Insights Into Layering in the Cratonic Lithosphere Beneath Western Australia

Abstract

The characteristics of internal lithospheric discontinuities carry crucial information regarding the origin and evolution of the lithosphere. However, the formation and mechanisms of the midlithosphere discontinuity (MLD) are still enigmatic and controversial. We investigate the midlithospheric discontinuities beneath the Archean Western Australian Craton, which represents one of the oldest continents on the globe, using a novel receiver‐based reflectivity approach combined with other geophysical information comprising tomographic P and S wave velocity, radial anisotropy, electrical resistivity, and heat flow data. The MLD is rather shallow with a depth of 68–82 km. Multiple prominent discontinuities are observed in the lithospheric mantle using constructed high‐frequency (0.5–4 Hz) P wave reflectivities. These multiple discontinuities coincide well with the broad‐scale reduction of relative P and SV wave velocities at the top of the graded transition zone from the lithosphere to the asthenosphere. Strong radial anisotropy in the upper lithosphere mantle tends to be weak across the MLD, which might reflect quasi‐laminar lithospheric heterogeneity behavior with a horizontal correlation length that is greater than its vertical correlation length. Broad‐scale electrical resistivity variations show little coherence with the MLD. Given these various geophysical observations, the upper lithosphere exhibits rigid and elastic properties above the MLD, while the lower lithosphere tends to be ductile and rheological or viscous. A model comprising quasi‐laminar lithospheric heterogeneity could effectively represent the MLD characteristics beneath the Archean continent.

The Australian Continent: A Geophysical Synthesis

“…An additional constraint on the nature of lithospheric heterogeneity comes from observations of high-frequency P wave reflectivity profiles derived from the autocorrelograms of vertical component records at seismic stations (Kennett, 2015;Sun et al, 2018). These P reflectivity profiles suggest vertical changes in the character of the fine-scale structures in the Australian continent, indicating stronger reflectivity in the crust and upper lithosphere underneath the cratons.…”

Detection of seismic events on Mars: a lunar perspective

“…Heat flow from interior to surface is another useful geophysical measurement that would provide direct information of deep mantle tectonic activity. Cratons are considered to be the oldest and the most stable tectonic units on Earth, with heat flow values as low as 40 mW/m 2 or lower, e.g., the West Australian Craton (Sun WJ et al, ), but also twice or triple that value, reaching ~100 mW/m 2 , for example, in the destructed North China Craton (e.g., Sun WJ and Kennett, ).…”

Crustal Imaging With Bayesian Inversion of Teleseismic P Wave Coda Autocorrelation

“…As the standard autocorrelation technique only needs one component of the seismogram (e.g., the vertical component), it has a further advantage over the receiver function methods in areas where only the vertical component of seismograms are available, for example, earlier deployments of short-period stations in Australia. Furthermore, it has been shown by Sun et al (2018) that P wave reflectivity traces obtained from global events with epicentral distances between 30 • and 90 • (slowness range of 0.04-0.08 s/km) are scarcely affected by conversions and multiples, which is not the case for receiver function methods. (2)).…”

“…Despite the success of many studies on the processing and/or forward modeling of autocorrelograms (e.g., Becker & Knapmeyer-Endrun, 2018;Clayton, 2018;Daneshvar et al, 1995;Gorbatov et al, 2013;Heath et al, 2018;Ito & Shiomi, 2012;Kennett et al, 2015;Kennett & Sippl, 2018;Nishitsuji et al, 2016;Oren & Nowack, 2017;Pham & Tkalčić, 2017, 2018Romero & Schimmel, 2018;Ruigrok & Wapenaar, 2012;Saygin et al, 2017;Sun & Kennett, 2016Sun et al, 2018;Taylor et al, 2016;Tibuleac & von Seggern, 2012), to our best knowledge, there are no published studies on the inversion of autocorrelograms for mapping major discontinuities in the crust and upper mantle. Here, we investigate the inversion of autocorrelograms for crustal imaging.…”