Although positive buoyancy of young lithosphere near spreading centers
does not favor subduction, subduction initiation near ridges may occur
upon forced compression due to their intrinsic rheological weakness. It
has been repeatedly proposed that detachment faults may directly control
the nucleation of new subduction zones. However, recent 3D numerical
experiments suggested that direct inversion of a single detachment fault
does not occur. Here, we further investigate numerically this
controversy by focussing on the influence of brittle-ductile damage on
the dynamics of near-ridge subduction initiation. We model
self-consistently the inversion of inherited long-term spreading
patterns using 3D high-resolution thermomechanical numerical models
combining strain weakening of faults with grain size evolution in
lithospheric mantle. Numerical results show that development and
evolution of detachment faults are strongly affected by the
brittle-ductile damage coupling. Forced compression predominantly
thickens the weakest near-ridge region of oceanic lithosphere, and
reactivates inherited extensional faults. This results in rotation of
blocks along reactivated faults leading to their subsequent locking. As
the result, the development of a new megathrust zone occurs, which
accommodates further shortening and subduction initiation. Strain
weakening has a key impact on the collapse of thickening mid-ocean ridge
region and the occurrence of near-ridge subduction initiation. In
contrast, grain size evolution of mantle plays a subordinate role in
these processes by slightly modifying the localization of shear zones
near brittle-ductile transition. Through comparing with the geological
record, our numerical results provide new helpful insights into natural
near-ridge subduction initiation processes recorded by the Mirdita
ophiolite of Albani.