Precambrian deformation belts in compressive tectonic regimes: A numerical perspective

Jonathan Poh (1) , Philippe Yamato (1, 2) , Thibault Duretz (1) , Denis Gapais (1) , Patrick Ledru (3)

1 GR - Géosciences Rennes
2 IUF - Institut universitaire de France
3 Orano Canada Inc

The thermal state of the lithosphere is often considered as the main factor controlling the distribution of the structural and metamorphic features in tectonic systems (ancient versus modern tectonics). Deformation in ancient (weak and hot) lithospheres is distributed whereas deformation in modern (strong and cold) lithospheres is localised into prominent shear zones. The distributed deformation during the Precambrian suggests lower compressive strain rates are required, implying a long compression duration. However, the effects of variable strain rate on the compression of ancient lithospheres remain under-explored. A series of numerical models mimicking Precambrian lithospheric conditions is proposed and a broad range of thermal profiles and shortening rates is tested to investigate their influence on the resultant deformation modes. Two broad deformation styles were found to be significantly influenced by the magnitude of the shortening rates and stand out from the parametric study: (i) pop-downs and upper crustal thrusting at high strain rates that favour the formation of shear zones, and (ii) sedimentary cusping deformation at slower strain rates that generates well-defined vertical finite strain patterns. These two deformation modes were compared with natural examples, providing further insight into the evolution of their respective deformations. The vertical structures at the Hearne Craton (western Canadian Shield) could be explained via the sedimentary cusping mechanism by constraining our models with available geological data. Meanwhile, the vertical finite strain patterns from the proposed reference model now provide a tectonic template for future fluid-thermal convection simulations, to predict fluid flow and mineralisation potential.

Mots clés: Ancient structures; Rheology of the lithosphere; Precambrian tectonics

Domaines: Tectonique

Jonathan Poh, Philippe Yamato, Thibault Duretz, Denis Gapais, Patrick Ledru. Precambrian deformation belts in compressive tectonic regimes: A numerical perspective. Tectonophysics, 2020, 777, pp.228350. ⟨10.1016/j.tecto.2020.228350⟩. ⟨insu-02458916⟩