Résumé
Genesis and tectonic setting of the Paleoarchean chert-barite-sulphide deposits from the North Pole Dome (Eastern Pilbara craton) are still controversial, including models of deposition within a shallow marine, evaporative basin or volcanic caldera with an active hydrothermal system. Here we report new (SM)-S-147-Nd-143 data from low-grade metamorphosed volcanic and sedimentary rocks and related hydrothermal precipitates from the North Pole Dome. An Sm-Nd isochron age of 3.48 +/- 0.09 Ga is in good agreement with a U-Pb zircon age from the Dresser Formation, which indicates preservation of the Sm-Nd isotope signature since the Paleoarchean. Hence, our data clearly show that the hydrothermal event was contemporaneous with precipitation/deposition of the chert-barite deposits. The initial epsilon(Nd) value of -3.3 +/- 1.0 is well below the epsilon(Nd) range of depleted values for Archean rocks and suggests the involvement of much older crustal protolith in the formation of this dominantly mafic crustal section, with Nd model ages of similar to 4.0-4.4 Ga. Such old fragments of continental crust have not previously been reported from the Pilbara Craton.