ARCHEAN EVOLUTION OF THE WONGAN HILLS GREENSTONE-BELT, YILGARN CRATON, WESTERN AUSTRALIA

Ion microprobe and conventional U-Pb analyses on single zircons from a felsic porphyry from the Wongan Hills Greenstone Belt in the Western Gneiss Terrain of Western Australia define an age of 3010 ± 7 Ma. This is a minimum age for volcanism in the greenstone belt. A sample of gneiss from near the belt contains two populations of zircons with ages of 2997 ± 47 Ma and 2800 ± 9 Ma. The ca 3.0 Ga zircons are interpreted as dating the formation of the granitic parent of the gneiss, and the ca 2.8 Ga zircons are interpreted as dating gneiss formation. This latter event may be an early manifestation of the major 2.65-2.75 Ga granite-greenstone episode which affected the entire Yilgarn Craton and is expressed at Wongan Hills by the emplacement of post-tectonic porphyritic granite dated at 2651 ± 4 Ma, and greenschist facies retrogressive metamorphism, dated at 2646 ± 11 Ma by U-Pb analyses of cogenetic sphene. The present results confirm the significance of ca 3.0 Ga volcanism in the north and western Yilgarn Craton and suggest that this event was coeval with granitoid emplacement. No zircons older than 3.0 Ga, which would support models for an older crustal origin for these rocks, were found in the present samples. © Taylor & Francis Ltd.