Late Orogenic Heating of (Ultra)High Pressure Rocks: Slab Rollback vs. Slab Breakoff

Abstract

Some (ultra)high-pressure metamorphic rocks that formed during continental collision preserve relict minerals, indicating a two-stage evolution: first, subduction to mantle depths and exhumation to the lower-crustal level (with simultaneous cooling), followed by intensive heating that can be characterized by a β-shaped pressure–temperature–time (P–T–t) path. Based on a two-dimensional (2D) coupled petrological–thermomechanical tectono-magmatic numerical model, we propose a possible sequence of tectonic stages that could lead to these overprinting metamorphic events along an orogenic β-shaped P–T–t path: the subduction and exhumation of continental crust, followed by slab retreat that leads to extension and subsequent asthenospheric upwelling. During the last stage, the exhumed crustal material at the crust–mantle boundary undergoes heating from the underlying hot asthenospheric mantle. This slab rollback scenario is further compared numerically with the classical continental collision scenario associated with slab breakoff, which is often used to explain the late heating impulse in the collisional orogens. The mantle upwelling occurring in the experiments with slab breakoff, which is responsible for the heating of the exhumed crustal material, is not related to the slab breakoff but can be caused either by slab bending before slab breakoff or by post-breakoff exhumation of the subducted crust. Our numerical modeling predictions align well with a variety of orogenic P–T–t paths that have been reported from many Phanerozoic collisional orogens, such as the Variscan Bohemian Massif, the Triassic Dabie Shan, the Cenozoic Northwest Himalaya, and some metamorphic complexes in the Alps.

Numerical modeling of tectonic underplating in accretionary wedge systems

“…Figure 1B illustrates a simplified schematic clockwise pressure-temperature (P-T) path for material following a typical particle path of shallow-dipping underthrusting and subvertical uplift (e.g., Likhanov, 2020). However, P-T paths of deeply subducted rocks commonly indicate more complicated multiphase burial and exhumation histories (e.g., Angiboust et al, 2018;Sizova et al, 2019). Sediments accreted at the wedge front may also experience elevated pressures and temperatures when further incorporated in the wedge body, but they show a distinct difference in the relative timing between thrusting and peak metamorphism (van Gool and Cawood, 1994): basal accretion occurs at peak metamorphic conditions, while peak metamorphism postdates thrust imbrication related to frontal accretion ( Fig.…”

Evidence for and significance of the Late Cretaceous Asteroussia event in the Gondwanan Ios basement terranes

“…It is no different in the Cyclades. The Cycladic archipelago preserves the results of the destruction of an extensive terrane stack that extended from the Hellenides in Greece to the Taurus Mountains in Turkey (Gautier and Brun, 1994a, b;Kempler and Garfunkel, McKenzie, 1977;Taymaz et al, 1991). The debate as to the nature of exhumation processes will not be resolved by a sole focus on the Cycladic eclogite-blueschist belt, as demonstrated in this paper.…”

“…Such effects were not observed in the Cyclades. Sizova et al (2019) also showed the "peeloff" model (Brun and Faccenna, 2008) to be unlikely in the Aegean region.…”

Evidence for the Late Cretaceous Asteroussia event in the Gondwanan Ios basement terranes

“…Although the slab-peel model is consistent with enhanced heat flow during crustal stretching after the accretion event, Lister and Forster (2009) show that such a model requires the asthenosphere to be uplifted to sufficiently shallow levels that a period of major basaltic volcanism would have taken place, with volumes comparable to those observed in some large igneous provinces. Sizova et al (2019) also showed the "peel off" model (Brun and Faccenna, 2008) to be unlikely.…”