagnétiques. Ces travaux ont été effectués le long d'une traverse menant de l'Anti-Atlas jusqu'au Rif durant les années 1983 et 1988.Dans différentes profondeurs de la croûte terrestre des zones de résistances électriques très basses ont pu être découvertes ce qui peut être attribué à l'évolution tectonique de l'Atlas. Une couche de résistances très basses (conductance vers 2000 Siemens) s'étend entre le bord au sud du Haut Atlas et l'Atlas Moyen au nord. Cette couche peut être le signe d'un détachement de l'écorce et d'une poussée très vaste. Cette forme tectonique »thick- & thin-skinned« semble être essentiellement responsable du processus de la formation orogénique de l'Atlas. Une zone de bonne conductance se trouve dans la croûte terrestre supérieure (profondeur < 10 km) dans l'ouest de l'Atlas Moyen aux environs de l'activité volcanique caractérisant une relation directe entre une haute conductance électrique et des événements volcaniques et post-volcaniques. Vers le nord de l'Atlas Moyen les structures de résistance subissent un changement total: Au Pré- et partiellement aussi au Subrif se trouve une bonne couche guide (conductance vers 6000 Siemens). Aucune autre couche de conductance supérieure — comme au-dessous du Haut Atlas — n'a été découverte dans la croûte du Rif. On en décèle, par contre, dans le manteau supérieur.

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1983 1988 - . , , , . ( 2000 Si). , , . , »thick- & -thin-skinned«, , . , ( 10 ) . , - . : - , , - , : 6000 Si. . .

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TREK: A cosmic-ray experiment on the Russian space station MIR     

P. B. Price  D. M. Lowder  A. J. Westphal  R. D. Wilkes  R. A. Brennen  V. G. Afanasyev  V. V. Akimov  V. G. Rodin  G. K. Baryshnikov  L. A. Gorshkov  N. I. Shvets  O. S. Tsigankov 《Astrophysics and Space Science》1992,197(1):121-143

The goals of the TREK experiment, now in place on the MIR Space Station, are to resolve and measure the composition of both odd-Z and even-Z cosmic-ray nuclei up to uranium, to measure the isotopic composition of Fe-group nuclei, and to search for transuranic nucleic and exotic particles such as strangelets. To collect tracks of ultraheavy cosmic rays, exterior panels holding an array of BP-1 phosphate glass 1.2m² in area and 16 plates thick are now mounted outside the Kvant-2 module on MIR. Heaters and relays regulate the temperature of the glass at 25°±5°C. The detectors will record 10³ cosmic-ray tracks withZ50 during 2.5 years. An interior panel consisting of an array 0.09 m² in area and 32 plates thick and mounted on the inside wall of the Soyuz spacecraft (attached to the Space Station) will collect tracks of about 13000 Fe and 500 Ni nuclei.  相似文献   

The almost constant-speed two-body problem with resistance     

A. G. Mavraganis 《Celestial Mechanics and Dynamical Astronomy》1991,51(4):395-405

The almost constant-speed motion of a mass acted upon by a Newtonian attraction and a resisting force is treated. The equation of orbit is derived for a specific type of resistance which covers the familiar case of Danby's drag(=r ^–2) whilst the vector invariants are obtained by direct operation on the vector form of the equation of motion.  相似文献   

New observations of solar noise storm radiation at decameter wavelengths     

G. Thejappa  M. R. Kundu 《Solar physics》1991,132(1):155-171

We report multifrequency observations of storm continuum and other radio bursts. Based on their positional study and their correlation with other coronal and photospheric features, we deduce that the storm source is located in the magnetic field lines lying above a single bipolar active region. Energetic electrons trapped in the magnetic structures above the spots must be responsible for the storm radiation. We show that spontaneous emission of Langmuir waves by anisotropic distributions can explain both storm continuum and bursts self-consistently. Whenever the collisional damping ( _c ) is more than the growth (- _A ), there is a steady emission responsible for the continuum, and whenever _c = - _A (which may be satisfied randomly) there is a sudden jump in T _b giving rise to bursts. The number density of energetic particles required to explain the storm continuum at 73.8, 50, and 30.9 MHz frequencies is estimated to lie in the limits n _b /n _e 10^–10–10^–9 in the context of the present observations. The brightness spectrum of the storm continuum is computed and compared with observations.On leave from Indian Institute of Astrophysics, Bangalore 560034, India.  相似文献