12,3,4- 1University of Glasgow, College of Science and Engineering, School of Geographical and Earth Sciences, Glasgow, United Kingdom of Great Britain – England, Scotland, Wales (antoniettegreta@gmail.com)
- 2Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196 10100 Burnet Road, Austin, 78758-4445, TX, USA
- 3Department of Earth and Planetary Sciences, Jackson School of Geosciences, The University of Texas at Austin, 2275 Speedway Stop C9000, Austin, 78712-1722, TX, USA
- 4The Oden Institute for Computational Engineering & Sciences, The University of Texas at Austin, 201 E 24th Street, Austin, 78712-1229, TX, USA
The shallowing of subducting slabs within the upper ~200 km of the mantle, commonly referred to as flat slab subduction is associated with extensive petrological and structural modification of the continental lithosphere. Anomalously buoyant oceanic lithosphere, upper-plate overthrusting, and interactions with cratonic keels have all been proposed as mechanisms promoting shallow slab geometries, yet the dynamics governing the initiation and duration of flat slab subduction remain to be fully understood. Here, we investigate self-consistent flat-slab subduction dynamics using the finite element code ASPECT with adaptive mesh refinement and a free surface boundary condition. We explore the influence of the overriding plate structure, including the presence of continental keels, as well as the role of heterogenous subduction interface strength on shallow slab dynamics. Our results show that flat slab geometries develop when a weak, sediment-rich subduction interface is combined with a positively buoyant overriding continental lithosphere. Substantiating previous studies, we further find that the presence of a strong cratonic keel near the continental plate margin enhances shallow slab underthrusting and encourages flat slab configurations. Importantly, we show that the timing of interface weakening, such as due to influx of sediments, exerts a first-order control on the onset and the longevity of slab flattening. As the slab flattens, pronounced subsidence, extension and transient marine inundation develop within the foreland region of the upper plate, superimposed on broader, large-scale subsidence of the continental interior. Regional uplift and subsidence are thus not solely linked to flat slab emplacement and removal, but also reflect evolving slab dynamics within the shallow upper mantle. Our results provide new constraints on the geodynamic controls of flat slab evolution and their role in driving continent-scale deformation and sediment redistribution.
How to cite: Grima, A. G. and Becker, T.: How interface weakening and continental structure promote flat slab subduction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5782, https://doi.org/10.5194/egusphere-egu26-5782, 2026.
