Mapping crustal structure across southern Australia using seismic ambient noise tomography

The rocks of southern Australia record over 3 billion years of Earth’s evolution, but the basement geology is veiled by sedimentary cover. Geophysical data are needed to unveil the geological structure. The 2018-2022 Lake Eyre Basin and 2020-2022 AusArray SA seismic arrays expand seismic coverage in South Australia. In conjunction with permanent and preceding temporary arrays, we extracted Rayleigh wave phase velocity dispersion data from ambient noise recordings at a total of 501 seismic stations spanning the transition from Precambrian to Phanerozoic Australia. The dispersion data were used to develop Rayleigh wave phase velocity maps of southern Australia at periods 3-20 s, corresponding to upper to mid-to-lower crustal depths. At shorter periods, low velocity structure tracks Phanerozoic sedimentary accumulations. The Moyston Fault, regarded as the boundary between the Delamerian and Lachlan Orogens, has an intermittent expression in the phase velocity maps; it is marked by a velocity contrast between ∼36.5-37.5◦ S in Victoria, has no obvious signature in Victoria north of ∼36.5◦ S, and coincides with a velocity contrast tracing the southern edge of the Darling Basin in western New South Wales. An arcuate velocity contrast characterising the western edge of deep, sedimentfilled troughs of the Darling Basin is a good candidate for the transition from Precambrian to Phanerozoic crust. Fluid derived from neotectonic metamorphic devolatilization and/or remnant hydrated mantle is our preferred hypothesis for explaining seismicity and coincident seismic and conductivity anomalies in the mid- to lower crust beneath the Ikara–Flinders Ranges. Our maps suggest that the Olympic Dam and Carrapateena IOCG deposits reside above the margin of a low seismic velocity zone in the mid-to-lower crust. We surmise that this signature might reflect past metalliferous fluid movement associated with the Olympic Cu-Au Province, akin to low reflectivity and low resistivity zones evident in 2D reflection seismic and magnetotelluric profiles, respectively. Citation: J.P. O’Donnell, S. Agrawal, C.M. Eakin, S. Thiel, K. Brand, A. Gorbatov, B. Goleby, Mapping crustal structure across southern Australia using seismic ambient noise tomography, Gondwana Research, Volume 121, 2023, Pages 307-324, ISSN 1342-937X, https://doi.org/10.1016/j.gr.2023.04.013.