The mechanisms underpinning Cenozoic intraplate volcanism in eastern Australia: Insights from seismic tomography and geodynamic modeling

Abstract

Cenozoic intraplate 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 likely promote decompression melting. However, due to the intermittent nature of the lava field volcanics over the last 50 Ma, it is probable that transient mechanisms 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.

Lateral Variations in Lithospheric Mantle Structure Control the Location of Intracontinental Seismicity in Australia

“…These occur in a seemingly discontinuous band spanning the continent from the northern coast to the Gawler craton in the south (Figure a). Another region of particularly low attenuation is found in east‐central Australia, within the Phanerozoic part of the continent, and is well correlated with high velocity anomalies in the uppermost mantle (Rawlinson et al, ). A band of high attenuation runs down the southeastern coast, becoming increasingly attenuating toward the south and extending into Tasmania.…”

The Australian Continent: A Geophysical Synthesis

“…Their concept is that the northward motion of Australia at about 7 cm/yr gives rise to a trailing flow from the southern edge of the thick cratonic lithosphere that comes to the surface further south, creating the volcanic province. This view is challenged by Rawlinson et al (2017), who suggest the influence of plume influx for the Newer Volcanic Province. However, they reiterate the importance of cavities in the lithosphere to generate vigorous mantle upwellings, which can promote decompression melting and eruptive products.…”

Structure of the crust and upper mantle beneath Bass Strait, southeast Australia, from teleseismic body wave tomography

“…Their study suggests that the plume source of the hotspot track passed by the eastern edge of the NVP shortly before volcanism initiated nearly 5 Ma. In another study, Rawlinson et al (2017) suggest that an interaction between this passing plume and preexisting Edge Driven Convection (EDC) (King and Anderson, 1998) and Shear Driven Upwelling (SDU) (King and Ritsema, 2000) (caused by a huge central cavity in the lithosphere, which corresponds to the central low velocity zone north of the NVP in our model) was responsible for the NVP volcanism. A more recent study by Wei et al (2018) using 3-D S n traveltime tomography finds strong heterogeneities in S wave speed in the upper mantle across the entire Australian continent.…”

“…However, as noted previously, this does not necessarily rule out the existence of Precambrian continental material. Apart from the influence of recent plume activity, two possible explanations include delamination of the mantle lithosphere beneath the fragment triggered by edge driven convection and shear driven upwelling (Rawlinson et al, 2017), or so-called rift-induced delamination (Wallner and Schmeling, 2010). Interestingly, mantle velocities below 200 km depth beneath Bass Strait (Fig.…”