We conducted a set of numerical experiments to study the evolution of a
subduction-collision system subject to spontaneous slab breakoff. The
study takes into account complex theological behaviour including
plasticity, viscous creep and Peierls creep.
By varying the oceanic slab age and initial plate convergence rate, four
different end-members were observed. In this parameter space, breakoff
depth can range from 40 to 400 km. Each of those breakoff modes displays
complex rheological behaviour during breakoff. Peierls creep in olivine
turns out to be a key mechanism for slab breakoff, generally causing
slabs to break earlier and at shallower depths.
Models involving different depths of breakoff are subject to different
topographic evolution, but always display a sharp breakoff signal. Post
breakoff uplift rates in foreland and hinterland basins range between
0.1 km/My for deep detachment and 0.8 km/My for shallow detachment. Our
systematic study indicates an approximately linear relationship between
the depth of breakoff and the rate of uplift.
Continental crust subduction was observed in breakoff experiments
involving oceanic lithosphere older than 30 My. Different exhumation
processes such as slab retreat and eduction occur according to the depth
of breakoff. These models are likely to undergo large rebound following
breakoff and plate decoupling if the subducted oceanic slab is old
enough. (C) 2010 Elsevier B.V. All rights reserved.