Some thermomechanical aspects of the subduction of continental lithosphere

Abstract

On the basis of thermal and mechanical modeling, it is concluded that the subduction of continental lithosphere can lead to its breakup and the formation of a new plate contact within the middle or lower crust. As a result, (part of) the subducting continental crust is transferred to the upper plate. Breakup is caused by the resistive forces acting upon subducting continental crust, due to the buoyancy of crustal material and to friction at the plate contact, as well as the decrease in strength of the subducting crust once it has been subducted to a depth of a few tens of kilometers. The crustal thickness and the thermal and compositional structure of the continental crust just before the onset of subduction have a large influence on the depth to which continental crust can be subducted (prior to its breakup). The depth to which continental crust can be subducted coherently decreases as the surface heat flow or the crustal thickness of the subducting continental plate increases. In many cases, breakup is found to occur at a time when the upper surface of the continental plate has been subducted to a depth of 25–50 km. The subduction of a cold continental shield or of continental lithosphere with a relatively small crustal thickness, on the other hand, may lead to the subduction of both upper and lower crust to mantle depths.

Subduction Zone Geodynamics

“…However, the eclogitized granulites are associated with Precambrian gabbros, anorthosites and peridotites (Tucker et al, 1991). In both cases, garnet peridotites are associated with continental rocks and their exhumation is explained by decoupling of the continental slice from the descending oceanic lithosphere due to the positive buoyancy of sialic continental rocks within the subduction channel (Van der Beuckel, 1992;Ernst, 1999Ernst, , 2005. If this hypothesis is confi rmed, it reinforces the idea that only the upper crust is exhumed.…”

“…Furthermore, sialic crustal rocks remain buoyant during subduction because their density is not signifi cantly modifi ed during subduction. 12d) (Van der Beuckel, 1992;Davies and von Blanckenburg, 1995). Decoupling of a crustal slice from the descending slab requires the buoyancy forces exceeding the strength of the upper crust, which may occur at a depth of 90 to 140 km (Fig.…”

Garnet–chloritoid–kyanite assemblages: eclogite facies indicators of subduction constraints in orogenic belts

“…Importantly, Carry et al. (2009), along with the earlier work of den Beukel (1992), showed that thermal weakening of the slab top is a critical control on when detachment occurs.…”

From subduction to collision: Control of deep processes on the evolution of convergent plate boundary

“…1. Extension forces in the slab eventually result in slab break‐off, when they are large enough to overcome the strength of the entire subducting slab [ van den Beukel , 1992; Davies and von Blanckenburg , 1995; Yoshioka and Wortel , 1995; Wong A Ton and Wortel , 1997]. Published numerical simulations show that slab detachment is expected to occur following subduction and during the early stages of continental collision.…”