Evidence for a missing late veneer from 182W and 142Nd systematics in the Archean São Francisco Craton

Abstract

The oldest crustal remnants on Earth are represented by greenstone belts and tonalite-trondhjemite-granodiorite (TTG) associations that form most of Archean blocks worldwide. Although several studies reported combined long-lived radiogenic isotope and trace element data of Archean rocks, the chemical evolution of the early Earth is still a matter of debate, often due to younger metamorphic disturbance that overprints primary patterns. To provide further insights, combined data for short-lived (¹⁴⁶Sm–¹⁴²Nd and ¹⁸²Hf–¹⁸²W) and long-lived (¹⁴⁷Sm–¹⁴³Nd and ¹⁷⁶Lu–¹⁷⁶Hf) isotope systems were acquired from a set of Eo- to Paleoarchean amphibolites, TTG gneisses, granites and a gabbroic rock in the northern segment of the São Francisco Craton (SFC) in Brazil, a largely unexplored area regarding short-lived radiogenic isotope datasets. Our samples cover an age range from ca. 3.65 to 3.30 Ga comprising both mafic and felsic rocks. Excesses of µ¹⁸²W in the samples indicate the presence of a long-lasting Hadean component in the source of Archean rocks from the SFC, which was preserved for at least ca. 1.0 Ga. Conversely, all samples depict µ¹⁴²Nd similar to modern upper mantle values. The most plausible interpretation of the µ¹⁸²W and µ¹⁴²Nd data is a (partially) missing Hadean late veneer component similar to that previously found, for example, at the Pilbara Craton, in NW Australia.