Journal article

Mantle-like Hf-Nd isotope signatures in-3.5 Ga greenstones: No evidence for Hadean crust beneath the East Pilbara Craton

Jan F Tympel, Janet M Hergt, Roland Maas, Jon D Woodhead, Alan Greig, Robert Bolhar, Roger Powell



The geological setting of extensive ~3.5 Ga greenstone sequences in the Pilbara Craton (Australia) has been controversial for many years. Models range from a purely oceanic origin to emplacement over a pre-existing, possibly Hadean, sialic basement. Here we present new isotopic (Nd[sbnd]Hf) and trace element data for a geographically extensive suite of komatiitic-tholeiitic metavolcanic rocks which comprise much of the Pilbara Supergroup. Most of the samples have flat to mildly enriched normalised trace element patterns, often associated with a slight Nb[sbnd]Ta depletion. A small subset of samples, represented throughout the stratigraphy, show strong LREE enrichment and pronounced HFSE anom..

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Funding Acknowledgements

We express our gratitude to the late Bruce Chappell for provision of XRF data. Robert Bolhar and Jan Tympel were the recipients of University of Melbourne Graduate research scholarships. The Geological Survey of Western Australia (GSWA) provided permission to sample and use drillcore from the Pilbara Drilling Project; David Mole (formerly CSIRO Kensington, WA, now Laurentian University, Sudbury, Canada) is thanked for selecting the PDP samples analyzed here at the GSWA drillcore store in Perth. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.