Sm‐Nd model ages across the margins of the Archaean Yilgarn Block, Western Australia; northwest transect into the proterozoic gascoyne province

Abstract

A transect of Sm‐Nd model ages across the NW margin of the Archaean Yilgarn Block into the Proterozoic Gascoyne Province was undertaken to investigate the ages and possible origins of the gneiss terrains in this portion of the Proterozoic Capricorn Orogen. The nine sample localities show a decline in model ages from c. 3.5 Ga in the Archaean terrain to c. 2.0 Ga in the heart of the Gascoyne Province. These ages may be interpreted as times of generation of new sialic crustal material, and lend support to a model of crustal accretion against an older stabilised craton. The ages measured are in conflict with the geological evidence that the gneisses within the Proterozoic orogen are reworked Archaean basement. No unique interpretation is possible for the seemingly simple model age progression. It could indicate either the existence of an extended sialic crust‐forming event at c. 2.0–2.4 Ga, or a progressively diminishing degree of mixing of Archaean rocks into Proterozoic crust (<2.0 Ga) across the orogen.