**2. The Ampferer-type subduction: convergence and assembly of the previously rifted lithosphere**

Ampferer-type subduction occurs only at passive continental margins that hyperextend into rift basins, often accompanied by exhumation of the (subcontinental) mantle and may reach the stage of (magma-poor) embryonic oceans [7]. Such an embryonic basin-margin system is likely to be more laterally homogeneous than ocean basins, which contain significant spreading ridges. Under these conditions, the mechanical weakness of the serpentinized mantle and the hyper-thinned continental lithosphere serve as focal points for the initiation of convergence and downward thrusting of these basins beneath passive continental boundaries [7, 30–32]. The main features for recognizing Ampferer-type subductions are (i) coherent structural units or nappes (flake tectonics) transported over long distances modified by moderate deformation and comprising the (ultra-) high-pressure continental and oceanic fragments and (ii) the lack of Penrose-type oceanic crustal fragments [7, 38]. The Ampferer-type subductions instead comprise fragments of basins flooded by exhumed subcontinental mantle, like the magma-poor Iberia-Newfoundland oceancontinent transition zones (OCTs) [39–41].
