Thermo‐Mechanical Effects of Microcontinent Collision on Ocean‐Continent Subduction System

Microcontinents are globally recognized as continental regions partially or entirely surrounded by oceanic lithosphere. Due to their positioning, they may become entangled in subduction zones and undergo either accretion or subduction. High-pressure metamorphism in subducted continental rocks supports the idea that microcontinents can be subducted, regardless of their low densities. In this study, we used 2D numerical models to simulate collision of microcontinents with different lengths located at various distances from the upper plate in a subduction system characterized by different convergence velocities, in order to examine their effects on the thermo-mechanical evolution of subduction systems. Specifically, we analyzed the conditions that favor subduction or accretion of microcontinents and investigated how their presence affects the thermal state within the mantle wedge. Our results reveal that the presence of microcontinents can lead to four styles of subduction: (a) continuous subduction; (b) continuous subduction with jump of the subduction channel; (c) interruption and reinitiation of the subduction; (d) continental collision. We discovered that longer microcontinents and higher velocities of the subducting plate contrast a continuous subduction favoring accretion, whereas farther initial locations from the upper plate and higher velocities of the upper plate favor the subduction of the microcontinent. In addition, we observed that the subduction style has direct effects on the thermal state, with important implications for the potential metamorphic conditions recorded by the subducted continental rocks. In particular, models characterized by parameters that favor the subduction of a larger amount of continental material from the microcontinent exhibit warm mantle wedges.