Sagduction: Could This Explain Early Earth Tectonics? A Modeling Perspective

Sagduction, the downward movement of dense crustal material into the underlying mantle, is considered one of the plausible tectonic mechanisms operating during the Archean time, when the lithosphere was hotter and weaker than today (Bedard, 2006; Johnson et al., 2014; Sizova et al., 2015; Sizova et al., 2018; Piccolo et al., 2019). Understanding the physical conditions that enable sagduction is key to deciphering the early evolution of Earth’s crust and mantle lithosphere.

In this study, we employ a suite of 2D numerical models using ASPECT code, to systematically investigate the dynamics of sagduction under varying rheological and thermal conditions. We vary the viscosity structure and the depth at which lower crustal metamorphism initiates, to test how mantle’s viscosity and metamorphic density changes influence the style and efficiency of sagduction. Our results reveal how the interplay between viscosity layering and metamorphic phase transitions controls the timing and extent of downward crustal recycling.

We further examine how these parameters influence the long-term evolution of the lower crust and the mantle lithosphere beneath it. Our findings provide new insight into the dynamics of Archean lithosphere and the mechanisms that may have governed early continental differentiation.

 

References

Bedard, J.H., 2006. A catalytic delamination-driven model for coupled genesis of Archaean crust and sub-continental lithospheric mantle. Geochim. Cosmochim. Acta 70, 1188–1214. https://doi.org/10.1016/j.gca.2005.11.008.

 

Johnson, T., Brown, M., Kaus, B., van Tongeren, J., 2014. Delamination and recycling of Archaean crust caused by gravitational instabilities. Nat. Geosci. 7, 47–52. https:// doi.org/10.1038/ngeo2019.

 

 

Sizova, E., Gerya, T., Stüwea, K., Brown, M., 2015. Generation of felsic crust in the Archean: A geodynamic modeling perspective. Precambr. Res. 271, 198–224. https://doi.org/10.1016/j.precamres.2015.10.005.

 

Sizova, E., Gerya, T., Brown, M., Stüwea, K., 2018. What drives metamorphism in early Archean greenstone belts? Insights from numerical modeling, Tectonophysics 746, 587–601. https://doi.org/10.1016/j.tecto.2017.07.020.

 

 

Piccolo, A., Palin, R., & B.J.P. Kaus, R.W. (2019), Generation of Earth’s Early Continents From a Relatively Cool Archean Mantle, Geochemistry, Geophysics, Geosystems, 20, 1679–1697, doi:https://doi.org/10.1029/2018GC008079.