The subduction dichotomy of strong plates and weak slabs

Abstract

Abstract. A key element of plate tectonics on Earth is that the lithosphere is subducting into the mantle. Subduction results from forces that bend and pull the lithosphere into the interior of the Earth. Once subducted, lithospheric slabs are further modified by dynamic forces in the mantle, and their sinking is inhibited by the increase in viscosity of the lower mantle. These forces are resisted by the material strength of the lithosphere. Using geodynamic models, we investigate several subduction models, wherein we control material strength by setting a maximum viscosity for the surface plates and the subducted slabs independently. We find that models characterized by a dichotomy of lithosphere strengths produce a spectrum of results that are comparable to interpretations of observations of subduction on Earth. These models have strong lithospheric plates at the surface, which promotes Earth-like single-sided subduction. At the same time, these models have weakened lithospheric subducted slabs which can more easily bend to either lie flat or fold into a slab pile atop the lower mantle, reproducing the spectrum of slab morphologies that have been interpreted from images of seismic tomography.

Depletion of the upper mantle by convergent tectonics in the Early Earth

“…As established in our previous study 20 , values of λ fluid = 0.1 and λ melt = 0.01 provide realistic volumes and compositions of arc volcanic rocks for contemporary intraplate subduction. Our rheological model also accounts for slab weakening at depths greater than 200 km 61 by gradually decreasing the upper cutoff viscosity value from 10 25 to 10 22 Pa s in the depth interval between 200 and 400 km. No viscosity increase has been applied at the perovskite transition in the mantle.…”

Effect of Plate Length on Subduction Kinematics and Slab Geometry: Insights From Buoyancy‐Driven Analog Subduction Models

“…We choose this advanced stage of the free sinking phase, because the slab has enough time to evolve self-consistently, canceling the initial bending radius imposed at the start of the experimental run, while the slab is not much affected yet by the bottom boundary. The measurement was performed by manually fitting a circle to the outer surface of the bending part of the slab from the trench to a depth of 4.25 cm (Figure 7c), which is the depth range over which the slab experiences its greatest curvature, and herein the radius of the circle represents the slab bending radius, which is similar to the "depth" method described in Petersen et al (2017). The slab bending radius varies between the different models ( Figure 7a).…”

Geodynamic diagnostics, scientific visualisation and StagLab 3.0

“…Worrisome visualisation pitfalls arise that make figures confusing, unreadable or even misleading and hence unscientific. The rainbow colour map strongly deteriorates, for example, the underlying scientific data (Pizer and Zimmerman, 1983;Ware, 1988;Tufte, 1997) due to the inhomogeneous colour sensitivity of the human retina (Thomson and Wright, 1947). On top of that, it is confusing to people with some of the most common colour-vision deficiencies.…”

“…The subduction bending radius, R B , can be fully automatically calculated using the current plate geometry. A spline method with temperature contours can be used to outline the subducting plate shape (see Petersen et al, 2017, for other methods). A certain temperature threshold thereby extracts cold plate portions including a sinking slab if present.…”