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  • 1
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Major element, Ni, Mn and Ca electron microprobe analyses of olivine phenocrysts in one of the most primitive basalts from the FAMOUS area of the Mid-Atlantic Ridge, 527-1-1, reveal two different olivine populations, distinguished by their zoning characteristics. The often skeletal Group I olivines have zoning profiles with high forsterite, high Ni, low Mn, and low Ca cores. These profiles can be explained by low pressure crystallization from the 527-1-1 magma on cooling. The equant, often megacrystic Group II olivines also have high forsterite, low Mn cores, but the cores have low Ni compared to rims. Thus they are normally zoned with respect to Mg, Fe, and Mn but reversely zoned with respect to Ni. For example, Ni ranges from 1,700 ppm at Fo90.5 in the core to 2,100 ppm at Fo89.5 at the rim. In view of the published whole rock and mineral data of le Roex et al. (1981), the most likely explanation for these data is that the Group II olivines are xenocrysts assimilated from solidified “plagioclase-pyroxene” basalts through which the 527-1-1 basalt ascended. The diffusion rate of Ni and size of the xenocrystic olivines are used to calculate the residence time of the assimilated olivines in the magma. An alternative hypothesis would be a high pressure origin for the Group II olivines. This would be possible if future experiments show that with increasing pressure the partition coefficient for Ni decreases relative to the partition coefficient for Mg for a given bulk composition. Current evidence suggests this is unlikely. The data from 527-1-1 and other samples from the FAMOUS area require magmas with distinct Ni-MgO-FeO characteristics. In general, MORB from different ridge segments fall on distinct trends on plots of MgOvs. Ni as well as MgOvs. FeO. Calculation of the MgO and Ni contents of primary magmas suggests a mechanism by which such distinct trends could come about.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 369 (1994), S. 704-705 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE presence of water is one of the most important attributes of the Earth as a planet, of central importance to the surface envelope of ocean, atmosphere and life. It is also pivotal in the behaviour of the solid Earth — it is incorporated into the ocean crust during hydrothermal circulation ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 364 (1993), S. 191-192 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE distributions of temperature and composition in the Earth's mantle are questions being tackled from many directions, and lines of attack from separate disciplines often proceed in isolation. When evidence from two disciplines converges, the results from each become strengthened ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 362 (1993), S. 739-743 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] TABLE 1 Sediment fluxes into trenches and arc basalt compositions Arc Guatemala Mexico Java Tonga East Aleutians North Antilles Vanuatu Marianas ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 322 (1986), S. 422-429 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Lavas from the fast-spreading East Pacific Rise are geochemically diverse even within a single tectonically defined spreading cell. Within such spreading cells, small offsets of the rise axis are often boundaries between petrologically distinct magmatic units which must be supplied independently ...
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  • 6
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Closely spaced sampling of basalts around the East Pacific Rise, made possible by a new sampling technique, reveals spatial patterns of change in the composition of the sea floor. The patterns demonstrate the scale and magnitude of temporal variability in the basalt chemistry, and suggest that the ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 326 (1987), S. 15-16 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A SUBSTANTIAL step towards clarification of the controversy about magma chambers has been taken in the past year by a team of investigators from three US oceanographic institutions who carried out a comprehensive multi-channel seismic survey of the East Pacific Rise. On page 35 of this issue1, ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 325 (1987), S. 217-223 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Tholeiitic basalts collected over an area of less than 100 km2 near the Oceanographer transform fault have isotopic compositions interpreted as mixing between three chemically distinct mantle sources. Of the two enriched sources, one has an isotopic composition not previously ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 375 (1995), S. 274-275 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] MELTING of the Earth's mantle has long been understood to be the primary driving force behind most volcanism on the Earth's surface. In recent years, better experimental data, physical models and observations have much improved our ability to model mantle melting and apply the ...
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  • 10
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Lead is anomalously enriched in the Earth's continental crust, and in the magmas that give rise to new continental crust at convergent margins. A detailed study of volcanic rocks from the Aleutian island arc shows that this enrichment is a continuing process, and results from the efficient ...
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