Evolution of a ~2.7 Ga large igneous province: a volcanological, geochemical and geochronological study of the Agnew Greenstone Belt

Australian Institute of Geoscientists > Events > Agnew greenstone, exploration, gold, komatiites, nickel, VMS deposits > Evolution of a ~2.7 Ga large igneous province: a volcanological, geochemical and geochronological study of the Agnew Greenstone Belt

Evolution of a ~2.7 Ga large igneous province: a volcanological, geochemical and geochronological study of the Agnew Greenstone Belt


Speaker: Patrick Hayman, Newly appointed Lecturer in Economic Geology, QUT

Presented by the Geological Society of Australia Queensland Division.  The talk will be preceded by the GSA Queensland Division Annual General Meeting.

The thick package of ~2.7 Ga mafic and ultramafic lavas and intrusions that are preserved among the Neoarchean stratigraphy of Western Australia provide valuable insight into the beginnings of the most prodigious episode of growth and preservation of juvenile continental crust in Earth’s history. Unfortunately, limited exposures have led to uncertainty about their ages, characteristics and stratigraphic relationships, which has, in-turn led to uncertainty about regional correlations between the mafic and ultramafic successions and thus interpretations of their tectonic setting and magmatic evolution. However, a recent stratigraphic drilling program of the Neoarchean stratigraphy of the Agnew Greenstone Belt in Western Australia has provided large and continuous exposures through a very thick (about 7 km) sequence of these mafic and ultramafic units. Here, we present the results of a detailed volcanological, lithogeochemical and chronological evaluation of the ultramafic–mafic stratigraphy from the Agnew Greenstone Belt that has important implications for interpreting the architecture and evolution of these rocks. The results of our work show that the Agnew Greenstone Belt records ~30 Ma of episodic ultramafic–mafic magmatism that consists of two cycles, each of which begins with komatiite and is overlain by units that become increasingly more evolved and contaminated. Our data together provide an improved basis for regional correlations. Cycle I magmatism began at ~2720 Ma and ended ~2705 Ma, whereas cycle II began ~2705 Ma and ended at 2690.7±1.2 Ma. This research has implications for the evolution of Archean greenstone belts, and the new stratigraphic correlation presented for the Kalgoorlie Terrane has important implications for exploration, especially for stratigraphically hosted ultramafic Ni and VMS deposits.