The Subductability of Continental Lithosphere: The Before and After Story

Reconstructing the Alps–Carpathians–Dinarides as a key to understanding switches in subduction polarity, slab gaps and surface motion

“…In addition, geodynamic modeling has shown that continental subduction is possible where the crust, especially the lower crust, is thin and the underlying lithospheric mantle is sufficiently cold and thick to render it neutrally, or even negatively buoyant (Capitanio et al 2010;Afonso and Zlotnik 2011). All of these conditions are met by the Southern Alpine lithosphere, which has a very dense lower crust comprising Paleozoic granulite-facies rocks (e.g., Ivrea Zone : Fountain 1976;Zingg et al 1990) and which was severely attenuated during Early Mesozoic rifting (Bernoulli et al 1990(Bernoulli et al , 2003Handy and Zingg 1991;Handy et al 1999;Manatschal et al 2007).…”

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

“…Because of their geographic relation to continents (as part of the passive margin architecture), continental fragments will most likely precede continents into the subduction zone and continent-continent collision. But not all continental crust will accrete; the subductability of continental crust has been proven by coesite found in exhumed ultrahigh pressure terranes (Chopin, 2003) and geodynamic modeling (Afonso and Zlotnik, 2011). The collision of continental fragments with continents can lead to slab detachment and then exhumation of these continentally derived terranes.…”

“…Although buoyancy is an enabling factor in crustal accretion at subduction zones, it is likely that accretion can occur because weak layers in the FAT crust enable detachments and shear zones to develop within the subduction zone as the crust is subducting. Recent geodynamic experiments show that if a weak zone or detachment fault is present within the crust of the subducting crustal region, whether it is an island arc, oceanic plateau, or continental fragment, accretion will occur and leave a severely thinned terrane (Afonso and Zlotnik, 2011;Tetreault and Buiter, 2012). In island arcs, possible delamination units are the felsic middle crust and the CMTL.…”

“…Finally, the force of the subducting slab drives subduction and can most likely overcome the buoyancy of small crustal units (Molnar and Gray, 1979;Cloos, 1993). In addition, eclogitization of the oceanic lithosphere will increase the negative buoyancy of the slab and even allow continental crust to subduct (Afonso and Zlotnik, 2011).…”

“…Seno (2008) calculated the forces in the subduction zone necessary for a crustal block of continental affinity to shear off of a subducting plate and concluded that accretion can only occur in a relatively dry (low pore pressure) subduction interface. More recently, analog and numerical geodynamic experiments have examined the subductability of oceanic LIPs, submarine ridges, island arcs, continental submarine plateaus, and microcontinents and the effects on the subduction zone dynamics after subduction (Ellis et al, 1999;van Hunen et al, 2002;Boutelier et al, 2003;Martinod et al, 2005;Espurt et al, 2008;De Franco et al, 2008;Mason et al, 2010;Afonso and Zlotnik, 2011;Tetreault and Buiter, 2012). Of course, observations of thick oceanic LIPs subducting (such as the Ontong Java and Hikurangi plateaus; Mann and Taira, 2004;Scherwath et al, 2010;Bassett et al, 2010) and the relative absence of entire island arc crusts in the geologic record (Condie and Kröner, 2013) indicate that the accretion, subduction, and collision of thick crustal regions might not always follow the analytical and geodynamic estimates.…”