The Deep Roots of Geology: Tectonic History of Australia and its Margins expressed as Mantle Anisotropy
Australia is an old stable continent with a rich geological history. Limitations in sub-surface seismic imaging below the Moho, however, mean that is unclear to what extent, and to what depth, this rich geological history is expressed in the mantle. Studies of seismic anisotropy, which reflect past/present mantle deformation, can offer potential insights. One commonly employed technique is shear wave splitting, in which the wave polarisation is measured. New such results from the BILBY array, a linear transect of seismic stations that crossed the Australian continent from north to south, reveals a pattern of anisotropy that is consistent with past deformation of the Australian lithosphere that has been preserved for over 300 million years. Another informative technique is to use scattered surface waves, called Quasi-Love waves, that can detect lateral gradients in seismic anisotropy. The first such study for the region finds that scatterers are preferentially located near (1) the passive continental margins, and (2) the boundaries of major geological provinces within Australia. Such lateral anisotropic gradients within the continental interior imply pervasive fossilized lithospheric anisotropy, on a scale that mirrors the crustal geology at the surface. Beneath the continental margins, lateral anisotropic gradients may indicate small-scale dynamic processes in the asthenosphere, such as edge-drive convection, that are tied to the margins.
Caroline Eakin is an observational seismologist at the Australian National University, in the Research School of Earth Sciences, and is currently an ARC DECRA Fellow. She joined RSES as a Research Fellow in 2016 and was promoted to Fellow at the end of last year. She has a PhD in seismology from Yale University, and did her undergrad in geophysics from Imperial College London. Before arriving in Australia she held a postdoctoral fellowship at the University of Southampton. Much of her research involves fieldwork deploying seismometers in remote places, including current projects surrounding Lake Eyre in central Australia, and deploying ocean-bottom seismometers along the Macquarie Ridge in the Southern Ocean.