Prof Nick Rawlinson, Cambridge University
Cenozoic intra-plate volcanism is widespread throughout much of eastern Australia, and manifests as both age-progressive volcanic tracks and non-age progressive lava-fields. Various mechanisms have been invoked to explain the origin and distribution of the volcanism, but a broad consensus remains elusive. We use results from seismic tomography to demonstrate a clear link between lithospheric thickness and the occurrence, composition and volume of volcanic outcrop. Furthermore, we find that non age-progressive lava-fields overlie significant cavities in the base of the lithosphere. Based on numerical simulations of mantle flow, we show that these cavities generate vigorous mantle upwellings, which promote decompression melting. However, due to the intermittent nature of the lava-field volcanics over the last 50 Ma, it is likely that transient mechanisms must also operate to induce or enhance melting. In the case of the Newer Volcanics Province, the passage of a nearby plume appears to be a likely candidate. Our results demonstrate why detailed 3-D variations in lithospheric thickness, plate motion and transient sources of mantle heterogeneity need to be considered when studying the origin of non age-progressive volcanism in continental interiors.
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