Seismological evidence for secular mantle cooling beneath cratons

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• Federico Munch -- ETH Zürich
• Wednesday 01 November 2023, 16:00-17:00
• Wolfson Lecture Theatre.

If you have a question about this talk, please contact Lisanne Jagt.

Cratons are thought to be underlain by a thick ‘root’ of mantle that has experienced very high degrees of partial melting, resulting in a cold, strong, and buoyant mantle compared to its oceanic counterpart. However, the degree to which such cratonic regions are stabilized due to differences in composition as opposed to their thermal structures remains debated.

Analyses of xenoliths provide insights on the thermal structure and composition of the continental mantle. However, xenoliths only record a temporal snapshot of an often geographically limited region of the mantle lithosphere. In order to provide a more spatially extensive view of the nature of the sub-continental lithospheric mantle, geophysical techniques are invaluable. Current inversions of seismic data, for example, consider the mantle to be a binary mixture of basalt and harzburgite, which is then used to compute the stable mineral assemblage at the desired pressure and temperature (Munch et al., 2020; Bissig et al., 2021). However, a simple binary mixture cannot account for the high Mg# (Mg/[Mg+Fe]) and low Mg/Si ratios recorded in xenoliths from cratonic regions induced by metasomatic processes (Boyd, 1989; Canil, 2004; Pearson et al. 2022) .

In this study, we extend the chemically-differentiated oceanic-lithosphere (basalt-harzburgite) model to better capture the compositional diversity observed in cratonic mantle peridotites (Canil, 2004) in the stochastic inversion of seismic data for mantle temperature and composition. This new framework is applied to the inversion of receiver function waveforms and fundamental-mode Rayleigh wave dispersion data recorded at 40 seismic stations located in different tectonic settings around the world.

The retrieved mantle compositions are in overall agreement with the compositions and thermal profiles obtained from analyses of mantle xenoliths. Our results suggest that the geotherms recorded by xenoliths are compatible with steady-state conductive conditions in and around the lithosphere/asthenosphere. We find a decrease in mantle potential temperature under cratons as a function of their age, reflecting the secular cooling of the lithospheric mantle.

This talk is part of the Bullard Laboratories Wednesday Seminars series.

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• Bullard Laboratories Wednesday Seminars
• Department of Earth Sciences seminars
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