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Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower 142 Nd/ 144 Nd ratios than the terrestrial standard (ϵ 142 Nd = –0. 07 to –0. 15). Within a mafic amphibolite unit, 142 Nd/ 144 Nd ratios correlate positively with Sm/Nd ratios and produce a 146 Sm- 142 Nd isochron with an age of, 10pt, legalpaperarticle amssymb amsfonts amsmath empty document \ (4280-₈₁^+53\) document million years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth.
OʼNeil et al. (Fri,) studied this question.