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

Abstract

Subduction style is controlled by a variety of physical parameters. Here we investigate the effect of subducting plate length on subduction style using laboratory experiments of time-evolving buoyancy-driven subduction in 3-D space. The investigation includes two experimental sets, one with a lower (~740) and one with a higher (~1,680) subducting plate-to-mantle viscosity ratio (η SP /η M). Each set involves five models with a free-trailing-edge subducting plate and variable plate length (20-60 cm, scaling to 1,600-4,800 km), and one model with a fixed-trailing-edge subducting plate representing an infinitely long plate. Through determining the contact area between subducting plate and underlying mantle, plate length affects the resistance to trenchward motion of the subducting plate and thus controls the partitioning of the subduction velocity (v S) into the subducting plate velocity (v SP) and trench velocity (v T). This subduction partitioning thereby determines the subduction style by controlling the dip angle of the slab tip once it first touches the 660 km discontinuity. The low η SP /η M models display two subduction styles. Short plates (≤40 cm) induce a higher subduction partitioning ratio (v SP /v S), promoting trench advance and slab rollover geometries, whereas longer plates (≥50 cm) lead to a lower v SP /v S , producing continuous trench retreat and backward slab draping geometries. In contrast, the high η SP /η M models exclusively show trench retreat with draping geometries, as the high η SP /η M enables less slab bending before its tip touches the 660 km discontinuity. Our study indicates that future modeling work should consider the effects of plate length on the style and evolution of subduction.

Overriding Plate Deformation and Topography During Slab Rollback and Slab Rollover: Insights From Subduction Experiments

“…(2008) and Faccenna et al. (2009) were based on subduction models without an overriding plate, while the current models include an overriding plate, and the complexity that plate length also influences the subduction style (Xue et al., 2020). Indeed, earlier studies have shown that a variety of physical parameters can affect the subduction mode (e.g., Bellahsen et al., 2005; Di Giuseppe et al., 2008; Funiciello et al., 2008; Garel et al., 2014; Magni et al., 2014; Schellart, 2008a; Xue et al., 2020).…”

“…To achieve dynamic similarity between model and nature, we assume that the slab sinking velocity follows the Stokes' settling law (Jacoby, 1973). With the dynamic scaling using the Stokes' settling law described in earlier works (Duarte et al., 2013; Strak & Schellart, 2016; Xue et al., 2020), we simulate the upper mantle with a viscosity that represents ∼8.4 × 10 19 Pa s in nature, which is comparable to estimates of 10 19 –10 21 Pa s (Harig et al., 2010; Peltier, 2004), and a subducting oceanic plate with a viscosity representing 1.1 × 10 23 Pa s in nature.…”

“…For one particular viscosity ratio, one might observe, when increasing the slab thickness (and thus decreasing the mantle depth/slab thickness ratio), that the subduction style changes from rollover to rollback, while for another viscosity ratio, one might observe, when increasing the slab thickness, that the subduction style changes from rollback to rollover (see e.g., Figure 13 in Schellart [2008a] or Figure 11 in Ribe [2010]). We add to this the complexity that the regime diagrams and the studies from Di Giuseppe et al ( 2008) and Faccenna et al (2009) were based on subduction models without an overriding plate, while the current models include an overriding plate, and the complexity that plate length also influences the subduction style (Xue et al, 2020). Indeed, earlier studies have shown that a variety of physical parameters can affect the subduction mode (e.g., Bellahsen et al, 2005;Di Giuseppe et al, 2008;Funiciello et al, 2008;Garel et al, 2014;Magni et al, 2014;Schellart, 2008a;Xue et al, 2020).…”

“…Previous geodynamic models (Bellahsen et al., 2005; Di Giuseppe et al., 2008; Funiciello et al., 2008; Heuret et al., 2007; Ribe, 2010; Schellart, 2008a; Xue et al., 2020) and tomographic models (Van Der Voo et al., 1999; Widiyantoro et al., 1999; Wortel & Spakman, 2000) of subducting slabs have distinguished three main subduction styles as determined by the trench motion and the slab geometry: (1) continuous trench retreat with a slab rollback geometry (lazy “S” or “Z” slab geometry, Xue et al. [2020]; e.g., Calabria subduction zone, Scotia subduction zone, Tonga subduction zone), (2) long‐term trench advance and slab rollover forming a “U” shaped slab geometry rotated 90° (e.g., India‐Eurasia collision zone, Makran subduction zone), and (3) intermittent trench retreat and trench advance forming a steep folded slab pile (e.g., Mariana subduction zone). The first and the third subduction styles are relatively common in nature, and the patterns and mechanisms of OPD in these subduction styles have been investigated in buoyancy‐driven subduction modeling works (Alsaif et al., 2020; Chen et al., 2015, 2016; Duarte et al., 2013; Hertgen et al., 2020; Holt et al., 2015; Yang et al., 2018).…”

“…We present four dynamic upper‐mantle subduction analog models with an overriding plate that evolve in three‐dimensional space and which are driven only by the negative buoyancy of the slab, following an approach developed in earlier works (Chen et al., 2016, 2017; Duarte et al., 2013). Different subduction styles can be achieved by varying different geophysical parameters, for example, viscosity ratio of the subducting plate and ambient mantle material (Di Giuseppe et al., 2008; Funiciello et al., 2008; Garel et al., 2014; Ribe, 2010; Schellart, 2008a), plate thickness (Bellahsen et al., 2005; Ribe, 2010; Schellart, 2008a), plate length (Xue et al., 2020) and inclusion of lateral continental margins (Magni et al., 2014). In this study, we include two experimental sets that differ by their subducting plate thickness, to produce the two different subduction styles.…”