Granite–greenstone crust formation on the Archaean Earth: a consequence of two superimposed processes

New U–Pb zircon age data reveal that volcanism in the greenstones of the eastern part of the Yilgarn Craton of Western Australia was coeval with that in the Abitibi Subprovince of the Superior Craton of Canada, and that komatiites in the Eastern Goldfields and Abitibi terranes were erupted synchronously at 2705 Ma. However, major granitoid intrusion and compression episodes in the eastern Yilgarn Craton post-date those in the southern Superior Craton by at least 15 Ma. Intrusion of late-tectonic syenites, movement on major shear zones, metamorphism and deposition of post-tectonic clastic sequences also occurred 25–40 Ma later in the eastern Yilgarn Craton than in the southern Superior Craton, indicating that these cratons occupied different tectonic settings between 2720 and 2620 Ma. These comparisons, and the synchronous eruption of ultramafic magmas in the southern Superior, Pilbara and Kaapvaal cratons at 2715 Ma, provide evidence of global-scale magmatic eruption events during the Late Archaean. These considerations indicate that two superimposed processes — global-scale catastrophic convective overturn of the Earthʹs mantle, and plate tectonic processes — were in operation during formation of granite–greenstone crust in the Late Archaean.