How Aseismic Ridges Modify the Dynamics of Free Subduction: A 3-D Numerical Investigation

Abstract

The subduction of positively buoyant features has been implicated in the development of flat and shallow dipping slabs, the formation of cusps in trench geometry, and the cessation of associated arc magmatism. However, how such buoyant anomalies influence subduction dynamics to produce these different tectonic expressions remains debated. In this paper, using a series of multi-material 3-D simulations of free subduction, we investigate how linear buoyant ridges modify subduction dynamics, in particular downgoing plate velocities, trench motions and slab morphology. We examine the sensitivity of results to downgoing plate age (affecting buoyancy and strength), ridge buoyancy and ridge location along the trench, finding that buoyant ridges can locally change slab sinking and trench retreat rates, in turn modifying the evolution of slab morphology at depth and trench shape at the surface. In all cases examined, trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young, weak plates, the change in trench shape is more localised than on old, strong plates. Slab shallowing at the ridge only occurs for young plates, while the stronger and more negatively buoyant older plates pull down the ridge at a steeper angle than the rest of the slab. On old plates, ridges located near regions of trench stagnation or advance, which typically develop in wide slabs, have a stronger effect on trench and slab shape. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the formation of a flat slab, a variation in expressions also observed on Earth.

How Slab Age and Width Combine to Dictate the Dynamics and Evolution of Subduction Systems: A 3‐D Spherical Study

“…Interactions with nearby past or ongoing subduction zones may also affect the sinking velocity and slab penetration of the mantle transition zone (e.g., Becker & Faccenna, 2011; Čížková & Bina, 2019; Fukao & Obayashi, 2013; Fukao et al., 2009). The subduction of locally thickened oceanic lithosphere, such as oceanic plateaus, aseismic ridges or seamount chains, has been proposed to influence the shape of the trench and change the geometry of subducting slabs (e.g., Capitanio et al., 2011; Cross & Pilger, 1982; Gutscher, Malavieille, et al., 1999; Martinod et al., 2005; Suchoy et al., 2022). The higher compositional buoyancy of oceanic plateaus and ridges could resist slab sinking into the mantle and, thus, potentially lead to flat slab subduction (e.g., Mason et al., 2010; van Hunen et al., 2002).…”

How slab age and width combine to dictate the dynamics and evolution of subduction systems: a 3-D spherical study

“…Interactions with nearby past or ongoing subduction zones may also affect the sinking velocity and slab penetration of the mantle transition zone (e.g., Fukao et al, 2009;Becker & Faccenna, 2011;Fukao & Obayashi, 2013b;Čížková & Bina, 2019). The subduction of locally thickened oceanic lithosphere, such as oceanic plateaus, aseismic ridges or seamount chains, has been proposed to influence the shape of the trench and change the geometry of subducting slabs (e.g., Cross & Pilger, 1982;Gutscher, Malavieille, et al, 1999;Martinod et al, 2005;Capitanio et al, 2011;Suchoy et al, 2022). The higher compositional buoyancy of oceanic plateaus and ridges could resist slab sinking into the mantle and, thus, potentially lead to flat slab subduction (e.g., van Hunen et al, 2002;Mason et al, 2010).…”

Comparing the Dynamics of Free Subduction in Cartesian and Spherical Domains

“…Previous studies have found that trench motion is retarded in the vicinity of buoyant features, pinning the trench in a cusp shape (e.g., Mason et al, 2010;Suchoy et al, 2022). Suchoy et al (2022) investigated the subduction of buoyant anomalies with Cartesian numerical models using a similar setup to the C_W2400 case analyzed here, and found that their effect is dependent upon their location along the trench. When the buoyant ridge impinges at the center of the trench, where trench motion is already hindered by plate width, trench retreat is further reduced locally, leading to significant along-strike variations in trench shape and locally reducing slab dip.…”

“…One example is how the presence of buoyant anomalies, such as oceanic plateaus and ridges, influence the evolution of subduction systems. Previous studies have found that trench motion is retarded in the vicinity of buoyant features, pinning the trench in a cusp shape (e.g., Mason et al, 2010;Suchoy et al, 2022). Suchoy et al (2022) investigated the subduction of buoyant anomalies with Cartesian numerical models using a similar setup to the C_W2400 case analyzed here, and found that their effect is dependent upon their location along the trench.…”

“…One example is how the presence of buoyant anomalies, such as oceanic plateaus and ridges, influence the evolution of subduction systems. Previous studies have found that trench motion is retarded in the vicinity of buoyant features, pinning the trench in a cusp shape (e.g., Mason et al., 2010; Suchoy et al., 2022). Suchoy et al.…”