Geodynamics of divergent double subduction: 3‐D numerical modeling of a Cenozoic example in the Molucca Sea region, Indonesia

Abstract

Geological observations reveal existence of a unique form of plate subduction featuring subduction on both sides of one single oceanic plate, which is termed divergent double subduction (DDS). DDS may play an important role in facilitating tectonic processes like closure of oceanic basins, accretion and amalgamation of magmatic arcs, and growth of continents. However, this type of subduction has been largely a conceptual model and the geodynamics behind DDS are still poorly constrained. The Molucca Sea subduction zone in SE Asia has been considered as a Cenozoic example of DDS based on geophysical and geological data and provides an opportunity for detailed assessment of how DDS occurs. Here we present 3‐D numerical modeling with aims to reproduce the geodynamic processes of DDS. Several factors that may have important influences on the evolution of DDS are evaluated, including the geometry of the subducting plate, the order of subduction initiation on both sides, the far‐field boundary conditions and thickness of the overriding plates, and the negative buoyancy of the subducting plate. Our results reproduce the observed asymmetrical shape of the subducting Molucca Sea plate and the bending of Halmahera and Sangihe arcs and suggest that DDS is possible if effective escape of the slab‐trapped upper mantle overcomes the space problem, otherwise the slab‐trapped mantle may hinder the sustainability of subduction. We therefore conclude that DDS is associated with closure of narrow and short oceanic plate, and large‐scale double subduction is rare in nature probably owing to space problem.

Modeling Slab‐Slab Interactions: Dynamics of Outward Dipping Double‐Sided Subduction Systems

“…These results add weight to recent studies that emphasize the importance of interactions between proximal slabs (Di Leo et al, ; Holt et al, ; Király et al, ; Zhang et al, ). In natural double‐sided subduction zones, slabs do not always behave as single entities, but their evolutions are strongly linked to neighboring slabs through the lithosphere or the mantle, depending on the distance between the two subduction zones.…”

“…The evolution of the two oppositely dipping oceanic slabs is ideally symmetrical, as it was shown in previous numerical results (Di Leo et al, 2014;Holt et al, 2017;Zhang et al, 2017). This was also observed in the laboratory models, in which the subducting slabs achieve symmetry during their evolution ( Figure 3).…”

“…Furthermore, independent of initial geometric asymmetries, the symmetry of the system is obtained after both slabs reach the bottom boundary, which means that the system is self-stabilizing. However, when mechanical heterogeneities are included in the setup, the evolution departs from this simple case illustrating the relevant role of slab interaction, as previously shown by Zhang et al (2017).…”

Seismic Anisotropy in the Java‐Banda and Philippine Subduction Zones and its Implications for the Mantle Flow System Beneath the Sunda Plate

“…The trench‐normal signature is consistent with that observed in the local S wave splitting measurements from deep events (Di Leo et al, ), which has been associated with the westward Sangihe subduction process. The trench‐normal fast directions observed in this study can be readily developed by the 2‐D corner flow in the mantle wedge controlled by the westward subduction of the Philippine Sea Plate, and the westward deep subduction of the Molucca Sea Plate perhaps further enhances the trench‐normal flow (Zhang et al, ). The subduction of the Molucca Sea Plate may thus play an important role in influencing the regional mantle dynamics due to its deep subduction.…”

“…In addition, the Sunda Plate is also characterized with the existence of divergent double subduction, which is a form of plate subduction featuring subduction on both sides of one single oceanic plate. More specifically, the Molucca Sea subduction in Southeast Asia has been considered as a Cenozoic example of divergent double subduction, which could thus have played an important role in tectonic evolution of Southeast Asia (Király et al, ; Zhang et al, ). It is worth mentioning that double‐slab subduction with inward‐dipping directions is also a characteristic feature of Southeast Asia; for example, the South China Sea Plate is subducting underneath the Philippine Sea Plate, whereas the Philippine Sea Plate is penetrating below the southern Sunda Plate (Figure a).…”