Structure and evolution of the upper mantle of the Australian Plate from waveform tomography with massive datasets

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• Janneke de Laat -- University of Cambridge
• Wednesday 04 October 2023, 16:00-17:00
• Bullard Labs tearoom, Department of Earth Sciences, Madingley Rise.

If you have a question about this talk, please contact Yihe Xu.

In this talk I present a new S-wave velocity tomographic model of the upper mantle beneath the Australian Plate and its boundaries, Aus22, and the insights obtained from it. Aus22 includes azimuthal anisotropy and is constrained by waveforms from 0.9 million vertical-component seismograms, with the densest data sampling in the hemisphere centred on the Australian continent, using all available data covering this hemisphere. Waveform inversion extracted structural information from surface waves, S- and multiple S-waves and constrained S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle, down to the 660- km discontinuity. The model was validated by resolution tests and, for particular locations in Australia with notable differences from previous models, by independent inter-station measurements of surface-wave phase velocities. As the model is generated with data extending beyond the boundaries of the Australian Plate, it images the both the Australian Plate as well as its boundaries in detail.

Aus22 offers new insights into the structure and evolution of the upper mantle of the Australian Plate and its boundaries. Thick, high-velocity (and, by inference, cold) cratonic lithosphere occupies nearly all of western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it collides with island arcs, without subducting. Diamondiferous kimberlites and lamproite deposits are underlain by cratonic lithosphere, except for the most recent diamondiferous lamproites in the King Leopold Orogen. The rugged eastern boundary of the cratonic lithosphere resolved by the model provides a lithospheric definition of the Tasman Line. The eastern part of Australia is underlain by thin, warm lithosphere, evidenced by low seismic velocities. All the sites of Cenozoic intraplate volcanism in eastern Australia are located on thin lithosphere. A low-velocity anomaly is present in the mantle transition zone beneath the Lord Howe and Tasmanid hotspots, indicative of anomalously high temperature and consistent with a deep mantle upwelling feeding these hotspots and, possibly, also the East Australia hotspot. High seismic velocities are observed in the transition zone below northeast Australia and indicate the presence of subducted lithospheric fragments trapped in the transition zone, possibly parts of the former northern continental margin of Australia.

This talk is part of the Bullard Laboratories Wednesday Seminars series.

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• Bullard Laboratories Wednesday Seminars
• Bullard Labs tearoom, Department of Earth Sciences, Madingley Rise
• Department of Earth Sciences seminars

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