Chapter 20 - The Oldest Well-Preserved Felsic Volcanic Rocks on Earth: Geochemical Clues to the Early Evolution of the Pilbara Supergroup and Implications for the Growth of a Paleoarchean Protocontinent

Abstract

This chapter examines the geochemical clues to the early evolution of the Pilbara Supergroup and implications for the growth of a Paleoarchean protocontinent. Geochemical studies of mafic rocks can potentially provide direct clues on mantle evolution, mantle conditions, and juvenile crust formation, whereas geochemical studies of felsic rocks can provide clues as to how the crust differentiated. The Warrawoona Group, in the Pilbara Craton of northwestern Australia, is a basalt-dominated volcano-sedimentary sequence formed through essentially continuous volcanism from 3.515 to 3.426Ga. The Pilbara Craton is divided into the 3.53–3.17Ga East Pilbara Terrane, the 3.27–3.11Ga West Pilbara Superterrane, and ∼3.2Ga Kurrana Terrane, distinguished by unique lithostratigraphy, structural map patterns, geochemistry, and tectonic histories. The early volcano-sedimentary history of greenstones within the East Pilbara Terrane is described by the Pilbara Supergroup, which is composed of four demonstrably autochthonous groups, of which the 3.53–3.426Ga Warrawoona Group is the stratigraphically lowest group. The petrogenesis of felsic volcanic rocks is also elaborated in the chapter.