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Oceanic crust generated by elusive parents: Sr and Nd isotopes in basalt-peridotite pairs from the Mid-Atlantic Ridge

¹ Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA, and Department of Earth and Environmental Sciences of Columbia University, New York, New York 10027, USA
² Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, New York 10964, USA, and School of Earth and Environmental Sciences, Queens College, and the Graduate Center of the City University of New York, New York, New York 11367, USA
³ Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, New York 10964, USA, and Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna 40129, Italy, and Dipartimento di Scienze della Terra, Università "La Sapienza," Rome 00187, Italy
⁴ Istituto di Scienze Marine, Consiglio Nazionale delle Ricerche, Bologna 40129, Italy, and Laboratoire P. Sue, Commissariat à l'énergie atomique (CEA), Départment de Recherche sur l'Etat Condensé, les Atomes et les Molécules (DRECAM), Gif sur Yvette 91191, France

Given that oceanic basalts form by partial melting of mantle peridotites that rise below mid-ocean ridges, peridotite and basalt should have identical Sr and Nd isotope ratios. We tested this concept on parallel sets of peridotites and basalts sampled from an exposed section of lithosphere representing 20 m.y. of accretion at the Mid-Atlantic Ridge. The ¹⁴³Nd/¹⁴⁴Nd ratios of the basaltic glasses stay constant, whereas those of the peridotitic clinopyroxenes extend both higher and lower than the basalt ratios, suggesting that the constant isotopic composition of the basalts results from mixing of melts released by peridotites from a broad region of the subridge mantle. The degree of melting undergone by the peridotites correlates inversely with their ¹⁴³Nd/¹⁴⁴Nd ratios. Small-scale isotopic heterogeneity of the peridotites may result from variable premelting metasomatism in the mantle, mostly during periodic, dynamic, subridge upwelling, possibly superimposed upon time-integrated radioactive decay of ancient heterogeneities.

Key Words: oceanic mantle • abyssal peridotites • mid-ocean-ridge basalts • isotopes • Vema Fracture Zone

This article has been cited by other articles:

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