Core Formation: Catastrophic or continuous? Sr and Pb isotope geochemistry constraints

The negative trend between 87Sr/86Sr and 206Pb/204Pb ratios shown by most oceanic island basalts and the Rb-Sr and Pb mantle isochrons are ascribed to the end of sulfide segregation, about 2 b.y. ago, in the deep mantle, because this process produces an opposite evolution of µ (238U/204Pb) and Rb/Sr ratios of the residual rocks. These sulfides probably contributed to the core growth. Other isotopic arguments lead to the conclusion of an early and quick core formation; it is, however, proposed here that the core growth continued, but at much slower rate, for ca. 3 b.y. after the initial separation.

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