A fictitious domain method for lithosphere‐asthenosphere interaction: Application to periodic slab folding in the upper mantle

Abstract

We present a new approach for the lithosphere-asthenosphere interaction in subduction zones.The lithosphere is modeled as a Maxwell viscoelastic body sinking in the viscous asthenosphere. Both domains are discretized by the finite element method, and we use a staggered coupling method. The interaction is provided by a nonmatching interface method called the fictitious domain method. We describe a simplified formulation of this numerical technique and present 2-D examples and benchmarks. We aim at studying the effect of mantle viscosity on the cyclicity of slab folding at the 660 km depth transition zone. Such cyclicity has previously been shown to occur depending on the kinematics of both the overriding and subducting plates, in analog and numerical models that approximate the 660 km depth transition zone as an impenetrable barrier. Here we applied far-field plate velocities corresponding to those of the South-American and Nazca plates at present. Our models show that the viscosity of the asthenosphere impacts on folding cyclicity and consequently on the slab's dip as well as the stress regime of the overriding plate. Values of the mantle viscosity between 3 and 5 3 10 20 Pa s are found to produce cycles similar to those reported for the Andes, which are of the order of 30-40 Myr (based on magmatism and sedimentological records). Moreover, we discuss the episodic development of horizontal subduction induced by cyclic folding and, hence, propose a new explanation for episodes of flat subduction under the South-American plate.

Topographic Fingerprint of Deep Mantle Subduction

“…Hence, the trench kinematics tunes the ability of the dynamic topography to go up and down. This finding agrees with previous studies (e.g., Cerpa et al, 2014;Guillaume et al, 2009;Lee & King, 2001), who show that slab dips vary in a time-dependent manner as soon as they encounter a strong barrier as the 670-km discontinuity inducing episodic changing in the trench velocity, and, in turn, building up topographic highs and lows close to the trench.…”

“…Slab shallowing, for example, is expected to produce down-warping of the upper plate and consequent marine transgression (e.g., Gurnis, 1990;Liu et al, 2008;Mitrovica et al, 1989). Variations in slab dip angle associated to slab folding are correlated with oscillation of surface topography (Cerpa et al, 2014;Cerpa et al, 2015;Guillaume et al, 2009;Martinod et al, 2016), whereas downward tilt of the upper plate toward the subduction trench has been shown to be due to the interaction of the slab with the upper lower mantle discontinuity (Crameri & Lithgow-Bertelloni, 2017;Hager, 1984).…”

Evaluating the Influence of Plate Boundary Friction and Mantle Viscosity on Plate Velocities

“…This viscosity range is consistent with the values estimated by post-glacial rebound and geoid studies to constrain the upper mantle viscosity structure (Mitrovica, 1996;Mitrovica & Forte, 1997). Similar values of the asthenospheric viscosity were obtained by Cerpa et al (2014), who studied the effect of mantle viscosity on the cyclicity of Andean slab folding.…”

Subduction-transition zone interaction: A review

“…As the slab accumulates in the transition zone, alternating phases of somewhat higher and lower retreat velocities (with accompanying changes in dip) tend to develop Lee and King, 2011;Čížková and Bina, 2013;Garel et al, 2014). These fluctuations are an expression of slab buckling, because even where the slab flattens at the base of the transition zone, the deformation is essentially a buckling response (Houseman and Gubbins, 1997;Ribe et al, 2007), as is seen most clearly in models with weaker slabs or ones where sinking is enhanced (Lee and King, 2011;Čížková and Bina, 2013;Cerpa et al, 2014). Trench-motion fluctuations due to buckling can be enhanced if the upper plate can break and heal (Clark et al, 2008).…”