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  • Articles  (4)
  • Geosciences  (4)
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  • Articles  (4)
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  • 1
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The objective of the 20 Nautile dives of the recent Kanaut cruise was to study the southern wall of the Kane Fracture Zone from its eastern intersection with the Mid-Atlantic Ridge (MAR) to 5 Myr in age. The geological mapping shows four successive massifs, wrench faulted and slightly tilted. The transform-facing walls of these massifs exhibit outcrops of fresh and serpentinized peridotites, gabbros and basalts. The entire crustal exposure is cataclased and metamorphosed to greenschist facies.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: One of the two objectives of the Vemanaute cruise of the French deep submersible Nautile, was the geological study of the eastern intersection area between the Mid-Atlantic Ridge (MAR) and the Vema Fracture Zone in the equatorial Atlantic. Fourteen dives were conducted that allowed detailed geological survey and sampling of the main morphostructural units of this area: the northern and southern walls of the fracture zone, the median ridge, the northern and southern troughs and the nodal basin. In situ observations of recent tectonic features such as furrows, ridges and circular depressions, concentrated within the southern trough, allowed us to establish the location and the size of the present-day displacement zone. Geological investigations have shown that the nodal basin is entirely floored by basalts thus contrasting with other equivalent areas such as the Kane and Oceanographer fracture zone-MAR eastern intersections. Finally, this study stresses the great opposition between the relatively old and tectonically inactive northern part of the fracture, and the southern part which shows active tectonics and recent volcanic activity.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 76 (1981), S. 386-393 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Metabasalts with abundant pumpellyite have been dredged in the Vema fracture zone, Atlantic ocean, and contain prehnite+pumpellyite±epidote+chlorite+white mica. The prehnite — pumpellyite association in these rocks differs from the prehnite-epidote association for most of the prehnite — pumpellyite facies metabasalts from the ocean crust described previously. The occurrence of pumpellyite is discussed in terms of temperature conditions, $$\mu _{H_2 O} $$ and oxygen fugacity and the pumpellyiterich metabasalts are believed to be recrystallized by hydrothermal circulation of seawater at about 250° C under a very low pressure (〈1 kb). The bulk composition of the rocks demonstrates a strong chemical modification during hydrothermal metamorphism, similar to what is observed under greenschist facies conditions, except for potassium which can be uptaken from seawater by the rocks.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 100 (1988), S. 496-509 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Gorringe Bank is an anomalously high structure of the eastern part of the north Atlantic, which was known to be composed of mantle-derived peridotites (layer 4) and gabbros (layer 3). During the submersible cruise CYAGOR II in 1981, the contact between layer 4 and layer 3 was observed on Mount Gettysburg and interpreted as tectonic. The overlying series of gabbro was extensively sampled on both mounts composing the bank, Gettysburg and Ormonde. Coarse-grained to pegmatoid clinopyroxene gabbros predominate and are associated with differentiated rocks (ferrogabbros and diorites). Cumulate gabbros are missing. The gabbroic section sampled is therefore interpreted as the upper part of the plutonic section. Most samples were strongly recrystallized during two distinct events. Metamorphism occurred close to the ridge axis, from interaction of a seawater-derived fluid with still hot gabbros. High temperature shear zones favoured fluid circulation, but the water/rock ratio — estimated from the sodium input — was very small in undeformed rocks (〈1). The low W/R ratio explains the strong evolution of the fluid phase and therefore some particular compositions of secondary minerals. Low temperature alteration occurred when the gabbros were tectonically emplaced close to the sea bottom.
    Type of Medium: Electronic Resource
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