2D numerical analysis on microcontinents subductability: subduction or collision?

Oceanic domains can be characterised by lithological heterogeneities, such as microcontinents and continental ribbons, with dimensions vary from tens to hundreds of kilometres. In particular, microcontinents are completely detached from continental margins and isolated by oceanic lithosphere (Gaina & Whittaker, 2020). While previous works have analyzed the impact of various rhological parameters on the evolution of subduction systems characterized by oceanic plateaus, seamounts, or microcontinents (e.g., De Franco et al., 2008; Tetreault & Buiter, 2012), these models typically focused on very large terranes located at significant distances from the initial trench (150-200 km), emphasizing mechanical effects with less attention to thermal effects. Here, our goals are 1) to evaluate the effects on the microcontinent subductability of different lengths (ranging from 25 to 100 km long) of microcontinents located at varying distances from the upper plate (ranging from 25 to 100 km) and of different velocities of the plates; and 2) to analyze the thermo-mechanical effects induced by the collision or the subduction of the microcontinents.

We observed that four different styles of subduction can develop when microcontinents are introduced into the system: (1) continuous subduction; (2) continuous subduction with jump of the subduction channel; (3) interruption and reinitiation of the subduction; (4) continental collision. Our results show a direct dependence between the length of microcontinents, the length of the inner ocean, and the capability to be subducted or accreted. In general, continuous subductions after the collision of the microcontinent do not occur if the microcontinent is equal to or longer than its initial distance from the trench. We also observed that subductability of the microcontinent is favored for higher velocities of the upper plate, while it is more difficult in case of higher velocities of the lower plate. Therefore, the velocity of both plates and the length of a microcontinent are significant parameters to consider for better constraining geodynamic reconstruction in the case of exhumed rocks characterized by contrasting maximum pressure recorded (Regorda & Roda, 2024).

References

C. Gaina & J. Whittaker, 2020. Microcontinents. Encyclopedia of Solid Earth Geophysics. Ed. by H. K. Gupta. Encyclopedia of Earth Sciences Series. Springer, Cham, doi:10.1007/978‐3‐030‐10475‐7_240‐1.

R. De Franco, R. Govers & R. Wortel, 2008. Nature of the plate contact and subduction zones diversity. Earth and Planetary Science Letters, 271, 245–253, doi:10.1111/j.1365‐246X.2008.03857.x.

A. Regorda & M. Roda, 2024. Thermo‐Mechanical Effects of Microcontinent Collision on Ocean‐Continent Subduction System. JGR: Solid Earth, 129, e2024JB029908, doi:10.1029/2024JB029908.

J. L. Tetreault & S. J. H. Buiter, 2012. Geodynamic models of terrane accretion: Testing the fate of island arcs, oceanic plateaus, and continental fragments in subduction zones. Journal of Geophysical Research: Solid Earth, 117, doi:10.1029/2012JB009316.