Significant anisotropic fabric across South Western Australia and the Yilgarn Craton revealed by the new WA Array

The southwest region of Western Australia comprises the Archean Yilgarn Craton, which is bounded by the Proterozoic Albany-Fraser and Pinjarra orogens. This ancient region has undergone significant deformation and reworking since its formation. We calculate shear wave splitting of the PKS and SKS teleseismic phases to investigate seismic anisotropy across the region. The temporary broadband seismic arrays that we use, including the new WA Array Phase 1 data, provide unprecedented seismic station density within the Western Australian continental interior. We find evidence for significant seismic anisotropy, with the regional average delay time of 1.13 s comparable to the global average of δt = 1 s. Although fast polarisation orientations show variation, they are not aligned with current, sub-lithospheric mantle flow associated with absolute plate motions. Instead, seismic anisotropy parallels dyke orientations across the cratonic interior. Fast polarisation directions in the Youanmi Terrane are oriented approximately parallel to the E–W trending Widgiemooltha dyke suite. This correlation is likely due to pre-existing mantle fabric that both formed a locus for the subsequent emplacement of the dykes during a period of ancient Archean lithospheric extension, as well as controlling the orientation of seismic anisotropy. Further evidence for this fabric comes from new isotope geochemistry analysis of primary ENE-trending architecture within the Yilgarn Craton. In the Southwest Terrane, fast polarisation orientations match both structural faults and dykes, suggesting crust-mantle coupling. The Youanmi Terrane shows less coherence between surface and mantle deformation, with structural faults oriented at an angle compared to the E–W and NE–SW trends in the anisotropy. Our results are evidence that large-scale, fossilised lithospheric fabric within the Yilgarn Craton is the dominant mechanism for seismic anisotropy in the region.