# Vertical ductile thinning and its contribution to the exhumation of high-pressure rocks: the Cycladic blueschist unit in the Aegean

The contribution of vertical ductile thinning to the exhumation of high-pressure rocks is evaluated by estimating finite strain
in 75 exhumed high-pressure rocks of the Cycladic blueschist unit in the Aegean Sea, Greece, and western Turkey. Strain data
indicate heterogeneous deformation; principal stretches are 1.24–5.03 for *S*_{X}, 0.63–2.53 for *S*_{Y} and 0.10–0.81 for *S*_{Z}, with a tensor average of *S*_{X}:*S*_{Y}:*S*_{Z}=1.52:1.28:0.51. A 1D numerical model, which integrates velocity gradients along a vertical flow path with a steady-state
orogen, is used to estimate the contribution of ductile thinning of the overburden of the high-pressure rocks to exhumation.
Using a strain-rate law that is proportional to depth, averaged results show that ductile flow contributed *c*. 20% to exhumation. A major implication is that the vertical strain in the exhumed rocks is an overestimate of the contribution
that ductile flow makes to the total exhumation. A proportional strain-rate law that scales linearly with depth implies that
material points rising towards the surface move quickly out of the more rapidly deforming part of the orogen. Therefore, very
large vertical strains >90% in deeply exhumed rocks are needed for vertical ductile thinning to be a major exhumation process.