K:Ar ages and geochemistry of the Sabah Cenozoic volcanic rocks

K-Ar dates for volcanic rocks of the southern Dent Peninsula confirm a Middle Miocene age, and K-Ar dates on the Semporna Peninsula also indicate a similar Middle Miocene age, older than previously held. The Pliocene rift-related subaerial basalts of the Mostyn Estate of the Kunak area are of the low K tholeiite series and also display MORB characteristics, indicating a rift-related magma genesis resulting in partial melting of an identical source to the Mesozoic ophiolite of the Segama area. The Miocene volcanic rocks of the Semporna and southern Dent Peninsulas, by contrast, have calc alkaline affinities and their trace element geochemistry indicates a subduction related genesis with typical enrichment in the light rare earth elements.