EarthByte Seminar Series: Dr. Antoniette Grima

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Join us for an insightful seminar with Antoniette from University of Glasgow. In this EarthByte Seminar Series event, Antoniette will talk about the evolution of slab morphology and topography at subduction zones. Her work can contribute to a better understanding of subduction processes from deep slab dynamics to continental deformation, the evolution of topography at subduction zones, and basin formation and continental extension.

Seminar Details:

On the Evolution of Slab Morphology and Topography at Subduction Zones

Subduction links the surface with the interior, it drives mantle flow and permanently deforms the continental lithosphere shaping thus, the thermo-chemical evolution of our planet. Here, we use 2D numerical models of subduction to investigate the dynamics of the slab as it journeys from the upper to the upper lower mantle. Our results show that the deep slab behaviour is controlled by the relative strength relationship between the subducting slab and the surrounding ambient mantle and is reflected in endmember deflected and penetrative slab morphologies. Linking these two morphologies is a new slab behaviour we term ‘orphaning’ where slabs undergo break-off directly at 660 km depth. Orphaning suggests that not all slab fragments imaged at the top of the lower mantle are the result of shallow slab break-off, subduction termination and thus, an overhaul of the tectonic regime. Instead orphaning suggests a more continuous long-lived subduction record.

Slab penetration into the lower mantle is also controlled to some extent by the overriding plate type. We find that when the overriding plate is continental and the viscosity jump occurs at 1000 km depth, slabs which would otherwise flatten at 660 km depth, sink to lower mantle depths. Furthermore, our recent work on continental heterogeneity at subduction zones shows that variations in continental margin and keel properties impact the slab retreat, and deformation patterns, topographic signals, and basin formation on the continental lithosphere. Our findings suggest that back-arc extension and subsidence are not solely controlled by slab dynamics but are also influenced by the heterogeneity of continental margin and keel. Our work can, therefore, contribute to a better understanding of subduction processes from deep slab dynamics to continental deformation, the evolution of topography at subduction zones, and basin formation and continental extension.

 

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