Nd isotopic heterogeneity of the oceanic upper mantle

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  • SANO Sakae
    Institute for Study of the Earth's Interior, Okayama University

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  • Nd同位体組成からみたマントルの不均質性
  • Nd ドウイ タイソセイ カラ ミタ マントル ノ フキンシツセイ

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Abstract

The auther has examined mantle heterogeneity by using the neodymium isotope data of oceanic region. It has been stated that the εNd values of MORBs originating from the most depleted mantle are characterized by the range between +9 and +12, However, from many collected data, it has been recognized that the εNd values of +10 and over are rare. The most depleted MORBs are distributed in restricted region of the Northern Hemisphere. On the other hand, the MORBs of the Southern Hemisphere are characterized by low εNd values as compared with those of the Northern Hemisphere, and form the isotopically anomalous zone. The most of new εNd data concentrate between +7 and +10, and the ranges of those values are different in each ocean. The εNd values of OIBs in the Southern Atlantic and the Indian Oceans are +1 to -2. They are lower than those of the other OIBs. It has been suggested that large-scale Pb and Sr isotopic mantle anomalies (Dupal anomaly) exist in the Southern Hemisphere. On neodymium isotopic composition, the auther also has been recognized the anomalous zone in the Southern Atlantic and the Indian Oceans. Furthermore, it has been clearly that the anomaly on OIBs is found in the same area on MORBs.

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