Dynamical effects of subducting ridges: Insights from 3-D laboratory models

TL;DR

This study uses 3D laboratory models to analyze how subducting buoyant ridges and plateaus influence slab dynamics, affecting subduction velocity, slab curvature, and geometry, with implications for understanding real-world subduction zones like South America.

Contribution

The paper provides new insights into the dynamical effects of buoyant ridges and plateaus on subduction processes through experimental modeling, highlighting long-term impacts on slab geometry.

Findings

Buoyant ridges parallel to the trench slow down subduction.

Large buoyant segments cause steeper slabs and reduce subduction velocity.

Subducted buoyant anomalies may explain features of the Nazca slab.

Abstract

We model the subduction of buoyant ridges and plateaus to study their effect on slab dynamics. Oceanic ridges parallel to the trench have a stronger effect on the process of subduction because they simultaneously affect a longer trench segment. Large buoyant slab segments sink more slowly into the asthenosphere, and their subduction result in a diminution of the velocity of subduction of the plate. We observe a steeping of the slab below those buoyant anomalies, resulting in smaller radius of curvature of the slab, that augments the energy dissipated in folding the plate and further diminishes the velocity of subduction. When the 3D geometry of a buoyant plateau is modelled, the dip of the slab above the plateau decreases, as a result of the larger velocity of subduction of the dense "normal" oceanic plate on both sides of the plateau. Such a perturbation of the dip of the slab maintains long time after the plateau has been entirely incorporated into the subduction zone. We compare experiments with the present-day subduction zone below South America. Experiments suggest that a modest ridge perpendicular to the trench such as the present-day Juan Fernandez ridge is not buoyant enough to modify the slab geometry. Already subducted buoyant anomalies within the oceanic plate, in contrast, may be responsible for some aspects of the present-day geometry of the Nazca slab at depth.