Rb/Sr evidence for the nature of the mantle, thermal events and volcanic activity of the Southeastern Australian continental margin

Rb/Sr isotopic data are presented for three different mantle-derived rock types from a single quarry in the Kiama area in southeastern Australia. These rocks comprise a latite (∼249 Ma), a basanitic dyke (∼191 Ma) and mantle-derived xenoliths entrained in the basanitic dyke. Interpretation of the Rb/Sr data with other geochemical results shows that significant crustal contamination of either the latite or the basanite is unlikely. It is suggested that metasomatic mantle events may closely coincide with the production of basaltic magma. Basaltic activity in this area in the late Permian, early Jurassic and Tertiary would imply that a high heat flow may have persisted in southeastern Australia over this time span. ⁸⁷Sr/⁸⁶Sr values of the rocks studied are within the range of intraplate basalts worldwide and support the concept of a REE-enriched upper mantle beneath eastern Australia.