Flat subduction versus big mantle wedge: contrasting modes for deep
hydration and overriding craton modification
Abstract
Subduction-induced deep hydration and water cycling may play significant
roles in the modification and destruction of the overriding cratonic
lithosphere. Two contrasting modes are generally proposed: (1) flat
subduction (FS) regime with slab subducting sub-horizontally beneath the
overriding lithosphere, and (2) big mantle wedge (BMW) regime with slab
flattening in the mantle transition zone. Here, systematic
petrological-thermomechanical models are conducted to investigate the
fluid/melt activities in the contrasting subduction regimes as well as
their effects on the modification of overriding lithosphere. The model
results indicate that the dehydration process in the FS regime can
significantly modify the overriding lithosphere for a region of about
600 km from the trench. During the progressive flat subduction, the
partial melting and magmatism migrate towards the inner land of the
overriding plate, which will be reversed and backward to the trench
during the transition from flat to steep subduction. On the other hand,
the deep hydration in the BMW regime is strongly dependent on the
sub-crustal serpentinite layer in the subducting slab, whereas the
oceanic crust cannot carry water to the transition zone. The
modification of the overriding lithosphere in the BMW regime occurs in a
larger region of >1000 km from trench, which is however
generally slower and weaker. The modification and destruction of North
China Craton is more likely to be controlled by the flat subduction of
paleo-Pacific plate in the late Jurassic to early Cretaceous, which may
be accompanied by the effects of deep water cycling in the BMW regime.