Composition and age constraints on a Hadean enriched mantle source revealed by the Paleoarchean São Tomé layered intrusion, NE Brazil

• Hadean enriched mantle source with µ 142 Nd as low as ∼ −20. • Differentiation happened at ∼4.44 ga with a 147 Sm/ 144 Nd of ∼0.18. • The enriched reservoir was likely a pyroxenitic mantle. Evidence for Hadean depleted mantle reservoir(s) is well-established by mantle-derived rocks from multiple Archean complexes showing excesses in 142 Nd compared to the modern mantle. Yet, the existence of an early enriched mantle source, which should have concomitantly formed during these Hadean silicate differentiation event(s), has only been recently confirmed by well-resolved 142 Nd deficits measured in Paleoarchean mafic amphibolites from the São José do Campestre massif of the Borborema Province, NE Brazil. To investigate the nature and extent of this early-formed enriched reservoir, a series of samples from the Seridó belt, NE Brazil, have been investigated for their geochemical and coupled 147,146 Sm- 143,142 Nd isotopic compositions, focusing on the Paleoarchean São Tomé layered intrusion. The São Tomé intrusion is composed of layers of metamorphosed mafic and ultramafic rocks with whole-rock trace element compositions and high olivine crystal Ni contents consistent with an incompatible trace element enriched pyroxenitic mantle source. Most analyzed samples from the Seridó belt yielded negative µ 142 Nd, as low as ∼ -20 (representing the lowest 142 Nd/ 144 Nd ratio ever measured in terrestrial rocks), with an average µ 142 Nd for the São Tomé intrusion of -9.6 ± 1.4. The São Tomé samples interpreted as the least isotopically disturbed yielded an 147 Sm- 143 Nd isochron age of 3551 ± 368 Ma, consistent with previous zircon U-Pb ages, with an initial ε 143 Nd = -1.7 ± 1.2. Coupling the long-lived 147 Sm- 143 Nd and the short-lived 146 Sm- 142 Nd systems for the São Tomé rocks suggests a Hadean enriched mantle source formed at ∼4.44 Ga with a 147 Sm/ 144 Nd of ∼0.18, which may be complementary to the early depleted mantle recorded by Eoarchean rocks from the North Atlantic Craton, possibly formed during magma ocean crystallization. These results also imply that the record of this Hadean enriched mantle source is not restricted to the São José do Campestre massif but extends to a larger portion of the Borborema Province.