Dynamic processes and mechanisms for collision to post‐orogenic extension in the Western Dabie Orogen: Insights from numerical modeling

Abstract

Post‐orogenic extension is the last stage of a tectonic process towards the end of each Wilson cycle in both ancient and modern continental collisional zones, but their dynamics, controlling factors, and roles for the post‐orogenic extension processes remain debatable. We present the first two‐dimensional thermo‐mechanical numerical model of double sutures inspired by the Western Dabie Orogen to investigate the dynamics of post‐orogenic extension. Our results indicate that the pro‐continent re‐subduction can delay or stop regional extensional deformation and subsequent voluminous magmatic activity caused by slab breakoff in the collision zone. After the end of the collision stage, the re‐subduction slab under the residual lithosphere in the model with lower convergence, as a strong unit, can maintain the gravitational balance of the whole post‐orogen system, whether crust eclogitization is considered or not. If the oceanic crust and micro‐continental crust eclogitization are applied to the model with medium convergence, the lower crust and the residual lithospheric mantle in the collision zone will be completely removed by the gravitational instability and upwelling of asthenospheric mantle. The lithospheric architecture of this model with the medium convergence and crust eclogitization is very similar to the present‐day tomography. However, in the model with higher convergence, lithosphere delamination can occur only by upwelling of asthenosphere, whether crustal eclogitization is considered or not. On the basis of a comparison of numerical results with field data from the Western Dabie Orogen, we suggest that the dynamics of post‐orogenic extension in the Western Dabie Orogen is controlled by re‐subduction of the North China Block and crustal eclogitization after high pressure/ultrahigh pressure collision. Thus, the observed regional extensional deformation and voluminous magmatic activity in the Western Dabie Orogen can be self‐consistently explained by interactions between the two sutures and crustal eclogitization.

Slab Rollback Versus Delamination: Contrasting Fates of Flat‐Slab Subduction and Implications for South China Evolution in the Mesozoic

“…The flat‐slab subduction is generally not stable and will evolve to the normal/steep subduction finally by either slab rollback or delamination. In addition, a segment of slab break‐off may also occur during and after flat‐slab subduction (Axen et al, 2018; Dai et al, 2017; Yang et al, 2018).…”

“…Slab rollback, which is driven by mantle flow pressure gradients or negative buoyancy anomalies, that is, from slab eclogitization (Nakakuki & Mura, 2013), has been proposed as the mechanism for the tectono‐magmatic evolution of the overriding plate after flat‐slab subduction in the Lhasa Terrane (Yang et al, 2018), the North China Craton (Wu et al, 2019), and the southwestern Gondwana (Navarrete et al, 2019). Slab delamination, which can be triggered by a lithospheric weak layer (Li et al, 2014; Liao et al, 2017) or gravitational instabilities such as the presence of eclogite (Dai et al, 2017; Z.‐H. Li et al, 2016, 2019), involves the foundering of the cratonic lithosphere into the asthenospheric mantle.…”

Dynamics of back‐arc extension controlled by subducting slab retreat: Insights from 2D thermo‐mechanical modelling

“…The most likely reason for the fast slab retreat rates of our models at developing stage is the steep subducting slab dip angle, which provides more downgoing force to accelerate the subduction. Another reason might be in part due to more hot mantle upwellings into the neck and the stretched underlying continental lithosphere, which favours to accelerate thinning and weakening the continental slab, eventually leads to fasten back‐arc extension and the slab retreat (Dai, Li, Li, Somerville, & Liu, ; Dai et al, ; Sheng et al, 2016).…”

Central China Orogen along the Silk Road (Part I): Tectono‐thermal evolution and its links

“…The identification of Yanshanian deformation in Western Shandong by J. Zhang et al () is suggested to mark the transition from Paleo‐Pacific to Pacific Plate subduction. Studies on numerical modelling by Dai, Li, Li, Somerville, and Liu () have been used to explain postorogenic extension in the Western Dabie Orogen. The paper by Zhou et al () discusses the Triassic Orocline in East Asia and the transition from passive margin to foreland basin in Eastern North China Block.…”