Chapter 21 - Geochemistry of Paleoarchean Granites of the East Pilbara Terrane, Pilbara Craton, Western Australia: Implications for Early Archean Crustal Growth

Abstract

This chapter presents the geochemistry of Paleoarchean granites of the East Pilbara terrane (EPT), Pilbara craton, Western Australia, and the implications for early Archean crustal growth. The Pilbara Craton is divided into the 3.53–3.07Ga EPT, which includes the Pilbara Supergroup, the 3.27–3.11Ga West Pilbara Superterrane, and the 3.2Ga Kurrana Terrane. Each of these is distinguished by unique lithostratigraphy, structural map patterns, geochemistry, and tectonic histories, and they are separated by late tectonic, dominantly clastic sedimentary rocks of the De Grey Supergroup deposited in the Mallina and Mosquito Creek basins. The exposure of preserved granite totals an area of ∼24,000km2. Most of the known periods of granite intrusion in the EPT either broadly correspond to the periods of greenstone development or postdate greenstone formation. The geological and Sm–Nd data further indicate that post-3.2Ga crustal growth extended to the western part of the EPT, and the post-3.2Ga granites in that region are, accordingly, petrogenetically grouped with those found in the Mallina Basin. It is found that the 3.32–3.24Ga granites have an expanded silica range but include much more silica-rich members than the older granites.