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  • 1
    Electronic Resource
    Electronic Resource
    Curved branching crystals and differentiation in comb-layered rocks (1975)
    Springer
    Contributions to mineralogy and petrology 49 (1975), S. 309-319 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Layering in which one or more of the component minerals has grown perpendicular to layer boundaries occurs, under a variety of names, in volcanic, hypabyssal nad plutonic igneous rocks. The most recent and best name is comb layering. The oriented minerals are elongate, are commonly branching and may be curved. Experimental crystallization of plagioclase and ternary feldspar melts confirms that a substantial degree of supercooling 01 a significant cooling rate is necessary to produce the curved or branching crystal morphologies typical of comb layering. The more viscous the melt, the less the supercooling required. Changes in the water content or confining pressure are mechanisms for inducing supersaturation in deep-seated magmas, that are consistent with field and experimental evidence. The change from modal dominance by a single elongate crystal phase in one comb layer to dominance by another phase in a contiguous comb layer is explained by the presence of constitutional supercooling ahead of the growing crystals of a given layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376183
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  • 2
    Electronic Resource
    Electronic Resource
    Petrology of the uppermost upper mantle deduced from spinel-lherzolite and harzburgite nodules at Calton Hill, Derbyshire (1978)
    Springer
    Contributions to mineralogy and petrology 65 (1978), S. 363-377 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A suite of protogranular- to porphyroclastic-textured spinel lherzolites and harzburgites from the Lower Carboniferous ankaramite vent at Calton Hill has been investigated for trends of modal variation and mineral composition and for variation in calculated bulk composition. The results indicate that the nodules are accidental xenoliths derived from a source at approximately 45 km depth and at 950 °C, i.e. within the mantle but above the Low Velocity Zone. The lherzolites and harzburgites have a complex petrogenetic history involving initital formation as residues from partial melting of peridotite; it is proposed that the residues were then admixed with veins of pyroxenite, followed by a complex series of metamorphic cycles of mineral reaction and exsolution, deformation, recrystallization and annealing and finally by rupture and incorporation in the ankaramite. During ascent to the surface chrome diopside in some nodules has undergone partial, incongruent melting to form a less sodic pyroxene and a soda-rich basalt melt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00372284
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  • 3
    Electronic Resource
    Electronic Resource
    Skeletal crystallization and residual glass compositions in a cellular alkalic pyroxenite nodule from Oldoinyo Lengai (1978)
    Springer
    Contributions to mineralogy and petrology 67 (1978), S. 139-149 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The alkalic pyroxenite nodule consists of megacrysts of diopside, apatite, perovskite and titanomagnetite in a groundmass consisting of diopside, apatite, titanomagnetite, nepheline, melilite, garnet and vishnevite crystals of various shapes, including previously undescribed skeletal and dendritic shapes, together with vesicles and residual glass. The residual glass is poor in SiO2 (38–40 wt%), and extraordinarily rich in Na2O (12.8–15 wt%), SO3 (1–1.5 wt%), and Cl (0.25–0.7 wt%), as a result of rapid, non-equilibrium crystallization of groundmass phases from a CO2-rich nephelinite melt. The Oldoinyo Lengai alkalic carbonatite lavas do not represent extreme products of the fractional crystallization of pyroxene, wollastonite, nepheline and alkali feldspar from the carbonated nephelinite melt. The most likely connection between the carbonatite and silicate magma types is one of liquid immiscibility, probably involving phonolite melt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046572
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  • 4
    Electronic Resource
    Electronic Resource
    Origin of carbonatites by liquid immiscibility (1979)
    [s.l.] : Nature Publishing Group
    Nature 279 (1979), S. 52-54 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] While previous experimental work suggests that high concentrations of Na2O are required for immiscibility7'14'15, the great majority of analysed carbonatites are rich in CaO with Na2O as only a minor constituent, seemingly ruling out a role for immiscibility in their genesis (for example, mean of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/279052a0
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  • 5
    Electronic Resource
    Electronic Resource
    An experimental investigation of olivine morphology (1976)
    Springer
    Contributions to mineralogy and petrology 57 (1976), S. 187-213 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Olivine crystals can adopt ten types of shape. Experimental crystallization of eight rock melts shows that there is a systematic change from polyhedral or granular olivines → hopper olivines → branching olivines → randomly oriented chain olivines → parallel-growth chain olivines → chain+lattice olivines → plate or feather olivines, with increase in cooling rate and with increase in degree of supercooling. This sequence involves changes from complete to progressively less complete crystals and from equant habit to elongate bladed habit (c〉a≫b) to tabular habit (a≃c ≫ b). The sequence is not affected by the phase relations of the melt. The larger the olivine content of a melt the slower the cooling rate at which a particular olivine shape grows, whereas the lower the melt viscosity, the greater the cooling rate. Irrespective of the melt composition, comparable crystal shapes grow at the same degrees of supercooling. By comparison of the shapes of olivine crystals in experiments with those in rocks of similar composition, it is possible to deduce the cooling rate through the olivine crystallization interval and the approximate degree of supercooling at which the olivine crystals nucleated and grew in the rocks. The various shapes of skeletal olivines in many picrites, olivine-rich basalts and the Archaean “spinifex” rocks are not due to rapid cooling, but to rapid olivine growth caused by the high normative olivine content of the magma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405225
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  • 6
    Electronic Resource
    Electronic Resource
    An experimental investigation of the delay in nucleation of olivine in Mafic Magmas (1979)
    Springer
    Contributions to mineralogy and petrology 69 (1979), S. 21-32 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The delay in nucleation of olivine in basaltic melts increases systematically with decreasing degree of supercooling, cooling rate, superheat, olivine content of the melt and with increasing melt viscosity. These findings imply homogeneous nucleation of olivine in melts run in the Pt-wire loop sample container used. Unlike plagioclase nucleation, the appearance of the first olivine crystal in a melt is predictable (to within 0.1–1 h of the event). The ‘metastable region’ (i.e., the minimum degree of supercooling necessary for nucleation) is less than 13 ° C. The cause of the delay in nucleation is discussed in terms of the finite growth rate of embryos and the progressive polymerization of the melt with decreasing temperature and increasing time. At degrees of superheat 〈18 ° the melts are inferred to be more highly disordered than expected. Some implications of the results for petrology and experimental petrology are discussed, including the possibility that continuous zoning may develop under isothermal conditions due to the sluggish attainment of equilibrium of melt structure following a sudden change in temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00375191
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  • 7
    Electronic Resource
    Electronic Resource
    Caldera formation in the Rum Central Igneous Complex, Scotland (2000)
    Springer
    Bulletin of volcanology 62 (2000), S. 301-317 
    Details
    ISSN: 1432-0819
    Keywords: Pre-eruptive caldera collapse Proto-caldera Rum igneous complex Intracaldera stratigraphy Ignimbrite feeder dykes Caldera resurgence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract. The Northern Marginal Zone of the Rum Central Igneous Complex in NW Scotland represents part of the early, felsic phase of the volcano. The marginal zone is a relic of the early caldera floor and the infilling of sedimentary and igneous rocks. Its formation has been explored through field examination of the ring fracture system of the Complex and its pyroclastic and epiclastic intracaldera facies. A sequence of magmatic tumescence and chamber growth caused initial doming, followed by the formation of a collapse structure without accompanying volcanism. This collapse structure, circular in plan, is akin in origin to a salt basin formed by crustal stretching above a rising diapir. We call this the proto-caldera. Collapse breccias, which represent the slumping and sliding of megablocks, blocks and boulders of the Torridonian sandstones which form the walls of the basin, were the original infilling. Logs of these deposits reveal considerable variation in thickness of the breccias (from 80–170 m) in the Complex, indicating an uneven floor to the proto-caldera, consistent with piecemeal collapse. Following accumulation of up to 〉70 m thickness of breccia, thin interbedded rhyodacitic crystal tuffs (10–30 cm) record the earliest eruptions of felsic magma in the caldera. Caldera formation was then interrupted by a period of quiescence, recorded by the presence of an epiclastic sandstone of locally several metres thickness, formed by washout of fines from the breccias. Subsequent resurgence created a fracture pattern characteristic of doming, along which rhyodacite magma rose in dykes and erupted up to perhaps 10 km3 of rhyodacitic intracaldera ignimbrites. This major eruption caused further incremental subsidence of the caldera floor into a now partly emptied magma chamber. Mafic inclusions in the ignimbrites point to the eruption being triggered by multiple injections of basic magma into a chamber occupied by felsic magma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450000099
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