Stable W isotope evidence for redistribution of homogeneous 182W anomalies in SW Greenland

We present the first high precision stable tungsten isotope data for a comprehensive Eoarchean rock suite from the Isua region of SW Greenland with the aim to reconstruct the sources and processes that controlled the inventory of W in Eoarchean time and to place constraints on the origin of W-182 anomalies in Eoarchean rocks. When compared to modern igneous rocks, the observed range of delta W-186/184 in the Eoarchean rocks is substantially larger, ranging from -0.072 to +0.249 parts per thousand. But unlike in modem igneous rocks, we find no co-variation of delta W-186/184 with other geochemical parameters. Multiple stage mobilisation and re-enrichment of W by metasomatic fluids entirely obscured pristine geochemical signals. However, our results illustrate the potential of applying stable W isotopes as geochemical tracer for alteration effects on primary W-182 signatures. Despite secondary alteration and the large variation in delta W-186/184 the excesses in W-182 that were previously observed in the same rock samples appear to be unaffected by alteration arguing that the excesses were most likely initially uniform in the whole Eoarchean assemblage of SW Greenland.