Potassium?argon ages of some northern Queensland basalts and an interpretation of late Cainozoic history

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Abstract
The palaeotopography of an east‐west valley on the eastern flank of the Great Divide is reconstructed from a consideration of early Tertiary and Palaeozoic rocks. This valley confined the olivine basalt lavas of the Nulla Province—the lavas originating from vents near the head of the valley. The distribution of vents shows that eruption took place along north‐east lineaments in the cratonic basement. The rates of entrenchment of streams in the province indicate that the area of the Great Divide where the basalts originated was actively rising during the eruptions and it is inferred that this uplift took place along the lineaments. Potassium‐argon ages from the eastern half of the province show that vulcanism was confined to brief episodes 4.0–4.5 m.y. ago, at 2.3 m.y., 1.3 m.y. and 1.1 m.y. ago, and, in more recent time, probably no longer than 100,000 years ago. These ages assist in providing a time scale for certain geological or geomorphic events within the province which, in turn, leads to a reconstruction of the late Cainozoic history of the area.
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