Opposite Subduction Polarity in Adjacent Plate Segments

Abstract

Active and fossil subduction systems consisting of two adjacent plates with opposite retreating directions occur in several areas on Earth, as the Mediterranean or Western Pacific. The goal of this work is to better understand the first‐order plate dynamics of these systems using the results of experimental models. The laboratory model is composed of two separate plates made of silicon putty representing the lithosphere, on top of a tank filled with glucose syrup representing the mantle. The set of experiments is designed to test the influence of the width of plates and the initial separation between them on the resulting trench velocities, deformation of plates, and mantle flow. Results show that the mantle flow induced by both plates is asymmetric relative to the axis of each plate causing a progressive merging of the toroidal cells that prevents a steady state phase of the subduction process and generates a net outward drag perpendicular to the plates. Trench velocities increase when trenches approach each other and decrease when they separate after their intersection. The trench curvature of both plates increases linearly with time during the entire evolution of the process regardless their width and initial separation. The interaction between the return flows associated with each retreating plate, particularly in the interplate region, is stronger for near plate configurations and correlates with variations of rollback velocities. We propose that the inferred first‐order dynamics of the presented analog models can provide relevant clues to understand natural complex subduction systems.

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

“…We measured the trench curvature in all models (Figures 10a–10d) by fitting the trench with a circular segment and define the ratio ( h/s ) of segment height ( h ) and the chord of the segment ( s ) as the trench curvature (Figure 10e), following the method in Peral et al (2018). The trench attains a concave geometry toward the mantle wedge in all experiments (Figures 10a and 10b).…”

Evidence of Segmentation in the Iberia–Africa Plate Boundary: A Jurassic Heritage?

“…Further east, the westernmost Mediterranean is floored by HP metamorphic basement (Alboran segment), which transitions to a highly intruded and oceanic-type Neogene crust (Algerian segment). The feasibility of tectonic processes dominated by opposite subduction polarity in adjacent plate segments has been demonstrated by analog modelling [55]. The diffuse character of the IAPB is related to (i) the complex tectonic pattern resulting from the convergence between the Iberia and Africa margins with its inherited en-echelon geometry, (ii) the arcuate slab roll-back of the Alboran segment with the formation of an accretionary wedge in the Gulf of Cadiz and the back-arc Alboran basin, and (iii) the tightening of the Betic-Rif orogen owing to protracted Iberia-Africa convergence.…”

Analog and Numerical Experiments of Double Subduction Systems With Opposite Polarity in Adjacent Segments

“…Furthermore, in settings where oceanic plates are highly segmented, subduction is commonly characterized by very arcuate trenches of limited extent showing different slab dip orientations. Indeed, we can observe double subduction systems with parallel trenches with inward-dipping polarity as in Luzon [Bautista et al, 2001], outward-dipping polarity as in Molucca Sea [Zhang et al, 2017], or same-dipping polarity as in Philippine Sea [Faccenna et al, 2018]. In addition, there are subduction systems characterized by two adjacent slabs retreating in opposite directions as in Taiwan [Lallemand et al, 2001], New Zealand [Lamb, 2011], the Western Mediterranean [Vergés and Fernàndez, 2012] and the Alps-Apennine junction in Italy [Vignaroli et al, 2008].…”

“…The dynamics of double subduction systems have been investigated by a wealth of numerical and analog experiments involving different configurations [e.g., Di Leo et al, 2014;Holt et al, 2017;Mishin et al, 2008;Pusok and Stegman, 2019]. In particular, subduction systems characterized by two adjacent slabs retreating in opposite directions have been tested with 3D numerical [Király et al, 2016] and analog experiments [Peral et al, 2018]. Whereas Király et al [2016] focused on the interactions between the return flows generated by the respective retreating slabs, Peral et al [2018] investigated plate deformation and variations in trench retreat velocities.…”