The Influence of Lithospheric Thickness Variations Beneath Australia on Seismic Anisotropy and Mantle Flow

被引:2
作者
Eakin, C. M. [1 ]
Davies, D. R. [1 ]
Ghelichkhan, S. [1 ]
O'Donnell, J. P. [2 ,3 ]
Agrawal, S. [1 ]
机构
[1] Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT, Australia
[2] Geol Survey South Australia, Dept Energy & Min, Adelaide, SA, Australia
[3] Geol Survey Western Australia, Perth, WA, Australia
基金
澳大利亚研究理事会;
关键词
seismic anisotropy; shear-wave splitting; Gawler Craton; lithosphere; asthenosphere; mantle flow; WAVE SPLITTING MEASUREMENTS; AZIMUTHAL ANISOTROPY; TECTONIC EVOLUTION; CURNAMONA PROVINCE; PLATE-MOTION; DEFORMATION; CONSTRAINTS; INSIGHTS; ASTHENOSPHERE; ORIENTATION;
D O I
10.1029/2023GC011066
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Rapid plate motion, alongside pronounced variations in age and thickness of the Australian continental lithosphere, makes it an excellent location to assess the relationship between seismic anisotropy and lithosphere-asthenosphere dynamics. In this study, SKS and PKS shear-wave splitting is conducted for 176 stations covering the transition from the South Australian Craton to eastern Phanerozoic Australia. Comparisons are made with models of lithospheric thickness as well as numerical simulations of mantle flow. Splitting results show uniform ENE-WSW aligned fast directions over the Gawler Craton and broader South Australian Craton, similar to the orientation of crustal structures generated during an episode of NW-SE directed compression and volcanism similar to 1.6 billion years ago. We propose that heat from volcanism weakened the lithosphere, aiding widespread lithospheric deformation, which has since been preserved in the form of frozen-in anisotropy. Conversely, over eastern Phanerozoic Australia, fast directions show strong alignment with the NNE absolute plate motion. Overall, our results suggest that when the lithosphere is thin (<125 km), lithospheric contributions are minimal and contributions from asthenospheric anisotropy dominate, reflecting shear of the underlying mantle by Australia's rapid plate motion above. Further insights from geodynamical simulations of the regional mantle flow field, which incorporate Australian and adjacent upper mantle structure, predict that asthenospheric material would be drawn in from the south and east toward the fast-moving continental keel. Such a mechanism, alongside interactions between the flow field and lithospheric structure, provides a plausible explanation for smaller-scale anomalous splitting patterns beneath eastern Australia that do not align with plate motion. Plain Language Summary The Australian continent is moving rapidly northward at around 7-8 cm per year. As the continent moves, it is expected to shear or deform the warmer and weaker layer of the Earth below, called the mantle. The actual pattern of deformation within the mantle can be investigated by studying how seismic waves are polarized as they pass through this material. Results show that for one of the geologically oldest regions in Australia, an area in South Australia, the deeper part of the continent here was substantially deformed 1.6 billion years ago. This deformation was likely aided by volcanism that occurred at the same time that would have warmed and weakened the material, making it easier to deform. This material has since cooled and strengthened over time, freezing in the ancient pattern of deformation. Meanwhile in eastern Australia, the continental material here has a much younger geological age (<550 million years old). The results from this region instead show agreement with the present-day direction of shear due to the fast northward motion of the Australian continent, as initially expected.
引用
收藏
页数:16
相关论文
共 94 条
  • [1] Tracking crustal thickness at the sediment inundated edge of the Gawler Craton, South Australia
    Agrawal, Shubham
    Eakin, Caroline M.
    ODonnell, John P.
    [J]. TECTONOPHYSICS, 2023, 862
  • [2] Characterizing the cover across South Australia: a simple passive-seismic method for estimating sedimentary thickness
    Agrawal, Shubham
    Eakin, Caroline M.
    O'Donnell, John
    [J]. GEOPHYSICAL JOURNAL INTERNATIONAL, 2022, 231 (03) : 1850 - 1864
  • [3] AusPass, 2016, IRIS DMC, DOI 10.7914/SN/1Q_2016
  • [4] Seismic Azimuthal Anisotropy Beneath a Fast Moving Ancient Continent: Constraints From Shear Wave Splitting Analysis in Australia
    Ba, Kailun
    Gao, Stephen S.
    Song, Jianguo
    Liu, Kelly H.
    [J]. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 2023, 128 (02)
  • [5] Thermal Structure of Eastern Australia's Upper Mantle and Its Relationship to Cenozoic Volcanic Activity and Dynamic Topography
    Ball, P. W.
    Czarnota, K.
    White, N. J.
    Klocking, M.
    Davies, D. R.
    [J]. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 2021, 22 (08)
  • [6] Insights into the structure and dynamics of the upper mantle beneath Bass Strait, southeast Australia, using shear wave splitting
    Bello, M.
    Cornwell, D. G.
    Rawlinson, N.
    Reading, A. M.
    [J]. PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 2019, 289 (45-62) : 45 - 62
  • [7] The 1800-1100 Ma tectonic evolution of Australia
    Betts, PG
    Giles, D
    [J]. PRECAMBRIAN RESEARCH, 2006, 144 (1-2) : 92 - 125
  • [8] Lateral Variations in Lithospheric Mantle Structure Control the Location of Intracontinental Seismicity in Australia
    Bezada, M. J.
    Smale, J.
    [J]. GEOPHYSICAL RESEARCH LETTERS, 2019, 46 (22) : 12862 - 12869
  • [9] Anisotropic structure of the Australian continent
    Birkey, Andrew
    Ford, Heather A.
    [J]. FRONTIERS IN EARTH SCIENCE, 2023, 10
  • [10] SHEAR-WAVE SPLITTING IN THE UPPER-MANTLE WEDGE ABOVE THE TONGA SUBDUCTION ZONE
    BOWMAN, JR
    ANDO, M
    [J]. GEOPHYSICAL JOURNAL OF THE ROYAL ASTRONOMICAL SOCIETY, 1987, 88 (01): : 25 - 41