Late Miocene (U+Th)-4He ages of ferruginous nodules from lateritic duricrust, Darling Range, Western Australia

Abstract

(U+Th)-4He dates are presented for hematite/maghemite and hematite separates from pisolitic nodules from four rock specimens of lateritic duricrust sampled in an area of about 1 km2 in the Darling Range about 50 km northeast of Perth, where the duricrust forms a continuous cover over rocks of the Archaean Yilgarn Craton. Textures and compositions of the separates were checked by X-ray diffraction and scanning electron microscopy. Hematite/maghemite separates from three of the specimens yielded ages of about 10 Ma, identical within error (weighted mean, 9.9 0.9 Ma, 2s), whereas the hematite separate from the fourth specimen gave a U-He date of 7.5 Ma, all within the Late Miocene. While questions remain as to whether initial and boundary conditions of dating are adequately fulfilled, the iron oxide 4He dates are in good agreement with estimates by palaeomagnetic dating and other methods for the age of laterite formation in the Darling Range and other parts of south Western Australia. This study demonstrates the potential of (U+Th)-4He dating as a serviceable, directly applicable tool for dating lateritic duricrust.