Age and style of intraplate basaltic volcanism at Stanley, northwest Tasmania, Australia

We present the first ⁴⁰Ar/³⁹Ar ages for the intraplate basaltic volcanic rocks at Stanley that together with new detailed field observations reveal that the entire sequence was deposited relatively rapidly in shallow submarine to emergent environments. The Stanley Beds at the base are a sequence of basaltic volcaniclastic rocks that unconformably overlie the Neoproterozoic Togari Group. Cross-cutting the Stanley Beds are basanite dykes (<i>ca</i> 11 Ma) and the Circular Head teschenite (11.06 ± 0.15 Ma). The Green Hills Volcanics (10.38 ± 0.03 Ma) comprise basanite pillow lavas, megapillows, lava lobes and sheet and massive lavas that overlie the Stanley Beds. The Green Hills Volcanics, the basanite dykes and the Circular Head teschenite were emplaced before the Stanley Beds were lithified. The new data support the interpretation that the Circular Head teschenite, known locally as ‘The Nut’, is a ponded lava, formed inside a coastal tuff cone that has since eroded, as suggested by previous research. The new ⁴⁰Ar/³⁹Ar age for the Green Hills Volcanics (10.38 ± 0.03 Ma) is about 2 Myr older than previously published K/Ar age for the youngest Cenozoic volcanism in Tasmania (8.5 ± 0.1 Ma). First ⁴⁰Ar/³⁹Ar geochronology is given for the Stanley basaltic intraplate volcanic succession. The Stanley volcanic succession was emplaced relatively rapidly in shallow submarine and emergent environments. The youngest age of Cenozoic basaltic volcanism in Tasmania has been revised to 10.38 ± 0.03 Ma.