Abstract
During closure of an ocean through subduction and continental collision,
bathymetric highs such as microcontinents can accrete, collide, or
partially or completely subduct. Such interaction of future accreted
terranes (FATs) with the overriding continent will modify the dynamics
of the subduction zone, affecting its length and frictional resistance,
and thus the force balance of the subduction system. Accreted
microcontinents and microcontinental fragments are preserved in backarcs
and collisional orogens, demonstrating that multiple terranes can
accrete during a single Wilson-cycle, in what is termed accretionary
orogenesis. In this study, we use thermo-mechanical numerical
experiments of microcontinent-continent collision events to investigate
parameters that influence whether microcontinents accrete, subduct, or
collide. Our results indicate that multiple accretionary episodes are
possible, but that a weak basal detachment layer within each FAT is
paramount for such a scenario to occur. The introduction of a
microcontinent, or FAT, in the subduction zone will affect the balance
between slab-pull, far-field forces, and the subduction interface
resistance. The strength (and rheological stratification) of the FATs
determines the evolution of the subduction interface resistance
throughout the collision event, exerting a first order control on the
resulting geodynamic scenario. Collision with a strong FAT significantly
increases the subduction interface resistance promoting terrane
subduction and localization of deformation away from the subduction
interface. In turn, collision with a weak FAT increases subduction
interface resistance only mildly, allowing for multiple accretion
events.