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Books reviewed in this article:
Richard. Pierre J. H. 1481: Paléophytogéographieposlglaciaire en Ungava par l'analyse polliniquc. Puléo-Québec 13. 相似文献
Richard. Pierre J. H. 1481: Paléophytogéographieposlglaciaire en Ungava par l'analyse polliniquc. Puléo-Québec 13. 相似文献
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Petrology and Geochemistry of Metabasalts from the 1.95 Ga Jormua Ophiolite, Northeastern Finland 总被引：9，自引：0，他引：9
The Jormua Ophiolite exposes a unique fragment of Red Seatypeoceanic crust formed in a setting related to continental break-up1950 Ma ago. Two distinct types of basalt are represented: the‘early dykes’ and the ‘main basalt suite’.‘Early dykes’ have fractionated (H) REE patterns,OIB-like trace element patterns, low Zr/Nb (6) and ENd(1.95Ga)–0.6, indicative of their derivation from an enrichedsource. The remaining dykes and all lavas belong to the second,E-MORB-like ‘main basalt suite’, which is characterizedby high mg-number and Cr contents, flat REE patterns, Zr/Nb= 6–17, chondritic Th/Ta and only moderately depletedisotopic signatures [END (1.95 Ga)+1.9]. Most ‘main suite’samples cannot be related solely by fractional crystallizationto a common parental magma. Rather, they represent distinctmelt fractions that underwent variable amounts of chromite +olivine plagioclase fractionation during ascent. A significantpart of the compositional diversity of the ‘main basaltsuite’ can be explained by mixing a depleted source witha relatively uniform proportion of an enriched component similarto that represented by the OIB-like ‘early dykes’.It is probable that during the latest stages of continentalrifting the OIB-type melts metasomatized the upper part of thedepleted asthenospheric mantle, which became the source of the‘main basalt suite’ soon after the old continentallithosphere was ruptured. The complete absence of any evidencefor a subduction-related component in the basalts implies thatJormua is not a back-are ophiolite.
*Fax: +358 0 462 205. e-mail: petri.peltonen{at}gsf.fi 相似文献
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Book reviewed in this article:
Wright. H. E., Jr. (ed.) 1983: Late-Quaternary Environments of the United States . Vol. 1 The Late Pleistocene , edited by Stephen C. Porter. 相似文献
Wright. H. E., Jr. (ed.) 1983: Late-Quaternary Environments of the United States . Vol. 1 The Late Pleistocene , edited by Stephen C. Porter. 相似文献
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HANNU HYVÄRINEN 《Boreas: An International Journal of Quaternary Research》1976,5(4):276-278
The various problems in defining and dating a Pleistocene/Holocene boundary in Core B 873, proposed as the world boundary-stratotype by N.-A. Mörner, are pointed out. It is suggested that a terrestrial-lacustrine section might be a better alternative. 相似文献