The Palaeoproterozoic Earaheedy Basin in Western Australia lies at the southern end of the Capricorn Orogen. The Earaheedy Group, the sole lithostratigraphic unit comprising the basin fill, is a 5 km thick succession of shallow-marine silicielastic and carbonate sedimentary rocks. It consists from oldest to youngest of the Yelma, Frere, Windidda, Chiall, Wongawol, Kulele and Mulgarra formations.
U-Pb age data for 312 detrital zircon grains from seven siliciclastic samples from the Yelma Formation, the Wandiwarra and Princess Ranges members of the Chiall Formation and the Mulgarra Sandstone reveal the presence of both Archaean (3.4-2.5 Ga) and Palaeoproterozoic (2.4-1.8 Ga) detritus. Zircon grains of Archaean age are dominantly in the range 2.7-2.6 Ga, similar to those of the Yilgarn Craton, which unconformably underlies the southern margin of the Earaheedy Basin. Age peaks in the range 2.3-2.2, 2.0 and 1.8 Ga, characterise the Palaeoproterozoic detritus. The two younger ages overlap with those of the adjoining Gascoyne Complex of the Capricorn Orogen to the west of the basin. Source components with ages in the range 2.3-2.2 Ga are extremely rare in Western Australia. Undeformed granite in the Mullingarra Complex within the Pinjarra Orogen to the west of the Darling Fault yielded an age of around 2.2 Ga. In addition, rare rims on detrital zircon grains from gneisses within basement of the Glenburgh Terrane of the Gascoyne Complex as well as a few detrital grains in metamorphosed quartz arenites of the terrane have yielded ages of around 2.4-2.2 Ga, suggesting early Palaeoproterozoic activity in this region.
Detrital grains as young as 1800 Ma, combined with deposition of the unconformably underlying strata in the Yerrida Basin at c. 1840 Ma and deformation of the Earaheedy Group at around 1750 Ma, provide a relatively tight constraint on the depositional age of the Earaheedy Group. Crown Copyright (C) 2003 Published by Elsevier B.V. All rights reserved.
- PALAEOPROTEROZOIC CAPRICORN OROGEN
- DETRITAL ZIRCONS