Crust and upper mantle structure beneath southeast Australia from ambient noise and teleseismic tomography

- Seismic tomography was used to image the lithosphere in southeast Australia.
- For the first time, a joint crust and upper mantle model was developed.
- Archean/Palaeoproterozoic blocks have characteristic velocity signatures.
- The Delamerian/Lachlan boundary is marked by a strong velocity contrast.
- Cenozoic intraplate basaltic volcanism only occurs above thin lithosphere.

In the last decade, the lithospheric structure beneath southeast Australia has been intensively studied using passive seismic data from WOMBAT, the largest transportable seismic array in the southern hemisphere. The two primary imaging methods that have been applied are ambient noise tomography for the crust and teleseismic tomography for the upper mantle. Despite these recent studies, no attempt has yet been made to provide an integrated view of the crust-mantle system. Here, we perform teleseismic tomography using WOMBAT data that includes a detailed crustal model from ambient noise tomography in the starting model. A Moho surface from the Australian seismological reference Earth model (AuSREM) is also included. This has the dual benefit of accounting for the unresolved crustal component of the teleseismic arrival time residuals, and producing a model that reveals a high level of detail in both the crust and upper mantle. Our new integrated P-wave model contains a number of noteworthy features, including (i) low velocity anomalies in the lower crust and high velocity anomalies in the lithospheric mantle beneath the Gawler Craton and Curnamona Province, which are of Paleoproterozoic-Archean origin; (ii) a marked velocity transition in the crust and lithospheric mantle near the Moyston Fault, which we interpret as the boundary between the Lachlan and Delamerian orogens; (iii) a rapid eastward decrease in upper mantle velocity ~ 200 km inboard of the east coast of Australia, which is consistent with a marked thinning of the lithosphere; (iv) an increase in upper mantle velocity north of the Gawler Craton and Curnamona Province, which points to the presence of thicker lithosphere associated with the Precambrian shield region of the Australian continent; (v) Cenozoic intraplate basaltic volcanic centres distributed exclusively above the zone of thinner lithosphere inboard of the east coast, with the exception of low volume leucitite volcanics.