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  • 1
    Electronic Resource
    Electronic Resource
    The biotite isograd, Central Pyrenees: a deformation-controlled reaction (1997)
    Oxford, UK : Blackwell Science Ltd.
    Journal of metamorphic geology 15 (1997), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The biotite isograd reaction in Cambro–Ordovician pelites from the Garonne dome in the Central Pyrenees involves the production of biotite at the expense of chlorite, and the gradual reduction in the celadonite (Si) content of individual white micas. The mineral assemblages in the biotite-bearing rocks in the Melles area retain abundant evidence of chemical disequilibrium, due to the sluggish nature of major element diffusion within the white micas. The progress of the isograd reaction is strongly controlled by the progressive development of regional Variscan fabrics, and chemical exchange in the white micas in these metamorphic conditions is only possible during active deformation. Chemical resetting of the white micas takes place via the development of compositional zoning in the deforming micas; this probably occurs as a consequence of the introduction of defects and dislocations, causing more efficient diffusion within parts of individual grains. In the absence of deformation, this biotite isograd reaction would take place at significantly higher temperature and be controlled by the relatively high closure temperature of major element diffusion in white micas. Thus, assigning thermal significance to such continuous isograd reactions is impossible without independent constraints: kinetic factors such as deformation may be the dominant influence in many cases, not the thermodynamic controls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.1997.00039.x
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  • 2
    Electronic Resource
    Electronic Resource
    Textural evolution of the rapakivi granites, south Greenland —Sr, O and H isotopic investigations (1991)
    Springer
    Contributions to mineralogy and petrology 107 (1991), S. 459-471 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The development of rapakivi texture in feldspars from the Ketilidian granitoids of south Greenland has been investigated using Sr, O and H isotopes. A low temperature signature is found in the Sr and O data which seemingly contradicts some textural features that point to a magmatic origin of the plagioclase mantles around the K-feldspar ovoids. An origin for these mantles involving exsolution from an original alkali feldspar solid solution is proposed, which involves growth of mantles over a range of conditions determined by the mobility of the exsolving sodic feldspar. This mobility may be enhanced at high temperatures in the presence of melts or increased fluid pressures and at lower temperatures by the processes responsible for the transformation of K-feldspar to microcline. Rapakivi granites with both white and dark green feldspar occur in south Greenland but show no major isotopic differences, although the dark alkali feldspars contain significantly more fluid. Equivalent fluids in the white alkali feldspars may have escaped during plagioclase exsolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310680
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  • 3
    Electronic Resource
    Electronic Resource
    Zoning and recrystallization of phengitic micas: implications for metamorphic equilibration (1992)
    Springer
    Contributions to mineralogy and petrology 109 (1992), S. 526-537 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract White micas (phengites) in the metasediments of the Scottish Dalradian display a large range of compositions within single samples. The variations in the composition of these phengites are strongly controlled by their structural age, with early fabrics containing a paragonite-poor, celadonite-rich phengite whereas in later fabrics the micas are generally paragonite-rich and celadonite-poor. Retrograde phengite growth, identified using back scattered electron imaging, occurs as celadonite-rich rims on micas within all existing fabrics and appears to be preferentially developed along existing white mica-plagioclase grain boundaries. The presence of these chemically distinct phengite populations within single samples implies that chemical exchange between the individual micas was inefficient. It is proposed that diffusion-controlled exchange reactions in phengites have relatively high closure temperatures below which major element exchange is effectively impossible. This closed system behaviour of micas questions the ease with which phengites may equilibrate with other phases during prograde greenschist and lower amphibolite facies metamorphism. Many of the chemical variations preserved in phengites from such metamorphic rocks may reflect deformation/recrystallization controlled equilibria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00306554
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  • 4
    Electronic Resource
    Electronic Resource
    Metamorphic reactions in the biotite zone, eastern Scotland: high thermal gradients, metasomatism and cleavage formation (2000)
    Springer
    Contributions to mineralogy and petrology 138 (2000), S. 348-363 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Prograde metamorphic reactions involving the growth of phyllosilicates and accompanying cleavage development have been investigated in Dalradian metasediments from the biotite zone of eastern Scotland. Crystallization of muscovite within the psammites of the Southern Highland Group is linked to the replacement of plagioclase porphyroclasts. This reaction is triggered by significant alkali metasomatism during active deformation and plays an important role in the formation of a prominent spaced cleavage within the psammites. The Si content of most of these early-formed muscovites is partially buffered by the quartz content of the rock, although close to the Highland Boundary Fault, evidence of greater influence from externally derived fluids on muscovite compositions is preserved. Locally higher fluid fluxes adjacent to the fault are also indicated by a relatively high δ 18O(SMOW) signature in the rocks. The biotite-producing reaction in these greenschist-facies rocks is linked to the later production of a celadonite-poor muscovite which formed as overgrowths around pre-existing white micas. This reaction is sensitive to the initial composition of muscovite and preferentially occurs in quartz-rich metasediments containing a celadonite-rich muscovite. A systematic increase in the progress of the biotite-producing reaction northwards across the biotite zone confirms the presence of high geothermal gradients along the southern margin of the Dalradian block, adjacent to the Highland Boundary Fault.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050568
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  • 5
    Electronic Resource
    Electronic Resource
    Localized uplift in the Scottish Dalradian (1984)
    [s.l.] : Nature Publishing Group
    Nature 307 (1984), S. 156-159 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The major structure of the Dalradian is dominated by pre-metamorphic nappe structures4, represented by the Tay and Tarfside Nappes in the present area5 (Fig. 1). The rocks considered in this study come from the roughly flat-lying, right way-up limb of the Tarfside Nappe, along the line ?-B in Fig. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/307156a0
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  • 6
    Electronic Resource
    Electronic Resource
    A new mechanism of granite emplacement: intrusion in active extensional shear zones (1990)
    [s.l.] : Nature Publishing Group
    Nature 343 (1990), S. 452-455 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our data come from the voluminous rapakivi granite suite of southern Greenland (Fig. 1). Reviews of the petrogenesis and significance of these early Proterozoic intrusions with their enigmatic large ovoid and mantled feldspars may be found elsewhere4'5. Although we comment later on the general ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/343452a0
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  • 7
    Electronic Resource
    Electronic Resource
    Garnet zoning and metamorphism of the Barrovian type area, Scotland (1985)
    Springer
    Contributions to mineralogy and petrology 89 (1985), S. 30-38 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A microprobe investigation of the high grade metamorphic zones from the Barrovian type area in Angus, Scotland, shows the importance of local zones of retrograde cation exchange between garnet, staurolite and biotite. The interpretation of this zoning, established during a slow cooling history, is critical to any study of metamorphic reactions or conditions. The extent and intensity of these diffusion effects are dependent on a number of parameters including grainsize, fabric orientation, heating and cooling history, and the modal abundance of the phases. Increasing diffusion within garnets with metamorphic grade, and the subsequent retrograde effects are modelled using Temperature-Time-Transformation diagrams and provide information on the activation energy for Fe-Mg diffusion in garnet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01177588
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  • 8
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    Late Proterozoic Charnockites in Orissa, India: A U-Pb and Rb-Sr Isotopic Study (1988)
    University of Chicago Press
    Details
    Publication Date: 1988-11-01
    Print ISSN: 0022-1376
    Electronic ISSN: 1537-5269
    Topics: Geosciences
    Published by University of Chicago Press
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  • 9
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    Quantification of the transient response to base-level fall in a small mountain catchment: Sierra Nevada, southern Spain (2007)
    American Geophysical Union
    Details
    Publication Date: 2007-09-26
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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  • 10
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    Zircon dissolution in a ductile shear zone, Monte Rosa granite gneiss, northern Italy (2008)
    Mineralogical Society of Great Britain and Ireland
    Details
    Publication Date: 2008-08-01
    Description: The sizes, distributions and shapes of zircon grains within variably deformed granite gneiss from the western Alps have been studied. Zircon shows numerous indicators of a metamorphic response in both the host gneiss and a 5 cm wide continuous ductile shear zone, within which the zircon grain sizes range from 50 μm. However, the very fine grain sizes are virtually absent from grain boundaries. Within this zone, zircons consistently have more rounded and embayed margins, which are interpreted as evidence of dissolution in response to fluid influx during shearing. Zircons are preferentially located near metamorphic muscovite in both the host gneiss and the shear zone and tend to show the poorest crystal shape, indicating that fluids linked to the formation and presence of muscovite may enhance both the crystallization of zircon and its subsequent dissolution. Larger zircon crystals typically show a brittle response to deformation when adjacent to phyllosilicates, with fractures consistently perpendicular to the (001) mica cleavage. The variety of metamorphic behaviour observed for zircon indicates that it may be highly reactive in sub-solidus mid-crustal metamorphic environments.
    Print ISSN: 0026-461X
    Electronic ISSN: 1471-8022
    Topics: Geosciences
    Published by Mineralogical Society of Great Britain and Ireland
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