Chapter 2 Archaean Granite–Greenstone Terranes of Western Australia

Abstract

Publisher Summary The principal concentration of rocks of Archaean age within Australia is found in the Western Australian Shield (or Western Shield), where such rocks occupy an area in excess of 700,000 km 2 . Within this shield two Archaean cratonic nuclei are recognized—the Yilgarn and Pilbara Blocks. The Yilgarn Block covers a rectangular area of about 650,000 km 2 within the coordinates 25°–35° S and 115°–124° E, roughly the southwestern part of the Australian continent. Most of this region is characterized by low rainfall (200–250 mm annually), poorly developed ephemeral drainages, sinuous systems of elongate, salt-encrusted dry “lakes,” and large areas of sand plain and laterite. The latter is a remnant of a Jurassic or Tertiary erosional surface—the Old Plateau. Geologically, the Yilgarn Block is bounded on the west by the Darling Fault which separates it from the Perth Basin—a graben-like structure filled with some 15 km of Palaeozoic to Tertiary sediments. A gross subdivision of the Yilgarn Block based primarily on tectonic style and lithological association recognizes three major provinces: Southwestern, Murchison, and Eastern Goldfields. Boundaries between the provinces do not, in some instances, appear to represent chronological or tectonic discontinuities. Greenstone belts of the Murchison and Eastern Goldfields Provinces are essentially similar in lithology and age, and subdivision into these two provinces is based on a change in dominant structural trend from N to NNW in the Eastern Goldfields Province to NE in the Murchison Province, and the arcuate discontinuous nature of greenstone belts in the Murchison Province as opposed to the more continuous, linear belts of the Eastern Goldfields Province.