Thermo-mechanical effects of microcontinent collision on ocean-continent
subduction system
Abstract
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 support 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 sizes 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 either 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: 1) continuous subduction; 2) continuous subduction
with jump of the subduction channel; 3) interruption and restart of the
subduction; 4) continental collision.
We discovered that larger microcontinents and higher velocities of the
subducting plate contrast a continuous subduction favoring accretion,
while farther initial locations from the upper plate and higher
velocities of the upper plate favor the subduction of the
microcontinent.
Additionally, we observed that the style of subduction has direct
effects on the thermal state, with important implications for the
potential metamorphic conditions recorded by 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.