Seismic anisotropy beneath Central Australia: A record of ancient lithospheric deformation
Date
2021-12-05
Authors
Eakin, Caroline
Flashman, Claire
Agrawal, Shubham
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
From 2008 to 2011 a broadband seismic array (BILBY) spanned the Australian continent from North to South, crossing the suture zone between the North and South Australian cratons, and traversing the Central Australian orogenic belt. Past tectonic events, including orogenies during the Proterozoic and Paleozoic, have left a long-lasting impression on the crustal and Moho structure of this inter-cratonic region. However, the impact of past tectonic activity on the lithosphere has been less clear. Here we present the first shear-wave splitting results for the BILBY array using a combination of SKS and PKS teleseismic phases to investigate patterns of deformation and seismic anisotropy within the upper mantle beneath central Australia. Null *KS observations are found to be abundant compared to observations of splitting, as has been widely reported by previous studies, but this appears to be largely due to a coincidental alignment of the inferred anisotropic fast direction with the back-azimuthal range at which most available events occur (140°-160°). Across the central Australian belt the station averaged fast directions tend to orientate ENE-WSW parallel with topographic, gravity, and magnetic trends. Northwards however, the fast directions switch orientation, instead following the NW-SE elongated geometry of the Tennant Creek Inlier, thus delineating a sharp lateral change in the underlying seismic anisotropy. Overall, evidence suggests that the splitting pattern likely reflects anisotropy inherent within the lithosphere generated by past deformational events over 300 million plus years ago, as opposed to the present-day mantle flow in the asthenosphere. While two distinct layers of anisotropy, present in both the asthenosphere and lithosphere, is supported by other evidence, it is not necessarily required by our current dataset. Instead, we can sufficiently model our results with only a single layer of anisotropy, consistent with the expected geometry of azimuthal anisotropy in the lithosphere.
Description
Keywords
Seismic anisotropy, Australia, Shear-wave splitting, Continental deformation, Suture zone, Lithosphere
Citation
Collections
Source
Tectonophysics
Type
Journal article
Book Title
Entity type
Access Statement
Open Access
License Rights
Creative Commons Attribution-NonCommercial-NoDerivs License
Restricted until
Downloads
File
Description
Accepted Article