Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth’s history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides1, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia2. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback3 and transient episodes of orogenesis and crustal shortening4,5,6,7, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.
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L.M. acknowledges support from the Australian Research Council’s Discovery Projects funding scheme (projects DP130101946 and DP110101697) and use of the NCI National Facility in Canberra, Australia, which is supported by the Australian Commonwealth Government. P.G.B. acknowledges the support of the Monash Research Accelerator Program. M.S.M. acknowledges the support of the National Science Foundation under grant no. EAR-1054638. R.C. publishes with the permission of the Director of the Geological Survey of Victoria. Underworld development was supported by AuScope, under the National Collaborative Research Infrastructure Strategy.
Extended data figures
Evolution of the model with the 80 Myr old slab (grey with yellow grid) and weaker overriding plate (blue with light blue grid). The indenter is shown in red. The strain rate field close to the surface is superimposed on the colouring of the material domains to show high strain rates as red tones and intermediate strain rates in yellow/green. Snapshots of this video are shown in Extended Data Figure 3.
As video 1, but with a stronger overriding plate as described in Table 1. Snapshots of this video are shown in Figure 2.
Evolution of the model with the 80Myr old slab viewed from beneath the overriding plate looking towards the incoming indenting ribbon. Colours are the same as described for video 1. The white/red balls are finite strain markers located under the oceanic plate at the start of the simulation.
As video 1, but with a 120 Myr old plate.
As video 1, but with a 120 Myr old plate and a stronger overriding plate as described in Table 1. Snapshots of this video are shown in Extended Data Figure 3.
As video 3 but with a 120 Myr old plate.
About this article
Petrotectonic framework of granitoids and associated granulites at Nagavalli Shear Zone (NSZ), Eastern Ghats Belt: Evidence of a late transpression orogeny
Journal of Earth System Science (2015)