Sm-Nd model ages across the margins of the Archaean Yilgarn Block, Western Australia - II; southwest transect into the Proterozoic Albany-Fraser Province

This paper continues a survey of Sm-Nd age relationships at the margins of the Yilgarn Block, Australia's largest Archaean craton. Model ages have been determined along an irregular transect extending approximately 120 km from the extreme SW of the Western Gneiss Terrain of the Yilgarn Block through the western extremity of the Albany-Fraser Province, a major Proterozoic mobile belt. The ages demonstrate the significance of the Manjimup and Pemberton Lineaments as major crustal discontinuities. The sequence of ages across the lineaments strongly supports accretionary models of Precambrian crustal evolution, although some aspects of the age sequence can also be interpreted as mixing trends. Within the Western Gneiss Terrain, the Manjimup Lineament marks a change from older (c. 3.1 Ga) to younger (c. 2.7 Ga) Archaean gneisses. Further south the Pemberton Lineament, marking the northern tectonic boundary of the Albany-Fraser Province, defines a change from Archaean (c. 2.7 Ga) to Proterozoic (c. 2.1 Ga) mantle differentiation ages. The one exception within the mobile belt is a sample of granulite from Windy Harbour, the age of which (3.1 Ga) implies that the Proterozoic crustal material of the Albany-Fraser Province is sharply terminated to the west as well as to the north. The ages determined within the Albany-Fraser Province, together with those previously reported for the Gascoyne Province, point to the existence of a major crust-forming event surrounding a considerable portion of the Yilgarn Block about 2 Ga ago.