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Hafnium isotope variations in oceanic basalts
Author(s) -
Patchett P. J.,
Tatsumoto M.
Publication year - 1980
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl007i012p01077
Subject(s) - basalt , mantle (geology) , geology , mid ocean ridge , geochemistry , isotope , partial melting , hafnium , fractionation , chemistry , zirconium , inorganic chemistry , organic chemistry , quantum mechanics , physics
Routine low‐blank chemistry and 0.01‐0.04% precision on the ratio 176 Hf/ 177 Hf allows study of Hf isotopic variations, generated by β − ‐decay of 176 Lu, in volcanic rocks derived from the suboceanic mantle. Normalized to 176 Hf/ 177 Hf = 0.7325, 176 Hf/ 177 Hf ranges from 0.2828 to 0.2835, based on 24 basalt samples. 176 Hf/ 177 Hf is positively correlated with 143 Nd/ 144 Nd, and negatively correlated with 87 Sr/ 86 Sr and 206 Pb/ 204 Pb. Along the Iceland‐Reykjanes ridge traverse, 176 Hf/ 177 Hf increases southwards. The coherence of Hf, Nd and Sr isotopes in the oceanic mantle allows an approximate bulk Earth 176 Hf/ 177 Hf of 0.28295 to be inferred from the bulk Earth 143 Nd/ 144 . This requires the bulk Earth Lu/Hf to be 0.25, similar to that of the Juvinas eucrite. 60% of the Hf isotopic variation in oceanic basalts occurs among mid‐ocean ridge samples. Lu‐Hf fractionation probably decouples from Sm‐Nd and Rb‐Sr fractionation in very depleted source regions, with high Lu/Hf, and consequent high 176 Hf/ 177 Hf ratios developing in mantle residual from partial melting.