Delamination in collisional orogens: Thermomechanical modeling

Abstract

[1] Modes of mantle delamination in collision zones are discussed in the light of 2D numerical modeling. Freely evolving thermomechanical models take into account phase changes in the mantle and melting in the crust. Distinct modes are identified, in which orogens undergo mantle delamination concurrently or after collision. Delamination propagates along the Moho of the subducted plate together with the retreating trench, provided that slab pull is sufficient and that the meta-stability of the crust-lithospheric mantle interface is overcome. Topography is an instantaneous response to delamination and migrates with the focused and localized separation between crust and lithospheric mantle (delamination front). Early exhumation of high-pressure rocks is followed by exhumation of high-temperature, partially molten rocks. Convective stabilization of delamination outlasts slab break-offs and impedes renewed build-up of mechanically strong lithospheric mantle by static cooling. Parameter studies investigate the sensitivity of delamination to the age of the subducted oceanic plate, the collision rate, the mantle rheology, and explore the effects of melting and sedimentation. Mantle flow patterns that form around delamination and subduction are sensitive to and often limited by the semi-permeable 670 km spinelperovskite transition, demonstrating that phase-changes are essential factors. Delamination may account for the formation of complex boundary zones between continents, such as between Africa and Europe in the Mediterranean, where transient compression and extension, the lack of mantle lithosphere, and the exhumation of high-grade metamorphic core complexes are features also obtained in our modeling results.

Using open sidewalls for modelling self-consistent lithosphere subduction dynamics

“…Jadamec and Billen, 2010;Piromallo et al, 2006;van Hunen et al, 2011) may proof beneficial. In 3-D, flow patterns have larger degrees of freedom as toroidal flow can be excited, e.g.…”

“…These profiles clearly illustrate the difference between the flow regimes for these two models. Particularly for model OO6, it illustrates the channel flow regime of the asthenosphere as well as plate-like behaviour (van den Berg et al, 1991;Turcotte and Schubert, 2002). Flow velocities in the asthenosphere channel are much higher for the open boundary case, while plate velocities are higher for the closed boundary case with free plates.…”

“…, w is the half-width of kth transition zone, z tr and T tr are the reference depth and temperature of the phase transition, respectively, γ k is the Clapeyrone slope, T is the temperature (Cristensen and Yuen, 1985;van Hunen, 2001). …”

“…The limited spatial domain particularly requires prescribing boundary conditions on the vertical sidewalls of the domain. These conditions are an important influence on the development of the model interior (Quinquis et al, 2011;Duretz et al, 2011Duretz et al, , 2012Ueda et al, 2012). The usual attempt to reduce possible sidewall influence is by moving these far away from where subduction occurs by using a sufficiently large aspect ratio of model length to depth (e.g.…”

“…van Hunen et al, 2000;Baes et al, 2010;Quinquis et al, 2011), or periodic conditions requiring that the through-flow at one side is the mirror image of through-flow on the other (e.g. Enns et al, 2004;Capitanio et al, 2010).…”