Rare evidence for the existence of a Hadean enriched mantle reservoir

Abstract

Short lived isotopic systems can help unravel the complex early differentiation history of the Earth's mantle. Excesses in neodymium-142 ( 142 Nd) measured in several occurrences of Archean mantle-derived rocks, compared to the modern upper mantle, imply the formation of an early depleted mantle in the Hadean. However, the existence of a complementary enriched reservoir, which should have also stemmed from such early differentiation event, remains equivocal. New data on 3.4 billion year old amphibolites from the São José do Campestre Massif, NE Brazil, show well resolved 142 Nd deficits compared to the modern upper mantle, down to −14.1 ppm. This provides the first clear evidence for an early enriched mantle source, which may represent the missing concomitant reservoir complementary to Earth's early depleted mantle.

Neoarchean marine chemical sediments as archives of Hadean silicate differentiation

“…The parent isotope, 146 Sm, was only present during the first ∼500 Ma of the solar system, and as such records silicate differentiation during the Hadean. To date, a wide number of (meta)igneous rock samples have been analysed which record μ 142 Nd anomalies (where Hadean depleted mantle and negative if derived from a trace element enriched reservoir (Caro et al, 2006(Caro et al, , 2017Bennett et al, 2007;O'Neil et al, 2012O'Neil et al, , 2016Rizo et al, 2012Rizo et al, , 2013Debaille et al, 2013;Morino et al, 2017;Schneider et al, 2018;Garcia et al, 2023).…”