Potassium‐argon dates on some Cainozoic volcanic rocks from Northeastern New South Wales

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Abstract
There are few definitive data on the ages of those volcanic rocks in New South Wales that are generally regarded as Cainozoic in age. Potassium‐argon dates measured on selected samples show that widespread and prolonged volcanic activity in northeastern New South Wales occurred in the Miocene. During this period the Warrumbungle, Nandewar and Tweed volcanoes were built and the lavas in the Inverell, Armidale, Ebor and Lansdowne areas were erupted. Oligocene lavas are found near Glen Innes. The Square Top intrusion near Nundle, and the volcanic sequence at Barrington Tops are Eocene or Palaeocene. In this whole region the volcanic rocks are mainly alkaline basalts and their differentiates, displaying varying degrees of undersaturation. However, lavas with tholeiitic affinities are also present, as indicated by new chemical data on a number of the dated samples.