Nd isotopic evolution of Archean tonalitic–granodioritic rocks of the Napier Complex, East Antarctica

Abstract

We examined Sm–Nd isotopes of samples from the Archean tonalitic–granodioritic orthogneiss mass of Mt. Riiser-Larsen in the Napier Complex, East Antarctica. Analytical data show εNd ≈ 0 of ca. 3.27 and ca. 3.07 Ga at the time of protolith formation, as determined by SHRIMP zircon analyses. This differs from previously reported Sm–Nd whole-rock isotope data from the oldest tonalitic orthogneisses of Mt. Sones in the Napier Complex, which show εNd = 0 at 3.87 to 3.80 Ga (T_CHUR), which is coincident with ca. 3.8 Ga from SHRIMP zircon analyses. These data suggest that the voluminous and homogeneous tonalitic–granodioritic rocks retained the εNd ≈ 0 signal throughout the protolith–metamorphic process and that the source materials of the rocks showed εNd ≈ 0 at ca. 3.80, 3.27 and 3.07 Ga. Tonalitic–granodioritic orthogneisses from the Napier Complex may contain genetic information regarding Nd isotopic evolution from the Paleoarchean to Mesoarchean.