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  • 1
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Fourteen core samples of Precambrian granitic gneisses from a well drilled in the Green Township, Scioto County, Ohio were studied to determine the origin of alkali feldspar in these rocks. The well intersected the basement at a depth of 1,700 m and penetrated 11.3m of Precambrian crystalline rocks. Petrographically the samples in the upper 6.4 m of the basement core show evidence of severe alteration by the presence of hematite, limonite and chlorite and by the absence of plagioclase. Alkali feldspars from this part of the core are turbid, have a low 2 V of about 10°, are highly enriched in K, have low Na and Rb concentrations, lack cathode luminescence, and form a straight line on a Rb-Sr isochron diagram yielding a date of 599±69 Ma. Core samples from below 6.4 m appear relatively fresh and unaltered. Alkali feldspar from this portion of the core is orthoclase, shows uniform blue luminescence and gives a Rb-Sr date of 1,162±11 Ma. These results indicate that feldspars in the lowest part of the core are primary minerals that crystallized during the Grenville Orogeny, whereas the K-feldspar in the top of the core is of low-temperature secondary origin. The formation of this feldspar is explained as a consequence of chemical weathering of primary feldspar during late Precambrian time to clay minerals that were later reconstituted under low-temperature hydrothermal conditions as K-feldspar (adularia) by reactions with brines derived from the overlying Mt. Simon Formation of Cambrian age.
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  • 2
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Four progressive mineral zones I (chloritoid+quartz), II (staurolite+chlorite+muscovite), III (kyanite+biotite) and IV (sillimanite + muscovite) have been mapped in a well-defined stratigraphic unit of ferruginous pelitic composition from north to south over a distance of about 15 km in the Unazuki area, Hida terrane, central Japan. Textural and chemical evidence indicates that a given metamorphic mineral assemblage was formed from the mineral assemblage that precedes it in a spatial sequence of mineral zones. An unusually large number of chloritoid-bearing mineral parageneses have been found within a small area in zone I, suggesting that they were equilibrated close to the seven-phase invariant point consisting of staurolite, chloritoid, garnet, chlorite, biotite, muscovite, and quartz in the five-component system Al2O3-FeO-MgO-K2O-SiO2 at a fixed $$P_{{\text{H}}_{\text{2}} {\text{O}}}$$ . Chloritoid also has been found as inclusions in garnet from zones II and III, but is never in direct contact with quartz in these zones. All garnets in the chloritoid-bearing rocks from zones I, II, and III are characteristically poor in Mn and Ca at the cores, suggesting, in conjunction with textural and modal evidence, that they were formed as the products of chloritoid-consuming reactions. Compositional and textural features of the garnets in the chloritoid-bearing rocks suggest that rocks in zones II and III bypassed the seven-phase invariant point on the high pressure side during prograde metamorphism. Thus the metamorphic geotherm based on the progressive mineral zones is not always identical with the P-T paths followed by rocks.
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  • 3
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Remarkable spinel+quartz associations are observed in some xenoliths found in the Basaltic rocks from Tallante. The main primary parageneses are: * quartz — plagioclase — sillimanite — spinel — garnet — ilmenite — graphite * quartz — plagioclase — garnet — orthopyroxene — spinel — ilmenite. A thin cordierite rim is often developed between spinel and quartz, and is the result of the reaction (1) 2Sp+5Q→1 Cd. The existence around garnet of glass enclosing euhedral spinels has been ascribed to a garnet±sillimanite±plagioclase melting reaction. These aluminous rocks are interpreted as xenoliths in thermal equilibrium with a basaltic magma (≃1,100° C). According to available geobarometers, the primary parageneses crystallized at about 7 kb. These xenoliths could represent fragments of the walls of a magma chamber which would have been located at a depth of about 26 km. From these data and others available in the literature, it is shown that the exchange reaction (2) Fe spinel+Mg cordierite⇌Mg spinel+Fe cordierite can be used for geothermometric purposes, and a Sp-Cd geothermometer is calibrated: T°K=−1,763/ln Kd+0.378. In addition, the association spinel — quartz — cordierite (reaction (1)) is a potential geobarometer: P=P Fe-(RT ln (a Fe Cd Cd /a Fe Sp Sp 2 / ΔVs) with P Fe=−8.4T° C+9,295; T° K= −1,763/ln Kd+0.378 and ΔVs=1.075 cal/bar. It indicates a pressure of about 4 kb for the crystallization of the secondary cordierite from Tallante. A method to predict the geometrical relationships of divariant fields in P-T diagrams and their evolution as a function of changes in composition is developed. It is applied to phase relationships between spinel, sillimanite, orthopyroxene, garnet and cordierite (+excess quartz) in the systems Al2O3-FeO-MgO and Al2O3-(FeO+MgO) and a model is proposed for K2O-depleted SiO2-saturated metapelites at high temperature. The Tallante xenoliths are considered to be samples of a lower crust seriously modified by an important thermal anomaly which is also responsible for the volcanism.
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  • 4
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The influence of a deformation on the zircon U/ Pb system was studied using the example of the western margin of the Iforas granulitic unit (Mali) where undeformed sub-alkaline leptynites have evolved to strongly foliated mylonites and then to ultramylonites. The deformation episod was late Pan-African and occurred at low temperature. Zircons show evidences of a brittle behavior with microcracks development, then, fracturation of the crystals and dispersion of the fragments in the ductile matrix. An equilibrium grain size was reached which probably depended of the stress, but was independant of the initial size of the zircons and of the strain. In order to establish an accurate radiochronology of the studied area before the deformation, three rocks, not affected by the late Pan-African shear zone, have been dated by U/Pb method on zircons. In agreement to previous U-Pb, Rb-Sr and Sm-Nd data, the present results show that in the Iforas as in the western Hoggar, a main granulite facies metamorphism occurred 2,120±20 Ma ago. U/Pb data on zircons with inherited cores were interpreted by a multistage model with two episodic radiogenic lead losses, the first one at 2,120 Ma and the second one during Pan-African events. Then, a systematic investigation of the behavior of two chronometric systems (U/Pb on zircons and Ar39-Ar40 on feldspars) during a strong deformation episod at low temperature, was carried out. For the mylonitic episod, an upper limit of 566±8 Ma, is deduced from U/Pb data on non magnetic, coarse zircons of a late Pan-African granite, intruded in the western margin of the Iforas granulitic unit and slightly deformed by the mylonitic episod. Furthermore inherited cores are commonly present in these zircons, thus, the U/Pb data also indicated that this granite was formed 566±8 Ma ago, by partial melting of rocks with an apparent age of 2,609±200 Ma. A lower limit for the mylonitic episod was defined at 535±6 Ma by Ar39-Ar40 on K-feldspars extracted from a mylonite and an ultramylonite. An Ar39-Ar40 age of 900 Ma obtained on K-feldspars from an undeformed leptynite has no clear geological significance; the disturbing effect of the very closed shear zone, was probably not strong enough to reset totally the Ar chronometer. Finally, U/Pb data on zircons extracted from an ultramylonite indicated that the U-Pb system of these zircon fragments, remained closed during the deformation episod at low temperature. The distinct behavior of the two radiochronological systems (Ar39-Ar40 on feldspars and U-Pb on zircons) is emphasized. For ultradeformed samples at low temperature, the age of the deformation and the age of the rocks which have undergone this deformation, can be determined using the two complementary chronometers.
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  • 5
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Balmuccia peridotite shows evidence, in the form of a network of dykes, of partial melting and flow crystallization processes. The partial melting processes probably occurred over a fairly long time interval, and seem to have been related to different “melting pulses”. Resultant liquids were broadly picritic. Melting occurred incongruently according to the scheme cpx+opx+(ol+sp)=Mg-richer ol+Cr-richer sp+L. Partial melts tended at first to accumulate in horizontal layers; then, as the critical melting threshold was exceeded, liquids were able to filter slowly towards lower pressure zones. In doing so liquids fractionated initially in situ, via crystallisation of websteritic dykes of the Cr-diopside suite, and later, in the overlying mantle, via crystallisation of transitional dykes and those of the Al-augite suite. This filter-pressing stage, when flow velocities were very low and discontinuous, probably corresponded to the period of maximum deformability of the peridotite. The type of differentiation testified by the dykes of the Balmuccia peridotite, is characterized by a decrease in SiO2, a rapid enrichment in Al2O3 and a mild increase in FeO, and is substantially in accordance with experimental trends from the fo-an-di-SiO2 system in the spinel-peridotite stability field. A close relationship between type of differentiation, flow velocity and mechanical behaviour of the mantle peridotite is a feature of the proposed model.
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  • 6
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The coarse-grained, submersible-collected rocks from the Mid-Cayman Rise in our study span a vertical section of about 700 m and range from amphibolite to gabbro. Petrographic and mineralogic studies showed that: (1) some deformation is present in all rocks; (2) the distribution of deformation is not uniform within a specimen; and (3) alteration has taken place preferentially in the deformed zones. The abundance of amphibole decreases with sample depth and argues that seawater flux into the oceanic crust decreased with depth. The compositional changes in rocks indicate that partially exchanged seawater was the metamorphic fluid that supplied Na, K, and H2O to and removed Ca from the rock. In all, about 15% of the original rock has been transformed to amphibolite in the 700 m vertical section. Our study indicates that deformation of oceanic crust is necessary for providing pathways for seawater penetration which in turn is necessary for the submarine metamorphism to occur. If deformation continues to take place during the spreading of seafloor, alteration may also continue to occur along newly formed fractures and cracks.
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  • 7
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Stylolites and pressure-solution seams can form during diagenesis of rocks subjected to stress through a feedback involving texture and pore-fluid solute concentration. This feedback destabilizes the state of uniform texture (represented here only by porosity, for simplicity). A mathematical kinetic model that includes pressure solution, diffusion, and reprecipitation predicts the spontaneous generation, even in initially uniform rocks, of regions alternatingly (in space) more and less soluble. A region that becomes more soluble also becomes simultaneously more porous. The kinetic theory predicts that Stylolites can form at roughly constant spacings; this agrees with many field and petrographic observations. Bedding planes between beds that have initially different texture are shown by the theory to be the focus of a porosity instability that can lead to the formation of a stylolite and to the generation of more Stylolites within each bed. This prediction agrees with the observation that many Stylolites have developed at bedding planes. Finally, the theory, on the basis of transport, kinetic and thermodynamic properties for calcite and quartz and their aqueous ions, predicts the order of magnitude of both the spacing between Stylolites and their time of formation. For limestones the predicted spacing has a very large range, perhaps from 10−4 to 102 cm, and for quartz arenites, chert, and quartzites it is between 0.025 and 3 cm. These values agree crudely with spacings observed in rocks. The predicted times of formation of Stylolites in quartzose rocks are not unreasonable: 6,300 to 1.7×106 years. The range of formation times for Sstylolites in limestones is very large due, as for the predicted spacings, to the sensitivity of both the solubility and growth/dissolution kinetics of calcite to pH, $$P_{{\text{CO}}_{\text{2}} }$$ , and many inhibitors.
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  • 8
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Na, Be cordierites (Alpe Sponda) and normal Na-, Be-poor cordierites (Miregn) from the same tectonic unit are compared. The Alpe Sponda samples (Na2O: 1.1–1.5 wt.%, BeO: 0.6–0.8 wt.%), which occur in paragonite mica schists, reveal low optic angles (2V x : 45°–55°) and low distortion indices (Δ: 0.139–0.172). Chemical analyses suggest a substitution of the type Na + Be → Al. Heating in a reducing atmosphere expels the volatile channel occupants and increases 2 V x to 72.4°–73.9° and Δ to 0.194–0.223. The normal cordierites from Miregn replace kyanite and occur in biotite mica schists interbedded with leucocratic layers. These specimens exhibit optic angles between 64° and 79°; Δ ranges between 0.232 and 0.250. The gas contents (2.0 and 2.3 wt.%) of cordierites from Alpe Sponda are significantly higher than in the Miregn samples (1.5 and 1.8 wt.%). IR spectra show that H2O is the major component in both localities and CO2 does not exceed 0.4 wt.%. Degassed Na, Be cordierites have higher refractive indices than degassed normal cordierites with the same F-value (F[mol] = (Fe + Mn)/(Fe + Mn + Mg)). This behavior is mainly caused by smaller cell dimensions and increased density due to the Na + Be → Al substitution.
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  • 9
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A new age determination has been made on the Greenstones of the Agnew-Jones Creek Area, Western Australia by use of the Zircon U-Pb dating procedure. Late stage granophyre from the differentiated Kathleen Valley doleritic sill provided zircons which are otherwise unobtainable from mafic rock suites. An upper intercept age of 2,795 + 38 Ma, extends the known length of the otherwise tightly established, late Archaean tectonic cycle at Agnew from 250 Ma to 320 Ma. A lower intercept of age 1,345 ± 153 Ma is interpreted to record either a hitherto unknown very low temperature heating, or a hitherto unknown tectonic, uplift and cover removal, in the mid-Proterozoic. The existance of a postulated ancient unconformity of craton size dimensions may be being confirmed and dated. Apart from some inconclusive olivine and pyroxene Rb-Sr isotopic data from 190km to the west, the only evidence known that could support either possibility is found outside the Yilgarn Block itself. Minor perturbations to a simple two-stage discordia pattern imply further small amounts of lead loss at later times. Studies of this nature could eventually provide information on the later history of stabilized cratons.
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  • 10
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
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  • 11
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Two mineralogic geobarometers based on the assemblages olivine-plagioclase-garnet and orthopyroxeneplagioclase-garnet-quartz have been calibrated from the reaction (1) fayalite+anorthite⇋garnet (Gr1Alm2). The reaction boundary has been determined to within 0.2 kbar using piston-cylinder apparatus. It is located at 4.7, 5.1, 5.5, 5.8, 6.2, 6.6, and 7.0 kbar at 750, 800, 850, 900, 950, 1,000, and 1,050° C, respectively. Summation of ΔG for reaction (1) and fayalite +quartz⇋ferrosilite locates to within 0.3 kbar the following model garnet-forming reaction for quartz-saturated granulites: (2) ferrosilite+ anorthite⇋garnet(Gr1 Alm2) + quartz. Geobarometers based on (1) and (2) are widely applicable in granulite terranes and yield precise pressures that are in agreement with other well-calibrated barometers. Pressures of 7–10 kbar are inferred for many granulite terranes requiring the widespread development of 60–70 km thick continental crust by mid-Proterozoic.
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  • 12
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Modern rift zone hydrothermal brines are typically CaCl2-bearing brines, an unusual chemical signature they share with certain oil field brines, fluid inclusions in ore minerals and a few uncommon saline lakes. Many origins have been suggested for such CaCl2 brines but in the Reykjanes, Iceland, geothermal system a strong empirical case can be made for a basalt-seawater interaction origin. To examine this mechanism of CaCl2 brine evolution some simple mass balance calculations were carried out. Average Reykjanes olivine tholeiite was “reacted” with average North Atlantic seawater to make an albite-chlorite-epidotesphene rock using Al2O3 as the conservative rock component and Cl as the conservative fluid component. The excess components released by the basalt to the fluid were “precipitated” at 275° C as quartz, calcite, anhydrite, magnetite and pyrite to complete the conversion to greenstone. The resulting fluid was a CaCl2 brine of seawater chlorinity with a composition remarkably similar to the actual Reykjanes brine at 1750 m depth. Thus, the calculations strongly support the idea that the Reykjanes CaCl2 brines result from “closed system” oceanic basalt-seawater interaction (albitization — chloritization mechanism) at greenschist facies temperatures. The calculation gives a seawater: basalt mass ratio of 3∶1 to 4∶1 (vol. ratio of 9∶1 to 12∶1), in keeping with experimental results, submarine vent data and with ocean crust cooling calculations. The brine becomes anoxic because there is insufficient dissolved or combined oxygen to balance all the Fe released from the basalt during alteration. Large excesses of Ca are released to the fluid and precipitate out in the form of anhydrite which essentially sweeps the brine free of sulfate leaving an elevated Ca concentration. The calculated rock-water interaction basically involves Na + Mg + SO4 ⇌ Ca + K, simulating chemical differences observed between oceanic basalts and greenstones from many mid-ocean ridges.
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  • 13
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Fifteen samples across a 4 m thick komatiite flow from the Val d'Or region in the southeast portion of the Abitibi greenstone belt have been analysed for major oxides and trace elements including the rare earth elements (REE). The flow has been subjected to low grade regional metamorphism: virtually all primary mineralogy (olivine and clinopyroxene) has been obliterated although primary textures are well preserved. Compositional differences between the upper, spinifex textured portion and the underlying massive portion of the flow are largely consistent with the primary fractionation of approximately 30% olivine with a composition close to Fo92. Variations in incompatible element ratios across the flow and in enrichments between the spinifex and massive units suggest that Si, Ce and possibly Lu have been lost to, and Ca, Sr and possibly Y have been gained from, the surroundings. Remobilization of other elements (e.g. Zr, Hf, and alkali metals and most of the REE) appears to have been confined within the flow. AI, Ti, V and Sc appear to have been immobile during alteration of the flow. For the flow as a whole values for many element ratios (e.g. Al/Zr, Al/Sc, Sc/Yb, Zr/Hf, K/Rb) are very similar to chondritic values. If the flow represents a 40% melt approximately, and if the residue was essentially dunitic then the source abundance for most elements was close to chondritic; exceptions are the REE (1.5 to 2×chondrite), Ti (enriched relative to chondrites), and V (depleted relative to chondrites).
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  • 14
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Eifelite of variable composition is uniaxial positive withn 0 near 1.543 andn e near 1.544, a between 10.14 and 10.15 Å, andc about 14.22 Å, space groupP 6/m 2/c 2/c. There is a complete series of solid solution between the eifelite end member KNa3Mg4Si12O30 and roedderite, KNaMg5Si12O30, following the 2 Na⇌Mg substitution. Both eifelite and roedderite have milarite-type structures, but Na is always in six-coordinated sites: In roedderite Na occupies solely a newly defined B′[6]-position which is slightly displaced alongc from the ideal B[9]-position lying on the (001/2)-mirror plane in K2Mg5Si12O30. In eifelite Na is located both inB′[6] and in theA [6]-positions, where it partially replaces Mg. Eifelite has the highest cation occupancy of all osumilite group minerals known thus far. Both eifelite and roedderite occur in vesicles of contact metamorphosed basement xenoliths ejected with the leucite tephrite lava of the Quaternary Bellerberg volcano in the Eifel, West Germany. They are considered to be precipitates from highly alkaline, MgSi-rich, but Al-deficient gas phases that originated through interaction of gaseous igneous differentiates with the xenoliths.
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  • 15
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Bad Vermilion Lake anorthosite complex (2,700 m.y.) is exposed over an area of about 100 km2 near Rainy Lake, Ontario. As is typical of other Archean anorthosites, it is composed of coarse (1–30 cm across), equidimensional, euhedral to subhedral, calcic (An80) plagioclase, in a finer grained mafic matrix. The amount of mafic matrix in individual samples ranges from none to about 70% by volume. The complex has been variably metamorphosed to greenschist facies. Zoisite, chlorite, and hornblende are abundant, but primary plagioclase is preserved in many places. The anorthosite complex is associated with gabbro and with mafic to felsic metavolcanic rocks, and is cut by tonalite plutons and by mafic dikes. Some gabbros contain local concentrations of Fe-Ti oxides and/or apatite, but no chromite. The mafic groundmass of the anorthositic rocks is similar in major and trace element chemistry, including rare earth elements, to the associated basaltic metavolcanics, suggesting that the anorthositic complex may have accumulated from a subvolcanic magma chamber which fed mafic lavas to the surface during its crystallization. Mafic flows and dikes chemically similar to the mafic metavolcanics contain plagioclase megacrysts akin to those of the anorthositic rocks, and thus may represent a link between the anorthosite complex and associated mafic lavas. Elongate pretectonic tonalite intrusions were comagmatic with the felsic metavolcanics, but not with the anorthosites or metabasalts. These silicic rocks may represent low-pressure partial melts of the mafic rocks. There is no direct or indirect evidence for significant volumes of ultramafic material at the present exposure level of the complex. An estimate of the bulk composition of all rocks presumed to be comagmatic with the anorthosites, including gabbros and mafic metavolcanics, is an aluminous basalt with about 20 wt.% Al2O3. This composition has REE abundances unlike those of typical Archean high-Al basalts and probably does not represent that of a primary or evolved melt. The possibility must be considered, therefore, that a substantial fraction of material comagmatic with the anorthosites has been separated from the complex, either by magmatic or tectonic processes.
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  • 16
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In previously published papers the presentation of experimental results involving two liquids has not adequately addressed the quaternary aspects of the phase equilibria. A theoretical examination of the types of quaternary and pseudo-ternary phase diagrams to be expected is prestend here. When applied to much of the previous data, such quaternary diagrams cope with the variation in the K2O∶Al2O3 ratio of coexisting liquids, and all the previous data are shown to be in agreement with the existence of the assemblage tridymite-fayalite-two liquids for a limited temperature range along the field boundary between primary tridymite and primary fayalite. The absolute values of temperature in the different investigations are not easily reconciled without appealing to differences in experimental techniques, to differences in oxygen pressure, or to differences in K2O loss during the experiments, as possible explanations of temperature differences greater than reasonable interlaboratory variations.
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  • 17
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
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  • 18
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Basaltic glasses from the three alkalic areas of Iceland (Snaefellsnes Volcanic Zone, Sudurland Volcanic Zone and Vestmannaeyjar Volcanic Area) contain plagioclase, olivine, clinopyroxene, chromian spinel and titanomagnetite as phenocryst phases. The glasses are hypersthene to nepheline normative alkali basaltic with FeO/ MgO ratios between 1.4–4.7. Olivine ranges in composition from Fo90 to Fo55, plagioclase from An90 to An50 and clinopyroxene from En45Fs10Wo45 to En40Fs17Wo43. Clinopyroxene reveals systematic Ti:Al metastable crystallization trends related to the composition of the enclosing glass. Two types of phenocryst are present in most glasses and show a bimodality in size and composition. Microphenocryst phases are those most likely to have crystallized from the enclosing glass, while macrophenocrysts may have crystallized from a liquid of slightly less evolved composition. The glasses show complex phenocryst-glass relations which can be related to a polybaric effect. The normative glass compositions are related to 2-phase cotectic surfaces in the basalt tetrahedron and define the position of the 3-phase cotectic line. In general with increasing FeO/MgO in the glass the phenocryst assemblages vary from clinopyroxene, olivine and plagioclase along a clinopyroxene-olivine surface to olivine and plagioclase along an olivine-plagioclase surface. The normative glass compositions show a deflection from clinopyroxene-bearing to clinopyroxene-free glasses. The appearance of plagioclase together with clinopyroxene and olivine can be explained in the light of experimental investigations of the effect of pressure on phase relations. The major element variation of the glasses is interpreted as representing mantle derived magma batches of primary liquids, modified to some degree by high (6 kbar) and intermediate to low pressure (below 3 kbar) crystal fractionation towards equilibrium phase relations during ascent and residence in crustal magma chambers. The observed deflection in normative compositions of the glasses marks the position of the high pressure 3-phase cotectic line. The bimodality in size and composition of plagioclase and olivine phenocrysts can be related to high pressure crystal fractionation in the melt. The Fe-Ti basalt glasses from Sudurland are believed to be quenched high pressure compositions.
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  • 19
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Phenocryst assemblages in ocean-ridge basalts generally show an increasing proportion of plagioclase as the total amount of phenocrysts increases. The variations in phase assemblages, as well as most crystal-liquid Kd's, are similar to variations (equimodal trends) predicted by low-pressure laboratory experiments, suggesting that many of these basalts have experienced varying degrees of low-pressure cyrstallization prior to quenching, with little sorting of crystals and liquid. Important exceptions include moderately to highly phyric basalts enriched either in plagioclase or olivine which lie well off the experimental trends. In these basalts, megacrysts and xenocrysts usually cited as evidence for magma mixing commonly represent a small proportion of the total crystalline phase assemblage. However, phase proportions for many of these basalts lie well outside the range that could be produced by simple mixing; selective gravitative sorting either prior or subsequent to mixing appears to be the likely explanation for these phyric basalts. A relation between spreading rate and phase proportions is neither supported nor refuted by the data, which as yet do not adequately represent fast-spreading ridges. Pyroxene-phyric varieties are especially common among LIL-element enriched (Group 2) basalts, and these basalts also show the greatest abundance of olivine-enriched (picritic) samples. Selective enrichment in plagioclase is more common among LIL-element depleted (Group 1) basalts, and pyroxene appears in Group 1 basalts only at relatively high degrees of crystallinity. These differences are consistent with expected compositional effects (including volatiles) on phase boundaries, as well as likely differences in depth (pressure) of mantle melting and magma fractionation. Sparsely to moderately phyric basalts tend to contain only olivine (±spinel) as phenocrysts, and lie in the olivine field in the projection from plagioclase in the CMAS tetrahedron. This is consistent with the concept that these magmas approach low-pressure equilibrium by olivine fractionation from a more picritic parent. The origin of these basalts, and relationships between them, remains an important fundamental problem. Phenocryst phase assemblages are consistent with the low-pressure phase saturation indicated by the projected positions of the associated glasses in CMAS. It is suggested that, in contrast to the classical practice of classifying basalts according to phase proportions, a classification based on presence and/or first appearance of each crystalline phase is both practical and petrogenetically significant for water-quenched submarine basalts.
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  • 20
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Equilibration of natural olivine with (Fe, Ni)S in sealed silica glass tubes yields a value for the distribution constant for Ni/Fe exchange (KD3) of 27.7±3.5, for 1,200° C, product olivine and sulfide compositions in the ranges 96 to 97 mol% Fo and 15 to 70 mol% NiS, respectively, and run durations of 28 days. Electron microprobe analysis of product olivine was made on ∼50 μm diameter grains separated from the sulfide matrix to eliminate the severe matrix interference experienced with in situ determination of trace and minor amounts of Ni. The present KD3 value is in general agreement with previous experimental results indicating KD 3∼30 in the temperature range applicable to hypothesized magmatic models for Ni-Cu sulfide ore formation and with inferred KD3 values for the temperature range 400 to 600° C. The olivine and sulfide compositions of a selection of Ni-Cu sulfide deposits yield KD3 values appreciably lower than the corresponding equilibrium values, which argues against concentration of the sulfides to ore grade in their present locations as early magmatic sulfides. However, KD3 is significantly higher for Ni-Cu sulfide deposits metamorphosed to medium and high grade conditions. The good correlation of increasing approach to chemical equilibrium with increasing grade and pervasiveness of metamorphism is related to the marked temperature dependence of the mobility of Ni in olivine.
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  • 21
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The late tholeiitic lavas of southwestern Ubekendt Ejland (63-54 Ma) are intruded by lamprophyre dykes (∼33 Ma). The compositional and temporal differences would seem to preclude any genetic relationship between the two igneous episodes. Competing models of renewed partial melting versus extended batch fractionation are considered to explain the origin of the lamprophyres. Mathematically modelled lamprophyres produced by batch fractionation are very close to observed lamprophyre compositions and this, combined with other temporal and spatial evidence, suggests that renewed partial melting of the mantle is not the best way to explain such bimodal suites.
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  • 22
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A geochemically and mineralogically diverse group of granitoids is present within an area of 900 km2 in the southern Snake Range of eastern Nevada. The granitoids exposed range in age from Jurassic through Cretaceous to Oligocene and include two calcic intrusions, two different types of two-mica granites, and aplites. The younger intrusions appear to have been emplaced at progressively more shallow depths. All of these granitoid types are represented elsewhere in the eastern Great Basin, but the southern Snake Range is distinguished by the grouping of all these types within a relatively small area. The Jurassic calcic pluton of the Snake Creek-Williams Canyon area displays large and systematic chemical and mineralogical zonation over a horizontal distance of five km. Although major element variations in the pluton compare closely with Daly's average andesite-dacite-rhyolite over an SiO2 range of 63 to 76 percent, trace element (Rb, Sr, Ba) variations show that the zonation is the result of in situ fractional crystallization, with the formation of relatively mafic cumulates on at least one wall of the magma chamber. Models of trace element and isotopic data indicate that relatively little assimilation took place at the level of crystallization. Nonetheless, an initial 87Sr/86Sr value of 0.7071 and δ 18O values of 10.2 to 12.2 permil suggest a lower crustal magma that was contaminated by upper crustal clastic sedimentary rocks before crystallization. The involvement of mantle-derived magmas in its genesis is difficult to rule out. Two other Jurassic plutons show isotopic and chemical similarities to the Snake Creek-Williams Canyon pluton. Cretaceous granites from eastern Nevada that contain phenocrystic muscovite are strongly peraluminous, and have high initial Sr-isotope ratios and other features characteristic of S-type granitoids. They were probably derived from Proterozoic metasediments and granite gneisses that comprise the middle crust of this region. Another group of granitoids (including the Tertiary aplites) show chemical, mineralogic, and isotopic characteristics intermediate between the first two groups and may have been derived by contamination of magmas from the lower crust by the midcrustal metasediments.
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  • 23
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    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract This paper presents a method for the systematic trace element modelling of a cogenetic suite of lavas. It is based on the geochemical inversion technique of Allègre and coworkers and utilizes the variations in the trace element concentrations of the lavas to calculate initial concentrations and source mineralogy. We reduce this inversion to a simple, step-by-step procedure: (1) correcting for fractional crystallization; (2) testing the inferred primary melt compositions for consistency with a model of equilibrium partial melts (with constant partition coefficients) formed from identical sources; (3) estimating the proportions of mineral phases entering the melt; (4) computing concentrations and bulk partition coefficients in the initial source relative to the concentration of a common reference element; (5) estimating relative mineral abundances in the source. Except for the fractionation correction, the calculations are done element by element using a direct analytic solution. For the purpose of comparison we apply this method to the same set of data used by Minster and Allègre (1978), a suite of lavas from Grenada (lesser Antilles) originally analyzed by Shimizu and Arculus (1975). The results of both methods agree well for the source abundances of the light REE, whereas the heavy REE abundances are shown to be poorly constrained by the data. Both methods require residual clinopyroxene and garnet in the source, but the ratio of these minerals is not well constrained. We are unable to reproduce the shape of D0 pattern (=bulk partition coefficients of the initial source) given by Minster and Allègre. The reason for this cannot be evaluated without repeating their calculations in detail. The set of data from Grenada is useful for comparison of the methods only, because it is now known from isotopic data that the samples are not truly cogenetic. Possibly better suited sets of samples for petrogenetic modelling are presented in parts II and III of this series.
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  • 24
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The simplified model of basalt genesis described in Part I of this series, equilibrium partial melting followed by Rayleigh-type fractional crystallization, is applied to a stratigraphically controlled sequence of basalt flows from Kohala volcano. Major-element compositions were determined for 52 samples and show a time-stratigraphic progression from tholeiites through transitional basalts to alkali basalts. Twenty-six of these samples were analyzed by isotope dilution for K, Rb, Cs, Sr, Ba and the REE, 13 for87Sr/86Sr, and 19 for Co, Cr, Ni and V by atomic absorption. After a simple, first-order correction for the effects of fractional crystallization (involving mostly olivine and aluminous clinopyroxene), the major element concentrations cluster tightly, and the incompatible trace elements show monotonic increases in concentration as a function of stratigraphic height. The process identification plot shows that all the (fractionation corrected) melt compositions can be explained by equilibrium partial melting of compositionally identical batches of source material. The REE and Sr are fractionated because of the presence of residual clinopyroxene. Garnet may also be present but in much smaller amounts. In this respect our results differ significantly from those of Leeman et al. (1980). The calculated chondrite-normalized REE patterns of the source are nearly flat to slightly convex upward. Therefore there is no need to invoke special mechanisms, such as metasomatic REE preenrichment of the source, in order to explain the petrogenesis of the suite of lavas. Specifically, Ce concentrations ranging from 20 to 250 times chondritic are all explained by the same calculated source pattern having a chondrite-normalized ratio of Ce/Sm=0.9±0.2. However, the normalized ratio Ce/Ba≅2 shows that the source is not simply primitive mantle.
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  • 25
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Tigalak intrusion is a dominantly dioritic layered body, about 80 km2 in area, which ranges in composition from norite to granodiorite. Local areas of the layered rocks display upward fractionation from norite to ferrodiorite. Periodic reversals of mineral composition trends record the emplacement of less fractionated dioritic magma. Heterogeneous mixtures of dioritic and granodioritic rocks occur widely in mappable lenses and layers that alternate up section and along the strike with more uniformly layered rocks. In these mixtures, chilled dioritic pillows occur abundantly in a hybrid cumulate matrix of granodiorite to diorite composition. Cross-cutting granodioritic dikes grade upward into stratigraphically-bound lensoid masses of the hybrid cumulates. It appears that the hybrid rocks formed as a result of the emplacement of the granodioritic magma through lower cumulates into the dioritic magma chamber and that the dioritic pillows represent chilled bodies of Ferich dioritic magma that commingled with cooler granodioritic magma and settled to the floor of the Tigalak magma chamber. The restricted distribution of these mixtures of hybrid cumulates and chilled pillows indicates that mixing between granodioritic and dioritic liquids was limited in time and lateral extent. Periodic injections of granodioritic liquids may have collected as a separate layer below the roof of the magma chamber and above dioritic magma.
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  • 26
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Low pressure phase equilibria for natural mafic systems may be calculated utilizing empirically derived single component distribution coefficients and the constraints placed upon mineral-melt equilibria by stoichiometry and mass balance, without any knowledge of thermochemical properties of melts (Langmuir and Hanson 1981). Variations in distribution coefficients caused by differences in melt composition may be largely eliminated by the application of a two-lattice melt model based upon the models of Nielsen and Drake (1979), Drake (1976b), and Bottinga and Weill (1972). In the two-lattice melt model, the melt is assumed to be made up of two independent quasi-lattices, the network formers, composed of the components SiO2, NaAlO2, and KAlO2, and the network modifiers, composed of the free oxides of Ca, Mg, Fe, Al, Ti, and Cr. Compositionally independent mineral-melt distribution coefficients were calculated for all the major and some minor components in olivine, plagioclase, high-Ca pyroxene, low-Ca pyroxene, spinel, and ilmenite. Regression constants were calculated from data from 1 atmosphere, anhydrous, equilibrium experiments on natural and synthetic mafic compositions including data obtained from the literature and from new synthetic spinel-melt experiments in the Fo-Ab-An system doped with Ti, Mn, Ni, and Fe. The distribution coefficients are internally consistent within 3 mole % (1σ) for all components. The effects of variable oxygen fugacity on mafic mineral-melt equilibria were calculated utilizing the relations of Sack et al. (1980) for the determination of the Fe+3/Fe+2 ratio, and the results of Schreiber and Haskin (1976) for Cr+3/Cr+2. A computer program, EQUIL.FOR, incorporating the derived mineral-melt distribution coefficients, calculates the sequence of mineral and melt compositions, and liquidus temperatures for mafic melt compositions undergoing equilibrium or fractional crystallization. This program reproduces, within 15° C, 52 experimentally determined crystallization sequences collected from the literature. These published crystallization sequences are for mafic systems not represented in the data set used to calculate the mineral-melt distribution coefficients.
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  • 27
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Mineral compositional relationships have been studied in a variety of alkaline basic rocks from small, highlevel intrusions. These small intrusions must have cooled quickly as the phases are all zoned, especially those forming the matrix of some of the rocks which seem to have formed under conditions of almost perfect fractional crystallization. The compositions of nephelines from the various rocks define an overall evolutionary trend in which Na2O, K2O and CaO decrease and SiO2 increases. The most SiO2-rich nephelines plot in the nepheline plus feldspar stability field and must have crystallized metastably from the melt. Clear, interstitial analcime is definitely not a primary phase. It appears to be restricted to rocks which crystallized primary SiO2-rich nepheline and formed from this phase by subsolidus recrystallization processes. Most of the rocks studied appear to have crystallized plagioclase as the first felsic mineral. In some rocks this phase is zoned from ∼An70-60, through anorthoclase compositions to rims of composition ∼Or50 and this is the only feldspar present in the rocks. In other rocks the “plagioclase” shows zoning to similarly potassic compositions (Or40–50) but this is accompanied by separate grains of orthoclase cryptoperthite. The zoning trends of the coexisting “plagioclase” and alkali feldspar allow the feldspar critical end point compositions to be estimated for these rocks. Rocks containing strongly zoned plagioclase as the only feldspar species are believed to have evolved towards relatively K2O-rich low-temperature melting compositions due to the presence of mafic components. The crystallization histories of the rocks are considered in terms of three planes in the An-Ne-Ks-Qz system i.e. Ne-Ks-Qz; (Ne60Ks40)-An-Qz; and An-Ab-Or. Mineral and bulk rock compositional data together with textural criteria are used to modify phase equilibrium relations in these simple experimental systems to take account of the additional components (e.g. mafics) present in natural magmas.
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  • 28
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Crystallization of spinel minerals in transitional and alkali basalts from Iceland can be related to the FeO, MgO, TiO2 and Cr contents of the coexisting melt. Chromian spinel occurs in glasses in which TiO2 is less than 2.8 wt.% and the weight ratio FeO/MgO is less than 2.0, whereas titanomagnetite occurs when the same parameters are greater than 4 wt.% and 2.7, respectively. In addition, chromian spinel only occurs in basalts with Cr greater than 200 ppm. It is suggested that chromian spinel crystallizes, together with olivine, from liquids with olivine liquidus temperatures ranging from above 1,200° C to approximately 1,150° C. A discontinuity in spinel crystallization follows until below 1,100° C, where titanomagnetite starts to crystallize. Compositional variations in chromian spinel attached to, or included, in homogeneous olivine phenocrysts, however, cannot be related to equilibrium relations. Textural relations suggest homogeneous nucleation for titanomagnetite, whereas chromian spinel nucleates heterogeneously, dependent on growth of olivine phenocrysts. The composition of chromian spinels cannot in detail be related to physical and compositional parameters of the average melt, but may be related to local compositional relations in the melt adjacent to growing crystals. Such compositional variation around growing olivine crystals may be the prime reason for the non-equilibrium precipitation of included chromian spinels.
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  • 29
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Subsolidus marginal zoning in calcium-poor clinopyroxenes and intermediate zoning in discontinuously zoned subcalcic- to calcium-rich clinopyroxenes from ironrich igneous rocks is used to calculate the interdiffusion coefficient, DCa−(Fe,Mg), parallel to the crystallographic caxis. Wagner's mathematical models describing the displacement of interfaces in solids as the result of isothermal diffusion are adopted. The steady-state heat flow equation is used to approximate the diffusion times. The calculated interdiffusion coefficients are of a reasonable order of magnitude, viz. 6.0×10−20−2.0×10−17cm2· sec−1 at about 900° C.
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  • 30
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Sector zoning has been experimentally reproduced in CaMgSi2O6-CaTiAl2O6 clinopyroxene crystals by isothermal crystallization using seed crystals. Element partitioning in different growth sectors and between the core and rim portions in single crystals was analysed in relation to growth rate R and degree of supercooling Δ T. The TiO2 and Al2O3 contents increase with increase in R and Δ T, but when they are compared between different sectors in a single crystal grown at the same Δ T, they correlate negatively with R. The order of faces in respect of contents of TiO2 and Al2O3 is (100)〉(110)≳(010)≳(111) at ΔT= 13° C and 18° C but changes to (110)〉(100)〉(010)〉(111) at Δ T= 25° C. The growth mechanism is concluded to be controlled by interface kinetics at ΔT= 13–25° C for all these faces, while at Δ T=45° C this relation holds for (100) and (010) faces, but not for (110) and (111), based on the growth rate versus supercooling relation and surface microtopographic observations. The interface kinetics play the essential role in the formation of sector zoning, when the layer growth mechanism takes place.
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  • 31
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Metamorphic assemblages and mineral compositions in basic to intermediate volcanic rocks of two Precambrian units (the sub-Jotnian and Jotnian) in the Dala region, central Sweden, reveal a history comprising two metamorphic episodes. The sub-Jotnian rocks were metamorphosed during a first episode: the metamorphic grade ranges from prehnite-pumpellyite facies (in a displaced block with sub-Jotnian (?) lava occurring in the border zone of a major impact structure), to pumpellyite-actinolite facies, and to greenschist facies in the lower part of the unit. The unconformably overlying Jotnian rocks were metamorphosed to prehnite-pumpellyite facies during a subsequent episode, which also left its imprint in the sub-Jotnian basement. Two other Jotnian sequences in central Sweden are in the same facies. There are systematic chemical differences in some of the secondary minerals. Sphenes contain more Al, and epidotes and pumpellyites are more Fe-rich in Jotnian (prehnite-pumpellyite facies) rocks compared with sub-Jotnian rocks of pumpellyite-actinolite facies. Most epidotes in Jotnian lavas are remarkably rich in Fe, with a replacement of Al by Fe3+ up to 1.5 atoms per formula unit (Ps50). Compositions of epidote and pumpellyite in pervasively altered rocks vary sympathetically. Pumpellyite composition is partly controlled by the extent of alteration in its host rock. There is a trend for the compositional field of pumpellyite to shrink and shift away from the Al corner of the Al-Fe*-Mg triangle with increasing extent of host rock alteration. This trend is most evident in Jotnian rocks. Since the fields in the Al-Fe*-Mg triangle given in the literature as representative of pumpellyites from different metamorphic fades are partly based on analyses of samples containing relicts, these fields should be adjusted if future investigations show that the trend is of general validity.
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  • 32
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Some 150 white K-micas from the Central Alps were analysed for their polymorph and phengite content. Pre-Alpine white K-micas and those belonging to the Meso-Alpine Lepontine Metamorphic “High” show exclusively the 2M1 polymorph. The 3T structural form, on the other hand, has been found in one third of the white K-micas formed during the Alpine regional metamorphism. In most cases this trigonal structure coexists with varying amounts of the 2M1 form. The 3T distribution pattern suggests that this polymorph originated during the Eo-Alpine high-pressure/“low temperature” metamorphism. Provided this interpretation is correct, the sporadic occurrence of this polymorph within the Meso-Alpine staurolite zone may be used as a tracer for the Eo-Alpine metamorphism. The following improved correlation between the (060, 331) reflections of 2M1 white K-micas and the RM-content (= 2Fe2O3+FeO+MgO in molar proportions), based on 24 micas from granitoid rocks, is presented: d(060, 331)= 1.498+0.082 RM. The phengite content of Alpine white K-micas belonging to the assemblage muscovite-biotite-K-feldspar-quartz was estimated from RM values or derived from chemical analyses and was found to be clearly related to metamorphic grade. Phengite-rich micas were formed during the Eo-Alpine high-P/“ low-T” metamorphism while aluminous muscovite was found within the Meso-Alpine thermal high of the Lepontine gneiss area. White K-micas from areas which underwent both the Eo-Alpine and the Meso-Alpine metamorphism display variable phengite contents. Although these micas show Tertiary Rb-Sr and K-Ar ages, the variable phengite content presumably reflects conditions during the Eo-Alpine high-P/“low-T” metamorphism. This interpretation implies that the cations occupying the interlayer positions are more easily equilibrated than those in octahedral and tetrahedral structural sites. A compilation of 3T white K-mica occurrences described in the literature is given in the appendix.
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  • 33
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The data published earlier on zircon and sphene fission track ages and annealing are discussed in the light of different etching conditions used for age determination and annealing experiments in order to explain the age discordances of some zircon and sphene pairs, as well as numerous closing temperatures obtained for individual minerals. Using the new set of simple etching conditions, zircon (KOH melt) and sphene (HF+HCl), the annealing experiments indicate that tracks in sphene are annealed more easily than in zircon. The closing temperature of zircon and sphene have been calculated at 300° and 250° C respectively. The study reveals that both the fission track age and the closing temperature of a mineral can vary considerably if different etchants are used. For different etching conditions the closing temperatures (T) of sphene have the following order: T NaOH〉 T HF+HCl+HNO3+H2O〉 THF+HCl〉THCl. An alternative method can be used to obtain thermal histories of rocks by selectively applying various etchants on the same mineral.
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  • 34
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Nybö eclogite pod in Norway is characterized by a great variety of clinopyroxene compositions with Jd contents ranging from less than 5% up to nearly 80%, whilst Ac+Hd contents remain almost constant (mostly within 10±5%). Unconstrained X-ray structure refinement has been carried out on 16 pyroxene crystals (8 with C2/c and 8 with P2/n space group) from the Nybö eclogite, and also on one omphacite crystal (from Lago Mucrone in the Sesia-Lanzo Zone, Western Alps) which displays the highest degree of cation ordering yet described. The final discrepancy factors range from 0.014 to 0.029. The population of the sites has been determined on the basis of bond length considerations and of the results of the site occupancy refinement. Six of these crystals were subsequently analysed by electron microprobe. The tetrahedral sites are occupied by Si with negligible amounts of Al. Al, Mg, Fe3+ and Fe2+ occur at the octahedral sites; in the ordered P2/n crystals Al and Fe3+ are concentrated at the M11 site, whilst Mg and Fe2+ are concentrated and the M1 site. The eight-coordinated sites contain Ca and Na with negligible amounts of Fe and/or Mg. Ordering of Ca and Na takes place in the P2/n samples in such a way that in the most ordered crystal the M2 site contains almost exactly 0.75 Na+0.25 Ca and the M21 site 0.25 Na+0.75 Ca. Some geometrical features of the tetrahedra as well as of the octahedra (e.g. tetrahedral quadratic elongation and TILT angle) are not a simple linear function of composition, even when no change in space group occurs. The crystals evidently do not behave like a binary system of the two components, Di and Jd, but behave rather as if the composition Di0.50 Jd0.50 was a distinct end member. The boundaries between disordered and ordered phases in the Nybö pyroxenes fall at about 0.35 and 0.65 Jd/(Di+ Jd), in close agreement with the previous TEM investigations. The degree of order varies with composition following a bell-shaped curve: different coaxial bell-shaped curves can be drawn for crystals which have similar compositions but come from different metamorphic environments. The order vs composition diagrams may be useful for the interpretation of the P-T-t histories of the host rocks.
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  • 35
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Diabase dykes containing spherical patches of carbonate intrude the Tarr albitite complex of SE Sinai. The morphology of these dykes indicates a highly gas-charged magma. Petrographic evidence points toward equilibrium during cooling of immiscible carbonate ocelli and silicate matrix. Dolomite is the main component of these ocelli, which are geochemically and isotopically similar to carbonatite. However, the low total REE content, and the presence of considerable marble in the country rock, suggest a process of stoping and melting of carbonate, followed by the “in situ” development of silicate-carbonate immiscibility.
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  • 36
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Archean volcanic rocks in the Confederation Lake area, northwestern Ontario, Canada, are in three mafic to felsic cycles collectively 8,500 to 11,240 m thick. Each cycle begins with pillowed basalt and andesite flows and is capped with andesitic to rhyolitic pyroclastic rocks and minor flows. Seventy five samples from this succession were analyzed for major and trace elements including the rare earth elements. In two cycles, tholeiitic basalts are overlain by calcalkaline andesite to rhyolite. In the third, cycle, the tholeiitic basalts are overlain by tholeiitic rhyolites. Fe enrichment in basalts is accompanied by depletion of Ca, Al, Cr, Ni, and Sr, and enrichment in Ti, P, the rare earth elements, Nb, Zr, and Y. This is interpreted as open system fractionation of olivine, plagioclase, and clinopyroxene. Si enrichment in dacites and rhyolites is attributed to fractional crystallization of plagioclase, K-feldspar, and biotite. Tholeiitic basalt liquids are believed to be mantle-derived. Intercalated andesites with fractionated rare earth patterns appear to be products of mixing of tholeiitic basalt and rhyolite liquids and, andesites with flat rare earth patterns are probably produced by melting of previously depleted mantle. Felsic magmas are partial melts of tholeiitic basalt or products of liquid immiscibility in a tholeiitic system perhaps involving extreme fractionation in a high level magma chamber, and assimilation of sialic crust. It is concluded that Archean cyclical volcanism in this area involves the interplay of several magmatic liquids in processes of fractional crystallization, magma mixing, liquid immiscibility, and the probable existence of compositionally zoned magma chambers in the late stages of each cycle. The compositionally zoned chambers existed over the time period represented by the upper felsic portion of each cycle.
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  • 37
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The xenogeneic- and allogeneic immunological specificity of the hydrocoral Millepora dichotoma has been investigated. Xenogeneic histoicompatibility reactions have been observed between this hydrocoral and a series of species belonging to the Demospongiae and to the Anthozoa (both Hexacorallia and Octocorallia). The xenogeneic histoincompatibility reactions proceed in the following sequence: (a) Species-unspecific sensitization; (b) necrosis formation, which is very likely due to an autolytic process; (c) callus formation, due to an hyperplastic growth of stolons; and (d) formation of a contact barrier in form of a barrier layer or a restored stolonial layer. Allogeneic histoincompatibility reactions are restricted to those regions of the coral which are interspersed with polyps; allogenic fusion is observed between branches, with a high density of polyps and the “foot”-region, which is characterized by a low polyp density.
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  • 38
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Field and laboratory research at Carrie Bow Cay, Belize showed that macroalgae, grouped in functional-form units resisted fish and urchin herbivory in the following order (from high to low resistance): Crustose-Group, Jointed Calcareous-Group, Thick Leathery-Group, Coarsely Branched-Group, Filamentous-Group and Sheet-Group; thereby supporting the hypothesis that crustose, calcareous and thick algae have evolved antipredator defenses and should show the greatest resistance to herbivory with a gradation of increasing palatability towards filaments and sheets. Of the 21 species examined, several (e.g.,Dictyota cervicornis on grids,Laurencia obtusa andStypopodium zonale) had exceptionally low losses to fish grazing, probably due to chemical defences. The sea urchin,Diadema antillarum, was more inclined to feed on algae with known toxic secondary metabolites than were herbivorous fishes; hypothetically related to the differences in mobility and concomitant modes of feeding. Tough leathery forms such asSargassum polyceratium andTurbinaria turbinata resisted grazing by bottom feeding parrotfishes (Scaridae) and surgeonfishes (Acanthuridae) but were susceptible when suspended midway in the water column, possibly due to the presence of rudderfishes (Kyphosidae) which readily consume drift Sargassaceae. The overall tendencies support our predicted relationship between grazer-resistance and algal morphology. In conjunction with our previously reported findings concerning primary productivity, toughness and calorimetry for many of the same species, these results lend credence to generalizations relating form with function in marine macroalgae.
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  • 39
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Pocillopora damicornis (Linnaeus) has seasonal gametogenesis and planula release at Lizard Island, Great Barrier Reef, in contrast with several previous reports on the species at other locations. The number of planulae released and gonad development varied considerably among colonies sampled at the same time, but reproductive activity occurred predominantly in winter. P. damicornis planulae settled preferentially on algal-covered substrata, rather than bare coral substrata, but showed subsequent mortality inversely related to this settlement preference. Competition with algae and biological disturbance contribute to spat mortality at different stages of settlement and growth.
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  • 40
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    Coral reefs 2 (1983), S. 173-173 
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
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  • 41
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Fungia scutaria spawned vigorously with a lunar beriodicity during the summer months of 1981 and 1982. Spawning activity declined in the fall of both years and was absent in winter and spring (1983). There was only one short spawning event per lunar cycle. Each event occurred in the evening between 1700 and 1900 hours 1 to 4 days following the full moon. Fungia scutaria exhibits gonochorism. Females ejected eggs through their mouths into the seawater above. Many of these negatively buoyant eggs settled onto the oral discs and were moved off the edge by ciliary-mucoid activity. Spermatoza from males were similarly expelled in a jet of gastrovascular fluid. Spawned eggs were small and lacked endosymbiotic zooxanthellae. Rapid development led to ciliated solid planulae by the next morning. Within 24 h a mouth had begun to develop. Planulae may have been able to feed within 39 h. Infection with zooxanthellae occurred 4–5 days following spawning. Planulae may have become competent for settlement by 7 days, but attempts to docment settlement produced ambiguous results.
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  • 42
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The interstices of coral rubble, the most common deposits of many reefs, provide extensive surfaces for a variety of sessile and vagile coelobites (cavity-dwellers). In the northern Florida Reef Tract there are at least 80 different sessile coelobites in coral rubble collected from 21 stations from in-shore lagoon to fore-reef, depth 40 meters. Three microzones of coelobites on the undersides of rubble were distinguished on the bases of their dominant community assemblages; algal microzone in the peripheral area, sponge-bryozoan microzone in the transitional area, and foraminiferal microzone in the central area. In the transect that extends some 6–7 km across the reef tract, the biomass is largest in the rubble of the shallow (1–3 m) shelf margin and it decreases shoreward and in deeper water; however, the maximum variety of species comes in the fore-reef at depths of about 20–30 m. Four coelobite zones are recognized in the reef transect based on distribution pattern and relative abundance of diagnostic species; 1) in-shore lagoon zone, 2) lagoon-reef zone, 3) marginal reef zone, and 4) fore-reef zone. Although this paper does not propose a comprehensive explanation for the distribution of coelobites, it does emphasize the importance of two factors that affect coelobite development and distribution: interstitial sediment as a negative (limiting) factor and flushing as a positive factor.
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  • 43
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Field and laboratory research at Carrie Bow Cay, Belize showed that macroalgae, grouped in functional-form units resisted fish and urchin herbivory in the following order (from high to low resistance): Crustose-Group, Jointed Calcareous-Group, Thick Leathery-Group, Coarsely Branched-Group, Filamentous-Group and Sheet-Group; thereby supporting the hypothesis that crustose, calcareous and thick algae have evolved antipredator defenses and should show the greatest resistance to herbivory with a gradation of increasing palatability towards filaments and sheets. Of the 21 species examined, several (e.g., Dictyota cervicornis on grids, Laurencia obtusa and Stypopodium zonale) had exceptionally low losses to fish grazing, probably due to chemical defences. The sea urchin, Diadema antillarum, was more inclined to feed on algae with known toxic secondary metabolites than were herbivorous fishes; hypothetically related to the differences in mobility and concomitant modes of feeding. Tough leathery forms such as Sargassum polyceratium and Turbinaria turbinata resisted grazing by bottom feeding parrotfishes (Scaridae) and surgeonfishes (Acanthuridae) but were susceptible when suspended midway in the water column, possibly due to the presence of rudderfishes (Kyphosidae) which readily consume drift Sargassaceae. The overall tendencies support our predicted relationship between grazer-resistance and algal morphology. In conjunction with our previously reported findings concerning primary productivity, toughness and calorimetry for many of the same species, these results lend credence to generalizations relating form with function in marine macroalgae.
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  • 44
    ISSN: 1432-0983
    Keywords: Chromosome ; 4,6-diamidino-2-phenylindole ; Mitosis ; Fluorescence microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Three sets of mitotic chromosomes were observed in wild type or cdc mutants (nda3-KM311 and nda2-KM52) of the fission yeast S. pombe by the DAPI staining method. The block of microtubular functions by thiabendazole or by the mutations caused their individual appearance in mitotically arrested cells. The chromosomes have a characteristic size; the length ratio of short, medium and long ones was roughly 1:2:3, consistent with the previous genetical data (Kohli et al. 1977). Double staining with ethidium bromide and DAPI showed that the nucleolus was always associated with the shortest chromosome. Pair-like structures resembling sister chromatids were also seen.
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  • 45
    ISSN: 1432-0983
    Keywords: Transportable elements ; Insertion mutations ; Expression mutants ; Yeast CYC7 gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The plasmid YCpCYC7(2) was constructed containing the Saccharomyces cerevisiae CYC7 gene, encoding the iso-2-cytochrome c protein, replicative sequences and selective markers from both E. coli and yeast, and the centromere of yeast chromosome III. The expression of the plasmid-CYC7 gene in yeast was similar to the low level expression characteristic of the chromosomal CYC7 gene. A number of insertions into the sequences 5′ to the gene were constructed in vitro. The insertion at 142 by 5′ to the coding sequence of a 400 by fragment which lies 5′ to the CYC1 gene and is known to be essential for the high rates of CYC1 transcription increased transcription of the CYC7 gene to levels characteristic of CYC1 transcription. On the other hand, the insertion of random DNA fragments at the same position gave mostly decreased CYC7 transcription. In addition to these in vitro constructions, a mutant plasmid was selected which had increased CYC7 transcription. This mutation was caused by the insertion of the bacterial IS1 element 313 by 5′ to the CYC7 coding sequence. The significance of these results is discussed in terms of two alternative models for CYC7 gene expression.
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  • 46
    ISSN: 1432-0983
    Keywords: ATP synthase proteolipid subunit ; Plastid DNA ; Gene mapping ; Nucleotide sequence ; Spinach
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A 1.6 kbp DNA segment of spinach plastid DNA has been shown to carry the gene for the proteolipid subunit of the ATP synthase. Each plastid chromosome contains one copy of this gene which is located in the large single-copy region of the chromosome near that of the ATP synthase alpha subunit. These two genes are transcribed in the same direction and probably in distinct RNA species. The proteolipid gene was located by hybrid-selection mapping, by transcription/translation of recombinant DNAs and by nucleotide sequencing. The in vitro product was identified by electrophoretic criteria including its characteristic shift in electrophoretic mobility upon incubation with dicyclohexylcarbodiimide, and immunology. The nucleotide sequence of the proteolipid gene is uninterrupted. The deduced amino acid sequence coincides with the published amino acid sequence for this protein and shows little homology with the published sequence of the proteolipid subunit of E. coli.
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  • 47
    ISSN: 1432-0983
    Keywords: Cyanelle DNA ; Strain differences ; Cyanophora paradoxa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cyanelle DNA from two different strains of Cyanophora paradoxa (strain LB555UTEX and strain 1555) was investigated. The cyanelle DNA from both strains showed a buoyant density in neutral CsCI gradients of 1.692 g/cm3. The total molecular weight, as judged by restriction endonuclease analysis, of the two cyanelle DNAs differed. In strain LB555UTEX the size of the cyanelle DNA was equivalent to 127 ± 1 kb whereas in strain 1555 a size of 138 ± 1 kb was consistently found. The sizes of individual DNA fragments and the number of recognition sites for a particular restriction endonuclease appeared largely unrelated. A high amount of cross hybridization, as judged by reciprocal heterologous DNA hybridizations, however indicated a high degree of sequence homology between the two cyanelle DNAs. Under comparable conditions, cyanelle DNA hybridized nearly exclusively with the dG+dC-rich rRNA transcription units from plastid DNAs. Up to now conserved restriction endonuclease recognition sites between the two cyanelle DNAs were only observed within the cyanelle rRNA genes which are present twice on both cyanelle DNAs.
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  • 48
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    Current genetics 7 (1983), S. 151-157 
    ISSN: 1432-0983
    Keywords: Podospora anserina ; Mitochondrial DNA ; Ribosomal Genes ; Intervening Sequences ; Transcripts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have examined the structure of the rRNA genes from the mitochondrial genome of Podospora anserina. Using R-loop analysis, nuclease protection experiments, and Southern blot hybridization analysis we have observed two intervening sequences (IVS) in the large rRNA gene, and none in the small rRNA gene. the IVS sequences are 1.65 kbp and 2.73 kbp long, and the larger of the two is in the position of the conserved IVS found in the mitochondrial genomes of other fungi. We have detected precursor transcripts for the large rRNA, and these data support the observation of two IVS in this gene. We also note that the large and small rRNA genes are separated by approximately 6 kbp of DNA.
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  • 49
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    Current genetics 7 (1983), S. 145-150 
    ISSN: 1432-0983
    Keywords: Claviceps purpurea ; mt DNA ; Linear rut plasmids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In order to establish a system for gene cloning in the ergot fungus Claviceps purpurea mitochondrial DNA was purified from two wild strains and four descendants of production strains. A characterization of the mt DNA with respect to buoyant density, molecular weight (45 kb corresponding to acontour lenght of 14 μm) showed no differences. However, considerable differences were detected in the restriction pattern, with the exception of two commercial strains of possibly common origin. From this it follows that restriction patterns of mt DNA may be used as finger prints to identify related strains. In one of the wild strains plasmids associated with the mitochondria were found. A characterization of two species p11 and p12 having molecular weights of 6.6 and 5.3 kb revealed that these genetic units are linear having respective contour lengths of 2.1 and 1.7 μm. According to Southern blot analyses both plasmids show homology to each other, but not to the mitochondrial “chromosome”. Accordingly, p11 and p12, despite localization in the mitochondria, are evidently not an integral part of the mt “chromosome”. The possibility to use the mt DNA and mitochondrial plasmids to establish a vector system for molecular cloning in imperfect strains of Claviceps purpurea has been pointed out.
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  • 50
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Cephalosporium acremonium ; Mitochondrial hybrid vector ; Nuclear association
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The hybrid vector pCP2, consisting of the bacterial plasmid pBR325, the nuclear gene Leu-2 of Saccharomyces cerevisiae and a fragment of mitochondrial DNA from Cephalosporium acremonium, was found to associate with the nucleus in a transformed strain of Saccharomyces cerevisiae. This was inducted by (1) efficient expression of the Leu-2 gene as evidenced by a short generation time on selective medium; (2) independence of Leu-2 gene expression from mitochondrial protein synthesis, since pCP2 was shown to replicate and to be expressed in petite mutants; (3) association of pCP2 with isolated DNA from nuclei as proved by transformation experiments with E. coli.
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  • 51
    ISSN: 1432-0983
    Keywords: Intergeneric hybrid ; Protoplast fusion ; S. diastaticus ; H. capsulate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A hybrid of Saccharomyces diastaticus x Hansenula capsulate was obtained by conversion of the S. diastaticus parent to a petite, protoplasting and fusion of the strains and isolation of the hybrids on selective media, containing glycerol or galactose. All of the single-cell clones obtained resembled S. diastaticus in morphology, and fermented glucose, galactose, maltose, sucrose and starch. The hybrid sporulated, producing spores resembling those of S. diastaticus, but in asci which differed somewhat morphologically. The stability of the hybrid depended on the composition of the maintenance media, as hybrid clones maintained on glycerol medium lost their ability to sporulate after a few transfers and the cellular morphology altered to a form more closely resembling H. capsulate, and those maintained on glucose-containing medium lost the ability to utilize glycerol. Cultures maintained on yeast extract-starch medium retained the ability to sporulate and utilize glycerol. However, dissection of asci from the hybrid yielded clones, some of which had lost the ability to metabolize glycerol but which still sporulated. These clones had an unaltered cytochxome spectrum, and in other ways appeared to be respiratory competent. Washed cells of hybrids grown on galactose or starch as sole carbon source metabolized starch, as shown by respirometric measurements, but cells maintained on glycerol as sole carbon source had lost this ability. There was some evidence that the addition of vitamins stimulated oxygen uptake on starch by the hybrids. The formation of sporulating hybrids in the cross may permit the genetic analysis of other Saccharomyces x Hansenula crosses.
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  • 52
    ISSN: 1432-0983
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A virus-like particle (VLP) of 50 nm diameter has been isolated from the hydrocarbon-utilising yeast Yarrowia (Saccharomycopsis) lipolytica. The VLP contains a linear, double-stranded RNA molecule of MW 3.8 × 106 and has a major capsid protein of MW 75,700.
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  • 53
    ISSN: 1432-0983
    Keywords: UV ; C. albicans ; Linkage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Parasexual genetic studies of the medically important yeast Candida albicans were performed using the method of UV-induced mitotic segregation. UV-ir-radiation of the Hoffmann-La Roche type culture of C. albicans yielded a limited spectrum of mutants at a relatively high frequency. This observation suggested natural heterozygosity. Canavanine-sensitive (CanS) segregants were induced at a frequency of 7.6 × 10−3. Double mutants that were both CanS and methionine (Met−) auxotrophs were induced at a frequency of 7.4 × 10−3. The single Met− segregant class was missing indicating linkage. UV-induced CanS or Met−CanS segregants occurred occasionally in twin-sectored colonies. Analyses of the sectors as well as the observed and missing classes of segregants indicated that gens met and can are linked in the cis configuration. The proposed gene order is: centromere —met — can. Thus, it is concluded that the Hoffmann-La Roche strain of C. albicans is naturally heterozygous at two linked loci. These findings are consistent with diploidy.
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  • 54
    ISSN: 1432-0983
    Keywords: Saccharomyces ; δ-Aninolevulinic acid synthase ; Cloning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary HEM1, the structural gene for δ-aminolevulinic acid synthase, has been isolated on recombinant plasmids. A yeast genomic pool constructed in the E. coli — yeast shuttle vector YEp13 was used to clone the HEM1 gene by complementation. A leu2 hem1 yeast mutants was transformed with the yeast genomic pool and hybrid YEp13 plasmids carrying the HEM1 gene were cloned by their ability to complement both the leu2 and hem1 mutations in the recipient strain. The yeast transformants, bearing the HEM1-containing plasmids pYe(HEM1), showed a 24–28 fold increase in δ-aminolevulinic acid synthase activity and in the intracellular content of δ-aminolevulinic acid (5–8 fold) as compared to wild type strains, suggesting that the p(HEM1) gene is being expressed as a catalytically active enzyme which can be transported into the mitochondria. However, the transformant strains did not present higher-than-normal content of heme or cytochromes either in glucose or in glycerol media, indicating that the production of δ-aminolevulinic acid is not the rate-limiting step in heme biosynthesis in yeast.
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  • 55
    ISSN: 1432-0983
    Keywords: Cloning of DNA repair genes ; Photoreactivation repair ; Excision repair
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The photoreactivation repair gene (PHR1) of the yeast Saccharomyces cerevisiae was cloned in a hybrid plasmid (pJDB207), which is able to replicate as a multicopy episome in S. cerevisiae and Escherichia coli cells. The size of the DNA fragment found to have the photoreactivation activity was 3.0 kb, determined by recloning of the isolated fragment. In wild type cells transformed by the plasmid containing the PHR1 gene, the number of DNA photolyase molecules was 15 times greater than in wild type cells with pJDB207 only. Using the same receptor strain the excision repair gen RAD1 was also isolated. The size of the insert of the DNA which complements excision repair deficiency in recipient yeast cells was 5.7 kb. The recipient cells after transformation with the plasmid containing RAD1 showed the same UV-sensitivty as wild type cells with pJDB207 only.
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  • 56
    ISSN: 1432-0983
    Keywords: Fission yeast ; Membrane ATPase ; Amino acid uptake ; Drug resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cyh3 and cyh4, multiple drug resistant strains of Schizosaccharomyces pombe, show a much reduced uptake of trichodermin, chloramphenicol, cycloheximide, L-lysine, glycine, L-threonine, L-glutamine, L-arginine and L-glutamic acid when compared to wild type. The plasma membrane and mitochondrial ATPase activities of these mutants are also greatly reduced. Since the uptake of such compounds is likely to be driven by a proton electrochemical gradient set up by the membrane ATPase it is suggested that the primary effect of these mutations is at the level of the membrane ATPase. Another drug resistant strain, cyh1, which is resistant only to high levels of cycloheximide, shows increased uptake of trichodermin, L-lysine, glycine, L-threonine, L-glutamine when compared to wild type. The plasma membrane and mitochondrial ATPases of cyh1 are considerably greater than those of wild type. It has been shown previously that cyh1 possesses an altered 60S ribosonal subunit protein when compared to wild type and this makes it resistant to cycloheximide. There is no obvious explanation as to how this change could lead to the alterations in drug and amino acid uptake and in ATPase activities observed.
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  • 57
    ISSN: 1432-0983
    Keywords: Phycomyces ; Phototropism ; Hypertropic ; Dysgenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phycomyces mutants, recently isolated for enhanced bending responses (hypertropic phenotype), have unusual genetic properties. In sexual crosses between hypertropic mutants and other strains, the progeny showed the following features: a) many incomplete tetrads, b) distortion of segregation ratios, c) progeny with nonparental phenotypes when hypertropic strains carrying mutations in the same gene or even the same allele were crossed, and d) morphologically abnormal progeny with phenotypes unrelated to those of the parents. In particular, the mesophorogenic colonies, which produced short sporangiophores, were genetically unstable; their mycelia produced sectors with normal morphology and segregated several alleles for different markers. Most of the phenomena (mutation, segregation distortion, and sterility) described in this paper resemble the “hybrid dysgenesis” syndrome in Drosophila. The results suggest that all seven hypertropic mutations affect the process of meiosis and thereby lead to unstable aneuploid progeny.
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  • 58
    ISSN: 1432-0983
    Keywords: Disaccharide utilization ; Kluyveromyces lactis ; Anaerobic ; Aerobic ; Kluyver effect ; Respiratory chain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A mutant of Kluyveromyces lactis is described which did not grow with substrates giving the Kluyver effect. In addition it could not grow with non-fermentable carbon sources, although it was not respiratory deficient. Abolition of respiration by cyanide also caused inability to grow with substrates showing the Kluyver effect in the wild-type strain. When the yeasts were using substrates showing the Kluyver effect, shifting to anaerobic conditions gave an immediate decrease in the intracellular concentration of d-glucose 6-phosphate. The results obtained were consistent with the need of a common respiratory and/or anabolic pathway for the utilization of these substrates.
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  • 59
    ISSN: 1432-0983
    Keywords: Chlamydomonas ; Chloroplast genetics ; Triploid zygotes ; 5-fluorodeoxyuridine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Haploid cells or diploid cells homozygous (mt+/mt+ or mt−/mt−) or heterozygous (mt+/mt− phenotypically mt−) for the mating-type locus and homoplasmic for a chloroplast marker conferring resistance to an antibiotic were crossed with haploid cells of opposite mating-type and carrying another chloroplast marker. Before mating, one or both of the parental strains were grown for 8 days on agar containing 1 mM 5-fluorodeoxyuridine (FUdR), which selectively reduces the amount of chloroplast DNA in Chlamydomonas. In all cases, the chloroplast allele of the treated parent was less frequently transmitted to the meiotic progeny of the zygote than in the corresponding control cross. The effect of FUdR was more pronounced on haploid cells than on diploid cells which initially contained a two-fold higher amount of chloroplast DNA. The results are discussed in relation to current models for uniparental inheritance of non-Mendelian genes.
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  • 60
    ISSN: 1432-0983
    Keywords: Chloroplast DNA ; Gene organization ; Ribulose-1,5-bisphosphate carboxylase ; ATPase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have located the positions of the genes coding for the α, β and ε subunits of the ATPase complex on Spirodela oligorhiza chloroplast DNA by means of heterologous hybridization with Spinacia cpDNA fragments. The overall cpDNA sequence organization of Petunia hybrida and Spirodela was compared. We hybridized well-characterized, cloned Spirodela cpDNA fragments with size fractionated Petunia cpDNA digested by Sall. It appears that the monocotyledonous Spirodela and the dicotyledonous Petunia cpDNA share a common sequence organization around their entire circumference. These observations, together with data reported in the literature, indicate a strikingly similar genetic organization of the chloroplast genome in widely divergent plants.
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  • 61
    ISSN: 1432-0983
    Keywords: Chloroplast DNA ; Spirodela oligorhiza ; Ribosomal RNA genes ; Physical map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The organization of the chloroplast ribosomal RNA genes in Spirodela oligorhiza has been determined. We have therefore characterized two cloned BamHI fragments containing the genes for the large and small rRNA genes, and two PstI fragments, each containing one of the two large, invertedly repeated regions of chloroplast DNA. Characterization was performed by restriction endonuclease mapping, DNA/RNA hybridization and electronmicroscopic R-loop analysis. The results show that the rRNA genes are present in the order 16S, 23S, 4.5S and 5S. The 16S (1.5 kb) and 23S (2.9 kb) rRNA genes are separated by a spacer of 2.25 kb. There appears to be a close resemblance between the organization of the chloroplast rRNA genes in Spirodela oligorhiza and other higher plants so far examined.
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  • 62
    ISSN: 1432-0983
    Keywords: Plastid DNA ; Restriction and gene mapping ; Ribosomal RNA ; Protein genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Using the restriction endonucleases SaII, SmaI, BgII and KpnI, physical maps of chloroplast DNA isolated from normal and cytoplasmic male sterile (radish cytoplasm) lines of B. napus were constructed and compared. In this study, a rapid and simple procedure was developed for the isolation of chloroplast DNA restriction fragments from low gelling temperature agarose gels. The overall structural organization of N and cms B. napus appears to be rather similar to that of cpDNAs of other higher plants. It is composed of two identical sequences (each about 15 Md) arranged as an inverted repeat separated by two single copy-regions of different sizes (about 54 and 15 Md). In both genomes the ribosomal RNAs are encoded by duplicate genes situated at one end of the inverted repeat. The two chloroplast genomes are distinguished by a point mutation in the rRNA locus. Genes for the large subunit of ribulose-1.5-biphosphate carboxylase and a 32 kilodalton photosystem II polypeptide are separated by a minimum of 30 Md of DNA within the large single copy region.
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  • 63
    ISSN: 1432-0983
    Keywords: Mitochondrial DNA ; Neurospora crassa ; Cytochrome c oxidase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have sequenced the gene for cytochrome c oxidase subunit 1 (CO I) in Neurospora crassa mitochondrial DNA. The gene is coded by the same strand as the rRNA and tRNA genes. The coding sequence predicts a protein of 557 amino acids, starting with methionine, and ending with asparagine. Comparison to the N-terminal amino acid sequence of the mature protein (Werner et al. 1980) reveals that the methionine is located at position -2. No other upstream AUG codons have been found in frame. The C-terminal part of the gene is about 70 basepairs longer than the corresponding parts of the Saccharomyces and mammalian genes. The homology between the Neurospora coding sequence and those of yeast and mammals is very high. As compared to Saccharomyces, the introns il through i5 are absent.
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  • 64
    ISSN: 1432-0983
    Keywords: Yeast mtDNAs ; Size determination ; Restriction endonuclease digestion ; Use in taxonomy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Restriction endonuclease digestion of mitocondrial DNAs from the nine Dekkera/Brettanomyces yeasts have revealed that three separate pairs of species, namely D. bruxellensis/B. lambicus; B. abstinens/B. custersii and B. anomalus/B. clausenii have identical genomes. This observation suggests that such analysis of mtDNA could be an important procedure for yeast taxonomy. Sizes of mtDNAs showed a graded range from the 28 kbp molecule in B. custersianus to the 100 kbp molecule in B. custersii. Furthermore, although the mtDNAs from D. intermedia (72 kbp) and D. bruxellensis (82 kbp) differ in size by 10 kbp the restriction enzyme fragmentation patterns are generally similar. The differences are reminiscent of mtDNA polymorphisms found in strains of Saccharomyces cervisiae which result from insertions or deletions, chiefly within genic sequences. By analogy, the two Dekkera species may, on further analysis, be revealed as variants of a single species.
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  • 65
    ISSN: 1432-0983
    Keywords: Sporulation “petite negative” yeast ; Alternative respiration ; Mitochondrial inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Upon transition from growth medium to acetate sporulation medium buffered at pH 6.1 with 0.2 M PIPES, Hansenula saturnus showed a respiratory activity which was 88% antimycin A sensitive (1st) and 12% high azide sensitive (3rd), as in acetate complete growth medium. After ≅ 10 h, 3rd respiration declined and oxygen consumption was inhibited by the simultaneous addition of antimycin A and hydroxamate, a situation which lasted until the appearance of the first asci. Later on, 1st and 3rd respiration reappeared and asci formation was completed under these respiratory conditions. The growth in the presence of antimycin A or erythromycin affected only quantitatively the ascospore production and this is because in sporulation medium there was a de novo synthesis of the mitochondrial components of the respiratory chain. Cells which were avoid of 1st respiration but possessed 2nd or 3rd respiration could sporulate, indicating that these alternative respirations also have a role in the process. This was confirmed by the inhibition of sporulation as occurred in the presence of inhibitors of 1st, 2nd and 3rd respiration in sporulation medium.
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  • 66
    ISSN: 1432-0983
    Keywords: Distiller's Yeast ; Petites ; Sucrose Utilization ; Membrane Transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A number of yeast strains are known to be unable to metabolize several sugars (galactose, maltose, α-methylglucoside) when converted to their petite mutants. The basis of this phenomenon is considered to be the loss of the ability to transport the sugars across the cell membrane. However, sucrose is believed to be hydrolyzed before the products are transported into the cell, and the enzyme responsible (invertase) is thought to be either present in the periplasmic space or to be bound to the outer surface of the cytoplasmic membrane. Hence the loss of the ability to metabolize sucrose may infer the impairment of the mechanism for transport of invertase to its normal location outside the cytoplasm. We have found a distiller's yeast strain which has lost the ability to metabolize sucrose when it is converted to the petite mutant, and we report here some of its properties. We have shown that the cell produces invertase, which is present in the cell-free extract, but not in the pellet of cell walls and unbroken cells, though we have not determined whether the enzyme is present in the cytoplasm in the glycosylated or the unglycosylated form. The ability of the strain to ferment sucrose is also impaired in respiratory-competent cells, when the determination is made under anaerobic conditions.
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  • 67
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; DEL1 ; rad ; ste7
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In DEL1 strains of the yeast, Saccharomyces cerevisiae, the iso-1-cytochrome c (CYC1) region is flanked on either side by Tyl elements in direct orientation which promote cyc1 deletions of the bracketed DNA in the haploid cell. In this study, we asked which genes might control this event by testing the possibility that the DEL1 mutation mechanism requires an enzyme (or enzymes) that is also utilized in the repair of damaged DNA. To this end, we independently coupled eight repair mutations, rad3–2, rad4–4, rad6–1, rad6–3, rad9–1, rev3–1, rad50–1, and rad51-1, toDEL1 and asked whether DEL1 was still functional. We found that none of these rad mutations significantly affects the mutation frequency of 10−6-10−5 established in DEL1 strains for the CYC1 locus. Furthermore, we determined that ste7, a temperature-sensitive sterile allele known to alter gene regulation in Ty-mediated mutations, is not required for DEL1 function. Finally, DEL1 is not temperature-sensitive at 23° or 37 °C.
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  • 68
    ISSN: 1432-0983
    Keywords: Neurospora crassa ; Nitrogen metabolism ; Regulation ; Heterokaryons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The nit-2 gene of Neurospora crassa is a major regulatory gene for control of nitrogen metabolism. Synthesis of the enzyme L-amino acid oxidase requires a functional nit-2 gene product and is also controlled by amino acid induction and nitrogen catabolite repression. Electrophoretic variants of L-amino acid oxidase have been employed to demonstrate that in heterokaryons, a nit-2 + gene product can turn on the expression of this enzyme in its own nucleus and also in nuclei that possess a nit-2 mutant. This trans-nuclear effect is only partial since the variant coded for in the nucleus containing the nit-2 mutant allele is always present in lower amounts than the alternative form. Two additional putative nitrogen control genes, MS5 and en(am)1, have been found to have clear effects upon the expression of L-amino acid oxidase. The en(am)1 mutant appears to result in an unusual case of reversal of the control present in wild-type: the enzyme is expressed in a constitutive fashion and inducers, required for enzyme synthesis in wild-type, actually reduce the level of L-amino acid oxidase in en(am)1. The MS5 mutant shows a substantial release from the usual nitrogen catabolite repression exerted by glutamine in wild-type.
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  • 69
    ISSN: 1432-0983
    Keywords: Saccharomyces ; Killer ; L dsRNA ; [HOK]
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nucleic acid extracted from killer strains of Saccharomyces cerevisiae and run on agarose gels under sub-optimal conditions for M dsRNA yielded two species of L dsRNA (L1 and L2) which migrated at slightly different rates. L2 dsRNA was shown to be dependent upon MAK3, MAK10 and PES1 but not MAK1 nuclear genes for its maintenance. L1 was shown to be independent of all of these genes. [HOK] a non-Mendelian genetic element which enables a replication-defective M genome, [KIL-sd1], to be maintained in a SKl + host (Wickner and Toh-e 1982) was found to be present in an M-o derivative of the strain K7 which possesses L2 but not L1. Curing of L2 at elevated temperatures resulted in a co-curing of [HOK] and it is therefore concluded that either L2 is equivalent to or else it encodes [HOK].
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  • 70
    Electronic Resource
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    Current genetics 7 (1983), S. 69-72 
    ISSN: 1432-0983
    Keywords: Yeast ; Protoplast ; Cybrid ; Plasmid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Data presented here demonstrate that fusion of protoplasts of two different haploid strains of Saccharomyces cerevisiae having the same mating type leads to the formation of “fusants” and “cytoplasmic hybrids”. The nuclear and cytoplasmic genome of a “fusant” combine those of the parent haploid strains. The “cytoplasmic hybrid” possesses the haploid genome of one parent and the combined cytoplasmic genomes of both. In mouse cells lines such products have been termed “cybrids” and this term has therefore been adopted here (Bunn and Wallace 1974).
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  • 71
    Electronic Resource
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    Current genetics 7 (1983), S. 73-77 
    ISSN: 1432-0983
    Keywords: Transformation ; U. maydis ; Autonomous
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary U. maydis has been transformed to aminoglycoside antibiotic resistance by plasmid pMP81 DNA, which contains the yeast LEU-2 gene and 2-micron DNA inserted into pCRI, encoding a gene for an aminoglycoside phosphotransferase. The resistant phenotype of transformants is mitotically unstable in the absence of antibiotics. Closed, circular pMP81 DNA was detected in transformant DNA preparations by hybridization to pCR1 DNA and by transformation of Escherichia coli to kanamycin resistance. Plasmid pMP81 DNA recovered fr