Exhumation of (U)HP/LT rocks

Crustal rocks metamorphosed at ultra-high pressure (UHP) record burial to 100–150 km depths and subsequent return to the surface. Although it is well accepted that UHP rocks are formed by deep subduction of continental passive margin rocks, the mechanisms by which these rocks are exhumed remain debated.

Here, three-dimensional thermo-mechanical analogue models investigate how diachronous slab breakoff may lead to the exhumation of subducted continental crust. Slab breakoff initiates spontaneously in one location and migrates laterally along the plate boundary, causing a transient excess downward pull force on the plate boundary in front of the propagating slab tear. This pull force locally reduces the pressure between the plates, which promotes buoyancy-driven exhumation of subducted crust.

However, both the surface area undergoing the pressure reduction and its duration are limited. Our experiments show that the rate of slab breakoff propagation controls both the duration of the pull force and the magnitude of pressure reduction. Our results further demonstrate that exhumation occurs where the slab breakoff propagation rate is lowest, rather than where the pull force is strongest, corresponding to where the slab tear initiates or terminates.

Here is the link to the JSG paper.

Analogue modelling of diachronous slab break-off causing exhumation of subucted crust


Illustration of proposed dual-mechanism exhumation of (U)HP rocks associated with propagating breakoff. 1: Horizontal propagation of detachment in the subducted lithosphere; 2: Excess slab pull generated ahead of the propagating tear; 3: Normal pull is produced on interplate zone causing reduction of pressure; 4: Pressure reduction allows buoyancy-driven exhumation of subducted crust; 5: After passage of tear, the lower plate bounces upward causing normal push on plate boundary and increase in interplate pressure; 6: Increased pressure terminates and crustal units are squeezed further upward.

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