Helium isotopic evidence for recent subcrustal volcanism in eastern Australia

Abstract

A component with ∼6% mantle helium (³He/ 4 He=5‐9×10 −7 ) has been identified in borewaters from the Great Artesian Basin, Australia that is isotopically distinct from previously identified in situ production (³He/ 4 He = 1.6×10 −8 ) and a crustal degassing flux (³He/ 4 He = 6.75×10 −8 ). The occurrence of this component is limited to three identified localities (∼20.5°S 144°E; ∼25.5°S 146°E; ∼27°S 144.5°E) all within the region of high reduced heat flow in eastern Australia. No evidence for a mantle component was apparent in central Australia. This component is most probably the result of continued intrusive volcanism (<1 m.y.) associated with the Cainozoic lava flow fields in the region. Although the volcanic activity has no present‐day surface manifestation, its mantle helium was probably carried to the near‐surface by large‐scale fluid transport processes in the crust.