Evidence for isotopic equilibration of Sm sbnd Nd whole-rock systems in early Archaean crust of Enderby Land, Antarctica

Sm sbnd Nd isotopic data indicate that differential REE mobility occurred on a whole-rock scale during transitional amphibolite- to granulite-facies regional metamorphism (∼ 700°C, 7 kbar) in early Archaean rocks (∼ 3930 Ma) of the Napier Complex of Enderby Land, Antarctica. The degree of mobility is independent of metamorphic grade but correlates directly with development of tectonic fabric. Whole-rock samples with D ₃-M ₃ internal fabrics lie along an array corresponding to an age of 2410 ± 100Ma, whereas samples preserving only earlier fabrics preserve an older, albeit imprecisely defined isochron age. In contrast to a widely held belief, such changes did not require the presence of a large hydrous fluid flux. If the mechanism responsible for Sm sbnd Nd resetting at this locality (where T _CHUR ages range from 1990 Ma to 6090 Ma) is more widespread than is currently recognised, isolated Sm sbnd Nd model ages, particularly in complex terrains should be treated with caution.